NIREAS VOLUME 4
20 Nutrients The nutrients in reclaimed water provide fertilizer value for crop or landscape production. However, in certain instances, when nutrients are in excess of plant needs they can cause problems. Nutrients that are important to agriculture and landscape management include N, P, and occasionally K, Zn, B, and S. The most beneficial and the most frequently excessive nutrient in reclaimed water is nitrogen. The nitrogen in reclaimed water can replace equal amounts of commercial fertilizer during the early to midseason crop-growing period. Excessive nitrogen in the latter part of the growing period may be detrimental to many crops, causing excessive vegetative growth, delayed or uneven maturity, or reduced crop quality. If alternate low-nitrogen water is available, a switch in water supplies or blending of reclaimed water with other water supplies has been used to keep nitrogen under control, otherwise expensive seasonal denitrification would be required.
Other Problems Clogging problems with sprinkler and drip irrigation systems have been reported, particularly with oxidation pond effluent. Biological growth (slimes) in the sprinkler head, emitter orifice, or supply line causes plugging, as do heavy concentrations of algae and suspended solids. The most frequent clogging problems occur with drip irrigation systems. From the standpoint of public health, such systems are often considered ideal, as they are totally enclosed, minimizing the problems of worker exposure to reclaimed water or spray drift. In reclaimed water that is chlorinated, chlorine residuals of less than 1 mg/L do not affect plant foliage, but chlorine residuals in excess of 5 mg/L can cause severe plant damage when reclaimed water is sprayed directly on foliage.
4.3.1 Irrigation Methods Out of various irrigation methods used, modern technology might be of particular interest in irrigating with treated wastewater. Selection of any method, whether conventional or modern, should be handled carefully in order to operate the irrigation system efficiently and safely. Selection of the appropriate irrigation method depends on the quality of the effluent, crops to be grown, farmers tradition, background and skill of the farmers and the potential risk to workers and to public health.