Wastewater effluent reuse by in-line flocculation filtration process

Abstract

Granular media filtration is an important treatment process for various reuse applications. Size density, and attachment strength of filter deposits produced by the interaction of effluents with alum, alum-polymer aids and cationic polymers as primary flocculants and the filter media during contact filtration were calculated and compared using existing filtration models. Secondary effluent filtration without flocculant addition was relatively ineffective. Effective alum dose for contact filtration ranges 10-20 mg/L. The 10 mg/L is superior, while the latter creates bulky deposit. An addition of 0.05 - 0.1 mg/L of low anionic high molecular weight polymer strengthens the alum-particle bond. Grain size influence seems to be more pronounced at low approach velocities (5-10 m/hr). High cationic, medium to high molecular weight polymers performed equally or better than alum as primary flocculants. High molecular weight cationic polymer-effluent particle deposit has a higher attachment strength than that of the alum, resulting in a smaller detachment with increase of velocity or increase of filtration run length. Cationic, high molecular weight polymers are effective at doses as low as 0.5 mg/L, at different charge densities. High cationic, medium molecular weight polymers are effective at doses > 5 mg/L. The pressure gradient increase and the filtration efficiency is proportional to the polymer dose in the (1-7 mg/L) range. Compared to the high molecular weight polymer, the pressure build up is milder. High cationic, low molecular weight polymers are not effective at doses up to 7 mg/L. The pressure build up is slow following a slow ripening. In high particle loadings, the differences among the various treatments are less pronounced.