CLOGGING AND MAINTENANCE OF MICRO IRRIGATION SYSTEMS - Management, Performance, and Applications of Micro Irrigation Systems - page 87

novel technique that may be used as a standard to evaluate subsurface drip irrigation
systems.
Emitter clogging can be produced by physical, chemical, and biological causes
[2]. Physical clogging is caused by suspended inorganic particles (such as sand, silt,
clay, plastic fragments from the installation process), organic materials (spiders, ants,
snails, etc.), and microbiological debris (algae and protozoa).
Boman [1] determined that 46% of the clogging of microsprinklers was due to
algae, 34% from ants and spiders, 16% from snails, and 4% from physical particles
such as sand and fragments of PVC. Boman also found that the clogging rate was in-
versely related to the orifi ce area of the emitters. Filtering of the water and fl ushing of
manifolds and drip-lines are simple and necessary procedures that can help to prevent
or reduce physical clogging [19].
Filtration can help prevent inorganic particles and organic materials suspended in
water, and precipitates formed during chemical injection from entering the SDI sys-
tem. Flushing of drip-lines and manifolds removes the inorganic and organic materials
deposited on the inside wall of drip-lines from the system, thus helping to reduce clog-
ging [21, 22]. Chlorine injections, greater emitter orifi ce area, and a built

in fi ltration
area for the emitters can reduce biological emitter clogging produced by algae and
protozoa [6]. Another biological clogging problem can be produced by root intrusion
into the emitters especially in Bermuda grass irrigation, or in vines and trees, which is
commonly controlled by injections of trifl uralin [3, 5].
The chemical composition and pH of the water source and the water's interaction
with chemicals added during chemigation can have a very signifi cant infl uence on
the level of emitter clogging. Emitter clogging criteria were proposed by Bucks et al.
[2] for emission devices with discharges ranging from 2 to 8 L/h. The primary water
characteristics that can affect chemical clogging are: pH, salts, bicarbonates, manga-
nese, total iron, and hydrogen sulfi de [8, 9, 23]. Even phosphoric acid, which is often
injected in micro irrigation system water to prevent chemical clogging, can result in
phosphate precipitants with the calcium and magnesium when the injection rate is too
low allowing too much dilution of the acid (i.e., pH rises with dilution). For high pH
waters, it is advisable to consider mixing the phosphoric acid with urea

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‐ sulfuric ‐ acid

(e.g., N phuric 15/49) prior to injection to help ensure the water pH will remain at

3.0 or lower [3, 4]. Chlorine (e.g., sodium hypochlorite) and acid (e.g., sulfuric acid)
chemical injections are often needed to avoid emitter clogging caused by bacterial
growth, algae, iron and manganese oxides and sulfi des, calcium and magnesium pre-
cipitation, and root intrusion [3].
Micro-irrigation has been used with a variety of water sources such as ground
water, surface water, or treated effl uent. Secondary municipal effl uent has been suc-
cessfully used with surface drip irrigation by using sand media fi ltration and injecting
continuous chlorination to a free chlorine residue concentration of 0.4 mg/L without
reducing emitter discharge [12]. Beef lagoon effl uent has also been used successful-
ly with manageable clogging problems [24] with smaller emitters typically used for
freshwater applications perhaps too risky for use with effl uent even with disk fi ltration
to 75 microns (200 mesh). In a later report of the same study, Lamm et al. [14, 16]

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