RESEARCHING NEW WAYS TO REDUCE N2O EMISSION FROM A GRANULAR SLUDGE SEQUENCING BATCH REACTOR TREATING DOMESTIC WASTEWATER UNDER SUBTROPICAL CLIMATE CONDITIONS

ABSTRACT N2O emissions from wastewater treatment plants have become an important issue, since this compound is a significant greenhouse gas that affects the sustainability of sewage treatment. This work aimed to investigate and to reduce N2O emission from a pilot-scale aerobic granular sludge sequencing batch reactor (AGS-SBR) operated for carbon and nitrogen removal from domestic wastewater under subtropical climate condition. Three operational strategies (S-I, S-II and S-III) with different anoxic phase durations were compared regarding treatment efficiency and N2O emission. For all the studied strategies, volatile suspended solids (VSS) was between 1.0 and 1.2 g/L. S-III, with the longest anoxic phase, obtained the highest biological oxygen demand (BOD) and NH4+-N removal efficiencies (86% and 84%, respectively), the lowest N2O emission factor (16.99 gN2O-N/person·year) and the lowest total nitrogen (TN) to N2O conversion ratio (0.47%). The results indicated that the extension of the anoxic phase was an effective way to significantly reduce N2O emission and to improve treatment efficiency.