Abstract
Submarine groundwater discharge of legacy nitrogen can significantly contribute to coastal eutrophication. Permeable reactive barriers (PRBs) that intercept contaminated groundwater and provide a carbon source for microbially mediated denitrification are increasingly considered to remove nitrate before it reaches coastal surface waters. While woodchips have been shown to efficiently remove nitrate, open questions remain regarding the nitrogen removal performance of PRBs with different woodchip arrangements (trench-type vs column arrays), woodchip types (hardwoods vs softwoods) and the potential formation, release and fate of secondary byproducts, specifically greenhouse gases and dissolved iron. This dissertation aimed to address these knowledge gaps through a combination of field PRB installation monitoring, laboratory experiments, and reaction transport modelling to ultimately help make more informed decisions on optimal PRB design. Nitrogen removal and byproduct formation of different PRB configurations were assessed by monitoring PRB test cells installed behind a marine bulkhead in Hampton Bays, NY. Over the monitoring period between 2020 and 2023, PRB test cells with trenches and column arrays consistently removed groundwater nitrate. Model simulations were consistent with field observations and indicated comparable nitrate removal efficiency per unit volume of woodchips of trench-type and column array PRBs. Laboratory column experiments were conducted to quantify nitrate removal rates for different woodchip types under varying nitrate loading regimes and temperatures. Hardwood woodchips consistently outperformed softwood woodchips and rates were highly temperature dependent. Nitrate removal was limited iii under high flow conditions when oxygen penetrated deep into PRB media. Experiments revealed an apparent tradeoff between under- and overtreated nitrate plumes, as these conditions were related to formation and release of nitrous oxide and methane, respectively, consistent with field observations. Follow-up experiments as well as porewater surveys downgradient of the PRB test cells, however, indicated that a significant portion of the mobilized iron and greenhouse gases are unlikely to be discharged to surface water and the atmosphere as they were removed by redox processes downgradient of PRBs. It is concluded that nearshore, woodchip-based PRBs offer promising and cost-efficient technology to mitigate surface water eutrophication and can be designed to minimize the risk of pollution swapping.
Year
5-21-2025
Document Type
Dissertation
Keywords
Here are my key words: groundwater remediation, nitrogen removal, permeable reactive barrier, reaction-transport model, woodchip bioreactor, greenhouse gas
Degree Name
Doctor of Philosophy (PhD)
Department
Environmental Engineering
Advisor
Nils Volkenborn
Recommended Citation
Lin, Jing-An PhD, "Woodchip-based Permeable Reactive Barriers for Groundwater Nitrogen Removal: Design Optimization to minimize Greenhouse Gas Release informed by Experimental Studies and Reaction-Transport Modeling" (2025). Electronic Dissertations and Theses, 2010-current. 139.
https://commons.library.stonybrook.edu/electronic-disserations-theses/139