Effect Of Dissolved Oxygen On Simultaneous Removal Of Carbon, Nitrogen And Sulfur Process

Conventional biological wastewater treatment process for the removal of carbon, nitrogen, sulfur has many disadvantages, such as high content sulfide in the effluent, low elemental sulfur conversion rate, low utilization efficiency, leading to the high-cost, failing to meet the mission standard and needing follow-up treatment. In allusion to these drawbacks of anaerobic treatment, this study proposes integrated simultaneous removal of organic carbon, nitrate, and sulfate process under micro-aerobic condition, which realizes efficient and simultaneous substrate removal, greatly improve element sulfur conversion rate and eliminate the second environment pollution.Expanded Granular Sludge Bed (EGSB) is used in this study. Start-up and operation of the reactors was operating through two different running modes. Mode 1: direct start-up, start the reactor with organic carbon, sulfate and nitrate as substrate, after successful start-up, to micro-aerate and determine the optimal dissolved oxygen content; after that stop adding nitrate to the reactor. Mode 2: stepwise start-up, start the reactor with organic carbon and sulfate as substrate, after successful start-up, to micro-aerate and determine the optimal dissolved oxygen content, after that begin adding nitrate to the reactor. Under each mode, influence of different dissolved oxygen concentration on the performance and elemental sulfur conversion rate was investigated. Besides, the performances of reactor under two different running modes were compared.Mode 1, at 1.80 kg SO₄^2--S m-^-3d^-1,0.55 kg NO₃^--N m^-3d^-1 and 16 kg COD m?3d?1, the average removal of sulfate, nitrate and COD are 96.8%, 98%, 30%, respectively. The optimal DO concentration range is 0.14-0.16 mg/l. The elemental sulfur conversion rate is 72.9%. Afterwards stop adding nitrate to reactor, at 1.80 kg SO₄^2--S m-^-3d^-1, 16 kg COD m^-3d^-1 and 0.07-0.10 mg/LDO, the sulfate and COD removal rate are 97.5%, 70.3%. The elemental sulfur conversion rate is 58%. Mode 2, at 1.80 kg SO₄^2--S m-^-3d^-1 and 16 kg COD m^-3d^-1, optimal DO concentration range is 0.08-0.10 mg/l. The sulfate removal, COD removal and elemental sulfur conversion rate are 81.5%, 37% and 80%, respectively. Afterwards begin adding nitrate to reactor, at 1.80 kg SO₄^2--S m-^-3d^-1, 0.55 kg -NO₃^--N m^-3d^-1 16 kg COD m?3d?1 and DO 0.08-0.10 mg/L, the removal of sulfate, nitrate and COD is 98%, 97.1% and 89.8%, the elemental sulfur conversion rate is 89.8%. The performances of reactor operating in two modes are compared. Results indicate that mode 2 is preferable for carbon, nitrogen, sulfur removal and elemental sulfur production as end product, almost absolutely realizing resource utilization.