Abstract
The mitigation of adverse climate change requires holistic strategies. The strategies include the proper handling of biomass wastes such as cow dung. The handling of the wastes has to be efficient using appropriately designed anaerobic digesters. In addition, the operating status of these digesters has to be monitored for detection of any fault of the digesters. Unfortunately, existing approaches for designing and monitoring the working condition of digesters have limitations. This chapter presents the innovative and explicit conceptual design approach of adapting the biomass-fed anaerobic digester and the digester operating-status-indicators in semi-arid areas. The approach is recommended to the renewable energy system designers. Finally, the appropriate indicators are recommended to be applied by the biogas plant operators or users.
TopBackground
Biomass is a renewable energy resource that harvests solar energy and stores that energy in the form of chemical energy. It includes animal, agricultural, and municipal wastes. Various ways are available to convert biomass into bioenergy, e.g., biogas. The conversion of biomass may be done through the anaerobic digestion process. The process is run without air while employing microbial degradation to produce biogas, among other by-products. The process is a proven technology. Several factors, including temperature, influence the technology of sustainable biogas generation and the state of feedstock applied (Theuerl et al., 2015). Other factors affecting the efficient production of biogas from anaerobic digesters (ADs) include substrate pH, Carbon-Nitrogen ratio of feedstock, feedstock loading rate and particle size, hydraulic retention time and additives. The essential and critical factor, especially in batch-fed ADs, is temperature. It significantly affects biogas generation and other factors (Adekunle and Okolie, 2015). Here below is the information on the temperature relative to the biogas generation. The mesophilic state requires AD temperature to be within 20oC to 45oC. However, keeping the AD at a constant temperature, around 35oC, increases biogas generation. The biogas microbes survive optimally at a temperature variation of 0.5oC/day; henceforth, keeping ADs at temperature variations approaching this value is important (Rowse, 2011). Usually, biogas microbes can sustain temperature variation of ±3oC/day. Therefore, devising a simple temperature control system to reduce temperature variation of biogas digester toward 0.5oC/day is of paramount importance for sustainable biogas generation.
The feedstock employed in biogas generation may consist of dry matter of up to 15% wet basis for the liquid state digestion, i.e. liquid anaerobic digestion (LAD) or above 15% wet basis for the solid-state digestion, i.e. high solid anaerobic digestion (HSAD) (Li et al., 2011). The HSAD feedstock has a much longer retention time and lacks control over the biological process (Li et al., 2011). Therefore, it produces more biogas and needs less or no addition of water compared to the LAD feedstock. However, the HSAD feedstock needs a large amount of inoculum for exciting biogas generation (Yang et al., 2015).
Key Terms in this Chapter
Rural Semi-Arid Areas: In the sub-Saharan Africa context, a land of marginal crop production potential, quick maturing cereals, and carrying natural vegetation of Acacia-Themeda association but including dry Brachystegia woodland. It is a potentially productive grazing area, limited by bush encroachment, leached soils, and inadequate water.
Detailed Designing: The process in which the generated system design is refined where plans, specifications and estimates are created and ready for manufacturing or construction.
Adaptation: The reference to a process of varying the system or structure design to get its improved design with high performance for the betterment of the user or community.
Conceptual Designing: An act of extensive outlining of purposes and forms of a system or structure to be established for facilitating the conception of a clear user interface to understand and interpret the system or structure.