Pretreatment requirements of secondary effluent for drip irrigation.

摘要

The major concern associated with drip irrigation of wastewater effluent in agriculture and in domestic landscape is in the potential for emitter clogging. A pilot-scale treatment system for developing drip irrigation pretreatment criteria, was designed, and operated intermittently over a total time period of 5,300 hours using activated sludge secondary effluent. Principal unit processes studied were granular-medium filtration and screen filters for removal of suspended solids, ultraviolet, and chlorination treatment at various injection frequencies and concentrations to prevent biofilm formation in emitters and distribution lines. Three types of 4 L/h (1 gal/h) drip emitters were tested-automatic self flushing, continuous self flushing, and tortuous path turbulent flow.; Intermittent chlorination with 2 mg/L free residual chlorine during the last hour of an irrigation cycle was found as effective as continuous chlorination with 0.4 mg/L free residual chlorine in preventing biofilm formation in emitters and distribution networks. Adequate filtration by granular-medium filters reduced both the chlorination requirement and the frequency of lateral flushing.; The ultraviolet disinfection study was conducted in three phases with the filtered effluent exposed to an average UV dose of at least 100 mW{dollar}cdot{dollar}s/cm{dollar}sp2.{dollar} Filtration rate was reduced to improve disinfection in each subsequent phase. Granular-medium filtration to remove particles greater than 40 {dollar}mu{dollar}m, was necessary for effective UV disinfection to prevent clogging of the emitter types tested.