Nanohybrid membrane in algal-membrane photoreactor: Microalgae cultivation and wastewater polishing

Microalgae cultivation has gained tremendous attention in recent years due to its great potential in green biofuel production and wastewater treatment application. Membrane technology is a great solution in separating the microalgae biomass while producing high quality of permeate for recycling. The main objective of this study was to investigate the filtration performance of Ag/GO-PVDF (silver/graphene oxide-polyvinylidene fluoride) membrane in an algal-membrane photoreactor (A-MPR) by benchmarking with a commercial PVDF (com-PVDF) membrane. In this study, Chlorella vulgarismicroalgae was cultivated in synthetic wastewater in an A-MPR for ammoniacal-nitrogen and phosphorus recovery and the wastewater was further filtered using Ag/GO-PVDF and com-PVDF membranes to obtain high quality water. Spectrophotometer was used to analyze the chemical oxidation demand (COD), ammoniacal nitrogen (NH3-N) and phosphate (PO43−). The concentration of proteins and carbohydrates was measured using Bradford method and phenol-sulfuric acid method, respectively. The COD of the synthetic wastewater was reduced from (180.5 ± 5.6) × 10−6 ppm to (82 ± 2.6) × 10−6 ppm due to nutrient uptake by microalgae. Then, the Ag/GO-PVDF membrane was used to further purify the microalgae cultivated wastewater, resulting in a low COD permeate of (31 ± 4.6) × 10−6 ppm. The high removal rate of proteins (100%) and carbohydrates (86.6%) as the major foulant in microalgae filtration, with low membrane fouling propensity of Ag/GO-PVDF membrane is advantageous for the sustainable development of the microalgae production. Hence, the integrated A-MPR system is highly recommended as a promising approach for microalgae cultivation and wastewater polishing treatment.