NITROGEN CHANGES BY THE ALGAE AND BACTERIA IN THE FRESH WATER AND SEAWATER -EFFECT OF LIGHT INTENSITY ON NITROGEN CHANGES-

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To estimate the changes of nitrogen for studies of self-purification of water under the coexistence of algae and nitrifying bacteria, laboratory experiments were carried out using a continuous stirred tank reacter. Particularly, the effect of light intensity on nitrification and/or assimilation was studied in fresh water and seawater. NH_4Cl was fed as the only source of nitrogen to the reacter. One sets of five reactors made of vinyl chloride hard plate were placed in a water jacket tank in which the temperature was maintained at 25ﾟC. The volume and total area of each reactor were 5 liters and 1341 cm^2, respectively. A number of small vinyl chloride hard plates were mounted on each reactor's wall to evaluate the attached biomass. The reactor was mixed moderately with a small impeller at 100 rpm and the water surface of the reactor was illuminated all day long with fluorescent lamps with 10000 lux, 5000 lux, 2500 lux, 900 lux and 80 lux, respectively, at the water surface. The flow pattern of each reactor was completemixing type flow characteristics. Each real hydraulic retention time was 16 hour.CONCLUSIONS 1. In the fresh water system, pH value of the reactors were low. pH value of the reactors become higher as the percentage of sea water higher. pH value of reactors become higher as the light intensity become higher. 2. In fresh water system and sea-water system, SS, COD and chlorophylla concentration increased as light intensity increased because of algae activity. 3. Activity of algae and nitrifying bacteria is greater in sea-water system than in fresh water system.