Secondary sludge pumping is part of the treatment plant process. It includes return activated sludge (RAS), which is continuously pumped back into the secondary biological treatment tank as part of the treatment process, and waste activated sludge (WAS), which is excess from settled sludge that is pumped to the sludge handling process. Dewatering is typically the last step before disposal of sludge from secondary treatment and external sources. Sludge volume decreases by removing the water content in order to create a thicker and more manageable mass. Dewatering may also reduce handling costs and minimize leachates and odors at landfills.