1 Status Quo of Pollution Control in China's Paper Industry
According to statistical data in recent years, the national wastewater discharge from the pulp and paper industry accounts for about 10% to 12% of the total national wastewater discharge, ranking third; the CODcr in the discharged sewage accounts for about the total amount of emissions in the country. 40% to 45%, ranking first. The paper industry is one of the major industries polluting the environment in China.
Wastewater in pulp and paper production is mainly digested waste liquid, middle-stage waste water and papermaking white water. The pollution load of cooking waste liquid accounts for about 80% of all pulp and papermaking wastewater, and is the most important source of pollution, followed by the middle-stage wastewater. White water recycling technology has been widely promoted in China. Large-scale paper machines generally use multi-disk filters. SMEs use air flotation tanks or multi-disc filters to recover white water, so that white water can be fully reused, and some have achieved closed circulation. There is no technical obstacle to the pollution control of white water in papermaking. The pollution control of cooking waste liquid and middle-stage wastewater is the key and difficult point in pollution prevention and control in China's paper industry.
The pollution treatment of wood pulp and papermaking cooking waste liquid, whether it is alkaline or acid pulping, in the international, the technology has matured: alkali wood pulp cooking black liquor alkali recovery by burning, acid wood pulp cooking waste liquid The pollution problem has been solved through comprehensive utilization. The pollution of the middle-stage wastewater has also been resolved due to the use of elemental chlorine (ECF) and total chlorine-free (TCF) bleaching processes to eliminate the pollution of dioxins and other toxic compounds in the bleaching process. From a perspective, it has largely been resolved. At present, the pollution caused by the paper industry is even lower than that of domestic garbage and agriculture.
In China's papermaking raw materials, wood raw materials account for a very small proportion. In self-pulp, the proportion of wood pulp is less than 10%. Domestic chemical pulp mills using wood as raw materials basically all have an alkali recovery system. The alkali recovery rate can reach over 90%. Although the recovery rate is still lower than the international advanced level, it works well. The small-scale production of bleached wood pulp in the middle-stage wastewater, due to the use of traditional CEH three-stage bleaching, has not yet solved the dioxin contamination problem, but it can also meet the standard discharge after two levels of treatment.
China's papermaking raw materials are mainly non-wood raw materials, and non-wood raw materials are mainly wheat straws. The pulping method is mainly based on the alkali method, and there are still a small amount of acid pulping and ammonium sulfite pulping. The characteristics of non-wood cooking waste liquid are very different from those of wood raw materials. In addition, the pulp and paper companies that use non-wood as raw materials in China generally have the problems of small scale and relatively backward equipment. China's non-wood raw material pulping and papermaking wastewater pollution control level lags far behind the world average, there are many problems and problems, is the most important source of pollution. It is estimated that the annual output of wheat straw alkaline chemical pulp in China is about 3.4 million tons, and the amount of alkali used is about 1 million tons per year. At present, most companies do not have a matching alkali recovery system. Less than 5% of the base is recovered by the alkali recovery system, and more than 95% of the caustic soda is dissolved into the body of water together with dissolved organics. The national wheat straw CODcr emissions account for more than 74% of the total paper industry emissions.
Non-timber pulp and bagasse pulp, due to their black liquor alkali recovery system, achieved normal operation earlier, and most companies that use these materials have built alkali recovery and supporting mid-stream water treatment systems. Up to 80%, the bagasse pulp alkali recovery rate reached 78%, and the integrated wastewater can meet the discharge standards.
The Chinese government attaches great importance to the serious water pollution problem in the papermaking industry. As early as 1984, the State Council issued the "Regulations on Strengthening the Environmental Management of Townships and Street Enterprises", stating clearly that township and street enterprises are not allowed to engage in serious polluting production projects such as pulp and papermaking. The Ministry of Industry of the People's Republic of China formulated the “Planning and Implementation Rules for Water Pollution Prevention and Control of the Paper Industry†in 1986. In 1988, the State Environmental Protection Commission and the Ministry of Light Industry jointly issued the “Regulations on the Prevention and Control of Water Pollution in the Paper Industryâ€. However, due to people’s lack of awareness of the importance of protecting the environment a few years ago, the lack of environmental protection law enforcement and the fact that some regions are relatively economically backward, a large number of small and medium-sized paper mills without any pollution control measures continue to emerge, resulting in water for the papermaking industry. The pollution situation has reached a very serious level. In order to protect the environment, prevent pollution, and achieve sustainable economic development, our government has further strengthened environmental protection measures and law enforcement. In 1996, the State Council issued the "Decision on Strengthening Several Issues Concerning Environmental Protection" and requested that small-scale pulp mills with an annual output of no more than 5000 tons be closed before September 31, 1996, and that all industrial pollutants emitted by To meet national or local standards. By the end of 1996, a total of more than 4,000 small paper mills had been shut down across the country, significantly reducing the pollution of the paper industry.
2 Research and Exploration on Wastewater Treatment Technology by China Paper Industry
As already mentioned, the straw black liquor is the most important source of pollution in the paper industry in China. The traditional combustion alkali recovery of cooking black liquor is a mature technology using wood pulping and papermaking. Alkali recovery can not only control the pollution of cooking waste liquid, but also recover alkali and energy from black liquor, reduce pulping cost and sewage treatment cost, and is an indispensable part of the alkali pulp mill.
However, there are many technical problems in wheat straw black liquor alkali recovery. 1. Due to the large amount of fine fiber components in the wheat straw raw material, the poor drainage performance of the slurry and the low black liquor extraction rate. The current best extraction rate can reach 80% to 85%. 2. The viscosity of the black liquor is large, storage and transportation are difficult, the concentration of the black liquor is low, and the black liquor has poor combustion performance. Generally, the concentration of black liquor from the evaporation station is about 40% to 43%, and after passing through the disc evaporator, the concentration is 45% to 48%, which is far lower than the furnace black liquor concentration. 3. The silicon content in raw materials is high, and the evaporator is easy to foul. Low evaporation intensity. Due to the high silicon content, the white mud is poor in filtration and sedimentation and cannot be recycled.
These characteristics of the wheat straw raw material, making its alkali recovery and wood pulp are very different. In early China's wheat straw alkali recovery design, most of them refer to and follow the design parameters of wood pulp. As a result, the alkali recovery system is difficult to operate normally. High fuel consumption, high cost, low alkali recovery rate, and many operational failures. Due to the low alkali recovery rate, part of the pollution load is transferred to the middle-stage wastewater for treatment, making the treatment cost of the middle-stage wastewater high and difficult, which in turn affects the economic benefits of the entire enterprise. The economical and effective treatment of wheat straw pulping wastewater can not be realized, which is a major problem faced by the papermaking industry in China. In recent years, technical personnel and enterprises of China's paper industry have worked together for several years to make great progress in wheat straw alkali recovery technology. At present, 19 wheat straw pulp alkali recovery systems have been implemented throughout the country. The alkali recovery rate is the best at 72%, and the oil consumption and overall cost of the recovered alkali have been greatly reduced. The mid-stage water treatment system for supporting construction also achieved normal operation and discharge standards.
In view of the problems and difficulties in wheat straw slurry alkali recovery, there have been some researchers in China who have conducted research on other pollution control technologies and the methods have reached more than 10 kinds. For example, lignin and alkali are separately recovered by ultrafiltration and electrodialysis, and various cracking products such as caustic soda and acetic acid are recovered by a cracking method; others are obtained by acid precipitation of lignin, followed by biochemical treatment of a supernatant liquid, and the like. However, there are no industrial scale success stories so far. These explorations and practices have also made papermakers further realize that the traditional method of alkali recovery is still a more appropriate method for controlling black liquor contamination of wheat straw chemical pulp. Some technical problems in wheat straw alkali recovery, such as black liquor viscosity reduction, removal of silicon, increase extraction rate and alkali recovery rate, also need to continue research.
3 About China's paper industry water pollutant discharge standards
The "Paper Industry Water Pollutant Discharge Standard" currently being implemented in China was enacted on July 1, 1992. In view of the fact that the overall level of wastewater treatment in the papermaking industry in China was still relatively low and there was a significant gap in the level of technological equipment between old and new companies, the “emission standards†were based on old enterprises, newly built enterprises, and companies that were established after July 1, 1992. The types of emission standards have been separately specified, and the requirements for old enterprises have been relatively low, and the requirements for new enterprises have been relatively high.
In order to achieve sustainable economic development in China, we will further strengthen environmental protection. Recently, China's State Environmental Protection Administration has promulgated the new "Emission Standard for Water Pollutants in the Paper Industry". The new standard will be implemented from January 1, 2001. The new standard sets a uniform standard value for all paper-making companies, and the requirements are stricter than the old ones. The new paper industry water pollutant emission standards are as follows:
4 Countermeasures for Pollution Prevention and Control in China Paper Industry
Preventing pollution, protecting the environment, and implementing a sustainable development strategy are basic policies for China's economic development. According to the State Council’s orders, by the end of 2000, all industrial pollution sources in the country must meet the discharge standards. More stringent sewage discharge standards and time-limited compliance requirements are undoubtedly a serious challenge to Chinese papermaking companies. Solving the problem of pollution prevention and control in China's paper industry has become a very urgent task for the survival of papermaking companies. The relatively serious pollution situation in China's paper industry is caused by a variety of reasons. The most important reason is that the proportion of non-wood raw materials is too large, the scale of the enterprises is too small, and the backwardness of equipment has made it difficult to achieve economical and effective governance against pollution. To completely solve the problem of pollution in China's paper industry, we must combine the overall requirements of structural adjustment in the paper industry, and take comprehensive measures in terms of raw material structure, equipment level, and enterprise scale. Preliminary considerations include the following:
Item Category Discharge BOD Chemical oxygen demand Suspended material (SS) Can be adsorbed with PH (BOD5) (CODcr) Machine Halide (AOX)
M3/t product kg/t product mg/L kg/t product mg/l kg/product mg/l
Pulpwood color 150 10.5 70 15 100 6~9
Bleaching 220 15.4 70 22 100 2.64 12 6~9
Non-paste wood color 100 10 100 10 100 6~9
Bleaching 300 30 100 30 100 2.7 9 6~9
Papermaking General Mechanism Paper 60 3.6 60 6 100 6~9
,cardboard
1, adjust the structure of raw materials. Expand the use of commercial wood pulp and secondary fibers, fully recycle waste paper, actively promote the integration of forestry and paper, accelerate the development of papermaking fast-growing and high-yield forest bases, and strive to increase the proportion of wood raw materials.
2. Accelerate the pace of technological transformation of the paper industry. Support a group of key enterprises to achieve a more reasonable production scale through technological transformation, realize the leap in the level of equipment technology, and completely solve the pollution problem.
3. Support wheat straw chemical pulp production line with a scale of over 34,000 t/a. Through the construction of alkali recovery and mid-stage water treatment systems, it will achieve discharge standards.
4. For small-scale enterprises with a scale of 17,000 t/a or less, and with poorly equipped equipment and no development conditions, it is difficult to meet the standards for pollution control. For other types of SMEs, treat them differently according to specific circumstances. Support the use of secondary fiber or commercial pulp, combine the company's own conditions, give full play to its advantages, develop appropriate products, and develop papermaking production.
5. Summing up, popularizing and applying the successful experience of wheat straw black liquor alkali recovery, improving and perfecting the engineering design, further increasing the alkali recovery rate, reducing the pollution treatment cost, and improving the economic benefits of the company.
6. To strengthen the research and development of new technologies and new equipment in the field of environmental protection in the paper industry, learn from, learn from, and introduce advanced international technologies and equipment, gradually increase the level of pollution prevention and environmental protection in the paper industry, and realize the sustained and stable development of China's paper industry.
According to statistical data in recent years, the national wastewater discharge from the pulp and paper industry accounts for about 10% to 12% of the total national wastewater discharge, ranking third; the CODcr in the discharged sewage accounts for about the total amount of emissions in the country. 40% to 45%, ranking first. The paper industry is one of the major industries polluting the environment in China.
Wastewater in pulp and paper production is mainly digested waste liquid, middle-stage waste water and papermaking white water. The pollution load of cooking waste liquid accounts for about 80% of all pulp and papermaking wastewater, and is the most important source of pollution, followed by the middle-stage wastewater. White water recycling technology has been widely promoted in China. Large-scale paper machines generally use multi-disk filters. SMEs use air flotation tanks or multi-disc filters to recover white water, so that white water can be fully reused, and some have achieved closed circulation. There is no technical obstacle to the pollution control of white water in papermaking. The pollution control of cooking waste liquid and middle-stage wastewater is the key and difficult point in pollution prevention and control in China's paper industry.
The pollution treatment of wood pulp and papermaking cooking waste liquid, whether it is alkaline or acid pulping, in the international, the technology has matured: alkali wood pulp cooking black liquor alkali recovery by burning, acid wood pulp cooking waste liquid The pollution problem has been solved through comprehensive utilization. The pollution of the middle-stage wastewater has also been resolved due to the use of elemental chlorine (ECF) and total chlorine-free (TCF) bleaching processes to eliminate the pollution of dioxins and other toxic compounds in the bleaching process. From a perspective, it has largely been resolved. At present, the pollution caused by the paper industry is even lower than that of domestic garbage and agriculture.
In China's papermaking raw materials, wood raw materials account for a very small proportion. In self-pulp, the proportion of wood pulp is less than 10%. Domestic chemical pulp mills using wood as raw materials basically all have an alkali recovery system. The alkali recovery rate can reach over 90%. Although the recovery rate is still lower than the international advanced level, it works well. The small-scale production of bleached wood pulp in the middle-stage wastewater, due to the use of traditional CEH three-stage bleaching, has not yet solved the dioxin contamination problem, but it can also meet the standard discharge after two levels of treatment.
China's papermaking raw materials are mainly non-wood raw materials, and non-wood raw materials are mainly wheat straws. The pulping method is mainly based on the alkali method, and there are still a small amount of acid pulping and ammonium sulfite pulping. The characteristics of non-wood cooking waste liquid are very different from those of wood raw materials. In addition, the pulp and paper companies that use non-wood as raw materials in China generally have the problems of small scale and relatively backward equipment. China's non-wood raw material pulping and papermaking wastewater pollution control level lags far behind the world average, there are many problems and problems, is the most important source of pollution. It is estimated that the annual output of wheat straw alkaline chemical pulp in China is about 3.4 million tons, and the amount of alkali used is about 1 million tons per year. At present, most companies do not have a matching alkali recovery system. Less than 5% of the base is recovered by the alkali recovery system, and more than 95% of the caustic soda is dissolved into the body of water together with dissolved organics. The national wheat straw CODcr emissions account for more than 74% of the total paper industry emissions.
Non-timber pulp and bagasse pulp, due to their black liquor alkali recovery system, achieved normal operation earlier, and most companies that use these materials have built alkali recovery and supporting mid-stream water treatment systems. Up to 80%, the bagasse pulp alkali recovery rate reached 78%, and the integrated wastewater can meet the discharge standards.
The Chinese government attaches great importance to the serious water pollution problem in the papermaking industry. As early as 1984, the State Council issued the "Regulations on Strengthening the Environmental Management of Townships and Street Enterprises", stating clearly that township and street enterprises are not allowed to engage in serious polluting production projects such as pulp and papermaking. The Ministry of Industry of the People's Republic of China formulated the “Planning and Implementation Rules for Water Pollution Prevention and Control of the Paper Industry†in 1986. In 1988, the State Environmental Protection Commission and the Ministry of Light Industry jointly issued the “Regulations on the Prevention and Control of Water Pollution in the Paper Industryâ€. However, due to people’s lack of awareness of the importance of protecting the environment a few years ago, the lack of environmental protection law enforcement and the fact that some regions are relatively economically backward, a large number of small and medium-sized paper mills without any pollution control measures continue to emerge, resulting in water for the papermaking industry. The pollution situation has reached a very serious level. In order to protect the environment, prevent pollution, and achieve sustainable economic development, our government has further strengthened environmental protection measures and law enforcement. In 1996, the State Council issued the "Decision on Strengthening Several Issues Concerning Environmental Protection" and requested that small-scale pulp mills with an annual output of no more than 5000 tons be closed before September 31, 1996, and that all industrial pollutants emitted by To meet national or local standards. By the end of 1996, a total of more than 4,000 small paper mills had been shut down across the country, significantly reducing the pollution of the paper industry.
2 Research and Exploration on Wastewater Treatment Technology by China Paper Industry
As already mentioned, the straw black liquor is the most important source of pollution in the paper industry in China. The traditional combustion alkali recovery of cooking black liquor is a mature technology using wood pulping and papermaking. Alkali recovery can not only control the pollution of cooking waste liquid, but also recover alkali and energy from black liquor, reduce pulping cost and sewage treatment cost, and is an indispensable part of the alkali pulp mill.
However, there are many technical problems in wheat straw black liquor alkali recovery. 1. Due to the large amount of fine fiber components in the wheat straw raw material, the poor drainage performance of the slurry and the low black liquor extraction rate. The current best extraction rate can reach 80% to 85%. 2. The viscosity of the black liquor is large, storage and transportation are difficult, the concentration of the black liquor is low, and the black liquor has poor combustion performance. Generally, the concentration of black liquor from the evaporation station is about 40% to 43%, and after passing through the disc evaporator, the concentration is 45% to 48%, which is far lower than the furnace black liquor concentration. 3. The silicon content in raw materials is high, and the evaporator is easy to foul. Low evaporation intensity. Due to the high silicon content, the white mud is poor in filtration and sedimentation and cannot be recycled.
These characteristics of the wheat straw raw material, making its alkali recovery and wood pulp are very different. In early China's wheat straw alkali recovery design, most of them refer to and follow the design parameters of wood pulp. As a result, the alkali recovery system is difficult to operate normally. High fuel consumption, high cost, low alkali recovery rate, and many operational failures. Due to the low alkali recovery rate, part of the pollution load is transferred to the middle-stage wastewater for treatment, making the treatment cost of the middle-stage wastewater high and difficult, which in turn affects the economic benefits of the entire enterprise. The economical and effective treatment of wheat straw pulping wastewater can not be realized, which is a major problem faced by the papermaking industry in China. In recent years, technical personnel and enterprises of China's paper industry have worked together for several years to make great progress in wheat straw alkali recovery technology. At present, 19 wheat straw pulp alkali recovery systems have been implemented throughout the country. The alkali recovery rate is the best at 72%, and the oil consumption and overall cost of the recovered alkali have been greatly reduced. The mid-stage water treatment system for supporting construction also achieved normal operation and discharge standards.
In view of the problems and difficulties in wheat straw slurry alkali recovery, there have been some researchers in China who have conducted research on other pollution control technologies and the methods have reached more than 10 kinds. For example, lignin and alkali are separately recovered by ultrafiltration and electrodialysis, and various cracking products such as caustic soda and acetic acid are recovered by a cracking method; others are obtained by acid precipitation of lignin, followed by biochemical treatment of a supernatant liquid, and the like. However, there are no industrial scale success stories so far. These explorations and practices have also made papermakers further realize that the traditional method of alkali recovery is still a more appropriate method for controlling black liquor contamination of wheat straw chemical pulp. Some technical problems in wheat straw alkali recovery, such as black liquor viscosity reduction, removal of silicon, increase extraction rate and alkali recovery rate, also need to continue research.
3 About China's paper industry water pollutant discharge standards
The "Paper Industry Water Pollutant Discharge Standard" currently being implemented in China was enacted on July 1, 1992. In view of the fact that the overall level of wastewater treatment in the papermaking industry in China was still relatively low and there was a significant gap in the level of technological equipment between old and new companies, the “emission standards†were based on old enterprises, newly built enterprises, and companies that were established after July 1, 1992. The types of emission standards have been separately specified, and the requirements for old enterprises have been relatively low, and the requirements for new enterprises have been relatively high.
In order to achieve sustainable economic development in China, we will further strengthen environmental protection. Recently, China's State Environmental Protection Administration has promulgated the new "Emission Standard for Water Pollutants in the Paper Industry". The new standard will be implemented from January 1, 2001. The new standard sets a uniform standard value for all paper-making companies, and the requirements are stricter than the old ones. The new paper industry water pollutant emission standards are as follows:
4 Countermeasures for Pollution Prevention and Control in China Paper Industry
Preventing pollution, protecting the environment, and implementing a sustainable development strategy are basic policies for China's economic development. According to the State Council’s orders, by the end of 2000, all industrial pollution sources in the country must meet the discharge standards. More stringent sewage discharge standards and time-limited compliance requirements are undoubtedly a serious challenge to Chinese papermaking companies. Solving the problem of pollution prevention and control in China's paper industry has become a very urgent task for the survival of papermaking companies. The relatively serious pollution situation in China's paper industry is caused by a variety of reasons. The most important reason is that the proportion of non-wood raw materials is too large, the scale of the enterprises is too small, and the backwardness of equipment has made it difficult to achieve economical and effective governance against pollution. To completely solve the problem of pollution in China's paper industry, we must combine the overall requirements of structural adjustment in the paper industry, and take comprehensive measures in terms of raw material structure, equipment level, and enterprise scale. Preliminary considerations include the following:
Item Category Discharge BOD Chemical oxygen demand Suspended material (SS) Can be adsorbed with PH (BOD5) (CODcr) Machine Halide (AOX)
M3/t product kg/t product mg/L kg/t product mg/l kg/product mg/l
Pulpwood color 150 10.5 70 15 100 6~9
Bleaching 220 15.4 70 22 100 2.64 12 6~9
Non-paste wood color 100 10 100 10 100 6~9
Bleaching 300 30 100 30 100 2.7 9 6~9
Papermaking General Mechanism Paper 60 3.6 60 6 100 6~9
,cardboard
1, adjust the structure of raw materials. Expand the use of commercial wood pulp and secondary fibers, fully recycle waste paper, actively promote the integration of forestry and paper, accelerate the development of papermaking fast-growing and high-yield forest bases, and strive to increase the proportion of wood raw materials.
2. Accelerate the pace of technological transformation of the paper industry. Support a group of key enterprises to achieve a more reasonable production scale through technological transformation, realize the leap in the level of equipment technology, and completely solve the pollution problem.
3. Support wheat straw chemical pulp production line with a scale of over 34,000 t/a. Through the construction of alkali recovery and mid-stage water treatment systems, it will achieve discharge standards.
4. For small-scale enterprises with a scale of 17,000 t/a or less, and with poorly equipped equipment and no development conditions, it is difficult to meet the standards for pollution control. For other types of SMEs, treat them differently according to specific circumstances. Support the use of secondary fiber or commercial pulp, combine the company's own conditions, give full play to its advantages, develop appropriate products, and develop papermaking production.
5. Summing up, popularizing and applying the successful experience of wheat straw black liquor alkali recovery, improving and perfecting the engineering design, further increasing the alkali recovery rate, reducing the pollution treatment cost, and improving the economic benefits of the company.
6. To strengthen the research and development of new technologies and new equipment in the field of environmental protection in the paper industry, learn from, learn from, and introduce advanced international technologies and equipment, gradually increase the level of pollution prevention and environmental protection in the paper industry, and realize the sustained and stable development of China's paper industry.
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