Ferric and sulfate coupled ammonium oxidation enhanced nitrogen removal in two-stage partial nitrification - Anammox/denitrification process for food waste liquid digestate treatment.

[Display omitted] • A two-stage PNA/D process was established for nitrogen removal of liquid digestate. • Ammonium oxidation was enhanced by coupling with ferric and sulfate reduction. • Anammox and denitrification accounted for 75% and 25% of N loss in PNA/D system. • EPS-mediated EET between sulfate/ferric reducers and aerobic ammonium oxidizers. Liquid digestate of food waste is an ammonium-, ferric- and sulfate-laden leachate produced during digestate dewatering, where the carbon source is insufficient for nitrogen removal. A two-stage partial nitrification-anammox/denitrification process was established for nitrogen removal of liquid digestate without pre-treatment (>300 d), through which nitrogen (95 %), biodegradable organics (100 %), sulfate (78 %) and iron (100 %) were efficiently removed. Additional ammonium conversion (20 %N) might be coupled with ferric and sulfate reduction, while produced nitrite could be further converted to di-nitrogen gas through anammox (75 %) and denitrification (25 %). Notably, since increasingly contribution of hydroxylamine producing nitrous oxide, and up-regulated expression of electron transfer and cytochrome c protein, the enhanced ammonium oxidation was probably conducted through extracellular polymeric substances-mediated electron transfer between sulfate/ferric-reducers and aerobic ammonium oxidizers. Thus, the established partial nitrification-anammox/denitrification process might be a cost-efficient nitrogen removal technology for liquid digestate, benefitting to domestic waste recycling and carbon neutralization. [ABSTRACT FROM AUTHOR]