Exploring critical factors influencing on autotrophic denitrification by elemental sulfur-based carriers in upflow packed-bed bioreactors

Abstract

This study investigated the effects of hydraulic retention time, nitrate loading rate, as well as seed sludge on nitrate removal by using elemental sulfur-based carriers in upflow packed-bed bioreactors. The results showed that nitrate removal efficiency improved by 28 % with increasing hydraulic retention time from 1 h to 4 h. The nitrate removal rate achieved 84 ± 1% at a loading rate of 0.20−0.40 kgNO3−-N/m3/d and decreased by 54 % after triggering a loading rate of 1.20 kgNO3−-N/m3/d. Besides, nitrite accumulation was noticeable, with nitrite effluent concentration being 15.9–16.6 mgNO2−-N/L, as operating at nitrate loading over 0.80 kgNO3−-N/m3/d. Interestingly, after enriching seed activated sludge, the sum proportion of Thiobacillus and Sulfurimonas (well-known denitrifying bacteria) increased from 17.1 to 18.4% to 55.4–56.3 %, which improved nitrate removal efficiency to 90 ± 3%. Overall, the high nitrate removal rate of 0.36 kgNO3−-N/m3/d demonstrated that elemental sulfur-based carrier is a powerful candidate to apply for autotrophic denitrification.