Hydrocarbon and combustion products are collected in the wash water, which is circulated while operating in close mode. The Wash Water Treatment Unit which is installed to remove (purify) impurities, consists of a sludge settling tank and device that removes moisture from the sludge, for the maximum performance. A high speed coagulator using an inclined slate is applied with the precipitation device and the condensed facility of sludge contained in scrubber wash water, and this equipment is based on the f act that precipitation area has a greater effect on precipitation efficiency than duration time. The sludge, which is condensed in the settling tank, is re-condensed and the water and sludge are separated and the separated water is stored in the wash water tank and holding tank while the sludge is dehydrated again to decrease water content and minimize the amount of sludge that is discarded.