Ca2+ enhanced the wastewater treatment performance of microalgal-bacterial consortia: Response of extracellular polymeric substances and bacterial communities

Abstract

The technology of microalgae-bacteria consortia (MBC) for wastewater treatment is currently facing a variety of challenges. One of the main issues is the construction of structurally and functionally stable symbiont. Ca²⁺ may be involved in this process, but the underlying mechanism is not well understood. Here the response of MBC to the regulation of Ca²⁺ was systematically explored from the perspectives of extracellular polymeric substances (EPS) and bacterial communities. The results showed that the exogenous addition of Ca²⁺ (10–50 mM) not only promoted the production of extracellular polysaccharides and proteins of MBC, but also increased the proportion of some functional groups and components of EPS, such as CO and α-helix. The change of EPS characteristics was conducive to provide more sites for bining Ca²⁺, which in turn favored the formation of compact MBC via overcoming electrostatic repulsive effect. Besides, the supplementation of Ca²⁺ favored the recruitment of more EPS-producing bacteria (such as Rhodobacter, Pedobacter, Rhizorhapis, and Sphingopyxis) and indole acetic acid producing bacteria (such as Hydrogenophaga and Agromyces). The enrichment of these functional bacteria not only promoted the adhesion between bacteria and microalgae, but also promoted the growth of symbiotic microalgae, which contributed to the formation of stable large-sized MBC. The change in structure and function of MBC was ultimately reflected in the improved performance in treating municipal wastewater. The findings of this study provided insights into the mechanism underlying the enhanced performance of MBC for wastewater treatment under the influence of Ca²⁺.