Nutrient and heavy metal removal from piggery wastewater and CH4 enrichment in biogas based on microalgae cultivation technology under different initial inoculum concentration.

Abstract

Three microalgae-based treatment technologies were applied for removing nutrients in piggery wastewater and CO2 in biogas simultaneously. Chlorella vulgaris (C.vulgaris), Scenedesmus obliquus (S.obliquus), and Neochlorisoleoabundans (N.oleoabundans) were selected for mono-cultivation or co-cultivation with fungi or activated sludge. The effects of initial inoculum concentration (low of 62.06±6.23mg/L, medium of 121±9.34mg/L, and high of 180±12.78mg/L) of microalgae/algal symbiont on the pollutant removal efficiency were evaluated. The results showed that cultivation of S.obliquus with activated sludge had a relatively high CO2 and nutrients removal efficiency at a medium concentration of initial inoculum. The highest removal efficiency of total organic carbon, total nitrogen, and total phosphorus in piggery wastewater was 87.29%, 87.26%, and 90.17% by co-cultivation of S.obliquus with activated sludge. The highest CO2 removal of 64.28% could be achieved under co-cultivation of S.obliquus and fungi at medium initial inoculum concentrations. This work will be helpful to promote the study of microalgae-based biogas upgrading and piggery wastewater purification. PRACTITIONER POINTS: Nutrient and CO2 were efficiently removed in moderate microalgal initial inoculum. Scenedesmus obliquus-activated sludge cultivation achieved the highest nutrient removal. Co-cultivation of S.obliquus and fungi showed the highest CO2 removal. Zinc was removed efficiently in high microalgal initial inoculum. Chlorella vulgaris/S.obliquus-activated sludge performed economically.