NOVELTY - Water treating unit (1) comprises ammonia concentration measuring device (11) to measure ammonia-nitrogen concentration of natural water. A water quantity adjustment mechanism branches natural water and adjusts the branched water quantity ratio. Biological-oxidation processing mechanism performs biological-oxidation processing of the natural water in a mixing tank (14). A chlorine agent addition apparatus (16) adds a chlorine agent to the mixing water. A UV-irradiation device (20) irradiates a UV-ray to the chlorinated water.    USE - Water treating unit for processing ammonia contained in natural water. Can also be used in water-purifying processing, environmental clean-up, industrial water treatment, sewage treatment, and waste water treatment.    ADVANTAGE - The water treating unit provides branching of in a part of natural water, and the biological-oxidation processing is carried out. After combining the biological treatment water and the remaining natural water, a chloric acidized processing and UV-irradiation processing are performed. The branched water quantity ratio is adjusted according to the ammonia-nitrogen concentration in natural water. The water treating unit and the water-treatment method reduce the use of chlorine.    DETAILED DESCRIPTION - Water treating unit for processing ammonia contained in natural water, comprises ammonia concentration measuring device to measure the ammonia-nitrogen concentration of natural water. A water quantity adjustment mechanism branches natural water and adjusts the branched water quantity ratio according to the ammonia-nitrogen concentration in the natural water. Biological-oxidation processing mechanism performs biological-oxidation processing of the natural water. A mixing tank mixes the biological treatment water by which the biological-oxidation processing was carried out, and the remainder of the natural water. A chlorine agent addition apparatus adds a chlorine agent to the mixing water. A UV-irradiation device irradiates a UV-ray to the chlorinated water. An INDEPENDENT CLAIM is included for a water-treatment method of processing ammonia contained in natural water comprising utilizing the above water treating unit.    DESCRIPTION OF DRAWING(S) - The figure shows a schematic view of water treating unit (Drawing includes non-English language text).    Water treating unit (1)    Ammonia concentration measuring device (11)    Mixing tank (14)    Chlorine agent addition apparatus (16)    UV-irradiation device (20)