Degradation Of Petrochemical Wastewater By Using Biofilm-activated Sludge Hybrid Process And Advanced Treatment

Petrochemical wastewater which contains numerous toxic and refractory organic pollutants is greatly harmful to the environment. At present, the core process of many domestic petrochemical wastewater treatment plants (WWTPs) is traditional or improved activated sludge process (ASP). This process has many problems such as unstable organics removal efficiency and poor nitrogen removal capacity. Thus it cannot meet the current standards of petrochemical wastewater treatment. To solve these problems, treatment of petrochemical wastewater using biofilm-activated sludge hybrid process (HP) was studied in this thesis. It was expected that some theoretical and technical information could be obtained from this study to improve the performance of petrochemical WWTPs.The pollutants removal efficiency, resistance capacity to shock loadings, performance of sludge and oxygen utilization ratio of HP were compared with those of ASP in this thesis. The results showed that HP was slightly better than ASP in the removal of CODCr in petrochemical wastewater. Moreover, HP was obviously superior to ASP on the removal of NH3-N. In addition, the two processes had similar removal rate of S2- and oil. When the influent loads were increased, HP showed stronger resistance to shock loadings. When the inflow was 2 L/h and the average concentrations of CODcr, NH3-N, S2- and oil in the petrochemical wastewater were 895 mg/L,42.8 mg/L,23.8 mg/L and 47.1 mg/L, respectively, the average concentrations of CODcr, NH3-N, S2" and oil in the effluent of HP were 116 mg/L, 0.82 mg/L,0.053 mg/L and 12.1 mg/L, respectively, with average removal efficiencies 87.0%, 98.1%,99.8% and 74.3%, respectively. RIS (ribosomal intergenic spacer) fingerprints technique and 16S rDNA gene sequencing were used. The results indicate that there are many differences between microbial communities of aerobic reactors of the two processes, and the differences of the performances between the two processes are explained. Compared with ASP, HP is of higher oxygen utilization ratio, reduced sludge yield, decreased reflux quantity, lower power consumption, and easier operation. Thus HP is proper for upgrading of petrochemical WWTPs which are overloaded or cannot nitrify effectively.The concentrations of CODcr and oil in the effluent of HP didn't attain class 1 of the National Wastewater Integration Discharge Standard (GB8978-1996). Thus micro-electrolysis process (MEP) and Fenton oxidation process (FOP) were respectively used to treat the effluent of HP. The optimal operating conditions were selected under which the removal efficiencies of CODCr and oil were investigated. The results showed that MEP and FOP both have high treatment efficiency for HP effluent. Under the optimal operating conditions, the concentrations of CODCr and oil in the effluent of MEP are 49.4 mg/L and 3.7 mg/L, respectively, and the removal efficiencies of them are 53.9% and 65.1%, respectively. On the other hand, the concentrations of CODCr and oil in the effluent of FOP are 30 mg/L and 3.3 mg/L, respectively, and the removal efficiencies of them are 60% and 68%, respectively. The concentrations of CODCr and oil in the effluent of MEP and FOP attained class 1 of the National Wastewater Integration Discharge Standard (GB8978-1996). Compared with MEP, FOP has higher pollutant removal efficiency and lower operating cost. Thus FOP is more proper for advanced treatment of petrochemical wastewater.