Efficient nutrient removal of Pyropia-processing wastewater and rapid algal biomass harvesting by Scenedesmus obliquus combined with chitosan

The discharge of massive nutrient-rich Pyropia-processing wastewater (PPW) will result in severe environmental pollution. To explore an efficient strategy to purify PPW, the nutrient removal efficiency and growth performance of Scenedemus obliquus on PPW were investigated under the conditions of different culture substrates, and the impacts of chitosan-based flocculation on the nutrient elimination rates were analyzed under various pH values. Results showed that, after cultivating S. obliquus in PPW for 7 days, the removal rates of chemical oxygen demand (COD), phycobiliprotein (PP), total nitrogen (TN) and total phosphorus (TP) reached 53.87 %, 89.36 %, 85.75 % and 93.61 %, respectively. Interestingly, the maximal COD removal efficiency could increase to 82.82 % by adding 40 mg/L chitosan to flocculate the cultures under a pH level of 9, where the aggregation rate on algal cells reached ∼100 %. Besides, the increments in biomass and lipid productivity of S. obliquus cultured in PPW were 1.25 and 1.53 times higher than that of BG11, and intracellular protein content and productivity separately increased by 29.79 % and 1.92-fold. These results demonstrate S. obliquus could efficiently decrease various nutrients in PPW, which was markedly further improved by combining with chitosan, simultaneously achieving the rapid harvest of microalgal biomass.