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)

www.hyg.dewww.hyg.deDVGW 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]

www.hyg.dewww.hyg.deaerator (seen from the front and the back)

www.hyg.dewww.hyg.deDVGW W 270: GoalThe 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: ScopeTest 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: EvaluationSatisfactory 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: AssessmentFrom 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 descriptione.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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