Treatment of oilfield wastewater using algal–bacterial fluidized bed reactor

This study was carried out to investigate the ability of an artificial microalgal–bacterial consortium to remediate an oilfield wastewater using laboratory-scale fluidized bed reactors (FBRs) under lighting. The consortium consists of an oil-degrading bacterial community and a microalgae, Scenedesmus obliquus GH2. The microbes were immobilized onto Ca-alginate beads and filled to the FBRs. The influence of hydraulic retention time (HRT) on the removal of chemical oxygen demand (COD), total nitrogen, NH₃-N and oil concentration was investigated over 40 operational days. The synergistic relationship in the algal–bacterial microcosm was clearly demonstrated, since for the four parameters tested, the highest removal was recorded in the system inoculated with both algae and bacteria. In the algal–bacterial FBR, at 16 h HRT, the average effluent concentrations of COD, NH₃-N and oil were 92, 24 and 4.8 mg/L, respectively, corresponding to removal efficiencies of 70.8%, 61.2% and 84.2%, respectively. The effluent could meet the grade 2 as required by the national discharge standard of China. However, the effluent quality of the bacterial- or algal-only case could not satisfy the grade 3 discharge standard at 16 h HRT. The algal–bacterial biomass exhibits lowest effluent microtoxicity and highest dehydrogenase activity in comparison with bacterial-only and algal-only cases. This study reveals that the consortium containing dual microbial species has potential for microbial remediation of oilfield wastewater.     

Advanced treatment of textile dyeing wastewater through the combination of moving bed biofilm reactors and ozonation

A four-stage lab-scale treatment system [anaerobic moving bed biofilm reactor (MBBR)-aerobic MBBR-ozonation-aerobic MBBR in series] was investigated to treat textile dyeing wastewater. The MBBRs were operated in a continuous horizontal flow mode. To determine the optimum operating conditions, the effect of hydraulic retention time (HRT) and ozonation time on pollutant removal were analysed by continuous and batch experiments. The optimum operating conditions were found to be 14 h HRT for both anaerobic and no. 1 aerobic MBBRs, 14 min ozonation time and 10 h HRT for no. 2 aerobic MBBR. The average influent concentrations of chemical oxygen demand (COD), suspended solids (SS), ammonia and colour were 824 mg/L, 691 mg/L, 40 mg/L and 165°, respectively. Under these conditions, the average effluent concentrations of COD, SS, ammonia and colour were 47 mg/L, 15.2 mg/L, 5.9 mg/L and 6.1°, respectively, corresponding to total removal efficiencies of 94.3%, 97.8%, 85.3% and 96.3%, respectively. The final effluent could meet the reuse requirements of textile industry. The anaerobic MBBR process improved the biodegradability of the raw wastewater, while the two aerobic MBBRs played an important role in removing COD and ammonia. The ozonation process enhanced the biodegradability of no. 1 aerobic MBBR effluent, and finally, deep treatment was completed in no. 2 aerobic MBBR. The combined process showed a promising potential for treatment of high-strength dyeing wastewater.