|
CRANFIELD
UNIVERSITY
SCHOOL
OF WATER SCIENCES
MRes
Thesis
Academic
Year 1995-1996
JOANNA
ELIZABETH STARMER
Magnetic
treatment of swimming pool water for enhanced chemical
oxidation and disinfecting.
Supervisor:
Dr. Simon A. Parsons
September
1996
ABSTRACT
Magnetic
water treatment is potentially of great benefit to pool
water treatment in terms of the reduction in use of
oxidizing chemicals in water treatment. Magnetic
treatment has been variously shown to stabilize solution
pH, eliminate corrosion of materials and reduce system
downtime. In addition to the reduction in running
costs, physical water treatment is generally viewed as
being more environmentally acceptable; reducing the use
of the strong oxidizing chemicals conventionally
employed for disinfecting.
This
study determines the efficacy of a magnetic treatment
device on the inactivation of a model micro-organism (Escherichia
coli), chlorine consumption and concomitant disinfecting
by product formation in a swimming pool water analogue.
Effects of magnetic water treatment on physical
parameters such as scale deposition; conductivity and pH
are reported, as well as the key performance
determinands of chlorine consumption, micro-organism
inactivation rate and trihalomethane (THM) formation.
A commercially available magnetic treatment device
(Magnetizer) was used throughout.
It
was found that in all cases chlorine loss was more rapid
in the control than in the magnetically treated water.
The bactericidal efficiency of the free chlorine was
unaffected by magnetic treatment, such that the E. coli
kill rate for a given disinfectant dose was increased by
an average of 25% by this physical conditioning.
In addition, it was found that generation of THMs was
reduced by magnetic treatment at any one free chlorine
level.
ACKNOWLEDGMENTS
I
would like to thank the representatives of Magnetizer in
the UK for the sponsorship of this project.
I
would also like to thank my supervisor, Dr. Simon
Parsons, and Dr. Simon Judd for their assistance.
MAGNETIC
TREATMENT OF SWIMMING POOL WATER FOR ENHANCED CHEMICAL
OXIDATION AND DISINFECTING.
1
INTRODUCTION
1.1
Background
Many
industries, including the swimming pool industry, are
being urged by regulatory bodies such as PWTAG and
pressure groups to use non-chemical treatment processes
wherever possible (Gosling, 1996). PWTAG also
places pressure on operators of swimming pools in the UK
to employ the “least hazardous option” in terms of
health and safety and environmental concerns (Gosling,
1996). The contaminants of swimming pool water are
mainly urine, sweat and micro-organisms introduced by
the swimmers. The major disinfectant used in
swimming pool water treatment is sodium hypochlorite
which has a bactericidal action that can be suppressed
to some extent by interaction with other chemical
contaminants (Black, 1996). Reaction with these
organic contaminants result in the generation of
disinfecting by products (DBPs), the simplest of which
are the trihalomethanes (THMs). The nature of
these products and the extent to which they are
generated depends upon the prevailing physical and
chemical conditions (PWTAG, 1995). However, they
are generally undesirable as they are all at least
suspected carcinogens, teratogens and mutagens (Gosling,
1996).
1.2
Magnetic water treatment (MWT)
1.2.1 Chemical effects
The
application of magnetic treatment to water has a long
history, and has been used mostly to remove and control
scale deposition (Donaldson, 1988; Baker and Judd,
1995). Calcium carbonate scale is estimated to
cost industry around £ 1 billion per year (Darvill,
1993). The benefits of magnetic water treatment
are claimed to include energy and water savings along
with a range of benefits which prolong the life of the
system's component parts and hence the life of the
system itself. Magnetic treatment has been shown
to stabilize pH, eliminate corrosion, reduce downtime,
maintenance and cleaning costs and bacteria and remove
the risks associated with the handling of chemical
detergents such as sodium hypochlorite used in swimming
pool water treatment (Ifill, 1994). Magnetic
treatment has been successful in a range of systems
including industrial heat exchangers, cooling towers,
water treatment plants and household use (Baker and
Judd, 1995), and may prove useful to the leisure
industry in reducing the heating and disinfecting
expenses involved in managing swimming pools. In
addition to this physical water treatment is more
environmentally acceptable than the use of strong
oxidizing chemicals.
1.2.2
Biological effects
Water
is the major component of bacterial cells and the
dissolved ion content in the intracellular water is the
source of nutrition for the cell. One report shows
that magnetic treatment of water can enhance the
solubility of ions in the water, and proposes this the
mechanism by which magnetic fields affect biological
systems (Lin and Yotvat, 1990). It has also been
proposed that magnetism may affect ion polarity,
increasing membrane permeability and hence the amount of
chlorine which can enter a cell, thereby enhancing its
disinfecting properties (Ayrapetyan et al, 1994).
A number of reports exist investigating the mechanisms
by which magnetically treated water affects the cells
and micro-organisms, the observed effects apparently
varying from stimulatory to inhibitory depending on
field strength and frequency of the magnetic field (Chizhov,
1975; Goodman et al, 1976; Moore, 1979; Berg, 1993).
Many reports are concerned with the nature of the medium
in which the micro-organisms exist (Berg, 1993; Okuno et
al, 1993). Strong magnetic fields have been seen
to enhance the growth of the model bacterium Escherichia
coli cultured on a range of growth media (Okuno et al,
1993), but on the other hand, low strength alternating
and pulsed fields have been shown to inhibit growth
(Smith et al, 1993).
1.3
Magnetic treatment of swimming pool water
The
last few years have seen the development of magnetic
treatment devices (MTDs) for, amongst other
applications, swimming pool water treatment. It is
claimed by the suppliers of these devices that such
devices have a number of beneficial effects including:
§
The reduction of scale.
§ The suppression of chlorine volatilization.
§ The inhibition of microbial growth.
Of
special interest, and as a direct consequence of the
above, is filter surface loading or fouling.
Fouling of sand filters in swimming pool treatment can
be largely attributed to clogging of the surface of the
filter by organic materials, such that backflushing
becomes necessary long before the full capacity of the
filter has been reached. The application of a
magnetic field via the specified magnetic treatment
device might thus be expected to reduce the fouling of
the filters by:
a)
Inhibition of biological growth and/or
b) Enhanced breakdown of organic materials due to the
maintenance of higher chlorine levels in the water
It
is these two key phenomena that form the basis of the
study.
One
of PWTAGs stated main principles is that “the less
disinfectant and other chemicals needed to maintain good
water quality, the better”, and that “the only
chemical you should use is a lot of water” (Gosling,
1996). In addition to this basic premise, enhanced
disinfecting would be of great benefit in terms of cost.
At the moment, pools in the UK spend an average of £500
per annum on disinfectants. Should the 25% saving
previously claimed be possible, the 1600 pools in this
country would save a total of £2 million on
disinfecting costs per year (Ifill, 1994).
2
LITERATURE SURVEY
To
assess the extent of the possible benefit MWT could have
for the treatment of swimming pool water, the literature
survey covered the following areas:
1)
The operation and standards of swimming pools
2) Disinfecting of swimming pools*
3) Chemical contamination of swimming pools
4) Biological contamination of swimming pools
5) Factors affecting disinfecting
6) Magnetic treatment of water
7) The effects of magnetic fields on biological activity
8) The effects of magnetic fields on chemical activity
*Where
“disinfecting” is defined as the conscious
inactivation of pathogenic organisms and viruses.
2.1
The operation and standards of swimming pools
The
Pool Water Treatment Advisory Groups (PWTAG’s) Pool
Water Guide (1995) sets out guidelines and outlines
legislation which ensures water quality and therefore
public safety. The regulations control water
temperature and chemical additions and bather load in
order to ensure bather safety and good water quality.
The treatment of swimming pool water is made compulsory
by The Swimmers Pools Regulations of September 1991 4
(1) in Britain, and on the continent by other European
legislation such as DIN standard 19 643 in Germany.
PWTAG guidelines give maximum bather load as 1 bather
per 2.5 m² for safety, whereas the Department of
Environment (DOE) uses the formula below in order to
maintain water quality. PWTAG lay down strict
guidelines for pool water quality in terms of suspended
and dissolved solids as well as physical properties
(Table 1).
Materials
The
study was conducted on the laboratory scale. The
device was tested on simulated swimming pool water of
known chemical and microbiological composition using a
water of specification within PWTAG recommended
concentration ranges (Table 8). Tests were
restricted to relatively hard waters where scaling is
more visible, although effects on scale formation were
not rigorously quantified. Faecal coliform was used as
the microbiological contaminant throughout the course of
study, and human urine and sweat analogues were added
(specified in Table A1, Appendix A). All tests
were conducted using Spectrosol grade sodium
hypochlorite with 12% free available chlorine (w/v) as
the disinfectant and calcium bicarbonate to represent
hardness of 200 ppm as CaCO3, which would encourage
scale formation while remaining within PWTAG’s
guidelines.
Limiting
values of physiochemical parameters
Component
Low High Reference
Sodium Hypochlorite (mg/l) 0.42 1.40 1.05
Free chlorine (mg/l) 0.50 1.50 1.00
Sodium bicarbonate (mg/l) 168.00 336.00 336.00
Calcium Chloride (mg/l) 55.00 222.00 222.00
Sodium Humate (mg/l) 0.00 0.02 0.01
Sodium Chloride (mg/l) 0.00 2000.00 0.00
Sodium Sulphate (mg/l) 0.00 1500.00 0.00
PH 7.20 7.80 7.80
Temperature (°C) 28.00 32.00 32.00
*Body fluid simulant (ml/l) 0.00 0.05 0.05
*
Simple analogue of human urine and sweat: Table A1.
3
OBJECTIVES
The
investigation was focused on the suppression of chlorine
desorption, and increased bactericidal action.
Previous work within the School of Water Sciences (Ifill,
1994) has revealed that magnetic treatment has a small
but significant effect on the retention of free
chlorine, as well as on calcium carbonate scale
formation. It was intended that further work be
carried out to verify trends observed in the previous
study, and determine the extent to which the observed
chlorine retention affects the formation of THM
by-products. In addition, the direct influence of
magnetic forces on bacteria viability will be studied.
The
aim of the work was to test the efficacy of a magnetic
treatment device (Magnetizer) in conditioning simulant
swimming pool water so as to enhance chemical
disinfecting. To this end, the effect of the
magnetic treatment on both microbiological and chemical
activity was to be quantified.
It
was intended that quantitative or semi-quantitative
assessment of the effect of MTD’s on free chlorine
level, combined chlorine level, disinfecting by-product
formation, with specific reference to trihalomethanes
and disinfecting capability for faecal coliform would be
provided, and that the results would refer to chemical
conditions simulating those persisting in a normal
swimming pool.
Mean
chloroform concentrations after an initial free chlorine
dose of 0.4 ppm
ANCOVA
of mean chloroform concentrations at 0.4 ppm initial
dose
Source
of Variation Sum of Squares DF Mean Square F Sig of F
CovariatesCombined CI (ppm)Free CI (ppm)PHTemperature (°C)Time
(hours) 1.0900.9760.1901.76975.514 11111
1.0900.9760.1901.76975.514 0.3070.2750.0530.50721.298
0.0580.6010.8180.4790.000
Main EffectPresence of MTD 20.429 1 20.429 5.660 0.000
ExplainedResidualTotal 120.415283.651404.006 68086
20.0693.5464.698 19.000 0.000
Summary
of effects of MWT
1)
The pH of pool simulant solutions increased when organic
compounds were present and decreased when they were
absent.
2) No changes in solution conductivity were found.
Magnetizer comment: This is to be expected since there
was no evaporative water loss.
3) No scale was formed, so no conclusive results were
obtained.
Magnetizer comment: With virtually no make up water or
loss, scaling could not be significant.
4) The turbidity of the solutions increased by an
undetermined amount.
Magnetizer comment: If a filter would have been used in
the test rig, particles could have been filtered out.
5) No direct biocidal effects were observed.
Magnetizer comment: Test was only run in 8 - hour day
shift.
6) The cell death rate of E coli was significantly
raised owing to increased aqueous chlorine.
7) Concentrations of free chlorine in solution were
significantly increased by MWT at 0.8 and 1.2 ppm free
chlorine doses.
8) Concentrations of combined chlorine in solution were
significantly increased by MWT at and 1.2 ppm free
chlorine doses.
9) Cell kill was improved at 0.4, 0.8 and 1.2 ppm
initial free chlorine doses.
10) Chloroform production was suppressed at 0.4 and 1.2
ppm initial free chlorine doses; at 0.4 ppm this was
significant.
|
