The effect of chlorine on emitter clogging induced by algae and protozoa and the performance of drip irrigation

Limited information exists on the use of chlorine in drip irrigation systems (DIS) to prevent or reduce emitter clogging induced by biological clogging agents (BCAs), such as algae and protozoa (AP), and to enhance the performance of drip irrigation. The objectives of this study were to quantify the impact of AP-induced changes on discharge rate and uniformity from different types of emitters under two management schemes of without (S1) and with (S2) chlorine injection into the irrigation water at the Tohaku irrigation project, Japan. In a field experiment, six types of emitters on each of six laterals in two similar subunits of DIS, for S1 and S2, were assessed for AP-induced emitter discharge performance. The assessment also included different orifice area (OA), with or without a pressure compensation (PC) system, and with or without built-in filtration area (FA) in the emitters. The discharge from emitters increased with chlorine injection into the irrigation water and with increasing OA and FA, but decreased with increasing algae counts. The values for the mean discharge ratio variation (Dra) indicated that the cumulative impact of manufacturing variations (Vm) and that induced by AP and chlorine on emitter discharge was classified as low during the irrigation season when chlorine was injected into the irrigation water (S2). The values for the statistical uniformity coefficient (Uc) were higher than 93% for both S1 and S2, indicating that the uniformity of emitter discharge along a lateral was high. Due to the reduction in emitter discharge induced by AP, the clogging was uniform along a lateral. The values for field performance variation (Vf) along a lateral were in the order S1 > S2 for each emitter. The values were classified low to medium, particularly in PC emitters.