Management of Pulp and Paper Mill Waste

The production of paper consumes high quantities of energy, chemicals and wood pulp. Consequently, the paper production industry produces high environmental emission levels mainly as carbon dioxide due to energy consumption, or solid waste streams which include wastewater treatment sludges, lime mud, lime slaker grits, green liquor dregs, boiler and furnace ash, scrubber sludges and wood processing residuals. In terms of volume, most solids or liquids are those from the treatment of effluents, although waste from wood is also produced in large quantities. Wastewater treatment plant residuals are the largest volume residual waste stream generated by the pulp and paper industry. The general background of waste management in pulp and paper industry are presented.

In the Pulp and Paper Industry several types of solid wastes and sludge are generated. Solid waste is mainly produced from pulping, deinking processes and wastewater treatment. The waste generation is strongly affected by the production process and wastewater treatment technologies. About 40–50 kg of sludge (dry) is generated in the production of 1 tonne of paper at a paper mill and of that approximately 70 % is primary sludge and 30 % secondary sludge. The amount of sludge on a dry mass basis may vary from 20 % in a newsprint mill to 40 % in a tissue mill. The data on waste generated in pulp and paper mills and deinking mills are presented in this chapter. Waste generated through production of different paper grades from recycled fibre are also presented.

The composition of waste generated in pulp and paper industry are presented. The composition of sludge depends on the raw material, manufacturing process, chemicals used, final products and the wastewater treatment technique. In case of recycled papers, it also depends on the type of paper used and the number and types of cleaning stages used in the recycling operation. The wastes are generated at different stages of the production process namely in the debarking, chipping, screening and cooking liquor clarification operations, in the maintenance of the plant and also in the treatment of fresh water and wastewater. The main solid by-products are lime-mud, green liquor sludge (dredge), recovery boiler ash, grits, bark, ashes and wastewater treatment sludge. If bark and other wood residues are not burned for energy recovery, they would represent the major fraction of the residues. Green liquor, lime mud and sludge mainly consist of calcium carbonate. Ash from the recovery boiler mainly consists of sodium sulphate and, to a lesser extent, sodium carbonate. Bark ash consists mainly of calcium oxide/ calcium carbonate and potassium salts. Grits mainly consist of calcium carbonate. Sludge from primary clarification consists primarily of fibres, fines and inorganic material in mills that employ fillers in their products. Sludge from biological treatment contains a high proportion of organic material. This sludge and the sludge from primary clarification represent the bulk of the wastes when using virgin fibres. Waste sludges from a mill using secondary fiber differ from a mill using virgin materials, not only by amount but also by composition.

Pretreatment technologies of sludge – thickening, conditioning, dewatering, drying – are discussed. Thickening is a fundamental stage of sludge pretreatment. Pre-dewatering technologies include rotary sludge thickeners, gravity thickeners, dissolved air floatation clarifiers and belt presses. The most widespread thickening method is gravity thickening. Sludge from wastewater treatment plants is frequently conditioned, using chemical or physical means to alter the floc structures of the sludge imparting sufficient stiffness and incompressibility to the structures so that water entrained in the sludge can rapidly be drained through filtering or other means. Dewaterability of the sludge is very important because it determines the volume of waste that has to be handled. Dewatering of sludge is performed by using vacuum filters, belt filter presses, centrifuges, and membrane filter presses. Centrifuges and belt filter presses are currently the most popular dewatering methods due to their good operation and cost efficiency. The primary sludges can be dewatered easily as these are high in fiber and low in ash. The most difficult are the solids from the high-rate biological treatment systems. The primary sludge most difficult to dewater is that containing ground wood fines. Drying of sludge using flue gases from combustion process is a standard method. Fluidized bed dryers, rotary dryers, and multiple hearth dryers are found to be effective for sludge drying.

New Technologies – Pyrolysis, Direct liquefaction, Wet Air Oxidation, Super Critical Water Oxidation, Steam Reforming, Gasification (Plasma Gasification, Super Critical gasification) for energy recovery from waste are discussed. The operating conditions (temperature, pressure, atmosphere and products, etc.) vary among the methods. For example, gasification and SCWO methods utilize air or oxygen while some methods are conducted under oxygen depleted or anaerobic conditions. Pyrolysis and gasification operate at high temperatures; Pyrolysis targets a high yield of oil, and gasification favors production of gas. The greatest sludge volume reduction (over 90 %) can be achieved with the high-temperature methods which is advantageous as it effectively reduces the physical amount of sludge for disposal. The major disadvantage for these high-temperature processes is their lower net energy efficiency for the treatment of secondary sludge containing very high content of water, resulting from the need of the energy intensive operations of dewatering/thickening and complete evaporation of the water in the sludge. In contrast, the other treatment methods, i.e., direct liquefaction, SCWO operate at a relatively lower temperature and more importantly without the need of dewatering /thickening and complete evaporation of the water in the sludge. Accordingly, these methods are more promising for the treatment of secondary sludge from the standpoint of energy recovery.

Utilization of Pulp and Paper mill solid waste for Landfilling, Land application (Composting), Vermicomposting, Incineration, Recovery of Raw Materials, Production of Ethanol, Production of Lactic acid, Production of Animal Feed, Pelletization of Sludge, Anaerobic digestion, Paper and Board industry (Fiberboard products, Moulded pulp, Millboard, Softboard), Mineral Based Products (Cement and cementitious products Cement mortar Pozzolanic material, Concrete Ceramic material Lightweight aggregates, Plasterboard Insulating material), Wood adhesive, Sorbent production, Filler in nylon biocomposite production, Landfill Cover Barrier, Bacterial Cellulose and Enzymes, Cellulose-based specialty products, Nanocomposites, Paving and fibrous road surfacing additives are presented.

Examples of Pulp and Paper Mill Waste Implementation are presented. Several Pulp and Paper mills – April, Inc. mills, Cartiere Burgo Verzuolo, Italy, Cartiere Burgo Mantova, Italy Jamsankosken Voima Oy, Finland; Aanevoima Oy, Finland; Vamy Oy/Vattenfall Oy, Finland; Modo Paper AB Husum; Sweden; Monsteras, Sweden; Elektrocieplowni Ostroleka, Poland; Metsa-Serla Oy Simpele, Finland; Oy Metsa-Botnia Kaskinen, Finland Boise mills, The Catalyst Paper mill, International Paper, Neenah paper, Nippon Paper Group, Norske Skog’s modern mills, Stora Enso, Parenco paper mill, Duluth Mill, Minnesota Paper mill. Metsäliitto Group mills, Nippon Paper Company, VAR (a recycling company) – are implementing a number of waste stream reduction and re‐use initiatives.

It is necessary to continue research on different applications of wastes, while taking into account the environmental and economical factors of these waste treatments. Pulp and Paper mills are already implementing a number of waste stream reduction and reuse initiatives. Some additional considerations for greater participation include: Resource savings and resource efficiency; Substituting fossil energy sources for waste based sources and on site composting can be a potential source of carbon credits for mills participating in emerging carbon markets; Waste products can be used to support mills’ infrastructure with such items as road building components, soil amendments, fuel for electricity, and construction materials. Future research by government and non profit organizations as well as the industry will reveal the extent of potential cost savings associated with these options for waste stream. However, the minimisation of waste generation still has the highest priority.