Date of Award

8-2016

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Legacy Department

Environmental Engineering and Science

Committee Member

David A. Ladner, Committee Co-Chair

Committee Member

Annick Anctil, Committee Co-Chair

Committee Member

David L. Freedman

Committee Member

Terry H. Walker

Abstract

In the wastewater industry the concept of sustainability addresses how complex systems, aimed at mitigating or preventing pollution, involve tradeoffs in life cycle impacts. Advanced treatment systems designed for high quality effluent often come at the cost of increased chemical and energy use, and alternatives which minimize the impacts in all categories are desirable. Algaculture is a promising technology for sustainable wastewater treatment, but quantifying the impacts of these systems is prudent before they are implemented on a large scale. This work enhances the growing body of research on the topic, contributing assessments of algaculture wastewater treatment systems using model-based life cycle assessment (LCA), laboratory investigations, and data-based LCA. The integration of algaculture into conventional activated sludge systems was investigated. Process modeling was used as the basis of a comparative LCA to determine environmental impacts. Integrating algaculture prior to activated sludge proved to be beneficial for all impact categories considered; however, this scenario would also require primary sedimentation and impacts of that unit process should be considered for implementation of such a system. Membrane photo-bioreactors are proposed for use in algae-based wastewater to achieve nutrient removal with a relatively small footprint compared to other algaculture systems, but membrane fouling is problematic in these systems. Laboratory-scale bioreactors and membrane filtration procedures were used to determine the impact of nutrient limitation and culture density on fouling. Nitrogen limitation was found to exacerbate membrane fouling, and it is proposed that accumulation of carbon-rich intracellular metabolites and subsequent diffusion from cells was the mechanism observed. Lagoon systems, once a common method of wastewater treatment which has fallen out of favor partially due to their unreliable ammonia control, can be retrofitted with rotating algal biofilm reactors (RABR) to improve treatment. This hybrid system was compared to an activated sludge systems in terms of operational, construction stage, and avoided life cycle impacts. Results show that the lagoon with an RABR system reduced eutrophication impacts more than the activated sludge system. Additionally, the resulting increase in global warming potential and cumulative energy demand for the RABR system was smaller than that of the activated sludge system.

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