Enhancing biomass yield, nutrient removal, and decolorization from soy sauce wastewater using an algae-fungus consortium

Soy sauce wastewater (SW), owing to its high levels of nutrients and chromaticity, may cause serious eutrophication if discharged directly into natural water bodies. Microalgae and fungi have great potential for removing nutrients and chromaticity from wastewater and producing value-added biomass. We determined the most robust algal strain, which was isolated from local water bodies, screened in SW, and identified using 18S rRNA gene sequencing analysis. Subsequently, the algal strain and fungal strain, Penicillium sp. were mono- or co-cultured in SW at different inoculum amounts or ratios for achieving maximum biomass yield, nutrient removal, and decolorization from SW. The results suggested that locally isolated NCU-183 (Nanchang University-183) was the most robust algal strain of the four candidates and was identified as Chlorella pyrenoidosa. In monoculture, the maximum biomass yield (2.2 g L−1) and nutrient removal rates (564.7, 20.2, 22.3, and 3.3 mg L−1 d−1 for chemical oxygen demand (COD), ammonium nitrogen (NH4+-N), total nitrogen (TN), and total phosphorus (TP), respectively) were obtained from algal cultivation with an initial dry weight of 0.25 g L−1 (i.e., 5 × 106 cells mL−1) in 100 % SW; the maximum decolorization rate (55.0 PCU d−1) was attained from fungal cultivation at an inoculum density of 103 spores mL−1. Compared to monoculture, the constructed algae-fungus consortium showed higher biomass yield (2.8 g L−1), nutrient removal rates (616.7, 22.8, 25.0, and 4.1 mg L−1 d−1 for COD, NH4+-N, TN, and TP, respectively), and decolorization rate (61.0 PCU d−1) in 100 % SW at an inoculum ratio of algal cells to fungal spores of 5000:1. The consortium biomass with higher protein content (65.3 %) had great potential as a value-added feedstock for animal/fish feed production as compared to the protein-rich C. pyrenoidosa biomass (62.6 %). In conclusion, the algae-fungus consortium showed practical utility for SW remediation and value-added biomass production.