Startup of granulation of sludge in sequencing batch airlift reactor for simultaneous removal of nitrogen and organic carbon from tannery wastewater

Abstract

The transition from flocculent to granular sludge process was investigated in Sequencing Batch Airlift Reactor (SBAR) for the treatment of synthetic tannery wastewater. Chemical Oxygen Demand (COD) loading rate of 6.3 kg/m3.d and nitrogen loading rate of 0.425 kg/m3.d were applied to the reactor for 105 days using simulated tannery wastewater. The flocculent sludge was transformed to granular sludge when the operating settling time was reduced sequentially. Based on the current findings of the study, the aerobic granules formed had a MLSS concentration of 12.3 g/L, biomass density of 6.1 g /L granule, settling velocity of 30−40 m/h, SVI of 16−20 ml/g TS and size distribution in the range 1.8–3.2 mm. Evaluation of the performance of the reactor showed a very good quality effluent with average COD, NH4-N and TN removal of 97.7 ± 1.5 (%), 87.1 ± 11.8 and 74.43 ± 11.7 (%) respectively. The effect of granulation on the existence and relative abundance of selected bacteria gene involved in nitrogen cycle was analyzed by PCR and qPCR. The result confirmed the existence of AOB-amoA, nirK and PLA46+Amx820 gene. The results for qPCR also confirmed that the relative abundance of AOB-amoA and PLA46+Amx820 was higher in the reactor compared to the control.