Influence of C/N ratio on MBBR denitrification for advanced nitrogen removal of wastewater treatment plant effluent

High total nitrogen (TN) content is an urgent issue for the reuse of wastewater treatment plant (WWTP) effluent, and moving bed biofilm reactor (MBBR) is preferable for advanced denitrification of WWTP effluent. The influence of COD/NO3--N (hereinafter referred to as C/N) ratio on nitrate removal was studied. The results showed that the denitrification rate was influenced by influent NO3--N concentration, and the maximum value (13.9 +/- 2.7 mg NO3--N.(L.d)(-1)) was achieved for 4.6 C/N ratio; dissimilatory nitrate reduction to ammonium (DNRA) might be occurred under higher C/N ratios (8.0 and 8.4), and reduced the TN removal rate because of NH4+-N accumulation. Dissolved organic matter (DOM) concentration of effluent was lower than that of influent, except for 6.7 C/N ratio. 8.0 C/N ratio had the lowest community structure diversity and evenness of denitrification nosZ gene, and the narG and nosZ gene content of 4.6 C/N ratio was the highest. Overall, 4.6 C/N ratio was the optimum choice for nitrogen removal of WWTP effluent by denitrification MBBR.