Anaerobic filter treatment of municipal wastewater: Biosolids behavior

Three 12.5 L upflow anaerobic filter (AF) reactors, with ceramic saddle, plastic ring, and crushed stone packing, were employed to evaluate the treatment of raw municipal wastewater under a wide range of hydraulic and organic loadings and operating conditions. Emphasis is placed in this paper on column profile sampling, draining, and biomass evaluation studies conducted to ascertain the functioning of the reactors and accumulation of biosolids. The concentration of organics and solids within the AF gradually increased, starting at the low end and progressing to higher elevations. The peak chemical oxygen demand value measured within the reactors was 11,500 mg/L and was noted in the stone-packed unit at 20 cm after 1,009 days, and the stabilization of suspended material was greater in lower column sections. Packing material morphology influenced the removal by draining of entrapped biomass, and the volume of drainage recovered was substantially smaller than available void space. Biosolids retained in the saddle-packed unit after 34 months totaled 33 kg/1,000 m(3) wastewater treated, and no signs of clogging were observed in any of the reactors.