Applicability of anoxic-oxic process in treating petrochemical wastewater

Abstract

To explore the applicability of anoxic-oxic (A/O) activated sludge process for petrochemical wastewater treatment, the relationship between bacterial community structure and pollutants loading/removal efficiencies was investigated by gas chromatograph-mass spectrometry (GC-MS), polymerase chain reaction-denaturing gradient gel electrophoresis (PCR-DGGE) and other conventional techniques. It showed that when the concentrations of the influent chemical oxygen demand (COD) and ammonia nitrogen (NH4+-N) were 420∼560 mg/L and 64∼100 mg/L, respectively, the corresponding average effluent concentrations were 160 mg/L and 55 mg/L, which were 1.6 and 2.2 times higher than those of the national standards in China, respectively, demonstrating the inefficient performances of A/O process. Analysis of GC-MS indicated that refractory pollutants were mainly removed by sludge adsorption, but not by biodegradation. PCR-DGGE profile analysis suggested that the biological system was species-rich, but there was apparent succession of the bacterial community structure in different locations of the A/O system. Variations of bacterial community structure and pollutant loadings had obvious influences on pollutants removal efficiencies. Thus, A/O process was inapplicable for the treatment of complicated petrochemical wastewater, and strategies such as the reinforcement of pre-treatment and two-stage A/O process were suggested.