Insight into the formation mechanism of algal biofilm in soy sauce wastewater

Microalgal-biofilm-based wastewater treatment refers to a microalgae-dominated biofilm community in non-axenic systems, in which co-existing bacteria and microbial extracellular polymeric substances (EPS) are crucial for the formation of algal biofilm. However, algae-bacteria consortium biofilm-forming mechanism has rarely been studied in wastewaters including soy sauce wastewater (SW). In this study, we conducted algal biofilm cultivation in raw SW (RSW) and sterilized SW (SSW), and determined the characteristics of algal biofilm and its EPS in the two SW treatments. The results demonstrated that the co-existing bacteria in the algal biofilm system significantly enhanced attached biomass and nutrient removal from RSW, compared to SSW without bacteria. The enhancement may be attributed to EPS excreted by dominated Acinetobacter and Comamonas (both Proteobacteria) in the co-existing bacteria community. The algae-bacteria consortium from algal biofilm in RSW excreted the contents of relatively high tightly bound EPS (TB-EPS) and its proteins (TB-PN), which were conducive to forming the algal biofilm. The high TB-EPS content was related to soluble microbial by-product-like substances (mainly proteins), and its high TB-PN content was mainly caused by the increases in hydrophobic glycine and serine contents for stable biofilm formation. Based on these results, we enhanced our understanding of the formation mechanism of algal biofilm in SW remediation, which provided the theoretical basis for biofilm formation by algae-bacteria synergism. [Display omitted] •The co-existing bacteria enhanced attached biomass and nutrient removal from RSW.•The enhancement may be induced by EPS excreted by dominant Acinetobacter and Comamonas.•Algae-bacteria consortium in RSW excreted high TB-EPS and TB-PN for biofilm formation.•The high TB-EPS content was related to SMP (mainly proteins) from microbial cells.•The high TB-PN was mainly caused by the increases in hydrophobic glycine and serine.