Polypropylene random [PPR] has been tested as pipe material in contact with drinking water. The influence of the pipe’s dimensions, surface and volume in contact with water, of the temperature and of the stagnation period of water in pipes on the germs and bacteria growth has been studied, using unchlorinated drinking water and drinking water, from the same source, chlorinated into the laboratory, at a minimum level and at the maximum level allowed by the law. After 9 hours of contact with PPR, water has been submitted to a microbiological and physical-chemical analysis. The total number of germs [NTG] developed at 22°C and respectively 37°C, Coliform bacteria [CB] and E. coli numbers of colonies, as well as water turbidity [T], have been determined.
INTRODUCTION
Although water represents a resource of great importance to both humans and animals, its storage mode and effects of its transit through household drinking water networks is little studied for a perishable product. The temperature of storage and the material from which the pipes are made, represent important factors in water quality deterioration, with serious consequences on human health.
Consequently, the hazard analysis and
critical control point (HACCP) system and SR EN
ISO 22000: 2005 Food Safety standards must be
continuously and responsible applied to drinking
water, as well as with other food products.
Degradation of water quality in the distribution
network is due to both chemical contaminants (a)
as well as microbiological contaminants (b).
*
(a) Contaminants of chemical nature coming
from distribution pipes can seriously damage
human health through their accumulation in the
body over time. Recent studies on water that has
passed through metal pipes in the network of
17 families have indicated that overnight stagnant
water presented in some cases concentrations of
metals Cu (copper), Pb, Ni or Al) (over the maximum
threshold allowed by legislation.1 Besides metals,
other dangerous chemical compounds from the
pipes can migrate into drinking water, with serious
consequences on human health. For example, in
England, a study performed on pregnant women
draws attention to the fact that contamination with
tetrachloroethylene, coming from the pipes,
increases the risk of congenital anomalies.2 It also
draws attention to the fact that one of the causes of
endocrine disorder is the consumption of water
* Corresponding author: st.patachia@unitbv.ro, Tel: +40741649792, Fax: +40 268 410525
904 Nicoleta Damian et al.
from PVC networks and cancer may be due to
chemical compounds leached from plastics used
for storing drinking water.3 Unlike biological
contaminants, the toxic compounds accumulate
over time and do not cause immediate clinical
manifestations, and thus health measures are
usually taken very late.
(b) Microbiological contaminants are equally
dangerous to human health and in some cases can
lead to death. It is well known in this regard, the
epidemic of dysentery in Detroit (USA), which
included over 50,000 cases of disease. Unlike
chemical contaminants, microbiological ones
produce immediate symptoms, health degradation
being made very rapidly. Microbiological risk can
be induced by external factors in the distribution
network, but little is known about the fact that the
distribution network itself may constitute a risk in
microbiologically altering the quality of drinking
water.
Moreover, it has been demonstrated that PPR
pipes manufacturers take into consideration only
the physical-chemical aspects, as evidenced by the
certificate of quality of the product, where
chemical resistance is an exhaustive chapter treated
in accordance with ISO / TR 1035: 1993, making
reference to chemical resistance to 140 different
substances, while microbiological resistance
remains an untreated issue. The present work aims
to monitor the microbiological activity evolution of
water distributed through PPR pipes, depending
both on the volume of the pipe, and on the pipe
surface in contact with water for 9 h at 22°C.
In this study, microbial activity monitoring of
stagnant water in random polypropylene pipes
(PPR) with different diameters has been achieved,
depending on the volume of the water and the
surface in contact with the water. The study takes
into account that not all consumers use chlorinated
water sources, so the water quality monitoring has
been performed for both chlorinated and nonchlorinated
water, using the same source. The
study takes into account the chlorination level of
water, as it is known that the consumers from the
beginning of the distribution network have a higher
concentration of free chlorine than the end
consumers of the network. For these reasons the
study was performed on water with free chlorine
concentration close to the minimum and maximum
allowed values, ie. 0.1 mg/L Cl2 and 0.5 mg /L Cl2
according to Law no. 458/2002 on drinking water
quality (republished) - completed by Law no.
311/2004, so the experimental data involves all the
categories of consumers.
The PPR material was not randomly chosen,
but in accordance to the current state of art in the
field of hydro constructions. So far, for both
financial and technical reasons (pressure and
corrosion resistance, lower weight, low expansion
coefficient, easy maneuverability), only polymer
pipes are used, among which PPR is the most
frequently used.
MATERIALS and METHODS
1. Materials
Drinking water (non-chlorinated) was sampled
from Ciucaş source, Zone II of the Water
Distribution Company Brasov, Roumania. The
initial quality of the water used for the experiments
was determined in accordance with the
requirements of Law 458/2002, Annex 2 on the
quality of drinking water supplied to the city
mains. Because this source of drinking water is a
natural one, the characteristic parameters varied at
different sampling time due to amount of rains and
temperature. As example, we reported in this
paper the behavior of three initial samples with the
following particular characteristics:
a) Sample 1 with turbidity [T] 0.15 NTU;
coliform Bacteria [CB] 1 cfu /100 mL, E. coli
0 cfu/100 mL, Intestinal enterococci 0 cfu/100 mL;
Clostridium Perfringens 0 cfu /100 mL ; total
number of germs [NTG]: 37˚C 15 cfu/1 mL; NTG
22˚C 10 cfu/1 mL
b) Sample 2 with T 0.25 NTU; CB 3 cfu /
100 mL, E. coli 0 cfu /100 mL, Intestinal
enterococci 0 cfu /100 mL; Clostridium
Perfringens 0 cfu /100 mL; NTG 37˚C 18 cfu/
1 mL; NTG 22˚C 22 cfu/ 1 mL
c) Sample 3 with T 0.09 NTU; CB 0 cfu /
100 mL, E. coli 0 cfu /100 mL, Intestinal
enterococci 0 cfu / 100 mL; Clostridium
Perfringens 0 cfu /100 mL; NTG 37˚C 17 cfu/
1 mL; NTG 22˚C 17 cfu/ 1 mL
and commune characteristics:
pH: 7.89- 7.96; conductivity: 226-227 μS/cm;
[Al3+]< 0.009 mg / L; [NH4
+]< 0.007 mg / L;
[NO3
-]: 6.07-6.35 mg / L; [NO2
-]< 0.007 mg /L;
[O2]< 0.6 mg / L; 6.67 °d; [Cl- ]: 6.00-6.15 mg / L;
Sodium hypochlorite for chlorination of water
to ~0.1 mg /L Cl2 (minimum concentration of free
chlorine under the laws in force) and ~ 0.5 mg /L
Cl2 (maximum concentration of free chlorine under
the laws in force). This solution has been used to
check the effect of chlorination on the microbial
activity developing in stored water.
Drinking water quality 905
Fig. 1 – PPR pipes having the same volume but exhibiting different surfaces for contact with water.
Table 1
Dimensional characteristics of PPR pipes used in the study
Vct = 150.000 cm3 Sct = 430.000 cm2
Ø (cm) L (cm) S (cm2) Ø (cm) L (cm) V (cm3)
1.400 97.500 428.610 1.400 97.800 150.475
1.800 59.000 333.468 1.800 76.000 193.298
2.000 47.800 300.184 2.000 68.500 215.090
where: Ø is the pipe diameter, L is the length of pipe, S is the interior surface of the pipe, V is
the interior pipe volume.
12 PPR pipes, from Valrom-Industrie srl.,
Bucharest-Roumania, cut according to the
dimensions shown in Tab.1, so as to contain either an
equal volume of water (one set for chlorinated water
and another set for non-chlorinated water) at different
surfaces contact with water, or to contain different
volumes of water in contact with the same pipe
surface. The pipes with three diameters have been
sealed at one end with a plastic cover and at the other
end with valves from the same material (Fig. 1).
The pipes have been repeatedly washed with
water and then disinfected with a 70% ethanol
solution. Aiming a high level of disinfection, the
pipes have been subjected to UV irradiation (λ =
253.7 nm) for 48h.
PPR, pipes material, is a mixture of
polypropylene (-C3H6-)n with different molar mass,
which confers the material a better impact resistance.
As a function of chain arrangement and size,
polypropylene materials can be classified as shortchain
polypropylene (PPS), long-chain
polypropylene (PPH) and polypropylene with
randomly-sized and displaced macromolecular chains
(PPR).
In contrast with other plastic materials, PPR is
more rough and rigid4 (TC003, 2006 technical
bulletin, www.valrom.ro). The roughness of the
materials represents one of the factors that facilitate
bacterial adhesion, as proven by Katsikogianni.5
The PPR pipes, filled with water in a microbiologically
controlled environment have been
submitted to stagnation for a 9 hours period (the same
period of time the water stagnates in household
distribution networks overnight) at 22˚C (average
room temperature). The experiments have been
performed in triplicate.
2. Methods of analysis
2.1. Coliform and Escherichia coli bacteria
counting and detection
For the determination of lactose-positive bacteria,
the filtering membranes method has been used. The
principle of this method consists in filtration of
determined volumes of water through membranes
with 0.2-0.45μm porosity. The bacteria from the
water sample remain on the surface of the membrane,
and then the membranes containing the bacteria are
placed on a selective culture medium (Tergitol TTC),
which contains lactose, triphenyltetrazolium chloride
(TTC) and sodium heptadecylsulphate (Tergitol).
The culture media have been purchased in a ready to
use form (Nutri Disks Tergitol TTC from Dr.
MӦLER & SCHMETZ), which includes sterile
Petri dishes with the culture medium and the
corresponding filtering membrane, for each Petri
dish. The testing has been performed in accordance
with SR EN ISO 9308-1/2004 AC:2009.
From each storage recipient, 100 mL of water has
been sampled and filtered through the membranes.
The membranes have been placed in the Petri dishes
containing the hydrated culture media and incubated
for 24 h on 36±2˚. After the incubation period, the
membranes have been examined and all the yelloworange
lactose-positive bacteria and red lactosenegative
bacteria colonies developed have been
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