green fuel

Recycled fuel can reduce air pollution, save costs and help protect the environment. Will we be able to turn paper waste into environmentally friendly fuel in the future? A new Israeli study offers an original way to do this

By: Galia Ariel

One of the obstacles to the production of biofuels from many organic materials, such as agricultural waste, is the cellulose (cellulose) they contain. Cellulose is found in the barks of many plants and it does not break down easily. Man, for example, is unable to digest cellulose, which is a polymer of the monosaccharide glucose, which may provide a lot of useful energy.

Prof. Ed Bayer, from the Department of Biological Chemistry at the Weizmann Institute of Science, studies bacteria that break down the cellulose chain into monosaccharide units that feed them. In the eighties of the last century, in collaboration with Prof. Raphael Lemmed from Tel Aviv University, Prof. Bayer discovered the "machine" that allows bacteria to break down cellulose, and the principles of its operation. "This machine, called a cellulosome, is made up of a group of enzymes that work as a system, and that's how they manage to overcome the cellulose and break it down into its components, a job that creatures much larger than bacteria are unable to perform," he says.

Cellulose makes up about half of the material at waste sites, with the bulk of this waste being paper that piles up and accumulates year after year. Unfortunately, bacteria equipped with cellulosomes that allow them to digest (decompose) natural cellulose, have difficulty dealing with the cellulose in industrial paper. To enable them to perform this task, Prof. Bayer began looking for ways to perfect the cellulosomes of the bacteria. In collaboration with Prof. Lemmed, he used methods of genetic engineering to create hundreds of different versions of cellulosomes, hoping that one of them would be characterized by the ability to break down the cellulose in paper with sufficient efficiency.

At this point they were joined by Prof. Gideon Schreiber, an expert in protein design and matching their activity, from the Department of Biological Chemistry at the Weizmann Institute of Science. Working together, the scientists succeeded in developing an artificial cellulose with increased activity, which is capable of turning a laboratory plate full of shredded paper into a liquid of simple sugar molecules within one day.

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From waste to fuel?

The simple sugars that are created in this process can be converted into ethanol - biofuel. These days, scientists are trying to increase the efficiency of this process, so that it can be operated on an industrial scale. Success in this field may lead, in the future, to the development of a process of turning paper waste, which is an environmental threat, into an efficient and environmentally friendly fuel.

Another direction of Prof. Bayer's research is testing the ability of cellulose to break down polymers, but those that originate directly from plants. The biomass of plants can be converted into clean and environmentally friendly fuel, but this conversion is not yet carried out on a large scale, partly because of its high cost. It turns out that converting the biomass at an atomic level may make it more efficient - this is according to a study conducted by Bayer in collaboration with scientists from the National Renewable Energy Laboratory in the United States.

The study, published in the scientific journal Science, confirmed the theory that one of the biggest obstacles in converting biomass is lignin, the hard polymer that strengthens plants. The conversion usually begins with pretreatment, where the lignin is crushed mechanically or destroyed using chemicals. In this study, the scientists developed an innovative method that made it possible for the first time to observe the destruction of lignin at the resolution of individual molecules and atoms, using an advanced laser microscope. The pictures showed that the lignin does interfere with the enzymes to break down complex sugar molecules located in the plant cell walls. Thanks to this discovery, the scientists characterized the ideal pre-treatment: removing the lignin without damaging the sugars (which are later converted to ethanol).

Later, the scientists compared the ability of the two methods to break down sugars. One method relied on individual enzymes extracted from mushrooms, in another method the decomposition was done by the cellulosome. The scientists discovered that the individual enzymes penetrated deeper into the plant cells, while the cellulosome acted mainly on their surface. Understanding the mechanisms involved in breaking down the cellulose biomass may help to design enzyme systems that will more efficiently break down the plant cell walls.

In this research, Prof. Bayer collaborated with scientists from the National Renewable Energy Laboratory in the United States, including Dr. Shi-Yu Ding who conducted post-doctoral research in Bayer's laboratory at the Weizmann Institute of Science in the late nineties of the last century. Dr. Ding and Dr. Yu-San Lee developed the methods for visualizing the effects of different chemicals on the plant cell wall, in different resolution ranges in six orders of magnitude (the largest of which is a million times larger than the smallest): from millimeters to nanometers (millionths of a millimeter). The other members of the group in the United States were Dr. Michael Himmel, Dr. Yuning Zeng and Dr. John Baker. The research findings may help researchers develop an optimal pretreatment for biomass and improve the activity of the enzymes that break it down. These improvements will increase ethanol yield and reduce the cost of biofuel production.

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