Effect of liquid carbon sources on nitrate removal, characteristics of soluble microbial products and microbial community in denitrification biofilters

This study investigated the effects of different carbon sources on the denitrification performance, soluble microbial products (SMPs), and microbial community in lab-scale denitrification biofilters (DNBFs) treating simulated secondary effluent. Three biofilters, named D1, D2, and D3, were fed with sufficient supplies of sodium acetate, methanol, and glucose, respectively. The denitrification efficiencies and denitrification rates of the three DNBFs followed the order D2 > D1 > D3. The final effluent SMP concentrations were 26.24 ± 3.55 mg/L, 24.95 ± 2.67 mg/L, and 28.00 ± 2.44 mg/L in D1, D2, and D3, respectively. The results also showed that the proteins were the main components of SMPs. External carbon sources were also involved in the initial denitrification in D1 and D2, while denitrifying bacteria were induced to utilize SMPs in D3. The total relative abundance of these denitrifying bacteria followed the order D1 > D2 > D3. Moreover, fluorescent soluble microbial byproduct-like substances inhibited the growth of functional bacteria, resulting in a decrease in denitrification efficiency. Therefore, because the SMPs also significantly affected nitrate removal in the DNBFs, their different components exhibited differing effects on denitrification.