Date of Award

8-2017

Document Type

Thesis

Degree Name

Master of Science (MS)

Department

Environmental Engineering and Earth Sciences

Committee Member

Dr. Ezra Cates, Committee Chair

Committee Member

Dr. David Freedman

Committee Member

Dr. David Ladner

Committee Member

Dr. Mark Schlautman

Abstract

Photocatalysts have been increasing in popularity in recent years for the use of degrading contaminants in water treatment. Compared to other treatment methods, photocatalysts have the advantages of being reusable, being able to degrade contaminants of concern, and being relatively non-toxic. One major problem with implementing photocatalysts for water treatment on a large scale is their difficulty to recover after treatment. Although a significant amount of research success has been accomplished in degrading contaminants in a lab setting, few commercial treatment systems exist as a result of the recovery problem. One recently-discovered photocatalyst, BiPO4, shows promise for overcoming the recovery issue due to its large particle sizes and high density. This work focuses on characterizing the size and settling behavior of BiPO4 particles to determine whether gravity settling could be used to recover this material. Particle size measurements were first conducted using a dynamic light scattering (DLS) instrument to estimate the expected settling velocity. An average size of 2.35 μm was measured which, according to Stokes' Law, gives an expected settling velocity of approximately 1.60·10-3 cm/s. To verify this calculated settling velocity and determine the distribution of settling velocities in a sample of BiPO4 particles, a column test was conducted using small, customized settling columns. A settling curve (C/C0 vs. settling velocity) was obtained and the median settling velocity was determined to be 2.90·10-3 cm/s. Using the calculated and measured settling velocities, a lab-scale rapid clarifier was designed and constructed to determine whether the BiPO4 particles could be easily removed from a water stream using gravity settling. The tank dimensions consisted of a length of 0.26 m, a width of 0.12 m, and a height of 0.33 m; the lab-scale clarifier was made from sheet acrylic with aluminum sheets to serve as the plate settlers. Various polyvinylchloride (PVC) fittings were altered for flow input and exit from the clarifier. Experiments were run using a BiPO4 slurry fed to the lab-scale rapid clarifier by a 600 rpm Masterflex® pump; the flow rate was varied in order to determine the maximum overflow rate that would result in approximately 90% removal of the material. At an overflow rate of 0.4 m/h (0.011 cm/s), or 9.6 m3/m2·d, a removal percentage of 96% was measured. Lastly, the design of the rapid clarifier was scaled up to determine if the overflow rate measured in the lab-scale experiments for BiPO4 particle removal would be feasible at a large scale. Based on the experimental results, a design for a full-scale rapid clarifier was derived which is able to treat a flow rate of 131 m3/d to remove approximately 96% BiPO4. Implementation on a large-scale would likely require multiple rapid clarifiers in parallel in order to treat a reasonable flow rate using BiPO4 PAO technology.

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