Treatment of non-sterile biogas slurry from a pig farm using microalgae isolated from the activated sludge of sewage plants

Microalgae treatment is regarded as a green and environmentally acceptable method of treating pig farm biogas slurry (BS). Numerous studies have been conducted on the use of microalgae to treat sterilized BS. Nevertheless, in large-scale application settings, this method will undoubtedly result in high costs and low efficiency. In this study, microalgae were isolated from activated sludge, and their capacity to treat non-sterile BS with high ammonium nitrogen levels was investigated, along with examining alterations in microbial composition within BS. The results showed that both Chlorella sp. HH01 and Chlorella sp. HS02 treatments effectively removed ammonia nitrogen and phosphorus from BS. They also showed some removal capabilities for chemical oxygen demand, heavy metals, and antibiotics. Algal treatment significantly reduced the number of species, richness, variety, and pathogens within the microorganisms of BS, according to the results of metagenomic research. Meanwhile, algal treatment demonstrated a significant removal effect on certain antibiotic resistance genes, while increasing the abundance of some others. This study provides a comprehensive exploration of microalgae-mediated mitigation effects on antibiotic resistance genes in BS. Numerous studies have been conducted on the use of microalgae to treat sterile biogas slurry (BS). However, in large-scale applications, this approach undoubtedly results in high costs and inefficiencies. Therefore, it is crucial to identify microalgae capable of growing in non-sterilized and undiluted BS while effectively treating major pollutants. The findings of this study reveal that microalgae isolated and purified from activated sludge in sewage treatment plants can withstand crude BS containing high concentrations of ammonia nitrogen and effectively remove ammonia nitrogen and total phosphorus. Additionally, they exhibit some removal capabilities for chemical oxygen demand, heavy metals, pathogens, antibiotics, and certain antibiotic resistance genes.