Formatted Title
Permeable Reactive Barriers for Removal of Nitrate from Groundwater through Injection of Emulsified Vegetable Oil: A Sustainable Solution
Background/Objectives
Nitrate levels in groundwater and surface water are elevated in many areas of the world because of anthropogenic sources of nitrogen to groundwater, notably discharge from septic systems and nitrogen-containing fertilizers from agriculture. Discharge of nitrogen-enriched groundwaters to coastal embayments can lead to eutrophication, a process which negatively impacts water quality, ecology and human health while also adversely impacting the local economy from reductions in tourism and commercial fishing and decreasing property values. In addition to reducing human health risks, compliance with the federal Clean Water Act and state water quality standards is a key driver to finding methods for reducing nitrogen in the groundwater that feeds into surface water bodies. Identifying economical and sustainable methods for reducing nitrogen entering surface water bodies is an objective for communities across the United States and globally.
Approach/Activities
One such method utilizes permeable reactive barriers(s) (PRBs) to remove and/or treat contaminants in groundwater. PRBs can address multiple sources of nitrogen, treating the groundwater in-place before the nitrate discharges to surface water. PRBs have been widely used for removal and/or treatment of a range of contaminants.
This paper will focus on PRBs for the in situ biological treatment of nitrate in groundwater using direct injection of carbon substrate electron donors, specifically emulsified vegetable oil (EVO). This paper is supplemented by a design manual (WHOI et al., 2023) which utilizes best practices developed in the groundwater treatment industry. The EVO is prepared from renewable feedstocks (soybean oil and bio-based surfactants). Direct injection of the EVO has lower carbon dioxide generation and impact on the landscape than other methods of PRB construction like mulch PRB installed by soil trenching or installation of sewers and sewage treatment plant.
Results/Lessons Learned
This paper will look at the key learnings and results from treatability studies and four in situ demonstration/pilot PRBs for denitrification completed between 2016 and 2023 on Cape Cod (in the Towns of Orleans, Eastham, and Falmouth) and Martha’s Vineyard (Tisbury).
Nitrate removal PRBs provide an effective approach and one key tool in the “nitrate reduction toolbox.” Nitrate removal PRBs provide a viable, cost-effective, and sustainable strategy to provide nearly immediate decreases in nitrate in impacted watersheds.