Abstract
A systematic literature review was conducted to compare the efficacy of biological, chemical, physical, and combined pretreatments in enhancing biomethane production from crop residues (CR). Three electronic databases viz., Science Direct, EBSCOhost, and PubMed were used to identify the studies in literature. The pretreatment methods were compared in terms of their advantages and disadvantages with reference to techno-economic aspects. The techno-economic aspects considered included rate of hydrolysis, energy use, effectiveness, cost, and formation of toxic compounds. A total of 3167 studies, covering the period 2014 - 2018, were screened for relevance to the study. Forty-four records (n=44) consisting of 36 research papers (n=36) and eight narrative reviews (n=8) met the inclusion criteria. The results show that physical and chemical methods are the most effective and fastest. These methods have limited utility due to high cost of resources, operation, and energy as well as formation of inhibitory by-products. Despite generation of toxic compounds, combined methods are regarded as fast and costeffective. Biological method is inexpensive, eco-friendly, and low energy-consuming. However, it is a nascent technology that is still developing. A combination of trends in research and development provide the best pretreatment alternative to improve the biomethane production from CR.
Highlights
Biogas is a renewable fuel with wide applications the world over (Weiland, 2010; Achinas et al, 2017; Alhassan et al, 2019)
The number of publications regarding pretreatment of crop residues (CR) for biogas production rose between 2014 and 2017. This points to sustained research effort on the subject. This can be ascribed to the fact that pretreatment of feedstock is a focal technology in biogas production (Kigozi et al 2014; Horváth et al 2016; Achinas et al 2017)
Kougias and Angelidaki (2018) reported an increase in the number of articles retrieved from Scopus and Web of Science databases based on the keyword “biogas” between 1977 and 2017
Summary
Biogas is a renewable fuel with wide applications the world over (Weiland, 2010; Achinas et al, 2017; Alhassan et al, 2019). Parameters used to estimate the potential of OM to produce biogas include anaerobic biogasification potential (ABP) and biochemical methane potential (BMP) These parameters allow direct evaluation of biogas yield, which can be achieved by the AD process (Jingura and Kamusoko, 2017). The BMP of feedstock is affected by several biochemical characteristics (Gould, 2015; Strong et al, 2016; Jingura and Kamusoko, 2017) These include nutrient content, VS content, chemical oxygen demand (COD), biological oxygen demand (BOD), carbon to nitrogen ratio (C/N), and presence of inhibitory substances (Babaee and Shayegan, 2011; Kwietniewska and Tys, 2014). To the best of our knowledge, this is the first systematic review study that has been undertaken to compare the efficacy of pretreatment methods in enhancing biomethane production from CR. These were adapted from Wagner et al (2018) and Venturin et al (2018). Wagner et al (2018) considered factors such as low capital and energy use, applicability to a range of feedstock, high product yields, and low waste management. Venturin et al (2018) considered avoidance of inhibition of AD steps, high degree of simplicity, and effectiveness as some of the characteristics of an ideal pretreatment method
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