Use of sorghum crop for biogas production

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The world is emphasizing to reduce the CO2 emissions, increase energy efficiency and the proportion of renewable energy sources in total energy production to 0.20 by 2020. Biogas is one of the important renewable energy sources. Biogas production from agricultural biomass is getting importance due to offering different environmental benefits. Many types of crops are being used for biogas production including maize, sorghum, sunflower, sudan grass, fodder beet, poor oat grass meadows, small-sedge poor-fen, meadow, and montane hay meadow. Biogas consists mainly of methane (CH4) and carbon dioxide (CO2), CH4 being the energy-carrying compound. Biogas production systems are therefore aimed to optimize the methane yield.

Sorghum (Sorghum bicolor L. Moench) is a C4 annual grass which can produce high forage biomass yields per unit of land. The most important producers of grain sorghum are USA, India, Nigeria and China. Within the species Sorghum bicolor which is characterized by a diploid set of chromosomes (2n = 20) are several subspecies or races with different morphological and physiological characteristics. Since plant breeders found first lines with cytoplasmatic male sterility in 1950ies years hybrid breeding technology is established in Sorghum bicolor too.

Worldwide, sorghum has been used for human food, animal feed, building material and fencing. Traditionally, sorghum is used in unfermented and fermented breads, porridges, couscous, rice-like products, snacks, and malted alcoholic and non-alcoholic beverages in many African and Asian countries. Sugar in biomass of sweet sorghum is readily fermentable and thus it can be considered as a tremendous raw material for fermentative hydrogen production. Sorghum has been thoroughly investigated as an energy crop for bioethanol and methane production, it can also be used as a potential source for hydrogen production. Sorghum biomass could be fully exploited for hydrogen production since both soluble and complex carbohydrates can be utilized, either in a single step or separately after extraction.

Fermentative hydrogen production from biomass can be attained either by using mixed acidogenic microbial cultures or a pure culture of a saccharolytic strain. Ruminococcus albus is a non spore-forming, obligatory anaerobic, coccoid bacterium, the natural habitat of which is the first stomach (rumen) of the ruminants.

Anaerobic digestion is a process that takes place in the presence of biodegradable biomass (substrate), anaerobic micro-organisms (facultative as well as obligatory), and a milieu (digester) free of molecular oxygen (O2)”.The process converts the biomass into energy in a gaseous mixture otherwise known as biogas. The composition of biogas consists of gases mainly methane (CH4) and carbon dioxide (CO2) together with small to minute concentrations of other gases. This composition depends on quality of the substrate, conditions of digestion environment and the type of microorganisms involve in this process. In the present global energy crises, many none oil producing countries see the employment of anaerobic digestion as a means to convert waste material and energy crops into methane that can reduce their dependency on petroleum and natural gas. The complex process of anaerobic digestion can be divided into four phases of degradation, such as hydrolysis, acidogenesis, Acetogenesis, and Methanogenesis. This whole process of biogas production can be performed using mesophilic digester operated at 38°C. Liquid manure can be provided as source of microbes for the 21 day anaerobic digestion process in a digester composed of chopped whole plant material and of liquid manure. A Ritter wet meter was used for the measurements of biogas volumes. It consists of a multi-chamber rotary measuring drum containing water. The drum is attached to a counting mechanism consisting of scales and needle-dials. It functions upon the principle of positive displacement. It contains an inlet and outlet for connecting the gas sac and expelling the measured gas respectively. The specific methane yield of sorghum ranged from 300 to 450 nL kg-1 of volatile solid.

Sorghum is well adopted crop under the climatic condition of Pakistan. It is well known drought and heat tolerant and can produce high biomass using low inputs. Pakistan is facing very serious crises of energy since many years. To reduce the problem we have to rely on renewable energy resources. Therefore, sorghum can be efficiently used for the production of renewable energy (biogas production) resource in Pakistan.


Published in: Volume 05 Issue 43

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