Simultaneous ammonia removal and sulfate reduction in a UASB reactor with high concentration of organic substance co-existing: Process and mechanism

Ammonia nitrogen removal with the aid of sulfate in sewage itself under anaerobic condition is thought to bring a great advantage for domestic wastewater treatment. But how to achieve it is yet to be fully understood. Ammonia oxidation in high strong chemical oxygen demand (COD) condition in a Upflow Anaerobic Sludge Blanket (UASB) reactor was studied and the valence state change of iron ion during the ammonia oxidation and sulfate reduction (AOSR) were investigated in this study. The experimental results show that, AOSR reaction was successfully realized in the UASB within the removal rates of ammonia nitrogen and sulfate were above 80 % and 70 % respectively. The experiments of adding ammonia nitrogen or sulfate independently have proved that the denitrification and desulfurization reactions can be carried out independently. In the batch test, adding 40 mg/L iron ion significantly improved the efficiency of ammonia removal, and noted the production of ferrous ion. In the test, the total amount of iron ions almost did not change, so it was judged that ammonia was removed by anaerobic iron ammonia oxidation. In addition, the reaction also occurred in organic wastewaters with different carbon source, and the effect of glucose was the most obvious. This study shows that in high COD environment, ammonium oxidation and iron reduction can take place at the same time, rather than sulfate reduction, and ferrous ion is oxidized to ferric ion and sulfate reduction at the same time, which indicates that it might be used to remove ammonia from domestic sewage.