In the past In 50 years, the world has left 7 billion tons of plastic waste, known as "white pollution". Plastic garbage is the most obvious pollution to the sea. According to Science magazine, 8 million tons of plastic are washed into the sea every year. What is more frightening is that a large number of plastic particles produced by them enter the human body through seafood, sea salt and other ways, causing huge health hazards. Cracking the harm of "white pollution" has always been an important direction for global scientists.
Recently, foreign media reported that Tel Aviv University in Israel has developed a bioplastics polymer with the latest technology. This process does not require land and fresh water, but comes from microorganisms that feed on algae. It is biodegradable, can produce zero toxic waste, and can be recycled into organic waste. What is the background of biotechnology? What is the domestic development prospect? With a series of questions, the reporter of Science and Technology Daily interviewed relevant scientists.
Petrochemical plastics are difficult to degrade once they are synthesized
The ordinary plastic polyester is made from non renewable petroleum by polycondensation of polyols and polybasic acids. Because of its convenience, durability, waterproof and low price, it is widely used.
Professor Chen Guoqiang, chairman of the 2018 International Biopolyester Conference (ISBP) and director of the Center for Synthesis and Systems Biology of Tsinghua University, introduced to the reporter of Science and Technology Daily that at present, there are 120 million tons of disposable plastic products in the world every year, of which only 10% are recycled, another 12% are incinerated, and more than 70% are discarded into soil, air and sea.
In China, the amount of agricultural plastic film remaining in the soil every year is as high as 350000 tons, with a residual film rate of 42%. A large amount of agricultural film remains in the 0-30cm plough layer of farmland, which poses a great threat to agricultural production and food safety. The most important reason why the "white pollution" caused by plastic waste is so bad is the chemical properties of plastic. Plastics are polyethylene, polystyrene and other high molecular polymers polymerized from monomers. Unlike other wastes, decomposers in the environment cannot digest and degrade the chemical bonds connecting monomers in plastics, so they cannot be re decomposed into monomer forms. In other words, once the plastic is synthesized, there will be no "turning back".
Can we manufacture such a material, which has excellent polymer properties like traditional plastics, and can be easily degraded into monomer by microorganisms? The international biological polyester academic community has worked hard for decades for this purpose.
Finding New Carbon Sources from Algae Cultivation
The only way to solve the problem of overflowing plastic waste is to replace it with bioplastics, which does not use oil and degrades quickly. But generally speaking, bioplastics also have environmental costs. Cultivating biological substrates requires fertile soil and fresh water. However, many countries do not have such resources.
Department of Environmental and Earth Sciences, Tel Aviv University, Alexandria, Israel ·This new achievement, which Dr. Gulberg and Professor Michael Gusin of the School of Chemistry cooperated, uses a Mediterranean wild type microorganism to generate a polymer called polyhydroxyfatty acid ester (PHA) in the simulated seaweed hydrolysate culture medium. The biological plastic made of this polymer not only produces zero toxicity waste, It can also be turned into nutrients that can be decomposed and utilized by microorganisms and fed back to the natural environment. However, using microorganisms and algae to produce biodegradable plastics is still facing many challenges, including dependence on pure carbon source of glucose, technical requirements of organic substitutes for the production of different types of PHA, pollution generated in downstream processing, and possible use of a large number of solvents.
"It is a good idea to use seawater to cultivate algae. The sea area is large, and kelp and other large algae grow faster than food." Professor Chen Guoqiang said that the innovation of this achievement is to find a new biological polyester carbon source.
In China, the performance of bio polyester synthesized with corn, potato, cassava and other substrates is close to that of traditional plastic products, and has been recognized by some European manufacturers. "The bioplastics products we developed can even be used by animals." Chen Guoqiang said that relying on the knowledge reserve of traditional biology and the progress of gene synthesis, sequencing, systems biology, bioinformatics and other technologies, the latest research has made the structure of PHA constantly develop and change, which can be used for various applications, except for packaging materials, agricultural films, fibers, biofuels, etc, PHA has a very broad market prospect in medicine, cosmetics, animal feed, etc.
Using algae as raw material is still a new concept
Based on the existing cutting-edge achievements, including those of Chinese scientists, Gulberg and his collaborators said in the internationally renowned journal Biological Resources Technology that the lack of cheap and usable matrices hindered Mass production of PHA. They use macroalgae to obtain carbon matrix for PHA production mainly based on this substrate. In the ocean, most algae, including kelp, red algae and brown algae, have this ability. However, due to the massive propagation of algae, it will lead to eutrophication of water bodies, and its governance is a major problem. So they focused on a green giant alga, which not only has the function of water environment repair, but also can be used to produce PHA, which is expected to provide sustainable solutions for the production of bio polyester.
They initially screened There are 7 kinds of algae species, and the production potential of these algae to synthesize PHA is different. From the test combination, the green giant alga composition has obtained the maximum production rate of PHA. They also studied the effect of hydrolysates of different concentrations on PHA, determined the structural characteristics of the newly synthesized PHA, and found that the results were the same as those reported previously using other carbon sources as substrates. The research results prove that the seaweed growing in the offshore can become a sustainable and environmentally friendly substitute for long-term production of biopolymers, and in the process of experiment demonstration, the production of PHA does not use fresh water, which indicates the possibility of expanding the scale of sustainable process, which has taken a step forward for the development of biological processing and biological refining technology.
However, Professor Chen Guoqiang believes that this is still a new concept. It should be 20 to 30 years before mass production is realized, especially in terms of cost control, it is still difficult to be as cheap as polyethylene. In addition, the cost of collecting algae on the sea is relatively high.
our country Pilot test of "Blue Water Biotechnology" process completed
Professor Chen Guoqiang introduced that biological industry has obvious advantages over traditional chemical industry. Most biological reactions require relatively mild conditions and do not require harsh conditions such as high temperature and high pressure. The raw materials and metabolic wastes used are not harmful to the environment, so the research on biological polyester is developing rapidly in the world. In China, biodegradable plastics, especially bio polyesters such as polylactic acid（ PLA), polyhydroxy fatty acid ester, polybutylene terephthalate (PBAT), carbon dioxide copolymer (PPC) and other basic research and industrialization have made rapid progress, leading the international peer level.
It is reported that the "Next generation industrial biotechnology" has completed the pilot test of PHA industrial production in December 2017, realizing the mass production capacity of low cost PHA through open continuous fermentation without sterilization. In order to realize the rapid industrialization of this technology, with the support of Tsinghua University, the R&D team of Beijing Lanjing Microbiology Technology Co., Ltd. has developed a low-cost production technology based on halophilic microorganisms - "Blue Water Biotechnology", which has revolutionically simplified the synthesis process of PHA, and the pilot production base has also been completed and put into operation. It is expected that in the next five years, the cost of PHA in China will continue to decrease, and the market share may increase significantly.
Chinese "Blue Water Biotechnology", on the one hand, can realize open and continuous fermentation without sterilization, reduce the energy consumption in the sterilization process and the complicated operation and labor costs, and achieve efficient production; On the other hand, the cultivation of halophilic microorganisms requires a substrate medium containing high concentrations of salt, which means that seawater can be used to replace freshwater resources, thus avoiding water resource problems. In addition, the need for sterilization also means that the bioreactor does not need to use stainless steel materials to withstand high temperature and high pressure steam, and can use materials such as plastics or ceramics, thus reducing equipment costs. At present, the world's first 5-ton plastic bioreactor has been assembled and put into operation, but there are still many challenges facing the market.
Professor Chen Guoqiang said that although the current industrial technology has become increasingly mature and the cost is declining year by year, from a global perspective The intensity of "white pollution" is far from enough, and policy guidance and promotion is still a universal problem.
