Study identifies efficient method to replace thermal drying of plant biomass

Researchers from Okayama University have identified an effective mechanical compression system for drying plant biomass for power generation without the need for thermal drying. This is significant because, since plant biomass contains more than 50% moisture, mechanical methods (or heating and natural seasoning) need to be implemented to reduce this to about 35% - to increase power generation efficiency when the biomass is used as fuel.
This novel method can be applied on both woody and herbaceous plants and generates a compression liquid with water-soluble lignin that has basic antiviral properties against influenza and pig epidemic diarrhea viruses.
According to the university, the current system of mechanical compression is inefficient as the requisite thermal drying process is energy- and time-heavy, and can often involve expensive, cumbersome equipment. Not only that, but 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 myriads of applications.
The researchers were led by Dr Toshiaki Ohara, an assistant professor in the Department of Pathology and Experimental Medicine, Faculty of Medicine, Dentistry and Pharmaceutical Sciences at Okayama University. The study detailed the researchers' use of cedar wood board and chips as woody biomass and the ginger herb species Alpinia zerumbet as herbaceous biomass to test the novel mechanical rolling compression method. They found that cedar board and  Alpinia zerumbet were compressed more effectively than cedar chips.
"Using our technique, all plants could be compressed; however, cedar board and Alpinia zerumbet were more effectively compressed than cedar chips, which were compressed in a random direction. This indicates that compression along plant vessels, such as straw, is essential for efficacy,” said Dr Ohara. Plant vessels are tissues in vascular plants associated with the conduction of nutrients and water.
After compression, the researchers crushed and pelletised the residues to determine their combustion performance, an indicator of their potential as biomass for power generation. The liquid obtained as a byproduct of compression was filtered, its lignin content and structure determined and its antiviral properties evaluated using cell viability assays.
The cedar board pellets showed a higher heat value on combustion, which matched the ISO standards, attesting to their higher energy performance. The ginger herb species yielded more water-soluble lignin, but its heat value on combustion was slightly lower, at 95% of the ISO standards. However, both cedar board and Alpinia zerumbet compression liquids significantly inhibited influenza and porcine epidemic diarrhea virus infection.
Dr Yuta Nishina from the Research Core for Interdisciplinary Sciences, Okayama University, a co-author of the study, observed: “The non-chemically extracted water soluble lignin obtained by this method can find applications in the fields of medicine, cosmetics, and livestock husbandry.”
Besides, the high-carbon content water-soluble lignin may find use in carbon nanomaterial production and contribute to reducing carbon-driven pollution.
Summarising the benefits of their technique, Dr Ohara stated: “Our method does not require time, a stockyard or additional thermal drying, allowing for on-site operation. This compressor can squeeze both wood and herbs allowing us to promote biomass electric power generation using locally grown plants. These characteristics are beneficial for advancing local sustainability.”