An overview on cell and enzyme immobilization for enhanced biohydrogen production from lignocellulosic biomass

Abstract

Hydrogen gas, a carbon-free energy carrier, can be produced via fossil fuel reforming, coal gasification, water electrolysis, photocatalysis, or biological process. Biohydrogen production from lignocellulosic biomass (LCB) in this regard, appears as an environmental benign, sustainable, non-food competing second generation fuel. LCB serves as the largest potential carbon source for sustainable biohydrogen production with an enormous global annual capacity of more than one trillion tons. Enzymes in this case, are widely used to hydrolyse the LCB into fermentable sugars, and subsequent hydrogen production is carried out by dark fermentation. However, the untapped non-food competing LCB is currently impeded by several critical bottlenecks including sensitivity of cells and enzymes to numerous denaturing conditions, recyclability, and high cost of enzyme. Low productivity of hydrolysis and hydrogen production in this regard, lead to a larger bioreactor and capital expenditures (CAPEX) requirement, which in turn, making this approach to be less competitive in commercial application. These bottlenecks can be overcome by immobilization technique, which enables the recyclability, improves stability and productivity of the enzyme and cells. Current review accommodates for the important outlook and critical insights into the immobilization techniques, providing important guidelines for the operation of immobilization techniques to elevate commercial competitiveness of biohydrogen production from LCB in the future. The effect of geometry, surface charges, and wettability of different type of carriers for cell immobilization to enhance biohydrogen production are discussed. The critical aspects of the immobilization parameters, such as temperature, pH, and duration which could significantly affect the properties of immobilized enzymes are thoroughly examined in this review. Suggestions and future directions of this field are provided to assist the development of an efficient, economic, and sustainable hydrogen production process.