Affiliations: Department of Water Engineering and Science, College
of Civil Engineering, Hunan University, Changsha 410082, China | Centre for Environmental Engineering Research,
Department of Civil Engineering, The University of Hong Kong, Hong Kong
Abstract: A synthetic wastewater containing phenol as sole substrate was
treated in a 2.8 L upflow anaerobic sludge blanket (UASB) reactor at ambient
temperature. The operation conditions and phenol removal efficiency were
discussed, microbial population in the UASB sludge was identified based on DNA
cloning, and pathway of anaerobic phenol degradation was proposed. Phenol in
wastewater was degraded in an UASB reactor at loading rate up to 18 gCOD/(L
˙ d), With a 1:1 recycle ratio, at 26 ± pH 7.0–7.5. An UASB reactor
was able to remove 99% of phenol up to 1226 mg/L in wastewater with 24 h of
hydraulic retention time (HRT). For HRT below 24 h, phenol degradation
efficiency decreased with HRT, from 95.4% at 16 h to 93.8% at 12 h. It further
deteriorated to 88.5% when HRT reached 8 h. When the concentration of influent
phenol of the reactor was 1260 mg/L (corresponding COD 3000 mg/L), with the HRT
decreasing (from 40 h to 4 h, corresponding COD loading increasing), the
biomass yields tended to increase from 0.265 to 3.08 g/(L ˙ d). While at 12
h of HRT, the biomass yield was lower. When HRT was 12 h, the methane yield was
0.308 L/(gCOD removed), which was the highest. Throughout the study, phenol was
the sole organic substrate. The effluent contained only residual phenol without
any detectable intermediates, such as benzoate, 4-hydrobenzoate or volatile
fatty acids (VFAs). Based on DNA cloning analysis, the sludge was composed of
five groups of microorganisms. Desulfotomaculum and Clostridium were likely
responsible for the conversion of phenol to benzoate, which was further
degraded by Syntrophus to acetate and
H_2/CO_2. Methanogens lastly converted
acetate and H_2/CO_2 to methane. The role
of epsilon-Proteobacteria was, however, unsure.
