MANAGEMENT OF BY-PRODUCT SOLIDS GENERATED IN THE PULP AND PAPER INDUSTRY

The U.S. pulp and paper industry generates approximately 15 million dry tons per year of wastewater treatment residuals and other by-product solids such as boiler ash and causticizing residues. This paper provides an overview of the generation, characteristics, and management of these materials.Onsite wastewater treatment is practiced at many pulp and paper mills, and residual solids arise from primary clarification and biological treatment. Major uses for wastewater treatment residuals are combustion for energy recovery, usually done at the mill, and land application as an organic soil amendment. There are examples of many other uses finding full-scale application. These include low-permeability landfill and strip mine caps, animal bedding, industrial absorbents, recovered papermaking fiber and filler, glass aggregate production, synthetic soil ingredient, and compost feedstock.Most mills generate steam for process use and space heating, and many generate electrical power. Wood and coal are the common fuels for these endeavors that yield appreciable ash. Common uses for boiler ash are land application as a liming agent and earthen construction for roadbeds, berms, and other structures. Additional beneficial uses encompass landfill daily cover, cement kiln feedstock, concrete additive, synthetic soil ingredient, soil and waste stabilization, and compost feedstock.Integral to the efficiency of the kraft pulping process is the recovery cycle in which energy and chemicals are obtained from spent pulping liquor. Three solids, collectively known as causticizing residues, are expelled in the recovery cycle: slaker grits, green liquor dregs, and excess lime mud. Land application as a liming agent is probably the most commonly practiced beneficial use. Other possible uses include cement kiln feedstock, wastewater neutralization, landfill daily cover, and clay brick additive.Although disposal in landfills is still the major means of management for paper industry byproducts, the level of beneficial use is significant. Paper companies are actively seeking beneficial use opportunities, and novel uses are increasingly explored and utilized.