Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
CA 02385953 2002-05-10
-1-
Title: WATER TREATMENT SYSTEM AND METHOD
FIELD OF THE INVENTION
The invention relates to a method and apparatus for the treatment of
water. The water treatment method and apparatus may be applied to fluids
such as grey or black water to be treated prior to discharge or raw water to
be
treated prior to consumption.
BACKGROUND OF THE INVENTION
In the field of grey/black water disinfection, great efforts are
continuously being made to reduce the quantity and concentration of
pollutants found in grey/black water being discharged into rivers, lakes,
surface and ground water supplies, etc. This is evidenced by more and stricter
government regulations and requirements relating to grey/black water
treatment processes and discharges. The quantities of human wastes
requiring treatment are constantly and rapidly increasing. In the field of
potable water purification, available surface and ground water sources are
rapidly deteriorating due to pollution caused by contaminates generated by a
growing population and their careless use of water and improper disposal of
waste products.
Many methods exist for the treatment of grey/black water. Biological or
chemical disinfection of the grey/black water to neutralize the harmful micro
organisms within grey/black water are common methods employed to reduce
bacteria loading found in grey/black water. Biological disinfection of
grey/black
water requires large tanks for micro organisms to consume the biological
waste contained within the grey/black water. Chemical disinfection of
grey/black water is not acceptable for water based communities and activities.
Many methods also exist for the purification of potable water which
include the use of chemical disinfectants, microfiltration and ultra violet
radiation. The most commonly used disinfectant is chlorine and when water
containing organic material and compounds is chlorinated, a range of
carcinogenic trihalomethanes is generated and considerable contact time is
required for effective disinfection. When microfiltration is used to remove
CA 02385953 2002-05-10
-2-
biological contaminants, the filtering devices require constant and regular
servicing. When ultra-violet radiation is used to make water potable, the
effectiveness is limited by the clarity of the water being treated. These
physical and chemical factors place severe limitations on these methods of
disinfection in recreation facilities.
SUMMARY OF THE INVENTION
In accordance with the invention, a method for treating water to reduce
bacteria, viruses, parasites and spores prior to discharge comprises the steps
of collecting a predetermined quantity of water to be treated in a treatment
tank and thereafter mixing with the predetermined quantity of water to be
treated, ozone. The selected quantity of water to be treated is mixed with the
ozone for a selected period of time. Thereafter the mixed water is discharged
to waste.
In accordance with the invention, there is a system for treating water
for discharge. The water is treated to reduce bacteria, viruses, parasites and
spores in the water prior to discharge of the water. The system comprises
collecting a predetermined quantity of water Q to be treated in a treatment
tank and thereafter mixing ozone with the quantity of water to be treated by
injecting ozone through an injector as the water to be treated passes through
the injector. The method further includes mixing the predetermined quantity of
water with the ozone for a selected period of time and preventing any
additional water to be treated from entering the treatment tank while the
predetermined quantity of water is mixed with ozone. The selected treatment
time is less than five minutes.
In a preferred embodiment of the invention, a method for treating waste
water involves carrying out such treatment in accordance with process
parameters given by the formula:
T=13
0
CA 02385953 2002-05-10
-3-
wherein T is the treatment time in hours, 0 is the amount of ozone generated
in milligrams per hour, I is the amount of ozone injected per liter of water
being treated as the water passes the ozone injector and Q is the batch size
of the water to be treated, in liters. In a particularly preferred embodiment
of
the invention, the amount of ozone injected into the predetermined quantity of
water to be treated is at least 1.25 milligrams per liter.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention will now be discussed in association with the following
drawings, which illustrate preferred embodiments of the invention.
Figure 1 illustrates a system embodying a first aspect of the invention;
Figure 2 illustrates a system embodying an alternate aspect of the
invention;
Figure 3 illustrates an alternative embodiment of a portion of the
system of Figure 1;
Figure 4A illustrates a first arrangement of parts of a portion the system
of Figure 1, and
Figure 4B illustrates an alternate arrangement of the parts of the
portion of the system of Figure 1 illustrated in Figure 4A.
DETAILED DESCRIPTION OF THE INVENTION
The term "grey water" is used in this description and in the claims to
describe water which is not human sewage but results from use by humans
such as in washing and the like. The term "grey water" can encompass
effluent from sinks, showers and the like. The term "black water" is used in
this description and claims to refer to water in which human sewage is a
significant component. Black water normally results from effluent from toilets
and the like.
The term "potable water" is used in this description and claims to refer
to water which is fit for human consumption.
CA 02385953 2002-05-10
-4-
The term "raw water" is used in this disclosure and claims to refer to
ambient liquid such as may be found in surface water comprising lakes, rivers,
streams and the like, and in addition, ground water such as may be contained
in wells, whether dug or drilled, as well as run off water such as collected
rain
water and the like. The term "raw water" is intended to cover all liquids
other
than water which is primarily either grey water or black water.
The term "disinfection" as used in this disclosure and the claims, refers
to treatment of water to reduce bacteria, viruses, parasites and spores
content
of the water. In the case of use of the term "disinfection" with grey water or
black water, the term is intended to encompass reducing the bacteria, viruses,
parasites and spores content of the water to a level acceptable for discharge
to the intended environment, whether that be on land or into other surface
water. In connection with the term potable water, the term "disinfection" is
intended to encompass reducing the bacteria, viruses, parasites and spores
content of raw water to the state that the water, after treatment, is suitable
for
human drinking consumption.
The embodiment of the water treatment system illustrated in Figure 1 is
illustrated generally at 10. The principal components of the system include a
treatment tank 20, a solenoid controlled discharge valve 30, a controller 80,
and an ozone generator 40. Preferably, the system includes a collection tank
60 for collecting water to be treated. Optionally, the system may also include
a
black water collection tank 70.
The water treatment system 10 includes a treatment conduit 22
comprising withdrawal conduit 24 and a return conduit 26, a circulating pump
28, and a treatment mixer 42. The system 10 further comprises a supply
conduit 44 and a vent conduit 46. The system 10 also includes a discharge
conduit 32, and an air inlet 41.
The valve 30 includes a solenoid for controlling the position of the valve
30.
CA 02385953 2002-05-10
-5-
The collection tank 60 includes an inlet 62, a transfer pump 64 and a
transfer conduit 66 which advantageously includes a check valve 68.
The embodiment illustrated in Figure 1 is particularly adapted for use in
vehicles having relatively reduced space for collection of grey water and
advantageously black water. Such vehicles may include recreation vehicles,
water vessels and the like. It should be understood, however, that while the
invention is discussed in association with its application to a marine vessel,
the system is equally applicable to use in land based mobile vehicles such as
recreational vehicles and the like and also to fixed installations such as in
buildings not having connection access to sewage treatment systems such as
rural properties, cottages and the like.
Water to be treated is collected by suitable piping from all sinks,
showers, washing facilities and the like and directed to the water inlet 62.
Water to be treated continues to enter the collection tank 60. The transfer
pump 64 may be located in the bottom of the water collection tank 60 and
may be operated by means of a float switch or the like. Upon operation of the
transfer pump 64, water collected in the collection tank 60 is transferred via
the transfer conduit 66 through the check valve 68 to the treatment tank 20.
The transfer pump 64 will operate until such time as a determined quantity of
water is contained within the treatment tank 20. The treatment tank 20
includes a high level sensor 82 which may be a float which is connected to the
controller 80 by input line 84. The volume of the treatment tank 20 as
determined by high level sensor 82 defines a selected volume Q1 of water to
be treated.
When the high level sensor 82 senses that the volume Q, of the water
is in the treatment tank 20, the controller 80 shuts off the transfer pump 64
via
line 86 to ensure that no additional water to be treated is added to the
treatment tank 20. As a further option, the transfer conduit 66 may include a
solenoid controlled valve 69 controlled by controller 80 through line 88 to
ensure no gravity flow from collection tank 60 to treatment tank 20.
CA 02385953 2002-05-10
-6-
Once the treatment tank 20 has been filled with quantity Q1, the
controller will cycle the circulating pump 28 which is connected to the
controller by line 90. Upon operation of the circulating pump 28, liquid will
be
circulated through the treatment conduit 22. Liquid will be withdrawn through
withdrawal conduit 24 to the pump 28 by valve 30 and through return conduit
26 to the tank 20. The valve 30 is positioned at all times during treatment to
direct flow from the withdrawal conduit 24 into the return conduit 26 and
prevent flow through the discharge conduit 32 until opened by controller 80.
The ozone generator 40 is a commercially available ozone generator.
A particularly suitable equipment for a marine application is the ozone
generator sold by A.H. Simpson Industries Limited of Ontario, Canada, under
the model designation SW400. The ozone generator 40 draws in ambient air
through the inlet 41. To enhance efficiency of the ozone generator, the inlet
41 advantageously directs the ambient air through a dryer 43. The air is then
fed to the ozone generator 40 so that ozone is generated. The ozone
generated then passes along the supply conduit 44 to the inlet point of a
treatment mixer 42 located in the return conduit 26. Preferably the treatment
mixer is a venturi injector. A suitable venturi injector is the equipment sold
by
Mazzei Injector Corporation of California, U.S.A., under the model designation
384. The controller 80 turns on the ozone generator 40, which is connected by
line 92, when the circulating pump 28 is cycled.
Under the effect of the circulating pump 28, liquid to be treated is
continuously withdrawn from the treatment tank 20, circulated through the
withdrawal conduit 24 where it passes by the valve 30 and into the return
conduit 26. The passage of the liquid by the treatment mixer 42 draws ozone
into the liquid to be treated thereby ensuring delivery of ozone to the fluid
circulating in the treatment conduit and ensuring intimate mixing of ozone
with
the liquid travelling along the treatment conduit.
The treatment of water in accordance with this invention is a batch
system. The volume of water to be treated is determined by the volume of the
treatment tank 20. The designated volume of water to be treated, Q, is thus
CA 02385953 2002-05-10
-7-
circulated by the circulating pump 28 continuously through the treatment
mixer 42. The circulating pump 28 and the ozone generator 40 operate for a
predetermined period of time T, to ensure that a suitable supply of ozone is
injected into the liquid to be treated and to provide suitable contact between
the ozone and all of the liquid to be treated.
After a designated period of time, T, of operation of the circulating
pump 28, the controller 80 moves valve 30 to the discharge connect position
by means of control line 94. At this time, the circulating pump 28 then
withdraws liquid from the treatment tank 20 and discharges that liquid through
the discharge conduit 32. The circulating pump 28 continues to run until the
treatment tank 20 is emptied. Emptying of the treatment tank 20 is sensed by
a low level sensor 96. A signal is passed through line 98 to controller 80.
The
controller then stops the pump 28 and the generator 40 and resets all
controlled items ready to handle another batch.
Since this is a batch process, the amount of liquid Q, to be treated is
known. The treatment time T, can also be set by the controller to ensure
treatment for any desired length of time. The amount of ozone generated by
the ozone generator 40 in time T, will also be known. As during the treatment,
ozone is admixed continuously into the liquid being treated by the mixer 42,
sufficient contact time can be ensured to ensure treatment of the quantity Q,
of water to any desired level. The volume of the treatment tank 20 can be
configured to meet whatever constraints drive the overall size of the
equipment. Where the equipment is to be installed on a marine vessel, space
may be at a premium and the batches treated may be relatively small batches
in the order of 3 gallons. With a small volume of Q1, the treatment time T,
may
be relatively short, in the order of 3 minutes. Where space is not quite such
a
premium, then the treatment tank may be larger; with a larger treatment
volume Q1, longer circulation times T, can be programmed into the controller
to ensure satisfactory contact of the batch with the ozone to provide suitable
treatment prior to discharge. One of the advantages of providing the
collection
tank 60 is the provision of additional storage of grey water prior to
treatment .
CA 02385953 2010-03-17
-8-
Thus, if a shower is being used, the grey water from the drain may be
collected at
any convenient flow rate which is not subject to the batch treatment
limitation, Q, and
T1. The size of the grey water collection tank will be determined by desired
interim
storage capacity and the treatment parameters of time and quantity. The
process can
be repeated continuously to treat a total amount of water which is larger than
the
batch size Q. Thus quantities of size 2Q and larger can be treated by
repeating the
method on a new batch as many times as required.
The process may be carried out on board a marine vessel floating in ambient
water and the treated water may then be discharged into the ambient water.
In circumstances such as marine vessels and the like there will still be
required, holding tanks for black water. Black water emanating from the
vessel's
toilet will need to be collected in a black water collection tank 70. As the
primary
constituent of such black water will be human sewage, this will normally be
stored in
the tank and subsequently pumped out in available pump out stations. However,
in
order to extend the capacity of the black water holding tank 70, the black
water
holding tank may be arranged so that an overflow conduit 72 may be arranged to
permit liquid above a certain level in the black water holding tank 70 to flow
over by
gravity into the grey water collection tank 60. Liquids at the top of the
black water
collection tank 70 may be, in essence, not substantially different than the
content of
the grey water input and thus may be suitable for treatment in the batch
system
discussed above. Sediment or other non liquid constituents of the black water
holding tank 70 would, however, be retained in the lower reaches of the black
water
holding tank where they will remain until pumped out at a sanitary pump out
station.
By providing an over flow of the black water holding tank 70 for the liquids
at the
upper reaches of the black water holding tank, the effective capacity of the
vessel
between required pump outs may be extended by treating the upper surface
liquids
in the grey water treatment system.
Advantageously the treatment system 10 also comprises an ozone vent
conduit 46. The vent conduit 46 communicates from the top of the treatment
tank 20,
ultimately to the discharge conduit 32. As ozone is continuously introduced
into the
batch during the operation of the circulating
CA 02385953 2002-05-10
-9-
pump 28, gas pressure may build up in the treatment tank 20. Any ozone
building up in the treatment tank 20 is then vented to the discharge conduit
32
ensuring that a continuous fresh supply of ozone from the generator 40 will be
introduced into liquid being treated through the treatment mixer 42.
Advantageously, the ozone conduit vent 46 may be directed to the collection
tank 60. Thus, any ozone from conduit line 46 will achieve slight pretreatment
and deodorization in the collection tank 60. The collection tank 60 is vented,
in
turn, through conduit 46A to the discharge conduit 32. Check valves 47A and
47B ensure no back flow in vent conduit 46 and 46A respectively. Also, as
shown diagrammatically, the vent conduit 46A contains a vertically upwardly
directed run 48 to prevent inadvertent draining of collection tank 60 directly
to
discharge conduit 32 which might occur while a vessel is moving through
wave action or other motion.
Figure 2 illustrates a modified version of the treatment system shown in
Figure 1. The treatment system in Figure 2 is essentially similar to the
treatment system shown in Figure 1 with the addition of a potable water
treatment system utilizing the same ozone generator. Similar parts of the
system 110 shown in Figure 2 corresponding to those in Figure 1 have been
given like numbers with the prescript 1. Thus, ozone generator 140 in Figure 2
corresponds to ozone generator 40 in Figure 1.
Accordingly, the water treatment system 110 as shown in Figure 2
comprises a collection tank 160, treatment tank 120 and ozone generator 140.
The circulating pump 128 circulates liquid to be treated through the
withdrawal
conduit 124 and through return conduit 126. The return conduit 126 includes a
treatment mixer 142. After treatment for the set time the valve 130 in the
treatment conduit 122 is opened by controller 180 so that the circulating pump
128 discharges through the discharge conduit 132. Advantageously a black
water collection tank 170 is fluidly connected to the collection tank 160 by
an
overflow conduit 172. The transfer pump 164 transfers liquid from the
collection tank 160 through the transfer conduit 166 by check valve 168, into
the treatment tank 120.
CA 02385953 2002-05-10
-10-
The system 110 includes a potable water treatment system illustrated
generally at 175. In the system 110 illustrated in Figure 2, the supply
conduit
144 comprises a second conduit 144A for delivery of ozone from the ozone
generator to the potable water system 175.
The potable water treatment system comprises a raw water inlet
system 177, check valve 179, a filter 181, a supply pump 183, a supply mixer
185, a retention and air release tank 187 and a carbon filter 189. The supply
mixer 185 may be similar to treatment mixer 142 and treatment mixer 42. The
potable water treatment system 175 comprises a potable water outlet 191
which may be connected to taps, tanks or other desired sources of drinking
water within the facility in which the system 110 is installed.
The potable water purification system 175 commences to operate upon
operation of the supply pump 183. The supply pump 183 may be cycled by
demand such as with a manually operated switch such as a foot switch or the
like. When the supply pump 183 operates the controller receives a signal
through line 193 and the ozone generator 140 is also turned on to supply
ozone. Raw water from ambient such as a lake, river, or stream, in the case of
a boat, or a well or other suitable surface water at a cottage or rural
dwelling,
is drawn through the raw water inlet 177. The check valve 179 prevents any
back flow. The raw water is first passed through a filter 181 to remove any
gross particles in the water prior to entry into the supply pump. The supply
pump 183 then forces the water to be treated through the supply mixer 185.
The supply mixer draws the ozone from the generator 140 and ensures
mixing and contact with the raw water. The tank 187 provides a facility for
releasing any gases or ozone contained in the water for collection in the tank
187. A final "polishing" of the water is achieved by passing the water through
the carbon filter 189. In addition, the carbon filter 189 converts any ozone
molecules in the raw water to oxygen molecules. After passage through the
filter 189 the water is delivered to the source of drinking water.
The system 110 provides a very compact system for use in vehicles
where storage capacity is limited. As all incoming raw water is treated, the
CA 02385953 2002-05-10
-11-
need to maintain large fresh water storage tanks on a vessel can be
substantially reduced, if not totally eliminated. The amount of holding tank
capacity for black water may be reduced and the opportunity for treatment of
all grey water before overboard discharge will eliminate the need for
substantial grey water holding capacity.
As set out above, the size of the batch of material to be treated, Qi,
can be determined by the designer of such a system based on available
space requirements. The treatment time T, is advantageously selected to
ensure appropriate treatment of the waste water to meet applicable discharge
regulations. The treatment need of grey water is often specified in terms of
biological oxygen demand (BOD) and chemical oxygen demand (COD). Grey
water will be wide ranging from waste water which has a very low BOD and
low COD to waste water having a much higher BOD and a much higher COD.
There are two additional factors which are advantageously considered when
determining the treatment time Ti. These include the amount of ozone that is
available for mixing with the water being circulated by the circulating pump
28
and also the success in dissolving the available ozone in the water. The
contacting of the available ozone with the water occurs initially in the
treatment mixer 42, but of course continues in the turbulence which occurs as
the water is circulated through the treatment conduit 22, the pump 28 and the
treatment tank 20. We have carried out tests for these features to determine
preferred operating conditions of the system.
A first group of tests were carried out using dechloronized, deionized
and filtered laboratory water as the water to be treated. This low demand test
water has essentially no BOD nor COD. This low demand test water was then
used in tests to determine the effectiveness of ozone injection and dissolving
of the ozone in the water. The effectiveness was determined by measuring
the residual ozone in the low demand water using a spectrometer. For these
tests, a ozone generator available from A.H. Simpson as outlined above was
used in the test system together with different sizes and numbers of injectors
from Mazzei Injector Corp.
CA 02385953 2002-05-10
-12-
Surprisingly, the first batch of tests showed an unsatisfactory residual
ozone created in the low demand water. Observed ozone levels generally
were less than 0.5 mg/litre of low demand water.
Various steps were taken to attempt to increase the residual ozone
amount. Ambient air typically contains about 20% oxygen with most of the
remainder being nitrogen. Commercially available oxygen has much higher
concentrations of oxygen depending on intended use. These include divers
oxygen or medical oxygen intended for administration to human beings and
commercial oxygen not intended to be administered to a human. These all
may have oxygen contents of from about 40% up to almost 100%. As one
test, the air inlet 41 was equipped with a supply of commercial oxygen. Using
commercial oxygen produced increased residual ozone in the water
circulating in the treatment conduit 22. Also, as might be expected,
increasing
the processing time T also tended to increase the residual ozone in the water.
As an additional part of this testing program, a high demand (high BOD
and COD) test fluid was created in the laboratory. Because of the high
demand, it was felt that such tests would be a useful indicator to determine
whether the required amount of ozone necessary to treat grey water or
contaminated water was in fact available and dissolved in the water. The tests
were carried out using commercial oxygen supplied to the inlet 41. After
running the system for times slightly less and slightly greater than 2
minutes, it
was determined that the residual ozone in the high demand water being
treated was either zero or only slightly above zero. This lack of residual
ozone
appears to indicate that all available ozone was consumed by the BOD and
COD demand of the water and from this it may be inferred that insufficient
treatment may have occurred.
In order to overcome the apparent limitations as set out in these first
experiments, various techniques were tested. As stated above, providing a
commercial oxygen supply rather than using ambient air, initially provides
greater oxygen to the generator, thus resulting in more conversion to ozone
and a greater quantity of ozone is available in supply conduit 44.
CA 02385953 2002-05-10
-13-
Another aspect of solution of these observations was to obtain better
mixing of the available ozone. While a single ozone injector is described and
illustrated in Figure 1 and labelled treatment mixer 42, use of a plurality of
injectors assists in both the flow of ozone into the treatment liquid and
additionally mixing of the available ozone into the water to be treated. Thus,
tests were carried out using a plurality of injectors operating in parallel to
see
if this would show increased levels of residual ozone in low demand water.
Finally, consideration was given to using two circulating pumps in place of
the
single circulating pump 28 illustrated in Figure 1, to provide enhanced
circulation. Using pumps operating in parallel, a higher volume of flow of
water
through the treatment conduit 22 would be achieved. This, in turn, would
produce higher vacuum in the treatment mixer or mixers, thus drawing more
ozone into the system as well as assisting in mixing the ozone generated with
the water being treated.
In subsequent testing, another avenue was explored in an effort to
ensure suitable treatment. This included the use of larger ozone generators.
Firstly, tests were done using a generator produced by the A.H. Simpson
company which was rated as being capable of generating 400 mg of ozone
per hour. A still larger A.H. Simpson generator capable of producing 800 mg
of ozone per hour was then used. This step helped to increase the residual
oxygen in the low demand water, but at increased cost for the larger ozone
generator.
Tests which had been conducted were conducted using atmospheric
air available in the laboratory where the tests were being carried out, or a
supply of commercial oxygen available in the laboratory was used for input to
inlet 41. As beneficially increased results were occurring using commercial
oxygen as the source of gas entering inlet 41, avenues were then explored to
determine whether there was sufficient oxygen available in the gas being
drawn into the inlet 41. As an experiment on this point, additional ducting
was
added to the inlet 41 so as to draw in outside air rather than indoor air
available in the laboratory. This also gave increased residual ozone in the
low
CA 02385953 2002-05-10
-14-
demand water being tested. The outside air being drawn in had a higher
relative humidity. This then showed that use of a dryer such as dryer 43 in
inlet 41 gave much better production of ozone from the generator. Thus, in
preferred embodiments, particularly when moisture laden air is drawn in to
inlet 41, a dryer is advantagously used.
As an additional step in enhancing the effectiveness of dissolution of
the ozone generated, into the water being circulated, a surfactant was added
to the low demand water. The use of a surfactant, when other test conditions
remained the same, increased the residual ozone in the water being
circulated. This indicates that the surfactant aids in the uptake of the ozone
so
that there is in fact a higher residual ozone content of the mixed water,
thereby leading to enhanced treatment. The surfactant added more closely
mimics grey water which will naturally contain surfactants in the form of
detergents or other soaps, in most cases.
A test was then carried out on a laboratory created simulated highly
contaminated water. The system as shown in Figure 1, was operated using a
Simpson ozone generator rated as being capable of producing 800 mg/hour
of ozone. Three Number 3, Mazzei injectors operating in parallel were used.
The Simpson ozone generator was supplied with pure oxygen available in the
laboratory. The batch size was 10.9 litres or 2.40 imperial gallons. The
system
was operated for a processing time of just over 50 seconds with low demand
water. First, the residual ozone in low demand water was measured at slightly
over 1.5 mg/litre. A test was then run on this sytem with a simulated highly
contaminated water. The water treated was generated in the laboratory to
simulate water having a very high BOD and a very high COD typical of the
highest levels of demand normally experienced when dealing with grey water
and to make the test more severe, the test sample additionally contained a
concentrated sewage from a sewage collection facility.
This highly contaminated water was then used to determine the
percentage reduction which might be achieved in respect of the Total
Coliform, Fecal Coliform and E-coli using the system described above. The
CA 02385953 2002-05-10
-15-
amount of Total Coliform, Fecal Coliform and E-coli was analyzed before
treatment and after treatment and the figures compared. Although severe, it is
considered that this is an apt test to demonstrate the effectiveness of the
system. The ozone introduced into the highly contaminated water will first be
used up in satisfying the BOD and the COD. Any ozone remaining after
satisfying these demands is then available to kill any bacteria, viruses,
parasites and spors which may be present in the water to be treated. By
determining the reduction in Total Coliform, Fecal Coliform and E-coli, a
useful measure of the effectiveness of the system is obtained.
The system was operated for 25 seconds in a first test, 53 seconds in a
second test and 95 seconds in the third test on this highly contaminated
water. When run for 25 seconds, the analysis of the treated fluid showed that
E-coli had been reduced by 18%, Total Coliform did not show any significant
reduction and Fecal Coliform had been reduced by 10%. This result shows
insufficient treatment of the water. When the system was run for 53 seconds,
the treated water showed that E-coli had been reduced 35%, Total Coliform
count had been reduced by 37% and Fecal Coliforms had been reduced by
67%. This shows improved results, but this level is still likely to be
insufficient
to meet most discharge requirements.
When the system was operated for 95 seconds, analysis of the treated
water showed that E-coli had been reduced by 99.40%, Total Coliform had
been reduced by 99.67% and Fecal Coliform had been reduced by 94.60%.
This is an excellent result.
In another test the system was operated first using atmospheric air as
an input to the ozone generator and second using commercial oxygen as an
input to the ozone generator both for 100 seconds. When the system was
operated for 100 seconds using atmospheric air as the input to the ozone
generator, analysis of the treated water showed that the E-coli had been
reduced by 99.962% and the total Coliform had been reduced by 99.880%.
When the system was operated for 100 seconds using commercial oxygen as
the input to the ozone generator, analysis of the treated water showed that
the
CA 02385953 2002-05-10
-16-
E-coli had been reduced by 99.997% and the total Coliform had been reduced
by 99.992%. This is a significant result.
The results of these tests do show, as indicated above, that the time of
treatment Ti is a significant factor in producing a satisfactory treatment
level.
The test using the system operating as explained above for a time of 95
seconds shows excellent treatment of the highly contaminated water, a result
which would permit overboard discharge from a marine vessel in accordance
with most discharge regulations. Such a system is thus able to treat a batch
of
approximately 10.9 litres of highly contaminated water in just over one and a
half minutes.
As the system described above in connection with these tests has
been demonstrated to operate successfully, further tests were then carried out
to optimize the system components. Tests were performed utilizing a series of
larger generators from the A.H. Simpson company. While these tests indicate
slightly increased residual ozone in low demand water, the increase in
available ozone did not appear to offset the increased cost of providing a
larger generator. Surprisingly, during these tests, it was ascertained that a
factor in the amount of ozone produced arises from the fact that the ozone
system as explained above was not pressurized. Ozone is supplied in the
treatment conduit as outlined in Figure 1 by reason of the negative pressure
developed by the treatment mixer 42. The treatment mixer 42, being of the
venturi type, produces a suction pressure which draws the ozone into the
treatment mixer. An advantageous modification of the structure illustrated in
Figure 1 is illustrated in Figure 3. The inlet 41 for the ozone generator 40
includes a dryer 43 and an air pump 45. The air pump 45 thus pressurizes the
feed to the ozone generator 40. Using pressurized air, satisfactory residual
ozone was produced in the fluid to be treated when determined by using a
sample fluid having little or no BOD and COD. Pumping air into the ozone
generator gives successful results using fresh ambient air so that commercial
oxygen which otherwise would increase cost of operation is not required.
CA 02385953 2002-05-10
-17-
Another surprising aspect that developed during such testing, is the
role played by the arrangement of the batch treatment tank. Figures 4A and
4B show diagrammatically, two different arrangements of the batch treatment
tank. In Figure 4A, the return conduit 26 enters the treatment tank 20 at the
upper regions of the tank substantially adjacent to the high level sensor 82.
In
Figure 4B, the return conduit 26 enters the treatment tank 20 substantially
below the level of the fluid in the tank adjacent to the low level sensor 96.
With
the arrangement of the return conduit 26 adjacent the upper region of the
treatment tank as shown in Figure 4A, it was noted that additional flow of gas
was achieved in supply conduit 44. With the return conduit 26 located
adjacent the lower region of the treatment tank as shown in Figure 4B, there
was less flow in the supply conduit 44. However, the flow of greater amounts
of ozone in supply conduit 44 with the configuration of Figure 4A did not lead
to increased residual ozone in the water to be treated. In fact, the greatest
residual ozone level was achieved with the arrangement shown in Figure 4B.
Operating the device as illustrated in Figure 4A using atmospheric air rather
than pressurized air to the inlet 41 showed an increased flow in supply
conduit
44 of 4.75 cubic feet per hour, but a residual ozone in the low demand water
of only .23 mg/litre after 96 seconds cycle time. Using the same equipment,
but with a bottom feed to the treatment tank 20 as illustrated in Figure 4B,
the
flow rate in supply conduit 44 was observed to have fallen to 3 cubic feet per
hour. However, after the same processing time, the residual ozone in the low
demand water had increased to .39 mg/litre. These figures appear to indicate
that returning the water from the treatment mixer 42 to the bottom of the
batch
treatment tank 20 further assists in dissolving the ozone into the water where
it is available for treating the water.
Based on all of the foregoing tests and experiments, various
parameters and preferred operating conditions have been developed.
Preferably, as this is a batch system, the selected time period should be less
than 5 minutes. By processing each batch within a 5 minute time frame, the
equipment can be kept relatively compact and yet will be large enough to
handle relatively low flow rates as are typical in most applications. One of
the
CA 02385953 2002-05-10
-18-
principal advantages of the invention is the ability to ensure treatment to a
particular level. In part, this arises because no additional water to be
treated is
permitted to enter the treatment tank once the treatment process is initiated.
Thus, once the quantity Q of water is fixed by limiting any further inflow to
the
tank, the treatment parameters and conditions can be controlled by the
equipment and the operating controller. It has been determined, that the
biologicial oxygen demand plus the chemical oxygen demand of even the
most severely contaminated water is in the order of approximately 1.00 mg of
ozone per liter. With this amount of ozone injected into the water, the BOD
and COD of the water will be fully satisfied. Thus, if a highly polluted test
liquid
is run through the system, and if sufficient ozone is supplied to the fluid so
that a total of 1.00 mg of ozone per liter is supplied to the fluid, then
subsequent testing may fail to detect any residual oxygen showing that all
ozone supplied has been used up to meet the COD and BOD demand of the
water. If this occurs, this will result in unsatisfactory treatment for
bacteria,
viruses, parasites and spores in such highly contaminated fluid. It has also
been established that the density of ozone needed to reduce bacteria,
viruses, parasites and spores by five logarithm in water to be treated is up
to
0.25 mg of ozone per liter. Combining these two requirements, it can be
shown that providing 1.25 mg of ozone per liter of fluid to be treated, will
be
sufficient to treat even very highly contaminated fluids to satisfy the BOD
and
the COD of the contaminated fluid, and to give a five logarithm reduction in
bacteria, viruses, parasites and spores which may be present in that highly
polluted water. Thus, a system which supplies at least that amount of ozone
per liter of water will in almost all cases completely satisfy the BOD and COD
of the water as well as give the desirable reduction in bacteria, viruses,
parasites and spores.
This provides another parameter for sizing and controlling the
equipment. Another aspect of the preferred embodiment of the process is to
ensure appropriate mixing of the ozone provided with the fluid to be treated
With the system as shown in the figures of this patent, a circulation pump is
used to withdraw the water to be treated from the treatment tank and circulate
CA 02385953 2010-03-17
-19-
the water through the treatment conduit and through the ozone injector. In
order to ensure good mixing of the ozone with the water to be treated, we
have determined that it is desirable that the pump provided be capable of
pumping at a rate of at least 2Q per minute. This, in turn, means that if the
selected time T is greater than one minute, then all of the fluid on average
would be circulated through the injector twice. More preferably, it has been
noted that good mixing occurs when a pump pumping at a rate of at least 2Q
liters per minute operates for a long enough period of time T such that at
least
3Q of water is passed through the treatment conduit and through the ozone
injector. This effectively means that on average, all of the fluid to be
treated
passes through the ozone injector three times. This three-times passage
helps to ensure proper mixing of the ozone with the water and effectively
provides a slightly longer period of time within which to supply the ozone as
compared to attempting to supply all of the necessary ozone in a single pass.
In accordance with a preferred embodiment of the process, the process
is carried out such that the time T in hours is equal to 13 Q over 0 where I
is
equal to the amount of ozone injected per liter of fluid as fluid passes
through
the ozone injector, Q is the batch size of water to be treated in liters and 0
is
the amount of ozone generated in milligrams per hours.
Based on the above testing, a commercially effective arrangement
involves the use of an air pump feeding a moderate sized ozone generator
such as the Simpson generator rated at 800 mg/hr production, with the air
pump moving a supply of fresh air drawn in through a dryer. The use of larger
ozone generators does not seem to be cost justified. One MazzeiTM No. 8
injector also appeared to be sufficient although a No. 6 injector may also be
sufficient. Use of multiple parallel venturi injectors did not produce results
sufficiently enhanced to offset the expense of the multiple injectors. Best
results were achieved using a bottom feed to the treatment tank 20.
From reviewing the above examples and description, it will be
appreciated that a relatively compact system can be created for successful
treatment of highly contamined water having very high BOD and COD and
CA 02385953 2002-05-10
-20-
various pollutants to the point where the treated water is substantially
enhanced before being discharged. The effectiveness of the system in
treating contaminated water also shows that the system may be used in a
combined system, for enhancing the quality of drinking water produced from
raw water which may be available from a lake or on board the vessel or
facility
where the system is installed.
Although municipal regulations may not yet permit the discharge of
black water after treatment in such system, the above tests with highly
contaminated fluids show that even water having very high BOD and very
high COD and other pollutants can be treated in the system in accordance
with this invention. Such a system may be acceptable for treatment of the
non-solids portion of black water or at least a portion of the contents of a
black
water holding tank.
While the system has been described in connection with preferred
embodiments of the system, various changes and modifications to the system
may be made. The full scope of the invention is to be determined by reference
to the following claims.
