During normal summer operations, each pump is on 2 minutes and off 13 minutes. Each thickener has a surface area of 380 square feet and a side water depth of 10 feet. Solids are held in these units for several hours to thicken. Gravity thickened primary sludge can be withdrawn from any one of the three gravity thickeners by an individual centrifuge sludge-feed pump. Thickened sludge to the centrifuges contains an average of seven percent solids.
Polymer solution is added to the sludge feed prior to dewatering.
Kaolin clay and lime are added to the dewatered sludge cake prior to incineration to inhibit clinker formation. Centrifuge centrate is returned to the head of the plant. Scrubber water, which contains ash and particulate matter, is sent to a common ash decant tank and the decant liquid is returned to the head of the plant. Both incinerator units are operated continuously during the summer except during maintenance downtime. During the off-season months, one incinerator is used at a time, alternating north and south incinerators.