CLOGGING AND MAINTENANCE OF MICRO IRRIGATION SYSTEMS - Management, Performance, and Applications of Micro Irrigation Systems - page 92

FIGURE 3 Roots penetrating an emitter in the drip-line.

7.2.4 INJECTING CHLORINE
At a low concentration (1 to 5 ppm), chlorine kills bacteria and oxidizes iron. At a high
concentration (100 to 1000 ppm), it oxidizes (destroys) organic matter.

7.2.4.1 BACTERIA PROMOTED BY DISSOLVED IRON AND MANGANESE
The most serious problems with bacteria occur in waters that contain ferrous or soluble
iron. Iron and/or manganese concentrations higher than 0.1 ppm can promote bacte-
rial growth and chemical precipitation that clogs emitters. Iron bacterial growth looks
reddish, whereas manganese bacterial growth looks black. These bacteria oxidize iron
and/or manganese from the irrigation water. In the western part of Texas, these bacte-
ria often are associated with well water.
Extreme caution should be maintained when injecting chlorine into irrigation wa-
ter containing dissolved manganese since chlorine can oxidize this element and cause
precipitation beyond the fi lter system.
It is hard to eliminate iron bacteria, but it may be controlled by injecting chlorine
into the well once or twice during the season. It might also be necessary to inject chlo-
rine and acid before (upstream of) the fi lters. When the water contains a lot of iron,
some of the iron will feed the bacteria and some will be oxidized by chlorine to form
rust (or insoluble iron, ferric oxide). The precipitated ferric oxide is fi ltered out and
fl ushed from the system. If iron concentration is high and problems persist, aeration
of the irrigation water will help to oxidize the iron and facilitate settling of sediment.
Aeration can be accomplished by pumping water into a reservoir and then repumping
it with a booster pump to the irrigation system.
A swimming pool test kit can be used to test for free or residual chlorine in the
water at the end of the lateral line. It is worth noting that some of the injected chlorine
may be removed from solution through chemical reactions with other constituents
or absorbed by organic matter in the water. For continuous injection, 1 ppm of free
residual chlorine at the ends of the laterals will be enough to kill most bacteria. For
intermittent injection (once every several days) the chlorine concentration should be
maintained at 10 to 20 ppm for 30 to 60 min.