High-efficient nitrogen removal from mature landfill leachate and waste activated sludge (WAS) reduction via partial nitrification and integrated fermentation-denitritation process (PNIFD)

Abstract

Biological nitrogen removal from mature landfill leachate is ineffective due to the extremely low carbon/nitrogen (C/N) ratio. Moreover, a large amount of waste activated sludge (WAS) is inevitably generated from WWTPs during the municipal sewage treatment process. In this study, an innovative process was developed to enhance nitrogen removal from low C/N (1:1) mature landfill leachate and to reduce the WAS during a 300-day operation. Two sequencing batch reactors (SBRs) were involved in this process. Firstly, the mature landfill leachate was pumped into an aerobic reactor to undergo partial nitrification (PN-SBR). Then, the PN-SBR effluent and WAS were pumped into an anoxic reactor to undergo integrated fermentation and denitritation (IFD-SBR). The pH profile was treated as a real-time parameter to precisely control the duration of the PN and IFD processes. Partial nitrification and integrated fermentation-denitritation (PNIFD) system achieved a total nitrogen removal efficiency of 95.0% and an average nitrogen removal rate (NRR) of 0.63 kg/m3·d during the last operational phase. Due to a variety of refractory contaminants, the effluent COD concentration was 1865.9 mg/L and a 19.7% COD removal efficiency was obtained under an influent concentration of 2324.5 mg/L. Compared with the traditional nitrogen removal process, PNIFD not only decreased requirements for oxygen by 25% and the external organic carbon by 100%, but also achieved simultaneous reduction of external WAS. More than 53.7% of the external sludge was reduced during the IFD-SBR operational cycle, with an average external sludge reduction rate (SRR) of 5.09 kg/m3·d. Fermentation/denitritation related microorganisms, such as Anaerolineaceae, Acidimicrobiaceae and Thauera, accounted for up to 41.5% of the total abundance in the IFD-SBR. Based on the long and stable operation, this study provides a simple and promising approach for synchronous nitrogen removal and WAS reduction.