Microalgal-bacterial consortia for efficient wastewater treatment: Optimization using response surface methodology

Abstract

The performance of microalgal-bacterial consortia in wastewater treatment and biomass production needs to be further optimized to meet increasingly stringent effluent standards and operating costs. Besides, due to uncontrollability of ambient conditions, it is generally believed that operating conditions (e.g., aeration) respond to ambient conditions (e.g., illumination). Therefore, response surface methodology (RSM) based on Box-Behnken design was used in this study to analyze the removal of chemical oxygen demand (COD), NH₃ -N and TP, and algal biomass of the microalgal-bacterial consortia within 48 h. The results showed that under medium illumination intensity (5000 lx), photoperiod (12:12) and aeration rate (0.55 L min ^-1 ), the removal efficiency of COD, NH₃ -N and TP was the highest, and the maximal biomass growth rates were 95.43%, 95.49%, 89.42% and 99.63%, respectively. However, as the limited critical removal requirements of TP, the effluent standards can only be achieved within the small illumination intensity and photoperiod available range, even under medium aeration conditions, which means that under fixed operating conditions, the effective operation range will be very limited. In addition, based on RSM and differential equation analysis, the further study indicated that the effective treatment range can be greatly expanded within aeration responding, which meets the discharge standard of pollutants in China. PRACTITIONER POINTS: Illumination was responded by aeration for optimizing performance of microalgal-bacterial consortium for wastewater treatment and biomass productivity. The strategy of optimization was based on response surface methodology. The maximum effect on wastewater treatment and biomass productivity was based on partial differential equations and quadratic inhomogeneous equations. Limited to critical TP-removal requirements, effluent standards can meet only in the small-usable range of illumination, under medium aeration.

Keywords: aeration responding; microalgal-bacterial consortia; optimizing performance; response surface method (RSM).