Study On Nitrate Removal From Groundwater By The Combination Of Sulfur And Eggshell/Ferrous Sulfide

Nitrate pollution in groundwater as a prominent environmental problems, is becoming more and more serious, due to extensive use of nitrogenous fertilizers in agriculture, and unrestricted discharge of industrial wastewater. Human beings’ health is threatened by nitrate-contaminated groundwater. Sulfur-based autotrophic denitrification(SAD) can convert nitrate or nitrite to nitrogen utilizing sulfur or sulfur compounds as electron donor and inorganic carbon as carbon source. SAD process is widely researched due to its high stability and strong applicability. Hydrogen iron as a product of SAD process would lead to the decline of system pH and inhibit nitrate removal rate. Therefore, suitable alkaline materials to minimize the impact of pH variation on SAD process attracted attention of many researchers.This study discussed the treatment effect for nitrate in groundwater by the combination of sulfur and eggshell and the combination of sulfur and ferrous sulfide. We first investigated the feasibility for raw or cooked eggshell to control pH compared with oyster shell and limestone. Denitrification performance of sulfur-based autotrophic denitrification with eggshell(SADE) was discussed at different conditions, such as different sulfur/eggshell(w/w) ratios, temperatures and hydraulic retention times(HRTs). At the same time, the applicability of sulfur-ferrous sulfide autotrophic denitrification(SFSAD) was investigated. The denitrification capacity of SFSAD process was studied at different conditions, such as different sulfur/ferrous sulfide(w/w) ratios and HRTs.The results showed that eggshell could control pH for SADE process. System pH was maintained at 7.02 ~ 7.74. Nitrate removal efficiency was above 97%. The optimum sulfur/eggshell ratio was 2:3. SADE process could remove nitrate completely even under 15 ℃. The nitrate removal efficiency of denitrification column was above 96% when HRT was 48 h and the dominant microorganism for denitrification in column ES1 were T. denitrificans and S. denitrificans. While in column ES2 which was not inoculated seed sludge, T. denitrificans were the main bacteria. The denitrification efficiency of SFSAD process was better than that of SAD and FSAD process. System pH in SFSAD process was maintained at 7.28 ~ 7.88 and sulfate concentration achieved only 194.37 mg/L. The optimum sulfur/ferrous sulfide was 1:2. Nitrate removal efficiency reached 98% in column FS1 and FS2 when HRT was 48 h. The dominant microorganisms for denitrification in SFSAD system were T. denitrificans. This study illustrated that eggshell as the solid waste can be used as alkaline material for SAD process. The application of eggshell provided reference for SAD development and made contributions to environment protection simultaneously.