Application of bio-slow sand filters for drinking water production: Linking purification performance to bacterial community and metabolic functions

Bio-slow sand filters (BSSFs) are widely employed in rural drinking water treatment ascribing to its economic applicability, easy operation and high efficiency. This study investigated the influence of particle size, filter thickness, water quality and filtration rate on decontamination performance, bacterial community and metabolic function of BSSFs. The effluent ammonia nitrogen during stable operation period basically met the standards for drinking water quality in China (0.5 mg/L). The average removal efficiencies of fine sand were about 4 % higher than those of coarse sand, and thick filter layer showed more stable performance. Schmutzdecke removed most turbidity and organic pollutants, playing an overwhelming role in water purification. Filtration rate was a key factor in shaping bacterial community structure. Proteobacteria and Cyanobacteria were dominant phyla, whose relative abundance significantly decreased and increased as filtration rate increasing, respectively. Co-occurrence patterns were dominant within bacterial communities. Function bacteria (e.g. Hyphomicrobium and Methylophilus) and rare genera (Curvibacter and Simplicispira) were identified as hub genera in the networks. The bacterial communities exhibited a metabolic versatility. Several pathways for secondary metabolism significantly shifted under different conditions, such as xenobiotics biodegradation and metabolism. Moreover, filtration rate and dominant genera greatly affected pollutant removal performance. Many species of Proteobacteria and Bacteroidota were closely related to carbohydrate metabolism, energy metabolism and nucleotide metabolism, and metabolic functions corresponded more cohesively to conditional abundant taxa, conditional rare or abundant taxa, conditional rare taxa. This study highlights the adaptability and bacterial community characteristics of BSSFs, and provides references for their practical application.