• TABLE OF CONTENTS
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 Front Cover
 Table of Contents
 Introduction & Causes of emitter...
 Prevention of emitter plugging
 Injection methods
 Backflow prevention
 Summary
 Reference
 Back Cover














Group Title: Bulletin
Title: Causes and prevention of emitter plugging in micro irrigation systems
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 Material Information
Title: Causes and prevention of emitter plugging in micro irrigation systems
Series Title: Bulletin
Physical Description: 20 p. : ill. ; 23 cm.
Language: English
Creator: Pitts, Donald J ( Donald James )
Haman, D. Z ( Dorota Z )
Smajstrla, A. G ( Allen George )
Publisher: Florida Cooperative Extension Service, University of Florida
Place of Publication: Gainesville
Publication Date: 1990
 Subjects
Subject: Irrigation engineering   ( lcsh )
Microirrigation -- Equipment and supplies   ( lcsh )
Genre: government publication (state, provincial, terriorial, dependent)   ( marcgt )
bibliography   ( marcgt )
non-fiction   ( marcgt )
 Notes
Bibliography: Includes bibliographical references (p. 19-20).
Statement of Responsibility: D.J. Pitts, D.Z. Haman and A.G. Smajstrla.
General Note: Cover title.
General Note: "April 1990."
 Record Information
Bibliographic ID: UF00008536
Volume ID: VID00001
Source Institution: University of Florida
Holding Location: University of Florida
Rights Management: All rights reserved by the source institution and holding location.
Resource Identifier: ltqf - AAA6798
ltuf - AHL3228
oclc - 22942344
alephbibnum - 001589256

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Table of Contents
    Front Cover
        Page i
    Table of Contents
        Page ii
    Introduction & Causes of emitter plugging
        Page 1
        Page 2
        Page 3
        Page 4
    Prevention of emitter plugging
        Page 5
        Page 6
        Page 7
        Page 8
        Page 9
        Page 10
        Page 11
        Page 12
        Page 13
        Page 14
    Injection methods
        Page 15
        Page 16
    Backflow prevention
        Page 17
    Summary
        Page 18
    Reference
        Page 19
        Page 20
    Back Cover
        Page 21
Full Text




April 1990


Bulletin 258


Causes and Prevention of
Emitter Plugging In Micro Irrigation
Systems

D.J. Pitts, D.Z. Haman and A.G. Smajstrla








S". of Florida









Florida Cooperative Extension Service
Institute of Food and Agricultural Sciences
University of Florida, Gainesville
John T. Woeste, Dean for Extension


R @ n ,TA T








Table of Contents


Introduction ................................... 1
Causes of Emitter Plugging ......................... 1
Influence of the Water Source .................... 1
Physical ....................................... 2
Biological ...................................... 2
Chemical .................................... 3
Fertigation ..................................... 5
Prevention of Emitter Plugging ................. ..... 5
Water Quality Analysis ........................ 6
Filters' for Prevention of Physical Plugging ........... 7
Settling Ponds ............................. 10
Flushing ................................... 11
Chemical Treatment ......................... 11
Chlorine Injection ........................ 12
Acid Treatment .......................... 13
Scale Inhibitors ......................... 14
Pond Treatment .............................. 15
Injection M ethods ............................... 15
Backflow Prevention .............................. 17
Sum m ary ...................................... 18
References ...................... ............... 19



















D. J. Pitts is an Assistant Professor and Water Management Specialist,
Southwest Florida Research and Education Center, Immokalee; D. Z.
Haman is Associate Professor and Water Management Specialist, Agricul-
tural Engineering Department; and A. G. Smajstrla is Professor and Water
Management Specialist, Agricultural Engineering Department; Institute of
Food and Agricultural Sciences, University of Florida, Gainesville, 32611.








Causes and Prevention of Emitter Plugging
In Micro Irrigation Systems
by
D. J. Pitts, D. Z. Haman and A. G. Smajstrla

Introduction
Micro irrigation systems can deliver water and nutrients in
precise amounts and at controlled frequencies directly to the plant's
root zone. With micro irrigation systems an extensive network of
pipes is used to distribute water to emitters which discharge it in
droplets, small streams or through mini-sprayers.
In the past decade, the use of micro irrigation to provide water
to horticultural crops has increased dramatically. Micro irrigation,
properly managed, offers several potential advantages over other
methods of irrigation:

greater water application uniformity.
improved water use efficiency.
minimized deep percolation and runoff.
enhanced weed control.
reduced bacteria, fungi, disease, and other pests that require
a moist environment.
efficient delivery of fertilizer (fertigation) and other chemicals
(chemigation) through the irrigation system.
ability to irrigate land too steep for irrigation by other means.


The plugging of emitters is one of the most serious problems
associated with micro irrigation use. Emitter plugging can severely
hamper water application uniformity.

Causes of Emitter Plugging
Emitter plugging can result from physical (grit), biological
(bacteria and algae), or chemical (scale) causes. Frequently, plugging
is caused by a combination of more than one of these factors.

Influence of the Water Source

The type of emitter plugging problems will vary with the source
of the irrigation water. Water sources can be grouped into two









categories: surface or ground water. Each of these water sources
produce specific plugging characteristics.
Algal and bacterial growth are major problems associated with
the use of surface water. Whole algae cells and organic residues of
algae are often small enough to pass through the filters of an
irrigation system. These algal cells can then form aggregates that
plug emitters (Haman, 1987c). Residues of decomposing algae can
accumulate in pipes and emitters to support the growth of slime-
forming bacteria. Surface water can also contain larger organisms
such as moss, fish, snail, seeds, and other organic debris that must
be adequately filtered to avoid plugging problems. Chemical precipi-
tation is normally not a major problem when using surface water.
Groundwater, on the other hand, often contains high levels of
minerals in solution that can precipitate and form scale. Water from
shallow wells (less than 100 ft) often will produce plugging problems
associated with bacteria; chemical precipitation is more common with
deep wells (Knapp et al., 1986). Physical plugging problems are
generally less severe with groundwater.

Physical

Sources of physical plugging problems include particles of sand
and suspended debris that are too large to pass through the
openings of emitters. Sand particles, which can plug emitters, are
often pumped from wells. Water containing some suspended solids
may be used with micro irrigation systems if these suspended solids
consist of clay-size particles, and flocculation does not occur.
Research has shown that using water with over 500 ppm suspended
solids did not cause emitter plugging as long as the larger particles
were filtered (Pitts, 1985).
Under some conditions, however, clay will flocculate and form
aggregates causing plugging. Unflocculated clay and silt-sized
particles are normally too small to plug emitters. Turbidity is an
indicator of suspended solids, but turbidity alone is not an accurate
predictor of the plugging potential of a water source. Turbidity
should be combined with a laboratory filtration test to measure
plugging potential (Gilbert and Ford, 1986).

Biological

A micro irrigation system can provide a favorable environment
for bacterial growth, resulting in slime buildup. This slime can
combine with mineral particles in the water and form aggregates








large enough to plug emitters. Certain bacteria can cause enough
precipitation of manganese, sulfur, and iron compounds to cause
emitter plugging. In addition, algae can be transported into the
irrigation system from the water source and create conditions that
may promote the formation of aggregates.
Emitter plugging problems are common when using water that
has high biological activity and high levels of iron and hydrogen
sulfide. This is a frequent problem in Florida, because iron and
sulfur are common constituents of many Florida waters.
Soluble ferrous iron is a primary energy source for certain iron-
precipitating bacteria (Gilbert and Ford, 1986). These bacteria can
attach to surfaces and oxidize ferrous iron to its insoluble ferric iron
form. In this process, the bacteria create a slime that can form
aggregates called ochre, which may combine with other materials in
the micro irrigation tubing and cause emitter plugging (Ford and
Tucker, 1975). Ochre deposits and associated slimes are usually red,
yellow, or tan.
Sulfur slime is a yellow to white stringy deposit formed by the
oxidation of hydrogen sulfide commonly present in shallow wells in
Florida. Hydrogen sulfide (H2S) accumulation in groundwater is a
process typically associated with reduced conditions in anaerobic
environments. Sulfide production is common in lakes and marine
sediments, flooded soils, and ditches; it can be recognized by the
rotten egg odor. Sulfur slime is produced by certain filamentous
bacteria that can oxidize -hydrogen sulfide and produce insoluble
elemental sulfur.
The sulfur bacteria problem can be minimized if there is not air-
water contact until water is discharged from the system. Defective
valves or pipe fittings on the suction side of the irrigation pump are
common causes of sulfur bacteria problems (Ford and Tucker, 1975).
If a pressure tank is used, the air-water contact in the pressure tank
can lead to bacterial growth in the tank, clogging the emitter. The
use of an air bladder or diaphragm to separate the air from the
water should minimize this problem.

Chemical

Water is often referred to as the universal solvent since almost
everything is soluble in it to some extent. The solubility of a given
material in water is controlled by variations in temperature,
pressure, pH, redox potential, and the relative concentrations of
other substances in solution. Three gases (oxygen, carbon dioxide,
and hydrogen sulfide) are important in determining the solubility
characteristics of water. These gases are very reactive in water, and







they determine to a significant extent the solubility of minerals
within a given water source.
In order to predict what might cause chemical plugging of micro
irrigation system emitters, the process of mineral deposition must be
understood. Carbon dioxide gas (CO2) is of particular importance in
the dissolution and deposition of minerals. Water absorbs some CO2
from the air, but larger quantities are absorbed from decaying
organic matter as water passes through the soil. Under pressure, as
is groundwater, the concentration of CO2 increases to form carbonic
acid. This weak acid can readily dissolve mineral compounds such as
calcium carbonate to form calcium bicarbonate which is soluble in
water. This process allows calcium carbonate to be dissolved,
transported, and under certain conditions, again redeposited as
calcium carbonate.
Calcium carbonate is the most common constituent of scale.
Calcite, aragonite, and vaterite are mineral forms of calcium
carbonate that have been found in carbonate scale. Calcite is formed
at temperatures common within micro irrigation systems, and is the
most common and stable of the mineral forms.
Calcium minerals occur extensively in the form of limestone and
dolomite (magnesium-calcium carbonate). Calcite is the principal
constituent of limestone, and occurs in many calcareous metamorphic
rocks such as marble. Therefore, it is not surprising to encounter
calcium carbonate in solution in almost all surface and ground
waters, especially in Florida where much of the groundwater is
pumped from large underlying limestone formations. As groundwater
passes through these limestone formations it dissolves the limestone
and carries calcium carbonate with it.
Chemical plugging usually results from precipitation of one or
more of the following minerals: calcium, magnesium, iron, or
manganese. The minerals precipitate from solution and form
encrustations (scale) that may partially or completely block the flow
of water through the emitter. Water containing significant amounts
of these minerals and having a pH greater than 7 has the potential
to plug emitters. Particularly common is the precipitation of calcium
carbonates, which is temperature and pH dependent. An increase in
either pH or temperature reduces the solubility of calcium in water,
and results in precipitation of the mineral.
When groundwater is pumped to the surface and discharged
through a micro irrigation system, the temperature, pressure, and
pH of the water often changes. This can result in the precipitation
of calcium carbonates or other minerals to form scale on the inside
surfaces of the irrigation system components. A simple test for
identifying calcium scale is to dissolve it with vinegar. Carbonate








minerals dissolve and release carbon dioxide gas with a fizzing,
hissing sound known as effervescence.
Iron is another potential source of mineral deposit that can plug
emitters. Iron is encountered in practically all soils in the form of
oxides (Cowan, 1976), and it is often dissolved in groundwater as
ferrous bicarbonate. When exposed to air, soluble ferrous bicarbonate
oxidizes to the insoluble or colloidal ferric hydroids and precipitates.
The result is commonly referred to as 'red water,' which is some-
times encountered in farm irrigation wells. Manganese will some-
times accompany iron, but usually in lower concentrations.
Hydrogen sulfide is present in many wells in Florida. Precipita-
tion problems will generally not occur when hard water, which
contains large amounts of hydrogen sulfide, is used. Hydrogen sulfide
will minimize the precipitation of calcium carbonate (CaCO3) because
of its acidity.

Fertigation

Fertigation is the application of plant nutrients through an
irrigation system by injection into the irrigation water. Fertilizers
injected into a micro irrigation system may contribute to plugging.
Field surveys have indicated considerable variation in fertilizer
solubility for different water sources (Ford, 1977). To determine the
potential for plugging problems from fertilizer injection, the following
test can be performed:

(1) Add drops of the liquid fertilizer to a sample of the irrigation
water so that the concentration is equivalent to the diluted
fertilizer that would be flowing in the lateral lines.
(2) Cover and place the mixture in a dark environment for 12
hours.
(3) Direct a light beam at the bottom of the sample container to
determine if precipitates have formed. If no apparent
precipitation has occurred, the fertilizer source will normally
be safe to use in that specific water source (Gilbert and
Ford, 1986).

Prevention of Emitter Plugging
A properly designed micro irrigation system should include
preventive measures to avoid emitter plugging. Differences in
operating conditions and water quality do not allow a standardized
recommendation for all conditions. In general, however, the system
should include the following:








a method of filtering the irrigation water.
a means of injecting chemicals into the water supply.
in some cases a settling basin to allow aeration and the removal
of solids.
equipment for flushing the system.

Prevention of plugging can take two basic approaches: 1)
removing the potential source of plugging from the water before it
enters the irrigation system; or 2) treating the water to prevent or
control chemical and biological processes from occurring. Both
approaches will be discussed. In many cases, a combination of both
approaches will be applicable.

Water Quality Analysis

Knowing the quality of proposed irrigation water is necessary
before designing a micro irrigation system. Water quality analyses
are performed at water testing laboratories (e.g. IFAS Soil and
Water Testing Laboratory, University of Florida, Gainesville). A
water analysis specifically for micro irrigation should be requested.
The analysis should include the factors listed in Table 1. If the
source is groundwater from a relatively deep well (over 100 ft),
analysis for bacteria population may be omitted. Conversely, if the
source is surface water, hydrogen sulfide will not be present and can
be omitted.
Table 1 provides concentration levels for evaluating the water
quality analysis in terms of the potential for emitter plugging.
A water quality analysis usually lists electrical conductivity in
micromhos per centimeter (timho/cm). To estimate parts per million
(ppm) dissolved solids as shown in Table 1, multiply Lmho/cm by
0.64. For example, if the electric conductivity meter reads 1000
Limho/cm, then dissolved solids can be estimated as 640 ppm.
Hardness is primarily a measure of the presence of calcium (Ca)
and magnesium (Mg), and is another indicator of the plugging
potential of a water source. If Ca and Mg are given in ppm rather
than hardness, hardness can be estimated from the following
relationship:
Hardness = (2.5 x Ca) + (4.1 x Mg), (Eq. 1)
where calcium (Ca) and magnesium (Mg) are given in milligrams
per liter (mg/L or ppm).







Table 1. Criteria for plugging potential of micro irrigation water sources.
Plugging Hazard Based on Concentration
Factor Slight Moderate Severe
Concentrations (ppm)

Physical
Suspended solids < 50 50 to 100 > 100
filterablee)
Chemical
pH < 7.0 7.0 to 7.5 > 7.5
Dissolved solids <500 500 to 2000 >200 0
Manganese < 0.1 0.1 to 1.5 > 1.5
Iron < 0.1 0.1 to 1.5 > 1.5
Hydrogen sulfide < 0.5 0.5 to 2.0 > 2.0
Hardness" <150 150 to 300 > 300

Biological
Bacteria < 10,000 10,000 to 50,000 >50,000
(population)

(Modified from Nakayama and Bucks, 1986)
"Hardness as ppm CaCO3, Todd, 1980

Note that 1 mg/L equals 1 ppm. If the analysis lists the Ca and
Mg concentrations in milliequivalents per liter (meq/1), they can be
converted to ppm by the following factors:
Ca (meq/L) x 20 = Ca (ppm), (Eq. 2)
Mg (meq/L) x 12 = Mg (ppm). (Eq. 3)
This method of estimating hardness may give results that vary
somewhat from results obtained for total hardness by laboratory
methods. However, the estimate is normally adequate for use in
Table 1.

Filters for Prevention of Physical Plugging

Many types of micro irrigation filter systems that will perform
adequately are available commercially. Important factors to consider
in selecting a filtering method are emitter design and quality of the
water source. Consider the emitter's minimum passageway diameter
when selecting the filter mesh size. Filters should be sized according
to the emitter manufacturer's recommendations or, in the absence
of manufacturer's recommendations, to remove any particles larger
than one-tenth the diameter of the smallest opening in the emitter
flow path.








Screen filters come in a variety of shapes and sizes. A typical
design is shown in Figure 1. Screen material may be slotted PVC,
perforated stainless steel, or synthetic or stainless steel wire. Mesh
size -- the number of openings per inch -- determines the fineness
of the material filtered.
Surface water sources should have a coarse screen filter installed
on the pump inlet (suction) line to block trash and large debris. To
avoid floating debris, the pump inlet should be located two feet
below the water surface but suspended above the bottom.
Screen filters remove only small amounts of sands and organic
material before clogging and causing a flow rate reduction. Two or
more filters installed in parallel will increase the time between
screen cleaning. Screen cleaning can be a manual or automatic
operation. For more information on screen filters, see Agricultural
Engineering Fact Sheet AE-61, Screen Filters for Irrigation Systems.
OUTLET

INLET---

FILTER BODY CAP
Figure 1 Screen Filter

Wafer (disc) filters consist of a stack of washers that provide a
filtering surface area for the water to pass over as it flows through
the filter (see Figure 2). These filters are sized based on the
equivalent screen mesh filter size. They also require periodic
cleaning. Some manufacturers provide an automatic backflush
feature. Wafer filters provide more filter surface area than screen
filters of the same size.
Media (sand) filters are available with the capacity to efficiently
remove most types of physical plugging sources (see Figure 3). These
filters will remove colloidal and organic material usually present in
surface waters. The size and type of media used determines the








Figure 2 Water (disc) Filter









degree of filtration. The finer the media, the smaller the particle size
that will be removed. Table 2 shows the relationship between sand
grade and screen mesh size.
FILTRATION PROCESS BACKWASHING PROCESS
BACKFLUSH








SUOUTLET L U OUTLET
Figure 3 Media Filters


Table 2. Sand media size and screen mesh equivalents
Sand Sand Sand Screen
Number Diameter (in) Pore Diameter (in) Mesh

8 0.059 0.008 70
11 0.031 0.004 140
16 0.026 0.003 170
20 0.018 0.002 230
30 0.011 0.001 400
(after Fereres, 1981)

Size of the media filter required is determined by the flow rate
of the system, and is measured by the top surface area of the filter.
Media filters should be sized to provide a minimum of one square
foot of top surface area for every 20 GPM of flow, or as the
manufacturer recommends.
Filters are cleaned by reversing the direction of waterflow through
them; this procedure is call backwashing. Backwashing can be
manual or automatic, on a set time interval or at a specific pressure
drop. When using a media filter, install it with an additional screen
filter (200-mesh or manufacturer's recommendation) downstream to
prevent the transport of sand to the irrigation system during the
backwash procedure. For more information on the selection,
operation and maintenance of media filters, see Agricultural
Engineering Fact Sheet AE-57, Media Filters for Trickle Irrigation
in Florida.








Vortex or centrifugal filters (Figure 4) effectively remove sand
and larger particles, but are not effective at removing algae, very
fine precipitates, and other light-weight materials. This type of filter
should be used as the first filter if the water source is a sand
pumping well or a fast-moving stream. It should be followed by a
media and screen filter for surface water sources, or screen or wafer
filter for well water.
OUTLET

INLET













Figure 4 Vortex Filter


Settling Ponds

In addition to filtration, the quality of water with high levels of
solids can be improved with settling ponds or basins to remove large
inorganic particles. Settling ponds can also be used for aeration of
groundwater containing high amounts of iron or manganese.
Experiments have shown that a ferrous iron content as low as
0.2 ppm can contribute to iron deposition (Gilbert and Ford, 1986).
Iron is very common in shallow wells in many parts of Florida, but
it can often be economically removed from irrigation water by
aeration (or by some other means of oxidation), followed by
sedimentation and/or filtration.
Existing ponds can sometimes be used as settling basins. They
need not be elaborate structures; however, settling basins should be
accessible for cleaning, and large enough that the velocity of the
flowing water is sufficiently slow for particles to settle out. Ex-
perience based on municipal sedimentation basins indicates that the
maximum velocity should be limited to 1 foot per second.








A settling basin should be designed to remove particles having
equivalent diameters exceeding 75 microns, which corresponds to
the size of a particle removed by a 200-mesh screen filter. The basin
works on the principle of sedimentation, which is the removal of
suspended particles that are heavier than water by gravitational
settling. Materials held in suspension due to the velocity of the
water can be removed by lowering the velocity. In some cases,
materials that are dissolved in solution oxidize (through exposure
to a free air surface), precipitate, and flocculate to form aggregates
large enough to settle out of the water.
Settling ponds are also recommended when the irrigation water
source is a fast-moving stream. Velocity of the water is slowed in
the settling pond, thus allowing many particles to settle out.
For details on the design of settling basins, see Agricultural En-
gineering Fact Sheet AE-65, Settling Basins for Trickle Irrigation
in Florida.

Flushing

To minimize sediment build up, regular flushing of drip irriga-
tion pipelines is recommended. Valves large enough to allow
sufficient velocity of flow should be installed at the ends of mains,
submains, and manifolds. Also, allowances for flushing should be
made at the ends of lateral lines. Begin the flushing procedure with
the mains, then proceed to submains, manifolds, and finally to the
laterals. Flushing should continue until clean water runs from the
flushed line for at least two minutes. A regular maintenance
program of inspection and flushing will help significantly in prevent-
ing emitter plugging.
To avoid plugging problems when fertigating, it is best to flush all
fertilizer from the lateral lines prior to shutting the irrigation system
down.

Chemical Treatment

Chemical treatment is often required to prevent emitter plugging
due to microbial growth and/or mineral precipitation. The attach-
ment of inorganic particles to microbial slime is a significant source
of emitter plugging. Chlorination is an effective measure against
microbial activity (Ford; 1977, 1979a,b,c; Tyson and Harrison, 1985).
Use chlorine and all other chemicals only according to label
directions. Acid injection can remove scale deposits, reduce or
eliminate mineral precipitation, and create an environment
unsuitable for microbial growth (Cowan, 1976).








Chlorine Injection


Chlorination is the most common method for treating bacterial
slimes. If the micro irrigation system water source is not chlorinated,
it is a good practice to equip the system to inject chlorine to
suppress microbial growth. Since bacteria can grow within filters,
chlorine injection should occur prior to filtration.
Liquid sodium hypochlorite (NaOC1) -laundry bleach- is available
at several chlorine concentrations. The higher concentrations are
often more economical. It is the easiest form of chlorine to handle
and is most often used in drip irrigation systems. Powdered calcium
hypochlorite (CaCOC12), also called High Test Hypochlorite (HTH),
is not recommended for injection into micro irrigation systems since
it can produce precipitates that can plug emitters, especially at high
pH levels (Tyson and Harrison, 1985).
The following are several possible chlorine injection schemes.
Inject continuously at a low level to obtain 1 to 2 ppm of free
chlorine at the ends of the laterals.
Inject at intervals (once at the end of each irrigation cycle) at
concentrations of 20 ppm and for a duration long enough to reach
the last emitter in the system.
Inject a slug treatment in high concentrations (50 ppm) weekly
at the end of an irrigation cycle and for a duration sufficient to
distribute the chlorine through the entire piping system.
The method used will depend-on the growth potential of micro-
bial organisms, the injection method and equipment, and the sched-
uling of injection of other chemicals. Ford (1979c) developed a key
that recommends chlorine injection rates for Florida conditions and
irrigation systems.
The amount of liquid sodium hypochlorite required for injection
into the irrigation water to supply a desired dosage in parts per
million can be calculated by the following simplified method:
I = (0.006 x P x Q)/ m Eq. 4
where,
I = gallons of liquid sodium hypochlorite injected per hour,
P = parts per million desired,
Q = system flow rate in gpm,
m = percent chlorine in the source, normally 5.25 % or 10 %.
For more detailed information on injection rates, volumes and
durations, the reader is referred to Clark et al. (1988).
When chlorine is injected, a test kit should be used to check to
see that the injection rate is sufficient. Color test kits (D.P.D.) that








measure 'free residual' chlorine, which is the primary bactericidal
agent, should be used. The orthotolidine-type test kit, which is often
used to measure total chlorine content in swimming pools, is not
satisfactory for this purpose. D.P.D. test kits can be purchased from
irrigation equipment dealers. Check the water at the outlet farthest
from the injection pump. There should be a residual chlorine
concentration of 1 to 2 ppm at that point. Irrigation system flow
rates should be closely monitored, and action taken (chlorination) if
flow rates decline.
Chlorination for bacterial control is relatively ineffective above pH
7.5, so acid additions may be necessary to lower the pH to increase
the biocidal action of chlorine for more alkaline waters. This may be
required when the water source is the Floridian aquifer.
Since sodium hypochlorite can react with emulsifiers, fertilizers,
herbicides, and insecticides, bulk chemicals should be stored in a
secure place according to label directions.

Acid Treatment

Acid can be used to lower the pH of irrigation water to reduce the
potential for chemical precipitation and to enhance the effectiveness
of the chlorine injection. Sulfuric, hydrochloric, and phosphoric acid
are all used for this purpose (Kidder and Hanlon, 1985). Acid can
be injected in much the same way as fertilizer; however, extreme
caution is required. The amount of acid to inject depends on how
chemically base (the buffering capacity) the irrigation water is and
the concentration of the acid to be injected. One milliequivalent of
acid completely neutralizes one milliequivalent of bases.
If acid is injected on a continuous basis to prevent calcium and
magnesium precipitates from forming, the injection rate should be
adjusted until the pH of the irrigation water is just below 7.0. If
the intent of the acid injection is to remove existing scale buildup
within the micro irrigation system, the pH will have to be lowered
more (Cowen and Weintritt, 1976). The release of water into the
soil should be minimized during this process since plant root damage
is possible. An acid slug should be injected into the irrigation system
and allowed to remain in the system for several hours, after which
the system should be flushed with irrigation water. Acid is most
effective at preventing and dissolving alkaline scale. Avoid concentra-
tions that may be harmful to emitters and other system components.
Phosphoric acid, which is also a fertilizer source, can be used for
water treatment. Some micro irrigation system operators use
phosphoric acid in their fertilizer mixes. Caution is advised if









phosphoric acid is used to suppress microbial growth. Care should
be used with the injection of phosphoric acid into hard water since
it may cause the precipitation of calcium carbonate at the interface
between the injected chemical and the water source.
For safety, dilute the concentrated acid in a non-metal, acid-
resistent mixing tank prior to injection into the irrigation system.
When diluting acid, always add acid to water, never water to acid.
The acid injection point should be beyond any metal connections or
filters to avoid corrosion. Flushing the injection system with water
after the acid application is a good practice to avoid deterioration of
components in direct contact with the acid.
Acids and chlorine compounds should be stored separately,
preferably in epoxy-coated plastic or fiberglass storage tanks. Acid
can react with hypochlorite to produce chlorine gas and heat;
therefore, the injection of acid should be done at some distance (2
feet), prior to the injection of chlorine. This allows proper mixing of
the acid with the irrigation water before the acid encounters the
chlorine.
Hydrochloric, sulfuric, and phosphoric acids are all highly toxic.
Always wear goggles and chemical-resistant clothing whenever
handling these acids. Acid must be poured into water; never
pour water into acid.

Scale Inhibitors

Scale inhibitors, such as chelating and sequesting agents, have
long been used by other industries. A number of different chemicals
are being marketed for use in micro irrigation systems to prevent
plugging. Many of these products contain some form of inorganic
polyphosphate that can reduce or prevent precipitation of certain
scale-forming minerals. These inorganic phosphates do not stop
mineral precipitation, but keep it in the sub-microscopic range by
inhibiting its growth. Probably the most commonly used of these
materials is sodium hexametaphosphate -- as little as 2 ppm can
hold as much as 200 ppm calcium bicarbonate in solution (Cowan
and Weintritt, 1976).
Sodium hexametaphosphate is not only effective against alkaline
scale, but also forms complexes with iron and manganese and can
prevent depositions of these materials. Although the amount of
phosphate required to prevent iron deposits depends on several
factors, a general recommendation is 2 to 4 ppm phosphate for each
ppm of iron or manganese (Cowen and Weintritt, 1976).








These phosphates are relatively inexpensive, readily soluble in
water, nontoxic, and effective at low injection rates.

Pond Treatment

Algae problems which often occur with surface water sources such
as a pond can be effectively treated with copper sulfate (CuSO4).
Dosages of 1 to 2 ppm (1.4 to 2.7 pounds per acre foot) are sufficient
and safe to treat algae growth. Copper sulfate should be applied
when the pond water temperature is above 60 F. Treatments may
be repeated at 2- to 4-week intervals, depending on the nutrient load
in the pond. Copper sulfate should be mixed into the pond(i.e.,
sprinkled into the wake of a boat). The distribution of biocides into
surface water must be in compliance with EPA regulations.
Copper sulfate can be harmful to fish if alkalinity, a measure of
the water's capacity to neutralize acid, is low. Alkalinity is mea-
sured volumetrically by titration with H2SO4 and is reported in
terms of equivalent CaCO3. Table 3 provides a reference for
determining rates to add copper sulfate given different alkalinity
levels. Repeated use of copper sulfate can result in the buildup to
toxic levels for plants.

Table 3. Copper Sulfate (CuSO4) Levels Safe for Fish

Alkalinity Value (CaCO3, mg/1) Addition of Copper Sulfate
below 40 do not use
40-60 1.0 Ib per acre-ft of water
60-100 1.3 Ib per acre-ft of water
over 100 2.7 Ib per acre-ft of water
(1 ppm = 2.7 Ib per acre-ft)
(Dupress and Huner, 1984)

Injection Methods
Several types of injection systems, available commercially through
irrigation equipment suppliers, are commonly used with micro
irrigation: venturi, pressurized mixing tank, pump suction line
method, and metering pumps (see Figures 5 through 8). Whichever
method is used, there must be some way of controlling injection
rates.
Figure 5 shows a venturi- injector in which the injection rate
depends upon the creation of a 'low' pressure area as water flows
through a constriction in the line. Since injection is based on the
pressure differential that results, the rate of injection depends on
pressure, flow, and the level of solution in the supply tank.









BACK FLOW PREVENTOR


Figure 5 Venturi Chemical Injector

Figure 6 shows the pressurized mixing tank where the solution is
placed in a flexible membrane. Water entering the supply tank
displaces solution from the membrane into the line. The injection

PRESSURIZED
CONTAINER
GATE --
VACUUM VALVE
BREAKER\
PRESSURE
GAUGE
PUMP *

CHECK IRRIGATION
VALVE LINE
LOW PRESSURE FLOW RESTRICTOR
DRAIN

Figure 6 Pressurized Mixing Tank


rate is controlled by adjusting valves both on the main line and from
the solution supply tank.
The pump suction line method is shown in Figure 7. With this
method the pump must be resistant to any chemical that is to be
injected. Because of backflow prevention regulations, this method is
only permissible under certain conditions. See IFAS Extension
Bulletin 217 Backflow Prevention Requirements for Florida Irriga-
tion Systems for permissible application of this method.
Figure 8 shows a metering injection pump. These are often
positive displacement injectors which rely on either a diaphragm or
a piston-driven pump which produces a higher pressure in the
chemical injection line than that in the irrigation pipeline. The
injection rate can be very precisely controlled with this method, and
it is recommended when a constant level of chemical concentration


FLOW RESTRICTOR



























Figure 7 Pump Suction Line Method


TROL VALVE
ELECTRIC
L .METERING
PUMP


FIELD


VALVE


IRRIGATION


Figure 8 Metering Injection Pump



must be maintained in the system supply line such as when
pesticides are injected. For more information on chemical injection
methods and calibration the reader is referred to IFAS Extension
Bulletin 250, Injection of Chemicals into Irrigation Systems: Rates,
Volumes, and Injection Periods.


Backflow Prevention

To ensure that the water source does not become contaminated,
Florida law, EPA regulations, and county and municipal codes
require backflow prevention assemblies on all irrigation systems








injecting chemicals into irrigation water. For detailed information
on these requirements, the reader is referred again referred to IFAS
Extension Bulletin 217. Appropriate backflow prevention should
include the following setup:

a check valve upstream from the injection device to prevent back-
ward flow.
a low pressure drain to prevent seepage past the check valve.
a vacuum relief valve to ensure a siphon cannot develop.
a check valve on the injection line.

Figure 9 shows the proper arrangement of equipment. If an
externally-powered metering pump is used for injection, it should
be electrically interlocked with the irrigation pump. This interlock
should not allow the injection pump to operate unless the irrigation
pump is operating.
If irrigation water is being used from municipal or other public
water supply systems special backflow precautions must be taken.
See IFAS Extension Bulletin 248.

VACUUM BREAKER CHEMICAL INJECTION
VACUUM.BREAKER POINT
S CHECK VALVE
FROM- TO
PUMP FILTER
LOW PRESSURE DRAIN
2" MINIMUM CLEARANCE



Figure 9 Backflow Prevention Components


Summary
* Emitter plugging can occur from physical, biological and chemical
causes.
* A water quality analysis is vital to the proper design and opera-
tion of the micro irrigation system.
* Every micro irrigation system needs some method of filtration.
* Regular flushing of the lateral and main lines will help to prevent
plugging.
* Most micro irrigation systems will require a method of chemical
treatment of the water source, and a backflow prevention system
will also be required.









References


Clark, G.A., and D.Z. Haman, and F.S. Zazueta. 1988. Injection of
Chemicals into Irrigation Systems: Rates, Volumes, and Injection Periods
Agricultural Engineering Extension Report 88-8. IFAS, University of
Florida.

Cowan, J.C. and D.J. Weintritt. 1976. Water-formed Scale Deposits. Gulf
Publishing Co. Houston TX.

Dupress, H.K. and J.V. Huner. 1984. Third Report of the Fish Farmer.
United States Department of Interior, Fish and Wildlife Service. PP. 202.
Washington, D. C.

Fereres, Elias. 1981. Drip Irrigation Management. Leaflet 21259 Division
of Agriculture, University of California.

Ford, H.W. and D.P.H. Tucker. 1975. Blockage of Drip Irrigation Filters
and Emitters by Iron-Sulfur-Bacterial Products. Hort Science 10 (1): 62-
64.

Ford, H.W. 1979a. The Present Status of Research on Iron Deposits in
Low Pressure Irrigation Systems. Fruit Crops Mimeo Report FC 79-3,
IFAS, University of Florida.

Ford, H.W. 1979b. The Use of Chlorine in Low Pressure Systems Where
Bacterial Slimes are a Problem. Fruit Crops Mimeo Report FC 790-5.
IFAS, University of Florida.

Ford, H.W. 1979c. A Key for Determining the Use of Sodium Hypochlorite
(Liquid Chlorine) to Inhibit Iron and Slime Clogging of Low Pressure
Irrigation Systems in Florida. Lake Alfred, CREC Research Report CS
79-3. IFAS, University of Florida.

Ford, H.W. 1977. Controlling Certain Types of Slime Clogging in Drip/
Trickle Irrigation Systems. Proceedings of the 7th International Agricul-
tural Plastics Congress, San Diego, California.

Ford, H.W. 1987. Iron Ochre and Related Sludge Deposits in Subsurface
Drain Lines. Extension Cir. 671. IFAS, University of Florida.

Gilbert, R.G and H.W. Ford. 1986. Operational Principles, Chapter 3,
Trickle Irrigation for Crop Production. (ED. Nakayama and Bucks)
Elsevier Science Publishers. Amsterdam, Netherlands.

Haman, D.Z., A.G. Smajstrla and F.S. Zazueta. 1987a. Settling Basins for
Trickle Irrigation in Florida. Agricultural Engineering Fact Sheet AE-65.
IFAS, University of Florida.









Haman, D.Z., A.G. Smajstrla and F.S Zazueta. 1987b. Media Filters for
Trickle Irrigation in Florida. Agricultural Engineering Fact Sheet AE-57.
IFAS, University of Florida.

Haman, D.Z., A.G. Smajstrla and F.S. Zazueta. 1987c. Water Quality
Problems Affecting Micro-irrigation in Florida. Agricultural Engineering
Extension Report 87-2. IFAS, University of Florida.

Haman, D.Z., A.G. Smajstrla and F.S. Zazueta. 1988. Screen Filters for
Irrigation Systems. Agricultural Engineering Fact Sheet AE-61. IFAS,
University of Florida.

Knapp, M.S., W.S. Burns and T.S. Sharp. 1986. Preliminary Assissment of
the Groundwater Resources of Western Collier County, Florida. Technical
Publication #86-1, South Florida Water Management District.

Nakayama, F.S. and D.A. Bucks. 1986. Trickle Irrigation for Crop Pro-
duction. Elsevier Science Publishers. Amsterdam, Netherlands.

Pitts, D.J., J.A. Ferguson and J.T. Gilmour. 1985. Plugging Characteristics
of Drip-Irrigation Emitters Using Backwash from a Water-Treatment
Plant. Bulletin 880, Arkansas Agricultural Experiment Station, University
of Arkansas, Fayetteville.

Pitts, D.J. and P.L. Tacker. 1986. Trickle Irrigation: Causes and Preven-
tion of Emitter Plugging. MP 271, Cooperative Extension Service,
University of Arkansas.

Smajstrla, A.G., D.Z. Haman and F.S. Zazueta. 1986. Chemical Injection
(Chemigation) Methods and Calibration. Agricultural Engineering
Extension Report 85-22. IFAS, University of Florida.

Smajstrla, A.G., D.S. Harrison, W.J. Becker, F.S. Zazueta and D.Z. Haman.
1988. Backflow Prevention Requirements for Florida Irrigation Systems.
Extension Bulletin 217. IFAS, University of Florida.

Smajstrla, A.G. 1988. Backflow Requirements When Using Public Water
Supplies. Extension Bulletin 248. IFAS, University of Florida.

Todd, D.K. 1980. Groundwater Hydrology. p. 282. John Wiley and Sons,
N.Y.

Tyson, A.W. and K.A. Harrison. 1985. Chlorination of Drip Irrigation
Systems to Prevent Emitter Clogging. Misc. Publ. 183. Cooperative
Extension Service, University of Georgia.























































This publication was produced at a cost of $863.40, or 43.20 cents
per copy, to provide information on the causes of emitter plugging
in micro irrigation systems. 06-2M-90


COOPERATIVE EXTENSION SERVICE, UNIVERSITY OF FLORIDA, INSTI-
TUTE OF FOOD AND AGRICULTURAL SCIENCES, John T. Woeste, director,
in cooperation with the United States Department of Agriculture, publishes this
information to further the purpose of the May 8 and June 30, 1914 Acts of
Congress; and is authorized to provide research, educational information and
other services only to individuals and institutions that function without regard to
race, color, sex, age, handicap or national origin. Single copies of extension publications (excluding
4-H and youth publications) are available free to Florida residents from county extension offices.
Information on bulk rates or copies for out-of-state purchasers is available from C.M. Hinton,
Publications Distribution Center, IFAS Building 664, University of Florida, Gainesville, Florida 32611.
Before publicizing this publication, editors should contact this address to determine availability.




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