Immobilization of Nitrifying Bacteria and Its Application for Wastewater Treatment

Methods for effective removal of nitrogen compounds in wastewater by the use of immobilized nitrifying bacteria were investigated. Six gels of natural (k-carrageenan) and artificial (polyacrylamide, photosensitive resin (ENTG3800), urethane polymer, polyelectrolyte polymer and photocrosslinkable resin (PVA-SbQ)) polymers were tested for immobilization of bacteria. Cells immobilized in polyacrylamide and ENTG3800 gels did not show the nitrifying activity, whereas cells in polyelectrolyte polymer complex and PVA-SbQ gels showed stable and constant activity. Therefore the latter two gels were examined to see whether their fundamental characteristics were appropriate for application to wastewater treatment, and their usefulness was evaluated. Although cells immobilized in polyelectrolyte polymer complex gel showed durable and stable nitrifying activity, the high cost and technical difficulty of the preparation represent serious drawbacks. Preparation of PVA-SbQ gel was easy, and immobilized nitrifying bacteria in the gel showed almost the same activity as the free cells. Furthermore, the immobilized cells were more stable than the free cells to low temperature and acidic pH. These results suggest that nitrifying bacteria immobilized in PVA-SbQ gel might be practically useful for removal of nitrogen compounds in wastewater.