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

The recycling reverse osmosis (RO) membrane concentrate of some high-ammonia nitrogen(NH4+-N) organic wastewater to the biological unit could cause potassium ion (K+) accumu-lation,thereby affecting the removal of NH4+-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 (NO2-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 en-sured the removal rate of NH4+-N was maintained above 93％.However,high K+ stress (15g/L KC1) inhibited the activity of NO2-N oxidizing bacteria (NOB) and reduced the abundance of NOB,thus leading to the accumulation of NO2-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 pro-vide a reference for the optimization of the biological performance in treating high-NH4+-N organic wastewater with activated sludge coupled RO membrane treatment process.