Management of Wastewater Treatment Sludges

Abstract

A variety of solid wastes are generated by pulp and paper mills that need final disposition. In addition to bark, wood waste, boiler ash, pulping residuals, and mill trash, it also generates wastewater treatment sludges like deinking sludge, primary clarifier sludge, and biological sludge. The quantity of sludges varies from site to site. On average, Canadian pulp and paper mills with activated sludge wastewater treatment system produce primary sludge of 31 kg(od)/ton of pulp while the secondary (biological) sludge generation is 16 kg/ton (Table 10.1).1 A typical floatation deinking plant produces 80-150 kg of dry sludge/ton of recycled pulp.2 Table 10.2 illustrates how the quantity of sludge generation varies with the type of pulping and paper making or both.3 In the US, an NCASI study indicated that in 1988,50 kg/ton of wastewater treatment sludge was generated averaged across the industry as a whole. Primary sludge accounted for 18%, secondary sludge 7%, and deinking sludge 2% of all the solid waste generation in US pulp and paper industry in 1986.4 The US industry generated approximately 4.6 million tons of dry sludge solids in 1989.4