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Description  |
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BACKGROUND OF THE INVENTION
In the field of water pollution, the potential quantity or amount of
pollution that a substance may cause is commonly stated in terms of the
effect it would have upon the dissolved oxygen in a body of water or
aqueous stream. The more dissolved oxygen that would react with the matter
to completely oxidize it, the higher its chemical oxygen demand (COD). The
higher the COD, the more such matter is regarded as a pollutant because as
more dissolved oxygen is consumed in oxidation reactions with oxygen
demanding matter, the less there is remaining to support aquatic plant and
fish life. Hence, acceptable pollution levels are stated in terms of the
COD of the body of water or stream being monitored and the concentrations
of bacteria, virus, and other undesirable germs and micro-organisms.
Conventional pollution control technology at present is separated into
various categories or stages of treatment known as primary, secondary and
tertiary. Primary treatment is initially by means of a relatively
inexpensive process which should effectively oxidize and thereby eliminate
a relatively large percentage of such compounds. Compounds which are
refractory and remain relatively uneffected by the primary treatment are
then oxidized by secondary and tertiary treatments which are more
expensive per unit of unoxidized compound than the primary treatment, but
effectively oxidize the refractory compounds. Thus, a savings is effected
without sacrificing overall treatment efficiency by first using a
relatively low cost per unit of COD method on the raw, untreated waste
steam, and then oxidizing the remaining, refractory compounds with a
relatively higher cost but more efficacious method or methods.
One conventional primary treatment well known in the art is comprised of
feeding the waste stream into aerated setting ponds where bacteria which
feed on the waste products will metabalize the compounds, thereby
eliminating much of their COD.
There are several considerations, however, which indicate that this
treatment method is less than perfect. The bacteria which feed on and
break up the oxygen demanding compounds multiply rapidly but eventually
die and then they require dissolved oxygen to oxidize their remains, thus
replacing a portion of the oxygen demand that has been used to eliminate
them. In order to overcome this problem, as well as safeguard against any
adverse health effects a significant amount of such bacteria might cause,
it is common practice to kill the bacteria as well as any other
undesirable micro-organisms prior to the discharge of the treated aqueous
waste by adding chlorine. Though the chlorine will effectively sanitize
the discharged aqueous waste, it will also form compounds with various
hydrocarbon compounds found in the treated waste stream as well as in the
body of water or stream into which the chlorine-treated waste is
discharged. Recent laboratory experiments strongly suggest that a wide
variety of such chlorinated compounds may cause cancer in humans when
taken internally. Furthermore, the foregoing known process is unsuitable
for use aboard a naval vessel because space and treatment time
requirements are incompatible with the shipboard constraints with respect
to these variables.
The wet oxidation process is another primary treatment known in the art,
but has an advantage over the previously discussed bacteriological process
in that, though it may be used on dry land, it is also acceptable for use
aboard a naval vessel. Essentially the process oxidizes the waste
compounds by forcing compressed air through heated aqueous waste that is
contained in a pressurized vessel, thus facilitating an oxidation reaction
between the waste compounds and the oxygen in said compressed air.
However, it has been determined that acetic acid (or acetate), an organic
compound, is one of the last residual organic compounds to be oxidized
whenever the aqueous waste stream containing human excrement is oxidized.
Thus, this primary treatment process as was the case with the one
previously discussed herein, is unable to significantly reduce the COD
caused by acetic acid when operated at its respective nominal efficiency
modes. It is known that the efficiency of the wet oxidation process may be
increased by increasing its operating temperature, i.e. the temperature to
which the pressurized aqueous waste is heated and maintained, and that
operation in such a mode will enable the oxidation of acetic acid to
occur. However, the concomitant increase in operating pressure would more
than likely require the structural modification of existing facilities,
and the construction of a facility possessing the capability to operate at
the high efficiency mode would be more expensive than one built to
withstand only nominal efficiency operating pressures. In addition, the
high efficiency mode is unacceptable for use aboard a naval vessel due to
space, weight, and power constraints.
Reverse osmosis may be employed as a secondary treatment to eliminate
virtually any refractory organic from an aqueous waste stream. The process
involves forcing the waste stream through a semipermeable membrane, said
membrane being impermeable to any or all of the refractory organic
pollutants. The process will thereby separate the polluting compounds from
the waste stream but, though it provides for their collection, their
ultimate disposal remains a problem, i.e., the pollutants are not oxidized
into non-oxygen demanding compounds such as CO.sub.2 and H.sub.2 O. The
membrane will also require periodic cleansing in order to operate
efficiently. Standby procedures must also be considered to prevent the
discharge of untreated waste in the event that the membrane suffers a
rupture from the application of excessive pressure. Thus, time and power
requirements, as well as potential maintenance problems, may make this
process unattractive for use abroad a naval vessel.
For background purposes, air oxidation or organic compounds is believed to
follow the initiation step:
O.sub.2 + H:CH.sub.2 - R .fwdarw. .sup.. O.sub.2 H + .CH.sub.2 - R
where R represents a carbon based organic molecule or chain. Acetic acid,
##STR1##
is relatively more resistive to this initiation step than other organic
compounds, and, therefore, to further oxidation because the inductive
effect of the --CO.sub.2 H group makes the initial hydrogen atom
abstraction more difficult. In order to accomplish the initiation step,
the relatively strong force between the H proton and its electron and the
C nucleus caused by the inductive effect must be overcome by an oxidizing
agent which has the power to abstract the H atom (H.sup..). It is known to
those experienced in the chemical arts that the hydroxyl radical, noted as
.sup.. OH, is a more reactive species than O.sub.2. It is also known that
.sup.. OH has the requiste chemical reactivity necessary to abstract the H
atom from the carbon atom on acetic acid.
It is known that .sup.. OH may be generated by mixing H.sub.2 O.sub.2 with
Fenton type reagents such as Fe.sup.2.sup.+ or Cu.sup.2.sup.+, for
example:
Fe.sup.2.sup.+ + H.sub.2 O.sub.2 .fwdarw. Fe.sup.3.sup.+ + OH.sup.- +
.sup.. OH
Fe.sup.3.sup.+ + H.sub.2 O.sub.2 .fwdarw. Fe.sup.2.sup.+ + H.sup.+ +
.sup.. O.sub.2 H
Thus, it appears that acetic or virtually any oxygen demanding organic may
be oxidized by adding appropriate proportions of H.sub.2 O.sub.2 and a
Fenton type reagent. However, other reactions in the decomposition
mechanism compete with the organic pollutants for the available active
oxidant in the H.sub.2 O.sub.2, and thereby render a portion of the
theoretical oxidizing potential of the H.sub.2 O.sub.2 unavailable for
oxidizing organic pollutants.
Fe.sup.2.sup.+ + .sup.. OH .fwdarw. Fe.sup.3.sup.+ + OH.sup.-
Ho.sub.2.sup.. .revreaction. o.sub.2.sup.+ + h.sup.+
fe.sup.3.sup.+ + O.sub.2.sup.- .fwdarw. Fe.sup.2.sup.+ + O.sub.2
H.sub.2 o.sub.2 + .oh .fwdarw. ho.sub.2.sup.. + h.sub.2 o
the practical applicability of this last method is significantly limited by
the fact that it will function and effectively remove COD only for pH
between 3 and 5.
In addition, should the ferrous or ferric ion be used as the metallic ion
catalyst, a portion of the metallic ions will eventually form iron oxide,
commonly known as rust. It follows that any body of water into which the
treated waste stream containing the ferrous or ferric ion is discharged
will suffer discoloration from the iron oxide in solution; the surface of
any solid object coming into contact with such water and causing the iron
oxide to come out solution will also suffer discoloration.
SUMMARY OF INVENTION
The treatment method of the present invention effectively oxidizes all
known refractory organic compounds except fluorinated hydrocarbons,
eliminating their COD by reacting with the polluting compound to cause its
ultimate distruction into non-oxygen demanding compounds, i.e., CO.sub.2
and H.sub.2 O. In general, this is done by the use of hydrogen peroxide
and ultraviolet light reacting with each other and acting simultaneously
on the aqueous waste body containing the pollutants.
The present invention may conveniently and efficiently be used as secondary
treatment in conjunction with any known primary treatment without
requiring the modification of the primary treatment's nominal operational
mode or physical facility. Its operating characterists are such that its
use may be compatible with the time, space, and power constraints of a
naval vessel or shore based installation.
Concomitant with eliminating refractory organics, the treatment by the
present process will kill bacteria, virus, germs, and other undesirable
micro-organisms carried by the waste stream without requiring the addition
of the suspected carcinogen chlorine provided the irradiation is of
adequate intensity and duration.
Applicant's method of treatment essentially creates .OH from H.sub.2
O.sub.2 added to the waste stream. The subsequent oxidation of the
refractory organic is accomplished due to the relatively high oxidation
power of the generated .OH as previously explained in the discussion
concerning the prior art metallic-ion method. However, the treatment
method of the invention generates the desired .OH without concomitant
ancillary reactions that render an appreciable portion of the theoretical
oxidation potential of the added H.sub.2 O.sub.2 unavailable for oxidizing
the refractory organics. Among the advantages of the present invention
are: As direct consequences of the relative efficiency in the use of
H.sub.2 O.sub.2, the treatment requires less per gallon of treated aqueous
waste than the metallic-ion method and therefore is lower in cost. The
method functions efficiently over a wider pH range, in contrast to the
restrictive pH 3 to 5 range of the metallic-ion method. The esthetically
offensive discoloration of the water due to the formation of iron oxide
when an iron salt is used in the metallic ion method cannot occur when the
invention is used because, outside of the oxidizing agent H.sub.2 O.sub.2,
no additioned foreign substance is added to the waste stream. The process
requires negligible maintenance and human operational supervision. The
risk of malfunction is nil. Also, the invention is particularly useful
aboard a seagoing vessel where space is limited and as well as an dry
land, where time and space constraints are significant.
An object of the invention is to oxidize any and all organic compounds
typically found in waste stream or other aqueous body including those
organic compounds which have heretofore proven highly resistant to
oxidation by conventional treatment methods.
Another object of the invention is to achieve such oxidation in a manner
which is simple to operate, requires very little human operational
supervision and maintenance, and is extremely effective.
The treatment method of the present invention is compatible with any
primary treatment it is used in conjunction with without requiring
modification of such primary treatment's normal operating mode and
functions to effectively and efficiently oxidize any refractory organics
surviving any such primary treatment.
The invention provides for the ultimate disposal of oxygen demanding
organics by oxidizing them into CO.sub.2 and H.sub.2 O. Concomitant with
the aforementioned oxidation process, the waste stream is sterilized so as
to destroy all bacteria, virus, germs, and other undesirable
micro-organisms without the addition of the suspected carcinogen producing
chlorine.
BRIEF DESCRIPTION OF DRAWINGS
A more detailed description of the invention follows in conjunction with a
drawing wherein:
FIG. 1 schematically illustrates the operation of the present invention;
and
FIG. 2 graphically illustrates the inter-relationship of the operational
variables such as the intensity of the ultraviolet light, the duration of
the irradiation by said light, and the consequent reduction in the COD in
the treated body of water; and
FIG. 3 illustrates the manner in which the method of the present invention
may compatibly be used in conjunction with a known primary treatment.
DETAILED DESCRIPTION
Referring to FIG. 1 there is shown, by way of illustration only and not be
way of limitation, apparatus for achieving the results of the invention. A
container 20 is supplied with the waste stream containing the pollutants
by conduit 22 (under pressure if necessary) located at one end of the
bottom of the container. After measuring the chemical oxygen demand of the
waste stream by any standard method an aqueous solution of H.sub.2 O.sub.2
is supplied under pressure to conduit 24 which joins conduit 22 slightly
downstream. An in-line mixer or agitator 23 throughly mixes the H.sub.2
O.sub.2 into the waste stream and the resultant mixture is passed through
the container in the direction of the arrows to eventual discharge by
means of conduit 26. An ultraviolet (UV) lamp 28 is immersed in the
flowing waste stream. The UV light dissociates the H.sub.2 O.sub.2 into
the desired oxidization agent .OH which subsequently achieves the desired
oxidation of the refractory organic pollutants into non-oxygen demanding
compounds, CO.sub.2 and H.sub.2 O.
It is assumed that except for special situations the waste stream been
partially treated by a conventional primary treatment process before in
appears at location 2 on conduit 22 as the stream advances to the in-line
mixer 23. The COD of the stream is measured at this point, and the
required amount of H.sub.2 O.sub.2 to be added is calculated.
The required amount of H.sub.2 O.sub.2 is then added to the waste stream in
an aqueous solution at location 4 and the stream passed through the
container 20 in the direction of the arrows for discharge into conduit 26.
Between the line mixture and the discharge conduit the mixture in the waste
stream is irradiated by the ultraviolet lamp 28 immersed in the advancing
stream. The ultraviolet irradiation causes the formation of .sup.. OH
radicals from the H.sub.2 O.sub.2, which subsequently oxidize the
refractory organics to form H.sub.2 O and CO.sub.2. The irradiation and
.sup.. OH also kills all of the bacteria, virus, and germs carried by the
waste stream. The oxidized and sanitized waste stream is discharged from
conduit 26 into a natural stream or body of water.
As a result of this treatment by the invention the COD in a waste stream
caused by organic compounds is substantially reduced or eliminated by
oxidation to H.sub.2 O and CO.sub.2 and the bacteria, virus, and germs in
the waste stream are also destroyed without using chlorine.
Many organic compounds are susceptible to oxidization by more economical
primary treatment methods. However, research has indicated that such
methods are unable to oxidize certain compounds such as acetic acid (or
acetate) and phenols at acceptable operating temperatures and pressures.
Thus, it is of significant importance that the treatment by the invention
is able to oxidize virtually any refractory organic compound, including
acetic acid and phenols.
This amount of dissolved molecular oxygen required to oxidize acetic acid
may be calculated according to the equation
2 O.sub.2 + CH.sub.3 CO.sub.2 H .fwdarw. 2 CO.sub.2 + 2 H.sub.2 O
the process requires an amount of H.sub.2 O.sub.2 to oxidize the same
amount of oxygen demanding organic according to the equation
4 H.sub.2 O.sub.2 + CH.sub.3 CO.sub.2 H .fwdarw. 2 CO.sub.2 + 6 H.sub.2 O
thus, the relationship between the required amount of H.sub.2 O.sub.2 and
COD is given by the ratio of required H.sub.2 O.sub.2 to dissolved
O.sub.2, where each oxidize the same amount of oxygen demanding organic:
##EQU1##
Thus, the amount of H.sub.2 O.sub.2 required to effectively eliminate the
COD in the waste stream will vary in proportion to the COD of the stream
as measured immediately upstream of the point at which the H.sub.2 O.sub.2
is to be added.
The H.sub.2 O.sub.2 should be uniformly dispersed throughout the waste
stream to reduce the probability that any .OH radicals subsequently formed
will react with each other and thereby reduce the oxidizing potential of
the added H.sub.2 O.sub.2.
As any thermal energy transmitted by the waste stream to the H.sub.2
O.sub.2 bonds that would facilitate their cleavage is insignificant in
comparison to the energy supplied by the ultraviolet light, the rate and
efficiency of the .OH radical formation and the subsequent oxidation of
the refractory organic molecules will not be appreciably effected by the
stream temperature under normal operating conditions (0.degree. -
50.degree. C). However, at higher temperatures this energy may become a
significant contributing factor. The process of the invention can be
practiced at higher temperatures but the hardware required to maintain
these higher temperatures and accompanying pressures will add to the
overall cost.
The production of .OH radicals from H.sub.2 O.sub.2 will occur upon
irradiation from an ultraviolet light source of a wavelength of or less
than 2600 angstroms. The wavelength below 2600 angstroms may vary over the
widest possible range depending upon the energy of the irradiating source.
The formation of .OH radicals and, hence, the oxidation of the refractory
organics, will vary with light intensity which varies with the average
distance between the ultraviolet light source and the H.sub.2 O.sub.2
molecules in the waste stream, the wavelength of the ultraviolet light,
and the total number of impacting photons. This relationship may be
expressed as, Reduction of
##EQU2##
where N = total number of impacting photons
C = speed of light
h = Planck's constant
.lambda. = wavelength of the ultraviolet light
R = average distance traveled by photon
As N = g (t), where t = time of exposure to the ultraviolet radiation, the
expression for reduction may also be expressed as
##EQU3##
where n = number of photons impacting per unit of time. Light is commonly
expressed in terms of intensity, I, where I =
##EQU4##
per unit of time, the reduction of COD may alternatively be expressed as
##EQU5##
This relationship has been empirically determined through experimentation.
The results are shown plotted in FIG. 2.
The calculations disclosed in the immediate application assume that the
waste stream does not contain metallic ions. As previously explained
herein, H.sub.2 O.sub.2 will dissociate to form .OH in the presence of
such ions and the .OH molecules will proceed to oxidize the refractory
organics. However, as the .OH molecules will also react with the metallic
ion catalysts, this mechanism of oxidizing the refractory organics is less
efficient than the method of the invention and therefore the presence of
certain metal ions in the waste stream will cause the efficiency of the
present treatment process to suffer.
As the rate and total reduction of COD is directly limited by the amount of
.OH present to oxidize the refractory organic molecules, it is recommended
that somewhat more than the stochiometrically calculated amount of H.sub.2
O.sub.2 per gram of COD be added to the waste stream, e.g. [H.sub.2
O.sub.2 ]/[COD] .apprxeq. 2.3 to ensure the presence of an adequate amount
of .OH reactants to achieve the desired reduction in COD. The requisite
number of grams (mass) of H.sub.2 O.sub.2 equals approximately 2.3 times
the concentration of COD in grams per liter (mass per volume) times the
number of liters of waste water to be treated, but no less than 2.1.
Table I
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Data Obtained on H.sub.2 O.sub.2 - Acetic Acid/Acetate Reaction
Initiated by U. V. Light. Temperature 25.degree. C
__________________________________________________________________________
% Removal of
Reaction
Acetic Acid-
%H.sub.2 O.sub.2 re-
Ratio-O.sub.2
Reactants Time Acetate maining CO.sub.2
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Acetic acid +
20 35 45% .87
H.sub.2 O.sub.2
Ammonium acetate +
20 72 37% .14
H.sub.2 O.sub.2
45 >95 4% .12
Ammonium acetate
20 0 -- --
Ammonium acetate +
20 0 -- --
O.sub.2 *
Sodium acetate +
30 93 8% .14
H.sub.2 O.sub.2
Sodium monochloro-
20 84 7% .07**
acetate + H.sub.2 O.sub.2
Sodium trichloro-
45 60 0 2.4
acetate + H.sub.2 O.sub.2
__________________________________________________________________________
*O.sub.2 bubbled in at 1 atm.
**No Cl.sub.2 or chloride containing product found other than
Note: Data is average of at least two experiments. U. V. light was from a
Hg. vapor source. Initial atmosphere, 14cm. Ar.
FIG. 2 and Table II and III shows how the chemical oxygen demand (COD) of
an acetate solution changes with time and UV light intensity I.sub.o.
These solutions were initially 0.54 molar in hydrogen peroxide and 0.125
molar in sodium acetate.
Table II
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I.sub.o = 4 .times. 10 .sup.-.sup.4 einsteins/liter-min, Temp. 25.degree.
C.
Time (min)
Concentration H.sub.2 O.sub.2
Conc Acetic Acid
COD
______________________________________
0 0.54 Molar 0.125 Molar 4.00 g.
20 0.31 0.077 2.46
40 0.16 0.040 1.28
60 0.08 0.020 0.64
______________________________________
Table III
______________________________________
I.sub.o = 2 .times. 10 .sup.-.sup.4 einsteins/liter-min, Temp. 25.degree.
C.
Time (min.)
Conc. H.sub.2 O.sub.2
Conc. Acetic Acid
COD
______________________________________
0 0.54 Molar 0.125 Molar 4.00 g.
20 0.42 0.105 3.30
40 0.31 0.077 2.46
60 0.22 0.056 1.80
80 0.17 0.042 1.35
100 0.12 0.030 0.96
______________________________________
FIG. 3 shows how a flow or batch waste treatment system utilizing
photochemically induced oxidation by hydrogen peroxide according to the
invention may be used as a secondary treatment method.
The specific apparatus of FIG. 1 is merely presented for the purpose of
illustration. In it, the waste water is in a flowing stream and may be
treated while flowing. It should be noted, however, that the invention may
be employed to treat an agitated body of water. Such a treatment would
involve the same treatment steps regarding ascertaining the COD, adding
and throughly mixing in the required amount of H.sub.2 O.sub.2, and
irradiating the mixture with U. V. light. Stated another way, the
fundamental teachings of the invention do not necessarily involve a stream
or flow situation.
The process of the invention is especially useful where the waste body to
be treated contains human excrement. The size of the container for the
waste body depends on the amount of waste to be treated. A small unit as
represented in FIG. 1 may be 6 feet long by 2 inches in diameter. It is
not essential that the UV light source be immersed in the waste body. A
highly light reflecting surface concentrating the UV light over the length
of one or more light sources toward the waste body to be treated will also
be effective.
Obviously, many modifications and variations of the present invention are
possible in light of the above teachings. It is therefore to be understood
that, within the scope of the appended claims, the invention may be
practiced otherwise than as specifically described.
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