Search

Various sole and mixed electron donors were tested to promote the denitrification rate and nitrate removal efficiency in biofilter systems with high phosphate and ammonia removal efficiency (92.6% and 95.3% respectively). Compared to sole electron donors, complex organic carbon (bits of wood and straw) substantially improved the denitrification rate and nitrate removal efficiency (from 6.3%-18.5% to35.4%) by shifting the denitrifying microbial community composition, even though the relative abundance of functional genes mediating denitrification decreased. The mixed electron donor combining complex organic carbon with sulfur, iron and CH 4 further promoted nitrate removal efficiency by 37.2%. The significantly higher abundance and diversity of bacteria mediating organic carbon decomposition in the treatments with complex organic carbon indicated the continuous production of organic carbon with small molecular weights, which provided sustainable and effective electron donor for denitrification. However, sole sulfur or iron did not effectively promote the denitrification rate and nitrogen removal efficiency, even though the related microbial community had been formed. Image 1 • Phosphate and ammonia removal efficiencies were high in all treatments of the biofilters. • Nitrate removal efficiency were significantly higher in biofilters amended with complex organic carbon. • Relative abundance of bacteria related to nitrogen cycle was low in biofilters amended with complex organic carbon. • Genes related to organic carbon decomposition controlled nitrate removal in the biofilters. • Microbial community composition rather than relative abundance facilitated nitrate removal. [ABSTRACT FROM AUTHOR]