| Material Information
||The use of surface water for low volume irrigation systems
||Lake Alfred AREC research report - Lake Alfred AREC ; CS75-2
||2 p. : ; 28 cm.
||Ford, Harry W., 1922-
Agricultural Research and Education Center (Lake Alfred, Fla.)
||unknown ( endowment )
||University of Florida, IFAS, Agricultural Research and Education Center
||Place of Publication:
||Lake Alfred, Fla.
||April 18, 1975
||Irrigation water -- Quality -- Florida ( lcsh )
||government publication (state, provincial, terriorial, dependent) ( marcgt )
non-fiction ( marcgt )
||Statement of Responsibility:
||Harry W. Ford.
||"4/18/75 (Revised 11/5/80)-HWF-100."
| Record Information
||University of Florida
||University of Florida
||All rights reserved by the source institution and holding location.
||oclc - 406518688
Lake Alfred AREC Research Report-CS75-2
4/18/75 (Revised 11/5/80)-HWF-100
THE USE OF SURFACE WATER FOR 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.
Filters and Algae. The major clogging problems with surface waters in Florida occur
from decomposition residues of filamentous green algae and completed iron.' Most surface
waters must be filtered and the best filtration is probably a manual or automatic
backflush-type sand filter. Without chemical treatment, the green remnants of algae will
develop throughout the sand tank. Organic residues of algae, including diatoms, can pass
through the sand. Residues of decomposing algae can accumulate in lines, emitters, and
microsprinklers. Algae transported into the black polyethylene pipe of the irrigation
system will not continue to grow because the algal residue consists of ruptured cells
which form a soft gelatinous organic slime. The soft non-sticky deposit can accumulate
iron and support growths of iron bacteria and many other filamentous and slime forming
bacteria. In low volume irrigation systems with algal problems, iron has been found in
emitters and at the ends of lines. Iron, detected in concentrations as low as 0.1 ppm in
canal water, will become concentrated in the algal organic slime that may accumulate in
the irrigation lines.
Using White PVC Pipe. Green filamentous algae have been found growing in the thin
white translucent PVC pipe which is often used above ground as suction and transport
lines. It is essential that all pipes and containers located above ground either be
painted to prevent light penetration or use a type of PVC pipe that does not permit light
penetration. All surface waters probably contain algae at some time during the irrigation
season. The level of algae fluctuates because of many different factors. One of the
major and rather sudden increases occurs during an algal bloom.
Surface water can be used for low volume irrigation if treated with 1 ppm (mg/L) free
available chlorine (sodium hypochlorite). The liquid chlorine should be injected into the
suction line as close to the inlet as possible for 45 minutes any time during the day but
no later than 1-1/2 hours before stopping the system. The treatment should be repeated
every 6 to 12 hours of accumulated irrigation time. The best time for the injection is
just after backflushing the filter. It is essential that the chlorine pass through the
filter in order to prevent bacterial growths from sticking to the sand in the filter.
Treating immediately after backflushing also reduces the amount of chlorine required and
minimizes sticking action of the slimes as they are trapped in the filter; so backflush
characteristics are also improved.
Chlorine Injection Systems. Chlorine can be injected through calibrated orifices as
a suction system or by use of a motor driven liquid chlorine injection pump. The entire
system can be automated when a variable rate chlorine injection pump is used. All that is
required is a timer that can be set to inject chlorine for 45 minutes every 6 to 12
hours. The timer is attached to the circuit controlling the irrigation pump. The timer
The Use of Surface Water for
Low Pressure Irrigation Systems -2-
will run only during the period that the irrigation system is "on"; consequently, the
timer automatically accumulates total irrigation time.
An orifice type suction injection system cannot be automated. They are subject to
clogging and the rate of injection may vary with pressure changes. Orifices should be
constructed from teflon or other materials that are not damaged by chlorine. Brass and
all metals should be avoided. Teflon, PVC, PE .(polyethylene) type materials are
satisfactory. Orifice type systems should be confined to operations in which the pumping
capacity is greater than 100 gpm. The orifice must be large enough to pass small
particles. I have found that orifices used on systems less than 100 ppm may clog easily
from particles in the chlorine solution.
It is essential that a DPD type chlorine test kit be purchased and used to read total
chlorine and free available (residual) chlorine. Store the test kit in a dark cool
place. Total chlorine includes all chlorine that reacts with organic matter plus extra
chlorine for killing bacteria. Free chlorine is the excess chlorine over and above all
chemical reactions and other type reactions in the system. It is the type of chlorine
that kills bacteria and algae. Chlorine should be injected to obtain a minimum of 1.0 ppm
fmg/L] free residual chlorine assuming the pH of the water is below 7.5. IMPORTANT: REAU
THE COLOR WITHIN 15 SECONDS FOR FREE CHLORINE. This reading should be obtained at the
last emitter or microsprinkler on the irrigation system. Such an "end of line"
measurement is often inconvenient since one cannot be certain when the chlorine will reach
the last emitter. A more convenient method is to take a reading close to the pump. This
reading should be at least 2 ppm of free residual chlorine. The best method is to read
both locations initially and adjust the pump reading according to the reading at the last
emitter. Initially, the amount of chlorine required will be very high because of
contamination in the system. With treatments over a period of time, the amount of
chlorine probably can be reduced.
If there is insufficient free chlorine, all of the chlorine injected is wasted and may
actually stimulate bacterial growth.
Surface water systems, that do not contain iron, will encounter little or no
difficulty with the chlorine treatment if the pH is below 7.5. Higher pH values for
surface water may result in certain organic precipitation reactions for which we have no
control at this time.
Surface waters containing iron can be treated with chlorine for 45 minutes every 6
hours providing the pH is less than 6.5. Above pH 6.5 certain organic precipitation
reactions combined with completed iron may gradually clog the irrigation system.
A survey of lakes and ditches in Florida has indicated that total chlorine
requirements may vary from 3 to 10 ppm. This could require the use of 7 gallons of 10%
sodium hypochloride in 45 minutes for a pumping system of 800 gpm.
Hand flushing or end-of-line flush valves. Surface waters with or without chlorine
treatment will accumulate suspended sludge at the ends of the lines. This material must
be flushed out at intervals. Flush valves have several advantages but one can do the job
by hand. The suspended sludge can clog emitters if not removed from the lines.