Effect of Increasing Nitrobenzene Loading Rates on the Performance of AMBR and Sequential AMBR/CSTR Reactor System

A laboratory scale sequential anaerobic migrating blanket reactor (AMBR)/aerobic completely stirred tank reactor (CSTR) system was operated to investigate the effect of increasing nitrobenzene (NB) concentrations on the performance of AMBR/CSTR reactor system. The reactor system was operated at increasing NB loading rates from 1.93 to 38.54 g NB m(-3) day(-1) and at a constant hydraulic retention time of 10.38 days. In this study, chemical oxygen demand (COD) and NB removal efficiencies, variations of bicarbonate alkalinity (Bic.Alk.), total volatile fatty acid (TVFA), and total methane gases were monitored. COD removal efficiencies were 93-94% until a NB loading rate of 5.78 g m(-3) day(-1) in the AMBR reactor. For maximum COD removal, the optimum NB loading rate and NB concentration were found to be 5.78 g m(-3) day(-1) and 60 mg L-1, respectively. COD removal efficiencies decreased from 94 to 87% and to 85% at NB loading rates of 1.93-28.90 and 38.54 g m(-3) day(-1), respectively. COD was mainly removed in the first compartment. NB removal efficiencies also were approximately 100% at all NB loading rates in the effluent of the AMBR reactor. The maximum total gas and methane gas productions were found to be 2.8 L day(-1) and 1.3 mL day(-1), respectively, at a NB loading rate of 5.78 g m(-3) day(-1). The TVFA concentration in the effluent of AMBR was low (17 mg L-1) at a NB loading rate as high as 38.54 g m(-3) day(-1). Overall COD removal efficiencies were found to be 99 and 96% at NB loading rates of 1.93 and 38.54 g m(-3) day(-1), respectively, in a sequential AMBR/CSTR reactor system. In this study, NB was reduced to aniline under anaerobic conditions. Aniline removal efficiencies were 100% until a NB loading rate of 17.34 g m(-3) day(-1) in aerobic CSTR reactor while aniline removal efficiency decreased to 90% at a NB loading rate of 38.54 g m(-3) day(-1) in an aerobic reactor. In the aerobic step, aniline was mineralized to catechol. The contribution of aerobic step is not only the degradation of aniline, it may also increase the COD removals from 85 to 99% at a NB loading rate as high as 38.54 g m(-3) day(-1)