Degradation of phenol in wastewater in an upflow anaerobic sludge blanket reactor

Phenol in wastewater could be effectively degraded in an upflow anaerobic sludge blanket (UASB) reactor. With a 1:1 effluent recycle ratio, over 97% of phenol was removed at 37°C and pH 6.9-7.5 with 12 h of hydraulic retention time for phenol concentration up to 1260 mg·1^-1, corresponding to 3000 mg·1^-1 of chemical oxygen demand (COD) and a loading rate of 6 g-COD·1^-1·day^-1. The seed sludge took about 7 wk to develop the phenol-degrading capability which was sensitive to shocks. The bioactivity deteriorated readily when the granules were exposed to sudden changes of temperature and loading. Although the damage was not permanent, the recovery of bioactivity was gradual and lengthy. At 6 g-COD·1^-1·day^-1, each gram of granules was able to convert 0.49 g of COD into methane daily. On the average, about 94.7% of the total COD removed was converted to methane, while the rest was converted to biomass with a net yield of 0.038 g-VSS·(g-COD-removed)^-1. Electron micrographs show that the granules were composed of, among others, Syntrophus buswellii-, Methanothrix-, Methanospirillum- and Methanobrevibacter-like bacteria.