N2O reduction during municipal wastewater treatment using a two-sludge SBR system acclimatized with propionate

A two-sludge denitrifying phosphorus removal process (A2N-SBR), acclimatized with propionate, was proposed as an efficient method for nitrous oxide (N2O) reduction during municipal wastewater treatment. Compared with the conventional nitrification–denitrification process (AO-SBR) operated in parallel, the A2N-SBR not only significantly improved total nitrogen and soluble phosphorus removal efficiencies by around 32.3% and 23.5%, respectively, but also greatly reduced N2O generation by around 31.5%. Moreover, like the anoxic stage of AO-SBR, nearly zero N2O (merely 0.054% of the removed nitrogen) was generated during the anoxic stage of A2N-SBR. The substantial N2O reduction achieved in the proposed A2N-SBR can be reasonably explained by: (i) the use of independent nitrification reactor resulting in higher activity of nitrifying bacteria and no occurrence of heterotrophic denitrification in aerobic stage, and (ii) the use of propionate as carbon source decreasing nitrite accumulation in anoxic stage.

► Compared with AO-SBR, A2N-SBR reduced N2O generation by around 31.5%.
► Only 0.054% of the removed nitrogen in anoxic stage of A2N-SBR was converted to N2O.
► Autotrophic nitrification contributed to 95.4% of total N2O generation in N-SBR.
► The separate nitrification reactor reduced N2O generation in aerobic stage.
► The use of propionate as carbon source reduced N2O generation in anoxic stage.