Note: Descriptions are shown in the official language in which they were submitted.
CA 02236375 1998-04-30
W O 97/19025 PCT/SE96/01506
METHOD OF DIS~N~CTING WATER
TECENICAL ~1 ~LD
s The invention re}ates to the water ll'CaL~ technique and especially to a method of
disinfecting water intPn-le-l for baths, paIticularly for public baths, at which the water has
a pH value > 7.8 before the ~icinf~ction However, in a wider perspect*e, it is possible
that the invention can also be used to ~licinfect rlrinking water.
10 BACKGROUND OF 1~ lNVENTION
In general the disinfectant that is used for bathwater and ~lrinking water is chlorine or
certain active chlorine compounds. The chlorin~tinn is also used to f~rilit~te the
pnrifir,~tic~n ofthe water by oxi~lati~n In general rhlorine gas, sodium llypochlorite,
NaClO, or calcium hyporhlc ritç, Ca(CI0~2, is used. Either chlorine gas, sodium
15 hypochlorite or calcium hypochlor;te is used, an e~ - is reached in the water
between the reactive species hypochlorous acid, HClO, and hypochlorite ions, CIO-, that
both are so called free active rlllorine
It is widely known that chlorin~tinn has a number of negative side effects: undesirable
20 organic chlorine cornpounds are formed when free active chlorine reacts with organic
compounds in the water, the chlorine can have an initating e~ect on sensitive persons
and chlorine has an unpleasant smelL Furthermore the h~nflling of chlorine or active
chlorine compounds is very dangerous for the staffwho operate the pllrif s~tion plant.
Despite these disadvantages chlorination has been crn~i~lPred to be irreplaceable for
25 ~ nfection of bathwater and (1rinking water.
However, cornpounds and techniques have been developed to reduce the amount of
added rhl~rine or chlorine cornpounds. Chlorination has e. g. been combined withliti-~n of oxitli7in~ agents. Among other things ozone and hydrogen peroxide have
30 been used in combination with chlorine dosage. Furthermore W-r~ tion in
comhin~tic-n with a~1-iit;on of ~hll~rin~ting agents have been used.
.,
~ince at least ten years another method in which is used hydrogen peroxide in combina-
tion with W- r~rli~tif-n, is also known~This method, however, only has a limited3s disinfection potential, that among other things is shown iu growth of organic matter on
filters and in tlle boundary layer between water and air. Other inconveniences that
CA 02236375 1998-04-30
W O 97/19025 PCT/SE96/OlS06
c~ ule to the fact that this method has not come into general use, are its high need of
Iabour input and its high costs for inct~ ti~n and operation.
BRIEF DISCLOSIJ~E OF ~ ~ INVENTION
s The purpose of the invention is to offer a method to disinfect water that has enough
capscity of .l;~... r~ ;r~n, that does not have high inct~ t;nn and operating costs and that
does not require any col,L~il uLion of chlorine or active chlorine cornpounds. This can be
~tt~in~rt by the invention by a~ cting the pH value to a value < 7.8, suitably c 7.6 and
preferably <7.5, and by adding hydrogen peroxide to the water in order to oxidize
10 existing micro-o~ .,.c and other orgaruc matter in the water at the mrnt;r ne~t lower
pH value without presence of free active chlorine. Preferably the hydrogen peroxide is
added in at least stoichiometric proportion to oxidi7e existing rnicro-u~ ".~ and other
organic rnatter in the water.The pH value should not be lowered so much that the water
gives an acid reachon. The lower pH limit is therefore set to 7.0, preferably to 7.1. The
pH value should be adjusted to some value between 7.1 and 7.5, preferably between 7.3
and 7.4. The pH value is suitably atljucte~l by adding C02 or carbonic acid.
It is also suitable that the ~Ik~l;nity ofthe water is kept at a value between 50 and lOO,
suitably at a value between 60 and ~0 mg H:C03- / I water, in which case the rnethod of
20 the invention is used for rticinfPction of water in a swirnming-pool.
The pH value and the aL~calinity can be adjusted to the desired levels by adjusted addition
of CO2 (herein is in the following also included carbonic acid3 and H2O2, that preferably
is added into a pipe parallel to the main pipe in a circular fiowpath, that also includes the
25 swimming-pool. If only CO2 is added, the alkalinity expressed as the amount of HCO3- /
1 water decreases. On the other hand if both CO2 and ~I2~2 are added at the same time
into the pipe, HC03- will be produced, ie. the ~Ik~linity increases. For the best control
and re~lt~ti- n of both pH value and alkalinity it is ap~lul~lia~e that CO2, H2O2 and CO2
+ H2O2 are added at ~ ~L periods that do not overlap. A control sequence can thus
30 comprise a first period when CO2 but no H202 is added to the pipe, a second period
when H202 but no CO2 is added into the pipe and a third period when both CO2 andH202 are added into the pipe.
In the case the invention refers to rti~infection of water in baths, water is continuously
3s lost by evaporation. This water, together with other water that can vanish or divert from
the system, is compensated by fresh water. Normally fresh water contains metals whicl
can be in a soluble state as metal ions or as complex ions. If these metals are not
CA 02236375 1998-04-30
W O 97/19025 PCT/SE96/01506
removed before fresh water is added into the water in the pool, the metals will gradually
be accnm~lqtefl in the water. Some metals, as Rt~ -ll, copper, iron and mRn~Rnese
can have a great di tlulbiug effect on the fli~;. . rt;~ process by stim~ tinf~ the
decornDosition of the hvdrogen peroxide, i.e. that it does not fulfil the purpose, or the
s amount of added H2O2 has to increase cfm~ift~rRhly to have the desired pnrifir"tinn
effect. To avoid these problems, incoming fresh water should be purified from such
metals which can decompose the hydrogen peroxide. The incoming fresh water should be
cleanedsothatthewaterinthepoolwilicontain ...~x;...--... 0.20ppmAl,preferably
x;~ O.O9 ppm Al~ l x;~ o. lo ppm and preferably mq~imllm o.oo5 ppm of each
10 ofthe metals Cu, Fe and Mn. The pllrifirqtioll of the incoming fresh water from the
mf ntinned metals can be carried out by an ion exchanger.
BRIEF DESCRIPTION OF DRAWING
The drawing shows srh~m~tir~lly the water pllrifir,~ticm system for a swimming-pool that
15 works in accordance with the method ofthe invention.
DESCRIPTION OF A PREFERRED ~MBODIMENT
In the drawing a swirnming-pool is d~ociPn~ted 1. From the bottom ofthe pool an outlet
waterpipe 2 leads to a coarse screen 3. From the pool 1 also surface water is directed
20 through a pipe 4 to a co~npensation tank 5 and from there through a pipe 6 to the ahready
mentioned outlet pipe 2, a~er w~ich the~oined flows are directed to the coarse screen 3.
Fresh water can be directed through a pipe 7 to the compensation tank 5. In the pipe 7
there are two ion exchange columns 30 and 31 connected in series of which one is an
anion ~Yrh~n~e column and the other a cation exchange colurnn, to remove ~ ...;.l;...",
2s copper, iron and manganese from the water.
From the coarse screen 3 the water is circulated further by means of a pump 10 to three
filters 11, 12, 13 connected in parallel and through these. Afcer the filters 11, 12, 13 the
liquid fiow is divided into two fiows. One by-pass that ~ es~ls 5-25% ofthe total
30 circulating flow is led through a branch pipe 14 while the main part is directed through a
~-.-;.-l-;l-e 15 which is parallel to the branch pipe 14. Both flows in the pipes 14 and 15
are joined in an inlet pipe 16, through which treated water is directed into the pool 1. For
mea~ule~,nL ofthe content of hydrogen peroxide and the pH value ofthe water in
~ e 15, a very httle flow is at the m~ nng points directed through a pipe 17 for3s analysis of H~02 in the measure e4...~ 18 and for analysis of pH in the measure
c~l..;p..~ 19 and then back to outlet pipe 2.
CA 02236375 1998-04-30
W O 97/19025 PCT/SE96/01506
The branch pipe 14 goes Lhl.~u~ a safety cabin 21. ~n this safety cabin there is one or
several cnnt~inPr.c 22 c~ H2O2. From a cnnt~in~r 22 hydrogen peroxide is dosed
into the water in branch pipe 14 by means of a pump 32 w13ich pumps hydrogen peroxide
from the container 22 and directs it into the branch pipe 14 at a point in the safety cabin
s 21. AfLer, before and/or cimllh~neously with the a-1-1itinn of hydrogen peroxide, carbon
dioxide is added to the water in the branch pipe 14 from one or several carbon dioxide
bottles 24 via a pipe 25 with a valve 34.
The mea 7ul~cllt test results of the H2O2 and the pH ~ cred by the me~lrin~
lo equipment 18 and 19, are processed in a computer 33 in accordance with a control
program that has been pro~ mmP-(l into the computer for controlling the pump 32 for
supply of H2O2, as well as the valve 34 for supply of CO2 to the branch pipe 14. A
control sequence can consist ofthe following parts. First the valve 34 is opened for
adding of CO2 and is kept open during a certain period oftime, depending on pH value
registered by the mP~cnnn~ e4ui~ L 19, after the valve 34 once again is closed at
cn.. ~ l from the computer 33. The pump 32 is during this first period inactive. Then
the pump 32 starts and a certain amount of H2O2 is pumped into the pipe 14 from the
bottle 22 depending on the content of H2O2 registered in the mP~lnn~ equipment 18
and in accordance with the program in the co~u~e~ 33, after which the pump 32 is20 stopped once again. During the third period the pump 32 is once again active and is
pumping H2O2 from the container 22 into the pipe 14, cimlllt~neously as the valve 34 is
open, so that also CO2 is led into the pipe l4 to rise the ~Ik~linity to the desired level.
Alfern~tively the second and third period can follow directly after each other, i. e. the
pump 32 has to work cnntin--ously during the mPnt;nnefl second and third periods. It
2s should be realized that this control sequence can be varied, so during certain control
seq -Pnces only some ofthe mentioned periods are active. It is also possible during each
control se~ ~pnre to lead in H2O2 first and then CO2. The PccPnt;~l point is that CO2 and
EI202 can be added separately as well as cimnlt~neously for deliberate and controlled
mixing of CO2 and H2O2, so that it is possible to regulate during a control sequence
30 either the pH value, the value of H2O2 or the ~Ik~linity.
ACHIEVED RESI~LTS
The invention has been developed prirnarily for .1;~ water for public baths.
Normally such water has a pH value over 8 and there are pH values right up to about pH
35 9. ~ the expe~ Ls which the invention is based on, the above described e~ ..
was used, and the L1eaI~CLI~ was in the way that ;mmto~ tPly is evident from thedescription ofthe equipment. The volume ofthe pool 1, see figure, was 30 m3. The pH
CA 02236375 1998-04-30
W ~ 97/19025 PCT/SE96/01506
value was lowered by a~lrliti( n of carbonic acid, CO2 . lE3efore the adj..~ l of pH the
water had a pH value of 8.6. Hydrogen peroxide was added in varying amounts as ainfi~ct~nt In each experiment was in~ ;p;1 1 ecl how much hydrogen peroxide that had
to be added, at dilr~ pH values, to keep the conc~ntr~tinn of H2O2 in the water at 80
s - 90 pprn, after it had been cnnt~min~te~ by 30 persons. It was presumed that 30 persons
is a big enough population to give an acceptable statistic mean value ofthe whole
cnnt~min~tinn ofthe water in form of bacteria, other micro-o~ and other organic
matter. The results are shown in the following table.
pH value after adding CO~ Added amount of H2O2, litres
~.2 40
7.8 15
7.6 4.2
7.30 740 ~2.1
7.28 4.2
It is evident from the table that the capacity of the hydrogen p eroxide to oxidize organic
matter in water and thus its capacity to destroy micro-o~ C~ in other words its
disinfecting capacity, was strongly dependent on the pH value. While 40 litres of H2O2
were required to . .. ~ . a concentration of H2O2 of 80 - 90 ppm in the water at pH
8.2, which infli~tes a very high consumption of H2O2 to m~int~in the intpnrled oxidation
effect, only approximately 2.1 litres of H2O2were required to m~intRin the same effect at
pH 7.30 to 7.40. At pH values under 7.30 the f~ters started to silt up with organic
matter, which required increased ~ iition of H2O2.
cc~ccfi-l operation tests with a lowering ofthe pH-value in bathwater to approxim~tely
7.4 by adding CO2 and using H2O2 as t'ae only ~ inf~ct~nt, have verified the ~ of
the method. The u~h~ L pH in the plant in question was 7.37. The rehability ofthe
method in cli~ qtes that the concentration of H2O2 in water can be kept at a level lower
30 than ~0 pp~ According to this conce*able development H2O2 is added in such amount
that the conc~ntr~ti-n of H2O2 in water is,,. ;.. ~ ed within the interval 10 - 70 ppm,
preferably within the interval 10 - 50 ppnL
It should be reahzed that the invention is not hmited to the use of CO2 or carbonic acid
35 to lower the pH-vslue. Other acids msy probably also be used. However, other oxidation
agents, e.g. ozonej should not supplement the adtiiti~n of hydrogen peroxide, since it can
~istuIb the integrated process. On the other hand nothing obstructs that e.g. W-
CA 02236375 1998-04-30
W O 97/19025 PCT/SE96/01506
r~ tilm in a manner hlown per se, supplements the ~ . r~cL;~l by means of hydrogen
peroxide and eventually other rh~mira1 tlir~nf~ct~ntc, provided that chlorine or chlorine
compounds are llot used~ It can also be suitable to add cht?tnic~lc directly to the
~wih~ g-pool l, e.g. sodium bicarbonate, to increase the ~Ik~linity in the water in
5 question, which does not contain active chlorine. This can simply be rnade by throwing
the r~ mir.~ into the pool at the end ofthe day to let it mix and work during the night.
It is suitable that the alkalinity is at alevel corresponding to 60 and 80 mg HCO31 l
water.
