Group Title: Lake Alfred AREC research report - University of Florida Agricultural Research and Education Center ; CS-75-4
Title: The present status of research on slimes of sulfur in drip irrigation emitters and filters
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Permanent Link: http://ufdc.ufl.edu/UF00072458/00001
 Material Information
Title: The present status of research on slimes of sulfur in drip irrigation emitters and filters
Series Title: Lake Alfred AREC research report
Physical Description: 6 p. : ; 28 cm.
Language: English
Creator: Ford, Harry W., 1922-
Agricultural Research and Education Center (Lake Alfred, Fla.)
Publisher: University of Florida, IFAS, Agricultural Research and Education Center
Place of Publication: Lake Alfred FL
Publication Date: 1975
Edition: Rev. ed.
 Subjects
Subject: Irrigation -- Equipment and supplies -- Maintenance and repair -- Florida   ( lcsh )
Microirrigation -- Florida   ( lcsh )
Genre: government publication (state, provincial, terriorial, dependent)   ( marcgt )
non-fiction   ( marcgt )
 Notes
Statement of Responsibility: Harry W. Ford.
General Note: Caption title.
General Note: "4/18/75 (Revised 10/6/75)-HWF-100."
 Record Information
Bibliographic ID: UF00072458
Volume ID: VID00001
Source Institution: University of Florida
Rights Management: All rights reserved by the source institution and holding location.
Resource Identifier: oclc - 76804889

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/.i/ ^' -e Alfred AREC Research Report-CS75-4
18/75(Revised 10/6/75)-IIWF-100

THE PRESENT STATUS OF RESEARCH ON
SLIMES OF SULFUR IN DRIP IRRIGATION EMITTERS AND FILTERS
Harry W. Ford
University of Florida,IFAS
Agricultural Research and Education Center
Lake Alfred, Florida 33850



This handout has been prepared for the purpose of
indicating developments in our research program.
Many of the statements are based on preliminary
observations and data and should not be construed
as a general recommendation. The statements are
subject to change as more data are available.
The handout is not a formal paper to be copied or
cited as a reference.



Many wells in south and central Florida contain hydrogen sulfide in
the water. Hydrogen sulfide is usually associated with shallow wells and
with very deep artesian wells. One can recognize hydrogen sulfide by the
rotten egg odor and by the white cottony masses of slime growing on the
ground or near outlets of artesian wells that are permitted to flow. In
general, we have found that the deep artesian sulfur water wells have
clean water. Most deep wells contain little, if any, iron in the water.
Iron can be a serious sludge problem if present. We have found that iron
may be coming from rusty old pitted casings of the well and not necessarily
from the underground water stream. A PVC liner inserted in the well shaft
will correct that particular type of iron problem. The artesian deep wells
may contain some fine particulate matter such as sand that is easily
removed by filtration. The water usually does not contain organic color
agents or other matter that complexes metals. Thus we can use the artesian
well water for drip irrigation if precautions are taken to control slimes
of sulfur.

One must have a water analysis performed on his well water. This test
should be for hydrogen sulfide, iron, piH, and suspended solids. These fac-
tors are most important from the standpoint of evaluating potential sludge
formation. However, it would also be advisable to analyze for dissolved
solids which would give an indication of whether the water is too salty
for general irrigation. It is my own personal opinion that an accurate
reading for iron and sulfides in the water can best be done at the site;
however, most commercial laboratories transport water samples to the lab-
oratory and then conduct the analysis. I would prefer that samples being
transported to the laboratory for iron analysis first be acidified at the
site to keep the iron in solution. This can be done by adding about 10
drops of concentrated hydrochloric acid for each 300-500 ml of water sample.

If the water contains more than 0.1 ppm of total sulfides, there Ls
the possibility that slimes of sulfur can be formed in the drip irrigation
system. The slimes occur because there are certain filamentous bacteria
that can oxidize hydrogen sulfide to insoluble elemental sulfur. During






The Present Status of Research
on Slimes of Sulfur in Drip
-2-
Irrigation Emitters and Filters



this process, the bacteria make sulfur globules and a sulfur slime which
may be deposited within or outside the bodies of the organisms. The
bacteria are very long and stringy so that they can form an extensive Mac
which accumulates and clogs the fine tubes in the emitters. The same
thing can occur in filters if growths should be trapped at that point.
An important characteristic of the bacteria is that they require a small
amount of oxygen to survive. Normally, deep artesian sulfur water does
not contain oxygen. If there are pin holes in the casing of the well at
or below ground level, or if valves or pipe fittings exist between the
well and the pump (often used for filling spray tanks, etc.), air may
get into the system during the pumping process. We have found that the
sulfur organisms can develop when there is less than 0.1 ppm of oxygen in
the water. We have also found that the reaction between hydrogen sulfide
and oxygen is extremely slow; therefore, the organisms have a chance to
"grab" the oxygen. The bacteria are present everywhere in the environment.
They may have gotten into the system from the soil during installation.
They may also have been present, growing on the well outlet, at any point
where there could have been oxygen.

There are several important characteristics of the reaction that can
be used in a preliminary control program. First, if there is no oxygen
in the system there can be no bacterial growth. All of the hydrogen sul-
fide in the water flows out of the emitters without causing clogging. The
white slimes of sulfur may occur on the outside of the emitters and on
the ground. On the outside, it causes no serious trouble. The second
point is that the organisms found most predominant inside drip irrigation
systems are sensitive to pH. They do not develop extensively if the water
pH is below 6.4. Third, the organisms are sensitive to certain biocides
(chemical inhibiting agents). Killing does not dissolve the organisms.
If the organism is growing ahead of the site where the chemical treatment
is made, then those organisms floating in the water will continue to float
into the emitters. Chemical treatments applied to the system must be
ahead of the point at which the organisms are growing.

Procedures Worthy of Trial on an Experimental Basis for Controlling
Slimes of Sulfur

We have found that if a sulfur water system is run continuously, and
if there are no oxygen leaks, there will be no slime plugging problems in
the emitters. During the "off" cycle of the system, it is possible to
prevent additional growths(for those systems that are on level ground) by
bleeding in a small amount of water at very low pressure to keep the lines
full. One of our cooperators has found it worthwhile to use one artesian
well to handle several blocks of trees. Thus, his well is being pumped
almost continuously. Several blocks of trees are on the "off" cycle while
one particular block is being irrigated. During the "off" cycle, for a
particular block, the grower cracks a valve in order to give a slight
pressure head throughout the "off" system and thus prevent air from
entering the lines. One could just as easily incorporate a small bypass
rather than "crack" the valve. We have tested for air and have found it
to be zero in the system using this procedure. It must be emphasized that
the method is only worthy of trial by those people who have irrigation
systems on level ground. Another method (for groves on level ground and a






The Present Status of Research
on Slimes of Sulfur in Drip
Irrigation Emitters and Filters -3-



free flowing artesian well with positive pressure) simply involves the
elimination of the check valve at the pump. In order to use this method,
one must determine if the natural well pressure,when the pump is off,
will permit a very slow drip at the last emitter. This system can be
used only by those who have centrifugal pumps mounted above ground. It
will not work for deep turbine pumps. Chlorine, either as chlorine gas
injected from a pressure tank or as sodium or calcium hypochlorite
(NaOC1 or Ca(OCl) will oxidize hydrogen sulfide in artesian well water.
The reaction is almost instantaneous. The problem is that it requires
8.8 to 9 ppm or more of NaOCl to oxidize 1.0 ppm of hydrogen sulfide and
still leave 0.5 ppm of free residual chlorine for inhibiting the bacteria.
The free residual must be increased if the pH of the water is over 7.5.
The reason for the high levels of chlorine is that hydrogen sulfide must
be oxidized to the soluble sulfate form, otherwise there will be no
residual free chlorine present to kill bacteria. If the reaction stops too
soon by using lesser amounts of chlorine, then elemental sulfur is formed
in the water. The water becomes cloudy from the sulfur and may in time
contribute to clogging problems. It is usually not feasible to inject a
continuous stream of chlorine to oxidize hydrogen sulfide. It would be
much too expensive. An alternate procedure is to first make sure that the
well casing, lines to the pump, filter, and main header lines have no leaks
and do not permit oxygen to enter the system. During an irrigation cycle,
if no air is sucked in, the system will be free of oxygen and the
organisms will not be growing. The bacteria become established and de-
velop most extensively during that period shortly after the irrigation
cycle when air gets into the system through the emitters and at high
points in the lines. During the "off" cycle, if the "bleed in" or "check
valve" method of keeping the lines full cannot be used, then it is
suggested that you try chlorine injection. It is further suggested that
this trial first utilize NaOCI as either the 10% swimming pool type or as
the 5.25% household chlorine type in order to best evaluate the potentials
for the treatment. Chlorine gas injection will require a significant
expenditure of funds for the injection equipment. One should be certain
of the chlorine procedure before proceeding into this area. The solution
of sodium hypochlorite can be injected on the suction side of the pump
with a siphon system or on the pressure side with a small injection
pump calibrated to put in a certain amount over a period of time. I am
trying to develop an automatic system that would also prevent deterioration
of chlorine solutions. The injection of chlorine should )e made D2fo-e
completion of the irrigation cycle and for a period long enough
to completely fill the lines and reach the last emitter. This can be
roughly calculated as 0.85 to 0.97 ft/sec from the pump to the last
emitter. This process can be speeded up 60% by opening the ends of
secondary water lines so that they fill quickly with chlorinated water.
Movement into the small P.E. lines containing the emitters is much
slower unless there are pressure type controlled flush valves on the
lines.





The Present Status of Research
on Slimes of Sulfur in Drip
Irrigation Emitters and Filters '4


The system should be shut down after the chlorine has been injected.
The free residual chlorine excess requires about 30 min to effectively
inhibit the bacteria. You must check the system at the last emitter to
be sure you have a free chlorine residual that lasts for 30 min. The
free Cl residual must be 0.5 ppm below pH 7.5. It must be 1 ppm at
pH 8.0. We do not know how frequently one must use this chlorine in-
jection and it is my opinion that for the present each person will have
to find this out for himself. Perhaps twice a week if the irrigation
system is being used three times a week, or it may even be necessary
after each cycle. You must purchase a DPD type chlorine test kit that
measures free chlorine in one operation.

A method for determining approximately how much chlorine must be
injected and the period of injection is listed in the last section of this
report.

Cleaning a drip system already in trouble from sulfur slime: If a
drip irrigation system is already having difficulty from slimes materially
reducing the efficiency of emitters, then one should try the continuous
run procedure. Be certain that all emitters are at least dripping. Those
completely plugged must be cleaned or replaced. Run the irrigation system
continuously for 3 weeks. Be absolutely certain that there are no air
leaks into the system. Air would defeat the purpose of the procedure.
I have found that the bacteria responsible for slimes of sulfur tend to
disintegrate and the precipitated sulfur is reduced to hydrogen sulfide
during this operation. It is not a 100% perfect method, but it does
reduce the amount of slimes of sulfur in the system 75 to 98%. It would
be advisable during the 3-week period to use some method to flush the
emitters and ends of lines. Push the button on those types that are
supposed to be self-flushing, or any other means to improve a slow func-
tioning emitter. At the end of the 3-week period, proceed with any of
the treatments or procedures listed above, namely the use of chlorine or
the "bleed in" method. DO NOT USE CHLORINE IF IRON (more than 0.7 ppm)
IS ALSO IN THE WATER.

We have data to indicate that sulfur dioxide gas injected continuously
will give results similar to chlorine. The method of injection is simple
and automatic, however the cost is more than chlorine. It is not being
recommended.

It is possible to use hydrochloric acid or sulfuric acid injected
near the completion of the irrigation cycle. If this procedure is used,
the pH should be lowered to 5.0. This procedure may be more expensive
than chlorine. It is not as effective as chlorine or sulfur dioxide.
Based upon data at the present time, it is my opinion that the chlorine or
the "bleed in" methods are the best to follow.

Methods to Determine the Approximate Amount of Chlorine to be Injecte<

In order to use chlorine effectively, one must have a chlorine test kit.
The simple orthotolidine swimming pool test kits are not adequate for this
operation since you must know the free residual chlorine content of the
water. This is the key to inhibiting bacteria in addition to destroying
hydrogen sulfide plus having water that is free of elemental sulfur. The
best kit for this purpose is one designed to utilize the DPD procedure.
The chemical involved is N,N-diethyl-p-phenylenediamine (DPD). It is a





The Present Status of Research
on Slimes of Sulfur in Drip
Irrigation Emitters and Filters -5-



ferrous colorimetric procedure. These kits can be purchased from various
supply houses. You need the kit to determine whether you have a free
chlorine residual at the end of your line.

An accurate determination of the hydrogen sulfide content of the
water is essential. The "methylene blue" procedure, if run at the well
site, is sufficient if the operator recognizes the ramifications of the
test procedure. After determining the total sulfide content to the
nearest 0.1 ppm, multiply the ppm of total sulfides by 9. This will be
the amount of NaOCl required in the irrigation water to oxidize sulfides
and leave a free residual of chlorine. The first time you make an
injection you may want to multiply by 10. After the injection, you can
reduce or increase the amount of chlorine for the next injection if the
DPD test kit shows more than 1 ppm of free residual chlorine at the end
of the irrigation line (the last emitter). The total chlorine require-
ments will have to be increased if there are slimes and nitrogenous
materials in the lines. Slimes and nitrogenous matter take up chlorine
just like hydrogen sulfide.

During your first injection, you should test for the presence of
free chlorine at the first emitter beyond the pump (to establish if you
are injecting at a high enough level). If too low, you can increase the
concentration. The final determination is the amount at the end of the
line as noted above. If the filter is full of such things as iron sulfide,
then the chlorine will be used up oxidizing the iron sulfide. If iron
sulfide is on the filter, one should suspect iron in the water. Test for
iron. I do not recommend the chlorine injection if there are significant
amounts of iron in "sulfur" water.

Calculations for Injecting NaOCI

You must know the gpm of your irrigation system. As a rule of thumb,
for each 5 ppm of active chlorine injected, use 1 gal of 5.25% NaOCl (or
0.5 gal of 10% NaOCI) for each 10,000 gal of water. Twenty ppm of chlorine
injected would require 4 gal of sodium hypochlorite.

Determine the distance (in feet) from the pump to the last emitter via
the pathway that the water must travel to reach the emitter. Multiply the
distance by 0.85. This is the approximate length of time (in seconds)
required for injection assuming that most emitters are flowing within 75%
of capacity. Next determine the gallons of water involved during the
injection. Reduce or increase the number of gallons of sodium hypochlorite
(NaOCI) required depending on whether the gallons of water used are more or
less than 10,000.

An example: A 37-acre grove has a drip system with a pumping rate of
150 gpm. The distance from the pump to the last emitter is 3030 ft. We
want to inject 20 ppm of 5.25% NaOC1.

It would require 59 min for the chlorine to travel 3030 ft to the
last emitter [3030 ft 7 (0.85 ft/sec x 60 sec)]. In 59 min, 8850 gal of
water would be used [150 gal x 59 min]. Twenty ppm of 5.25% NaOCl in
10,000 gal of water would require 4 gal of NaOCI as shown in the paragraph
above. For the problem being solved, 8850 gal is 88% of 10,000. The amount
of NaOCI that you must inject in 59 min in order to get 20 ppm of NaOC1




The Present Status of Research
on Slimes of Sulfur in Drip
Irrigation Emitters and Filters -6-



into the drip line would be 3.5 gal [4 gal NaOCI x 0.88]. You would then
have to set your injection pump or suction system to a rate of 3.5 gal in
59 min [3.5 gal x 60 min 1 59 min]. Good luck!

A final Word of Comment

Sodium hypochlorite solutions are unstable. If you open the can or
bottle and or dilute with water for ease of injection, you cannot hold
the chlorine solution for extended periods. Hydrogen sulfide in the air
will react with your chlorine solution. Exposure to the air permits re-
lease of the chlorine. That is what you smell when you use bleach
around the house.

If you dilute your chlorine solution for ease of injection, be sure
to use water that does not contain calcium carbonate or iron. Both of
these materials will precipitate in your injection container. They could
clog the filters on your injection pump.

Remember that if the pH of the water is over 7.5, you must add
additional chlorine to kill bacteria.




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