Enhanced Cycling of Arsenic and Antimony in Renewable Natural Gas Operations: Accumulation and Mobilization Mechanisms

University Of Washington, Seattle WA

Investigators

Abstract

Landfills are confined mounds of municipal waste that generate gas (primarily methane, or natural gas) through the biological breakdown of the organic waste. Release of this gas into the environment negatively impacts nearby communities and ecosystems. Turning this gas into renewable natural gas (RNG) helps society as an energy source to reduce pollution resulting from fossil fuel use. However, the processes involved in RNG production create wastewater leachate that has high concentrations of toxic arsenic (As) and antimony (Sb). The overarching goal of this project is to advance the fundamental understanding of how toxic chemicals are generated and accumulated at RNG production sites, and how they are released and persist in the environment. Understanding the formation and release of toxic chemicals such as As and Sb at the RNG production sites will benefit society through the identification of strategies to prevent their release. Additional benefits to society will be achieved by disseminating the outcomes of the project at specialized conferences and seminars, and by developing teaching curricula that introduce students to the cross-disciplinary aspects of environmental engineering and renewable energy. RNG production from landfills contributes to environmental sustainability and reduces the need for fossil fuels. However, proper landfill leachate collection and treatment is crucial to minimize the risk of toxic chemical contamination at RNG production sites. The goal of this project is to advance the understanding of formation, accumulation, release, and transport of As and Sb at RNG production sites. The guiding hypothesis of this project is that the mobilization of As and Sb in landfills involves the generation of gaseous forms of organo-As and organo-Sb compounds. To test this hypothesis, the research team has three specific research objectives to: i) Determine how the gaseous forms of As and Sb are generated and retained by the solids phases of the treatment columns at the RNG production sites; ii) Quantify how and under what conditions the accumulated As and Sb are released from the exposed treatment columns; and iii) Elucidate the fundamental aspects of reactions causing As/Sb mobility and accumulation at RNG production sites. Successful completion of this project can assist municipalities and energy providers in reducing their waste management costs when removing As/Sb from landfill leachates and related waste streams. This project also contributes to a more interconnected and informed global community by including numerous student and faculty exchanges with universities in Italy and Taiwan. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.