Biological enzymes or washing paper industry 'original sin'

In order to achieve China's "double carbon" goal, it is necessary to vigorously promote the energy conservation and emission reduction of key industries such as textiles, paper making, and pharmaceuticals, and the application of biotechnology will undoubtedly accelerate the pace of green transformation of these industries. To this end, this newspaper launched a series of reports on "green biological manufacturing", focusing on how biotechnology can help traditional industries out of high energy consumption and high pollution.

If you compare today's paper with the past, it's not hard to see that paper has gotten better and whiter over the years.

However, behind the bright paper, it hides the "original sin" of high pollution and high energy consumption that the paper industry is difficult to get rid of.

At the same time, China has more people and fewer trees, and there is an extreme shortage of wood raw pulp, and papermaking raw materials rely on imported raw pulp and waste paper for a long time. According to the announcement jointly issued by the Ministry of Ecology and Environment and other ministries, China has basically achieved zero solid waste imports by the end of 2020, and relying on imported waste paper is no longer feasible.

In recent years, under the dual pressure of environmental protection and cost, non-wood raw materials such as straw and high yield mechanical pulp assisted by biological enzymes are making subtle changes in the raw material structure of the paper industry, bringing a revolution to the industry, especially the wrapping paper industry.

Paper behind the industry's pain

Papermaking is one of the four great inventions of China, and the annual production and sales volume of China's paper industry rank first in the world, accounting for about a quarter of the global total.

In recent years, with the development of Internet technology, e-reading has become popular. However, in a short time, paper is still irreplaceable in many fields, such as teaching materials, advertising printing, household paper and so on.

No matter what type of paper, it is necessary to start from a wood fiber. "Paper is made mainly from wood fibers in plant materials." Dai Hongqi, a professor at Nanjing Forestry University, said that in order to obtain wood fibers, plant raw materials need to be sliced or cut short; After high temperature boiling in alkali water or mechanical grinding, the fibers are separated to obtain pulp. The pulp is mechanically ground and dehydrated at a certain concentration on the paper machine to form a wet paper sheet, and then further dehydrated by pressing and dried into paper.

In order to obtain the wood fiber for the manufacture of pulp, human beings must invest a large amount of water, electricity, alkali and other elements, while producing a large number of black, smelly, toxic wastewater, so that many papermaking enterprises have repeatedly boarded the environmental black list.

Although China is large and abundant, but the forest resources are very scarce, the per capita forest area is only 1/7 of the world per capita level, in order to reduce domestic wood resources consumption, reduce the environmental pressure brought by wastewater discharge, in recent years, China has imported a large number of foreign wood pulp and waste paper to meet the needs of our national economic development.

"Imported wood pulp can be directly used for paper making, the production of white cardboard, household paper, special paper, etc. The imported waste paper is mainly used for the production of cardboard, wrapping paper and newsprint, such as packaging boxes, corrugated paper and kraft paper, which are widely used in the e-commerce express delivery industry." Dai Hongqi said.

At present, the proportion of pulp imported for papermaking in China is as high as 40%. In order to alleviate the shortage of papermaking fiber raw materials and reduce production costs, papermaking enterprises began to turn to the reasonable application of cost-effective non-wood raw materials.

"Pulp raw materials are divided into wood and non-wood two categories, in addition to trees, straw, bamboo, reed, awn stalk, cotton stalk are non-wood raw materials." Dai Hongqi told the Science and Technology Daily reporter that in the past, limited by technology and process, non-wood raw materials production of chemical pulp black liquor extraction rate and alkali recovery rate is low, pulp using elemental chlorine bleaching, the wastewater generated is not only difficult to treat, but also can adsorb organic halide (AOX) content is extremely high, causing great damage to the ecological environment, and human health is also a threat.

With the rapid development of China's economy and the strengthening of ecological environmental protection and pollution control, after 1990, almost all non-wood fiber pulp and paper enterprises were shut down. So far, only a few areas such as Sichuan bamboo pulp and paper enterprises are still in operation.

New opportunities for non-wood fiber pulping

Although the production of non-wood pulp has been completely banned, the research of non-wood fiber utilization technology has not stopped. In recent years, biomass refining technology and high-yield chemical mechanical pulp technology have become hot topics and received attention from the industry, allowing non-wood pulp to return to the stage of the paper industry.

"Bio-refining can recycle various components of non-wood fiber raw materials, especially the high-value utilization of hemicellulose and lignin." Dai Hongqi told reporters.

Lignin accounts for about 20%-40% of the composition of non-wood fiber raw materials, and traditional pulping is to remove lignin and obtain pulp fibers used as raw materials for paper making. Lignin is a polymer with a three-dimensional network structure connected by benzene propane units through ether bonds and carbon-carbon bonds. Depending on the type of plant fiber raw materials, the aromatic monomer composed of lignin has the function of gaining and losing electrons, can absorb ultraviolet rays, and is also a potential energy storage material.

In the past, the value of lignin has not been well developed and utilized, and the traditional practice of pulp mills is to recover heat energy by burning it. Dai Hongqi introduced that in recent years, based on the special function of lignin phenol hydroxyl aromatic monomer, researchers have replaced phenol with lignin as a green adhesive, energy storage electrolyte/energy storage electrode material, anti-ultraviolet film material and so on.

Another technology direction that is currently favored is high yield chemical mechanical pulp technology. This technology can not only alleviate the bottleneck of the shortage of papermaking fiber raw materials in China, but also has the advantages of low difficulty and low cost in wastewater treatment.

"This technology abandons the idea of extracting the hemicellulose and lignin left over from cellulose in the past, but uses all the wood fiber components as pulp for paper." Dai Hongqi introduced that the high yield chemical mechanical pulp is mainly based on mechanical methods, supplemented by a small amount of biological enzymes and chemical additives, so that the process of pulping wastewater treatment is greatly simplified and the cost is reduced, which can not only replace a large number of imported commercial wood pulp and waste paper raw materials, but also eliminate the huge air pollution problem caused by crop straw incineration.

Dai Hongqi revealed that the paper industry has implemented many scientific research projects and conducted pilot projects in individual enterprises to use wheat grass biological pulping to make household paper, wrapping paper and so on.

Biological enzymes may promote the green transformation of the paper industry

In fact, under the dual pressure of cost and environment, the paper industry is also eager to transform from a major polluter to a model of energy conservation and emission reduction.

In making the paper industry with high pollution and high energy consumption "correct", biological enzyme preparations are playing an increasingly important role.

Dai Hongqi said that biological enzymes have the characteristics of specificity and efficiency. At present, the technical research of the application of biological enzymes in the paper industry is mainly focused on grinding, deinking, bleaching and removing adhesives in the paper making process.

For example, biological enzymes can be used to modify the cell wall of the slurry fiber, so that the fiber can accelerate the moistening and soft, promote the effect of grinding, reduce the energy consumption of grinding, and improve the strength of paper. Studies have shown that bioenzymes can reduce the energy consumption per ton of mill pulp by 41.4%.

In addition, when the paper industry recycles a large amount of waste paper, it needs to be deinked.

The traditional deinking method is to use chemicals, at the appropriate temperature and mechanical action, to separate the ink particles from the fiber, and then use flotation, washing or a combination of the two methods to remove the stripped ink particles from the pulp. Enzymatic deinking is the use of enzymes to treat waste paper, and assisted by flotation or washing, and a combination of both processes, so as to remove ink.

Bleaching is also an important step in the papermaking process. The use of enzyme preparations can play a "biological aid bleaching" effect, reduce the amount of chlorine-containing bleaching chemicals, thereby reducing the discharge of adsorbable organic halides in bleaching wastewater, and reduce environmental pollution.

However, the application of biological enzymes in the paper industry is not smooth sailing.

Dai Hongqi said that the research and development of biological enzyme technology has made some achievements, but there are still bottlenecks in application. So far, there are no real biological pulping plants in the world. The reason is that there are a series of technical difficulties in the application of biological enzymes to complex and large-scale pulping production.

"In addition, pretreatment of raw materials by biological enzymes takes a long time, and manufacturers need efficiency to ensure continuous production, so they prefer to use more efficient physical or chemical pretreatment methods." Dai Hongqi said that some enzyme preparations themselves also have problems such as high cost, limited types, greater impact by temperature and acid and alkaline environment, and low effect. Therefore, at this stage, the application of biological enzyme technology is still auxiliary and can not play a leading role.

At the same time, he is optimistic about the application prospects of biological enzymes in the paper industry: "In general, biological enzymes have strong specificity and high efficiency, especially for the paper industry with high pollution and high energy consumption, the environmental protection effect is obvious, and it has unique advantages compared with chemicals." With the advancement of technology, it will dominate the paper industry in the future."