Pulp and Paper Industry Environmental Management

Author: Chief Editor: Lin Yuan
Publisher:
Publish Date: 1998-06-01
Features: Paper is an indispensable part of modern life, and the global paper consumption continues to grow. However, the papermaking industry consumes a significant amount of resources, and if not managed properly, it can have a substantial impact on the environment. Various raw materials such as wood, bamboo, sugarcane residue, grasses, and secondary fibers can lead to severe environmental consequences if their production is not carried out sustainably in terms of planting, cultivation, harvesting, transportation, and processing. Many paper mills use large amounts of water, resulting in considerable wastewater discharge. If production operations are not properly controlled, it can lead to the loss of a large amount of chemicals and fibers during the process. Most paper mills also consume a significant amount of power and energy for material transportation and heating, with most of the thermal energy derived from fossil fuels. In recent years, to reduce adverse environmental impacts and improve environmental management, pulp and paper companies have been committed to developing and adopting clean technologies. Through these methods, pulp mills or paper mills can now achieve very high environmental standards. However, most of the work has focused on large-scale wood-based pulp and paper mills, which only addresses the specific conditions of advanced industrial countries and pays little attention to the needs of smaller paper mills in developing countries. Since the early 1980s, the United Nations Environment Programme (UNEP) has been attempting to promote the development and adoption of clean technologies in the pulp and paper industry and has recognized the need to summarize clean production methods and control technologies applicable to small and medium-sized paper mills in the form of reports. This technical report is a document discussing the possibility of achieving clean production in smaller pulp and paper mills, which can be used for education and training, as well as for the planning, development, and implementation of environmental management systems to achieve the goal of reducing environmental impacts. Many examples in the technical report are derived from the collaboration between UNEP and companies.
Pulp and papermaking use three main fiber raw materials: wood, non-wood plants, and recycled paper. Most non-wood fibers come from agricultural waste, and these crops are not specifically grown and harvested for papermaking purposes. Their environmental impact is related to the use of land, water, fertilizers, and pesticides during cultivation, so this report also briefly introduces the precautions to minimize these impacts during harvesting or processing. Wood fibers can be sourced from slow-growing natural forests, which may not necessarily be the most reliable sustainable fiber resource for pulp and papermaking. From a long-term perspective, how to reasonably log papermaking forests is indeed a problem. However, to date, wood plantations also face certain environmental regulations regarding the planting, cultivation, and harvesting of trees. In the face of these challenges, various suggestions have emerged, aiming to solve problems while meeting environmental requirements and social intentions. These suggestions come from various countries and international organizations.
Recycled paper is the third source of raw materials for papermaking, and the environmental impact of its reuse largely depends on the collection methods and the quality requirements of the paper produced. If the appropriate grade of recycled paper is selected, it can significantly improve the quality of the final paper, but it will also affect production costs and the environmental impact of secondary fiber processing. In some cases, burning recycled paper to recover heat may be more suitable for use than papermaking. During the pulping process, fibers are separated (bleached if necessary) through mechanical or chemical methods and then processed to obtain the optimal fibers required for the final paper. The wastewater discharged carries soluble substances, solid materials (mainly fibers and bark pieces), and inorganic compounds. The pulping process and related operations (such as preparation, power generation, or alkali recovery) not only produce solid waste but are also major sources of wastewater and air emissions. Currently, clean technologies have emerged to reduce the environmental impact of sulfite pulping, particularly high-efficiency washing technologies and spent liquor recovery technologies. It is especially noteworthy that if a chemical pulp mill has a high rate of spent liquor recovery and waste residue utilization, it can achieve complete self-sufficiency in energy and fuel supply, thereby significantly reducing the environmental impact of production energy. Currently, systems such as delayed cooking, improvements in bleaching methods, high-efficiency washing, and chemical recovery are primarily developed and applied in large-scale wood pulp paper mills. From an ecological and economic perspective, it is crucial to make similar, effective technologies available to small and medium-sized paper mills. Experiences from China and India have shown that selecting high-efficiency washing equipment and chemical recovery systems for pulp mills with an annual output of over 50,000 tons can achieve technically feasible and economically reasonable results.
Non-wood fiber pulping processes often face high silicon content issues, which increase the viscosity of the black liquor and make pumping difficult. Introducing flue gas into the black liquor for carbonation treatment can lower its pH value, thereby controlling the precipitation of silicon and achieving the purpose of removing silicon. This method has been validated through expanded pilot and industrial trials. Other methods for removing silicon, such as precipitation from green liquor, have not yet been widely recognized in production practice. Another important issue to address is the discharge of air emissions, particularly those from chemical pulping and power generation processes. Combustion processes must be controlled to minimize the emission of sulfur and nitrogen. Common methods such as electrostatic precipitators and water membrane precipitators reduce the emission of gaseous and particulate air pollutants. Toxic compounds produced during the sulfite pulping process can be collected at the source and sent for combustion.
The environmental impact of the papermaking process is generally much lower than that of pulping. Through the combination of clean technologies and effective wastewater treatment, all types of paper mills can achieve a high level of environmental protection. The wastewater from paper mills mainly contains suspended solids and some dissolved solids. The power and thermal energy required for papermaking processes come from steam, which is typically generated by boilers and then used for power generation. Most boilers are coal-fired, so effective measures must be taken to control the generation and emission of pollutants. In terms of wastewater and waste management, as long as clean technologies are applied to fundamentally reduce the generation of wastewater and waste, the best environmental benefits can often be achieved. If appropriate clean technologies are not available and the current situation cannot be changed, or if the reduction in emissions still does not meet the requirements of wastewater discharge standards, pollution control devices must be installed. Wastewater treatment involves removing suspended solids and dissolved organic matter, typically using sedimentation/flocculation methods and various biological treatment methods. This report also discusses the disposal of sludge and precipitates from treatment facilities. Additionally, it addresses the issue of using wastewater for irrigation instead of discharging it into water bodies.
Pulp and papermaking produce various solid wastes. The first step in waste management is to conduct a waste stream audit. For this, appropriate clean technologies should be adopted to achieve efficient resource utilization and substantial economic benefits. Waste should be recovered and used as raw materials and energy whenever possible, with final disposal being considered only as a last resort. Establishing a system with clear objectives, reliable operation, and strict monitoring is key to effective waste management. The same principles also apply to noise control in all operational areas and surrounding communities. To promote the sustainable development of environmental protection, governments should propose stricter regulations and standards, strengthen environmental planning, pollution control, waste management, and environmental auditing to make them more comprehensive. In the face of these regulations and increasing environmental challenges, industrial enterprises are adopting more standardized work methods to make better use of resources when addressing environmental issues. Enterprises are increasingly using management tools such as environmental impact assessments, environmental audits, life cycle analysis, and emergency preparedness, which may become legally required methods. Additionally, efforts are underway to develop formal environmental management systems (EMS). In this regard, some regional and purpose-specific standards have emerged, such as the European Union's Eco-Management and Audit Scheme (EMAS) and the ISO 14000 series of standards proposed by the International Organization for Standardization, which cover EMS aspects for all.
Fragment: 2.1 Resource Utilization
The basic concept of pulping is to process raw materials to produce fibers with the properties required for papermaking. Fiber raw materials can be broadleaf or coniferous wood, non-wood plants, and agricultural waste (such as bamboo, grasses, and sugarcane residue), textile fibers, or recycled fibers. There are various pulping processes available, each suitable for different fiber raw materials and different papermaking requirements. In the pulp and papermaking process, water is primarily used as a medium for fiber transportation and sometimes creates conditions for chemical reactions to occur. Most pulping processes use chemicals to separate fibers, bleach them to the required brightness, and also for specific purposes (such as controlling sedimentation in pulp ponds or the increase of sludge). All pulping processes require power-driven pumps, grinders, conveyors, and other equipment, while thermal energy provides the necessary temperature to ensure the occurrence of chemical reactions. Figure 2-1 briefly outlines the fundamental principles common to all types of pulping processes. The main output of pulping is pulp, but it also discharges residual substances and energy into the atmosphere and water bodies. The main components discharged into the atmosphere are evaporated water from liquids, equipment, and boilers. The pulping process also produces small amounts of gaseous inorganic compounds, which are gases and dust from the chemicals used in production. Additionally, the discharged substances may contain small amounts of volatile organic compounds from the fiber raw materials (such as extractable substances) and products of chemical reactions between chemicals and fiber raw materials (such as organic sulfides). Most of the production water is eventually discharged as wastewater, carrying residual chemicals and dissolved fiber chemical components. Chemical pulping processes have an effective chemical recovery system that can recover nearly 100% of the chemicals used in pulping, with the remaining portion being discharged along with waste chemicals generated during the bleaching process. Mechanical pulping and secondary fiber pulping chemicals are completely discharged. The residual fiber raw materials can be solids (fiber fragments, bark) or dissolved carbohydrates and metal ions, with waste heat generally dissipated through steam and hot wastewater. These basic characteristics of the pulping process also exist in the papermaking process. Of course, the water consumption, energy consumption, and chemical usage in papermaking are typically much lower than in pulping, resulting in lower pollution loads in wastewater. In addition to environmental impact, water, energy, and raw materials that are not used in the product but are discharged from the production process also cause waste of resources and capital. The main wasted material is fiber. Bamboo or sugarcane residue stored for too long can easily rot, resulting in low production volume and quality. If black liquor is not utilized, it means wasting fuel and chemicals that could be reused in the production process. Excessive fiber loss in the papermaking process also equates to using more expensive pulp. Resource management in the production process should aim to minimize input and loss. At the same time, efforts should be made to find other uses for residual materials that cannot be utilized. To achieve this overall goal, multiple approaches are needed, including on-site management, investment in equipment upgrades, establishing an environmental management system, and conducting these activities in an orderly manner to improve economic efficiency.