Application of anammox within an integrated approach to sustainable food waste management and valorization

•Effluent from 2-stage anaerobic digestion of food waste (2sAD-FW) was treated by anammox after partial nitration (PN) step.•Partial by-pass of PN reactor was used to regulate NO2/NH4 ratio in anammox influent.•An alternative plant layout for 2sAD-FW wastewater treatment was proposed.•Color evolution in granular anammox fed with real wastewater was investigated.•FISH results correlated well with changes in operating conditions. In this study, the anammox process was applied for the first time to the treatment of ammonium-rich liquid residues produced by the two-stage anaerobic digestion of food waste (2sAD-FW); such residues may represent a significant environmental issue if not properly managed. A granular anammox reactor was fed with a progressively increasing share of partially nitritated 2sAD-FW wastewater. An alternative operating strategy based on partial by-pass of the partial nitritation unit was tested, in order to regulate the influent NO2/NH4 molar ratio without chemical addition. High nitrogen removal efficiency (89 ± 1%) and negligible nitrite discharge rates were achieved, together with high nitrogen removal rate/nitrogen loading rate (NRR/NLR, 97 ± 1%) and stable specific anammox activity (0.42 ± 0.03 gN2-N/gVSS d). The observed NH4-removed/NO2-removed/NO3-produced molar ratio was in agreement with anammox stoichiometry, as confirmed by the low contribution (