Optimization of biogas yield from lignocellulosic materials with different pretreatment methods: a review

Abstract

Population increase and industrialization has resulted in high energy demand and consumptions, and presently, fossil fuels are the major source of staple energy, supplying 80% of the entire consumption. This has contributed immensely to the greenhouse gas emission and leading to global warming, and as a result of this, there is a tremendous urgency to investigate and improve fresh and renewable energy sources worldwide. One of such renewable energy sources is biogas that is generated by anaerobic fermentation that uses different wastes such as agricultural residues, animal manure, and other organic wastes. During anaerobic digestion, hydrolysis of substrates is regarded as the most crucial stage in the process of biogas generation. However, this process is not always efficient because of the domineering stableness of substrates to enzymatic or bacteria assaults, but substrates’ pretreatment before biogas production will enhance biogas production. The principal objective of pretreatments is to ease the accessibility of the enzymes to the lignin, cellulose, and hemicellulose which leads to degradation of the substrates. Hence, the use of pretreatment for catalysis of lignocellulose substrates is beneficial for the production of cost-efficient and eco-friendly process. In this review, we discussed different pretreatment technologies of hydrolysis and their restrictions. The review has shown that different pretreatments have varying effects on lignin, cellulose, and hemicellulose degradation and biogas yield of different substrate and the choice of pretreatment technique will devolve on the intending final products of the process.

Anaerobic Digestion of Lignocellulosic Waste Materials

“…Lignin and hemicelluloses produce a protective sheath around the cellulose, inhibiting the depolymerization of hemicelluloses and cellulose to plain mono-sugars, necessary for productive conversion of biomass into biogas. Therefore, it is essential to pretreat the lignocellulosic raw materials [23].…”

“…The principal aim of pretreatments is to ease the accessibility of the enzymes to the chemical components (lignin, cellulose, and hemicelluloses), which results in depolymerization of the substrate. Additionally, the use of pretreatment for catalysis of lignocellulosic materials degradation is advantageous for an economical and environmentally friendly production method [23]. Moreover, pretreatment methods should not generate inhibitory substances or cause compounds losses.…”

“…The production of inhibitory and toxic substances in the material during the pre-treatment process usually adversely affects both the biogas generating bacterial and biodigesters. This constitutes a challenge that raises serious concerns, since most of the benefits coming from pretreatment process could vanish during AD, attributed to the adverse nature of these materials to methane generating bacteria [23].…”

“…The single cost of pretreatments is usually similarly high to other production processes [20,24]. Unfortunately, no pretreatment technique has been found that is suitable for all types of lignocellulosic materials [23]. Typically, a combination of two or multiple pretreatment methods is more effective and economic, and thus a preferable solution compared to single treatments [20,23].…”

Physical–chemical properties of cell wall interface significantly correlated to the complex recalcitrance of corn straw

“…Thus, a consensus can be reached that the high heterogeneity of plant biomass leads to the significant complexity of recalcitrance, which further influences the overall conversion efficiency of plant biomass. A further complication is that the complexity commonly causes empirically implemented enzymatic saccharification process and drastic pretreatment for recalcitrance more than necessary [ 8 ]. Hence, this immense heterogeneity is considered as the chief reason why the precise mechanisms of recalcitrance are still ambiguous and also closely influence the optimal choice of pretreatment and enzymatic hydrolysis strategy.…”