Biological treatment of actual petrochemical wastewater using anaerobic/anoxic/oxic process and the microbial diversity analysis
A large-scale combined ponds-wetland system was applied for advanced treatment of refractory pollutants in petrochemical industrial wastewater. The system was designed to enhance bioactivity and biological diversity, which consisted of anaerobic ponds (APs), facultative ponds (FPs), aerobic pond and wetland. The refractory pollutants in the petrochemical wastewater to be treated were identified as alkanes, chloroalkanes, aromatic hydrocarbons, and olefins, which were significantly degraded and transformed along with the influent flowing through the enhanced bioactive ponds-wetland system. 8 years of recent operational data revealed that the average removal rate of stable chemical oxygen demand (COD) was 42.7 % and that influent COD varied from 92.3 to 195.6 mg/L. Final effluent COD could reach 65.8 mg/L (average). COD removal rates were high in the APs and FPs and accounted for 75 % of the total amount removed. This result indicated that the APs and FPs degraded refractory pollutants through the facilitation of bacteria growth. The changes in the community structures of major microbes were assessed by 16SrDNA-denaturing gradient gel electrophoresis. The same analysis was used to identify the main bacterial function for the removal of refractory pollutants in the APs and FPs. The APs and FPs displayed similar microbial diversities, and some of the identified bacteria degraded and removed refractory pollutants. The overall results proved the applicability, stability, and high efficiency of the ponds-wetland system with enhanced bioactivity in the advanced removal of refractory pollutants from petrochemical industrial wastewater.