Corn cob as a carbon source in ecological treatment of farmland runoff: Pollutant removal performance, effluent dissolved organic matter and microbial community structure

As a cheap, slow-release, environmentally-friendly carbon source, corn cob could promote denitrification performance, and was advantageous to ecological treatment of farmland runoff. The effects of corn cob in the ecological treatment planted with Myriophyllum aquatium were seldom explored. In this study, three treatments (MA: Myriophyllum aquaticum; CC: Corn cob; MACC: Myriophyllum aquaticum and corn cob) were used to decontaminate farmland runoff characterized by nitrate-dominated and low carbon content. Results showed that NO3- -N removal efficiencies increased by 37.08 % in CC and 64.87 % in MACC, TN removal efficiencies of CC and MACC increased by 36.72 % and 70.75 %, respectively, and TP removal efficiencies increased by about 15 % in MACC. Four components were identified in DOM, including fulvic-like (C1), humic-like (C2), tryptophan-like (C3) and a combination of tryptophan- and tyrosine-like substances (C4). C2 showed a correlation with microorganisms, which was consistent with that between TN removal and microorganisms. The proportion of typical genus for denitrification was MACC (19.92 %) > CC (3.35 %) > MA (0.56 %) in the water, and that in the substrate was MACC (38.38 %) > CC (36.48 %) > MA (7.11 %). Cellulose-degrading bacteria Pseudomonas appeared in substrates and the proportion was MACC (7.14 %)>CC (3.84 %)>MA (0.33 %). The coexistence and highest proportion of genus for denitrification and fermentation in MACC promoted carbon source release and nitrate removal. Results provided a natural-based treatment for farmland runoff, an understanding of the relationship among denitrification performance, effluent DOM and microorganisms, and inspiration for achieving more satisfactory nitrogen removal in the ecological treatment with biowaste addition.