Master of Science in Civil Engineering (MSCE)
Civil and Environmental Engineering
Uncontrolled discharge of ballast water by vessels has been considered one of the main mechanisms for the introduction of aquatic nuisance species (ANS). The typical size of species found ranges from 0.02 to 10,000 micrometer. This wide range of sizes consists of microorganism (protozoa, dinoflagellates, and cholera), planktonic species, plants, insects, other arthropods, worms, mollusks, and vertebrates. These species either remain suspended in ballast water or settle in ballast tank sediments. Providing treatment for ballast water is a challenging task due to space availability of ships and significant magnitude of flow rates and volumes of ballast water. Currently, open ocean ballast water exchange (BWE) is utilized for control of ANS. However, BWE has potential safety risk and it is not fully effective as a separation method for ANS. This thesis examines common ballast water control methods having potential for shore and vessel-based applications. In addition to BWE, other control methods including dissolved air flotation (DAF) are under consideration. Each control method is examined according to effectiveness, safety, capital and maintenance cost, and applicability. In addition, a screening assessment of DAF as a potential ANS separation technology is being investigated. Experimental bench-scale development of dissolved air flotation was selected and examined to evaluate the potential of DAF as a viable option for ballast water control. Freshwater (1 ppt) and saltwater (20 ppt) matrices were used with ballast water surrogates synthesized from aquaculture, fresh water, wastewater, and storm water. The samples were standardized to a similar turbidity range before application of DAF treatment. Bench-scale experimental results for ballast water surrogates based on particle number demonstrated particle removal efficiencies achieved as high as 99% and 98% for saltwater and freshwater matrix, respectively. Particle size distributions in DAF were modeled using a two-parameter power law function. From the power law model on index of the surface area concentration was obtained. Using a least-square analysis, the power law model was shown to provide a good fit (significant r-squared) for both influent and effluent particle gradations. The overall study results demonstrate the potential of DAF as a competitive and effective size-based separation technology.
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Voon, Eng Chong, "A screening assessment of dissolved air flotation for control of nonindigenous invasive species transported in shipping ballast water" (2002). LSU Master's Theses. 3511.