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Standard Methods for Integrity Testing and On-line Monitoring of NF and RO Membranes

Project: 12-07
Estimated Release: 2016
Type: Report

Program: Principal
Funding Partner: Pentair Foundation
Total Budget: $596,965 (Cash: $300,000, In-Kind cash and service: $296,965)

Principal Investigator: Dr. Joseph Jacangelo, Ph.D., MWH Americas, Inc.

Background

There is a lack of on-line membrane integrity testing currently for high-pressure membranes, which has resulted in penalties for the drinking water industry. Although it is recognized that these high-pressure membranes may offer excellent pathogen removals, the lack of recognized on-line integrity has allowed regulators to permit the membrane processes with lower pathogen removals (e.g. Giardia, Cryptosporidium, and virus) allowed under conventional filtration processes. Because of this, membrane plants permitted for potable water production may have to include additional treatment processes (e.g. disinfection or other pathogen inactivation) which ultimately increases the cost of water production.

The availability of methods to readily and accurately measure the integrity of high pressure membrane systems will aid utilities in obtaining maximum value from the system, help ensure production of treated water of consistently high quality, and minimize the need for redundant systems to achieve the required level of pathogen removal.

Goals and Objectives

The project will create scientifically-based method(s) for the integrity testing of high pressure membranes, including nanofiltration (NF) and reverse osmosis (RO) membranes. Once developed, the goal is to have the methods adopted as industry standards and approved for higher pathogen removal credits by regulatory agencies. The specific objectives include:

  • Identify parameter/s in the RO and NF system feed and desalinated water that can be monitored continuously, or frequently, which will allow the measurement of the actual ability of the RO and NF membranes to reject pathogens.
  • Develop protocol(s) and method(s) for high-pressure membrane integrity monitoring.
  • Complete bench or pilot-scale tests to simulate various potential defects and failures of high-pressure membranes and confirm the ability of the proposed test to detect these breaches of membrane integrity.

Research Approach

Task 1: Literature review: Document prior work related to integrity testing, summarize existing and proposed regulatory requirements related to pathogen removal credits, and identify candidate water quality parameters, techniques and methods that potentially could be considered for on-line RO and NF membrane integrity monitoring.

Task 2: Workshop: Solicit input from membrane manufacturers and regulators; define best approaches to integrity method development reflecting manufacturers’ and users’ experience and regulators’ acceptance requirements.

Task 3: Identify Easy-to-Measure on the Field Parameter Indicative of Membrane Integrity Conditions: Identify or develop parameters that directly or indirectly provides continuous information regarding membrane integrity, which utilize constituents present in the source waters; the selected parameters should be in sufficient quantity or concentration to yield removal levels that is equivalent to at least 4 logs or higher for pathogen removal between source and permeate; thought should be given to parameters that can be measured on-line rather than by grab sampling.

Task 4: Evaluate Existing or Develop New Instruments and Methodology for Measurement of the Membrane Integrity Indicator:

  • Develop and test the “universal” integrity test method for use in all water matrices (fresh, brackish, seawater, and reuse) for both RO and NF systems. Lab-scale testing using flat-sheet coupons and/or single, small diameter elements; pilot testing using multi-element array to quantify integrity losses within each part of the system.
  • If universal method is not feasible, develop and test matrix-specific test methods for low salinity (fresh or low TDS brackish) and high salinity (high TDS brackish and seawater).
  • Evaluate the economic effect of implementation of the proposed integrity test on equipment and operational cost of commercial NF/RO system.

Task 5: Confirm the Validity of the Proposed Membrane Integrity Indicator and Test Methodology by Bench, Pilot or Full-scale Testing: Validate the membrane integrity test through a minimum of bench- and pilot-scale testing, although the inclusion of full-scale testing is preferred; test matrices should include lower ( 10,000 mg/L TDS).

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