| Material Information
||The present status of research on iron deposits in low pressure irrigation systems
||Lake Alfred AREC reseach report
||3 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 5/14/79)-HWF-100."
| Record Information
||University of Florida
||All rights reserved by the source institution and holding location.
||oclc - 76804837
Lake Alfred AREC Research Report-CS75-3
4/18/75 (Revised 5/14/79)-HWF-100
THE PRESENT STATUS OF RESEARCH ON IRON DEPOSITS
IN LOW PRESSURE IRRIGATION SYSTEMS
.7 r- -- \ Harry W. Ford / (
University of Florida, IFAS
JUL 23 9179 Agricultural Research and Education Center
Lake Alfred, Florida 33850
..1 LqiLsodiLum ochlorite (NaOCl) is the only bactericide with
an EPA approved 24(c) label for use in low pressure irrigation
systems in Florida.
Any source of water used for low pressure irrigation that contains
more than 0.1 ppm (parts per million) of 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 precipitate organic suspended solids. Precipitated suspended
organic solids can clog emitters and also be an excellent medium for
Iron concentrations of only 0.1 ppm will contribute to growths of
clear to reddish slime masses in pipes and emitters, resulting in slight
to severe clogging. Iron concentrations of 0.4 ppm to 3.5 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. Iron concentrations above 3.5 ppm should not be used
for irrigation. Since bacteria can function in a pH range of 4.3 to 8.5,
one cannot control the problem simply by changing the pH of the water.
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 must be below 1.5 ppm
if the pH is above 6.5.
The iron problem is usually most severe when water is from a shallow
well. Shallow wells often contain soluble organic matter which contributes
to an organic-iron complex resulting in a red sludge deposit. Identifi-
cation of bacteria by microscopic examination is not usually necessary.
The Present Status of Research
on Iron Deposits in Low Pressure -2-
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 must first be
acidified at the site to keep the iron in solution by adding about 10
drops of concentrated acid (HC1) for each 300 ml of water sample. One
liter samples for sulfide analysis should be treated with 10 drops of
a 20% zinc acetate solution. There have been several instances where
laboratory measurements recorded lower values for iron and sulfides
than on-site readings.
Problems associated with the control of iron (ochre) deposits: Iron
sludge is difficult to control and each location presents a slightly
The correct amount of sodium hypochlorite (NaOCI) injected into
irrigation lines 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. We need more data on this procedure. Free residual 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 because the combination of iron and suspended
organic matter results in a rapid precipitation that can clog emitters.
Chlorine injected to a level of 0.5 ppm of free chlorine residual
(as measured at the last emitter) for a minimum of 40 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 that 2 hours before the end of a cycle. Chlorine
should be injected as deep into the well as possible.
There should be no pressure holding tanks in the irrigation system
as such 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 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 hypo-
chlorite in the lines for at least 12 hours which is supposed to
The Present Status of Research
on Iron Deposits in Low Pressure -3-
disintegrate the slimes. Organic matrices from Florida systems were not
dissolved using 1000 ppm chlorine although some emitters showed improved
flow rates. Therefore, it is not recommended. Such high concentrations
could damage citrus roots.
It has been observed that deep wells usually contain little or no
iron but may contain hydrogen sulfide which can contribute to a sulfur
slime problem. Sulfur slime is easier to control than iron ochre.
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.
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.
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."