Effect of Light and Dark Regimes on Cultivation of Microalgae-Bacteria Consortium for Oilfield Wastewater Treatment

Microalgae-bacteria consortium for wastewater treatment has great potential for use in nutrient removal and biodiesel acquisition. In this study, the effect of four different light/dark regimes (6/18 h, 12/12 h, 18/6 h, 24/0 h) on biomass production and pollutant degradation during the treatment of oilfield wastewater by the algae-bacteria consortium was investigated. The maximum algal biomass (0.2 g/L) and total chlorophyll content (812.76 mu gmg-1 cell dry weight-1) were obtained due to an appropriate illumination cycle ( 18 hlight/6 h dark) with enhanced dissolved oxygen content (5.87 mg/L), thus improving bacterial biomass (0.31 g/L). The ratio of microalgae to bacteria was essentially constant under different light/dark cycles. In addition, the highest removal rates of chemical oxygen demand (55.32%), ammonia nitrogen (50.75%), total nitrogen (64.53%), and total phosphorus (65.97%) were also obtained at the 18/6 h cycle, significantly different from the results of other light/dark cycles. The degradation efficiency of ammonia nitrogen by bacteria increased and then decreased with increasing light duration, while the removal rate of ammonia nitrogen by algae showed the opposite trend. The results indicated that the light and dark regimes had an important influence on the growth of the microalgae-bacteria consortium and their performance in treating oilfield wastewater.