Sequencing batch airlift reactor system for simultaneous removal of nitrogen and organic carbon from synthetic tannery wastewater

• Published in: Desalination and water treatment 2020-04, Vol.183, p.194-204
• Main Authors: Melesse, Aysanew Gorems, Srinivasan, Shanmugham Venkatachalam, Demissie, Berhanu Assefa, Chacko, Sabumon Pothanamkandathil
• Format: Article
• Language: English
• Subjects: Cycle time; Nitrogen removal; Sequencing batch airlift reactor; Sludge retention time; Tannery wastewater
• ISSN: 1944-3986; 1944-3986
• DOI: 10.5004/dwt.2020.25029

Tannery wastewater has high organic carbon and nitrogenous compounds due to the raw hides/skins and chemicals used during leather processing. Conventional single stage activated sludge process is effective in reducing the organic but not nitrogenous load in the wastewater. In the present study, a sequencing batch airlift reactor system was investigated for the simultaneous removal of nitrogen and organic carbon from synthetic tannery wastewater. The reactor was operated at constant 50% volume exchange ratio at low dissolved oxygen concentration (DO 1–2 mg L–1); different sludge retention times (SRTs) (7 and 20 d) and cycle times (CT’s) (18, 12, 10, and 8 h) for 250 days. The organic and nitrogen loading rates were increased stepwise to 7.875 kg COD m–3d–1 (COD is abbreviated as chemical oxygen demand) and 0.531 kg NH4–N m–3 d–1 respectively. Partial nitrification-denitrification was observed when the reactor was operated at SRT of 7 d, whereas complete nitrification-denitrification was observed when the reactor was operated at 20 d SRT. The total nitrogen (TN) removal efficiencies were observed to increase with the increase in the cycle time. In addition, the TN removals efficiency increased with cycle times. The optimum cycle time for (>90%) removal of COD and NH4–N was found to be 8 h at SRT of 20 d. The remaining nitrogen in the effluent was more in the form of nitrate at higher cycle times and in the form of nitrite for lower cycle times.