Nutrient removal and biogas upgrading by integrating fungal–microalgal cultivation with anaerobically digested swine wastewater treatment

This work mainly aimed to compare the growth and tolerance of fungal–algal cultures in various dilutions of anaerobically digested swine wastewater (ASW) and to determine their nutrient removal efficiency and role in biogas upgrading. Three species of microalgae, namely, Chlorella vulgaris, Scenedesmus obliquus, and Pseudokirchneriella subcapitata, were selected for ASW purification and biogas upgrading in photobioreactors with four different concentrations of 1300, 1000, 700, and 300 mg L−1 COD (chemical oxygen demand). Co-cultivation of the fungus Ganoderma lucidum and C. vulgaris in 300 mg L−1 COD was the most efficient for reduction of COD, total nitrogen, and total phosphorus by 79.74 ± 4.87%, 74.28 ± 6.13% and 85.37 ± 6.84%, respectively. With respect to biogas upgrading, co-cultivation of G. lucidum and P. subcapitata in 700 mg L−1 COD showed the maximum CO2 removal efficiency of 84.77 ± 3.04%. These results show the feasibility of simultaneously removing nutrients in ASW and CO2 in biogas using fungi-microalgae pellets.