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Potable Reuse: State of the Science Report and Equivalency Criteria for Treatment Trains

Project: 11-02 (Phase 2)
Year Released: 2012
Type: White Paper

Program: Principal
Funding Partners: Bureau of Reclamation, H2O Engineering, Upper San Gabriel Valley Municipal Water District
Total Investment: $1,735,903.35 (Cash: $550,671.37, In-Kind: $1,185,231.98)

Principal Investigator: R. Rhodes Trussell, Trussell Technologies, Inc.


Potable reuse is becoming increasingly important as a water supply alternative throughout the United States and the world due to a combination of increased demand and uncertain supply. At the present time, all operating potable reuse projects in the U.S. utilize an environmental buffer between the advanced water treatment train and the ultimate consumer. These environmental buffers, which are typically underground aquifers or surface water storage reservoirs, provide additional contaminant mitigation and agency response time.

In the past, such projects have been characterized as indirect potable reuse (IPR) to contrast them with direct potable reuse (DPR) projects that eliminate the environmental buffer and provide water directly to the user. The recent National Research Council (NRC) Committee stated that it cannot be demonstrated that such “natural” barriers provide public health protection that is not also available by other engineered processes. The Committee went on to conclude that the potable reuse of highly treated recycled water without an environmental buffer is worthy of consideration with the proviso that adequate protection is engineered into the system.

In essence, the Committee recommended that the industry dispense with the terms “direct” and “indirect” and just refer to projects as either potable reuse or nonpotable reuse, commenting that the distinction between indirect and direct potable reuse is not scientifically meaningful to the quality of the final product.

Goals and Objectives

The project clearly identifies the benefits and tradeoffs of various treatment process trains for potable reuse. The goals of this project are to:

  • Consider and examine criteria needed to evaluate the adequacy of treatment for direct and indirect potable reuse,
  • Develop a model that can allow for comparisons of alternate treatment trains for potable reuse, and
  • Test at least one advanced treatment train for direct potable reuse at a scale large enough to give information on real operating conditions.

Research Approach

The research approach was to gather key reuse and public health experts to hold a comprehensive workshop to discuss current and future regulations related to IPR and DPR and create a state of the science report with a set of criteria that are protective of public health to evaluate treatment technologies for DPR.

Findings and Conclusions

This report describes the state of potable reuse in the context of the previous framework (i.e., indirect vs. direct) but presents final conclusions based on this revised protocol.

The first section of the report provides an overview of the current state of the science of potable reuse. This review provides both domestic and international perspectives on the history of potable reuse, the configuration and treatment technologies employed, the regulations governing its use, and current research trends.

In order to support the evolution of potable reuse, the second section of this report assesses the equivalency of advanced treatment trains. This section provides criteria for determining equivalency with regard to the three main categories of interest: microbial, chemical, and aesthetic criteria. This comprehensive set of public health criteria was the product of a multistep process that included an extensive review of existing projects and guidelines, the development of an initial set of “Strawman” criteria, and the refinement of these criteria by a panel of public health experts following a two-day workshop where those Criteria were presented and discussed.

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