Abstract: In order to investigate the effect of volumetric exchange ratio on nitrogen removal in novel UniFed SBR process,two UniFed SBR reactors were operated at the volumetric exchange ratio of 25%and 42% respectively to treat real domestic wastewater.The effect of volumetric exchange ratio on nitrogen removal was analyzed by comparing the degradation rules of TN during a whole cycle and TN concentrations of effluent at 6 group identical feedρ(C)/ρ(N)ratios at 25%and 42%respectively.The results showed that when UniFed SBR process was operated at any volumetric exchange ratio,a corresponding maximum TN removal efficiencyη_1max during feed/decant period always existed.η_1max was only relative to volumetric exchange ratio and irrespective of feedρ(C)/ρ(N)ratio.When the carbon sources of influent were sufficient,the bigger the volumetric exchange ratio,the lowerη_1max was.When at the same feedρ(C)/ρ(N)ratio,the bigger the volumetric exchange ratio,the higher TN removal efficiency was.TN removal during feed/decant period contributed more to UniFed SBR process,so the use of smaller volumetric exchange ratio was beneficial to TN removal of the whole process.