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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