Nitrogen removal from wastewater and external waste activated sludge reutilization/reduction by simultaneous sludge fermentation, denitrification and anammox (SFDA)

•Simultaneous sludge fermentation, denitrification and anammox was demonstrated.•Long-term stable operation was observed with domestic wastewater as influent.•Efficient nitrogen removal was achieved by synergy of anammox and denitrification.•Accidental introduction of air into the system only caused limited negative effect.•External WAS reutilization promoted nitrogen removal and realized sludge reduction.

This work demonstrates the feasibility of simultaneous nitrogen removal and external waste activated sludge (WAS) reutilization/reduction by using the synergy of sludge fermentation, denitrification and anammox processes in up-flow reactors (SFDA). Pre-treated domestic wastewater and synthetic wastewater (containing nitrite ∼20 mg/L, ammonium ∼10 mg/L in both) were fed to 1# and 2# SFDA, respectively. Long-term operation of 1# SFDA was investigated with achieving the peak ammonium removal rate of 0.021 and nitrite removal rate of 0.081 kg N/(m3 d) as nitrogen loading rate elevated from 0.075 to 0.106 kg N/(m3 d). Negative effect of dissolved oxygen on anammox or fermentation in the 2# SFDA was demonstrated negligible due to rapid depletion by microorganisms. Furthermore, a “net” sludge reduction of 38.8% was obtained due to sludge decay and organics consumption by denitrification. The SFDA process was expected to potentially be used for nitrogen removal and WAS reutilization/reduction in full-scale application.

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