Background of the Study
Agriculture and food bio wastes present an opportunity for conversion into biogas, a source of renewable energy, through anaerobic digestion (Sau et al., 2014; Janke et al., 2015; Kader et al., 2015; Maile et al., 2017; Manyuchi et al., 2017; Wannapokin et al., 2017). Biogas is an odorless and colorless gas that has an ignition temperature of 650 °C to 750 °C, a calorific value of 20 MJ/m3 , and burns at approximately 60% efficiency (Ziauddin et al., 2015). Biogas presents an opportunity as an alternative fuel for heating and cooking purposes as well as combined power generation and has been increasingly been recommended for adoption as a renewable source of energy. Figure 1 shows the biogas production process as well as the potential energy generation and uses. Biogas production is mainly conducted under mesophilic conditions in dome shaped bio digesters and anaerobic digestate, also termed bio solids which can be further processed for fertilizer usage are obtained (Manyuchi et al., 2017). The biogas produced is rich in bio methane with compositions ranging from 55% to 70% and the other major composition is carbon dioxide with composition ranging from 25% to 35% (Ziauddin et al., 2015).
1.2 Statement of the Problem
The biogas calorific value can be enhanced by applying purifying techniques such as adsorption which separates the carbon dioxide to have bio methane content with more than 90% (Maile et al., 2017).
Another important by product from the anaerobic digestion of bio waste is the anaerobic digestate. This anaerobic digestate is also termed bio solids and contains nitrogen, phosphorous and potassium (NPK) as well as the other trace applications that make it applicable as a bio fertilizer (Makádi et al., 2012). Bio solids compositions of NPK ranging up to 4.27%N; 0.66%P and 4.71%K have been reported in literature (Makádi et al., 2012). On the other hand, the Southern African region being agro based, tea plantations are a common feature in countries like Zimbabwe, of which the tea is further processed to tea bags and tea leaves. At least 470 tons of tea is generated on an annual basis in Southern Africa (Apostolides et al., 2006). Tea waste is a potential source of agro waste that can be a raw material for biogas generated. Tea is mainly cultivated in the high rainfall regions in Southern Africa. During its harvesting and processing, huge amounts are generated and are a potential environmental threat if not properly managed. Several processes whereby tea bio waste is generated include the withering, rolling, fermentation, drying, sorting and grading stages (Oirere, 2015). Figure 2 shows the tea processing stages and all the amount of bio-waste generated. Tea waste in combination with other sources of waste like food waste have been reported to be a good source of biogas production with enhanced yields as high as 30% being reported (Sau et al., 2014).
1.3 Objectives of the Study
The main objective of this study is to investigate the potential of harnessing biogas from tea waste, as a source of renewable and alternative energy. Furthermore, the potential of using the resulting digestate as a biofertilizer is explored.
1.4 Scope of the Study
This study focuses on the Production of biogas and biosolids from Tea Waste Anaerobic Digestion.
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