Biomass is a reliable renewable energy source, as it is made up of organic matter from plants and animals. It is readily available in nature and its organic composition makes it the best choice for an environmentally friendly energy resource.
However, plant biomass contains more than 50% moisture, which must be reduced by mechanical methods or by natural heating and curing to around 35% to increase power generation efficiency when used as fuel. For optimal benefits, this drying process must be fast, economical, and energy efficient.
The current system of mechanical compression is inefficient as it requires a subsequent thermal drying process, which makes the operation energy and time consuming and can often involve cumbersome equipment of appreciable cost. Furthermore, the squeezed liquid produced as a by-product by most of these methods does not contain water-soluble lignin, an important structural polymer in plant cells with innumerable applications.
To address these issues, researchers in Japan led by Dr. Toshiaki Ohara, Assistant Professor in the Department of Pathology and Experimental Medicine, Okayama University College of Medicine, Dentistry and Pharmaceutical Sciences, identified an effective mechanical compression system for dry plant biomass for energy generation without the need for thermal drying. His novel method can be applied to both woody and herbaceous plants and generates a water-soluble lignin-containing compress liquid that has basic antiviral properties against influenza viruses and porcine epidemic diarrhea.
In their study, the findings of which were published on October 22, 2022, in the Journal of Material Cycles and Waste Management, the researchers used cedar wood planks and pellets as woody biomass and the ginger grass species Alpinia zerumbet as herbaceous biomass to test the new mechanics of the rolling compression method.
They found that cedar and Alpinia planks compressed more effectively than cedar pellets. Explaining this observation, Dr. Ohara said that “Using our technique, all plants could be compressed; however, cedar and Alpinia planks compressed more effectively than cedar pellets, which compressed in a random direction. This indicates that compression along plant vessels, such as straw, is essential for efficacy.” Here, it should be mentioned that plant vessels are vascular tissues associated with the conduction of nutrients and water.
After compression, the researchers shredded and pelletized the waste to determine its combustion yield, an indicator of its potential as biomass for power generation. The liquid obtained as a by-product of the compression was filtered, its lignin content and structure were determined, and its antiviral properties were evaluated by means of cell viability assays.
Cedar wood pellets showed a higher calorific value in combustion, which coincided with ISO standards, attesting to their higher energy yield. The ginger grass species produced more water-soluble lignin, but its calorific value on combustion was slightly lower, at 95% of ISO standards. However, both cedar planks and Alpinia zerumbet compression fluids significantly inhibited porcine epidemic diarrhea and influenza virus infection.
Dr. Yuta Nishina of Okayama University’s Research Center for Interdisciplinary Sciences, a co-author of the study, noted that “The chemically unextracted water-soluble lignin obtained by this method can find applications in the fields of medicine, cosmetics and livestock. In addition, high-carbon, water-soluble lignin may find use in the production of carbon nanomaterials and contribute to reducing carbon pollution.”
Summarizing the benefits of his novel technique, Dr. Ohara said that “Our method does not require additional time, storage or thermal drying, allowing for on-site operation. This compressor can squeeze both wood and grass, allowing us to promote biomass power generation using locally grown plants. These characteristics are beneficial to advance local sustainability”.