The Development of an Enumeration Method for Microcystis aeruginosa and its Subsequent Removal in Water Treatment Systems via Nanobubble-Enhanced Coagulation

Abstract

Coagulation is a critical step in conventional water treatment systems that plays a key role in reducing turbidity and removing contaminants. Industrial coagulants, such as polyaluminum chloride (PACl), are widely used due to their effectiveness in various water conditions. They do, however, come with drawbacks, including high costs, large supply requirements, and potential health risks if handled improperly. This thesis demonstrates that incorporating nanobubbles (NBs) into the coagulation process, which we refer to as NB-enhanced coagulation, enhances treatment efficiency compared to using PACl alone. NB-enhanced coagulation reduces the coagulant dosage while minimizing the environmental footprint and associated costs, which were evaluated through a life cycle assessment and cost analysis of implementing a nanobubble generator into a commercial-scale coagulation system. To evaluate this enhancement, a cyanobacteria species responsible for harmful toxic blooms in water bodies worldwide, Microcystis aeruginosa (M. aeruginosa), is used as a model contaminant. Additionally, M. aeruginosa offers the opportunity to study the effects of localized pressure gradients that occur during NB collapse by measuring the concentrations of intracellular cyanotoxins, which can be released upon cell lysis. Post-coagulation results indicate that cyanotoxin release in NB-enhanced coagulation experiments are comparable to traditional coagulation, confirming that NBs do not induce cell lysis or cause cyanotoxin release. This finding supports NBs’ role in enhancing coagulant strength and cell aggregation rather than disrupting cyanobacteria cells.

M. aeruginosa was introduced into coagulation experiments at constant and consistent concentrations, which was achieved by a novel enumeration and concentration method developed and presented in this thesis. By using an upright microscope, a Petroff-Hausser counting chamber, and a simple MATLAB algorithm, our M. aeruginosa concentration results were comparable to concentrations obtained via the highly reliable, but expensive, flow cytometry method at a fraction of the cost and expertise requirements.