Particle filtration for wastewater irrigation

Conventional water filtration methods cannot be generalized for use in direct wastewater filtration for drip (trickle) irrigation systems. Effluents from an oxidation ponds-reservoir system and from an activated sludge plant were filtered through granular beds and filter screens, for the purpose of evaluating particle filterability. The granular beds remove particles larger than 10 μm with an efficiency of 40 to 85%, depending on the existence of surface straining and effluent type, whereas smaller particles (1-2 μm in size) are hardly removed, suggesting that minimum transport theory applies. The removal ratio for all particles measured increases with grain size and with bed depth, and decreases with filtration velocity, affecting the lower particle size range more. Filter screens clog very rapidly even though they remove only about 1-2% of the total suspended solids (TSS). Both turbidity and TSS are inferior to particle size distribution measurements for filterability evaluation of wastewater effluents.