Response mechanism of microalgae-based constructed wetland to day-night alternations

Abstract

As an effective optimization strategy for constructed wetlands, microalgae-constructed wetland coupling systems (MCCSs) carry the potential risk of eutrophication during operation. Within MCCSs, the key microorganisms that trigger eutrophication are highly responsive to day-night alternations. Hence, optimizing the day-to-night ratio may be an effective measure to reduce the eutrophication risk from MCCSs. To verify this hypothesis, we analyzed the response characteristics of MCCSs under different day-night cycles (light/dark: 9 h/15 h, 12 h/12 h, 15 h/9h, and light 24 h). The results indicate that in response to day-night changes, the microbial communities in the MCCSs established stable microbial networks through competitive interactions. Furthermore, energy metabolism played a crucial role in the influence of the day-night alternations on the microbial functional metabolism in the MCCSs. Moderate extension of light time can provide additional electron donors for microbial denitrification, thereby maintaining the stability of denitrification while increasing the dissolved oxygen concentration. The results of the structural equation model also confirmed that the microbial communities contributed more to the environmental function of the MCCSs through energy metabolism under light conditions. This study provides valuable insights into the prevention of eutrophication and maintenance of stable operation in MCCSs.