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Title: Integration of biological wastewater treatment and algal growth for biofuels
Author: Uttley, P. J.
ISNI:       0000 0004 5358 7554
Awarding Body: University of Sheffield
Current Institution: University of Sheffield
Date of Award: 2014
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This thesis is concerned with the production of biofuels from microalgae that can be grown in wastewater on marginal land. Algal-derived biodiesel is a promising alternative to both the finite reserves of fossil fuels and also the current biofuel crops that take up agricultural land. The case for coupling biological wastewater treatment to the production of algal biodiesel is a compelling one that is explored in this research using a combination of mathematical modelling and laboratory experiments. Algae utilise by-products of the wastewater treatment process such as carbon dioxide, nitrate and ammonia. In this work, a mathematical model of an integrated wastewater treatment and algal cultivation system is presented. The model contains two units: an activated sludge unit for secondary wastewater treatment and a pond for the cultivation of algae. These units have both liquid phase and gas phase integration. For the liquid phase, the treated effluent from the activated sludge unit is transferred to the algal pond to provide nutrients for algal growth. The model also incorporates gas-phase integration whereby the CO2 rich off-gas from the activated sludge unit is captured and used to enhance the algal growth. In addition, the O2 enriched off-gas from the algal pond is recycled back to improve dissolved oxygen levels in the activated sludge unit. The mathematical model uses equations for algal growth that were developed using laboratory experiments to measure the effect of dissolved CO2, nitrate and ammonia on the growth kinetics of a typical strain of freshwater alga: Chlorella sp. The model includes the industry standard Activated Sludge Model No. 3 for wastewater treatment. An economic profit function is used in the model to find the optimal pattern of gas phase integration to maximise Net Present Value over a specified project lifetime. For the case considered, the model predicts that integration using the gas and liquid exchange described above is necessary for a profitable outcome. This is a general approach that can be used to retrofit biofuel production onto an existing wastewater site, or design a new integrated system from first principles.
Supervisor: Wilkinson, S. J. ; Gilmour, D. J. Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available