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.

Optimising biogas yields from anaerobic digestion of organic wastes is significant to maximum energy recovery in the biodigestion process and has become an important topic of interest. Substrate particle size is an important process parameter in biogas production, and it precedes other pretreatments methods for the majority of the lignocellulose materials. Optimisation of biogas yield using Response Surface Methodology (RSM) was done, and temperature, hydraulic retention time and particle size were considered variables to develop the predictive models. Pretreatment of groundnut shells was investigated using particle size reduction of mechanical pretreatment methods. After pretreatment, 30 samples were digested in a batch digester at mesophilic temperature. The experimental results showed that the temperature, hydraulic retention time and particle size had significant effects of interaction ( p < 0.05). The optimum experimental and predicted yields are: 44.70 and 42.92 (lNkgoDM) organic dry matter biogas yield, 20.80 and 19.09 (lN/kgFM) fresh mass biogas yield, 24.00 and 22.68 (lNCH4oDM) organic dry methane yield and 12.30 and 15.59 (lNCH4FM) fresh mass methane yield, respectively. The R2 recorded for the four yield components were 0.6268, 0.5875, 0.6109 and 0.5547. These values seem to be lower and a sign of the average fit of the model. Biogas production from groundnut shells was significantly improved with statistical optimisation and the pretreatment method.

Aim: To study the effects of different sizes of groundnut shell on biogas and methane yields using batch reactor at mesophilic temperature. Place and Duration of Study: The laboratory experiment was carried out at the Laboratory of the Department of Agricultural Engineering, Ladoke Akintola University of Technology, Ogbomoso, Nigeria, between August and October, 2018. Methodology: Batch experiment was set up for a period of 35 days with substrate reduced to 2, 4 and 6 mm sizes. The digesters were subjected to anaerobic digestion at mesophilic condition and the gas produced were collected with graduated gas sampling bottles dipped in measuring cylinders already filled with red liquid. The total gas produced was analyzed using gas analyzer to give the percentage composition of the gas components and Enwuff equation was used to calculate the biogas and methane yields of organic dry matter and fresh mass of the samples. Results: The total gas volume of 482.5, 605.0 and 732.5 ml were recorded for the sizes 2, 4 and 6 mm respectively. The organic dry matter biogas yields were 357.1, 514.31 and 324.5 lNkg-1oDM for treatment 2, 4 and 6 mm respectively; while organic dry matter methane produced were 222.41, 298.41 and 211.31 CH4kg-1oDM for 2, 4 and 6 mm, respectively. The fresh mass biogas yields were 147.6, 180.7 and 177.3 lNkg-1FM and fresh mass methane yield were 919, 104.8 and 115.4 lNCH4 kg-1FM for 2, 4 and 6 mm, respectively. Conclusion: Considering the yields recorded, the experiment shows that size reduction had effect on biogas yields and it is an important factor to be considered in biogas production. Treatment with particle size 4 mm seems to be the ideal size when considered the yields in terms of organic dry matter and fresh mass basis.

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Anaerobic co-digestion requires the digestion of two or more homogenous substrates to produce biogas. The superlative participated condition is when principal amount of most important substrate (example manure or sewage sludge) is combined and fermented with each other with lesser quantities of single, or a variety of additional substrate. The co-digestion of one or more substrates commonly improves the biogas output from anaerobic digesters owing to positive improvement brought about in the digestion medium and the furnishing of missing nutrients in one substrate by another. Anaerobic co-digestion of cow dung and jatropha cake for biogas production was carried out in the batch digester in the absence of oxygen at ambient temperature with different mixing ratios for 40 days. The result indicated that treatment with 75% jatropha 25% cow dung had the highest volume of biogas at the rate of 24.41% and treatment with 100% jatropha released has the highest percentage quality of biogas produced (methane) at the rate of 59.6%. Treatment with 50% cow dung 50% jatropha cake was found to be the appropriate mix ratio, since it was rank 2nd in both qualitative and quantitative analytical point of view from the experiment performed.

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