IL107329A - Photochemical process for water purification - Google Patents

Description

IMPROVED PHOTOCHEMICAL PROCESS FOR WATER PURIFICATION IMPROVED PHOTOCHEMICAL PROCESS FOR WATER PURIFICATION Field of the Invention The present invention relates to the use of various agents in a photochemical process for the destruction of microorganisms in water, for both decreasing the exposure time required to achieve the requested purification level and preventing bacterial growth following process completion. In particular - but not exclusively - the invention relates to the combination of one or more of said agents to potable or waste water in the presence of a photosensitizer, wherein the photochemical reaction occurs under solar radiation.

Background of the Invention In recent years, growing attention has centered on the increasing shortage of drinking water throughout the world. Due to rapid population growth, large scale droughts in different parts of the world and contamination of water sources, the water shortage is expected to grow. At the same time, there is an extensive, but almost unexploited, source of water: namely, waste water. At present, this water is usually dumped and wasted. The purification of water from microorganisms in a photochemical process has an obvious advantage while implementing the process over water containing large quantities of organic matter. The risk of producing carcinogenic chloro-organic compounds, which is a drawback of the conventional chlorination process, is avoided. Water originating from either municipal sewage or contaminated drinking water may at present be partly treated prior to its discharge to the environment. The result of such a treatment is the elimination of bacterial presence to a level suitable for the use of the treated water in a limited crop irrigation (such as cotton), or in recharging of aquifers. The conventional treatment is achieved by using a multi-stage chlorination. Further purification cannot be achieved by introducing additional chlorine, as the high chlorine concentration required would result in the formation of, for example, chloro-organic compounds.

Until the mid-1960s, solar radiation was never seriously proposed as an important factor influencing bacteria decay rates. In earlier literature reviews, it appeared that only the ultraviolet component of sunlight was considered destructive. Consequently, the effect of solar radiation was assumed to be negligible, as the UV effect of killing bacteria was found in layers up to only several centimeters and the UV component (wavelength of less than 450 nm) is only 4.3% of the total solar spectrum.

Only in 1965 it was found by Reynolds (Pollution Marines par les Microorganisms et les Produits Petrioliers Sym. de Monaco, 1965, p. 241) and then by Gamson and Saxon (Water Res. I, 279 (1967) that the solar radiation does have an impact upon bacteria.

The photochemical purification process, using solar radiation and catalyzed by suitable photosensitizers, results in a lethal effect on both bacteria and viruses.

The mechanism of light-dependent decay characterizing said process can be illustrated in the following way: - - 107329/2 ηυ + S → S* — > direct damage enzymatic decomposition -l H20 + 02 — » indirect damage or other products The initial step in said mechanism is the absorption of light by the photosensitizer (S) present, and the resulting excitation of said sensitizer (S*). The excited sensitizer may either: a) transfer the energy via electron transfer and thereby return to the ground state (S); b) react with and consequently damage some cell component; or c) combine with O2 to form superoxides (O2 , hydrogen peroxides (H2O2), or organic peroxides (R-HO2); and d) the reactive forms of O2 produced may then react with and damage some cell constituent or e) may be enzymatically decomposed to harmless products.

A large number of compounds, some of which are present in microorganisms, have been suggested as possible sensitizers, among which can be found porphyrins, cytochromes, cytochrome oxidase, chlorophylls (Kang and Spikes Arch. Biochem. Biophys., 172, 565 (1976)), flavins (Clayton, Light and Living Matter, Vol. 2, The Biological Part, McGraw-Hill, N.Y., 1971), eosin dyes, benzopyrene, tryphoplan (McCormick et al., Science, 191, 468 (1976)), methylene blue and other compounds.

A process for the photochemical purification of water includes the use of a photosensitizer absorbing radiation in a specific wavelength range, and subsequently being transformed into an excited state, which is the beginning of the chemical part of said process. The major drawback of such a process is that each of the known photosensitizers may be active in absorbing radiation in a narrow wave band. If the radiation source is solar, only a very small portion of the solar spectrum may be actually utilized for said photochemical process, thus rendering the process inefficient and uneconomical. Another drawback is the limited post process effect of said photosensitizer (as opposed to the chlorination process), for the period prior to the water discharge to the consumers.

Summary of the Invention It is an object of the present invention to improve the process of photochemical purification of water containing microorganisms, by substantially shortening the time required to achieve the required purification.

It is another object of the invention to prevent bacterial growth after completion of the said photochemical process.

Other objects of the invention will become apparent as the description proceeds.

In order to overcome the drawbacks of the prior art, an improved process for the photochemical purification of water has been developed. The process of the invention comprises adding to the water to be treated a biocidally effective amount of a mixture comprizing a photosensitizer and a photochemical synergistic agent, and then exposing the water to radiation which may originate either from an artificial or solar source. In the process of the invention, photochemical synergistic agent is selected from a photosensitizer, a fluorescent agent, a bacteriostatic and/or bactericidal agent (BBA), or a mixture thereof. BBA is selected from among a metallic ion (e.g., Ag, Cu, Zn, Pb), antibiotic agents or an oxidizing agent (e.g., chlorine, hydrogen peroxide, ozone), or a mixture thereof. Representative (but non-limitative) concentrations for each photochemical synergistic agent are up to 50 ppm. However, at low BBA concentrations it is desirable to employ a mixture of at least two photosensitizers.

According to a preferred embodiment of the invention, a process may be carried out wherein the photochemical synergistic agent is a photo sensitizer or a mixture of photosensitizers, wherein at least two of the photosensitizers used react at substantially different wavelengths.

According to another preferred embodiment of the invention, one or more fluorescent agent(s) are added, emitting energy in such wavelengths that correspond to the absorbing wavelengths of the photosensitizers present.

In still another preferred embodiment of the process, a shift spectrum filter is used to obtain a larger portion of the radiation spectrum input, converted into the suitable wavelength in which the photosensitizers operate.

Preferably, the process is operated wherin oxygen is added in an amount sufficient to supply the amount of molecules required by the photochemical reactions.

Preferably, the process is operated at temperatures of 20°-70°C, and still preferably the water pH is maintained in the range of 3-10.

Illustrative examples of photosensitizers responsible for the mechanism of creating reactive forms of oxygen are: Methylene blue 665 @ concentration of 10'5M 570-610 @ concentration >10"4M Benzyl viologen 555, 598 Porphyrins: (e.g., cytoporphyrin 550, 598) Neotetrazolium 520 Blue tetrazolium 520 Pyocyanine 239, 312, 379, 690 Eosin 490 Triphenyl tetrazolium 387 Phenazine methosulphate 264 1-Pyrenedodecanoic acid 1 -Pyrenemethyl 3 A-[Cis-9-octadeceneryloxyl- 22,23-bisnor-5-cholenate (PMC oleate) 1 -pyrenebutanol Merocyanine 540 Erythrosin isothiocyanates Malachite green isothiocyanates Illustrative examples of fluorescent materials which absorb radiation at certain wavelengths and consequently emit this energy at different wavelengths, suitable for the absorbing range of the photosensitizers, are: Bissarmine rhodamine 575 595 Fluorosclin isothiocyanate 495 520 1 -dimethylamino-naphtalene-5- sulphonyl-chloride 340 525 Iodoacetamides (e.g., Eosin iodoacetamide Erythrosin iodoacetamide Malachite green iodoacetamide Rhodamine iodoacetamide Courmarin iodoacetamide BodipyR iodoacetamide) Tetramethylrhodamine isothiocyanate IAEDANS derivatives Example 1 20 Ml of methylene blue (0.5 ppm) in distilled water was inoculated with 1.8-106 E. coli cells/ml and placed in sterilized petri dishes, to which 0.03 ppm Ag+ was added prior to exposing said dishes to solar radiation. Samples were withdrawn from the dishes at predetermined time intervals. The samples were serially diluted tenfold and 20 μΐ aliquots were placed by means of micropipette on nutrient agar plates. The plates were incubated for 24 hours and the micro-colonies developed were counted (Hober and Somersegaran, 1982 Appl. Environ. Microbiol. 44, 1246-1247). The results of the remaining bacteria after 5 and 10 minutes exposure to solar radiation are as follows: Additive used Surviving Surviving Time required bacteria/ml bacteria/ml to decrease bacte after 5 minutes after 10 minutes contentfrom lxlO5 to 1 [min.] Methylene blue only 1.7-104 375 19 Ag+ only 8.75-105 6.25-105 149.2 Methylene blue + Ag+ 1.1-104 200 17.7 EagmpHe ¾ The experiment was conducted in the same manner as in Example 1, with the exception that instead of 0.03 ppm of Ag+, 1 ppm of the photosensitizer Eosin was added to the solution. The time required to decrease bacterial content from 107 E. coli/ml to 1 by using methylene blue was 19 minutes, using Eosin as the only photosensitizer decreased the time required to 15.2 minutes only.

Exam e ¾ Example 1 was repeated, but no additives other than methylene blue were used. Solar radiation was passed through a wavelength filter, Irradiant 660, shifting part of the solar spectrum from 500-600 nm to 600-700 nm. Without said cover, the time required to decrease the bacterial content of the solution from 1-107 E. coli/ml to 1 was 19 minutes, whereas in the case where said filter was used, the time required was decreased to 16.1 minutes. 0 -9- 107329/3

Claims (24)

1. A process for the photochemical purification of water, comprising adding to the water to be treated a biocidally effective amount of a mixture comprising a photoeensitizer and a photochemical synergistic agent selected from one or more further photosensitizer(s), one or more fluorescent agent(s), one or more bacteriostatic and/or bacterial agent JB (ΒΒΆ), or a mixture thereof, and exposing the water to radiation..

2. A process according to claim 1, wherein the photochemical synergistic agent is BBA selected from among a metallic ion, an antibiotic agent, an oxidizing agent, or a mixture thereof.

3. A process according to claim 2, wherein the BBA is a metallic ion selected from among Ag, Cu, Zn, Pb, or a mixture the eof.

4. A process according to claim 2, wherein the BBA is an oxidizing agent selected from among chlorine, hydrogen peroxide, ozone, or a mixture thereof.

5. A process according to claim 1, wherein the photochemical synergistic agent is a photosensitizer or a mixture of photosensitizers, wherein at least two of the photosensitizers to be used react at substantially different wavelengths.

6. A process according to claim 5, wherein the photochemical synergistic agent is chosen from among the group consisting essentially of; Methylene blue; Benzyl viologen; Porphyrins; Neotetrazolium; Blue tetrazolium; Pyocyanine; Triphenyl tetrazolium; Eosin; Phenazine methosulphate; 1-Pyre edodecanoic acid; 1-Pyrebebutanol; Merocyanine; Erythrosin isothiocayanates; Malachite green isothiocayanates; and 1-Pyrenemethyl 3A- [Cis-9-octadeceneryloxyl-22f 23- bisnor-5-cholenate (PMC oleate).

7. A process according to claim 6 wherein the porphyrin is cytoporphyrin .

8. A process according to claim 1, wherein the photochemical synergistic agent comprises one or more fluorescent agent (s) emitting energy in wavelengths corresponding to the absorbing wavelengths of the photosensitizers present in the water. 107329/2

9. A process according to claim 8, wherein the photochemical synergistic agent is chosen from among the group consisting essentially of: Bissarmine rhodamine Fluorosclin isothiocyanate l-Dimethylamino-naphtalene-5-sulphonyl-chloride Iodoacetamides Tetramethylrhodamine isothiocyanate IAEDANS derivatives

10. A process according to claim 9, wherein the iodoacetamide ie selected from among: Eosin iodoacetamide; Erythrosin iodoacetamide; Malachite green iodoacetamide; Rhodamine iodo cetamide; Courmarin iodoacetamide; and BodipyR iodoacetamide.

11. Ά procese according to any one of claims 1 to 10, wherein the water is exposed to radiation while flowing through a channel .

12. A process according to claim 11, wherein the channel is an open channel.

13. A process according to claim 12, wherein said channel ia provided with a shift spectrum filter.

14. A process according to claim 13, wherein a major part of the spectral output of the filter is shifted from the yellow-green range (500-600 run) to the red (600-700 nm) .

15. A procees according to any one of claims 1 to 14, wherein oxygen is added in an amount sufficient to supply the amount of molecules required by the photochemical reaction.

16. A process according to any one of claims 1 to 15, wherein the operating temperature is 20 - 70 eC.

17. A process according to any one of claims 1 to 16, wherein the pH of the water is maintained in the range of 3 to 10.

18. It. A process according to any one of claims 1 to 17, wherein the radiation is solar radiation.

19. A procees according to any one of claims 1 to 18, wherein the radiation is artificial radiation in the range of 400 to 700 nm.

20. A process according to any one of claims 1 to 19, wherein the solar radiation is concentrated before reaching the water to be treated. 107329/2

21. A process according to any one of claims 1 to 20 for purifying waste water.

22. A process according to any one of claims 1 to 20 for purifying drinking water.

23. The use of the process according to claim 22 in swimming pools.

24. The use of the process according to claim 22 in a module for domestic water purification. B el