Effect of recycle ratio on performance of pre-denitrification moving bed biofilm reactors in treating coal gasification wastewater

A lab-scale sequential anoxic moving bed biofilm reactor (ANMBBR) and aerobic moving bed biofilm reactor (AEMBBR) for pre-denitrification system were used to treat real coal gasification wastewater. Removal efficiencies of COD, phenols, thiocyanate (SCN- ), ammonium (NH4+ –N), and total nitrogen (TN) were investigated at different recycle ratios, and then NaHCO3 was added into the inlet of the AEMBBR to promote nitrification. Maximal removal efficiencies of COD, phenols, and SCN- were 84.2, 88, and 99.9% at a recycle ratio of 3.0, respectively. NH4+–N and TN removal efficiencies could achieve 97.4 and 78.2% with the addition of NaHCO3 (3 g NaHCO3 per day). Concentrations of NO-2-N and NO-3-N were always below 0.2mg/L in the effluent of the ANMBBR. NO-2-N accumulation could be observed in the effluent of the AEMBBR after adding NaHCO3.