When nature engineered lignin, the fibrous woody substance that gives plants their rigid structure, it didn’t cut corners. Lignin is incredibly slow to break down and is extremely tough and long-lasting, making it resistant to bacteria and decay.
So what happens to the lignin waste from farmlands, breweries and paper mills? Most of it is burned or buried causing pollution and wasting potential renewable resources.
Researchers at Northwestern University have now developed a sustainable and inexpensive two-step process that can upcycle organic carbon waste containing lignin. By treating waste in a microbial-driven biorefinery, researchers are turning lignin into a carbon source, producing high-value plant-based pharmaceuticals and antioxidant nutraceuticals, as well as carbon-based fuels for drug and chemical delivery. Made it available for nanoparticles.
This study was published on the cover of the January issue of the journal ACS Sustainable Chemistry and Engineering.
“Lignin should be of tremendous value, but it is inherently viewed as a waste product,” said study leader Kimberly Gray of Northwestern University. “Lignin accounts for 20-30% of biomass, but 40% of energy. It is a large amount, but it is difficult to harness this energy source. Nature makes lignin intractable. So people didn’t understand how to use it.Researchers have been trying to solve this problem for decades.Using an oil refinery as a template, they could use the waste stream to We have developed a biorefinery that produces high-value products using
Gray is the Loxelyn and Richard Pepper Family Chair of Civil and Environmental Engineering and Professor of Civil and Environmental Engineering at Northwestern University’s McCormick School of Engineering.
natural building materials
Lignin, one of the most abundant organic polymers in the world, is present in all vascular plants. Lignin between the cell walls supports a strong, tough plant structure like a tree. Without lignin, wood and bark are too weak to support trees.And wooden houses and furniture easily collapse.
However, most industries that use plants, such as the paper and brewing industries, strip the lignin away, leaving cellulose, a type of sugar. Instead of utilizing nature’s super-resistant materials, industry teams burn lignin as a cheap fuel.
“Humans want to get rid of the lignin to get to the sugars,” said Gray. “They either ferment the cellulose to make alcohol or process it to make pulp. What do you do with the lignin? They burn it as a low-quality fuel.It’s a waste.”
bacterial fuel cell
To develop a biorefinery for degrading carbon waste containing lignin, researchers first designed a microbial electrolysis cell (MEC). Similar to fuel cells, MECs exchange energy between the anode and cathode. But instead of a metal-based anode, Northwestern University’s bioanode contains exoelectrogens, a type of bacteria that naturally produce electrical energy by eating organic matter.
“Microbes act as catalysts,” says study co-author George Wells, associate professor of civil and environmental engineering at McCormick. “Instead of using chemical catalysts, which are often very expensive and require high temperatures, we are using biology as the catalyst.”
The great thing about MEC is that it can treat all kinds of organic waste, be it human, agricultural or industrial. The MEC circulates waste-filled water to bacteria, which eat up the carbon. Here, they break down organic carbon to carbon dioxide and naturally breathe electrons. During this process, the extracted electrons flow from the bioanode to the cathode (made of carbon cloth) where they reduce oxygen to produce water. This process consumes protons and raises the pH of water, turning it into a caustic solution. From there, the caustic solution can be used for various applications, including wastewater treatment.
“Another benefit of this process is that it effectively treats wastewater to remove harmful organic carbon,” says Wells. “So the key product is clean water.”
However, researchers took the caustic and turned their attention back to lignin. there is. Each aromatic ring contains alternating double and single bonds that are very difficult to break.
Breaking the “unbreakable” bond
However, when researchers exposed lignin to bio-based caustic chemicals, the lignin polymers broke apart and the aromatic rings were preserved. rice field. Commonly used in medicinal chemistry, these rings can be used as plant-derived, sustainable precursors for inexpensive pharmaceuticals and supplements.
“It breaks polymer bonds, but selectively leaves the ring,” said Gray. “If we can preserve that ring, we can make a valuable material. Chemists have developed catalysts that break down the entire compound. After that, the ring has to be reassembled, but the valuable structure is preserved. It could be selectively dismantled for preservation..”
The remainder (~80%) of the processed lignin becomes carbon-based nanoparticles, which can be used to encapsulate substances for targeted drug delivery to humans or targeted nutrient delivery to plants. Nanoparticles can also provide a sustainable plant-based alternative for sunscreens and cosmetics.
“It is exciting to identify and explore routes for sustainable resource recovery from multiple waste streams,” said Wells. “We have large wastewater and lignin streams that are expensive to treat independently. We are rethinking them as a source of value.”
Resource recovery without hazardous chemicals
Researchers have also been able to use commercially available caustics to process lignin, but their MEC-based approach has many advantages. First, eco-friendly bio-based chemicals are more effective. Second, it is safer and cheaper, can be used in ambient conditions, and can produce chemicals at the point of need.
“There are many corrosive substances, such as sodium hydroxide, which is commonly used in many industrial processes and wastewater treatment,” says Wells. “But it requires the transportation and storage of large amounts of toxic chemicals, which are not only expensive, but harmful to public health. Generating chemicals from waste on-site is much safer and more sustainable. Yes, we can avoid bulk transportation and storage, we have large quantities of hazardous chemicals and we are not dependent on supply chains or trucks arriving on time, chemical on site when needed It gives you the flexibility and adaptability to create matter.”