Removal of Nutrients and COD in Wastewater from Vietnamese Piggery Farm by the Culture of Chlorella vulgaris in a Pilot-Scaled Membrane Photobioreactor

The treatment of nutrients and organic contaminants in wastewater using microalgae has drawn significant interest thanks to its advantages of environmental friendliness, low cost, CO2 emission reduction, and recycling of valuable biomass. Among other algae species, Chlorella sp. showed good vitality, simplicity in cultivation, and high nutrient accumulation in harsh conditions of wastewater. In this study, Chlorella vulgaris was inoculated in a membrane photobioreactor (MPBR) with piggery digestate to investigate the C. vulgaris growth rate and the removal efficiency of nutrients and chemical oxygen demand (COD). The results indicated that the cultivation of C. vulgaris in an MPBR system exhibited continuous and simultaneous removal of NH4+, PO43-, and COD from two-fold diluted piggery wastewater. Both the algae growth rate and nutrient removal depended on the liquid hydraulic retention time in the MPBR. The highest removal efficiency of NH4+ (74.55%), PO43- (70.20%), and COD (65.85%) was obtained in the longest HRT of 5 days with the highest microalgae biomass concentration of around 1.1 g/L. The algae washout phenomenon was negligible in the continuous cultivation in the MPBR system. Compared to the cultivation in batch mode, the MPBR could achieve a similar algae growth rate and treatment efficiency with a much shorter hydraulic retention time.