there is disclosed a pulsating sludge bed clarifier especially for the treatment of low turbidity waters , which uses incline plates in the sludge bed and some recirculated sludge . the clarification is greatly enhanced by recirculating a relatively small part of the sludge concentrate to a reactor chamber used for the premixing of water to be treated and the coagulant . the small amount of recirculated sludge cuts down significantly on the polymer flocculant , which is the most expensive chemical in the process that is required to be used , and can also serve to improve the adsorption of colors and similar materials , increase the density of the sludge blanket , and improve the rate of throughput of the system .