Treatment of tannery wastewater using a combined uasb (2 stage)-ozonation-baf system

Abstract

A four-stage lab-scale system was employed to treat tannery wastewater. This system was mainly comprised of a two-stage upflow anaerobic sludge blanket (UASB) reactor, an ozonation reactor, and a biological aerated filter (BAF) in series. The optimum operating conditions were found to be 42 h hydraulic retention time (HRT) for two-stage UASB, [O 3 ]/[COD 0 ] of 0.2 for 50 min, and 20 h HRT for BAF. Under these conditions, the removal ratios of chemical oxygen demand, total suspended solids, oil-grease, total nitrogen, ammonia, and chromium were all higher than 90%. The water quality of final effluent could satisfy the national discharge standard of China set for the leather tanning industry. The sulfidogenesis and methanogenesis were separated in two sequential UASB reactors. The first UASB process removed a considerable proportion of sulfate, which alleviated the possible toxicity of sulfide to methane-producing bacteria in the second UASB. The ozonation process enhanced the biodegradability of UASB effluent, and finally, post-polish treatment was completed in the BAF. The combined process demonstrated a promising potential for treatment of high-strength tannery wastewater.