Biotreatment of swine wastewater by mixotrophic Galdieria sulphuraria

Biotreatment of swine wastewater via microalgae is an environmentally sustainable and economical efficient strategy capable to transform nitrogen, phosphorous, and organic/inorganic carbons into value added products as lipids, carbohydrates, and proteins, while high ammonium tolerant microalgal species with efficient COD and ammonium removal efficiency is lacking, limiting its practical application. Thermophilic and acidophilic Galdieria sulphuraria (G. sulphuraria) are reported to have high ammonium removal efficiency, while its application in ammonium rich swine wastewater treatment without dilution is rarely reported. Accordingly, mixotrophic cultivation of G. sulphuraria has been tested for biotreatment of swine wastewater. The results indicate that G. sulphuraria can grow well in swine wastewater with maximum growth rate of 0.72 g/(L.d) when 15 g/L of glucose is added. Simultaneously, a maximum COD removal efficiency of 94.8% and ammonium removal rate of 550.5 mg/(L.d) are observed. The addition of glucose leads to decreases of lipid, protein and ash contents, and simultaneous increase of carbohydrates owing to the varied C/N ratios. The final microalgal biomass has relatively lower carbon content of 48.5% with 20 g/L glucose than 49.3% of control, consequently leads to a relatively lower HHV value of 20.64 MJ.kg(-1). Above all, mixotrophic cultivation of G. sulphuraria are promising strategy for swine wastewater treatment with high energy recovery, potentially providing an economical strategy for swine wastewater treatment.