Co-removal of nitrate and sulfate from groundwater by a sequential system of autotrophic denitrification, sulfate reduction and sulfur oxidation

Nitrate is the most common pollutant observed in groundwater in our country, and observed 5-10 times higher than the levels specified in TS266. The completed thesis is a continuation of the nitrate-related parts of the projects 113Y023 and 117Y014, which were previously completed by the thesis advisor. In this context, while high nitrate removal is achieved with sulfur-based denitrification, the sulfate in the effluent is removed from the system boundaries in the form of elemental sulfur with a biological process. For this purpose, two up-flow column reactors were established and sulfur-based denitrification was carried out in one reactor and ethanol-based sulfate reduction was carried out in the other reactor. Sulfur-based denitrification was operated on a sulfur/sulfide-based by sequentially connecting these reactors and recycling from the sulfate reduction reactor effluent to the denitrification reactor. The alkalinity produced in the sulfate reducing reactor was used in the denitrification reactor. While some of the effluent from the reducing reactor effluent was recycled to the denitrification reactor, the remaining portion was subjected to partial oxidation with limited aeration, allowing the sulfide to precipitate in the form of elemental sulfur. In the thesis, 100 mg of NO3--N/L was reduced by sulfur/sulfide-based denitrification. While theoretically 754 mg/L sulfate is expected to form in elemental sulfur-based denitrification, the sulfate concentration in the effluent was below the level specified in TS 266 due to the fact that (1) the system is operated on a sulfur basis and (2) a sulfate reduction and partial oxidation in the system allows the sulfur to leave the system as sulfur. In the last period tested, besides 100 mg NO3--N/L, 500 mg/L sulfate was added to the system feed. Nitrate was completely removed from the effluent, while the sulfate concentration was kept at 25.2±28.9 mg/L. This thesis is a first in terms of removing both sulfate and nitrate out of the system boundaries biologically.