Abstract: A process for treating a water containing chlorinated organic compounds, wherein a microorganism is introduced from a degradation tank to a separation tank and an energy source is supplied to the microorganism separated in the separation tank. A water-treatment apparatus having a structure capable of continuously introducing water to be treated through a degradation tank, a separation tank and a reactivation tank. A loss of the energy source such as methane or propane discharged from the separation tank can be reduced. A water-treatment apparatus having a degradation tank and a separation tank, wherein a microorganism can be cultivated in the separation tank. The reactivation tank can be omitted, whereby the entire size of the apparatus can be reduced.