Treatment of real aquaculture wastewater using marine Chlorella: Pollutant removal and microbial community dynamics

Abstract

This study comprehensively investigated the nutrient removal mechanisms of Chlorella sp. in authentic aquaculture wastewater, while also examining the dynamic shifts within its symbiotic microbial community. The results showed that the microalgae exhibited robust growth in the wastewater, effectively reducing concentrations of ammonium nitrogen, nitrate nitrogen, and phosphate with removal efficiencies of 95.0 %, 93.2 %, and 91.7 %, respectively. Fluctuations in pH during the initial cultivation period indicated a cyclical interplay between heterotrophic microbial activity and microalgal photosynthesis. In the later stages, enhanced synthesis of Chlorella carotenoids was correlated with deteriorating water quality and the onset of oxidative stress. Initially, the microbial community was dominated by organic matter degradation, nitrate reduction, and fermentation. However, as cultivation progressed, metabolic activities shifted towards the photoassimilation of inorganic nutrients. The Chlorella sp. symbiotic system facilitated a rapid succession of the microbial community, which was characterized by frequent bacterial population changes, ultimately leading to a unique, temporally stable community structure. The initially diverse microbial population was progressively supplanted by more adaptive bacterial strains, achieving a steady state by the seventh day. Notably, Alcaligenaceae demonstrated exceptional adaptability compared to other genera, underscoring its pivotal role within the Chlorella sp. symbiotic system. This research provides valuable theoretical insights into algal-bacterial interactions and highlights their potential for application in water quality remediation.