抄録
Nitrification by autotrophic bacteria is sensitive to low temperature and nitrification efficiency decreases in winter, however, the activity can be maintained when phosphate, which is eliminated through a coagulation-sedimentation process in potable water treatment plants, is amended prior to sand and GAC filtration. We examined seasonal changes in the population of nitrifying bacteria during the water treatment process and the effect of phosphate amendment in the laboratory. The population densities of nitrifying bacteria in the biofilm attached to sand and GAC observed in winter were of the same order as those in other seasons. The potential nitrifying activity in winter was about 0.5-to 1.8-fold that in summer when examined at 30°C. Filter sand seemed to be more sensitive to low temperatures than GAC as seasonal deviations in nitrifying activities were larger in sand. The immediate effect of phosphate addition was confirmed using a sand column and the population of ammonia-oxidizing bacteria did not increase significantly after 3 weeks of incubation. Phosphate addition enhanced ammonia-elimination rate more than nitrification products accumulation rate. When nitrifying activity was inhibited by the addition of allylthiourea, the respiration in phosphate-amended culture was more active than in culture without phosphate. Thus a possibility remained that addition of phosphate might have enhanced ammonification by heterotrophic bacteria in the biofilm resulting in an increase in nitrifying activity.
