| Material Information
||The present status of research on slimes of sulfur in low volume irrigation systems and filters
||Lake Alfred AREC research report
||2 p. : ; 28 cm.
||Ford, Harry W., 1922-
Agricultural Research and Education Center (Lake Alfred, Fla.)
||University of Florida, IFAS, Agricultural Research and Education Center
||Place of Publication:
||Lake Alfred FL
||Irrigation -- Equipment and supplies -- Maintenance and repair -- Florida ( lcsh )
Microirrigation -- Florida ( lcsh )
||government publication (state, provincial, terriorial, dependent) ( marcgt )
non-fiction ( marcgt )
||Statement of Responsibility:
||Harry W. Ford.
||"4/18/75 (Revised 11/15/80)-HWF-100."
| Record Information
||University of Florida
||All rights reserved by the source institution and holding location.
||oclc - 76883291
Lake Alfred AREC Research Report-CS75-4
4/18/75 (Revised 11/15/80)-HWF-100
THE PRESENT STATUS OF RESEARCH ON SLIMES OF SULFUR IN LOW VOLUME IRRIGATION
SYSTEMS AND FILTERS
Harry W. Ford
University of Florida, IFAS
Agricultural Research and Education Center
Lake Alfred, Florida 33850
Liquid sodium hypochlorite (NaOC'), commonly called household
or swimming pool bleach, is the only bactericide-that has a
24(c) approved EPA label for use in low volume irrigation systems
in Florida. Chlorine gas and HTH (calcium hypochlorite) do not
have a label.
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, I have found that the deep artesian sulfur water wells have clean
water. The water usually does not contain organic coloring agents or other matter thit-
can complex metals. Thus, we can use artesian well water for drip irrigation if
precautions are taken to control slimes of sulfur and the rooting zone does not become
saturated. A saturated zone'will release free hydrogen sulfide which is toxic to citrus
A water analysis should be performed on each well. Tests should be made for hydrogen
sulfide, iron, and pH. However, it would also be advisable to analyze for total dissolved
solids (TOS) which would give an indication of whether the water is too salty for general
irrigation. From experience I have learned that the most accurate readings for iron and
sulfides in water are made at the site; however, most commercial laboratories transport
water samples to the laboratory and then conduct the analysis. Samples being transported
to the laboratory for iron analysis must 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. Six drops of 20%zinc acetate should be added to a
separate sample to preserve hydrogen sulfide.
If the water contains more than 0.1 ppm of total sulfides, there is 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 this process, the bacteria make a sulfur slime which
is deposited both within and on the outside of the organisms. The bacteria are very long
and stringy so that they can form an extensive mat which accumulates and clogs the fine
tubes in emitters and micro sprinklers. 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, 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 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, giving
the organisms a chance to "grab" the oxygen.
The chlorine method for controlling sulfur bacteria. Chlorine as NaOCI (liquid sodium
hypochlorite) can be injected for a minimum of 45 minutes anytime but at least 1-3/4 hours
before the end of the irrigation cycle. This is necessary so that all emitters and
micro-sprinklers get exactly 45 minutes of contact time with the chlorine solution.
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. Exposure to the air permits release of the chlorine. That is what you
smell when you use bleach around the house. Sunlight and heat will also destroy chlorine:
It is essential that the free chlorine level be 1 ppm at the last emitter on the
irrigation system. INSUFFICIENT CHLORINE WILL STIMULATE THE BACTERIA TO GRO.! RAPIDLY SO
THAT YOUR CONTROL PROCEDURE WILL WORK AGAINST YOU RATHER THAN KILL BACTERIA. Frequent
monitoring of the free chlorine level is essential.
One problem is that 9.0 ppm of NaOCl is required to oxidize 1.0 ppm of hydrogen
sulfide and still leave 1.0 ppm of free chlorine. The free chlorine level must also be
increased if the water is above pH 7.5. Higher levels of chlorine are required for
sulfides because hydrogen sulfide must be oxidized to the soluble sulfate form, otherwise
there will be no free chlorine present to kill bacteria. If the reaction stops too soon
(by using lesser amounts of chlorine) elemental sulfur is formed .in the water. The waterr
becomes cloudy from the sulfur and may in time contribute to clogging problems. It is
uneconomical and unnecessary to inject a continuous stream of chlorine to oxidize hydrogen
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 one must
know the free residual chlorine content of the water. This is the key to inhibiting
bacteria. The best kit for this purpose is one designed to utilize the DPD ferrous
colorimetric procedure. The chemical involved is N,N-diethyl-p-phenylenediamine (D?D).
These kits can be purchased from various low pressure irrigation supply houses.
Remember to keep the chlorine test kit in a cool place. Do not leave chlorine
chemicals in a hot vehicle.
SEE ALSO: Lake Alfred AREC Res. Rept. CS79-3 "A key for determining the use of sodium
hypochlorite to inhibit iron and slime clogging of low pressure irrigation systems." The
key will permit you to determine the interval between chlorine treatments and the effect