ANOXIC TREATMENT OF LOW-STRENGTH WASTE-WATER BY IMMOBILIZED SLUDGE

Low levels of phenol and m-cresol were effectively removed from wastew ater under anoxic condition using immobilized sludge. A 138-day experi ment was conducted using wastewater containing NO3--N (22.3 mg.l(-1) p henol (10 mg.l(-1)) and m-cresol (5 mg.l(-1)) at 30 degrees C using su crose (50 mg.l(-1)) as co-substrate in an upflow reactor packed with p olyvinyl alcohol (PVA) beads entrapped with anoxic sludge and powdered activated carbon (PAC). Throughout the experiment, phenol and m-creso l in the effluent were below the detectable level of 1.0 mg.l(-1) even when HRT (hydraulic retention time) was as low as 0.55 hour. The effl uent quality in general decreased with HRT. At 5.9 hours of HRT, the r eactor effluent contained 5.9 mg.l(-1) of COD (chemical oxygen demand) and 1.3 mg.l(-1) of NO3--N; but at 0.55 hour, they were, 17.3 and 5.7 mg.l(-1), respectively. The effluent COD was from the unidentified so luble microbial products. Methane was not produced after the startup, and all PVA beads were not disintegrated. Results of a batch test show ed that organic substrate was preferably consumed by the denitrify bac teria in favor of methane-producing bacteria. Scanning electron microg raphs showed that most bacteria were populated on the bead surface due to the availability of nitrate and substrate. (C) 1997 IAWQ. Publishe d by Elsevier Science Ltd.