AU665391B2 - A method for the purification of water - Google Patents

Description

~k 665391

AUSTRALIA

Patents Act 1990 COMPLETE SPECIFICATION FOR A STANDARD PATENT a a. a *r Name of Applicant: Actual Inventor Zvi Elgat As above a a r+ e a a ar,, aS «d Q t oV i t t t r t Address for Service: Chrysiliou Moore Chrysiliou Solicitors and Attorneys CMC Centre, 143 Sydney Road Fairlight, Sydney, NSW 2094 Invention Title: A Method For Purification of Water The following statement is a full description of this invention, including the best method of performing it known to us: I I- I li-, i; I

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A METHOD FOR THE PURIFICATION OF WATER The present invention relates to a method for the purification of water. More particularly, the present invention relates to a method for the purification of water by the reduction of the amount of bacteria and organic material contained therein, using concentrated solar radiation.

The method of the present invention is applicable to the reclamation and purification of waste water, as well as to improving the quality of water supplied from natural and artificial reservoirs.

'The conventional process for treating sewage water is by oxidation aerial ponds and solids removal ponds, which results in a product (waste water) having a high concentration of organic Smaterials and bacteria which are harmful for human consumption, and which water cannot be recycled without further treatment.

It CC The waste water cannot be used for any human purposes other than irrigation for non-edible crops, such as cotton. For all other purposes, the water is wasted. There are methods for further purification of the water, such as ground filtration and chlorination, but each method has its own technical problems and -2 drawbacks, such as saturation of the filtration ground and the large areas needed for this type of filtration.

In an article by A. Acher and S. Saltzman, entitled "Photochemical Inactivation of Organic Pollutants in Water", Toxic Organic Chemicals in Porous Media, Ecological Studies, Vol. 73, Z. Gerstel et al. (1983), there is described a photochemical procedure for the inactivation of industrial and biological organic pollutants.

As explained in said article, due to the ever-increasing depletion of the natural resources of water, the reuse of treated municipal waste water for crop irrigation, for artificial ground water recharge, or even for potable purposes, has become a real necessity for countries of the arid and semi-arid zones, and the removal of organic pollutants from effluents is a prerequisite Sfor their safe reuse.

In the procedure described therein, sunlight is used as the energy source, oxygen dissolved in water as the oxidizing agent, a dye (sensitizer) as an intermediary for the transfer of the light energy to the oxygen molecule, and the organic matter as S the oxidation target.

As proposed by said article, use of sunlight for waste water treatment has several advantages. First, sunlight is a free energy source; therefore, energy costs with such systems are 4 -3minimal. Secondly, unlike chlorination, toxic organics such as chlorinated hydrocarbons are not formed. Thirdly, the structural facilities and instrumnentation associated with these systemrs are relatively simple to build, maintain and operate; and finally, with sensitizing agents, the contact time necessary for photochemical treatment is relatively short.

The procedure proposed in said article is based on dye-sensitized photooxidation reactions. These reactions, also referred to as "photodynamic action", are responsible for the oxidative processes which take place in surface waters exposed to solar radiation. They consist of the combined action of visible light and molecular oxygen dissolved in water upon organic matter (OM) through the intermediary of an appropriate photosensitizer The S is an organic molecule having a special electronic structure which enables it to absorb, and then to transfer, some of the light-radiated energy. The S is added to the aerated and light-exposed effluents and its absorbed energy is made available to the oxidation of OM. Either one or both of the following mechanisms can operate in aerobic photosensitized oxidations.

1. Primary interaction of the electronically-excited S* is 0 0~ with OM to generate reactive, short-lived intermediates 004*0which subsequently react with 02: 4 4 S hv S* (1) S* OM 02 transient species oxidation products S (2) (transient species free radicals, ion pairs, etc.) 2. The presences of 02 wi±l compete successfully with OM on receiving the excitation energy from The addition of this energy to 02 changes its ground electronic state (triplet state, 3 EgO0) to the first excited singlet state Ag0 2 which has a higher energy by 22.5 kcal mole When more energy is imparted to O0, another electronic state is formed 1 .g0 2 which corresponds to a level of 37.5 kcal mole-' above the 'EgO 2 From the properties of singlet oxygen (exceedingly short lifetimes of 'EgO 2 it seems likely that only 1 A gO 2 is important in solution photooxidations: 0a* 0 0 0 S* %g0 2 S 1 AgO (3) o 04 1 AgO, OM oxidation products (4) In both mechanisms the sensitizer is regenerated and S undergoes hundreds of cycles so that only minute amounts of it are required.

0*00 In view of the diversity of OM present in waste waters, it is very difficult to decide which mechanism operates in the I i 5 present process. The presence of singlet oxygen in natural waters was proven over ten years ago by R.G. Zepp, N.L. Wolfe, B.L. Baughman, and R.C. Hollis (1977), "Singlet Oxygen in Natural Waters", Nature 267: 421, and it is well known that it oxidizes unsaturated organic compounds (UC) to peroxides. The subsequent thermal and photochemical decomposition of these peroxides can further initiate free radical oxidation reactions which will also affect saturated compounds found in waste waters: AgO 2 UC ROOR 2RO- RO- R'H+ ROH (6) 02 ROO-, etc. (7) Beside 1 AgO,, other oxidative cher.'ical species like hydroxyl radical superoxide radical anion (02) and hydrogen S peroxide (H 2 might be generated in the aerated and irradiated effluents. As a result of the above reactions, vital biological components (proteins, lipids, polysaccharides) and industrial organic materials undergo oxidative degradations.

Said article then proceeds to report that the intentional promotion and enhancement of such photooxidation reactions in

S

surface water was used for detoxification of water from herbicide S residues Crosby and M.Y. Li (1969), "Herbicide Photodecomposition", in: P.C. Kearney, D.D. Kaufman (eds.), Degradation of Herbicides, Dekker, New York, pp. 321-363; N.L.

6 Wolfe, et al. (1976) "Chemical and Photochemical Transformation of Selected Pesticides in Aquatic Systems", U.S. Environment Protection Agency, Ecological Research Series PB, 258-848, p.

141; A.J.Acher and E. Dunkelblum (1979) "Identification of Sensitized Photooxidation Products of Bromacil in Water", J.

Agric. Food Chem. 27: 1164-1167; A.J. Acher et al. (1981) "Photosensitized Decomposition of Terbacil in Aqueous Solutions", J. Agric. Food Chem. 29: 707-711; S. Saltzman, et al. (1982) "Removal of Phytotoxicity of Uracil Herbicides in Water by Photodecomposition", Pestic. Sci. 13: 211-215; M. Rejto, et al.

(1983) "Identification of Sensitized Photooxidation Products of S-Triazine Herbicides in Water", J. Agric. Food Chem. 31: 138-142; M. Rejto, et al. (1984) "Photodecomposition of Propachlor", J. Agric. Food Chem. 32: 226-230; P.K. Freeman and K.D. McCarthy (1984) "Photochemistry of Oxime Carbamates, 1.

Phototransformations of Aldicarb", J. Agric. Food Chem. 32: 873-877; P.K. Freeman and E.M.N. Ndip (1984) "Photochemistry of S Oxime Carbamates. 2. Phototransformations of Methomyl", J. Agric.

Food Chem. 32: 877-881; W.M. Draper and D.G. Crosby (1984) "Solar 0: Photooxidation of Pesticides in Dilute Hydrogen Peroxide", J. i Agric. Food Chem. 32: 231-237]; for treatment of organic matter S in sewage affluents Acher and I. Rosenthal (1977) "Dye-Sensitized Photooxidation A New Approach to the Treatment of Organic Matter in Sewage Effluents", J. Water Res. 11: 557-562]; for disinfection Acher and B.I. Juven (1977) S "Destruction of Fecal Coliform in Sewage Water by Dye-Sensitized •00 Photooxidation", J. Appl. Environ. Microbiol. 33: 1019-1023; A.J.

I

7 Acher, et al. (1979) "Disinfection of Effluents by a Photochomical Treatment", Progress report to Israeli Council for R D, Jerusalem (Nov. 1979, in Hebrew); C.D. Gerba, et al.

(1977) "Disinfection of Waste Water by Photodynamic Action", J.

Water Pol. Control Fed. 49: 578-583] and for algal destruction Acher and A. Elgavish (1980) "The Effect of Photochemical Treatment of Water on Algae Growth", J. Water Res. 14: 539-543].

The most frequently used sensitizers for the UV range are acetone, benzophenone, acetophenone, benzonitrile, and for visible light range are mainly methylene blue riboflavin rose bengal (RB) and acridin orange (AO).

All of said prior art procedures involved irradiation with an UV lamp, sunlight or artificial white light; however, despite the fact that dye-sensitized photooxidation of organic pollutants Shas been proposed in the literature for more than a decade, the C a results obtained were not sufficient to encourage commercial S application of these procedures.

In contradistinction to the procedures described in said literature, there has now been surprisingly discovered an S improved method for the purification of water by reduction of the 6wwu amount of bacteria and organic material contained therein, S comprising introducing an inert non-toxic photosensitizer into said water, said photosensitizer being of the type which absorbs visible light and which, in turn, transfers some of the energy from said absorbed visible light to accelerate the oxidation of ELGAT.995\KR\ -8organic material found in said water; and exposing said photosensitizer-containing water to concentrated solar radiation without significantly heating said photosensitizer--containing water, whereby the concentrated radiation in the ultraviolet range of the solar spectrum serves to directly kill bacteria, while the concentrated light radiation in the visible range of the solar spectrum increases the effectiveness of said photosensitizer in promoting the photooxidation of organic material and bacteria contained in said water.

Preferably, said concentrated solar radiation has an energy intensity of at least 20 KW/m 2 As will be shown in the examples hereinafter, and with reference to the appended graph, it has been surprisingly discovered according to the present invention that concentrated solar radiation increased the effectiveness of the photosensitizer in promoting the photooxidation of bacteria contained in water by an order of magnitude of at least whereby non-concentrated solar radiation as taught and suggested by the prior art required 2,000 seconds to eliminate surviving bacteria, while concentrated solar radiation having an energy intensity of 24.5 KW/m 2 required only 100 seconds to achieve the same effect in the same system.

4 0, In various embodiments of the present invention, the solar radiation can be concentrated using mirrors or lenses in various configurations onto an open or closed conduit in which the target i- 9 water is flowing. The water can flow either in open channels onto which the light is focused by a concentrating/focusing mechanism, or in a tube which is transparent both to ultraviolet light and to light in the visible spectrum.

For this purpose, said tube is preferably made of quartz or acrylic material, and will preferably have a diameter of between about 13-17 cm. Especially preferred will be a tube made of quartz, since quartz is a UV-transparent glass-like material which, among its other properties, does not absorb the solar UV light, unlike ordinary glass.

When said conduit is an open channel, it preferably will have a minor axis of about 3-7 cm and a major axis of about 15-25 cm.

The photosensitizer agent can be added to the tube or channel on which the sunlight is concentrated, at the entrance thereto, or it can be embedded in a porous media such as a porous plastic or ceramic, and released into the waste water slowly and at a controlled rate. This method can reduce the total amount of the needed photosensitizer without reducing its concentration in the water, by the increased release efficiency.

Thus the photosensitizer can be added to the water at very low concentrations (0.5-2 ppm), and acts as an intermediary, 0 0s os 0 o Oel *L 0 00 81 0@ 0 0~ D*0 0 which absorbs the energy from the sunlight and transfers it to the dissolved oxygen that is in the water.

By using the concentrated sunlight (20 to 80 times or more), and adding the photosensitizer agent to the water, there is achieved an enhanced effect of purification as a result of two processes which take place at the same time, destruction of bacteria and organic matter by the concentrated ultraviolet energy, and destruction of bacteria and organic matter by the action of the excited oxygen atoms via the photosensitizer agent.

The fact that the photosensitizer is operational and active at visible light and not at the UV range, insures that the two processes do not compete with each other, and instead results in a complimentary effect.

o*o. The photosensitizer agent can be of the family of such known materials, such as methylene blue, riboflavin, rose bengal, etc.

S Methylene blue is especially preferred.

The invention will now be described in connection with certain preferred embodiments in the following illustrative examples and with reference to the following illustrative figures, so that S it may be more fully understood.

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-11- With specific reference now to the figures in detail, it is stressed that the particulars shown are by way of example and for purposes of illustrative discussion of the preferred embodiments of the present invention only and are presented in the cause of providing what is believed to be the most useful and readily understood description of the principles and conceptual aspects of the invention. In this regard, no attempt is made to show structural details of the invention in more detail than is necessary for a fundamental understanding of the invention, the description taken with the drawings making apparent to those skilled in the art how the several forms of the invention may be embodied in practice. Similarly, it will be understood that the following illustrative examples are not intended to limit the :i invention to these particular embodiments.

*0 In the drawings: Fig. 1 is a schematic illustration of a first arrangement for carrying out the method of the present invention; Fig. 2 is a schematic illustration of a second arrangement for carrying out the method of the present invention; S Fig. 3 is a schematic illustration of a third arrangement for o carrying out the method of the present invention; Fig. 4 is a schematic illustration of a fourth arrangement for carrying out the method of the present invention; Fig. 5 is a schematic illustration of a fifth arrangement for carrying out the method of the present invention; and 12 Fig. 6 is a graph showing comparative results of the experiments described in Example 1 hereinafter.

Referring first to Fig. 1, there is seen a plurality of parabolic mirrors 2 arranged in a trough-shaped row which focuses solar radiation onto a line focus running south-north, and which tracks the sun east-west: a one- dimensional tracking system. The trough mirrors are front surface mirrors, to also reflect the UV spectrum of the sunlight. Ordinary glass mirrors absorb most of the solar UV and are therefore replaced by front surface mirrors, which can be made in various ways: coated glass, plastic or other material suitable for specular light reflection.

Said parabolic mirrors 2 reflect solar radiation in a manner known per se to a secondary reflector 4 which in turn reflects the solar radiation onto a quartz tube 6 which is transparent to ultraviolet light and light in the visible range, which has a diameter of about 15 cm and through which the water 8 aartt to be treated flows.

4* In Fig. 2 there is illustrated an arrangement in which a i parabolic Fresnel lens 10 is positioned above a V-shaped channel 12 and concentrates the light onto a line focus along tracking I axis 14 which is along and in the water 16 flowing in said S channel. This is a transparent plastic (acrylic) parabolicshaped lens, which concentrates the light using the Fresnel optics principle. The parabolic trough Fresnel lens is a line concentrator with its longitudinal axis on the south-north, and iII it tracks the sun east-west, using a motorized tracking system !I (not shown).

i In Fig. 3 there is illustrated an alternative arrangement, utilizing a flat Fresnel mirror 18 in conjunction with a secondary concave mirror 20 for light concentration. The light impinges on the flat shaped mirror, and is reflected into the secondary parabolic concave-shaped mirror 20, which faces the :Vo flat mirror. The flat Fresnel mirror faces the sun, and the S secondary mirror faces said flat mirror with its back 22 to the *000.

sun. The light is concentrated via the secondary mirror and is reflected into a U-shaped open channel 24 having a minor axis of about 5 cm and a major axis of about 20 cm. The flat mirror tracks the sun along the east-west axis and is aligned along the south-north axis. i om In Fig. 4 there is illustrated a plurality of parabolic trough mirrors 26, each of which individually tracks the sun at a different angle and reflects the light upon a secondary reflector 28, which in turn concentrates the light upon the channel 30 in which the water 32 flows.

In Fig. 5 there is illustrated a single unit parabolic trough mirror 34 using a single tracking mechanism, and a secondary reflector 36. The light is focused upon an open channel 38 or a transparent tube, as in Fig. i.

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i: 14 Each of these methods concentrates the sunlight, including the UV spectrum, into the tube or channel in which the water runs, with a concentration ratio of 20 to 80 times, or more.

Example 1 Contaminated effluent water was placed in a closed glass Petri-dish and exposed to various light intensities, which correspond to concentrations of from 1 to 30 and to 60 times.

Before and after each experiment was carried out, a count of living bacteria was made, to find the exact effectiveness of the o method as purifier for effluent.

It was thereby established that a minimum energy intensity for effective bacteria destruction was about 20 KW per m. At an energy intensity of 24.5 KW per m 2 it was found that the °o bacteria level was reduced by seven orders of magnitude within a period of 130 seconds, while with no light concentration, the Ssame level was achieved only after 2000 seconds. The results are 000@ shown in the graph of Fig. 6.

The fact that the mirrors were made of glass, and that the Petri-dishes were also made from glass, insured that the effect was not due to any UV light, but only to the visible spectrum.

15 15 It will be evident to those skilled in the art that the invention is not limited to the details of the foregoing illustrated embodiments and examples, and that the present invention may be embodied in other specific forms without departing from the spirit or essential attributes thereof. The present embodiments and examples are therefore to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims rather than by the foreaoing description, and all changes which come within o :oo the meaning and range of equivalency of the claims are therefore intended to be embraced therein.

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Claims (9)

1. A method for the purification of water by reduction of the amount of bacteria and organic material contained therein, comprising: introducing an inert non-toxic photosensitizer into said water, said photosensitizer being of the type which absorbs visible light and which, in turn, transfers some of the energy from said absorbed visible light to accelerate the oxidation of organic material found in the water; and exposing said photosensitizer-containing water to concentrated solar radiation without significantly heating said photosensitizer-containing water, whereby the concentrated E" radiation in the ultraviolet range of the solar spectrum serves S to directly kill bacteria, while the concentrated light Sradiation in the visible range of the solar spectrum increases the effectiveness of said photosensitizer in promoting the photooxidation of organic material and bacteria contained in said water.

2. A method according to claim 1, wherein said concentrated i solar radiation has an energy intensity of at least 20 KW/m 2

3. A method according to claim 1, wherein said photosensitizer is introduced in a concentration of between about 0.5 to 2 ppm. TO Dr j K1 C C r It I C e I I I gC.: ~s -17-

4. A method according to claim 1, wherein said photosensitizer is methylene blue. A method according to claim 1, wherein said concentrated solar radiation is provided by a parabolic trough solar light concentrator.

6. A method according to claim 1, wherein said water to be purified is passed through an open or closed conduit.

7. A method according to claim wherein said conduit is a tube which is transparent to both ultraviolet light and light in the visible range, having a diameter of about 13-17 cm.

8. A method according to claim 6, wherein said conduit is made of quartz.

9. A method according to claim 6, wherein said conduit is an open channel having a minor axis of about 3-7 cm and a major axis of about 15-25 cm. A method for the purification of water substantially as hereinbefore described with reference to any one of Figs. 1, 2, 3, 4, and Dated this second day of February, 1993 ZVI ELGAT By his Patent Attorney KERRY MOORE CHRYSILIOU of Chrysiliou Moore Chrysiliou

18- A METHOD FOR THE PURIFICATION OF WATER ABSTRACT OF THE DISCLOSURE The invention provides a method for the purification of water by reduction of the amount of bacteria and organic material contained therein, comprising: introducing an inert non-toxic photosensitizer into the e a o water, the photosensitizer being of the type which absorbs visible light and which, in turn, transfers some of the energy from the absorbed visible light to accelerate the oxidation of S organic material found in the water; and exposing the photosensitizer-containing water to S concentrated solar radiation, whereby the concentrated radiation in the ultraviolet range of the solar spectrum serves to directly kill bacteria, while the concentrated light radiation in the visible range of the solar spectrum increases the effectiveness of the photosensitizer in promoting the photooxidation of organic S" material and bacteria contained in the water. I