Towards a mechanistic understanding of contaminant attenuation and greenhouse gas emissions in open-water engineered wetlands

Abstract

Engineered wetlands offer a sustainable supplement to conventional water and wastewater treatment by harnessing biological processes which occur naturally in the environment. In macrophyte-free open-water engineered wetlands, design parameters of a shallow water column and geotextile liner select for a benthic microbial biomat with parallels to periphyton biofilms in shallow streams. This dissertation aims to disentangle the microbial interactions that govern contaminant biotransformations and greenhouse gas emissions within this benthic biomat community, leveraging a demonstration-scale open-water engineered wetland in Corona, California. Through an integration of field-scale genome-resolved metatranscriptomics, porewater profiling, and greenhouse gas fluxes with inhibition microcosms manipulating redox conditions to interrogate specific metabolisms, pathways which occurred simultaneously in-situ were decoupled and associated with contaminant transformations. First, photosynthesis, nitrification, and denitrification were associated with the biotransformation of a suite of pharmaceutical compounds, including novel linkages of nitrate and nitrous oxide reducing activity with the biotransformation of an anti-viral (emtricitabine) and antibiotic (trimethoprim). Next, methane-oxidizing activity, catalyzed by the particulate methane monooxygenase as confirmed by field metatranscriptomics and inhibition microcosms, stimulated the biotransformation of sulfamethoxazole, an antibiotic that was highly recalcitrant under all other surveyed conditions. Finally, mechanistic insights were synthesized to construct a series of models which estimate the contributions of benthic metabolisms to greenhouse gas emissions, identifying methane-oxidizing bacteria as important ecological filters of climate forcing. Taken together, these findings are discussed in the context of open-water engineered wetland management and design, environmental contaminant fate and transport, and the critical intersection of these themes with climate change.