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.