Front Cover
 Back Cover

Group Title: Circular Florida Cooperative Extension Service
Title: Treating irrigation systems with chlorine
Full Citation
Permanent Link: http://ufdc.ufl.edu/UF00014458/00001
 Material Information
Title: Treating irrigation systems with chlorine
Series Title: Circular Florida Cooperative Extension Service
Physical Description: 4 p. : ; 28 cm.
Language: English
Creator: Clark, Gary A
Smajstrla, A. G ( Allen George )
Florida Cooperative Extension Service
Publisher: Florida Cooperative Extension Service, Institute of Food and Agricultural Sciences, University of Florida
Place of Publication: Gainesville
Publication Date: 1992
Subject: Irrigation water -- Quality   ( lcsh )
Chlorine and derivatives as disinfectants   ( lcsh )
Irrigation -- Management   ( lcsh )
Genre: government publication (state, provincial, terriorial, dependent)   ( marcgt )
bibliography   ( marcgt )
non-fiction   ( marcgt )
Bibliography: Includes bibliographical references (p. 3-4).
Statement of Responsibility: Gary A. Clark and Allen G. Smajstrla.
General Note: Cover title.
General Note: "July 1992."
 Record Information
Bibliographic ID: UF00014458
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: ltqf - AAA6899
ltuf - AJH3124
oclc - 26791013
alephbibnum - 001760040

Table of Contents
    Front Cover
        Front Cover 1
        Front Cover 2
        Page 1
        Page 2
        Page 3
        Page 4
    Back Cover
        Page 5
Full Text

Circular 1039

Treating Irrigation Systems
with Chlorine

Gary A. Clark and Allen G. Smajstrla

Florida Cooperative Extension Service
Institute of Food and Agricultural Sciences
University of Florida
John T. Woeste, Dean


July 1992

Gary Clark is an Associate Professor of Agricultural Engineering and Extension Irrigation Specialist, Gulf Coast Research and Educa-
tion Center, University of Florida, Bradenton, FL; Allen G. Smajstria is a Professor of Agricultural Engineering, Dept. of Agricultural
Engineering, University of Florida, Gainesville, FL

Chlorine is used in many water supply systems
and home swimming pools to keep algae and other
microorganisms from growing. Chlorine is also
used for cleaning and maintaining irrigation sys-
tems. Proper injection methods and amounts of
chemicals must be used to provide an effective wa-
ter treatment program without damaging any part
of the irrigation system or the crop being produced.

Irrigation systems can become partially or com-
pletely clogged from biological growths of bacteria,
fungi, or algae. Bacteria, fungi, and algae are
present in surface and ground water sources and
use chemical elements such as nitrogen, phospho-
rus, sulfur, or iron as nutrient sources. Generally,
filtration alone cannot effectively remove these mi-
croorganisms. Chlorination can be used to mini-
mize the growth of microorganisms within the
pipes and other components of irrigation systems.
Without proper water treatment, clogging of pipes,
fittings, and emission devices (sprinklers, drippers,
spray jets, etc.) can occur, resulting in decreased
growth and development of the irrigated crop be-
cause of reduced water application amounts, unifor-
mity, and efficiency. This publication provides in-
formation on the sources of chlorine and the
amounts required for treating irrigation water and
systems to control the growth of microorganisms.

Sources Of Chlorine
Chlorine is available in gas, liquid, and solid
(granular or tablet) forms. However, only the liq-
uid form (liquid sodium hypochlorite) is labeled for
use in irrigation systems in Florida.

Each of the three different chlorine forms reacts
differently with the irrigation water, depending on
the other chemicals or elements in the water. Re-
actions may be an alteration of the pH of the water,
or may involve precipitation of some element that
could result in clogging of microirrigation compo-

Chlorine Gas
Chlorine gas (Cl2) is commonly used in municipal
water treatment systems. As chlorine gas reacts
with water, hypochlorous acid (HOC1), hydrogen
(H*), and chloride (C1-) are formed. This reaction
lowers the pH of the irrigation water. The change
in pH depends on how much chlorine gas is injected
and on the buffering capacity of the water.

Chlorine gas is used in municipal water treat-
ment systems because it provides chlorine in the
most concentrated and economical form. Basically,
1 pound of chlorine gas will provide a 1 part per
million (ppm) concentration of Cl2 to 1,000,000 gal-
lons of water. Similarly, an injection of 1 pound of
chlorine gas per hour will provide a 1 ppm concen-
tration of Cl2 to a water supply with a flow rate of
2000 gallons per minute (gpm).

Chlorine gas is a respiratory irritant and affects
the mucous membranes. It can be detected as an
odor at a concentration of 3.5 ppm and can be fatal
after a few breaths at 1000 ppm. Therefore, the
user of chlorine gas must exercise extreme caution
and safety. Maximum air concentrations should
not exceed 1 ppm for prolonged exposure. This
form of chlorine is limited to water treatment sys-
tems or other applications by licensed users.

Solid Chlorine
Granular (powdered or tabular) forms of chlorine
are commonly used to chlorinate swimming pools.
Calcium hypochlorite is the form that is typically
used and found at local pool supply stores. Dissolv-
ing calcium hypochlorite in water will result in the
formation ofhypochlorous acid (HOC1) and hy-
droxyl ions (OH-), a reaction that raises the pH of
the water. The calcium hypochlorite form may re-
act with other elements in the irrigation water to
form precipitates that could clog microirrigation
emitters and thus counteract the purpose for chlo-

Calcium hypochlorite is used to treat swimming
pool water because the solid chlorine form is inex-
pensive, easy to store, and easy to use. It generally
has 65 to 70 percent of available chlorine. Thus,
approximately 1.5 pounds of calcium hypochlorite
will treat 1,000,000 gallons of water with a 1 ppm
concentration of Cl2.

Liquid Chlorine
Liquid sodium hypochlorite is most commonly
used as laundry bleach. However, it is also labeled
for use in irrigation systems. Mixing liquid sodium
hypochlorite in water results in the formation of
hypochlorous acid (HOC1) and hydroxyl ions (OH-),
a reaction that raises the pH of the water. Unlike
the calcium added in the solid chlorine form, the
sodium added in this liquid form does not contrib-
ute to clogging problems. Neither the sodium nor
the chlorine added to the water should be detri-
mental to crops or soils at the typical concentra-
tions used.

Effects Of Chlorine
Hypochlorous acid is the effective agent that con-
trols bacterial growths. The amount of HOC1 that
will be present in solution, and thus active, will be
present at greater concentrations at lower pH lev-
els (more acidic conditions). At extremely low pH
levels (or high acidity) chlorine gas (Cl2) will form.
Therefore, for safety it is very important to store
chlorine and acid sources separately.

Hypochlorous acid will react with iron in solu-
tion to oxidize the ferrous form to the ferric form,
which will then become the insoluble ferric hydrox-
ide as a precipitate. This reaction should take
place prior to the irrigation filters so that the pre-
cipitates may be trapped. Chlorine will also react
with hydrogen sulfide to form elemental sulfur. Be-
cause some of the chlorine is used up by reacting
with the sulfide or ferrous ions, additional chlorine
must be provided to supply enough residual to con-
trol the microorganisms such as sulfur or iron
slimes, or algae, which can clog microirrigation sys-

Most microorganisms will be inactivated and
controlled at free residual chlorine concentrations
of 1 ppm. However, higher injection levels are
needed due to the inherent chlorine demand of dif-
ferent water sources. As a start, use 2 ppm of chlo-
rine for each part per million of hydrogen sulfide,
plus 0.6 ppm of chlorine for each part per million of
ferrous iron. A water test can be used to determine
the levels of hydrogen sulfide or ferrous iron
present in solution. Surface water sources such as
lakes, ponds, or canals should be treated with ap-
proximately 5 to 10 ppm of chlorine. Higher levels
may be needed for water with high amounts of mi-
crobial activity such as during the warmer months
of the year.

The chlorine injection rate should be checked by
testing the treated water at the most distant part of
the irrigation system using a test kit designed to
measure "free" residual chlorine. Residual concen-
trations of 1 to 2 ppm indicate that active chlorine
still exists and that the water and system parts
have been appropriately treated. Active chlorine
may be tested using a color indicating test kit
(D.P.D.) that measures "free" residual chlorine. Do
not use a test kit that only measures total chlorine.
While levels of total chlorine iay appear appropri-
ate, the "free" residual form may not. Therefore,
ask for a D.P.D. test kitfrom either a pool or irriga-
tion supplier.

Chlorine Application Amounts
After determining the desired chlorine concentra-
tion, the proper application amount must be deter-
mined. The amount of chlorine to apply per unit of
irrigation water will depend on the desired concen-
tration in the irrigation system and the concentra-
tion or strength of the chlorine source.

Liquid sodium hypochlorite is the most conve-
nient and generally safest form of chlorine available
to inject into irrigation systems. Stock solutions are
available in concentrations of 5, 10, or 15 percent of
available chlorine. Table 1 or the following equa-
tions may be used to determine the chlorine solu-
tion injection rate in gallons per hour (gph) for dif-
ferent desired part per million injection levels and
irrigation system flow rates. Equations 1, 2, and 3
are specific for liquid chlorine injection and are de-
signed for stock solution chlorine concentrations of
5, 10, and 15 percent, respectively.

For a 5% available chlorine stock solution:

Inject. Rates, gph=(ppm) x (Irr. Fl. Rate, gpm)(1)

For a 10% available chlorine stock solution:

Inject. Rateo, gph=(ppm) x (Irr. Fl. Rate, gpm)(2)

For a 15% available chlorine stock solution:

Inject. Rate,,, gph=(ppm x (Irr. Fl. Rate, gpm)(3)
For example, an irrigation system has a flow
rate of 450 gpm and the water is to be treated with
8 ppm of available chlorine using a stock solution
with 10% available chlorine. Using Equation 2, the
injection rate of the stock solution should be
approximately 2 gph [(8 ppm) x (450 gpm)/1850 =
1.95 gphl. If the stock solution had just 5% avail-
able chlorine, the injection rate should be about 4

Table 1 may be used for smaller irrigation system
flow rates. For example, consider a microirrigation
system with a flow rate of 80 gpm. The water is to
be treated with a liquid chlorine stock solution with
5% available chlorine, and a 6 ppm treatment level
is desired. Using Table 1, at a 6 ppm treatment
level and a 5% stock solution concentration, the in-

jection rate should be about 0.7 gph per 100 gpm of
irrigation system flow rate. Since the actual flow
rate is 80 gpm, the injection rate should be 80/100
or 80% of 0.7 gph which is equal to 0.56 gph. If this
injection rate was too small for the injector, the
stock solution could be diluted with fresh water.
Thus, if the stock solution was diluted with 4 parts
fresh water and 1 part 5% chlorine solution, the
new stock solution would have 1% available chlo-
rine, assuming that the additional water did not tie
up any of the available chlorine. From Table 1, the
new injection rate would be 80% of 3.3 gph, which
equals 2.6 gph.

The sources of chlorine used to treat water for
microorganisms include chlorine gas, powder or
tablets of calcium hypochlorite (pool bleach), and
liquid sodium hypochlorite (laundry bleach). How-
ever, only liquid sodium hypochlorite is labeled for
use in irrigation systems in Florida. The concentra-
tion of available chlorine ranges from 5 to 15 per-
cent in liquid sodium hypochlorite. Therefore, the

amounts of these products used to treat water will
be very different. The user should check with the
chlorine supplier to ensure that the material is
labeled for injection into irrigation systems. In ad-
dition, safety and proper backflow prevention are
always required when injecting materials into an
irrigation system.

Related References
Clark, G. A., A. G. Smajstrla, D. Z. Haman, and
F. S. Zazueta. 1990. Injection of chemicals into irri-
gation systems: Rates, volumes, and injection peri-
ods. Bulletin 250. Fla. Coop. Ext. Ser. Univ. of
Florida, Gainesville, FL.

Ford, H.W. 1979. The Use of Surface Water for
Low Pressure Irrigation Systems. Fruit Crops
Mimeo Rep. FC79-1 Univ. of Fla., Gainesville.

Ford, H.W. 1979. The Present Status of Research
on Slimes of Sulfur in Low Pressure Irrigation Sys-
tems and Filters. Fruit Crops Mimeo Rep. FC79-2.
Univ. of Fla., Gainesville.

Table 1. Lquid chlorine (sodium hypochlorite) injection rates in gallons per hour (gph) per 100 gallons per minute (gpm) of Irriga-
tion system flow rate for different levels of stock solution concentrations of available chlorine (%) and the desired water treatment
level (ppm).

Treatment Concentration of available chlorine in stock solution
Level (percent)

1 2 3 4 5 10 15

(gph of injection per 100 gpm of irrigation flow rate)

2 1.1 0.6 0.4 0.3 0.2 0.14 0.09
4 2.2 1.1 0.7 0.6 0.4 0.22 0.15
6 3.3 1.7 1.1 0.8 0.7 0.3 0.2
8 4.4 2.2 1.5 1.1 0.9 0.4 0.3
10 5.5 2.8 1.8 1.4 1.1 0.6 0.4
15 8.3 4.1 2.8 2.1 1.6 0.8 0.6
20 11.0 5.5 3.7 2.8 2.2 1.1 0.7
25 13.8 6.9 4.6 3.4 2.8 1.4 0.9
30 16.5 8.3 5.5 4.1 3.3 1.6 1.1
40 22.0 11.0 7.3 5.5 4.4 2.2 1.5
50 27.5 13.8 9.2 6.9 5.5 2.8 1.8
75 20.6 13.8 10.3 8.3 4.1 2.8
100 27.5 18.3 13.8 11.0 5.5 3.7
150 27.5 20.6 16.5 8.3 5.5
200 27.5 22.0 11.0 7.3

*These are commercially available concentrations. Other concentrations are obtained by diluting with water.

Ford, H.W. 1979. The Present Status of Research
on Iron Deposits in Low Pressure Irrigation Sys-
tems. Fruit Crops Mimeo Rep. FC79-3. Univ. of
Fla., Gainesville.

Ingram, D., and B. Hoadley. 1986. Chemical In-
jection for Drip Irrigation in the Woody Ornamental
Nursery. Ornamental Horticulture Commercial
Fact Sheet OHC-6. Fla. Coop. Ext. Ser. Univ. of
Florida, Gainesville, FL.

Kovach, S.P. 1984. Injection of Fertilizers into
Drip Irrigation Systems for Vegetables. Circular
606, Fla. Coop. Ext. Ser., Univ. of Florida,
Gainesville, FL.

Nakayama, F.S., and D.A. Bucks. 1986. Trickle
Irrigation for Crop Production: Design, Operation,
and Management. Elsevier. Amsterdam. 383 p.

Pitts, D.J., D.Z. Haman, and A.G. Smajstrla.
1990. Causes and Prevention of Emitter Plugging in
Micro Irrigation Systems. Bul. 258. Fla. Coop. Ext.
Ser., Univ. of Fla., Gainesville.

Smajstrla, A.G., D.S. Harrison, W.J. Becker, F.S.
Zazueta, and D.Z. Haman. 1985. Backflow Preven-
tion Requirements for Florida Irrigation Systems.
Bulletin 217. Fla. Coop. Ext. Ser., Univ. of Florida,
Gainesville, FL.

Smajstrla, A.G., D.Z. Haman, and F.S. Zazueta.
1986. Chemical Injection (Chemigation): Methods
and Calibration. Agric. Engr. Ext. Report 85-22 (re-
vised). Fla. Coop. Ext. Ser., Univ. of Florida,
Gainesville, FL.

Yeager, T.H. 1986. Fertigation Management for
the Wholesale Container Nursery. Bulletin 231.
Fla. Coop. Ext. Ser., Univ. of Florida, Gainesville,

Yeager, T.H. and R.W. Henley. 1987. Techniques
of Diluting Solution Fertilizers in Commercial
Nurseries and Greenhouses. Circular 695. Fla.
Coop. Ext. Ser., Univ. of Florida, Gainesville, FL.

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is available from C.M. Hinton, Publications Distribution Center, IFAS Building 664, University of Florida, Gainesville, Florida32611. Before publicizing
this publication, editors should contact this address to determine availability. Printed 7/92.

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