Date of Award

8-2021

Degree Name

Master of Science

Department

Geological and Environmental Sciences

First Advisor

Dr. Donald M. Reeves

Second Advisor

Dr. Daniel P. Cassidy

Third Advisor

Dr. Duane R. Hampton

Keywords

Leachate, biosolids, mass flux, emerging contaminants, chemical transformations

Access Setting

Masters Thesis-Open Access

Abstract

The disposal and treatment of Per- and Polyfluorinated Alkyl Substances (PFAS) contaminated solid and liquid wastes, and associated cycling within the natural and engineered environment is a complex topic. PFAS data on contaminated sites, landfill leachates, the influent, effluent, and biosolids from wastewater treatment plants (WWTPs) within Michigan were compiled from publicly available and private sources. Most of the datasets are based on a 28-analyte suite generated using a modified form of the US EPA 537 analytical method, with a subset of data from the 18-analyte ASTM D7979-19 method. Approximately 70% of the 171 contaminated sites in Michigan have maximum groundwater concentrations less than 2000 ppt. Analysis of these sites by source release indicate that four dominant PFAS sources – landfills, aqueous film forming foams (AFFF), metal platers, and automotive/metal stamping – account for 75% of the contamination. Diverse chemical signatures were observed for leachates collected from 19 landfills (mostly type II municipal) with the dominant PFAS being PFOA and PFOS, as well as shorter-chained compounds (e.g., PFHxA, PFBA, and PFBS). Analysis of PFAS carbon chain length as a function of landfill age shows the transition of C8s in leachate from older landfills to C4s and C6s in younger landfills, consistent with the voluntary phasing out and replacement of C8s. PFAS mass flux in leachate for the landfills studied range between 5 – 2,000 g/yr and were highest for active landfills which generate greater leachate volumes and contain fresh PFAS wastes. Detailed study of 10 WWTPs with industrial pretreatment programs indicate numerous chemical transformations across the plants that yield PFAS effluent concentrations that are significantly (up to 19 times) greater than influent concentrations. These ‘apparent’ increases in total PFAS are attributed to transformations of undetected polyfluorinated precursors in the influent to stable perfluorinated compounds detected in the effluent. Perfluorinated compounds – PFOA, PFHxA, PFPeA, PFBA, and PFBS – show the greatest across the plant changes with increases ranging from 20% to nearly 2,000%. PFOS concentrations decreased across 6 WWTPs, consistent with the strong tendency to accumulate in biosolids. Estimated mass flux rates from the WWTPs to receiving water bodies of generally unregulated PFAS range from 40 g/yr to 128 kg/yr.

Download

Share

COinS