Comparison of the effects of different salts on aerobic ammonia oxidizers for treating ammonium-rich organic wastewater by free and sodium alginate immobilized biomass system.

Partial nitrification to nitrite by aerobic ammonium oxidizing bacteria (AOB) is an important pre-treatment step for subsequent denitrification and anammox. Ammonium-rich wastewater may contain different amounts of organic matter and salts, which can influent the growth and activity of AOB significantly. In this study we investigated the influence of various salts on the performance of a partial nitrification process with free and sodium alginate immobilized biomass. Immobilization of the AOB cells did not have a great effect on the activity of the biomass, and complete inhibition for the immobilized AOB was observed at sulfate, chloride and phosphate concentrations of 500, 1000 and 700 mM, respectively. Free biomass was already inhibited at 300, 500 and 500 mM concentrations of sulfate, chloride and phosphate. Both free and immobilized biomass contained Nitrosomonas europaea/eutropha-like AOB. Compared to free nitrifying biomass, immobilized biomass appeared to be less sensitive to salt stress (maximum 30%). Since no difference in the composition of the AOB was observed between free and immobilized biomass, the protection by the immobilization is the most likely factor explaining the observed differences.