Transcript W270

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Enhancement of Microbial Growth
on Materials which come into
Contact with Drinking Water –
Testing and Assessment
DVGW Technical Standard W 270
(November 2007)
Dr. Christiane Schell
Hygiene-Institut des Ruhrgebiets
Institut für Umwelthygiene und Umweltmedizin
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DVGW W 270: Motivation
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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]
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aerator
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(seen from the front and the back)
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DVGW W 270: Goal
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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
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DVGW W 270: Goal
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• 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
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DVGW W 270: Scope
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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
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DVGW W 270: Scope
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• 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
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DVGW W 270: Principle
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• 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
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DVGW W 270:
Basic requirements
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• 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
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DVGW W 270:
Basic requirements
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• 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)
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DVGW W 270:
Apparatus and reagents
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• 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
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DVGW W 270:
Apparatus and reagents
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• 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 module for pipes and hoses
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Composite materials
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Tube with two layers
How to test the inner
layer without
interfering effects of
the outer layer ?
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Test module for pipes, tubes and hoses
only the surface
in contact with
drinking water
is exposed and
tested
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DVGW W 270:
Apparatus and reagents
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• 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 module for pipes and hoses
• Scraper
– With rubber lid or made of hard plastic (breadth 12 - 15 cm)
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positive control:
paraffin
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negative controlHygiene-Institut des Ruhrgebiets
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DVGW W 270:
Apparatus and reagents
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• 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)
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A
A
B
0,07
0,05
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DVGW W 270:
Apparatus and reagents
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• 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
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DVGW W 270:
Test procedure
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• 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
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DVGW W 270:
Test procedure
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• 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
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DVGW W 270:
Test procedure
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Harvesting
microbial growth
biomass – tubes
and hoses
stopper with the
relevant inner
diameter on a rod
of stainless steel,
pushed through the
tube
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DVGW W 270:
Test procedure
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• 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)
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DVGW W 270:
Test Periods
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 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]
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DVGW W 270:
Evaluation
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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
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DVGW W 270:
Evaluation
negative control
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DVGW W 270:
Assessment
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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 microbiological point of view
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DVGW W 270:
Assessment
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• 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)
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DVGW W 270:
Assessment
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• 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
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DVGW W 270:
1-monthly
test periods
2-monthly
test periods
3-monthly
test periods
Assessment
after
4 weeks
after
8 weeks
after
12 weeks
optional:
after
16 weeks
harvest of surface biomass
(mean =
result 1a)
harvest of surface biomass
(mean =
result 1b)
harvest of surface biomass
(mean =
result 1c)
harvest of surface biomass
(mean =
result 1d)
harvest of surface biomass
(mean =
result 2a)
harvest of surface biomass
(mean =
result 2b)
harvest of surface biomass
(mean =
result 3a)
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DVGW W 270:
Report/Certificate
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• 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)
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Against microbial surface biomass on cpdw
Use
certified
cpdw !
gasket
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