Highly efficient partial nitrification by polyvinyl alcohol-alginate immobilized cells

Partial nitrification (oxidation of ammonium to nitrite by ammonium-oxidizing bacteria (AOB)) is a critical step in the process of removing biological nitrogen from nitrite. However, nitrite is unstable and easily oxidized to nitrate by nitrite-oxidizing bacteria (NOB) under aerobic conditions. In this study, a polyvinyl alcohol-alginate immobilization technique was utilized to entrap nitrifying bacteria for partial nitrification. The experimental results demonstrated that such immobilization limited the diffusion of dissolved oxygen (DO) into the immobilized cells to inhibit the activity of NOB. In this manner, stable and highly efficient partial nitrification was achieved. Nearly all of the ammonium was converted to nitrite rather than nitrate when the concentration of DO was between 0.5 and 2.0 mg L-1. Partial nitrification was also easily achieved at various concentrations of ammonium. Fluorescence in situ hybridization analysis indicated that AOB was the dominant bacteria in the immobilized cells (representing approximately 96% of the total microbial population).