Abstract: A sewage disposal plant comprising a deep-well type sewage treatment tank, which is provided with string-shaped contact members stretched therein, and which minimizes the installation area; a circulator pipe inserted into the sewage treatment tank and having a venturi portion at an intermediate section thereof; and an air intake pipe inserted into the circulator pipe extending into the venturi portion thereof, whereby exposure air can be sucked into the venturi portion of the circulator pipe naturally without using a compressor, thus saving power. Said string-shaped contact members has therearound ring type fuzzy hairs consisting of fibers.