Nitrogen removal enhancement using lactic acid fermentation products from food waste as external carbon sources: Performance and microbial communities

•Lactic acid-enriched FLFW was used as carbon sources for nitrogen removal.•Similar nitrogen removal rate were obtained with FLFW, lactate and acetate.•High bacterial metabolic diversity was found with FLFW as carbon source.•Microbial communities cultured with FLFW and other chemicals were compared. In this study, nitrogen removal using the lactic acid fermentation products from food waste and other external chemical carbon sources (sodium acetate, sodium lactate and starch) was investigated. Similar to sodium acetate and lactate, the lactic acid-enriched fermentation liquid from food waste (FLFW) exhibited a high denitrification rate (5.5 mg NOx-N/(g-VSS h)) and potential (0.16 g NO3−-N/g COD), and could achieve high NH4+-N and total nitrogen (TN) removal efficiencies during long-term operation. Using FLFW as supplementary carbon sources reduced the extracellular polymeric substances (EPS) content, improved the settleability and achieved a satisfactory biomass yield of activated sludge. Additionally, the increased microbial metabolic activity and bacterial community diversity and the accumulation of unique bacteria in the activated sludge cultured with FLFW further promoted the organics utilization rate and nitrogen removal efficiency, indicating that the FLFW prepared from solid waste was an ideal carbon source for wastewater treatment.