The new technology of “killing two birds with one stone” helps to alleviate white pollution

Beverage bottles, waste polyester, plastic bags, takeaway boxes… Plastic waste can be found everywhere in life, and the white pollution caused by its flood is one of the most serious environmental challenges of the 21st century, which will have an adverse impact on the ecological environment and human health.

The enzyme engineering and technology research group of Tianjin University, which has been making enzyme preparations for more than 30 years, has focused on solving the problem of white pollution, and they have been carrying out research on plastic degrading enzymes in recent years.

Recently, under the leadership of Qi Wei, the leader of the research group and a professor of the School of Chemical Engineering of Tianjin University, and the core member of the team, Associate Researcher You Shengping, a set of “efficient, energy-saving, economical and environmentally friendly” polyethylene terephthalate (PET) enzymatic hydrolysis and recovery process has been developed by reducing costs and increasing efficiency, which can significantly reduce production energy consumption and cost. The findings were published in Bioresource Technology.

There is an urgent need for a safe and environmentally friendly degradation method

According to data released by the United Nations, more than 200 million tons of plastic waste are generated globally every year, but only 10% is recycled. And plastic waste is polluting the world at a breakneck rate, even in the deepest Mariana Trench and the tallest Mount Everest.

Many people think that plastic waste doesn’t have an impact on themselves, but a paper published in Holistic Environmental Science in 2022 reported the first discovery of a build-up of microplastic pollution deep in the lungs of living people, such as polypropylene (PP) used in plastic packaging and straws, and PET, which is commonly used to make bottles.

Another study, published in Environment International in March of the same year, confirmed that human blood had also been contaminated with microplastics. For the first time, researchers have detected microplastic particles in human blood, which may be transported throughout the body by the bloodstream.

It is urgent to solve the problem of white pollution. However, the traditional solutions are not ideal, such as difficult to decompose after landfilling, easy to cause secondary pollution of land, and incineration will produce a large number of toxic and harmful gases. The use of chemical agents for degradation can introduce new contaminants.

In order to avoid these concerns and make some contributions in the field of environmental protection and life and health, five years ago, the enzyme engineering and technology research group of Tianjin University began to find a fit between biological enzyme preparations and plastic degradation.

“Our main goal is to develop biocatalysts that degrade these white contaminants, as well as a low-cost treatment process that minimizes the introduction of other new harmful substances while degrading plastics. Qi Wei, the corresponding author of the paper, said in an interview with China Science News.

It can not only reuse waste, but also produce the required enzymes

“Many biological reaction systems will produce a large number of salts, and we are also thinking about whether we can use these salt by-products as a raw material to specifically prepare some strains ‘for my use’. Qi Wei said.

After starting this project, the research group has successively carried out a number of graduate students to carry out chain research from enzyme preparation research and development to process optimization and then to device operation.

“According to the original design scheme, the PET enzyme gene sequence was constructed into the chassis cell, but we found that the recombinant bacteria did not express the target enzyme. We tried many methods in this process, and later on, although there was protein expression, the expression level was very low, and there was also the problem of protein aggregation. You Shengping, co-first author of the paper and associate researcher at Tianjin University, said in an interview with China Science News.

After a long period of scientific research, the team finally constructed a low-cost and high-efficiency engineering bacterium expressing PET enzymes, Vibrio halophilus, which increased the expression level of enzyme protein by 87.3% compared with Escherichia coli. The halophile can multiply and grow rapidly in a high-salt environment, while expressing an ideal catalyst enzyme that can then be used to degrade plastics.

“In this reaction system, the sodium salt produced in our process can be used as raw material, or it can be directly prepared by seawater fermentation, which solves the problem of large water consumption in the previous PET biodegradation process to a certain extent. You Shengping said.

This versatile and innovative solution provides reference and inspiration for the development of related biocatalytic processes.

New simplified process with 47.9% cost reduction

This new technology focuses on designing from the perspective of industrialization and opening up the entire process flow.

“While we are obtaining laboratory data, we are also carrying out process scale-up development at the industrialization pilot base in the field of biomanufacturing at Binhai Institute of Industrial Research of Tianjin University, which can make enterprises more confident in our technology. Qi Wei introduced that the pilot base was built by the research group of the R&D team, and was equipped with multiple sets of tonnage automatic fermentation systems, pilot reactors and pilot product purification systems, which provided necessary support for the development of related processes and products.

Courtesy of the research group

In order to realize the industrial application of technology, energy consumption and cost must be considered.

The traditional fermentation process requires a sterilization process, which is sterilized for 20 minutes at 121 degrees Celsius and one atmosphere, which consumes a lot of energy.

“Because the halophilic bacteria we obtained grow rapidly in an environment with high sodium salts, they can simultaneously inhibit the reproduction of miscellaneous bacteria, so that the developed process eliminates the need for sterilization, and the energy consumption can be reduced by 2.48 times according to preliminary estimates. In addition, according to the data evaluation at the laboratory stage, the cost of enzyme production in the whole fermentation was reduced by 47.9% due to the efficient use of by-product salts and the substantial increase in protein expression. You Shengping introduced.

“In the future, we will continue to improve the performance of enzymes, work with companies to improve the whole process, further scale up production, and prepare for larger-scale industrial preparation. Qi Wei said. (Source: Zhang Qingdan, China Science News)

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