PhD Theses (Energy Science and Engineering)

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Browsing PhD Theses (Energy Science and Engineering) by Subject "Anaerobic Digestion"

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    Experimental Investigations for the Enrichment of Biogas Employing Biomass-Based Scrubbing Agents and Bio-Electrochemical Approaches
    (2022) Bora, Deep
    Biogas produced from anaerobic digestion of organic waste is one of the potential alternative biofuels and is economically feasible, which might benefit the future energy supply demands as well as contribute to a reduction of greenhouse gas emissions. Biogas is primarily composed of methane (CH4) and carbon dioxide (CO2) as the major constituents, with trace amounts of other components like water vapour, hydrogen sulphide (H2S), hydrogen (H2), and nitrogen (N2). The presence of H2S in biogas needs special attention for cooking, power generation, as well as upgrading to bio-methane due to its foul-smelling odor, corrosion, health issues, and environmental problems. Scrubbing of CO2 is also essential for the upgradation of biogas, which increases the calorific value of the treated gas and enhances its efficiency for being used as vehicular fuel and power generation. Among various purification technologies, the absorption and adsorption methods are found to be simple, cost-effective, and easy to operate for the removal of CO2 and H2S from decentralized biogas plants installed in rural areas. Generally, the use of different alkaline chemicals in the chemical absorption and adsorption processes is a common technique for the removal of CO2 and H2S from biogas. But, the problem arises in the disposal of the used chemicals due to their toxic and environmentally unfriendly nature.
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    Prospects of Energy Production from Lignocellulosic Biomass, Solar Photovoltaic and Hybrid Systems
    (2023) Buragohain, Sachankar
    Fossil fuel energy sources have been the primary source of energy and has a major share in meeting the energy demands of the day-to-day activities. However due to constant depletion of fossil fuel sources and low replenishment rate, it has forced mankind to shift its approach towards more renewable and sustainable energy sources. In recent years, all nations have shifted their approach from a fossil reliant nation to a more sustainable and greener approach nations. India being an agriculturally rich country with abundant biomass resources and ample solar radiation for maximum time of the year has invested majorly in biomass and solar. Anaerobic digestion of organic and lignocellulosic biomass has been a major area of research in many parts of this region. Though large-scale anaerobic digestion of organic biomass has already been implemented in some cities, use of lignocellulosic biomass has not been extensively done. The lignocellulosic biomass resources are either dumped in fields or are burned down releasing more carbon dioxide in the atmosphere. Keeping in view the constant depletion of fossil fuel sources and ever rising energy demand, it is essential that application and feasibility of renewable energy sources at community level is emphasized. The study was thus sub divided into three parts focusing on energy generation from anaerobic digestion, solar photovoltaic and hybrid systems. The anaerobic mono- and co-digestion of three lignocellulosic biomasses viz. duckweed, switchgrass and rice straw were performed in 1 litre laboratory-scale batch reactors. The initial biochemical methane potential test was performed at three different total solids concentrations (10%, 15%, 20%) and cattle dung to feedstock ratios (1:1, 1:1.5, 1:2) under mesophilic conditions (28–32 °C) for 36 days. Co-digestion of feedstocks at 1:1 ratio yielded better results than other cattle dung to feedstock ratios. Optimized physical parameters were further implemented for a scale-up co-digestion study of biogas potential from 4 m3 community-size biogas digesters. The investigation was performed for 60 days maintaining a hydraulic retention time of 40 days, and a comparative analysis with mono digestion of cattle dung was also analyzed. Average daily biogas production for digester containing rice straw and cattle dung was 0.36 m3/kg-VS, whereas it was 0.34 m3/kg-VS and 0.32 m3/kg-VS for switchgrass and duckweed, respectively. An overall comparative analysis of the biogas production and its composition for both biochemical methane potential tests and continuous processes are discussed in this work.