Enhancing partial nitrification-endogenous denitrification with an A/O/A strategy by co-fermentation of excess sludge and corn straw to achieve advanced nitrogen removal from mature landfill leachate.

[Display omitted] • Co-fermentation liquid provided abundant VFAs as carbon source. • Co-fermentation liquid promoted the NAR to 99.07% to notably save energy. • The NRE of the PNED system reached 98.53% by enhancing endogenous denitrification. • The co-fermentation reactor could achieve a sludge reduction ratio of 21.72%. • The cooperative mechanism of HNADB, DGAOs and AOB in the oxic stage was revealed. In mature landfill leachate with high ammonia nitrogen and extremely low biodegradable organic matter, it is difficult to achieve advanced nitrogen removal through traditional nitrification–denitrification processes. In this study, a low- carbon/nitrogen mature landfill leachate treatment process with an anaerobic/oxic/anoxic strategy was constructed by inputting co-fermentation liquid of corn straw and excess sludge. Under the effect of the co-fermentation liquid, partial nitrification was enhanced. Meanwhile, with the cooperation of the heterotrophic nitrification-aerobic denitrification process, the nitrite accumulation ratio and simultaneous nitrification and denitrification ratio reached 99.07 ± 0.52% and 23.26 ± 1.02%, respectively. The carbon source from the co-fermentation liquid was efficiently converted into polyhydroxyalkanoates, which could drive endogenous denitrification to achieve advanced nitrogen removal. The nitrogen removal efficiency in this system reached 98.53 ± 1.21%. In addition to effectively supplying carbon sources, the co-fermentation reactor also achieved a sludge reduction ratio of 24.78 ± 1.68%. Through metagenomic analysis, the cooperative mechanism by which denitrifying glycogen-accumulating organisms, heterotrophic nitrifying-aerobic denitrifying bacteria and ammonia-oxidizing bacteria achieve nitrogen removal and nitrite accumulation in oxic stage was revealed. This study provides a new and efficient treatment process for mature landfill leachate and sludge reduction. [ABSTRACT FROM AUTHOR]