Analysis of the elemental composition and uptake mechanism of Chlorella sorokiniana for nutrient removal in agricultural wastewater under optimized response surface methodology (RSM) conditions

Microalgae exhibit large potential as an alternative to advanced biological nutrient removal in waste-water, but treatment efficiency is greatly influenced by process variables. Therefore, it is necessary to determine the optimum operating conditions for nutrient removal. In this study, Chlorella sorokiniana was used to remove ammonium (NH4+) and phosphate (PO43-) from palm oil mill effluent. Response surface methodology (RSM) was employed to evaluate the interactions of three main influential factors, i.e., light intensity, photoperiod and inoculum size, and their effects on nutrient removal efficiency. The nutrient preference, biomass elemental composition and nutrient removal mechanism of the microalgae were also investigated. Under the optimum conditions (200 mol photon m(-2)s(-1) 12 h photoperiod and 28% inoculum size), 93.36% of NH: and 94.50% of PO43- were successfully removed. The microalgae were found to adjust their internal composition in response to the external concentration. Biomass N and P increased from 6.16 to 8.68% and from 1.0 to 2.21%, respectively. The microalgae preferred NH; over organic N, and the removal mechanisms involved not only assimilation for growth but also over-uptake for cellular storage. These findings are highly beneficial for maximizing the nutrient removal potential of microalgae in agricultural wastewater. (C) 2018 Elsevier Ltd. All rights reserved.