Sources for lignocellulosic raw materials for the production of ethanol

Production of ethanol from non-crop plant cell walls represents a sustainable solution for biofuel production due to the abundance of these renewable resources on our planet. The resources for cellulosic raw material can be either dedicated bioenergy feedstocks such as fast growing trees and energy grasses, or those based on by-products and waste materials such as crop residues and municipal solid waste. The processing of lignocellulosic into biofuel still requires expensive and harsh pretreatments, some of which are not acceptable from environmental point of view. This is due to the high level crystallinity of the cellulose and cross linking of the carbohydrates with the lignin that form a barrier preventing efficient and economic biomass enzymatic digestion. The advances in plant genetic engineering enable genetic modifications of the plant cell wall structure and function and may provide solutions that will help to overcome the difficulty in utilizing energy crops and trees. Despite the current technological difficulties related to processing of the complex cell wall polymers into fermentable sugars, the demand for renewable liquid fuel motivates the search for practical solutions and development of innovative technologies.