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Critical Control Point Assessment to Quantify Robustness and Reliability of Multiple Treatment Barriers of a DPR Scheme

Project: 13-03
Program: Principal
Funding Partner: Metropolitan Water District of Southern California
Total Investment: $538,969 (Cash: $300,000, In-Kind cash and service: $238,969)


DPR systems require the use of multiple barriers to ensure the attenuation of microbial and chemical contaminants of concern. Multiple barriers function by 1) expanding the variety of contaminants and pathogens the process train can effectively address (i.e. robustness) and 2) by improving the degree to which the processes can be relied upon to remove any one of them (i.e. reliability). However, variability in influent quality, treatment process upsets, extreme events, and human error may affect treatment performance. Therefore, it is fundamental to develop design and operational practices, as well as response strategies for upset events to ensure system reliability. A formal framework to ensure ‘fail-safe’ operation is the hazard analysis and critical control point concept (HACCP) developed in 1959 by the National Aeronautics and Space Administration (NASA). However, the use of HACCP may not be the exclusive means by which reliability is ensured for potable reuse systems. The HACCP concept may be consulted and portions used, as applicable, to identify response plans and key process parameters for potable reuse systems.

Goals and Objectives

The project will:

  • Conduct hazard assessment for key unit operations for two or more direct potable reuse (DPR) treatment trains, including the following:
    o MF/UF – RO – UV/H2O2 – Cl2 – Engineered Storage
    o O3 – BAC – GAC – UV – Cl2 – Engineered Storage
  • Develop best design, monitoring, and operational practices by evaluating critical process control points in each of the DPR treatment trains evaluated to meet overall system robustness and reliability.
  • Develop standard design approaches and response strategies (i.e., operations plan and standard operating procedures) to mitigate upset events to strive towards ‘fail-safe’ operation of a DPR plant.

Research Approach

Task 1: Conduct hazard assessment for key unit operations and determine critical control points. This hazard assessment will identify health risks, identify water quality objectives, and identify critical control points for both full advanced treatment (FAT) of MF/UF-RO-UV/H2O2-Cl2 and the non-membrane O3-BAC-GAC-UV-Cl2. This will utilize a thorough literature review of previous research as well as full scale operating plant experience and operating data and will incorporate much of the work completed to date.

Task 2: Conduct bench/pilot level challenge test studies. This task will incorporate existing full-scale and pilot-scale data to develop the range of contaminant concentrations under normal modes and failure modes of operation. Where needed, additional full-scale, pilot-scale, and bench-scale challenge testing will be conducted at pilot sites in Arizona and elsewhere to augment the findings of Task 1.

Task 3: Conduct Monte Carlo risk analysis and develop standard design approaches, operational procedures, and response strategies. This analysis will develop a probabilistic risk assessment to characterize, quantify, and communicate the risk of failing to meet treated water quality targets. Additional work will build upon the risk analysis to develop operation and response procedures as well as to provide insight into design standard guidelines.

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