Nitrification performance evaluation of activated sludge under high potassium ion stress during high-ammonia nitrogen organic wastewater treatment.

l The enrichment of AOB under K+ stress ensured the efficient ammonia oxidation. l High K+ stress inhibited NOB activity and deteriorates the NO 2 −-N oxidation. l High K+ stress accelerates sludge settlement and enriches biomass in SBR. l The K+ concentration do not exceed 5.23 g/L to ensure efficiency of SBR. The recycling reverse osmosis (RO) membrane concentrate of some high-ammonia nitrogen (NH 4 +-N) organic wastewater to the biological unit could cause potassium ion (K+) accumulation, thereby affecting the removal of NH 4 +-N by activated sludge. Thus, the effects of high K+ stress on activated sludge nitrification performance was studied. The results showed that the high K+ stress promoted the floc sludge to produce more extracellular polymers (EPS), which accelerated the sludge sedimentation and enriched the biomass in sequential batch reactors (SBRs). The ammonia oxidation process and nitrite (NO 2 --N) oxidation process were further analyzed in the nitrification process. High K+ stress enriched ammonia oxidizing bacteria (AOB), which ensured the efficient ammonia oxidation process in SBRs, and ensured the removal rate of NH 4 +-N was maintained above 93%. However, high K+ stress (15g/L KCl) inhibited the activity of NO 2 −-N oxidizing bacteria (NOB) and reduced the abundance of NOB, thus leading to the accumulation of NO 2 −-N, and finally worsened the nitrification performance of activated sludge. In short, the performance of activated sludge will not be inhibited when the K+ in the wastewater does not exceed 5.23 g/L. The results could provide a reference for the optimization of the biological performance in treating high-NH 4 +-N organic wastewater with activated sludge coupled RO membrane treatment process. [Display omitted] [ABSTRACT FROM AUTHOR]