Date of Graduation

Winter 12-31-2024

Document Type

Thesis

Degree Name

Master of Science in Chemistry

College/School

College of Arts and Sciences

Department/Program

Chemistry

First Advisor

Amrita Bhattacharyya

Second Advisor

Michael Stevenson

Third Advisor

William Karney

Abstract

In current times, terrestrial and aquatic environment health have been increasingly threatened by the accumulation of toxic heavy metals such as chromium due to industrialization. Biosorption is an eco-friendly and effective method of toxic metal remediation currently being explored and adopted by many industries. Biochars, with high specific surface areas for sorption, easy affordability, and their eco-friendly nature are popular sorbents for removing toxic metals from soils and groundwater for future recycling and reuse. Biochars are produced by pyrolysis, a process in which biosolids are burned in an anoxic environment at an elevated temperature ranging from 200 – 1000 °C. By selecting an optimal pyrolysis temperature and feedstock source, biochar can serve as an effective, carbon-neutral remediation tool for toxic metal removal from contaminated sources. While there have been studies that show how biochars are effective sorbents, the specific impact of pyrolysis temperature on the sorption efficacy and physicochemical properties of the biochar is not well understood. This knowledge is critical in order to develop efficient management strategies and environmental regulatory policies related to the use of biochars for remediation purposes. Therefore, in this MS dissertation, (1) the physicochemical changes of biosolid and biochar produced from the same source feedstock were evaluated by various methods of characterization; and (2) the sorption efficacy of Cr(VI) onto biochar pyrolyzed at different temperatures was tested via a laboratory based batch sorption experiment. Wastewater sludge was procured from the Makena Wastewater Reclamation Plant from Maui, HI and pyrolyzed at three different temperatures (300 °C, 500 °C, 700 °C). The physicochemical properties of the original dried sludge and the resultant biochars were characterized using a variety of molecular scale analytical techniques such as Fourier-Transform infrared spectroscopy (FTIR), scanning electron microscopy/energy dispersive spectroscopy (SEM/EDS), and scanning transmission X-ray microscopy/near-edge X-ray absorption fine structure (STXM/NEXAFS). Biochar produced at 300 °C retained more oxygen-containing functional groups and a high phenolic/aromatic group ratio compared to the ones produced at 500 and 700 °C. Experimental data clearly indicates that pyrolysis at 300 °C created the biochar with the most consistent overall sorption of Cr(VI). This high sorption behavior at 300 °C is consistent with the spectroscopic observation and is attributed to high oxygen-containing functional group content (high phenolic/aromatic functional group ratio). These groups participate in the reduction of Cr(VI) to Cr(III) and the complexation of Cr(III) on to oxygen-containing groups like phenolic and carboxyl groups. This work highlights that both physicochemical properties of source feedstock and optimal pyrolysis temperature are critical for maximum removal of toxic contaminants from natural environments.

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Available for download on Thursday, December 16, 2027

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