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Information Letters

 

DWI Information Letter 11/2001

22 August 2001

To: Board Level Contacts of Water and Sewerage Companies and Water Companies in England and Wales

Dear Sir/Madam

The Water Supply (Water Quality) (Amendment) Regulations 1999: Cryptosporidium in Water Supplies - Listing of products capable of removing or retaining particles greater than 1 micron diameter

  1. DWI Information Letter 16/99 advised water companies of the Inspectorate’s interpretation of "sufficient treatment plant capable of continuously removing or retaining particles greater than 1 micron diameter". That letter also included a list of products that satisfied the Inspectorate’s criteria for removal or retention of 1 micron particles. This letter updates that list and provides further information on assessment criteria and arrangements for publicising future updates.
  2. I am enclosing for information, a copy of "Guidance on Submissions of Claims for removal of one micron particles - membrane treatment processes for Cryptosporidium removal". This is aimed at manufacturers and suppliers of membrane systems but paragraphs 6 et seq provide up to date information on test data requirements and experimental design. DWI will be issuing guidance on membrane integrity testing requirements shortly.
  3. I am also enclosing the latest list of products that satisfy the criteria for removal or retention of particles greater than 1 micron diameter. This list is posted on the Inspectorate’s website (www.dwi.gov.uk/regs/crypto/approval.shtm) and future amendments will be posted on this site. Water companies should note that membrane systems must be approved under regulation 25(1)(a) before the Inspectorate will assess the product for inclusion in this list.
  4. Copies of this letter are being sent to Mr Rupert Kruger, Water UK; Rodney Anderson, Water Supply and Regulation Division, Department for Environment, Food and 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; Dr W Emery and Rowena Tye, Office of Water Services; and Dr A Wight, Unit Head (PH6.2), Department of Health.
  5. Please acknowledge receipt of this letter using the enclosed slip and envelope.

Yours faithfully

A Lloyd

Superintending Inspector
Drinking Water Inspectorate

 

The following products are considered by the Inspectorate to be capable of continuously removing or retaining particles greater than 1-micron diameter:

Company Product
AEA Technology Ltd Kerasep Cross Flow Filtration Module
Degremont UK Ltd Aquasource UF Membrane Module
Kalsep Ltd Kalmem Polyethersulphone Hollow Fibre Element
Koch Membrane Systems Ltd Targa Modules V and H
TFC Membrane Elements
8131 UF Membrane Element
PCI Membrane Systems Ltd PCI Membrane Filtration System - Spiral Element
PCI B1 Module and Membrane - Tubular Element 1
PCI Tubular C10 Module and Membrane System (incorporating Tubular Element 1)
MEMCOR CMF Continuous Microfiltration Systems M1/M2 and M10
CMF-S Continuous Microfiltration System
X Flow BV X Flow Membrane Filtration Elements

The arrangements for applying to have products considered for inclusion in this list are given in "Guidance on submissions of claims for removal of one micron particles - membrane treatment processes for Cryptosporidium removal". To obtain a copy of this document, please e-mail dwi.enquiries@defra.gov.uk

 

GUIDANCE ON SUBMISSIONS OF CLAIMS FOR REMOVAL OF ONE MICRON PARTICLES - MEMBRANE TREATMENT PROCESSES FOR CRYPTOSPORIDIUM REMOVAL

Background

  1. Guidance on Assessing Risk from Cryptosporidium Oocysts in Treated Water Supplies has been developed by the Drinking Water Inspectorate (DWI) to support The Water Supply (Water Quality) (Amendment) Regulations 1999 (Statutory Instrument 1524). The provisions of the 1999 regulations have now been incorporated in to the Water Supply (Water Quality) Regulations 2000. Copies of the Guidance and the Regulations are posted on the DWI website: http://www.dwi.gov.uk/regs/index.shtm
  2. Section 2.2 of the Guidance provides that ‘any treatment works, in which all water passes through sufficient treatment plant capable of continuously removing or retaining particles greater than one micron diameter and where this process is subject to continuous monitoring and shutdown or turn out on failure, will not require continuous monitoring’.
  3. This report contains guidance on the information to be provided by membrane suppliers in support of an application to DWI for listing of products as satisfying the criterion for removal of Cryptosporidium. Product information is not eligible for consideration unless the product is included in List of Products and Processes Approved Under Regulations 25 and 26 For Use In Connection With The Supply Of Water For Drinking, Washing, Cooking And Food Production Purposes. A copy of the List of Approved Products and updates to the list are posted on the DWI website: http://www.dwi.gov.uk/cpp/index.shtm
  4. The assessment criterion is that products must be capable of continuous removal (or retention) of particles of one micron diameter and greater from a representative feed water. The report deals only with size exclusion. Advice on membrane integrity issues and systems for monitoring membrane integrity is the subject of a separate DWI Information Letter. DWI will ensure that assessments are made independently of the commercial interests of manufacturers and suppliers of membrane and other filtration systems.

Requests for assessment - initial submission

  1. Requests for an assessment of product data should be addressed to Anthony Lloyd, tel: 020 7944 8037, E-mail anthony.lloyd@defra.gsi.gov.uk. There are no specific requirements for format of submissions for assessment but suppliers must include:

Test data in support of submissions

  1. DWI Information Letter 16/99 advised that test data on removal of oocysts of Cryptosporidium must indicate removal of all oocysts. In this respect, Cryptosporidium challenge tests are unlikely to provide definitive evidence of compliance with the assessment criterion. This follows from the limitations in the reproducibility and detection limit of available analytical techniques. However, suppliers may wish to provide results of Cryptosporidium challenge tests as supporting evidence.
  2. Removal data on a range of alternative particles may be submitted as evidence for compliance with the test criterion e.g. bacteria, bacterial spores, viruses, phage particles and dissolved molecules or ions. The assessment will take account of possible differences in behaviour and size of the substitute particles and suppliers should provide a justification of why the behaviour of a particular particle is an adequate substitute for Cryptosporidium.
  3. Similarly, particle removal tests are unlikely to provide definitive evidence of compliance with the assessment criterion, because of the uncertainties associated with ensuring zero breakthrough. However, suppliers may again wish to provide results of particle removal tests as supporting evidence. Tests performed with particles having a maximum diameter greater than one micron will be of limited value for the purposes of the assessment.
  4. Imaging techniques such as electron micrography focus on the product rather than the process. The modal pore size of a membrane or filter may readily be estimated in this way. Evidence that the pores are generally of less than one micron in diameter is valuable confirmation of particle removal studies. However, by itself, evidence about the topography of the product is insufficient for a definitive assessment because (i) it addresses the assessment criterion indirectly, (ii) individual pores may be very much larger than the modal size, and (iii) parts of the filter surface may exhibit anomalous characteristics.
  5. Gas or liquid permeation tests and mechanical resistance tests may be submitted as corroborating evidence. By themselves, they are insufficient because they are indirectly related to the particle removal process. The test principles and calculations used should be fully detailed.

Guidelines for experimental design

  1. It is recommended that product performance tests be specifically designed to evaluate compliance with the assessment criterion. If the tests were carried out with other applications in mind, this must be clearly stated in the description of the testing. Standard methods should be used wherever they are available and appropriate to the particles under consideration.
  2. Test data may be obtained from experimental trials on production models or by monitoring the performance of working installations. Data from both types of studies will be advantageous. Data from working installations are particularly useful because they provide information on seasonal or episodic environmental variation, and human error. A complete operational record will generally be required.
  3. Customer applications tests and product quality control tests may be submitted. The reason for carrying out such tests must be stated and the detailed procedure must be provided. Independent academic studies may provide comparative data on related products, but the provider’s key contact must ensure that the product under assessment is clearly defined.
  4. The results of tests carried out during product development are not eligible for consideration. Data must be obtained with identifiable products of known specification, using the commercial product under assessment. If it is necessary to use only a part of the commercial product for a particular test, or to study the commercial product integrated with other processes, this must be clearly stated at the head of each such test or study.
  5. The Inspectorate will not consider tests results obtained in studies where two or more products are used in series. If it is necessary for water processed by the first unit to be treated by a second unit, then the product is not capable of complete removal of particles of the tested size and can not be assessed as meeting the assessment criterion.
  6. The following points should be considered when designing performance tests:

Reporting

  1. Test reports on product performance in the water treatment process should include the following:
  1. DWI will seek to identify whether the experimental basis for the submitted data is sufficiently rigorous. The information submitted should therefore cover the following details:

Assessment process

  1. DWI will examine and critically evaluate the information received against the assessment criterion, having regard to the relative significance of different types of information for this purpose. DWI will provide a written opinion as to whether or not the product meets the assessment criterion. Products receiving a favourable assessment will be included in the list "Approval of membrane and other filtration systems for Cryptosporidium removal". This list is posted on the DWI website: http://www.dwi.detr.gov.uk/cpp/approval.htm

Conditions of listing

  1. Listing is subject to the standard conditions of approval for all approved products in respect of: use in accordance with agreed Instructions for Use and approval of all changes to the product. Evidence about one product may be relevant to the assessment of a related product. For example, if the only intended difference is capacity. Nevertheless, the products should be clearly distinguished for the assessment. DWI will consider whether and to what extent cross-corroboration is appropriate.

These conditions of approval are as follows:

That use is in accordance with an Instructions for Use document. Approval holders must provide water companies with copies of the Instructions for Use Document that was considered by the Committee1 when approval was recommended.

That the approval of the Authorities2 is obtained in respect of the following: any change in the formulation of the approved product, including change in source or identity of raw materials; any change in the manufacturing process, including location of manufacture; any change in designation of the approved product; and any change in name or ownership of the organisation holding the approval.

1 The Committee on Products and Processes for Use in Public Water Supplies

2 The Secretary of State for Environment, Food and Rural Affairs and the National Assembly for Wales.

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