Microwave-Assisted Treatments of Biomass: Lignin Isolation from Lignocellulose and Natural Products Recovery from Bilberry Presscake

Abstract
Microwave thermal treatment has generated an increasing interest in biomass valorisation. In this research, softwood, hardwood and straw are processed by microwave-assisted acidolysis, producing high quality residual lignin without significant modification, especially softwood (purity 93%, yield 82%). Under equivalent conditions, microwave treatment produces lignin with higher yield and purity than conventional treatment. The aqueous hydrolysate is fermented by two oleaginous yeasts, Cryptococcus curvatus and Metschnikowia pulcherrima. Both yeasts could grow on the hydrolysate and produce an oil with similar properties to palm oil. This preliminary work demonstrates new protocols of microwave-assisted acidolysis and therefore offers an effective approach to produce high purity lignin and fermentable chemicals, which is a key step towards developing a zero-waste lignocellulosic biorefinery.
In addition, microwave conversions (lab and pilot scale) of bilberry presscake, aiming to fulfill multiple chemicals recovery, were carried out using only water as the solvent, ensuring all products are suitable for food grade status applications. Microwave hydrolysis gives much higher yield of mono-/disaccharides than conventional extraction, with the yield of rhamnose particularly high (10.8%). Pilot scale microwave conversions are also carried out with high conversion. It is believed microwave hydrolysis offers an efficient and green approach to convert bilberry presscake into value-added products for food industry and biorefinery.