To provide a system for efficiently treating and cleaning industrial wastewater, ground water or water of a public water area or the like containing a volatile organic compound including a volatile organochlorine compound using aerobic microorganisms capable of decomposing the volatile organic compound while preventing secondary pollution such as environmental pollution or the like or suppressing the same to the utmost.

An upward funnel or pipe end is fixed to the upper part of an aerobic reaction tank or floated above the aerobic reaction tank, and a water layer containing the volatile organic compound including the volatile organochlorine compound and microorganisms and air are sucked at the same time from the upward funnel or pipe end by the force of a pump and discharged from the interior or bottom part of the tank so as to generate water streams to treat and clean water. As microorganisms, a microorganism group and activated sludge resistant to tetrachloroethylene and capable of decomposing tetrachloroethylene under an aerobic condition can be used.