Chlorella vulgaris - Rhodobacter sphaeroides co-culture for enhanced lactic acid fermentation wastewater treatment: optimization and metabolomic analysis

To achieve efficient treatment of lactic acid fermentation wastewater, this study established a co-culture system of Rhodobacter sphaeroides and Chlorella vulgaris, optimized cultivation conditions, and investigated the algae-bacteria metabolomic changes through non-targeted metabolomics. The results indicated that under conditions of 7.094-fold wastewater dilution, C/N ratio of 22.143:1, pH 7.566, 0.1 mM K+ supplementation, 28 °C, and 1:1 algal-bacterial inoculation ratios, the chlorophyll a concentration in co-culture system reached 19.44 mg/L, exceeding the maximum value obtained in pure algal culture (15.68 mg/L). The co-culture achieved removal rates of 90.00%, 90.84%, and 90.58% for TOC, TN and NH3-N respectively, which were 1.32-, 1.14-, and 1.15-fold those of the pure algal culture and 1.70-, 1.19-, and 1.27-fold those of the pure bacterial culture, respectively. Metabolomic analysis identified co-culture-associated changes in metabolites related to signal transduction pathways, sulfur metabolism pathways, amino acid metabolism pathways, ABC transporters and lipid metabolism pathways. These changes may reflect metabolic adjustments associated with algal-bacterial interactions and may contribute to the enhanced algal growth and pollutant removal observed in the co-culture system. This research demonstrates that algal-bacterial co-culture efficiently treats lactic acid fermentation wastewater, providing theoretical support for constructing algal-bacterial systems.