Demonstrating the Benefits of Engineered Direct Potable Reuse (DPR) versus De Facto Reuse Systems
Project: 11-05
Year Released: 2014
Type: White Paper
Program: Principal
Investment: $63,519.33 (Cash: $49,942.57, In-Kind: $13,576.76)
Principal Investigator: Glen Boyd, Ph.D., P.E., The Cadmus Group, Inc.
Background
De facto reuse constitutes a phenomenon in which treated wastewater effluent is discharged into groundwater or surface water bodies that serve as source water resources, without specific plans or permits for augmenting these water supplies with treated wastewater. In the United States, as well as internationally, drinking water utilities that rely on surface water resources frequently are located downstream from wastewater treatment plant discharges into rivers or lakes.
Conventional wastewater treatment processes are designed to produce effluent that meets the Environmental Protection Agency’s (EPA) National Pollutant Discharge Elimination System standards. Moreover, all drinking water utilities are required to provide potable public water supplies that meet EPA’s enforceable primary and secondary drinking water standards, set in accordance with the Safe Drinking Water Act. As a result, de facto reuse historically has not been considered a scenario of public health concern in the United States.
The discharge of treated wastewater upstream of potable water intakes on rivers and lakes may affect finished drinking water quality for drinking water utilities located downstream of these releases. Examples of drinking water quality impacts include the presence of trace organic compounds (such as pharmaceuticals, personal care products or endocrine disrupting compounds) and nutrient loading. Such impacts may require additional water treatment to restore consumer confidence in drinking water quality.
Goals and Objectives
This project provides a quantitative assessment of water quality and impacts associated with de facto reuse and demonstrates how fully engineered approaches to direct potable reuse (DPR) result in water quality benefits.
Research Approach
This report documents the downstream water quality effects (if any) of upstream wastewater releases for three selected sites and compares the resultant water quality to that derived from fully engineered approaches. Specifically:
- Three case studies were developed on selected utilities serving different population sizes, representing different geographic regions, and located in different land use settings.
- Water quality and other data were collected from drinking water utilities, wastewater utilities, and other regional water organizations and evaluated on these systems.
- Quantitative models were developed to estimate the impacts of different discharges on the water quality of the receiving water bodies, which is representative of de facto reuse.
- Model results were compared to finished water quality from advanced treatment processes, which served as a method for comparing de facto reuse scenarios with direct potable reuse.
Findings and Conclusions
The findings of this study indicate that predicted concentrations of selected water quality parameters (DO, indicator bacteria, and trace organic compounds) in surface water bodies at the intakes of the selected drinking water treatment plants were largely dependent on dilution, background concentrations of contaminants in surface water, ambient temperature, and the residence time of the contaminants in the system. The impact of effluent discharges on water quality at intakes was considered negligible for these case studies. The findings of the comparison also revealed that the quality of water produced by engineered DPR systems provide greater reliability and consistently better quality than de facto reuse.
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