The use of chlorine in low pressure systems where bacterial slimes are a problem

Material Information

The use of chlorine in low pressure systems where bacterial slimes are a problem
Series Title:
Lake Alfred AREC reseach report
Ford, Harry W., 1922-
Agricultural Research and Education Center (Lake Alfred, Fla.)
Place of Publication:
Lake Alfred FL
University of Florida, IFAS, Agricultural Research and Education Center
Publication Date:
Rev. ed.
Physical Description:
3 p. : ; 28 cm.


Subjects / Keywords:
Irrigation -- Research -- Florida ( lcsh )
Irrigation -- Equipment and supplies -- Maintenance and repair -- Florida ( lcsh )
Chlorine ( jstor )
Low pressure ( jstor )
Hypochlorite ( jstor )
government publication (state, provincial, terriorial, dependent) ( marcgt )
non-fiction ( marcgt )


General Note:
Caption title.
General Note:
"5/15/75-HWF-100 (Revised 5/15/79)."
Statement of Responsibility:
Harry W. Ford.

Record Information

Source Institution:
University of Florida
Rights Management:
All applicable rights reserved by the source institution and holding location.
Resource Identifier:
76804936 ( OCLC )


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Lake Alfred AREC Research Report-CS75-5
5/15/75-HWF-100 (revised 5/15/79)



JUL 23 9-79 University of Florida, IFAS
Agricu tural Research and Education Center
S -l Unvida Lake Alfred, Florida 33850
i.F.A.S. -Univ. of Florida'
Only sodium hypochlorite (NaOCl) has an approved EPA 24(c)
label for use in irrigation systems in Florida.

Sof O

There has been considerable interest in chlorine for controlling all
types of bacterial sludges and algae. This report is an attempt to clarify
the present status of chlorine, based on research, for use in low pressure
systems in Florida.

Chlorine used correctly can be a control for several problems. It is
excellent for preventive maintenance. It is a waste of time and money to
inject chlorine into a system that is already clogged from sulfur slimes
or iron deposits. Chlorine above 100 ppm will dissolve elemental sulfur
globules but will not remove the bacterial cells of the matrix. Chlorine
precipitates soluble iron in water. It will not dissolve iron present in
the emmitters and microsprinklers. Chlorine will lossen sludge if main-
tained at a high level for an extensive period of time--an expensive and
potentially toxic practice.

Chlorine dissolved in water is an active oxidizing agent. Chlorine
has for many years been recognized and used as an efficient agent for
destroying microorganisms. It has been the primary ingredient for use
in potable drinking water and has become the most widely used disinfectant.
Chlorine gas (Cl1), sodium hypochlorite (NaOCI), and calcium hypochlorite
[Ca(OC12)] dissolved in water will hydrolize to form hypochlorous acid
(HOC1), a powerful oxidizing agent that is a stronger disinfectant than
C12 alone. The germ killing action of HOCI is either by oxidizing the
organism or by preventing the cells from oxidizing glucose, an essential
ingredient for life. The killing action works best below pH 7.5 since
HOC1 is a weak acid.

There has been considerable interest in adapting chlorine or certain
compounds of chlorine as the agent for eliminating all types of micro-
biological problems that contribute to clogging in drip irrigation systems.
Chlorine is not a "shotgun" type solution to all problems. Its most
promising use is in the area of preventive maintenance and it must be
mointored carefully.

Characteristics of Chlorine

Chlorine for use as an oxidizing agent and as a bactericide exists
as several compounds. It should not be confused with the chloride ion

, 5

The Use of Chlorine in Low
Pressure Systems where
Bacterial Slimes are a
Problem -2-

(Cl) which is a basic ingredient in liquid and dry fertilizers. Chlorides
have no oxidizing or biocidal properties. Chlorine gas is the most common
and cheapest source of chlorine, but it does not dissolve readily in water
by simple bubbling procedures so that expensive injection equipment kept
in good operating condition must be utilized. Chlorine is considered a
problem gas that can clog and corrode injection equipment.

Liquid sodium hypochlorite (NaOCI) is the easiest form of chlorine
to handle since amounts required can be measured rather accurately. There
is no residue to clog injection lines. Powdered calcium hypochlorite
[Ca(OC12) ], also called High Test Hypochlorite (H.T.H.) chlorine, can
be used but with certain disadvantages. H.T.H. calcium hypochlorite,
when mixed in concentrated injection solutions, forms a milky suspension.
A precipitate forms containing calcium oxalate, calcium carbonate, and
calcium hydroxide which clogs injection lines. It is also more difficult
to prepare a calcium hypochlorite solution without the use of a balance
for weighing the powder..

When chlorine is added to well water, some of it will combine with
organic substances that may be present in the water. This is called
combined chlorine. Chlorine will also react with any ammonium ions that
may be in the system from the injection of nutrient solutions. The com-
pounds formed are called chloroamineF. Some of the chlorine will react
with certain inorganic compounds such as hydrogen sulfide (H2S) and
iron (Fe) and be completely changed to a chloride. Chlorine that has
not reacted with anything and is therefore still in excess is called
free residual chlorine. It is the free residual chlorine that is
available to kill sludge forming bacteria. It is the hypochlorous acid
molecule (which exists below pH 7.8) that is responsible for most of the
organism killing action. The pH of the water should be less than 7.5
otherwise the free residual chlorine level must be increased by a
factor of 2 to 3 times to be effective.

In order to use chlorine effectively, one must have a chlorine
test kit that will measure the free chlorine residual. Several types
of kits have been evaluated for use with low pressure irrigation systems.
The best is a relatively new method designed to use the chemical N,N-
diethyl-p-phenylenediamine (DPD). The DPD kits for measuring free
residual chlorine can be purchased from a number of swimming pool supply
outlets and several low pressure irrigation companies in Florida.

Chlorine as a biocide kills by having a free chlorine contact
time of at least 30 minutes. Dumping large quantities of chlorine into
the irrigation system without careful monitoring, will not kill organism
populations (because of the contact time) but may injure young trees
if the level is above 30 ppm free residual chlorine. Anyone who monitors
his chlorine levels will never have concentrations approaching 30 ppm
(parts per million).

Since sodium hypochlorite (NaOCl) is the only chlorine compound
approved for use in Florida, it is necessary to use injection equipment

The Use of Chlorine in Low
Pressure Systems where
Bacterial Slimes are a
Problem -3-

that will permit control of the amount of chlorine solution being used.
There are injection pumps on the market that can be used on both the
suction and pressure side of irrigation pumps. The chlorine injection
pumps should be adjustable so that the injection'rates can be changed.
The easiest method for determining the amount of chlorine required is
to gradually increase the injection rate until a free residual chlorine
level is detected by using the chlorine test kit. SEE ALSO: AREC
Research Report May, 1979 "Using a DPD test kit." The amount of
chlorine required will change--sometimes daily. If there are slimes
already in the system, chlorine'requirements will be high. Chlorine
levels probably can be reduced as the system becomes free of slimes.
There will be less variation and less problems if the chlorine systems
are an integral part of the irrigation system at the time of installation.

The best concentrations and contact times for chlorine are reported
in other research reports such as "The use of surface waters for low
pressure irrigation," "Slimes of sulfur in low pressure irrigation" and
"Iron in low pressure irrigation."