For further removal of nitrogen and phosphorus from secondary sewage effluent, two strains of microalgae, Chlorella sp. ADE4 and Chlorella vulgaris, were selected for cultivation in the membrane photobioreactor. The Chlorella sp. ADE4, isolated from wastewater illustrated higher removal efficiency of T-N and T-P, and faster algal growth than the Chlorella vulgaris in a batch experiment using treated sewage effluent. The T-N and T-P removal efficiency was 66.5% and 94.5%, respectively, within HRT of two days when the photobioreactor of Chlorella sp. ADE4 was operated in continuous mode. The effluent water quality was 6.3 mg/L and 0.044 mg/L for T-N and T-P. It was estimated that the algal biomass productivity was 55 mg/L·d with T-N and T-P uptake rates of 6.25 and 0.483 mg/L·d, respectively, in the system. Operational flux below 58 LMH was found to be effective for separation of algal cell from effluent in membrane system.

A B S T R A C TThe purpose of the present study is to investigate the effects of nutrient starvation of microalgae on its nitrogen (N) and phosphorus (P) uptake, characteristics of extracellular polymeric substances (EPS), and algal sedimentation. An experiment was carried out by starving the wastewater-tolerant microalgae Chlorella sp. ADE4. The algal cultivation was put under various conditions of nutrient starvation in order to enhance nutrient removal and algal cell separation. The experimental results showed that 40 h of nutrient starvation prior to the cultivation did affect nutrient removal of Chlorella sp. ADE4. When using synthetic wastewater, the N-starved algae was the most effective in removing 82% of N in 48 h and 92% of P in 24 h. However, the starvation conditions did not cause noticeable removal improvement when microalgae were tested with real wastewater effluent. N and P removal efficiencies of 57 and 100%, respectively, were achieved in 48 h in real wastewater effluent. The lower N removal efficiency was caused by P limitation in the real sewage effluent. EPS were analyzed to evaluate if they play a role in algal cell agglomeration and subsequent microalgal separation. Carbohydrates and protein were indicated as major components in soluble and bound EPS. It was found that starvation of microalgae for 40 h could induce higher EPS production. Interestingly, the N-starved microalgae contained a large protein fraction in their EPS and low N content in their biomass. However, a significant correlation between EPS content and sedimentation efficiency was not observed in this study.

Abstract-To determine the performance of microalgae photobireactor for advanced wastewater treatment and microalgal biomass production, Chlorella vulgaris was cultured with final effluent from sewage treatment plant in batch condition. The average specific growth rate was 0.103 d -1 because low P concentration inhibited algal growth. 60% of N and P concentrations were removed from the system in 2 days. When the system operated under a semi-continuous condition with hydraulic retention time (HRT) 2 days, the microalgae showed growth rate of 0.452 d -1 and 0.277 d -1 in primary effluent and final effluent, respectively. 30% of N and 53% of P were removed from primary effluent and 44% of N and 84.2% of P were removed from final effluent. These results suggest that semi-continuous mode offers higher biomass production and appropriate HRT were needed for high N and P removals.Index Terms-Nitrogen and phosphorus removal, microalgae, photobioreactor, wastewater.