Dr. Christiane Schell

1Schell-Twinning 2009

Hygiene-Institut des RuhrgebietsInstitut für Umwelthygiene und Umweltmedizin

www.hyg.dewww.hyg.de

Enhancement of Microbial Growth on Materials which come into Contact with Drinking Water – Testing and AssessmentDVGW Technical Standard W 270 (November 2007)

DVGW W 270: Motivation

What was the reason?• Noticable problems, • Poor quality of drinking water and• Damages

caused by microbial growth of slimy, slicky consistency lead to the development of an easy and simple test method orientated at practical needs[Method developed by Prof. Dr. med. Schoenen, Hygiene-Institut, Universität Bonn (Director Prof. E. Thofern),1984]

aerator (seen from the front and the back)

DVGW W 270: Goal

The goal– To exclude microbial impact on drinking water by

materials which enhance microbial growth (by contact with drinking water)

– To identify materials without microbial growth promoting properties (biofilm)

• drinking water is not sterile, microorganisms may be present on the surface of materials in contact with drinking water; this limited development cannot be avoided and is therefore tolerated („natural“ colonisation)

• But: no tolerance for stimulation and promotion of microbial growth by compounds being released from the construction product and leading to the development of surface biomass

DVGW W 270: Goal

• Limited colonisation can be accepted because the quality of drinking water will not be affected

• Surface biomass developement can not be accepted as the the quality of drinking water may be affected:

– Surface biomass can affect the colony count numbers of drinking water

– Surface biomass can become a potential habitat for pathogenic microorganisms

DVGW W 270: Scope

Test method to determine microbial growth on

– organic materials – materials containing organic components

foreseen to get into contact with drinking water or with water to become drinking water

DVGW W 270: Scope

• Test method applies to materials – already finished (factory made products) and– site applied products (coatings etc.)

• The method is not applicable to greases and oils because of technical difficulties concerning the test procedure

• Testing is not necessary for materials containing no organics

DVGW W 270: Principle• Test pieces are

– washed in drinking water– cleaned with disinfectant – rinsed with drinking water– exposed to slowly flowing test water

• defined test container• defined periods of times

– removed from the water

• Surface biomass is harvested by– scraping– centrifugation– determination of biovolume

DVGW W 270: Basic requirements

• Test samples shall be representative to finished products– Composition– Treatment– Properties

• Composite products shall be tested as product• Material composition shall

– comply with national regulations, – be approved by the test laboratory

DVGW W 270: Basic requirements

• Reference materials

to insure that the test runs are undisturbed– Positive control: development of biomass by

deliverance of biodegradable substances (paraffin)

– Negative control: only surface colonisation but no biomass development (e.g. stainless steel)

DVGW W 270: Apparatus and reagents

• Test water– Without disinfectants– Temperature 12 5 °C

• Test container– Glass, stainless steel (inert material)– Volume approximately 100 liter– Water inflow at the bottom, outflow on top of the

container at the opposite side

• Test container– Glass, stainless steel (inert material)– Volume approximately 100 liter– Water inflow at the bottom, outflow on top of the container

at the opposite side

• Test module for pipes and hoses

www.hyg.dewww.hyg.deComposite materialsTube with two layers

How to test the inner layer without interfering effects of the outer layer ?

Test module for pipes, tubes and hoses

only the surface in contact with drinking water is exposed and tested

• Test container– Glass, stainless steel (inert material)– Volume approximately 100 liter– Water inflow at the bottom, outflow on top of the container at the

opposite side

• Test module for pipes and hoses• Scraper

– With rubber lid or made of hard plastic (breadth 12 - 15 cm)

positive control: paraffin

negative control

• Glassware for centrifugation– Type A: Specially designed

• calibrated scale 0.01 - 0.4 ml

– Type B: conical centrifugation tubes with a volume up to 15 ml are recommended for volumes of surface biomass expected to be more than 0.5 ml (e.g. positive control)

• Glassware for centrifugation– Type A: Specially designed

• calibrated scale 0.01 - 0.4 ml

– Type B: conical centrifugation tubes with a volume up to 15 ml are recommended for volumes of surface biomass expected to be more than 0.5 ml (e.g. positive control)

• Centrifuge– Swing out rotor, 3000 x g acceleration of gravity

DVGW W 270: Test procedure

• General– In each test container

• one positive and one negative control• different test pieces

– Total contact with flowing water at all sides– No contact with other test pieces or controls– Darkness– Permanent flow of 20 2 liter/hour, 12 5 °C

• Removal of the test pieces one by one from the container

• Removal of surface biomass by a scraper / stopper and complete transfer to the glassware for centrifugation

stopper with the relevant inner diameter on a rod of stainless steel, pushed through the tube

Harvesting microbial growth biomass – tubes and hoses

• Removal of the test pieces one by one from the container• Removal of surface biomass by a scraper / stopper and

complete transfer to the glassware for centrifugation• Contact cultures from samples without surface growth• Re-exposition of test pieces if necessary after harvesting

and cleaning under flushing water• Centrifugation (10 min 3000 x g or 5 min 4000 x g)• Determination of biovolume• Further examination of biovolume if necessary

(e.g microscopy)

DVGW W 270: Test Periods 1-monthly (2 test pieces, each of 800 cm² total surface)

– exposed for 4 weeks, examined: result 1a– exposed again for 4 weeks, examined: result 1b– exposed again for 4 weeks, examined: result 1c– exposed again for 4 weeks, examined: result 1d [optional]

2-monthly (2 test pieces, each of 800 cm² total surface)– exposed for 8 weeks, examined: result 2a– exposed again for 8 weeks, examined: result 2b [optional]

3-monthly (2 test pieces, each of 800 cm² total surface)– exposed for 12 weeks, examined: result 3a[optional expositions only under certain circumstances for

materials used for joints and gaskets – D1 and D2]

DVGW W 270: Evaluation

Satisfactory test performance– positive control: microbial surface biomass

1.5 ml / 800 cm²– negative control: no microbial surface biomass

< 0.01 ml / 800 cm², but positive contact cultures (microbial surface colonisation)

If there is no satisfactory test performance the whole test run has to be repeated

DVGW W 270: Evaluation

negative control

DVGW W 270: Assessment

From the parallel results (2 test pieces: 2 x 800 cm²) of each test period the arithmetic mean is calculated

• A) Materials which show over all test periods only surface colonisation or a microbial surface biomass (0.05 0.02) ml / 800 cm² comply with the requirements of the standard and can be used without restrictions from microbio-logical point of view

DVGW W 270: Assessment• B) Materials which show at one test period a

result of microbial surface biomass > (0,05 0,02) ml / 800 cm² do not comply with the requirements of the standard for general use in the range of drinking water

• C) Materials used for larger joints and gaskets (category D1):the limit values are (0,12 0,03) ml / 800 cm²– Exception: first 1-monthly test period– Additionally: values shall show equal or decreasing

tendency (1c 1b, 3a 2a)

DVGW W 270: Assessment

• D) Materials used for smaller joints and gaskets (category D2):the limit values are (0.20 0.03) ml / 800 cm²– Exception: first 1-monthly test period– Additionally: values shall show equal or decreasing

tendency (1c 1b, 3a 2a)

• E) Materials showing neither surface growth nor surface colonisation do not comply with the requirements of the standard with regard to be used in contact with drinking water

DVGW W 270: Assessmentafter

4 weeksafter

8 weeksafter

12 weeksoptional:

after16 weeks

1-monthlytest periods

harvest of sur-face biomass(mean =result 1a)

harvest of sur-face biomass(mean =result 1b)

harvest of sur-face biomass(mean =result 1c)

harvest of sur-face biomass(mean =result 1d)

harvest of sur-face biomass(mean =result 2b)

DVGW W 270: Report/Certificate

• Test report– Material / product description

e.g. manufacturer, compositional information (presented, evaluated and approved), method of production (presented), range of use

– Details to test sample / pieces – Test results, additional findings, assessment

• Test certificate– …. assessment, validity (remark: valid only

without changes in chemical composition)

Against microbial surface biomass on cpdw

Usecertifiedcpdw !

gasket

Dr. Christiane Schell

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