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Agricultural residues, such as lignocellulosic materials (LM), are the most attractive renewable bioenergy sources and are abundantly found in nature. Anaerobic digestion has been extensively studied for the effective utilization of LM for biogas production. Experimental investigation of physiochemical changes that occur during pretreatment is needed for developing mechanistic and effective models that can be employed for the rational design of pretreatment processes. Various-cutting edge pretreatment technologies (physical, chemical and biological) are being tested on the pilot scale. These different pretreatment methods are widely described in this paper, among them, microaerobic pretreatment (MP) has gained attention as a potential pretreatment method for the degradation of LM, which just requires a limited amount of oxygen (or air) supplied directly during the pretreatment step. MP involves microbial communities under mild conditions (temperature and pressure), uses fewer enzymes and less energy for methane production, and is probably the most promising and environmentally friendly technique in the long run. Moreover, it is technically and economically feasible to use microorganisms instead of expensive chemicals, biological enzymes or mechanical equipment. The information provided in this paper, will endow readers with the background knowledge necessary for finding a promising solution to methane production.

Clear understanding of enzyme adsorption during enzymatic hydrolysis of lignocellulosic biomass is essential to enhance the cost-efficiency of hydrolysis. However, conclusions from literature often contradicted each other because enzyme adsorption is enzyme, biomass/pretreatment and experimental condition specific, which makes descriptions and modeling of enzyme-substrate interaction difficult and inconsistent from case to case. This study investigated adsorption kinetics and isotherm under actual hydrolysis conditions with commercial cellulase and β-glucosidase on Avicel, dilute acid pretreated Creeping Wild Ryegrass (pCWR) and lignin residue of pCWR after enzymatic hydrolysis. It was found that β-glucosidase has little affinity to Avicel, but significant affinity to dilute acid pCWR and lignin with maximum adsorption capacity ( E max ) of 161.57 and 173.50 mg protein/g-substrate, respectively. During hydrolysis, adsorption of cellulase on Avicel was productive and reversible ( E max = 22.86 mg protein/g-substrate); however, nonproductive and irreversible adsorption of cellulase on pCWR ( E max = 42.55 mg protein/g-substrate) and lignin ( E max = 86.07 mg protein/g-substrate) became significant and resulted in cellulase deactivation. Lignin is a key issue causing high cost of enzymatic hydrolysis of lignocellulosic biomass. The nonionic surfactant, Tween 20 was found to significantly overcome nonproductive adsorption of cellulase and β-glucosidase on lignin by reducing the adsorption affinity. All adsorption data including with and without Tween 20 were fit well to Langmuir isotherm. The results from this research will provide useful data for model development of enzymatic hydrolysis. [ABSTRACT FROM AUTHOR]

Highlights: [•] Methane production potential, BD, and kinetics of various substrates were compared. [•] Both of elemental and organic analysis could be used to calculate the TMY and BD. [•] 15% VS of lignin was a critical point in AD of lignocellulosic and manure wastes. [ABSTRACT FROM AUTHOR]

Lignocellulosic biomass is the most abundant natural resource with high biomethane potential. However, complex structure of lignocellulosic biomass has hampered the efficient utilization of this bioresource. Previous studies have investigated the overall anaerobic digestion performance of lignocellulosic biomass, but the individual participation of each lignocellulosic component during anaerobic digestion remained unclear. Thus, this study investigated the methane production characteristics of cellulose, hemicellulose, lignin and their mixtures along with the microbial communities involved in anaerobic digestion. The results showed that the biomethane potential of cellulose was higher than that of hemicellulose; however, hemicellulose was hydrolysed more quickly than cellulose, while lignin was very difficult to be digested. The higher concentrations of acetic, n -butyric and n -valeric acids hydrolysed from the hemicellulose resulted in a lower pH and more severe inhibition on methane production than that of cellulose, and the methanogenesis gradually recovered after pH adjustment. The co-digestion of cellulose and hemicellulose increased the methane yield and biodegradability compared to mono-digestions. The addition of lignin to cellulose brought more significant decrease in the methane yield of cellulose than that of hemicellulose. Substrate-related bacteria such as Clostridium sensu stricto , Lutaonella , Cloacibacillus and Christensenella showed higher relative abundance in cellulose digestate, and sugar-fermenting bacteria such as Saccharofermentans , Petrimonas and Levilinea were more rich in the digestate of hemicellulose. Moreover, methanogenic Methanospirillum and Methanothrix likely contributed to the methane production of cellulose, while aciduric methanogens from Methanobrevibacter , Methanomassiliicoccus , Methanobacterium and Methanoculleus contributed to that of hemicellulose. This study provides a deeper understanding of the mechanism in the bioconversion of lignocellulosic biomass during anaerobic digestion. [ABSTRACT FROM AUTHOR]

Highlights: [•] Thermogravimetric analysis (TGA) of ionic liquid (IL) pretreated biomass performed. [•] Insight into the IL pretreatment revealed by TGA discussed. [•] Cleavage of side chains and degradation of backbone of xylan detected. [Copyright &y& Elsevier]

Highlights: [•] Interaction of biomass with ionic liquid (IL) pretreatment studied by XRD. [•] Swelling and dissolution of cellulose control the resultant crystalline structure. [•] Proper manipulation of IL’s swelling ability leds to low-order structures. [ABSTRACT FROM AUTHOR]