The activated sludge samples in a Pilot-Scale Demonstration of temperature-based nitrogen removal process. Raw sequence reads

Partial Nitrification/Anammox (PNA) is a promising wastewater treatment process known for its energy-saving potential. There are many derivative processes based on PNA. Simultaneous Anammox denitrification (SAD) can remove the nitrate produced by Anammox process through denitrification. Anammox Denitrification Sludge Fermentation (ADSF), on the other hand, uses sludge fermentation as a carbon source for nitrate removal realizing advanced nitrogen removal. However, low temperatures, particularly below 20 degrees Celsius, pose significant challenges to the robustness of the PN ADSF process, including the stability of PN and the activity of Anammox. In order to achieve efficient nitrogen removal at different temperatures, this study investigated the operational performance and transformation of processes based on PNA (above 20 degrees Celsius) and coupled complete nitrification and sludge fermentation denitrification (below 20 degrees Celsius) using a pilot-scale SBR-UASB system. In this mode of operation, effluent Total Inorganic Nitrogen (TIN) was consistently achieved low level below 15 mg/L across the 8.2-29.5 degrees Celsius, and measurements predominantly below 10 mg/L in the most time notably with an average of 7.9 mg/L. The findings of this study indicated significant Anammox contribution rates, averaging 88.4% at temperatures exceeding 20 degrees Celsius and 45.6% at temperatures between 15 and 20 degrees Celsius, accompanied by a remarkable 52% reduction of external sludge. Through 265 days operation, the ADSF process (dominated by denitrification) can be rapid start-up from SAD process (dominated by Anammox) by the addition of external sludge. And the SAD process can also recovered from ADSF process. The microbial community composition proved the appearance which Candidatus Kuenenia as the main AnAOB experienced a decrease and then an increase over the 265 days of operation, and reached enrichment levels of up to 7.13%. In summary, this study proposed a strategy of temperature-based nitrogen removal process, which provided valuable insights into seasonal adaptation of mainstream Anammox.