Impact of biological clogging agents on filter and emitter discharge characteristics of microirrigation systems

Water application efficiency of microirrigation systems (MIS) may depend, at least partially, on algae and protozoa (biological clogging agents, BCAs) induced filter and emitter clogging. In this study we assessed the impact of BCA-induced changes on water discharge rate and distribution uniformity from (i) emitters with different water flow cross-section (CS) area, pressure compensation (PC) systems, and inbuilt filtration areas (FAs), and (ii) filters either made of urethane, sand, or disk in the Tohaku irrigation project in Japan. In a field experiment, four types of on-line emitters on each of four laterals and four types of in-line emitters on each of another four laterals were assessed for BCA-induced emitter discharge performance without using filters in the field irrigation line. The emitters' discharge rate increased with increasing CS, FA, and working pressure (WP) and decreased when the emitters were on-line in the laterals and with increasing BCA counts. Because BCAs are the only dynamic variable in the above relationship, we conclude that BCA-induced clogging is a major issue when filters were not installed in field irrigation lines. The filter performance assessment based on the number of backwashings required to restore the working pressure to the recommended level indicated that BCA filtering by the sand filter was highest, followed by disk and urethane, respectively. Copyright (C) 2004 John Wiley Sons, Ltd.