| Material Information
||The present status of research on iron deposits in low volume irrigation systems
||Lake Alfred AREC reseach 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 -- Florida ( lcsh )
Water -- Purification -- Iron removal -- 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 - 76883352
Lake Alfred AREC Research Report-CS75-3
4/18/75 (Revised 11/15/80)-HWF-100
THE PRESENT STATUS OF RESEARCH ON IRON DEPOSITS IN LOW VOLUME IRRIGATION SYSTEMS
Harry W. Ford
University of Florida, IFAS
Agricultural Research and Education Center
Lake Alfred, Florida 33850
Liquid sodium hypochlorite (NaOCI), 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.
General Fundamentals of the Problem. Any source of water used for low volume
irrigation that contains more than 0.2 ppm (parts per million) of ferrous iron may be
subject to ochre (iron) deposition in lines and emitters. The sludge is a red amorphous
sticky mass. One form of ochre is associated with filamentous iron precipitating bacteria
which are capable of oxidizing soluble ferrous (reduced) iron to insoluble ferric
hydroxide. The organisms can attach themselves to plastics and metal and cannot be
removed easily by rinsing. There are also certain other kinds of bacteria (not true iron
bacteria) that can precipitate iron or trap precipitated iron in their jelly-like masses.
Sludges formed by slime-type bacteria are similar in appearance to filamentous ochre
formed by filamentous bacteria. Both types of sludges can clog emitters and
micro-sprinkler irrigation systems. Oxidized iron may also act as an organic suspended
solids precipitating agent. Precipitated suspended organic solids can'clog emitters and
are excellent media for filamentous bacteria.
Iron concentrations of only 0.2 ppm will contribute to growths of clear to reddish slime
masses in pipes and emitters, resulting in slight to severe clogging. Iron concentrations
more than 0.3 ppm may result in severe clogging from the action of iron precipitating
bacteria and slime-type bacteria assuming conditions are favorable for the development of-
the organisms. Since bacteria can function in a pH range of 4.3 to 8.5, one cannot
eliminate the problem simply by changing the pH of the water.
The iron problem is usually most severe when water is from a shallow well. A shallow
well often contains soluble organic matter which may react to form an organic-iron complex
resulting in a red sludge deposit. Identification of bacteria by microscopic examination
is usually not necessary.
Water Quality Analysis. One must have a water analysis performed for hydrogen
sulfide, iron, pH, and suspended solids. These measurements are most important from the
standpoint of evaluating the potential for iron sludge formation. It is preferable to
check for iron and sulfides directly at the well site; however, this is not always
practical. When the samples must be transported to laboratories, samples for iron
analysis should be acidified at the site to keep the iron in solution by adding about 10
drops-of concentrated acid for each 300 ml of water sample. One pint samples for sulfide
analysis should be treated with 5 drops of a 20% zinc acetate solution. On-site
measurements are preferred because there have been several instances where laboratory
measurements recorded lower values for iron and sulfides.
Chlorine can be used to control ochre if the pH is below 6.5 and the iron is less than
3.5 ppm. The iron concentration should be below 1.5 ppm if the pH is above 6.5 in order
to obtain consistent control of ochre.
Liquid chlorine in the form of sodium hypochlorite (NaOCI) will oxidize soluble iron
to the insoluble ferric form and also kill bacteria. Assuming no other reactions occur,
1.0 ppm of NaOCl will oxidize 0.7 ppm of iron. The reaction and precipitation of the iron
is fast. The precipitated iron should be removed by filtration. Free available chlorine
(the excess after all chemical reactions) of 0.5 ppm will inhibit growths of iron
precipitating bacteria. Do not use chlorine in systems where the iron content is above
3.5 ppm and suspended organic compounds are present. The combination of iron and
suspended organic matter results in a rapid precipitation that can clog emitters.
NaOC1 injected to a level of 0.5 ppm of free chlorine (as measured at the last
emitter) for a minimum of 45 minutes each 4-6 hours of irrigation, when the pH is below
6.5, has shown promising results for the control of ochre. Iron is precipitated only
while chlorine is being injected. The injection can be at any time during the irrigation
cycle but not less than 1-3/4 hours before the end of a cycle. Chlorine should be
injected as deep into the well as possible.
Pressure holding tanks in the irrigation system should have expanding plastic bellows
within the tank; otherwise, pressure holding tanks act as incubation chambers for bacteria.
Superchlorination has been used as a means of sterilizing wells temporarily where
iron-precipitating bacteria are multiplying; however, the procedure has had only limited
evaluation in Florida irrigation systems. Assuming that hydrogen sulfide is not in the
water, NaOCl is injected into the well at a point below the intake where bacteria may be
growing. The level of free residual chlorine in the system should be 8 ppm and the
holding time a minimum of 40 minutes. The precipitated iron and other debris must be
filtered and/or flushed out of the system. However, this method does not clean a system
that is already clogged. A method recommended in Australia to remove organic and
iron-like deposits from drip irrigation systems utilizes a solution of 100 ppm of sodium
hypochlorite in the lines for at least 12 hours which is supposed to disintegrate the
slimes. Organic matrices from Florida systems were not completely dissolved using 1000
ppm chlorine although emitters showed improved flow rates. Such high concentrations could
damage citrus roots.
End-of-line Flushing. Automatic or manually controlled pressure-type flushing valves
at ends of lines have considerable value in minimizing the formation of precipitated
materials which clog lines. Unfortunately, spring loaded-type flush valves that merely
drain the lines have little value in a sludge control program. The best flush valves
permit pressure-type flushing for any preselected time period.
Cleaning Clogged Emitters. Individual emitters and micro-sprinklers clogged by iron
ochre can be cleaned with a 2% acid treatment. Before using such materials as
hydrochloric acid, sulfur dioxide, or sulfuric acid, one must be certain that the acid
will not dissolve the particular brand of emitter being cleaned. In my studies, the acid
treatment had an undesirable side effect on soil by lowering the pH one full unit so that
copper moved into the subsoil--a condition that could damage citrus roots.
Iron in Ditch Water. Some citrus and vegetable growers have permitted well water,
high in iron, to flow into ditches in an attempt to oxidize and remove the iron. This
procedure reduces the iron content of the water because of aeration and iron bacteria.
However, all of the iron is not removed because soluble completing agents combine with the
iron. See AREC Research Report CS75-2 (revised 5/10/79), "The use of surface water in low
pressure irrigation systems."