Semester Award Granted

Spring 2025

Submission Date

May 2025

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Thesis/Dissertation Advisor [Chair]

Masoud Jahandar Lashaki

Thesis/Dissertation Co-Chair

Daniel Meeroff

Abstract

High phosphate levels and warm temperatures in surface waters can stimulate the overgrowth of certain alga types, causing harmful algal blooms (HABs). HABs may adversely affect public health and have negative economic impacts due to associated healthcare costs, required clean-up activities, and tourism revenue loss. The overarching objective of this study was to utilize an industrial ecology approach and convert algal biomass into chemically modified activated carbon adsorbent materials for phosphate removal. Cyanobacterial biomass was collected from Lake Okeechobee in Florida and processed before activation using fast and energy-efficient microwave heating. To improve phosphate removal, the surface of the adsorbents was modified using different mass ratios (0.5 to 2.0) of lanthanum chloride, zinc chloride, magnesium chloride, or magnesium oxide to precursor. The adsorbents were evaluated for phosphate uptake to identify performant materials for further assessment. Multiple materials modified with lanthanum chloride achieved near-complete phosphorus removal efficiency (greater than 99%) over a wide range of initial concentrations (5, 10, and 20 mg/L). The best-performing material which was prepared with a lanthanum chloride to precursor mass ratio of 1.5 and microwave heating duration of 3 minutes achieved greater than 90% phosphorus removal using a low adsorbent dosage of 0.2 g/L and a short contact time of 30 minutes. This final candidate was studied in the presence of natural organic matter (25-62 mg/L), and the results showed that phosphate removal performance was not adversely affected. The research findings showed the potential of lanthanum-modified algae-derived activated carbon materials to mitigate HABs through phosphate adsorption from surface waters. The superior performance of lanthanum-modified materials for phosphate removal is due to the formation of lanthanum phosphate (LaPO4.H2O; also known as rhabdophane), which precipitates in water and permanently sequesters phosphorus. A preliminary cost analysis estimated the total cost of treatment to be about $0.03 per gallon for an influent phosphorus concentration of 0.2 mg/L and 80% removal efficiency. The research findings have the potential to not only enhance air and water quality and public health in the impacted communities but also help maintain a thriving recreation and tourism industry.

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