Effect of Liquid Upflow Velocity and Recirculation Way on a Microaerobic EGSB Reactor System Treating Actual Coking Wastewater

To investigate the effect of liquid upflow velocity (V_up),inner sludge recirculation flow, and outer effluent recirculation flow on the performance of the microaerobic EGSB reactor system (consisted with EGSB I and EGSB II) treating actual coking wastewater at ambient temperature (25-28 °C), with 580-2160mg.L^-1 influent COD, 1.2L.h^-1 influent flow, and 2000ml.min oxygenation flow rate (air flow rate), the COD removal efficiencies were examined by changing V up (3.2m.h^-1→4.2m.h^-1), outer effluent recirculation flow and inner sludge recirculation flow (24L.h^-1+8L.h^-1→16L.h^-1+8L.h^-1). The results showed that the microaerobic EGSB reactor system treating actual coking wastewater could obtain high COD removal efficiencies and low effluent COD concentration. The most important was to keep about 3.2m.h^-1 V_up, and too high V_up (up to 4.2m.h^-1) damaged the granules and subsequently deteriorated the performance process (with 7%-14.2% COD removal efficiencies decreasing). Sludge inner recirculation could strengthen the expanding effect of the sludge bed and thus lead to a better contact between the wastewater and the biomass, and simultaneously the shear was not strengthened and the granules were not damaged. Through introduction a quantity of inner sludge recirculation of 8L.h^-1, combined with portion outer effluent recirculation of 16L.h^-1, still keeping 3.2m.h^-1 V_up , high COD removal of 90.7%-95.4% and low effluent COD concentration of 82-158mg.L^-1 could attain. And simultaneously the EGSB I and EGSB II had high biomass concentration of 35.6mg.L^-1 and 19.7mg.L^-1 and feasible mean particle size of the biomass of 0.9mm and 0.8mm, which indicated the long term stability of the high efficiency EGSB reactor system treating actual coking - astewater.