PRETREATMENT OF SECONDARY EFFLUENT FOR DRIP IRRIGATION

A pilot-scale treatment system, for developing drip-irrigation pretrea tment criteria, was designed, installed, and operated intermittently o ver 5,300 h using activated sludge secondary effluent. Principal unit processes studied were granular-medium filtration and screen filters f or removal of suspended solids, and chlorination treatment at various injection frequencies and concentrations to prevent biofilm formation in emitters and distribution lines. Two types of 4 LA/h (1 gal./h) dri p emitters were tested-automatic self-flushing and tortuous-path turbu lent-flow emitters. Adequate filtration reduced both the required freq uency of chlorination and lateral flushing. Intermittent chloriflation with 2 mg/LA free residual chlorine during the last hour of an irriga tion cycle was found as effective as continuous chlorination with 0.4 mg/LA free residual chlorine in preventing biofilm formation in emitte rs and distribution networks. Pretreatment recommendations for these t ypes of emitter designs are presented.