UK Drinking Water Inspectorate Information

Information Letters

DWI Information Letter 3/2002

21 January 2002

To: To: Board Level Contacts in Water Service Companies and Water Companies in England and Wales

Dear Sir or Madam,

CRYPTOSPORIDIUM IN WATER SUPPLIES: GUIDANCE ON LOW-PRESSURE MEMBRANE INTEGRITY MONITORING

Purpose

The purpose of the letter is to provide guidance on the criteria that should be used in preparing proposals for integrity testing of membrane systems installed under the provisions of the requirements of the Water Supply (Water Quality)(Amendment) Regulations 1999 (the Regulations) for the removal of Cryptosporidium oocysts from drinking water supplies.

The suitability of the membrane integrity monitoring system should be considered as part of the commissioning of membrane systems being installed under the agreed improvement programmes for Cryptosporidium removal.

Introduction

The Regulations require that, where there is a significant risk for Cryptosporidium as defined in the Regulations, a water undertaker uses a process for treating the water to secure compliance with the Regulations and monitors the effectiveness of that process. Under the associated guidance to the Regulations, treatment that is capable of continuously removing or retaining particles greater than one micron diameter will not require compliance monitoring provided the process is subject to continuous monitoring and shutdown or turn out on failure.

Appropriate approved membrane filtration will meet this specification. However an adequate level of integrity monitoring has to be incorporated into the process design in order to demonstrate that the required criteria are met fully.

At the end of January 2001, the Inspectorate appointed consultants to carry out an initial assessment of procedures being proposed, or already in place, for the integrity monitoring of low-pressure membrane systems. The Inspectorate is minded to accept the findings of the study, which will feed into a longer term and more detailed study that is being carried out in association with the American Water Works Association Research Foundation. This study is due for completion early in 2003 and the findings will be made available to the industry when the final report is published.

Provision of generic guidance

At this stage, with currently known membrane integrity technology and the lack of common operational practice, it is not possible to set out complete generic guidelines for integrity test procedures.

In the absence of operationally proven integrity test regimes water companies should employ the current ‘best available technology’ to meet the Inspectorate’s requirement of continuous removal of particles greater than one micron diameter. The Inspectorate considers a log removal approach to be invalid in terms of meeting the specific requirements of the Regulations. This is because log removal is empirical and based on tests carried out at a range that is outside the requirements of the treatment standard.

The five key aspects for achieving an integral membrane system are:

type of integrity test (for example Pressure Decay Test, Diffusive Airflow Test, or conductivity in the case of reverse osmosis membranes);

integrity test criteria and settings (pressures, alarm settings etc);

frequency of integrity test (daily, weekly etc);

performance requirements (ie meeting the continuous removal of particles greater than one micron diameter); and

management of process and information (data management, shutdown procedure etc)

These points are covered in more detail in Annex 1, along with guidance on the type of information that should be included in membrane integrity testing proposals.

A pragmatic approach needs to be adopted for the selection of the membrane integrity test, the test criteria and frequency of testing. The selection of the test criteria and frequency of testing should be based on the risks, economics, plant size and the practicalities of the type of test. A daily test frequency would be consistent with the requirements of the continuous regulatory sampling. Intermittent monitoring at an appropriate frequency, based on system design and risk of failure, may be more suitable if an acceptable level of risk can be demonstrated. However this would need to be agreed with the Inspectorate before being adopted.

The Inspectorate accepts that the process of integrity monitoring testing will evolve as more membrane systems are installed for Cryptosporidium removal. Further research may be needed in some areas, for example, on the feasibility of using a higher starting pressure for pressure decay tests to enable smaller diameter breaches to be detected, and to improve the sensitivity of the measurement. The Inspectorate will also take account of the advice given in the American Standards for Testing Materials standard practice for integrity testing of membrane systems, when this is published. Further guidance will, therefore, be given in the light of better knowledge.

Some water companies have assumed that membrane approval includes approval of the associated membrane integrity testing system. This is not the case. Membrane manufacturers and system suppliers need to work with the industry to develop suitable membrane integrity tests appropriate for the Regulations and companies must satisfy themselves accordingly.

Proposals for membrane integrity monitoring systems

Proposals for membrane integrity testing have to be submitted to the Inspectorate for each installation so that the Inspectorate can satisfy itself that they are consistent with current best practice. Such proposals should also form part of the commissioning process. Accordingly compliance monitoring should continue at those sites where it is currently in place until it can be demonstrated that the process is meeting the regulatory requirements.

Other matters

The Inspectorate would like to thank the membrane suppliers and water companies that provided an input into the study. Those parts of the report that are not considered to be ‘commercial in confidence’ will be made available to the industry and will appear on the Inspectorate’s web site.

Enquiries

Any enquiries about this letter should be addressed to or David Drury (020 7944 5976) or Claire Jackson (020 7944 5977).

Copies of this letters are being sent to Pamela Taylor, Chief Executive, Water UK; Rodney Anderson, Water Supply and Regulation Division, Department for Environment Food & Rural Affairs; Bob Macey, Environment Division, The National Assembly for Wales; Tim Hooton, Water Services Unit, Scottish Executive; Randal Scott, Drinking Water Inspectorate for Northern Ireland; and Rowena Tye, Office of Water Services.

Please acknowledge safe receipt of this letter using the enclosed slip and envelope.

Yours faithfully,

M J Rouse
Chief Inspector

ANNEX 1: Criteria to be included in membrane integrity proposals, including comments that can be taken as guidance.

TOPIC CRITERIA INFORMATION REQUIRED COMMENTS (RECOMMENDED GUIDELINES)

1 Site Details Responsibility
Membrane operation
Integrity testing
Water quality and Data management,
Maintenance and Service Arrangements Site organisation structure, identifying responsibilities Detail specific responsibilities for site and data management

Site name
Plant size
Location of Control Room Plant details and control structure Detail specific site information

Source
Risk information Source description and specific site risks Detail specific causes of significant risk and consider management systems

2 Water Treatment Process O&M manual for the site Existence and location of O&M Manual Located on site

Whole treatment process diagrams P&I diagrams Included in O&M manual

By-pass Details and management of by-pass. No by-pass if possible

3 Monitoring On line instrumentation
Parameters monitored
Data logging State any online monitoring additional to the MIT. (i.e. auxiliary monitoring) Include alarm and any shut down/trip settings. e.g. turbidity, particle counting Other continuous parameter(s) logged (e.g. Turbidity) on raw water feed for intake protection and or supporting information

4 Membrane Process Membrane flow diagrams P&I diagrams Included in O&M manual

System supplier
Membrane type System supplier
Membrane type Full details required

Regulatory Approvals Details of regulatory approvals/consents ( DWI CPP approvals, Cryptosporidium approval list and, where appropriate, Environment Agency Discharge consent) Membrane system to have CPP approval.
Membrane element/module approved for Cryptosporidium removal (DWI Information Letter 16/99)

5 Membrane Integrity System Membrane Element Type Description required, e.g.Hollow fibre, Spiral Wound or Tubular and UF, MF, NF or RO Hollow Fibre (MF & UF) Spiral Wound (NF & RO)
Source dependent

Name of Test and Description Name and describe MIT Pressure Based Tests (e.g. PDT and DAF) Conductivity Based Tests

Basis of Test to meet Cryptosporidium regulations Describe basis of test to meet regulations Aim to test for 1µm defect. Statement required on what defect size is detectable with test. Set-points to be specified for each train The settings should be based on sound empirical evidence

Test Initiation (manual/automatic) Description required Automatic required with manual override facility Automatic with manual override facility

Test settings Description required Based on empirical evidence. Specific for each type, manufacturer and configuration of membrane Specific for each type, manufacture, configuration of membrane and feed water quality

Alarm and Shut down/isolation settings/procedures Description required Should include an alarm/warning point The settings should be based on sound empirical evidence

Frequency and Justification Description required To be agreed with DWI Online and continuous

Automatic/Manually shut down/isolation Description required Automatic required with manual override facility

Identification of breach/failure, isolation, repair/replacement, spares and re-commissioning procedures. Description required All these procedures to be fully described and easily executed by operating personnel

6 Telemetry Arrangements for onsite/remote monitoring Description required to explain continuous monitoring Unmanned sites must utilise telemetry

7 Data & Information Data Management and Information Reporting Description of data management, recording, storage duration and information reporting MIT process parameters stored for 5 to 7 years or as long as the membrane element warranty. Parameters to include start test pressure, relevant measured variable over the test period. MIT process parameters stored for 5 to 7 years or as long as the membrane element warranty. Minimum guideline is storage of daily averages.

8 Other Additional relevant information, e.g Training comments Additional relevant information Additional relevant information, e.g. Operational training in place.

This guidance will be reviewed and, if necessary, re-issued in the light of new developments.

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Drinking Water Inspectorate,
Floor 2/A1, Ashdown House, 123 Victoria Street, London, SW1E 6DE
Telephone : 020 7944 5956 - Facsimile : 020 7944 5969
E-mail: dwi.enquiries@defra.gsi.gov.uk

Published 21 January 2002
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	TOPIC	CRITERIA	INFORMATION REQUIRED	COMMENTS (RECOMMENDED GUIDELINES)
1	Site Details	Responsibility Membrane operation Integrity testing Water quality and Data management, Maintenance and Service Arrangements	Site organisation structure, identifying responsibilities	Detail specific responsibilities for site and data management
		Site name Plant size Location of Control Room	Plant details and control structure	Detail specific site information
		Source Risk information	Source description and specific site risks	Detail specific causes of significant risk and consider management systems
2	Water Treatment Process	O&M manual for the site	Existence and location of O&M Manual	Located on site
		Whole treatment process diagrams	P&I diagrams	Included in O&M manual
		By-pass	Details and management of by-pass.	No by-pass if possible
3	Monitoring	On line instrumentation Parameters monitored Data logging	State any online monitoring additional to the MIT. (i.e. auxiliary monitoring) Include alarm and any shut down/trip settings. e.g. turbidity, particle counting	Other continuous parameter(s) logged (e.g. Turbidity) on raw water feed for intake protection and or supporting information
4	Membrane Process	Membrane flow diagrams	P&I diagrams	Included in O&M manual
		System supplier Membrane type	System supplier Membrane type	Full details required
		Regulatory Approvals	Details of regulatory approvals/consents ( DWI CPP approvals, Cryptosporidium approval list and, where appropriate, Environment Agency Discharge consent)	Membrane system to have CPP approval. Membrane element/module approved for Cryptosporidium removal (DWI Information Letter 16/99)
5	Membrane Integrity System	Membrane Element Type	Description required, e.g.Hollow fibre, Spiral Wound or Tubular and UF, MF, NF or RO	Hollow Fibre (MF & UF)	Spiral Wound (NF & RO) Source dependent
		Name of Test and Description	Name and describe MIT	Pressure Based Tests (e.g. PDT and DAF)	Conductivity Based Tests
		Basis of Test to meet Cryptosporidium regulations	Describe basis of test to meet regulations	Aim to test for 1µm defect. Statement required on what defect size is detectable with test. Set-points to be specified for each train	The settings should be based on sound empirical evidence
		Test Initiation (manual/automatic)	Description required	Automatic required with manual override facility	Automatic with manual override facility
		Test settings	Description required	Based on empirical evidence. Specific for each type, manufacturer and configuration of membrane	Specific for each type, manufacture, configuration of membrane and feed water quality
		Alarm and Shut down/isolation settings/procedures	Description required	Should include an alarm/warning point	The settings should be based on sound empirical evidence
		Frequency and Justification	Description required	To be agreed with DWI	Online and continuous
		Automatic/Manually shut down/isolation	Description required	Automatic required with manual override facility
		Identification of breach/failure, isolation, repair/replacement, spares and re-commissioning procedures.	Description required	All these procedures to be fully described and easily executed by operating personnel
6	Telemetry	Arrangements for onsite/remote monitoring	Description required to explain continuous monitoring	Unmanned sites must utilise telemetry
7	Data & Information	Data Management and Information Reporting	Description of data management, recording, storage duration and information reporting	MIT process parameters stored for 5 to 7 years or as long as the membrane element warranty. Parameters to include start test pressure, relevant measured variable over the test period.	MIT process parameters stored for 5 to 7 years or as long as the membrane element warranty. Minimum guideline is storage of daily averages.
8	Other	Additional relevant information, e.g Training comments	Additional relevant information	Additional relevant information, e.g. Operational training in place.