Abstract: A treating apparatus for drying wet sludge in batches or continuous feed which is circulated through the apparatus. The apparatus includes conveyor means for circulating the wet sludge in a closed loop and means for heating and circulating the dryer air around and about the conveyor means without contacting the sludge itself. It also includes means for heating and circulating cleaning air through the sludge to dry the sludge as it is circulating in the closed loop. A sensor is provided for determining the moisture content of the sludge and means are provided for discharging the sludge from the conveyor circulating means when the moisture content in the sludge reaches a predetermined level. A measured amount of cleaning air is drawn into the conveyor means from the atmosphere and circulates through the sludge itself to assist in drying and cleaning the sludge. This air is then withdrawn from the interior of the conveying means and exhausted through a cleaning means into the atmosphere.