Methods to improve dewatering in industrial and municipal sludges are described. One method involves admixing sludge from a papermaking process and modified cellulose to provide modified sludge with the modified cellulose present in an effective amount to improve dewatering in the treated sludge, such as in allowing use of reduced amounts of coagulant and/or reducing dewatering times, increased dewatered volumes, and reduced sludge product moisture contents, and the like. The dewatered sludge may be formed into a dried particulate, and may be used as filler or other component of concrete, rubber, asphalt, plastics, resin-wood composite products, and other composite products.