Title: Evaporation of sewage plant effluent
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Title: Evaporation of sewage plant effluent
Physical Description: xii, 103 leaves. : illus. ; 28 cm.
Language: English
Creator: Sullivan, James Haddon, 1937-
Publication Date: 1970
Copyright Date: 1970
 Subjects
Subject: Sewage disposal   ( lcsh )
Evaporation   ( lcsh )
Water -- Purification   ( lcsh )
Environmental Engineering Sciences thesis Ph. D
Dissertations, Academic -- Environmental Engineering Sciences -- UF
Genre: bibliography   ( marcgt )
non-fiction   ( marcgt )
 Notes
Thesis: Thesis - University of Florida.
Bibliography: Bibliography: leaves 99-101.
General Note: Manuscript copy.
General Note: Vita.
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Bibliographic ID: UF00098402
Volume ID: VID00001
Source Institution: University of Florida
Holding Location: University of Florida
Rights Management: All rights reserved by the source institution and holding location.
Resource Identifier: alephbibnum - 001133263
oclc - 20143458
notis - AFN0632

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EVAPORATION OF SEWAGE PLANT EFFLUENT




















Bp

JAMES HADDON SULLIVAN, JR.



















A DLSSERTATION PRESENTED TO THE GRADUATE COUNCIL OP

ME UNIVERSIN OP FLORmA

IN PARTI~IL FULFILLMENT OF THE REQUIREMENTS FOR TIIB
DhCREE OF WCTOR OF PHILOSOPHY














UNIVERSI'III OF FLORIDA

1970














ACKNOWLEDGEMENTS

I would like to acknowledge first, my committee chairman,

Dr. J. E. Singley. Throughout my entire graduate program he has

been not only my principal teacher and advisor, but also a personal

friend. His encouragement and support have been invaluable.

As I expressed in the dedication, this work would not even have

been started had it not been for Dr. C. I. Harding.

Thanks go also to the other members of my committee, Professor

T. deS. Furman and Dr. J. D. Winefordner, for their help and support.

Throughout this project, much has depended on our being able to

promptly secure goods and services both from within and outside of the

University. With his complete knowledge of administrative procedures

and willingness to help, Dr. W. H. Morgan has been an invaluable enabler.

I wish to thank Mr. Hugh Holburn and Mr. Stanley Ridgeway of

Indian River Construction Company for all their help in the design and

construction of the evaporator. They are responsible for the final

construction of the unit and they did an excellent job.

I express my thanks to Dr. R. S. Sholtes and Mr. Howard McGraw

for their help in setting up the evaporator instrumentation.

The volume of analytical work in this project was staggering,

and I wish to thank the three chemists who did such a fine job,

Mr. Ryosuke Miura, Mr. Roger Yorton, and Mr. Gary Ashley.

For their many long hours of help in operating the evaporator,

I wish to thank Mr. Donald Winsor and Mr. Gary Ashley.









My thanks also to Mrs. Jeanne Dorsey for typing this final

manuscript.

I wish to acknowledge the financial support of the Department of

the Interior through Federal Water Quality Administration Grant No.

5T1-1SP-119-03 and Contract No. 14-12-571.

Last, but by no means least, I wish to express my thanks to my

wifeRubyeand my sonJim. Their help and contributions to this

whole effort cannot be measured nor can my thanks to them be expressed

in words.















TABLE OF CO~ENTS


Page

ACKNOWLEDGEMENTS ................... ................... ........... iii

LIST OF TABLES ................... ................... ............. vii

LIST OF FIGURES ................... ................... ........., ix

ABSTRhCT ................... ................... ................... x

CHAPTER

I. INTRODUCTION............................ 1

General Background.............................. 1
Previous kTork on Evaporation of Treated Sewage....... 5
Objectives of this Research.......................... 9

II. THEORETICAL BACKGROUND ................... .............. 10

Separation by Evaporation............................ 10
Volatile Organics................................ 11
Armnoni a ................... ................... ....... 12
Scaling and Fouling................................. 17
Calcium Carbonate............................... 18
Calcium Sulfate. ................... ................ 20
Magnesium Hydroxide............................... 20
Silica.................................. 22
Organic Scale................................... 23
Bacteria or Virus Contamination...................... 23
Ultimate Disposal................................ 25

III. RESEARCH PLAN.............'. ................... ......... 27

Experimental Equipment ................... ........., 27
Effluent s Available. ................... .............. 28
Experimental Plan....... ............................. 29
Analytical Plan and Procedures....................... 30

IV. DESCRIPTION OF EQUIPMENT ................... ............ 35

Degasser................................ 35
Evaporator.............................. 38
Carbon Column.................................. 45
Ammonia Column ................... ................ 45









Page

V. EXPERIMENTAL RESULTS ................... ................ 46

Initial Testing.. ..............., ................... 46
Extended Aeration Plant Effluent................... 49
Contact Stabilization Plant Effluent............... 53
Trickling Filter Plant Effluent.................... 53
Activated Carbon Tfsts............................. 60
Ammonia Ion Exchange Tests......................... 61
Aeration Tests............ ......................... 62
Product Water Conductivity......................... 62
Scaling During Check-Out and Initial Testing....... 64
Long Term Runs .........,.,.,.. .......; ........., 66
First Extended Aeration Effluent Run............... 67
Trickling Filter Effluent Run...................... 71
Second Extended Aeration Effluent Run.............. 76
Three Effect Ammonia Distribution Tests.............. 79

vI. DISCUSSION OF RESULTS................................. 83


Product Quality................................. 83
Anrmonia Content ................... ................. 83
Chemical Oxygen Demand............................. 85
Odor.................................... 85
Conductivity............................ 86
Nitrate................................. 86
Bacteriological Tests.............................. 86
Evaporator Scaling................................. 87
Scaling by Extended Aeration Effluent........,..,.. 87
Scaling by Tritkling Filter Effluent............... 89
Heat Transfer Coefficients......................... 89

V11. CONCLUSIONS ................... ................... ...... 91

APPENDICES ................... ................... ................. 93

Appendix I....................................... 94
Test Results Campus Sewage Treatment Plant......... 94
Appendix II...................................... 96
Calculation of Heat Transfer Coefficients............ 96

LIST OF REFERENCES ................... ................... ......... 99

BIOGRAPHICAL SKETCH.................................. 102
















LIST OF TARLES

Tables Page

i. Typical Analyses of Sea Water and Secondary Effluent......... 2

2. Disassociation Constants for Aqueous Ammonia and Water...., 14

3. pnalytical Tests on Liquid Samples........................... 31

4. Analytical Tests on Scale................................... 34

5. Evaporator Operating Conditions for Initial Single Stage
Tests................................... 47

6. Initial Tests, Extended Aeration Effluent, Vacuum
Conditions.............................. 50

7. Initial Tests, Extended Aeration Effluent, Atmospheric
Conditions.............................. 51

8. Initial Tests, Extended Aeration Effluent, Pressure
Conditions.............................. 52

9. Initial Tests, Contact Stabilization Effluent, Vacuum
Conditions.............................. 54

10. Initial Tests, Contact Stabilization Effluent, Atmospheric
Conditions.............................. 55

11. Initial Tests, Contact Stabilization Effluent, Pressure
Conditions.............................. 56

12. Initial Tests, Trickling Filter Effluent, Vacuum
Conditions.............................. 57

13. Initial Tests, Trickling Filter Effluent, Atmospheric
Conditions.............................. 58

14. Initial Tests, Trickling Filter Effluent, Pressure
Conditions.............................. 59

15. Typical Analysis of Tap Water, Gainesville, Florida.......... 65

16. Analytical Results First Extended Aeration Effluent Run.... 70

17. Scale from First Extended Aeration Effluent Run............;. 72








Tables Page

18. Analytical Results Trickling Filter Effluent Run........... 73

19. Scale from Trickling Filter Effluent Run..................... 75

20. Activated Carbon Treatment of Products from Trickling
Filter Effluent Run..................................... 76

21. Analytical Results Second Extended Aeration Effluent Run... 78

22. BacteriologicaL Tests Second Extended Aeration Effluent
Run..................................... 80

23. Scale from Second Extended Aeration Effluent Run............. 81

24. Analytical Results Three Effect Ammonia Distribution
Tests................................... 82

25. Campus Sewage Treatment Plant Test Results, High Rate
Trickling Filter.................................. 94

26. Campus Sewage Treatment Plant Test Results, Contact
Stabilization Plant................................... 95


viii















LIST OF FIGURES

Figure Page

i. Distribution of NH3 and h7it as a function of pH and
Temperature .........,.,.,.. .........,.,.,.. ........., 15

2. Calcium Sulfate Solubility. ................... ............... 21

3. Overall Flowsheet............................... 36

4. Degassing System Flowsheet..............................; 37

5. Evaporator Flowsheet............................... 39

6. Evaporator.............................. 40

7. Vapor-Liquid Separator............................... 42

8. Product Receiver System Flowsheet............................ 44

9. Conduct ivity vs. Ammoni a Concent rat ion ................... .... 63

10. Product Rates, First Extended Aeration Effluent Run.......... 69

11. Overall Heat Transfer Coefficients........................... 74














Abstract of Dissertation Presented to the
Graduate Council of the University of Florida in Partial Fulfillment
of the Requirements for the Degree of Doctor of Philosophy

EVAPORATION OF SEWAGE PLANT EFFLUENT

by

James Haddon Sullivan, Jr.

August, 1970

Chairman: Dr. J. E. Singley

Major Department: Environmental Engineering

The technical feasibility of evaporation of sewage treatment plant

affluent for the purpose of reuse was investigated. The process used

was similar to one of the major processes used in sea water conversion,

evaporation in a long tube vertical (LTV) evaporator. As evaporator

feedwater, treated sewage has the advantage over sea water of having

much lower total dissolved solids. This should result in higher

evaporator operating temperatures, reduced scaling problems, and

negligible boiling point rise. The major disadvantages of treated

sewage as an evaporator feedwater are that the water usually contains

volatile organic materials and armnonia that may contaminate the product.

The objectives of the research were (1) to define the relation-

ships between product water quality, feedwater quality, and evaporation

conditions, (2) to define the relationships between post evaporation

polishing, feedwater quality, and evaporation conditions, and (3) to

define the relationships between evaporator tube scaling, feedwater

quality, and evaporation conditions.









The experimental equipment consisted of a three effect LTV

evaporator constructed of 316 stainless steel. Each effect was a

single one inch diameter tube with a four incl~ diameter steam jacket.

The effective heated Ifi~gth of the tube was 14 feet. Vapor-liquid

separators atop each effect separated the vapor from the liquid. The

evaporator could be operated as a single effect or triple effect unit.

Possible operating conditions varied from around 28 inches Mg vacuum

to about 55 psig. All evaporator feedwater was first degassed under

vacuum to remove dissolved gases. Prior to degassing, the pII was

adjusted to 4.9 so that all carbonates would be removed.

Feedwaters available to the evaporator included extended aeration

effluent, high rate trickling filter effluent, and contact stabilization

effluent. All three units treated raw waste from a large university

complex.

The experimental work was divided into two principal phases. The

first phase work was directed towards defining the product quality

relationships with the various variables. The second phase work was

directed towards defining the relationships between evaporator tube

scaling and the various variables. Most of the first phase work was

accomplished by making relatively short runs, three to five hours,

using only one effect of the evaporator. Post treatment processes

included aeration, activated carbon, and ammonia selective ion exchange.

In the second phase, the evaporator was operated as a triple effect

unit over an extended period of time. After each rug, the evaporator

tubes were mechanically cleaned and the scale analyzed.

Results of the first phase work showed that an odor-free product

could not be produced from any of the three feedwaters under any

xi








operating condition from 1120F to 2900F. The odor intensity increased

as the evaporator operating temperature and/or the chemical oxygen

demand of the feedwater increased. In all cases, post treatment with

activated carbon removed all odors. Aeration would not remove all

odors. Product produced under pressure conditions using trickling

filter feed contained significantly more organic contamination than

any other products. Product contamination by ammonia could not be

controlled by adjusting the ph of the feed in the range 5.1 to 8.7.

However, armnonia in the product water was removed by ion exchange.

The scaling evaluations were carried out under pressure conditions

using extended aeration and trickling filter effluent. Trickling

filter feedwater was judged unsuitable because of excessive scaling.

Scaling problems with extended aeration feedwater were minor, and

with post treatment by activated carbon, a high quality product water

was produced.

Because of increased efficiencies due to higher operating tem-

peratures and negligible boiling point rise, wastewater evaporation

should be more economical than sea water evaporation.














I. INTI~ODUCTION

General Background

The continuing increase in demand for potable water coupled with

increasing amounts of pollutants being discharged into the environment

has forced mankind to resort to poorer quality sources of water for

a potablk water supply. In some areas the availability of fresh water

is so limited that we have turned to the sea for our water supply.

Millions of dollars have been expended in research and development of

saline water conversion processes. This research has resulted in 627

desalting plants worldwide which were either in operation or under

construction as of 1968.1 The total capacity of these plants is

222 mgd, and distillation or evaporation accounts for 93% of this

capacity. It is estimated that the desalting capacity may reach 1 bgd

by 1975.1 Ic is now clearly evident that there are many places in the

world where desalting is either the most economical or only source of

potable water.

The research reported here examines the most cormnon type of de-

salting process, distillation or evaporation, used with an alternate

feedwater, sewage treatment plant effluent. This feedwater should be

available in any area having a central sewage collection system and

would in all cases be as close or closer to the consumers than sea

water. Typical analyses of sea water and a secondary effluent are

shown in Table i.2,3 The main differences between these two waters

are





























Chloride 19,353 130 75
Sodium 10,760 135 70
Magnesium 1,294 25 7
Sulfur 904 33 10
Calcium 413 60 15
Potassium 387 15 10
Gross Organics 55 52
BOD 25 25
Nitrate 0.04 3 15 10
Phosphate 0.003 0.3 25 25
Silica 50 15
Ammonia 20 20
Total Dissolved Solids 35,000 730 320



*Concentration increase from potable water to secondary effluent


TABLE 1

TYPICAL ANALYSES OF SEA WATER AND SECONDARY EFFLUENT


3
Increment
Added
mg/lk


Sea Water2 Secondary Effluent3
ppm mg/l







1) sea water has 35-50 times more dissolved salts than secondary

effluent

2) secondary effluent contains appreciable quantities of organics,

ammonia, and phosphates that are present only in trace amounts

in sea water.

It should be noted that in a total recycle process the concen-

tration of inorganic materials in the secondary effluent would be less

than the amounts shown in Table i. The figures in Table 1 are based

on a potable supply containing some dissolved inorganic materials. If

all potable water in a system were produced by evaporation, the level

of dissolved materials in the water would be very low and the treated

waste from that system would contain essentially only the increment of

dissolved materials added during one cycle from potable water to

treated wastewater. Typical increases are shown in Table i. Obviously,

if any portion of the potable supply were produced by some means that

did not provide complete demineralization, the dissolved solids content

of the treated wastewater would be increased accordingly.

These differences in sea water and secondary effluent should

markedly affect their relative desirability as evaporator feedwater.

In the case of sea water the very high dissolved salt content causes

problems with scaling, corrosion, and boiling point elevation.4'5

Scaling is controlled by pretreatment of feedwater and limitation of

maximum temperature to 2500F. Since heat transfer coefficients in-

crease with temperature, the 2500F limitation on sea water evaporators

significantly affects the overall economics. The high salt content

also affects overall economics by requiring certain high cost materials

of construction. The overall economic effects of boiling point rise




-4-


are significant also and usually dictate that concentration beyond 7%

solids (recovery of half the feedwater) is uneconomical.

By comparison, the maximum operating temperature for secondary

effluent should be considerably above 2500F since the concentrations

of scale forming materials are considerably lower in this water.

Materials of construction for a secondary effluent evaporation plant

would likely be different and possibly less expensive than for a sea

water plant. Copper alloys, common in sea water conversion plants,

probably would be unsuitable because of possible ammonia attack.4'6'7

The effects of boiling point rise would be negligible by comparison

since 97-98% of a secondary effluent feed could be recovered before

the solids concentration in the remaining 2-3% reached the 35,000 ppm

level of sea water. Hence, with regard to the effects of inorganic

salts, secondary effluent has a very clear advantage over sea water.

Organics in secondary effluent make this a less desirable feed

for evaporation since many of them are volatile and would be carried

over with the steam into the product water. These volatile organics

are expected to create taste and odor problems in the product water.

Ammonia, likewise, is expected to carry over unless the pH is kept low

and ammonia would be an undesirable addition to the product water.d

Regarding scaling, organics could be either very detrimental or possibly

helpful. Obviously, if organic fouling occurred, heat transfer would

be greatly lowered. However, it is possible that the organics could

act as a dispersing agent tending to keep insolubles from coating the

tube walls. Also, a light film of organics on heat exchanger surfaces

could promote drop-wise cond~nsation and thus increase heat transfer.

Only actual operation under representative conditions could determine




-3-


the full effects of organics in secondary effluent.

Phosphates should be advantageous in that they will precipitate

calcium as calcium phosphate which normally does not form scale-like

deposits. The dispersive actions of organics in the liquid phase may

serve to keep the calcium phosphate suspended in solution.

Overall, it appears that the potential economic advantages of

secondary effluent over sea water for fresh water production may more

than offset the disadvantages. Certainly this possibility seems likely

enough to justify further research..

Previous Work on Evaporation of Treated Sewage

Previous work on evaporation of sewage treatment plant effluent

has been limited to several desk top evaluations using presumably

reasonable assumptions and four studies that involved actual experi-

mental work.

In 1960 K. C. D. Hickman9 was commissioned by the Robert A. Taft

Sanitary Engineering Center to compare distillation with other unit

processes for the reclamation of wastewaters. Hickman concluded that

the relatively high cost of distillation (estimated at $1.00/1,000 gal.)

should limit it to processing only part of the water in a total recycle

scheme. Other less expensive treatment procedures should be used for

the remaining parts of the system. Hickman reported the results of

one experimental run using treated sewage from a Rochester, N. Y.,

sewage disposal plant. The specific evaporator used was not described

but operating conditions were reported as 1200F (1.69 psia). In the

author's opinion, "the physical properties, flavor, and odor of the

distillate were good, and that with mild chlorination, or equivalent,

the distillate would be potable and acceptable for municipal reuse."








Possible contamination of the distillate samples prevented any valid

conclusions based on actual analysis.

In 1963 an economic analysis and a pilot plant study of wastewater

distillation weremade by J. H. Neale4 of W. L. Badger Associates.

Neale proposed that distillation be used in parallel with some other

form of treatment and that the fraction of the total stream subject

to distillation be the minimum required to prevent build up of inor-

ganics in the overall system. Analysis of data from 22 cities indica-

ted that the fraction of the total stream that would have to be dis-

tilled ranged from 23.6% to 63.7% and averaged 42.7%. A pilot plant

study was carried out in a long tube vertical (LTV) evaporator

utilizing a single tube 14 feet long. The primary objective of the

tests was to evaluate tube fouling and no provision was made to separate

and collect product water. Using primary effluent and no pretreatment,

tube fouling was noted after four days. Operation was at 2121F. A

second seven day run at 2120F was made using secondary effluent with

no pretreatment. Again tube fouling was noted. The effervescence

noted when acid was added to this scale led Neale to conclude that it

was largely calcium carbonate. Subsequent runs were made using secon-

dary effluent treated with inhibited hydrochloric acid for ph adjustment.

Feed ph was maintained at less than 5.7 most of the time. An eight

day run at 2120F and a twelve day run at 2340F were made with no

scaling problems. Neale concluded "that waste treatment by distillation

will probably be applicable to renovation ofwastewater at temperatures

equal to or exceeding those used for sea water conversion, and that

raw sewage, after removal of most of the suspended matter, may be used

for distillation plant feed."




-I-


In June, 1963, American Machine and Foundry, Inc. obtained an

Advanced Waste Treatment Research contract from the government to

conduct research on flash evaporation of treated seruage.l0 The equip-

ment consisted of an eight stage flash unit. The still body was steel

with titanium heat transfer surfaces. Due to operating problems, very

limited testing was carried out. Using secondary effluent under

relatively high temperature conditions, 250-3000F, severe fouling of

the preheater and some fouling of the feed side of the condenser tuhes

occurred. The scale appeared to be largely organic. The product

water had a strong, disagreeable odor. However, treatment with activated
11-13
carbon removed the odor.

In 1965, O'ConnorB and co-workers at the Robert A. Tafr Sanitary

Engineering Center in CincinnatiOhioi conducted laboratory scale

tests on distillation of municipal effluents. Batch tests were made

using primary effluent, trickling filter effluent, and extended aera-

tion affluent. Temperatures used were 158, 212, and 3380F and pH

ranged from 3 to II. At the lower pH values it was hoped that the

ammonia would be retained in the concentrated liquid. At the higher

pH values, hopefully all the ammonia would distill over in the first

small fraction of product. All feed samples were filtered prior to

evaporation to remove solid particles larger than about 5 microns.

It was found that ammonia was present in the product water for all

feeds with pH above about 3.5. With feeds containing around 7-8 mg/l

NHJ-N, ammonia in concentrations above 1.0 mgll NW3-N typically was
found in the first 40-50% of the distillate. Even at pH II, ammonia

in the concentration above 1.0 mg/l NH11-N was found in at least

the first 30% of the distillate. Hence it appeared impractical to







try, on a large scale, either to eliminate ammonia from the dlstillate

by lowering tt~e feed pI1 or to concentrate all the ammonia in the first

small fraction of the distillate by raising the feed pH.

Tests with extended aeration plant effluent having ammonia

concentrations less than 2.2 mg/l NH3-N showed thatat feed pN values

under 5.5, all product fractions had ammonia concentrations less than

1.0 mg/l NH3-N. No carry over of nitrate was observed.

Odors were present in all products and seemed to be more

"prominent and enduring" at high temperatures. Product odor seemed i

to be independent of feed pN. Powdered carbon at 1 gm/l removed all

odors from products produced under vacuum and atmospheric conditions.

However, carbon treatment only partially removed the odors from the

products made at high temperature and pressure conditions.

Economic analyses of distillation of treated wastewaters have been
14
made by several people. Gerster has made a desk top study of multi-

stage flash, multiple-effect, and recompression-flash evaporation with

respect to how these processes might apply to wastewaters. Ne concluded

that "For all types of equipment the cost for the distillation step

alone is somewhat less than for sea water, but inclusion of costs for

feed pretreatment and ultimate disposal of blowdown, bring the cost up

to about that for sea water."

15,16
Stephan in 1965 predicted that wastewater evaporation should

cost about the same as sea water evaporation. Also, he concluded that

a parallel renovation system utilizing evaporation on half of the

recycle stream would cost about the same as using electrodialysis on

the entire stream.





Objectives of this Research

After reviewing the previous work on evaporation of sewage

treatment plant effluent, it appears that additional information is

needed in several areas. First, very little work has been done on a

continuous basis utilizing equipment simulating full scale operations.

Also, renovation by evaporation should be considered in relationship

to any additional pretreatment or post treatment processes that may

be required to render the water acceptable for reuse.

Based on these needs, the following objectives were set for this

research.

1) To define the relationships between product water quality.


feedwater

2) To define

required,

3) To define

feedwater


quality, and evaporation conditions.

the relationships between post evaporation polishing

feedwater quality, and evaporation conditions.

the relationships between evaporator tube scaling,

quality, and evaporation conditions.













II. THEORETICAL BACKGROUmD

Separation by Evaporation

Separation of two or more components in a liquid phase is possible

by evaporation and subsequent condensation of the vapor if the relative

concentrations of materials in the vapor are different than tile

relative concentrations in the original liquid state. In the case of

sea water conversion, the salt concentration in the original liquid is

about 35,000 ppm but is essentially zero in the vapor state. The

behavior of multicomponent systems can be described theoretically by

Raoult's law or Henry's law~17,18 Unfortunately, for most solutions,

neither of these laws can be applied over the complete range of con-

centrations. Raoult's law is generally applied to the solvent or

predominent component in a liquid system. The law states that the

partial pressure of component a, P_, is equal to the mole fraction of

a in the solution, Xa, times the vapor pressure of pure a at that same
temperature, pO

P = X PO (1)
a aa

Henry's law generally applies only to solutes in dilute concentrations

and states that the partial pressure of b, Pb, is equal to the mole

fraction of b in the solution, Xb, times a constant, k, termed
Henry's law constant.


Pb=Xbk (2)

The greatest practical application of these laws is in very




-LI-


dilute solutions. As X -t 1 Raoult's law becomes more exact and

as Xb ~ O Henry's law becomes more accurate. Hence, both can be

accurately termed limiting laws. Also, under ideal conditions, i.e.

where the intcrmolecular forces between molecules of A, B, and A and

B are all equal, the Henry's law constant, k, becomes ph and Henry's

law and Raoult's law are identical.

Volatile Organics

Unlike sea water, treated sewage does contain materials that can

be classified as volatile under temperatures likely to be encountered

in evaporation. These include numerous organic compounds and ammonia.

Since in all cases we are talking about very low concentrations, we

can assume that Henry's law will apply to the solutes. Unfortunately,

the limited work that has been done to characterize sewage treatment

plant effluent plus the day-to-day variations in effluent quality make

it virtually impossible to construct a predictive model for specific
19,20
compounds in the effluent. Also, k values are not available for

all the organic compounds that may be present. To complicate matters

further, it appears that some of the organics in the evaporator feed

are broken down by heat in the evaporation process to produce smaller,

more ~olatile compounds.8 This appears to be pareicularly true as

evaporator temperature is increased; Therefore it is impossible to

predict either the amount or the specific compounds one might expect

to carry over during evaporation.

Nevertheless, some volatile organic material in the evaporator

feed can be expected to carry over into the product water. Exactly

how much is carried over will be dependent on the relative volatility

of the compounds and the evaporator operating conditions. The effect







of these compounds in the product water will be to increase the COD

and probably to add some taste and odor.

Ammonia

Nitrogen in the form of ammonia is found in the effluent from

almost all biological treatment processes. The exception is treatment

involving extended oxidation conditions wherein the ammonia is

oxidized to nitrate. Even in the extended aeration processes it is

not unusual to find 0.5-1.0 mg/l M-~3-N.
21
The 1962 Public Health Service Drinking Water Standards set no

limit on ammonia concentration. Likewise the more stringent Water
22,23
Quality Goals established by the American Water Works Association

make no mention of ammonia. In a 1968 report issued by the Federal

Water Pollution Control Administration on raw water quality criteria

for public supplies, a permissible criteria of 0.5 mg/l NH3-N and a

desirable criceria of less than 0.01 mgll ~YHJ-N were recoaanended.24
The rationale for these low limits was given as follows. "Ammonia is

a significant pollutant in raw water for public water supplies because

its reactions with chlorine result in compounds with markedly less

disinfecting efficiency than free chlorine. In addition, it is

,,24
frequently an indicator of recent sewage pollution. In order to

satisfy a chlorine demand of 1 mg/l MI3-N and produce a free chlorine

excess, i.e. "breakpoint" chlorination, about 10 mg/l of chlorine are

required.8 Hence, for economic reasons alone, it appears undesirable

to have ammonia above 1.0 mg/l in the final product water. The fact

that no standard for ammonia in potable water exists probably reflects

that historically ammonia has not been a problem and not that ammonia

was not considered undesirable.






The volatilization of ammonia in an ammonia-water system is
influenced by several factors, pH, ammonia concentration, and solution

temperature. Ammonia dissolves in water to form NI1L~OII which is in
equilibrium with ammonium ion as follows.

NH3 + H20 -- NH1 + OH (3)

Kb .C~t3[o-3 (4)
~"3]

If values of Kb at various temperatures are known, the relative
concentrations of NH
1 and NH3 can be calculated as a function of pOH.
Now, since

Kw =[OR;JIH+] (5)

and values of I~ at various temperatures are known, the relative con-

centrations of NHt and NH3 as a function of pH can be determine.

[6'3= E~Htl v (6)
P"33 "b

pH= log[MIJ + pKw pKb (7)


Yalues of pKw25'26 and pKb27'28 for ammonia are sho~n in ~able 2.
Using these values and equation 7, the distribution of NH3 and NHq
was calculated as a fraction of pH at various temperatures. The
results are in excellent agreement with similar data published in an
American Water Works Association committee report on nutrients in
29
water. The source of their data was not given. Figure 1 shows

that at 200C and pH 7 more than 99% of the ammonia is present as

1 and hence not subject to evaporation. However, as the temperature
NH































0 14.9435 4.862
10 14.5346 4.804
20 14.1669 4.767
25 13.9965 4.751
30 13.8330 4.740
40 13.5348 4.730
50 13.2617 4.723
60 13.0171
100 12.30 4.87


TABLE 2


DISASSOCIATION CONSTANTS FOR AQUEOUS
AMMONIA AND WATER


Tgmp.
C


pK foT
warer25,26


PKb for Aqueous
AmmnniaZ7,28
















90




80




70




80



I
Z 50




40




30




20




10


g 10


Figure i. Distribution of NEg and NH~

of pH and Tenperature


as a Function




-IV-


increases, the equilibrium shifts and there is more ammonia available

for evaporation. This would explain the fact that O'Connor" found

that he had to lower the feed ph to under 5 in order to eliminate

ammonia in the product water.

The relative volatility of ammonia as compared to water strongly

influences the relative amounts of ammonia and water in the liquid

and gas phases during evaporation. At the very low ammonia concen-

trations encountered in treatment plant effluents Henry's law should

apply. Unfortunately, no data have been published for ammonia-water

systems in the 0-20 mg/l NB3-N concentration range. However, consider-

able data are available for animonia-water systems in ammonia concen-
30-32
traction above 1% (10,000 ppm). These data show the relative

concentration of ammonia in the vapor phase to be much higher than in

the liquid phase. This concentration factor increases as ammonia

concentration in the liquid decreases and is around 10 at the 1%

(ananonia in liquid) level. Therefore, at the much lower ammonia

concentration levels we are considering, the ammonia concentration

factor from liquid to gas should substantially exceed 10. Concen-

tration of ammonia by evaporation and condensation is well recognized

and is an accepted laboratory procedure in the analysis of ammonia.33

The effect of temperature on ammonia volatilization from an

ammonia-water system is that the ammonia concentration factor decreases

slightly as temperature increases.30 However, this effect does not

appear to be significant over the temperature range that would be

considered for evaporator operations.

From a theoretical standpoint, it appears that ammonia carry

over to the products is dependent on the pH of the feed solution and







the evaporation temperature. Since the ammonia-ammonium ion equilibrium

shifts in favor of ammonia as temperature increases, one might well

expect to find armnonia in the product water at pH values at least as

low as 6 if evaporation is occurring under pressures exceeding

atmospheric.

Scaling and Fouling

Loss of heat transfer efficiency may result from inorganic scaling,

organic fouling or a combination of the two.

Inorganic scaling occurs when the solubility of the scaling

compound is exceeded. This may occur because of temperature increase,

since the solubilities of many scale forming salts decrease with

increasing temperature. In an evaporator, the continual evaporation

of water concentrates the non-volatile ions in solution to the point

that the entire solution may be saturated with respect to a particular

salt. However, scaling may occur at localized points in the system

even though the solubility of the particular scaling salt is not

exceeded in the bulk of the water. This can occur because the thin

film of liquid immediately adjacent to the heating surface tends to

become more saturated than the remaining water.

In the first case, where the entire solution becomes super-

saturated, precipitation may occur in the solution. This precipitate

may remain suspended in the solution and be removed with the concen-

trated effluent. However, it may settle on the tube surfaces and

"bake" in place as a scale. The second case is more detrimental in

that the precipitation tends to occur directly on the heating surface

and there is little chance that the solid thus formed will be suspended

34,35
in the solution.




-LV-


With regard to boiler scaling, the Betz Handbook makes the following

comment s .

It is well to realize that the prevention of boiler
scale cannot be predicted by any basic chemical
principal. It is the physical characteristics of
the precipitate formed in the boiler water that
determines whether or not the precipitate will tend
to tightly adhere to the boiler heating surfaces -
the chemical characteristics of the precipitate
are relatively unimportant. Thus, from a chemical
standpoint sodium silicate will precipitate the
calcium and magnesium salts just as well as a
phosphate or carbonate. However, it is the
physical characteristics of the precipitate that
are of importance, for a precipitate of calcium
silicate will tightly adhere to the heating
surfaces .34

Treatment for prevention of inorganic scale may be external or

internal. External treatment involves removing the potential scale

forming materials from the water prior to its introduction into the

evaporator, boiler, etc. Internal treatment involves the selective

precipitation of the potential scale forming materials in the form

of non-scaling sludges. This may include the addition of materials

designed to keep the sludges fluid and in suspension so that they can

be removed from the boiler or evaporator in the blowdown or concen-

trated effluent.

The principal inorganic scale and/or sludge formers are calcium

carbonate, calcium sulfate, magnesium hydroxide, and silica.36

Calcium Carbonate

Calcium carbonate is one of the least soluble salts of magnesium

or calcium that is likely to occur in wastewater evaporation. At

temperatures below boiling this scale can be controlled by adjusting

the carbonate equilibrium system in favor of HZCO3 and HC03 by pH

control. Excellent discussions of this equilibrium system have been




'II-


37,38 39,40 and Waber and Stumm.41 However,
presented by Langelier, Dye,

pH control of the carbonate system cannot be accomplished under boiling

conditions where the C02 solubility is zero. Under such conditions

HC03 converts to COj and H2C03, and CaC03 can precipitate according to
the following reactions.

2HC03 = H20 + C02 + C03 (8)


cace + co; = cco, (9)


Since C02 solubility is zero, the continual removal of COa from the
system forces the complete decomposition of the HCO

The obvious way of controlling calcium carbonate scale is by

removal of the calcium. This could be done by hot or cold lime-soda
34-36,42
softening or by ion exchange. However, in the case of waste-

water evaporation, softening would add significant additional costs

to the overall system. Ion exchange is questionable because the effects

of organics on fouling of the exchange resin are not known.

Calcium carbonate scale also can be controlled by ph adjustment

and degassing prior to the evaporator.4 This involves lowering the

pH to put the carbonate in the H2C03 form and then removing it as

C02 by degassing.
Finally, calcium carbonate scaling may be controlled internally

by controlled precipitation of the calcium as a non-scaling sludge.34-36,42

The most common procedure is to precipitate the calcium as tricalcium

phosphate or as hydroxyapatite, a mixed calcium phosphate and hydroxide.

Several sodium phosphates may be used including trisodium phosphate,

disodium phosphate, sodium metaphosphate, and monosodium phosphate.34

In some cases it is necessary to add organic dispersants to prevent




-ZU-


the sludge from growing into aggregates. Typical types of organic

materials used for this purpose are tannins, lignins, glucose

34,35,42
derivatives, and starches.

Precipitation of calcium by phosphate and dispersal of the sludge

by organics has promise for use in wastewater evaporation since both

phosphates and organics naturally occur in this water. However,

individual wastewater streams may or may not contain sufficient phos-

phate and the dispersal abilities of the organics in wastewater are

not known.

Calcium Sulfate

Calcium sulfate presents a more serious problem than calcium

36,42
carbonate because it forms a very hard and adherent scale.

Calcium sulfate solubility decreases with temperature as shown in
43,44
Figure 2. It should be noted that this is the solubility of

pure calcium sulfate, anhydrite, in pure water. In wastewater; calcium

sulfate will have a higher solubility due to the increase in ionic

strength caused by the other ions in solution.

Control of calcium sulfate scale is accomplished in much the

same way as control of calcium carbonate. External treatment to re-

34-36,42
move or reduce the calcium content of the water is applicable.

Internal treatment to remove calcium by controlled precipitation with

34-36,42
phosphate can likewise be used. The comments made previously

regarding these control measures all apply here.

Magnesium Hydroxide

Magnesium hydroxide has a solubility of about 5 ppm at 2120F

decreasing to slightly less than 1 ppm at 3920F. Control of this

scale may be external by removal of the magnesium by softening or































































220 240 280 280 300 320 3

TEMPERATURE, OF

Figure 2. Calcium Sulfate Solubility





1 I 1 1
~40 380 380 400


I


700


850


800


550


500



450


400


350


300


200250 j


BOOTH INO BID~ELL (44)

o NEALE (4)

a LINKE (43)


SOLID PHASE CaSO4







34-36,42
ion exchange. Internal control can be accomplished by con-

trolled precipitation with phosphate. IIowever, magnesium phosphate

tends to form a sticky deposit and requires mechanical removal.34

Finally, since magnesium forms a hydroxide scale, it can be controlled

by maintaining the pH and hence hydroxide concentrations at a low

enough level so as to not exceed the solubility.

Silica

Silica tends to form complex scales which may include calcium,
34,36
magnesium, aluminum, or may be composed almost entirely of silica.

These scales are usually very hard, glassy, and adherent. McCoy42

gives a maximum permissible concentration of silica of 250 ppm at

3880F for boilers. This figure drops to 175 ppm at 4210F. Presumably

it increases for temperatures below 3880F,

In some cases tao low silica concentrations can cause problems.34

If magnesium concentration is high and phosphate is present, the

magnesium will precipitate a sticky magnesium phosphate sludge. How-

ever, if sufficient silica is present, magnesium silicate, which is

easier to handle, will be precipitated.

Control of silica scale may be external by hbt lime-soda
36,42
softening or by coagulation with ferric sulfate. Ion exchange

using a strongly basic anion exchange resin regenerated with sodium

hydroxide may also be used.36

Internal treatment for silica scale, if any treatment at all is

required, appears to be better suited for the wastewater evaporation

process. This involves maintaining a small excess of phosphate and

a ratio of alkalinity to silica of at least one to one.36







Organic Scale

Organic materials may cause heat transfer problems by any of

several different mechanisms. Suspended organics may simply deposit

on heat transfer surfaces. Oils or greases, which have a tendency to

coat metal surfacesmay cause problems. The high temperatures in the

evaporator may tend to polymerize some organics into high molecular

weight insoluble compounds that could coat tube walls. In the latter

stages of evaporation, as concentrations of both organic and inorganic

materials increase, the possibility of salting out exists.

Another potential organic fouling problem exists in the early

stage preheaters (temperature less than 1300F). This is the problem

of bacterial growth. It is possible that this could be adequately

controlled by periodic shock chlorination.

In contrast to all the potential problems with organic fouling,

there are some possible positive benefits. Certain organics may have

a dispersing effect which would tend to keep solids suspended. Also,

volatile organic vapors carrying over from one effect to the steam

chest of the next effect may promote dropwise condensation on the

evaporator tubes. If the organic material coats the condensing surface

and renders it non-wettable, condensation will occur dropwise and since

dropwise condensation gives higher heat transfer, the overall efficiency

of the process would be improved.45

Bacteria or Virus Contamination

Since in evaporation of sewage treatment plant effluent it is in-

evitable that bacteria and virus will be present in the feedwater, a

question that must be faced is what are the possibilities of these

organisms contaminating the product water. At least three highly







unlikely events must occur in order to contaminate the product with

live bacteria or virus. First, the organism would have to survive the

maximum feed temperature in the evaporator. The forward feed multiple

effect evaporator design requires that all fefdwater pass from the hot

end of the system to the cold end. Hence, all incoming water is heated

uniformly to the maximum operating temperature. In the case of sea

water this temperature is 2500F. However, as pointed out previously,

it is likely that the upper temperature limit for sewage treatment

plant effluent will be higher than this. For comparison purposes, C

milk is pasteurized at 161YF and microbiological laboratories sterilize

their equipment in autoclaves at 2500F.46 Sterilization times as low

as 10 minutes are used for small samples. Because of the uniform

heat conditions obtained in an evaporator, the somewhat shorter holdup

times at the maximum temperature should be at least as efficient as 10

minutes in an autoclave.

The second factor dictating against bacteria or virus contamination

in the product is the basic separation mechanism being used, i.e.

evaporation and condensation. Since bacteria and virus are non-

volatile, they cannot contaminate the product by evaporating and con-

densing with the product. To get into the product water it would be

necessary for any organisms to be physically carried over in the vapor

stream, i.e. entrainment. The extent to which this would be possible

would depend on the type and design of the vapor liquid separation

system in each effect.

The third factor that would be used to eliminate any danger from

bacteria or virus contamination would be chlorination. As with any

municipal potable water supply, all water from the plant would be
chlorinated.








Considering these facts, it seems reasonable to conclude that

possible danger from bacteria or virus in a forward feed multiple

effect evaporator system using sewage treatment plant effluent as

feed would be less than the same danger from a conventional coagulation

plant using surface sources of raw water.

Ultimate Disposal

practically all wastewater treatment processes involve separation

of the incoming liquid into a "clean" and "dirty" stream. In all cases

some final disposition must be made of the "dirty" or concentrated

waste stream. This problem exists in evaporation of sewage treatment

plant affluent. The final concentrated effluent stream from the

evaporator probably will be on the order of 3-10% by volume of the

incoming stream and contain essentially all the inorganic salts and

organic material in the feed stream. Ultimate disposal of the stream

will depend on the individual situations however, several possible

means would be ocean outfall, underground disposal, or solar evapora-

tion.

Because of the high temperature anticipated for wastewater

evaporation, the concentrated effluent should be completely safe for

ocean disposal in a well-designed outfall. Since the effluent would

have an appreciable organic content, provision should be made in the

outfall design to release the waste far enoug~ offshore so as to

preclude the possibility of contamination of beach or estuary areas.

In areas where contamination of ground water would not be a

problemunderground disposal of the concentrated effluent could be

considered.

Climatic conditions and availability of land would determine








whether or not disposal by solar evaporation would be possible.

Because of the relatively high cost of recovering water by

evaporation, it is assumed that this process would not be used if

other sources of fresh water were available. In effect, this says

that wastewater evaporation will be limited to very arid areas or

certain island or coastal areas where little or no fresh water is

available. Hence, there would be no possibility of dumping the con-

centrated effluent into an existing fresh water stream large enough

to assimilate the waste.

Finally, it should be noted that ultimate waste disposal problems

in an area would not be increased by evaporation of sewage treatment

plant ef-fluent. If evaporation were not used, the more dilute waste

containing the same absolute amounts of impurities would still have

to be disposed of. Therefore, it is likely that evaporation would

reduce rather than add to ultimate disposal problems.














III. RESEARCH PLAN

The objectivfs of this project, particularly with regard to scaling

evaluations, dictated that 1) the work be done in equipment of sufficient

size to simulate full scale operation, 2) operation be continuous rather

than batch, and 3) various efflucnts typical of what could be expected

from municipal waste treatment plants be used as evaporator feed.

Within these constraints the following approaches were taken to various

parts of the overall research plan.

Experimental Equipment

The long tube vertical (LTV) evaporator design was selected for

use in this work. In discussing all types of evaporators, Standiford47

points out that more evaporation is accomplished in LTV evaporators

than any other type and makes the following comments regarding the

LTV design.

The widespread use of the S~LTV evaporator is due partly
to the ability to build large single units, partly
because of the high heat-transfer performance exhibited
under most conditions, and partly because of the
simplicity and hence cheapness of construction (simply
a shell and tube heat exchanger surmounted by a vapor-
liquid separator).

Because of their high capacities, and lower costs than
for any other type, rising-film LII evaporators are
used whenever possible. ...While they cannot usually
handle crystallizing solutions, they are widely used
for viscous and mildly scaling liquors. They are well
suited to corrosive solutions because heat-transfer
coefficients are generally high requiring a minimum of
expensive heating surface, and tube replacement is
simple. ... The principal disadvantage of the rising-
film LTV evaporator is the poor heat-transfer perfor-
mance at low temperature-differences or at low
temperatures.




-LO-


For these reasons and because the rising-film LTV design is

readily adaptable to pilot scale size units, this type evaporator

was selected for use in this research. Consideration was given to

the use of a single effect unit. It was concluded that since any

full scale plant would be multiple effect, pilot plant data from a

multiple effect unit would be far more valuable than data from a unit

that would only simulate the first stage of a multiple effect system.

Since corrosion was not to be studied in this research, it was

deemed desirable to construct the evaporator of 316 stainless steel

to minimize the possibility of product contamination by corrosion.

As with the evaporator, the accessory equipment used for feed

preparation and product polishing was designed to operate continuously.

The entire system was designed by the author. In design of

the evaporator provision was made to allow operation as a single stage

unit or to operate all three effects in series. In either mode of

operation any pressure range from about 28 inches Hg vacuum to la0 psig

could be selected. Unfortunately, steam pressure available at the

site limited the upper pressure to 50-55 psig.

The evaporator was constructed by Indian River Construction Co.,

Jacksonville, Florida in cooperation with Reynolds, Smith, and Hills,

Architects and Engineers, Jacksonville, Florida.

Effluents Available

The experimental evaporator was set up adjacent to the 2 MGD

Campus Sewage Treatment Plant operated by the University of Florida.

This plant handles the flow from the main campus, the teaching

hospital and medical center complex, fraternities, sororities,

dormitories, an elementary ~chool, and several married student








apartment complexes. Flow from all these sources results in a waste

reasonably typical of municipal sewage. The Campus Plant operates a

primary treatment unit, a high rate trickling filter, a standard

rate trickling filter, and a contact stabilization activated sludge unit.

A 9,000 GPD extended aeration unit is also available for use but is

not operated routinely. Effluents from any of these units are avail-

able for experimental purposes.

Experimental Plan

The experimental work was divided into two principal phases. The

first phase was directed towards defining the relationships between

feedwater quality, product quality, and evaporation conditions, Zx-

perimental runs were to be made operating the evaporator as a single

effect unit and using progressively poorer quality effluents as feed-

water. By this procedure we would minimize the possibility of having

major difficulties with excessive organic fouling as was experienced
10-13
during the work done at American Machine and Foundry, Inc. Thus

testing was to proceed using, in order, extended aeration plant

effluent, contact stabilization plant effluent, high rate trickling

filter effluent, and primary effluent until either operational

difficulties or product water quality dictated that further testing

with poorer quality effluents was not justified. Evaporator operating

conditions were to be varied over the range from about 28 inches Hg

vacuum to about 50 psig. Also, the pH of the feed was to be varied

to see the effects on ammonia carry over to the pradurt. In addition

to measuring the relationships between these variables and product

water quality, the first testing phase included the evaluation of

several post treatment processes. These included activated carbon








treatment, aeration, and ammonia removal by ion exchange.

After completion of the first phase of the experimental work

some preliminary judgements were to be made regarding the practical

limitsfor both minimum fecdwater quality and maximum evaporator

operating temperature consistant with acceptable product water.

Using conditions at or near these limits, extended continuous runs

utilizing all three evaporator effects were to be made to evaluate

scaling or fouling. It was anticipated that these runs would last

one to two weeks each. Scaling was to be evaluated both directly and

indirectly. By analysis of the overall heat transfer coefficients,

Uo, for each stage we would be able to measure scaling by drop in Uo

Alsoafter each run we planned to clean the evaporator mechanically

and measure the amount of scale removed. Alsowe planned to analyze

the scale to determine the cause of the scaling.

In addition to providing data on scaling, the extended runs would

provide considerable additional data on the quality of product that

could be expected under the conditions we felt would be most likely

to be used in full scale operations.

Analytical Plan and Procedures

In the analytical work we were concerned with three types of

waters: 1) sewage treatment plant e~fluent or evaporator feedwater,

2) evaporator product water, and 3) the concentrated effluent from the

evaporator, and with one solid material, evaporator scale.

Table 3 lists the analyses made on the liquid samples and the

procedure used. The very large number of samples involved dictated

that automated analysis techniques be used as much as possible.

Chemical Oxygen Demand, GOD, was used as an indicator of the


























COD Alternate Procedure for Dilute Samples,
Standard Methods for the Examination of
33
Water and Wastewater


TABLE 3


ANALYTICAL TESTS ON LIQUID SAMPLES

Procedure


Test


Ammonia Nitrogen




Nitrate Nitrogen




pH


Odor


Industrial Method Ind.-19-69w of Techni-
con Corp. Used Technicon AutoAnalyzer


Method of Kahn and Brezenski modified
for Technicon AutoAnalyzer48



Corning Model 12 pH meter


Subjective opinion of operator


Residue on Evaporation at 1030C, Standard
Methods for the Examination of Water and
WastewaterS3


Total Dissolved Solids




-32-


organic content of the samples. We anticipated that the primary problem

here would be accurately measuring COD on the product samples. In

order to strengthen our ability in this area, we spent considerable

time over a period of several months trying to perfect a total organic

carbon procedure that would be accurate in the 0-3 mg/l range.

Unfortunately, with the equipment we had available, we were never able

to develop a procedure as precise as the dilute COD procedure and this

effort was finally abandoned.

Ammonia nitrogen was one of the most important variables in this

study and its significance has been discussed previously.

Nitrate nitrogen was used to indicate the degree of nitrification

in the various sewage treatment plant effluents used. Another very

significant use of nitrate results was to measure the degree of

physical carry over of material into the evaporator product water.

Since nitrate is non-volatile, a material balance over the evaporator

based on nitrate would be a very accurate measure of physical carry

over.

The importance of pH in arranonia distribution and in scaling has

been discussed previously. Measurements were made primarily on
o o
feedwater samples. Samples were adjusted to 25 C + 5 C prior to

measurement.

Odor was subjectively measured by the operating personnel at the

time the products were produced. The difficulties involved in obtaining

an odor-free room and an experienced panel dictated against more

rigorous odor testing.

Total dissolved solids were measured on a few of the feedwaters

and concentrated affluent samples, primarily to better characterize







the evaporator feedwater.

Some additional test results taken from the records of the Campus

Sewage Treatment Plant were used to characterize influent and effluent

materials from the various plant processes.

The scale removed from the evaporator was first dried at 103()C

and weighed to obtain a total weight figure. The samples were then

fired at 6000C to remove the organic material. The fired residues

were dissolved in dilute hydrochloric acid and the solution analyzed

as shown in Table 4.




















ANALYTICAL TESTS ON SCALE

Test For Procedure Used

Ca EDTA Titrimetric Method, Standard
Methods for the Examination of Water
and Wastewater33


Mg Atomic Absorption Method Using Beekman
DB-G Spectrophotometer


Na Same as above


Fe Phenanthroline Method, Standard Methods
for the Examination of Water and
Wastewater33



S04 Turbidimetric Mechad, Standard Methods
for the Examination of Water and
33
Wastewater


PO Method of Murphy and Riley49


Note: Fired scale samples were dissolved in 0.5N HC1


TABLE 4














IV. DESCRIPTION OF EqUIPMENT

A general flowsheet for the process is shown in Figure 3. Feed-

water for the system could come from either an extended aeration plant,

a trickling filter plant, or a contact stabilization plant. Before any

of these effluents were fed into the evaporator, the dissolved gases

and carbonates were removed. This was accomplished by adjustment of

the pH and degassing under a vacuum. After degassingthe liquid was

fed into a three effect, long tube vertical (LTV) evaporator. This

evaporator was built almost entirely of type 316 stainless steel.

After evaporation, provision was made to treat the product water

either in an activated carbon column or an ammonia selective ion

exchange column or both.

DcRasser

A diagram of the degassing equipment is shown in Figure 4. Effluent

from the various sources was put into a 175 gallon agitated tank for

mixing and ph adjustment. The agitator was a flat blade 30" in

diameter by 1 3/8" high and was driven at 100 rpm. From the mix tank,

the effluent passed through a packed column under vacuum to remove

dissolved gases. The packed column was 4" O.D. glass tubing. Vapor

and dissolved gases were removed from the column through a condenser

and liquid trap by a sliding vane type vacuum pump (Gast Manufacturing

Corp. No. 0765-V39). Degassed liquid was pumped from the bottom of

the column to one of two 55 gallon open top feed drums by a variable

speed screw type pump (Robbins & Myers, Moyno Model 114 Type CDQ).


-35-


















































Figure 3. Overall Flowsheet











TREITMEHT FLINT


YARIABLE SPEED DRIVE
STEAM SCREW TYPE PVMP






Figure 4. Degassing System Flowsheet




-JO-


The two feed drums were fitted with polyethylene drum liners. The

mixing tank, piping, and pump in the dcgassing system were of steel

construction,

Temperature in the column was measured by a thermometer inserted

into the column through a small port. Provision was made to introduce

steam into the bottom of the column.

Evaporator

A diagram of the evaporator is shown in Figure 5 and a picture of

the evaporator is shown in Figure 6. The evaporator was designed to

operate either as a triple effect unit or as a single stage unit

(3rd effect only). Possible operating conditions in the evaporator

ranged from about 28 inches of Hg vacuum to 100 psig. Actual operating

conditions under pressure conditions were limited to about 55 psig by

the steam pressure available at the site.

Heat for the evaporator could be supplied to either the first or

third effect. The heating medium could be either steam or hot water.

Steam was taken from the campus steam line and was reduced at the

inlet to the evaporator by a steam regulator (Cash-Acme Inc., No.

5681UE). When operating under high vacuum, it was necessary to reduce

the temperature of the heating medium to avoid unrealistically high

temperature drops. This was done by using a closed hot water system.

The water was circulated continuously through the evaporator and a

natural gas fired hot water heater (Odis Stove Manufacturing Co.,

No. 35DP).served as the heat source.

Feed was pumped into the evaporator by a diaphragm metering pump

(Yarway Cyclo/Phram Model No. 071-33-1431). A spring loaded, back

pressure valve on the downstream side of the pump prevented liquid










VLS VAPOR-LIPUIO SEPARATOR
LLC LIPUID LEVEL CONTROL
HWO HOT WATER OUT
HXI HOT WATER IN

CWO COOLING WATER DUT
CWI COOLING WATER IN

VAP.- VAPOR
LIO.- LIOUIO


NOTE: NOT TO SCALE
YARIABLE SPEED PUMP RECEIVERS 8 YARIABLE SPEEO PUMP

0.1 0.6 gpm DRAIN CONTROLLEDO BY LLC)


Figure 5. Evaporator Flowsheet




-40-


Figure 6. Evaporator








from being drawn through the pump when the system was operating under

vacuum conditions. Each of three effects was constructed of 1 inch

IFS Schedule 5 pipe, jacketed with 4 inch IFS Schedule 5 pipe. The

effective heated length of each effect was 14 feet.

Vapor-liquid separators atop each effect separated the steam-

liquid mix into two streams. This equipment is shown in Figure 7.

The demisters were 316 stainless steel mesh (Otto H. York Co., Style

326). Small vent lines (1/4" O.D. tubing) with needle type control

valves connected the steam Jacket of each effect with its vapor-

liquid separator.

Liquid seals were maintained between stages by float controlled

liquid drainers (Armstrong Machine Works, Model No. 21) having 7/32"

diameter orifices. These drainers were chrome plated cast iron with

stainless steel internals. Originally, drainers with 1/16" diameter

orifices were tried, but were replaced because the capacity was

marginal and chances of plugging were much greater than with larger

units.

To reduce heat loss to the atmosphere, the three evaporator

effects and connecting piping were insulated with 1 inch thick

asbestos type insulation. The three vapor-liquid separators were

completely enclosed with custom built foamglass type insulating

covers with aluminum exteriors.

Removal of the concentrated liquid effluent from the last effect

was accomplished by a diaphragnmetering pump identical to the feed

pump. This pump was automatically controlled ton-off) by liquid

level probes located in an enlarged section of the liquid line from

the third effect vapor-liquid separator. Cooling coils, located













PRESSURE


PRESSURE
RELIEF YALVE


TO TEMPERbTURE RECOROER







9
YIPOR

:MISTER
HICI;




IOTE: OEFLECTOR SUPPORTED BY
~ ROOS ITTACHEO TO THE
I~LL OF THE SEPIRATOR
BOOr.


i~M

SCILE: NONE


J
LI(IUIO


Figure 7. Vapor-Liquid Separator







between the liquid level probes and the pump, cooled the concentrated

effluent to prevent flashing of the hot liquid wl~en released to

atmospheric pressure. All concentrated effluent piping was steel.

The back pressure valve following the pump was a copper alloy.

Condensate was removed from the jackets of the three effects

through controlled disc type steam traps (Sarco Company, Type TD-50).

Vapor from the third effect was condensed in a water jacketed

condenser. The condenser was a 2" IFS pipe with an effective con-

densing length of 12 ft.

Product from the three stages was removed by several means,

depending on the evaporator operating conditions (See Figures 5 and

8). Under pressure conditions, product No. 3 was removed from the

final condenser through an adjustable back pressure valve (Watts

Regulator Co., No. 5300A). This valve was of chrome plated copper

alloy construction. Product Nos. 1 and 2 were removed through the

vacuum receiver system as shown in Figure s except that the system

was opened at valves D allowing the products to drain continuously

to glass carboys.

Under vacuum operation all three products were removed through

the vacuum receiver system. Under normal conditions, valves B and C

were closed and valves A were open. Valves D were check valves that

allowed flow from the upper to the lower tanks only. Hence, product

water would drain from the evaporator into the upper tanks and down

into the lower tanks through valves D. Vacuum was maintained on the

system by a vacuum p~rmp (Zeflex, No. 012-911-1), In order to remove

the product water from any one system, solenoid valves B and C were

opened and valves A were closed. The product water either drained









~~O -SOLENOIO
VALVES

~ CHECB VALVES

0-10 GALLON
RECEIVER TAN~S


VACUUM PUMP


Figure 8. Product Receiver System Flowsheet








through valves C by gravity or was drawn into evacuated carboys. When

the lower tank was empty, the cycle was reversed closing valves B and

C and opening valves A. Two 30 gallon tanks in the vacuum system

provided surge capacity when an air filled tank was cycled back into

the system. The instrumentation system provided for automatic

cycling of the receiver system to dump product water from each effect

on a timed sequence.

All six product receiver tanks were 10 gallon capacity.

Temperature was sensed by copper-constantan thermocouples at

various points in the system and automatically recorded by a 16 point

recorder (Minneapolis-Honeywe11 Reg. Co., No. Y153X64P16-X-41(v)).

The temperature range of this recorder was 0-350QF. Pressure gauges~

installed in the incoming steam line, in each vapor-liquid separator,

and in the final condenser, gave continuous visual indication of the

pressure at various points in the system.

Carbon Column

The carbon column was a 1.44" I.D. pyrex tube four feet long,

containing 42" of activated carbon. The column was fed by gravity

and flow rate was controlled by a polyethylene needle valve. The

activated carbon used was Nuchar WV-W, 12 by 40 mesh, manufactured

by West Virginia Pulp and Paper Co.

Ammonia Column

The ammonia ion exchange column was a 1.94" I.D. pyrex tube

13" long, containing 10.25" of ion exchange resin. The column was

fed by gravity and the flow rate was controlled by a polyethylene

needle valve. The ion exchange resin used was natural clinoptilolite,

20 by 50 mesh, from the Hector, California, area.














V. EXPERIMENTAL RESULTS

Initial Testing

Asstated in the research plan, the initial testing was designed

primarily to define the relationships among evaporator feedwater

quality, evaporator operating conditions, and product water quality.

Also, to be included was evaluation of several post treatment pro-

cesses and determination of how they might be included in an overall

reuse cycle.

With regards to effluents to be used, it was planned to begin

the testing with the highest quality effluent to reduce the likelihood

of severely scaling or fouling the evaporator tubes. Testing would

then proceed using progressively poorer quality effluents.

The tests on each different effluent were made at three tempera-

ture and pressure levels. These conditions are shown in Table 5.

In addition to the temperature variations, the ph values of the feed

were varied at each level to examine the effect on ammonia distribu-

tion between the concentrated effluent and product.

On selected evaporator products that would be unsuitable for

direct reuse, tests were made using activated carbon, ammonia selective

ion exchange resins, and aeration to determine the effectiveness of

these post treatment processes.

Before any sewage plant effluents were used as evaporator feed,

the evaporator was operated using tap water and distilled water. This

was done to clean out the inside of the equipment and to develop

-46-

























TABLE 5

EVAPORATOR OPERATING CONDITIONS FOR
INITIAL SINGLE STAGE TESTS


Evaporating Liquid
Temperature and Pressure

114-1200F
26.5-27" Hg vac.


2120F
O psig




286-2880F
39-41 psig


Heating Medium
Temperature and Pressure


Condition


Vacuum


Hot Water
140-1550F



Steam
228-2380F
5-9 psig


Steam
300-3050F
52-58 psig


Atmospheric





Pressure








familiarization with the operating characteristics of the equipment.

Steam was used to clean the product receiver tanks.

When the evaporator was operated as a single effect unit (3rd

stage only), equilibrium conditions for the entire system could be

reached in less than 15 minutes. The only exception occurred when the

feedwater was changed during a run. When this occurred it could take

as long as one hour to completely flush the system and obtain con-

sistant quality product water.

In these initial tests the operating procedure was as follows.

The effluent to be used was either pumped or drained by gravity from

the sewage treatment plant to the mixing tank. A sample was taken

for analysis and the plI of the remaining water was adjusted to the

bicarbonate endpoint (pH 4.8-5.0) with 6N sulfuric acid. The water

was heated to 120-1400F and then degassed under vacuum. The degassed

water was pumped to 55 gallon drums prior to being fed into the

evaporator. If required, a pH adjustment of the evaporator ieedwater

was made at this point using either sulfuric acid or sodium hydroxide.

In the degassing operation there was a 3-50F drop in temperature

caused by flashing as the water entered the top of the column. This

corresponded to the measured 0.3-0.5% (of incoming water) evaporation

rate from the degasser. The liquid evaporated during degassing usually

had a slight odor. However, the odor was normally no stronger than

the odor of products produced under atmospheric pressure conditions.

The average degassing rate was 2800 mi/min but ranged from 2100

to 3900 mi/min. This corresponds to an average loading rate in the

degassing column of 9.7 gpm/ft2 and a range of 7.2-13.4 gpmlft2

After evaporator start-up, from 30 to 90 minutes were allowed









to attain stable operating conditions and completely flush the system.

Product sampling was then begun, usually at 60 minute intervals. Since

far each operating condition one drum of feed was required, only one

feed sample was taken. One concentrated efiluent sample was taken

under each set of conditions. Total operating time, once product

sampling began, was usually 2 hours, but some runs as long as 5

hours were made.

Extended Aeration Plant Effluent

Since extended aeratian plant effluent was believed to be the

highest quality secondary effluent available, testing was begun using

this water. The effluent was from a 9,000 gpd capacity plant built

by Chicago Pump. This plant was fed raw sewage that had previously

been degritted and ground. Flow rate to the plant was maintained at

a constant rate by a constant head and weir arrangement. Excess raw

sewage from the Campus Sewage Treatment Plant was pumped to a constant

head headbox and the desired amount removed over a V-notch weir. The

excess was returned to the Campus Plant. Flow to the plant during the

period that the initial batch tests were being made was 6.2 gpm

(8,920 gpd), which is the rated capacity of the plant. The plant

had been in operation for about four months prior to the initial

tests and the mixed liquor suspended solids in the aeration basin had

stabilized at about 4,200 mg/l.

Thirteen runs were made using extended aeration plant effluent,

five each under atmospheric and pressure conditions and three under

vacuum conditions. The results of these runs are shown in Tables 6,

7, and 8.

All products had odors strong enough to eliminate the possibility













INITIAL TESTS, EXTENDED AERATION EFFLUENT,
VACUUM CONDITIONS

Run No.
1 2 3

Operating Conditions
Feed Rate, mi/min 647 647 632
Evaporation Rate, mi/min 93 95 117
% Evaporated 14.4 18.5
Hot Water Temp., F 144 144 155
First Stage ~emp., OF 116 116 122
Feed Temp., F 91-96 98-106 95-103

Feed, Before Degassing
Alkalinity, mg/l CaCO, 25 25 32
pH 6.5 6.5 6.5
GOD, mg/l 49 49 65
NI3-N, mg/l 0.8 0.8 0.1
NO
3-N, mg/l 19 19

Feed, After Degassing
pH 5.3 5.8 6.6
GOD, mg/l 46 47 71
NH3-N, mg/l 0.7 0.9 0.1
NO -N, mg/l 18

Product
pH 6.6 5.9 7.2
GOD, mg/l 1.3 2.6 4.5-6.3
NH,-N, mg/l 0.04 O.11 (0.1-0.3
NO=-N, mg/l 22

Concentrated Effluent
pH 6.1 6.2 7.2
GOD, mg/l 55 54 71
NHg-N, mg/l 1.0 1.0
NO -N, mg/l 22


TABLE 6










INITIAL TESTS, EXTENDED AERhTION EFFLUENT,
ATMOSPHERIC CONDITIONS

Run No.
1 2 3 4 5

Operating Conditions
Feed Rate, mi/min 640 630 630 655 640
Evaporation Rate, mi/min 156 146 177 186 293
% Evaporated 24.4 23.2 28.1 28.0 45.8
Steam Temp., F 226 226 230 229 238
First Stage aemp., OF 212 212 212 212 212
Feed Temp., F 96-104 106-114 88-104 90-104 80-82

Feed, Before Degassing
Alkalinity, mg/l CaCO, 27 27 34 40 50
pH 6.5 6.5 6.7 6.3 6.7
GOD, mg/l 23 23 27 57 85
NH3-N, mg/l 1.4 1.4 0.42 0.09 0.42
NO -N, mg/l 7.0 7.0 9.0 8.3

Feed, After Degassing
pH 5.4 5.9 6.1 6.3 6.5
GOD, mg/l 36 32 28 65 74
NH3-N, mg/l 0.35 0.37 0.31 0.08 0.43
NO -N, mg/l 7.5 7.3 9.0 8.3

Product
pH 5.5 5.7 5.9 6.0 6.1
GOD, mg/l 0.0-0.6 0.5-0.7 2.6-3.2 3.8-5.0 1.8-5.8
NH3-N, mg/l 0.05 0.10 0.16 0.03 0.36
NO -N, mg/l 0.00 0.00

Concentrated Effluent
pH 6.3 6.4 6.5 6.3 6.7
GOD, mg/l 41 40 37 87 137
NH3-N, mg/l 0.44 0.47 1.8 0.10 0.38
NO -N, mg/l 8.1 8.1 13 14


TABLE 7





TABLE 8


INITIAL TESTS, EXTISNDED AERATION XFFLUENT,
PRESSURE CONDITIONS


Run No.
2 3 4 5


Operating Conditions
Feed Rate, mi/min
Evaporation Rate, mi/min
Sb Evaporated o
Steam Temp., P
First Stage Temp., OF
Peed Temp., -F

Feed, Before Degassing

Alkalinity, mg/l CaCO3
pH
GOD, mg/l

NH3-N, mg/l
NO -N, mg/l

Feed, After Degassing
pH
GOD, mg/l

NH3-N, mg/l
NO -N, mg/l

Product
pH
GOD, mg/l

NH3-N, mg/l
NO -N, mg/l

Concentrated Effluent
pH
GOD, mg/l

NH3-N, mg/l
NO -N, mg/l


625
182
29.1
302
288
98-118



57
6.5
110
1.3
7.4



6.2
94
1.4
7.0



6.8
5.3-12.8
1.2


630
219
34.8
304
288
109-120



49
6.7
85
0.42
8,3



6.5
74
0.43
8.3



6.3
3.3-5.0
0.59


630
165
26.2
299
286
96-104




6.5
52
1.0
7.7


635
166
26.2
299
286
104-114




6.5
52
1.0
7.7


625
146
23.4
300
288
100-115



42
6.5
97
0.40
9.3



5.9
90
0.33
8.6



6.2
3.0-5.1
0.30


4.8 5.6
47 48
1.0 0.8
7.9 7.7


5.5
3.1-3.2
0.15
0.01


5.5
2.8
0.22
0.02



6.1
52
1.4
8.5


5.9
56
1.4
8.4


6.5
106
0.43
12


6.0 6.4
104 106
1.5 0.36
10 12







of direct municipal reuse. These odors ranged from very slight musty

for products produced under vacuum to moderately strong fecal for

products produced under pressure conditions.

Contact Stabilization Plant Effluent

Contact stabilization plant effluent was taken from the Campus

Sewage Treatment Plant. This unit treats about 0.7 MGD of raw sewage.

Performance data for this plant are shown in the appendix.

Effluent from this unit was taken from the final clarifier prior

to chlorination. Fourteen runs were made, five each under vacuum and

pressure conditions and four under atmospheric conditions. The

results of these runs are shown in Tables 9, la, and 11.

All products had odors sufficiently strong to eliminate the

possibility of direct municipal reuse.' These odors ranged from musty

for products produced under vacuum conditions to a rather strong,

disagreeable, fecal type odor for products produced under pressure

conditions.

Trickling Filter Plant Effluent

Trickling filter plant effluent was taken from the high rate

trickling filter operated by the Campus Sewage Treatment Plant. This

unit treats about 0.25 MGD of raw sewage. Performance data for this

plant are shown in the appendix.

Effluent from this unit was taken from the final settling basin

prior to chlorination. This effluent was noticeably different from

the two effluents used previously in that it had a grey color and a

slight odor. Six runs were made, two each under each of the three

temperature and pressure conditions. The results of these runs are

shown in Tables 12, 13, and 14.





4 5


aThis run iamnediately followed Run No. 5 and the high NH3-N result may
have been due to contamination from the previous run


TABLE 9


INITIAL TESTS, CONTACT STABILIZATION EFFLUENT,
VACUUM CONDITIONS


Run No.
1 2 3


~perating Conditions
Feed Rate, mi/min
Evaporation Rate, mi/min
"6 Evaporated
Hot Water, Temp., OF
First Stage,~Temp., OF
Feed Temp., F

Feed, Before Degassing
Alkalinity, mg/l CaCO3
pH
GOD, mg/l

NH3-N, mg/l
NO -N, mg/l

Feed, After Degassing
pH
GOD, mg/l

NH3-N, mg/l
NO Nmg/l

Product
dH
GOD, mg/l
~H3-N, mg/l
rid Nmg/l

concentrated Effiuent
PH
GOD, mg/l
NH3_N, mg/l
NO -N mg/l
7___~


630
78
12.4
140
114
89-98


635
88
13.9
141
113
87-93


625
90
14.4
141
114
91-96


645
128
19.8
146
113
92-108


630
79
12.5
140
114
93-106


70
6.9
23
5.1




5.6
29
6.4
0.5



6.9
3.6
1.6a


82
7.1
23
6.5
0.9



5.6
20
6.8
0.4



6.7
2.5
0.14


82
7.1
23
6.5
0.9



6.3
19
6.6
0.5


93
7.2
30
9.0
0.28



6.7
35
8.5
0.31


70
6.9
23
5.1




7.7
24
5.8




9.1
4.0
6.9




8.2
23
5.9


7.4 8.4
3.2 0.9-2.9
0.9 2.9
0.00


7.4 6.8 7.3 7.4
29 22 22 42
6.4 7.7 7.3 7.6
0.6 0.4 0.5 0.36























Run No.
1 2 3 4


TABLE 1D


INITTAL TESTS, CONTACT STABTLIZATION EFFLUENT,
ATMOSPHERIC COM)ITIONS


Operating Conditions
Feed Rate, mi/min
Evaporation Rate, mi/min
% Evaporated
Steam Temp., OF
First Stage ~an~., OF
Feed Temp., F

Feed, Before Degassing
Alkalinity, mg/l CaCO
pH
GOD, mg/l

NH3-N, mg/l
NO Nmg/l

Feed, After Degassing
pH
GOD, mg/l

NH3-N, mg/l
NO -N, mg/l

Product
pH
GOD, mg/l

NH3-N, mg/l
NO -N, mg/l

Concentrated Effluent
pH
GOD, mg/l
NH3-N, mg/l
NO -N, Ing/i


635
169
26.6
230
212
95-104




6.9
24
3.3
3.1


640
144
22.5
227
212
94-106



101
7.1
68
6.6
0.17


630
172
27.3
230
212
97-108




6.9
24
3.3
3.1


640
163
25.4
229
212
84-108



93
7.1
27
7.0
0.49


5.1 5.7
29 62
3.5
3.1 0.23


5.9 6.5
25 32
4.3 9.2
3.1 0.48


5.7
4.7-5.0
0.22


7.1
2.9-3.5
0.9


6.4
2.1-3.0
0.3


6.6
1.1-2.7
4.2
0.01


6.4 6.4
30 64
4.0
4.1 0.41


6.4 7.5
27 32
3.7 10.0
4.3 0.64


















INITIAL TESTS, CONTACT STABI~I~IZATION EFFLUENT,
PRESSURE CONDITIONS

Run No.
1 2 3 4 S


TABLIS 11


Operating Conditions
Feed Rage, mi/min
Evaporation Rate, mi/min

% Evaporated o
Steam Temp., F
First Stage Temp., OF
Feed Temp., -F


Feed, Before Degassing
Alkalinity, mg/l CaCO
pH
COO, mg/l

NH3-N, mg/l
NO -N, mg/l


Feed, After Degassing
pH
GOD, mg/l

NH3-N, mg/l
NO Nmg/l

Product
pH
GOD, mg/l

NH3-N, mg/l
NO -N, mg/l

Concentrated Effluent
pH
GOD, mg/l

NH3-N, mg/l
NO Nmg/l


635
152
24.0
299
286
94-103



91
7.0
23
6.7
0.1


630
160
25.4
299
286
86-96



69
7.1
24
4,6


630
173
27.4
300
287
102-111



91
7.0
23
6.7
0.1


615
212
34.4
301
284
91-104



88
7.0
35
7.5
0.38


630
170
27.0
299
286
97-108



69
7.1
24
4.6




7.2
24
6.4
1.1



6.6
1.5-3.4
9.4




6.8
27
4.0
1.3


5.2 5.7 6.5 6.6
22 23 22 25
7.5 5.7 7.2 8.1
0.2 0.1 0.2 0.31


6.3
1.7-2.5
2.2




6.8
24
8.5
0.3


6.0
4.2-4.7
4.5


6.9
4.0-4.9
3.3


6.6
4.8-5.2
3.5
0.02


8.3 7.3 6.8
28 25 39
5.3 7.8 8.9
0.9 0.4 0.55













TABLE 12


INITIAL TESTS, TRICKLING FILTER EFFLUENT,
VACUUM CONDITIONS

Run No.
1 2

Operating Conditions
Feed Rate, mi/min 645 640
Evaporation Rate, mi/min 100 97
% Evaporated 15.5 15.2
Hot Water Temp., -F_ 142 143
First Stage ~emp., F 113 114
Feed Temp., F 90-95 95-102

Feed, Before Degassing
Alkalinity, mg/l CaCO, 39 39
pH 6.6 6.6
GOD, mg/l 116 116
NH3-N, mg/l 5.4 5.4
NO -N, mg/l 15.2 15.2

Feed, After Degassing
pH 5.3 5.9
GOD, mg/l 101 127
NH3-N, mgll 6.0 5.5
NO -N, mg/l 13.0 13.4

Product
pH 5.8 6.6
GOD, mg/l 2.0 1.4
NH3-N, mg/l 0.1 0.6
NO N, mg/l 0.03 0.00

Concentrated Effluent
pH 6.2 6.5
GOD, mg/l --- 123
NH3-N, mg/l 6.4 6.3
NO N, mg/l 13.4 14.2












TABLE 13


INITIAL TESTS, TRICKLING FILTER EFFLUENT,
ATMOSPHERIC CONDITIONS

Run No.
1 2

Operating Conditions
Feed Rate, mi/min 645 650
Evaporation Rate, mi/min 172 172
% Evaporated 26.6 26.5
Steam Temp., OF 228 228
First Stage ~emp., F 212 212
Feed Temp., F 90-102 101-111

Feed, Before Degassing
Alkalinity, mg/l CaCO, 50 50
pH 7.0 7.0
GOD, mg/l 93 93
NH3-N, mg/l 5.1 5.1
NO N, mg/l 11.4 11.4

Feed, After Degassing
pH 5.5 6.1
GOD, mg/l 93 93
NH3-N, mg/l 5.9 5.7
NO -N, mg/l 10.0 10.8

Product
pH 5.8 6.5
GOD, mg/l 5.8-6.2 6.2-6.6
NH3-N, mg/l 0.9 1.6
NO -N, mg/l 0.06 0.02

Concentrated Effluent
pH 6.5 7.a
GOD, mg/l 105 93
WH~-N, mg/l 7.2 6.8
NO -N, mg/l 12.6 13.2











TABLE 14


INITIAL TESTS, TRICKLING FILTER EFFLUENT,
PRESSURE CONDITIONS

Run No.
1 2

Operating Conditions
Feed Rate, mi/min 630 630
Evaporation Rate, mi/min 140 165
% Evaporated 22.2 26.2
Steam Temp., OF 298 300
First Stage ~emp., F 286 286
Feed Temp., F 95-104 103-113

Feed, Before Degassing
65.7 65.7
Alkalinity, mg/l CaCO3
PH 7.0 7.0
GOD, mg/l 90 90
NH3-N, mg/l 7.5 7.5
NO -N, mg/l 16 16

Feed, After Degassing
PH 5.5 6.1
GOD, mg/l 84 80
NH3-N, mg/l 8.0 8.8
NO3-N, mg/l 9.4 9.4
Product
PH 6.0 6.3
GOD, mg/l 18.5-20.9 19.6-22.6
NH3-N, mg/l 2.4 3.7
NO -N, mg/l 0.28 0.17

Concentrated Effluent
PH 6.5 6.6
GOD, mg/l 75 76
NH3-N, mg/l ia.o 10.3
NO -N, mg/l 11.6 11.8





All products had odors as bad or worse than odors of products

produced from extended aeration effluent or contact stabilization

effluent. As in previous runs, odors tended to increase with increasing

operating temperature.

The products produced under high temperature and pressure condi-

tions had a definite hazy appearance. With this one exceptionally

effluents tested under all operating conditions produced products having

a crystal clear appearance.

Results of COD analyses made on these products indicated that

organic contamination was significantly worse than had been experienced

during previous tests using cleaner feedwaters. Since we seemed to

have reached a significant break-point with regards to product water

quality, the decision was made to conduct no further single stage

tests with poorer quality feedwater.

Activated Carbon Tests

In order to evaluate the effectiveness of activated carbon for

removal of any odors remaining after evaporation, a bench scale

granular activated carbon column was set up. This unit was 1.94" I.D.

and contained a 42" deep bed of Nuchar WV-W manufactured by West

Virginia Pulp and Paper Co. This grade of activated carbon has a

greater proportion of small pores and is specifically recommended for

removal of organics causing taste and odor problems in municipal water.

Since all products produced during the initial single stage

testing had some odor, it was necessary to test examples of products

produced under all conditions. Each test consisted of continuously

feeding the product water to the carbon column at a rate of about

1 gpmlft2 until several column volumes had been flushed through the







column. After this flushing, samples were taken of the column feed

and product for analysis. The operator would also make observations

to determine whether or not any odor remained in the water from the

column. In some cases the opinions of several people were secured

regarding the odor of the product water.

Twenty runs were made using the activated carbon column during

the initial testing phase. Six were made using products from extended

aeration effluent, ten using products from contact stabilization

effluent, and four using products from trickling filter effluent.

In all cases the odors were either eliminated or reduced to such a

level that they could be detected by only a minority of the odor test

panel. The worst sample tested was a product produced under high

temperature and pressure conditions using trickling filter effluent;

After activated carbon treatment only one out of five members of the

odor test panel detected any odor at all. COD values before and after

carbon treatment for this sample were 20.7 and 3.4 mg/l.

The average COD values in and out of the carbon column for the

twenty runs were 4.4 and 1.35 mg/l. Omitting the trickling filter

product noted above, these averages drop to 3.6 and 1.25 mg/l.

Ammonia Ion Exchange Tests

To evaluate the feasibility of removal of ammonia from the product

water by ion exchange, a bench scale ion exchange column was set up.

This column was 1.94" I.D. and contained 10.25" of clinoptilolite, a

natural exchange resin selective for ammoni~rm ion. In each test, the

column was operated continuously until the column had been thoroughly

flushed and then samples were taken of the column feed and product.

Surface loading rates of 1.2-1.4 gpm/ftl were used. A total of six









tests was made using feedwater containing from 2.5-5.0 mg/l hTH3-N.

Ammonia in the column effluent ranged from 0.12-0.32 mg/l NH3-N. In
all. cases ammonia removal exceeded 90% and averaged 94.4%.

Aeration Tests

Probably the most economical means of removing odors from the

evaporator product water would be aeration. However, the effectiveness

of this method was not knor~m. To evaluate aeration for odor removal,

a 13 Liter sample of product water was aerated in a 5 gallon carboy

using a diffuser stone to disperse the air. The product water used

was produced from extended aeration plant effluent under atmospheric

pressure and initially had only a mild odor. The sample was aerated

up to 1.5 ft3/gal. This air volume exceeds by an order of magnitude

the amount normally used in aeration for odor runoval.50 Little, if

any, change in odor could be detected in the water.

Because of the poor results from this test, no further evaluations

of aeration for odor removal were made.

Product Water Conductivity

Conductivity measurements were made on products produced under

atmospheric and pressure conditions using extended aeration effluent

and contact stabilization efflucnt as feedwater. It was found that

conductivity correlated closely with the amount of ammonia in the

product for products with less than 1.5 mg/l NH3-N. Data for 31
product samples are shown in Figure 9. A least squares regression

line for these data indicates a conductivity of 1.7 x 10~6 mho/cm at

70C for zero ammonia. Converting this to 200C gives a conductivity
-6
of about 2.5 x 10 mho/cm. By comparison, distilled water in

equilibrium with air has a conductivity of about 1 x 10~6 mho/cm and












































PROOUCT WATER FROM INITIAL
TESTS USING EXTENOEO AERATION
` AND CONTACT STABILIZATION FEED.



YEISURED AT 4-11 DC. TO CONVERT
TO 20 OC MULTIPLY BY 1.5



L,


NHO-N mg/l


Figure 9. Conductivity vs. Ammonia Concentration




-64-


a 1.0 mg/l solution of KC1 has a conductivity of about 2 x 10~6

mho/cm.l8

Scaling During Check-put and Initial Testing

Although there was no planned program of scale evaluation during

the check-out and initial testing phase, the evaporator was mechanically

cleaned several times and a few measurements made on the material

removed .

During the initial check-out of the system, the evaporator was

operated as a single effect unit (3rd stage only), intermittently, for

a total of about 30 hours using tap water from the water treatment

plant, Gainesville, Florida. Typical analysis of this water is shown

in Table 15, The upper end of the evaporator was inspected by re-

moving the vapor-liquid separator and a light tan scale was observed.

The evaporator was not cleaned at this time and was operated, again

on an intermittent basis, for an additional 40 hours using tap water

with the ph adjusted down to 4.1-6.4 with sulfuric acid. During this

period several inspections indicated that the scale was still present

but did not seem to be Setting any worse. At the end of this period

(70 hours total operating time) the evaporator tube was mechanically

cleaned with a power driven wire brush and the scale retained. A

total of 16.5 grams of dry scale was removed from the evaporator.

Approximate analyses on this scale indicated that it was largely

calcium carbonate.

Shortly after this cleaning, the degassing equipment was installed

and all feed was degassed prior to being put into the evaporator.

The evaporator was cleaned a second time after about 65 hours of

operation using degassed extended aeration and contact stabilization





























Total Hardness 95 mg/l as CaC03
Calcium Hardness 48 mg/l as CaC03
Magnesium Hardness 47 mg/l as CaC03
Total Alkalinity 73 mg/l as CaC03
Sulfate 32 mg/l as SO4
Chloride 20 mg/l as C1
Total Dissolved Solids 211 mg/l
pH 8.4


TABLE 15

TYPICAL ANALYSIS OF TAP WATER,
GAINESVILLE, FLORIDA








affluents. This time only 0.92 grams of scale were removed. No analyses

were made on this scale.

The evaporator was cleaned a third time after the completion of

the initial single stage tests. The scale removed was inadvertently

discarded before it could be analyzed.

Long Term Runs

Based on the results of the single stage tests, it appeared that

no combination of effluent feedwater and evaporator operating conditions

would give a product acceptable for municipal reuse without further

treatment. Likewise, all product water appeared amenable to treatment

by activated carbon to an acceptable quality level for reuse. Since

it would be economically desirable to operate a full scale unit at as

high a temperature and pressure as possible, it was decided to carry

out the long term tests under the high temperature and pressure

conditions used in the initial tests. All three evaporator effects

were used.

The major purpose of these tests was to evaluate the scaling

potential of the particular feedwater being used. Since the evaporator

was operated as a three effect unit, it was possible to evaporate a

greater percentage of the feedwater and thus observe the scaling that

might occur in the latter stages of a full scale unit. After each

extended runthe scale in each stage was mechanically removed and

analyzed. In addition, the overall heat transfer coefficients for

each effect were calculated as a function of time. Thus it was

possible to get some indication of scaling during a run without having

to shut down the equipment.

In addition to information on scaling, the long term runs gave








additional product quality data over a long period of time. Also,

quality data were obtained on products from the second and third

evaporator effects. Previous single effect tests had given information

only on the first effect product quality.

Operating and sampling procedures during the long term runs were

as follows. Fresh feed for the evaporator was prepared every 8

hours by degassing approximately 100 gallons of fresh effluent. Thus

two 55 gallon drums of feed were used every 8 hours. Samples of the

effluent being used, before degassing, were taken once every 8

hours and composited for 24 hours. Samples of the degassed feed and

concentrated effluent were taken every 4 hours and composited for

12 hours. All the product water from each stage was collected con-

tinuously and measured and sampled each hour. The product samples

were composited for 12 hours.

First Extended Aeration Effluent Run

The first long term run was carried out using extended aeration

effluent. It was planned to operate with 3000F steam and adjust the

third stage pressure to evaporate about 75% of the incoming feed.

The evaporator was operated for a total of 323 hours (13 days 7 hours).

This excluded 9 hours down time to make minor repairs on the equipment.

Other than these two brief shutdowns, one to tighten a leaking fitting

and another to repair a liquid seal, the run was reasonably routine.

Trouble was periodically encountered with maintaining the incoming

steam to the first effect at 3000F. It was determined that there were

actually two problems. First, the first effect pressure was too near

the supply line steam pressure, and at times there was not enough

pressure differential across the steam regulator to reliably maintain




VV


the first effect: pressure. Second, the steam trap in the condensate

line from the first stage was oversized and allowed a 5-10 degree

temperature drop every time it opened to discharge condensate. Con-

sequently, on the eighth day of the run the steam temperature to the

first effect was lowered to 292~F. This gave better control, but

some temperature variation was still caused by the oversized trap.

This problem had little effect on the validity of the scaling or

product quality results, but it did make it rather difficult to deter-

mine individual heat transfer coefficients.

During the run an attempt was made to maintain a temperature drop

of 32-34-F from incoming steam to third stage vapor-liquid separator

temperature. At a constant feed rate of 630 mi/min this gave an

average product rate of 422 mi/min or 67% of the feed rate. The

product rates are shown as a function of time in Figure 10. Problems

with steam control caused some variations in product rates. However,

there were other variations that could not be accounted for by this

factor. Overall, there was a slight increase in the total product

rate over the run. This increase was due to increases in the rates

from the second and third effects. These increases apparently were

the result of decreased heat losses which resulted when the slightly

damp insulation on these effects dried. There was a cycling pattern

in the output rate that occurred within the individual effects as well

as with the total. It was noted that the product rate occasionally

increased markedly immediately following some type of temporary

operationalupset. Also, there were times that the concentrated effluent

contained unusually high levels of dark-colored, suspended solids.

The analytical results for samples taken during this run are shown

in Table 16.











500





TOTAL


400








E 300






r: I FIRST EFFECT c

~ 200


SECDND EFFECT





rCo -I THIRO EFFECT










12 13 ~ 14 ~ 15 ~ Is ~ 1~ ~ Is 19 ~ 20 ~ 21 ~ 22 ~ 23 ~ 24 ~ 25 ~ 26

MARCH


Figure 10. Product Rates, First Xxtended Aeration Effluent Run

















___ ___1 _ ___


TABbE r6


ANALYTICAL RESULTS FIRST EXTENDED AERATION EFFLUENT RUN


Total
Dissolved
So lids"


Suspended Total
Solids" Hardnessb


NHI-N


NO~-N


Feed
Before Avg. 46.5 0.37 17
Degassing Range 35.4-63.8 0.28-0.59 12-21

Aft er Avg. 39.0 0.36 18
Degassing Range 28.3-49.4 0.20-0.62 12-24


404 20
398-410 15-24

388 16
354-428 10-20


1,084 56
938-1,222 31-101


6.6
6.3-7.0

95.3 5.8
93.6-97.8 5.5-6.2


6.2
5.8-6.6


Concentrated
Effluent


Avg. 105
Range 72-211


1.4 55
0.9-2.2 42-70


Products
ti


Avg. 5.9 0.12 0.16
Range 1.2-14.7 0.05-0.19 0.00-0.23


Avg. 5.0
Range 1.8-8.6

Avg. 4.3
Range 0.8-9.5


0.13
0.06-0.21


0.10
0.00-0.17


0.10 0.15
0.03-0.22 0.00-0.55


aSpot checks


on less than 5 samples


bA CaC03; spot check on 8 feedsamples and


l'concentraeed effluen~ sample









After the completion of the run the evaporator tubes were

mechanically cleaned and the scale retained. Results of the analysis

of this scale are shown in Table 17.

Trickling Filter Effluent Run

Based on the good results of the extended aeration effluent run,

it was decided to make an extended run under pressure conditions using

trickling filter effluent. Prior to the start of this run the over-

sized steam trap in the condensate line from the first stage was

replaced with a smaller trap. This change made it possible to control

the incoming steam temperature closer to 292~F. The operational and

sampling procedures were the same as were used during the first extended

aeration run.

The run lasted 285 hours (11 days 21 hours). Total down time was

one hour. The feed rate was held constant at 630 mi/min. For the

overall run the total product rate averaged 457 mi/min or 72.6"/. of

the feed rate. Daily averages for the total product rate ranged from

404 to 497 mi/min or 64.2 to 79.0% of the feed rate, The overall trend

in total product rate was downward. As in the previous test, cycling

in the product output rate and periodic increases in suspended solids

in the concentrated effluent were observed.

Analytical results for samples taken during this run are shown

in Table 18.

Close control of operating temperatures made it possible to

calculate accurate overall heat transfer coefficients for each effect.

The 12 hour averages for these results are plotted in Figure 11. In

general, the coefficients decreased with time, but tended to show a

cyclic pattern.


















Stage No.
1 2 3

Total Weig~it, gms_ 0.83 1.04 3.65
7. BenzeneSolublel 2.5 3.8 4.3
% Organic- 39.7 53.1 35.2

Analysis of Fired Residue
'/.S~luble in O ~N HCI 78.1 65.8 91.OC
% Calcium as Ca 14.3 11.3 12.4
% Magnesium as~Mg~ 1.4 1.6 0.7
4 Sodium as Na" 1.0 0.7 1.3
Z Iron as Fed 13.5 1.8 8.0
% Sulfate as SO 0.0 5.1 17.7
% Phosphate as ~04d 18.5 26.5 13.5


Soxhlet Extraction
bgenzene soluble + loss after firing at 600aC
CMore severe conditions used to dissolve this sample
dExpressed as percentage of soluble inorganic scale


TABLE 17

SCALE FROM FIRST EXTENDED AERATION EFFLUENT RUN










TABLE 18

ANALYTICAL RESULTS TRICKLING FILTER EFFLUENT RUN

Total
COD NH?-N NO?-N Solidsl pH

Feed
Before Avg. 112 12.1 6.3 --- 7.1
Degassing Range 85-133 2.7-17 0.7-11 --- 6.7-7.4

After Avg. 109 14 7.7 456 5.7
Degassing Range 77-140 7.6-20 4.4-12 365-562 4.8-6.5

Cone ent rat ed Avg. 286 40 35 1,635 5.8
Effluent Range ~202-367 19-66 15-6i 1,405-2,302 5.0-6.4

Produces
ai Avg. 22.2 2.9 0.08
Range 7.6-35.5 1.1-3.8 0.04-0.19

a2 Avg. 12.0 2.4 0.06
Range 7.4-23.6 1.0-3.1 0.03-0.11

~3 Avg. 9.4 2.7 0.10
Range 4.0-15.4 1.2-3.9 0.04-0.14


aSpot checks on 5 samples each














































































I I I I 1 I I I I I I
B 7 8 9 1D 11 12 13 14 15 18 17

APRIL


Figure 11. Overall Heat Transfer Coefficients





I-l~l I I I
30 1 2

MAY


1


700 1


FIRST STAGE


o SECOND STAGE

a THIAO STAGE


Y
D

N' 800






c
m

ur

z 500
u

o
rr.
LL
W
O
O

Y
Y
ur *00
r
4
~I
C

C
4
Y
r

_I
4
~ 300
;r
o


~






EXTENDED

AERATION

RUN


TRIC~LIND FILTER RVN


lr


200

























''Soft" Scale, Stage I"Hard" Scale, Stage
1 2 3 1 2 3

Total Wei~ht, gms 5.01 3.04 6.88 0.25 0.94
ZOrganic 52.4 63.5 54.4 35.8 26.9

Analysis of Fired Residue
% Soluble in 0.5N HC1 79.5 68.1 80.0 96.7 93.3
% Calcium as Cab 7.7 15.5 20.9 21.8 23.0
~ Magnesium as Mgb 0.8 1.4 0.7 0.3 0.1
% Sodium as fjab 2.6 3.4 0.8 0.8 0.6
% Iron as Fe 19.4 3.8 4.4 0.3 0.0
Z Sulfate as S04 b 7.3 20.0 38.2 54.8 51.5
% Phosphate as PO 18.4 17.1 8.5 13.3 4.2


TABLE 19

SCALE FROM TRICKLING FILTER EFFLUENT RUN


a
Loss after firing at 6000C
bExpressed as percentage of


soluble inorganic scale









After the completion of the run the evaporator tubes were

mechanically cleaned and the scale retained. As had been experienced

before, most of the scale was removed by the power-driven wire brush

in less than 5 minutes. However, there was some harder grey scale

in the upper portion of the evaporator tube in effects two and three.

Most of this scale was removed only after considerable additional

scrubbing with the wire brush. This "hard" scale was collected and

analyzed separately from the previously removed "soft" scale. Results

of the analysis of these scales are shown in Table 19.

To confirm the initial single stage test results with regards to

odor removal, samples of each product were treated in the activated

carbon column. The same column set-up used previously was used in

these tests. The column loading rate for all three products was

1.0 gpm/ft. The odor was completely removed from all three products.

COD results are shown in Table 20.


TABLE 20

ACTIVATED CARBON TREATMENT OF PRODUCTS FROM
TRICKLING FILTER EFFLUENT RUN

COD
Before Carbon After Carbon
Treatment Treatment

Product from Effect ~1 20.1 4.9

Product from Effect ~2 11.6 3.3

Product from Effect 83 10.6 0.1




Second Extended Aeration Effluent Run

A reasonable explanation for the cycling in product output and

heat transfer coefficients observed during the first two long term








runs seemed to be that relatively soft scale was alternately building

up and then flaking off the evaporator tube walls. The periodic

increases in suspended solids in the concentrated effluent was further

evidence that this was occurring. To further test this theory, a

second test using extended aeration effluent was made. This test was

limited to 5 days. If, after 5 days, quantities of scale were

found well out of proportion of what would be expected based on the

previous 14 day test, this would further confirm that scale was

alternately building up and flaking off.

The operational and sampling procedures used in this test were

identical to those used in the first two runs. However, from the

beginning of the run there was an abnormally high product rate from

the third effect. The liquid seal between the second and third effects

appeared to be leaking, allowing a small amount of vapor from the

second vapor-liquid separator to enter the bottom of the third effect.

It was felt that this would have little if any effect on the scaling

rate and the decision was made not to shut down for repairs. However,

the problem appeared to worsen with time, and on the third day of the

run the unit was shut down for 5 hours and the liquid seal repaired.

Other than the problem with this seal, the run was rather routine.

The evaporator was operated for a total of 113 hours (4 days 17 hours).

Total down time was 5 hours.

Analytical results for samples taken during this run are shown

in Table 21.

Heat transfer coefficients for the three effects were calculated

for the latter part of the run after the liquid seal was repaired.

These results, calculated as 12 hour averages, are shown in Figure 11.













TABLE 21


ANALYTICAL RESULTS SECOND EXTENDED AERnTION EFFLUZNT RUN


Total
Solidsa


NH?-N


NO?-N


Feed
Before
Degassing


Avg. 74
Range 38-97


0.39 14
0.25-0.52 14-15


0.37 14
0.28-0.51 14-16


6.8
6.7-7.0

5.7
5.5-6.0


Aft er Avg. 35
Degassing Range 29-43


335
328-341


Concentrated
Effluent


Avg. 136
Range 76-203


2.3
1.6-3.7


79
62-98


1,643 5.8
1,265-2,075 5.5-6.7


Products
1~1


Avg. 7.4 0.08 0.09
Range 3.4-13.2 0.00-0.11 0.05-0.13


Avg. 4.6
Range 1.4-8.2

Avg. 4.0
Range 0.9-7.5


0.12 0.13
0.06-0.17 0.04-0.26


0.08
0.02-0.11


0.00
0.00


aSpot check of 5 samples each









During the latter part of the run, three complete sets of samples

were taken for bacterioZogical analyses. Results of these tests are

shown in Table 22. In addition to the coliforrn tests, a test designed

to check bacterial sterility was run on all samples. In this test the

sample is incubated at 350C for seven days in nutrient broth. This

test revealed that all product samples from the first and second effects

were sterile. All other samples showed some biological activity.

After the run was completed the evaporator was mechanically

cleaned and the scale retained. Results of analysis of this scale are

shown in Table 23.

Three Effect Ammonia Distribution Tests

Some indication of ammonia carry over as a function of feed pH

and evaporator operating conditions was gained in the single effect

tests. However, additional information was needed regarding the

distribution of ammonia between product and concentrated effluent

in subsequent evaporator effects.

To obtain this information, a series of tests were made utilizing

all three evaporator effects. Degassed contact stabilization effluent

was used as the feedwater. The pI1 of the feed was varied from 6.0 to

8.7 and the evaporator was operated at least 4 hours under each pH

condition. Product samples were taken from the last 2 hours pro-

duction and composited. Feed and concentrated effluent samples were

taken at the end of each run. Feed rate was held constant at 630 mi/min

and the total evaporation rate varied between 447 and 545 mi/min or

71.0-86.5% of the feed rate.

The analytical results for samples taken during these runs are

shown in Table 24.





















TABLE 22

BACTERIO~L~GICAI, TESTS SECOND EXTENDED AERATION
EFFLUENT RUN

Total Coliform Fecal Coliform

Sample Time Date MPN/100 mi MPN/10O mi

Extended Aeration
Plant Effluent 2400 4/30/70 1,300,000 790,000
Feed 2400 4/30/70 <2.0 2.0
Product No. 1 2330 4/30/70 <2.0 <2.0
Product No. 2 2330 4/30/70 <2.0 <2.0
Product No. 3 2330 4/30/70 <2.0 c2.0
Concentrated Effluent 2400 4/30/70 <2.0 <2.0

Extended Aeration
Plant Effluent 0400 5/1/70 490,000 330,000
Feed 0400 5/1/70 8.0 2.0
Product No. 1 0330 5/1/70 <2.0 <2.0
Product No. 2 0330 5/1/70 <2.0 <2.0
Product No. 3 0330 5/1/70 <2.0 <2.0
Concentrated Effluent 0400 5/1/70 <2.0 <2.0

Extended Aeration
Plant Effluent 0800 5/1/70 490,000 109,000
Feed 0800 5/1/70 <2.0 <2.0
Product No. 1 0730 5/1/70 <2.0 <2.0
Product No. 2 0730 5/1/70 <2.0 <2.0
Product No. 3 0730 5/1/70 <2.0 <2.0
Concentrated Effluent 0800 5/1/70 <2.0 <2.0


-VV-






















Stage No.
1 2 3

Total Weight, gms 0.92 2.54 1.89
% Organic" 30.7 36.4 28.4

Analysis of Fired Residue
X Soluble in 0 ~N HC1 70.2 87.7 87.9
% Calcium as Ca 13.0 19.2 24.4
% Magnesium as Mg 0.8 0.8 0.6
% Sodium as Nab 0.6 0.7 0.9
X Iron as Feb 14.2 2.0 2.0
% Sulfate as SO 0.9 30.1 32.4
% Phosphate as 17.8 19.2 11.9


-~I-


TABLE 23

SCALE FROM SECOND EXTENDED AERATION EFFLUENT RUN


aLoss after firing at 6000C
blxpressed as percentage of


soluble inorganic scale

















Test No.
1 2 3 4 5 6


TABLE 24


ANALYTICAL RESULTS THREE EFFECT AMMONIA DISTRIBUTION TESTS


Feed
After Degassing


pH
NH3-N
COD



pH
NH3-N
COD




NH3-N
COD


NH3-N
COD


NH3-N
COD


6.0
8.3
35



5.8
35
147



2.7
16.3


1.9
3.3


2.2
4.5


6.7
8.0
49




18
184



5.0
4.8


2.9
8.0


2.2
4.5


7.6
2.8
24



7.3
2.8
57


8.0
9.2
26



5.9
21
137



6.3
4.7


3.5
3;2


2.6
0.9


8.7
2.3
23



6.9
3.4
65


Concentrated
Effluent




Products


4.9 1.7
5.6 1.0


2.9 1.0
0.6 0.3


2.1 0.8
1.8 2.6















VI. DISCUSSION OF RESULTS

Product Quality

The first objective of this work was to define the relationships

between product water quality, feedwater quality, and evaporation

conditions. The second objective involved defining the relationships

between the above variables and post evaporation polishing. The three

primary parameters used to measure product quality were ammonia

content, GOD, and odor. Of secondary importance in measuring product

quality were such things as conductivity and nitrate content. Product

quality with regard to each of these parameters is discussed separately

below.

Ammonia Content

Ammonia is an undesirable constituent in the product water because

it consumes more than six times its weight of chlorine and produces

chloroamines which have much lower disinfecting efficiency than free
24
chlorine. Previous laboratory investigations had indicated that only

by going to extremely acid or basic conditions could ammonia distribu-

tion between the evaporator feedwater and the product water be con-

trolled.- In the work reported here, feedwater ph values between 5.1

and 8.7 were used in both single effect and three effect tests. The

test results show that for a given pH value, the fraction of ammonia

carrying over to the product increases as operating temperature and

pressure increase. This is consistent with the theoretical distribu-

tion of armnonia and ammonium ion as a function of temperature.


-83-







As can be seen from the results of the single stage tests using

contact stabilization effluent and trickling filter effluent, under

vacuum conditions, arrsnonia in the product was less than 1 mg/l for

feed ph values up to around 6.5. Under atmospheric conditions, feed

pH had to be less than 6 to control armnonia in the product to less

than 1 mg/l. It should be noted that these results are for the first

effect product only. In all the single effect tests under vacuum and

atmospheric conditions using contact stabilization or trickling filter

,effluent as feedwater, the pH of the concentrated effluent was signifi-

cantly higher than the feedwater pH. This would mean that under the

multieffect conditions that would be used in full scale applications,

ammonia could be expected to contaminate the product water in the

later stages.

:~ _I Under pressure conditipns, there was fnore ~than Img/l ammonia in

A1~Llproducts from contact .stabiLFzation ior trickling filter. fqedwater

for pH values down to 5.1. Tests made while operating the evaporator

-as a three effect unit show that this contamination persists in the

second and third effects. Raising the feedwater pH as high as 8.7

did not eliminate contamination in the second and third effects.

, There appear to be no easy ways of controlling ammonia contamina-

~iqn of the product water short of removing the ammonia from the

.feedwater. This could be accomplished by using a highly nitrified

effluent as feedwater.
51,52
T.he tests repqrted here and the work of other Investigators

show that ammonia could be removed from the product water by ion

exchange using the natural resin clinoptilolite.





Chemical Oxygen Demand

The COD test was used as an indicator of the organic content of

the product water. For the products from extended aeration effluent

and contact stabilization effluent, the COD was generally less than

5 mg/l for all evaporator operating conditions. However, when

trickling filter effluent was used, the product COD increased signifi-

cantly as operating temperature and pressure increased. Thus it

appears, that because of problems with organic carry over to the

product, trickling filter effluent is a significantly poorer feedwater

than either of the other two effluents tested.

The COD of products from all three effluents at all operating

conditions was substantially reduced by treatment with activated carbon.

However, for product water produced under pressure conditions from

trickling filter effluent, the final COD after activated carbon

treatment was roughly equivalent to the COD of the other products

before carbon treatment.

Odor

Odor in the product water will be a particularly critical factor

in any full scale application of direct wastewater reuse because of

the obvious psychological barriers. In these tests, no combination

of wastewater feed and evaporation conditions produced completely

odor free water. Product odor tended to increase in intensity and

disagreeableness as evaporator temperature and pressure increased.

Also, the more completely treated effluents tended to produce less

odorous products.

Activated carbon was effective in removing the odor from all

products. Aeration was ineffective in removing product odors.




-~IO-


There was some speculation regarding the effectiveness of the

degassing operation in eliminating odorous compounds. Based on the

relative mild odor of the degasser condensate and the odor of products

from the degassed feedwater, the degassing operation seems to have

little effect on product odor.

Conductivity

Conductivity was measured on some of the products from the initial

testing. As shown in Figure 9, conductivity was generally related to

the ammonia content of the water. However, extrapolation to zero ammonia

shows the water was of extremely high quality with regard to inorganic

salts.

Nitrate

Nitrate in the product water was used primarily as an indicator

of physical carry over to the product, i.e. incomplete separation of

vapor from liquid in the vapor-liquid separator. In practically all

cases, nitrate test results showed that physical carry over was less

than 0.5% of the incoming feedwater and in many cases much less than

this.

Since it can be shown that product waters were not significantly

contaminated by physical carry over, the organic contamination that

did occur resulted from evaporation of volatile organics and subsequent

condensation.

Bacteriological Tests

The bacteriological tests generally confirm that water safe for

human consumption can be produced by evaporation. In all cases,

product water from effects one and two was sterile. Considering this,

it appears likely that the non-sterility of the product water from









effect three was due to contamination in the final condenser and

receiver system. In any case, the product water would be further

treated by chlorination before use.

Evaporator Scaling

The third objective of this work was to define the relationships

between ftedwater quality, evaporator operating conditions, and scaling

or fouling of the evaporator heat transfer surfaces.

The first indication of the potential seriousness of calcium

carbonate scaling came during the initial check-out of the evaporator.

Tap water that had not been degassed proved to be extremely scale

forming. The 16.5 grams of scale removed from the third effect after

the first 70 hours of operation was more than the total amount of scale

removed from that effect during the entire remainder of the testing

program. Thus it appears t~~at degassing of evaporator feedwater to

remove carbonates is essential.

The results of the three long term runs indicate that scaling

from trickling filter effluent is markedly worse than scaling from

extended aeration effluent. These are discussed separately below.

Scaling by Extended Aeration Effluent

Two long term runs, one lasting about 13 days and the other lasting

about 5 days, were made using extended aeration effluent. As

explained before, the purpose of the second run was to further investi-

gate the possibility that scale was alternately building up and flaking

off in the evaporator heat transfer surfaces. The results of the

second run seem to confirm this. The amount of scale in effects one

and two after 5 days was more than had been removed from these two

effects at the end of the 13 day run. These results, the cycling








effects observed in product output rates and heat transfer coefficients,

the periodic increase in suspended solids in the concentrated effluent,

and the occasional increases in product rates observed after operational

upsets, all indicate that the scale was lightly adhering and would

periodically flake off. Thus it appears that scaling problems with

extended aeration effluent would be minor.

Analyses of the scale showed it to be about one-third to one-half

organic. The inorganic portion contained significant quantities of

calcium, iron, sulfate, and phosphate. It is probable that the iron

came from the mixing tank and associated piping when the effluent pH

was lowered for degassing. With proper materials of construction in

this part of the process, iron should not be a problem. Calcium

sulfate scale was formed only in the second and third effects. This

reflects the increase in concentration caused by evaporation. It

should be noted that, during the long term tests, conditions in the

latter two effects were more severe than would occur in full scale

application of this process. In a full scale plant, the evaporation

of the same fraction of the incoming feed would occur over a larger

number of effects and hence the temperature of the more concentrated

liquid would be appreciably lower than the 260-2700F used in these

tests. At the lower temperature, calcium sulfate would be less likely

to form scale.

Regarding calcium sulfate scale, consideration should be given

to the fact that the ph adjustment prior to degassing was made with

sulfuric acid. Acid additions during the two runs ranged from 11 to

35 mg/l S04 If higher evaporation temperatures are to be attempted,
this amount of extra sulfate could become critical.




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