Biodegradation of Phenol with Wastewater as a Cosubstrate in Upflow Anaerobic Sludge Blanket

Anaerobic degradation of phenol mixed with a readily degradable synthetic wastewater (DSWW) as a cosubstrate was studied in a 12 L upflow anaerobic sludge blanket reactor at 30±2°C over a period of 632 days. DSWW was prepared by diluting sugar cane based molasses. The biomass was acclimatized to high phenol concentration by gradually decreasing the DSWW chemical oxygen demand (COD) of 4,000 mg/L. Feed made up of phenol COD and DSWW COD in the ratio of 7:3 (phenol concentration=1,176 mg/L) was successfully treated at a hydraulic retention time (HRT) of 12 h and organic loading rate (OLR) of 8 g COD/L day. Phenol removal ranged from 99.9 to 84% at phenol COD varying from 10 to 70% in the feed. During the entire operation, COD removal varied from about 74 to 91.3%. The influent COD was distributed into CH-COD (~72%), effluent COD (~17%), and sludge and unaccounted COD (~11%). The process failure occurred at 4:1 phenol COD: DSWW COD. Specific methanogenic activity of granular sludge exhibited uniform activity up to phenol COD of 70%. The performance of the reactor could not be maintained beyond 70% phenol COD even by reducing the sludge loading rate, increasing HRT, or decreasing OLR.