Water Resources Research Act Program

Details for Project ID 2020AZ027G

In-stream contaminant attenuation by sunlight: benefits for water reuse

Institute: Arizona
USGS Grant Number:
Year Established: 2020 Start Date: 2020-09-01 End Date: 2023-08-31
Total Federal Funds: $243,563 Total Non-Federal Funds: $243,564

Principal Investigators: David Quanrud

Abstract: This proposal fits in research priority 2: “Research to help society deal with water scarcity or water availability challenges…†Downstream water users on major river systems in the U.S. are recipients of trace organic compounds (TOrCs) that are only partially removed via upstream conventional wastewater treatment. Incidental reuse is already part of the nation’s water resources picture. In-stream chemical conversion processes are thus a matter of potential health significance. Detailed physicochemical understanding of the in-stream fates of many such compounds are lacking due to process complexities. Previous work by our group has shown that estrogenic activity in wastewater effluent is attenuated during in-stream transport and transformation kinetics can be reproduced under much simplified conditions. The components necessary to motivate chemical transformations include sunlight (or alternate light source), molecular oxygen and some component of wastewater effluent. Bench-scale experiments showed that the primary mechanism for water quality enhancement is indirect photolysis involving generation of singlet oxygen.We propose a multifaceted experimental program to fill remaining information gaps: (i) streamflow modeling supported by Lagrangian tracer studies to represent diurnal streamflow variation at the proposed field site—the lower Santa Cruz River near Tucson, AZ; (ii) parallel lab studies using monochromatic light sources to establish wavelength-dependent quantum efficiencies of photolytic transformation processes and to identify importance of specific compound transformation mechanisms—direct versus indirect photolytic pathways and the several available radical-dependent mechanisms that comprise indirect photolysis; and (iii) identification of chemical sensitizers among effluent organic matter and natural organic matter components—i.e., chemicals responsible for initiating indirect photolytic reactions under field conditions. These steps will advance understanding of photolytic TOrC transformations in natural waters and wastewater effluent. Modeling results will be site specific, but the approach and photochemical insights obtained from the experimental program can be universally applied.The project will yield quantitative information on fates of specific TOrCs during river transport and will improve mathematical representations of in-stream reaction kinetics and transport and support rational design for water reclamation based in part on light-initiated reaction pathways. Beneficiaries of proposed work include those entrusted with (i) protection of waters that receive treated wastewater and (ii) restoration of waters destined for reuse.The project includes substantial participation by USGS hydrologists from Water Science Centers in Arizona and Colorado, who will oversee field sampling design and also assist with data interpretation and modeling.All investigators, along with students employed on the project, will share in authorship of academic publications and professional presentations given at local, regional and/or national meetings. Other information transfer activities will be coordinated with the UArizona Water Resources Research Center (WRRC) and will include publicizing project results through WRRC publications, e-news, quarterly newsletter, annual conference, and brown bag seminar.