Utilization of Agricultural Wastes for Biogas Production

Introduction

Energy consumption has increased steadily over the last century as the world population has grown and more countries have become industrialized. Biogas, a renewable biofuel is becoming increasingly important as a consequence of major concern for depleting oil reserves, rising crude oil prices and greenhouse effect. Most of the biogas plants are almost fed with cow dung, mixture of human night soil, pig dung, stacks of feed grasses, etc. The rising greenhouse gas emissions, decreasing fossil fuel supplies and energy security have led to the introduction of renewable energy targets at national level [1].

Renewable energy has remained one of the best alternatives for sustainable energy development. The energy carrier focus, in this paper, is biogas, which is among the alternatives to fossil fuels. One of the most efficient energy sources is the biogas produced from green energy crops and organic waste matters. Biogas is distinct from other renewable energies because of its characteristics of using, controlling and collecting organic wastes and at the same time producing fertilizer and water for use in agricultural irrigation. Biogas does not have any geographical limitations nor does it require advanced technology for producing energy, also it is very simple to use and apply. It has a very positive impact on the environment, since less CO2 is formed during its combustion than used for photosynthesis by the plants from which it is produced [2, 3, 4, 5, 6].

Biogas production potential of different mixtures of unscreened dairy manure and food waste compared with the yield from manure was investigated. The methane yields of fine and coarse fractions of screened manure and unscreened manure after 30 days were 302, 228, and 241 L/kg, respectively. Approximately 93%, 87%, and 90% of the biogas yields could be obtained after 20 days of digestion. Average methane content of the biogas was 69%, 57%, and 66%, respectively [7].

Biogas and methane yields of food and green wastes and their mixture using batch anaerobic digesters have been studied. The mixture was composed of 50% food waste and 50% green waste, based on the volatile solids initially added to the reactors. The biogas yields were found to be 430, 372 and 358 mL/g, respectively, and the methane yields were 245, 206, and 185 mL/g, respectively [8]. The production of biogas from fermentable materials such as cow dung, poultry waste and water hyacinth was studied. Percentage of methane content (the main constituent) in biogas produced from different fermentable materials was almost the same [9].

Results and Discussion

A- Maize cob and cow dung (4:1) B- Maize stalk and goat dropping (4:1) C- Maize stalk and cow dung (4:1) D- Acha straws and cow dung (4:1) E- Maize cob and goat dropping (4:1)

Volume of Biogas Production

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Discussion

The analysis of moisture in solid substrates is co- related with growth of microorganisms [11]. As microbes can absorb only dissolved solids, so moisture in residues provide medium for metabolic and physiological processes [12]. Volatile solids of Acha straws (22%) were higher than that of maize cob (11%) and maize stalk (3.45%). ash content of acha straws (5.840%) was found to be higher when compared with that of maize cob (1.1%) and maize stalk (5.11%).

Copyright© Egga SE, et al.

Egga SE, et al. Utilization of Agricultural Wastes for Biogas Production. Pet Petro Chem Eng J 2019, 3(3): 000202.

From figure 1 above, the production of biogas from digester A (maize cob and cow dung) started on day 2 with an average volume of 65ml, digester B (maize stalk and goat dropping) began on day 2 with an average 55ml, digester C (maize stalk and cow dung) started on day 1 with an average volume of 90ml, digester D (Acha straws and cow dung)began on day 2 with an average of 50ml and finally, from digester E (maize cob and goat dropping) began on day 2 with an average of 34.57ml of the retention time. Fluctuation of biogas production occurs in all the digesters which had maximum peaks different retention times. Digester A (maize cob and cow dung) had maximum biogas volume of 65ml, digester B (maize stalk and goat droppings) had volume of 55ml, digester C(maize stalk and cow dung) had a volume of 90ml, digester D(Acha straws and cow dung) had maximum volume of 50ml and finally, digester E(maize cob and goat dropping) had a volume of 34.57ml. After this maximum peak, there was a fluctuating decrease of biogas production in each of the co-digesters as the retention time increases [13].

Comparing the five results after 15 days has shown that, maize stalk and cow dung gave the highest cumulative yield of biogas of 280ml, followed by maize cob and cow dung, maize stalk and goat droppings and acha straws and cow dung which had the same cumulative volume of 260ml and lastly, maize cob and goat dropping gave the least cumulative volume of 46ml. From the five digesters, the digesters containing cow dung and plant wastes produced biogas faster than others. This can be attributed from the positive synergetic effects of the co-digestion of cow dung and food waste in providing more balance nutrients, increased buffering capacity and decreased effect of toxic compounds [14]. The production of biogas follows first order kinetics [15, 16].

Conclusion

Biogas production from co-digestion of different agricultural wastes and animal manure through anaerobic process was established to be feasible at a temperature of 35°C.