The enhanced mineralization of organic nitrogen by bacteriophagous protozoa has often been reported, hoever, the effects of the protozoa on nitrification are not well known. In this study, the effects of Testacealobosia Arcella vulgaris on nitrification were investigated by batch culture experiments. A. vulgaris could grow well with two kinds of nitrifying bacteria, Nitrosomonas europaea and Nitrobacter winogradskyi. These results indicate that the predation of nitrifying bacteria by A. vulgaris may affect the biomass of nitrifying bacteria and nitrification activity in the food chain. Experiments in semi-continuous culture of A. vulgaris and nitrifying bacteria indicated that nitrification efficiency and activity of nitrifying bacteria were increased in the presence of A. vulgaris. The same tendency was found in the mixed culture system of A. vulgaris and activated sludge whose protozoa and micrometazoa were killed by heating with water bath for 5min. at 45°C. Nitrification efficiency was improved by adding a large number of A. vulgaris because of the increase of the activity of nitrifying bacteria, though the number of nitrifying bacteria decreased.
