Effect of Cycle Time Lengths on the Performance of Aerobic SBR Treating Tannery Wastewater

Abstract

Abstract Tannery industry generates significant quantities of wastewater which contains high organic matter, nitrogen, and chromium which needs to be treated before discharged into receiving water bodies. The aim of this study is to characterize tannery wastewater and to investigate the effect of cycle time length on performance of aerobic sequencing batch reactor (SBR) for treating a high load tannery wastewater. In this experimental study, an aerobic biological SBR with 50m3 capacity was used for treatment of wastewater at Modjo, Ethiopia. This paper reveals the results of treating tannery wastewater using pilot scale SBR at different operating conditions i.e. daily operation cycles (6, 12, 24 and 48h) on biological treatment of the industry effluent. A reactor was run for 56 days (including 21 days of acclimatization and 35 days of data gathering) for one phase. It was found that this wastewater has an average COD:N:P ratio about 900:5:1.3. At this ratio, the wastewater was found to have sufficient nutrients. The result also shows that removal efficiencies of COD, NH4-N and TKN were as high as 91%, 98% and 89.35 % at the cycle time of 24hrs. The 24hr cycle length with 12hr aerobic and 8hr anoxic conditions were selected as the optimum working conditions for enhanced removal of nutrient from tannery wastewater using SBR. Low COD and nitrogen removal at 6hr and 12hr cycle length can be attributed poor settling characteristics of sludge due to possible filamentous growth at low F/M (0.028) as compared to 24hr cycle length conditions, where F/M was 0.047. The effluent quality was satisfied with the discharge standard set by the local authority. According to the results, SBR performance in the removal of organic matter, nitrogen, and phosphorus at 24hr cycle time length is satisfactory, while the removal efficiency decreased by decreasing cycle time.