Persistence of Nitrite-Oxidizing Bacteria in Entrapped Cell-Based Partial Nitrifying Reactor Treating Ammonia-Rich Wastewater

A phosphorylated-polyvinyl alcohol (PPVA) entrapped cell-based reactor was employed to promote partial nitrification for ammonia-rich wastewater treatment. High partial nitrification (66% of nitrite accumulation in average) was achieved along the 165 days of operation indicating that the majority of nitrite-oxidizing bacteria (NOB) activity was suppressed probably as a result of low oxygen environment created within the PPVA gel matrix. However, some portion of nitrate (5-17.6% of the influent ammonia) always appeared in the reactor throughout the operation period. Next-generation sequencing and clone library techniques revealed that NOB with different substrate affinities including Nitrobacter, Nitrospira lineage I and II existed within the gel matrix. The finding speculates that substrate gradient-like microenvironment within the gel matrix probably serves the different physiological groups of NOB to maintain their cells and activities in the reactor. Therefore, instead of using low oxygen environment in gel matrix as a sole control strategy, an additional strategy like promoting free ammonia inhibition in reactor is also needed to affirm the stability of long-term partial nitrificatio