Pretreatment of Plant Biomass Waste for Better Resource Extraction: Conventional Technologies versus Nonthermal Plasma and Microwave

Abstract One of the biggest challenges in the bioprocessing field is a sustainable, clean, renewable, and cost-effective process that could significantly impact biomass waste valorization. Although biomass is readily available in nature, extracting valuable compounds requires several processing steps, including pretreatment, processing, and purification. Biomass is often made up of the supramolecular architecture of plant cells, which is both resistant to processing and requires disruption to access additional biomolecules contained within the cells themselves. Traditional methods in biomass pretreatment are effective concerning the valorization but fail to operate on a sound mechanistic understanding, referred to here as the ‘working principle’, which hampers the design of specialized reactors that would effectively support the specific working principle. While literature evidence from conducting case studies (information provided in the tables) and assessing performance is available (where they demonstrated that the effects can reach up to 90% biomass conversion), this is made on the backdrop of lacking understanding of the working principle and the design of specialized reactors. This review focuses on the mechanistic effects of pretreatment methods on biomass and provides a comprehensive study on the role of conventional technologies for pretreating biomass. The review further lists the opportunities that case studies demonstrated for nonthermal plasma (which can improve product yield by more than 40% than untreated samples, depending on the experimental conditions) and microwave (where enzymatic hydrolysis reached up to 85% compared to 60% in untreated and increased product yield by up to 40%) as emerging techniques. Finally, this accumulated knowledge is used to predict design alterations of current nonthermal plasma and microwave reactors as an interim stage toward future specialized reactors in biomass pretreatment.