Date of Award

5-2016

Degree Type

Dissertation

Degree Name

Doctor of Philosophy

Major

Environmental Engineering

Major Professor

Terry C. Hazen

Committee Members

Gary Sayler, Kimberly Carter, Qiang He

Abstract

Harmful algal blooms are cosmopolitan and can produce extremely dangerous toxins that can sicken or kill people and animals, and create dead zones in the water. The U.S. economic loss caused by algal blooms is $82 million every year. Clay-based flocculation techniques have been developed to mitigate algal blooms; however, the potential impacts on the microbial community are poorly understood. This dissertation includes multi-scale experiments (Jar, field, microcosms) to study the response of microbial community structure and function to clay flocculation of algal blooms.

Jar tests of removal of Microcystis aeruginosa by chitosan and two types of commercially available clays was studied with Tennessee River water. Acridine Orange Direct Count results showed the bacterial biomass decreased, but not significantly, after clay flocculation. Water microbial community in high removal efficiency tests was significantly different from low removal efficiency tests using 16S sequencing measurements.

China field tests were conducted to verify laboratory tests by applying chitosan-modified-local-soil in 800 m2 [meters squared] ponds. 16S sequencing revealed five bacterial groups that were increased in the water after flocculation. Total coliform tests showed clay flocculation significantly reduced the frequency of coliforms in the pond water.

In the China microcosm experiments, chemical measurements were combined with phospholipid fatty acid analysis and 16S sequencing to characterize the microbial community response to different flocculation techniques. This included clay flocculation only, clay flocculation with zeolite capping, and clay flocculation with oxygen loaded zeolite capping. Water bacterial biomass and sediment bacterial biomass measured by lipid concentration were not significantly altered by various flocculation techniques. However, sequencing results confirmed the presence of distinct water microbial communities between samples with and without zeolite-capping. The relative abundance of ammonia-oxidizing bacteria increased four-fold in zeolite capping sediments. Potential pathogens that are usually adapted to eutrophic water bodies were reduced after clay flocculation. The increased monounsaturated-epoxide-ratio in post bacterial biomass indicated zeolite capping may help the sedimentary bacterial community recover from environmental stress. These studies demonstrated clay flocculation did not decrease overall bacterial biomass but may reduce pathogenic contaminants in water. Zeolite capping may help prevent nutrients from being released back into the water.

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