Date of Award

5-2019

Document Type

Thesis

Degree Name

Master of Science (MS)

Department

Environmental Engineering and Earth Sciences

Committee Member

Sudeep Popat, Committee Chair

Committee Member

David Freedman

Committee Member

Ezra Cates

Abstract

Landfills are the primary method to dispose of municipal solid waste, and the water leaching from landfills contains products of physiochemical and biochemical reactions, presenting an important environmental challenge. In many cases, leachate is diverted to publicly owned treatment works (POTWs) for treatment. However, even if leachate contributes less than 1% of the total wastewater flow, recalcitrant dissolved organic matter (DOM) containing ultraviolet-quenching substances (UVQs) remains in the leachate after biological treatment, contributing to a low UV transmittance, thus also decreasing the effectiveness of UV disinfection. To analyze the removal of UVQS of landfill leachate before sent to POTWs, this study researches and compares coagulation/flocculation and Fenton’s oxidation, an advanced oxidation process, to remove UVQS in landfill leachate by analyzing the differences in soluble chemical oxygen demand (sCOD), dissolved organic carbon (DOC), UV absorbance at 254 nm (UVA254), specific UV absorbance at 254 nm (SUVA254) and tryptophan, fulvic acid, tyrosine, and marine humic acid-like fluorescent intensities with an excitation emission matrix (EEM) and functional groups with Fourier-transform infrared spectroscopy (FTIR) to better understand the removal mechanisms. This study also evaluates a Fenton’s dimensionless oxidant dose (DOD) of 0.7 for three different leachates to analyze trends in treatment levels. DOD is a normalization of the reactive oxygen present to the initial sCOD. During coagulation studies, three initial pH values (5.5, 6.5, and 8.2) and FeCl3 dosages (1 g/L, 5 g/L, 10 g/L) were studied. Initial pH of 6.5 and 10 g/L FeCl3 dosage reached the maximum DOC removal, and UVA254 and SUVA254 reduction, reaching 65.1%, 2.6 cm-1 (from 22.4 cm-1), and 0.62 L/mg-M (from 1.86 L/mg-M), respectively. This treatment also had large DOM removals with an affinity toward fulvic acids, however it was not effective in removing carboxylic acid functional groups. For Fenton’s oxidation, first, two leachate samples taken from a landfill in Greenville County, SC, at different times, treated with a 24-hour reaction time at a DOD from 0.07-0.72 with a molar ratio of 5:2 for H2O2:FeCl2 at pH 4, were studied. The 0.72 DOD dose led to the highest decrease in UVA254 to 4.2 cm-1 and SUVA254 to 0.63 L/mg-M, with a DOC removal of 48.8%. All treatments targeted fulvic acids above other DOM. The higher the DOD, the more DOM removed, and the better able Fenton’s oxidation was at breaking down the C=C in aromatics and COO- in carboxylic acids. From analyzing the precipitate formed during Fenton’s treatment, it was also found that at lower DOD doses the treatment is partially due to coagulation only, whereas at higher concentrations the treatment oxidation accounted for all DOC removal. When comparing these results to a leachate taken from a landfill in Orange County, FL treated with a 0.7 DOD, the removal trends of DOC, UVA254, and SUVA254 were not consistent, suggesting normalizing treatment requirements for UVQS removal may be better with SUVA254 instead of sCOD This research successfully shows that coagulation/flocculation and Fenton’s oxidation can remove UVQS, but due to the complex nature of the UVQS, neither treatment removes all constituents. The results indicate coagulation/flocculation will result in better treatment, but it is likely Fenton’s oxidation will result in a larger number of biodegradable organics that can be removed during biological treatment at a POTW.

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