Use of pulp and paper sludge to improve performance of topsoil layer in a landfill capping system

Sludge is one of the major solid waste products in the pulping process. It consists of wood fibers, fines, some inorganic fillers, and water. Prince George mills produce approximately 11,000 wet tons of sludge annually. Presently, the sludge is either landfilled or incinerated causing potential environmental problems. Pulp mill sludge may be used as soil amendment in the topsoil layer of a landfill cap to enhance plant growth and minimize the formation of cracks, hence reduce erosion and infiltration problems.;The objective of this research was to chemically and physically characterize sludge from two different pulping processes and to investigate their suitability as soil amendment in the topsoil layer of a landfill cap.;Chemical analysis of both sludge samples revealed that metal concentrations were below maximum allowable concentrations for municipal sewage biosolids. Both sludges have a high C:N ratio and a neutral to alkaline pH. The N immobilization and pH adjustment could be addressed with appropriate fertilization. The type of sludge under consideration will determine the fertilizer composition to enhance plant growth.;The high organic content and fibrous structure of the sludges decreased the bulk density of the soil and increased its water holding capacity. Water holding capacity (WHC) was determined by gravity and moisture retention curves were established for sludge and soil samples, various sludge-soil mixtures and sludge-soil layer systems. BCTMP sludge samples had a higher WHC than the soil, resulting in higher water retention and higher amount of plant available water. Kraft mill sludge samples showed the opposite effect on WHC, water retention and plant available water. Soil amended with increasing amounts of sludge resulted in increasing water retention. Layering systems showed that the soil layers exhibited attributes of constant WHC, while the sludge layers varied depending on their position within the layer system.;These attributes of the sludge used in this research would improve the performance of the topsoil layer with less environmental impact than current disposal options. The results and conclusions are not necessarily applicable to any sludge in the pulp and paper industry.