PhD Theses (Environment)

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Browsing PhD Theses (Environment) by Subject "Anaerobic Digestion"

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    Anaerobic digestion of water hyacinth : Effect of pretreatment and co-digestion on biogas production
    (2018) Barua, Visva Bharati
    Water hyacinth is considered to be the world’s worst aquatic due to its phenomenal reproduction potential. It can grow within a week and cover an entire freshwater body by forming thick dense mats. These thick dense mats hamper the aquatic ecosystem alongwith the health, livelihood and recreation of human beings. Water hyacinth is difficult to manage as it can re-grow miraculously even if it is completely eradicated. Presence of cellulose and its availability in abundance makes water hyacinth an attractive feedstock for biogas production through anaerobic digestion. Biogas production from water hyacinth can effectively manage the aquatic weed as well as mitigate environmental pollution which is caused by burning of fossil fuel. But the presence of lignin in water hyacinth makes hydrolysis the bottleneck of anaerobic digestion thereby delaying the hydrolysis phase and producing decreased amount of biogas. Therefore pretreatment of water hyacinth is essential for accelerated hydrolysis period and enhanced biogas production. In this study, thermal, electrohydrolysis and biological (microbial) pretreatment were investigated to enhance solubilisation of water hyacinth. Hot air oven pretreatment of water hyacinth at 90ºC for 1h demonstrated the highest solubilisation and biogas production when compared to the other pretreatment techniques. Even mono-digestion of water hyacinth produces lesser amount of biogas therefore co-digestion of water hyacinth is essential to balance the nutrients and dilute the toxic inhibitors. During the BMP assay F/M ratio 2 was observed to be ideal for untreated water hyacinth whereas for the pretreated water hyacinth F/M ratio 1.5 was observed to be ideal. Co-digestion of water hyacinth was tried not only with cow dung as inoculum but also with other organic wastes (i.e., food waste, Hydrilla verticillata, banana peels) with and without pretreatment. Pretreatment and anaerobic co-digestion of water hyacinth not only enhanced the quantity of biogas production but also the quality of the produced biogas by increasing the percentage of methane content. At last, a novel anaerobic digester was designed, fabricated and operated in continuous mode. The novel anaerobic digester proved its immense prospective in treating water hyacinth in untreated, pretreated or co-digested form. The design of the novel anaerobic digester is proficient in minimising the cost, difficulty in operation and manages space constraint when compared to the traditional two stage anaerobic digesters with mixing operation.
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    Enhancement of biogas production from rice straw by co-digestion and pretreatment techniques
    (2019) Kainthola, Jyoti
    Due to rapid economic development over the past few decades, global energy consumption has intensified continuously, causing not only greenhouse gas emissions, but also energy shortage, and in some areas even energy crises. This imminent energy consumption and demand have been the motivation for world scientists to explore alternative energy sources that could replace fossil fuels. Agricultural residues (i.e., wheat straw, rice straw, corn straw, etc.) are the most abundant resource of lignocellulosic wastes, and contribute a major role in producing low-cost and sustainable forms of energy via anaerobic digestion. Anaerobic digestion is a realistic approach to concurrently manage rice straw and harness renewable energy. Inoculum plays a major role in the process of anaerobic digestion; selecting appropriate inoculum is a crucial factor to initiate the anaerobic digestion process.It not only validates the several biochemical and microbial processes, but also enhances the overall methane yield. In order to select the appropriate inoculum for rice straw, biochemical methane potential (BMP) assay of anaerobic digestion of rice straw with digested cow dung and fresh cow dung revealed methane yields of 125.77 and 72mL/g-VSadded, respectively. The 16S metagenomics sequencing revealed that DCD is enriched with majority of anaerobes.