Optimization of membrane photobioreactor; the effect of hydraulic retention time on biomass production and nutrient removal by mixed microalgae culture

Abstract

In this study, the effect of hydraulic retention time (HRT) on the performance of microalgae membrane photobioreactor (MpBR) inoculate by mixed culture were with examined on biomass productivity and nutrient removal from synthetic secondary effluent. The optimization of HRT was aimed for the treatment of wastewater in MpBR operating at HRTs between 24 h and 72 h with at a fixed sludge retention times (SRT) of 3 d. The volumetric microalgae production rates were obtained to be from 0.118 g L−1day−1 to 0.064 g L−1day−1, respectively at increasing HRT from 24 h to 72 h at the stable conditions. The total nitrogen (TN) removal rate was calculated to be 5.55 mgL−1day−1 and the phosphate phosphorus (PO4–P) removal rate to 0.40 mgL−1day−1 where the highest biomass production rate was obtained at the HRT of 24 h. Although this work showed the potential use of mixed microalgae culture and membrane in both wastewater treatment and microalgae biomass production, it is looked that the treatment of the secondary effluent has not been able to meet the discharge standards according to EU and general directives unless optimization is made. But bioenergy power, namely lipid and protein ratios of dry biomass under the optimum conditions were also determined and lipid content was 8.94% and the protein content was 34%. Today, when there is a global food shortage, the oil and protein ratio in microalgae biomass obtained by treating wastewater is potentially competitive with traditional agricultural products.