Fast recovery of a single-stage partial nitrification/anammox-based hybrid bioreactor impacted by a sudden lactose shock load

Abstract

This study reports the recovery of single-stage partial nitrification (PN)/anammox bioreactor treating nitrite-free and ammonium-rich synthetic wastewater affected by a high concentration of lactose (2000 mg/l). The lactose shock led to the collapse of the PN/anammox process in <24 h. Major negative effects included significant washout of the suspended biomass and detachment of biofilm, changes in the colour of the biomass from reddish to blackish, and a significant drop in ammonium removal efficiency from 95% to <5%. Batch tests with biomass exposed to the lactose-free and lactose-containing ammonium-rich medium suggested that the lack of sufficient nitrite production during the PN process was the limiting factor for the low activity of anammox due to the limited oxygen available to the aerobic nitrifiers. The reduction of lactose from 2000 to 200 mg/l and temperature increase from 25 °C to 30 °C, led to the full recovery of the PN/anammox process in <40 days.