CHEMICAL TREATMENT FOR ALGAE CONTROL IN OPEN WATER SYSTEMS

Abstract: Algae growth in an open water system such as a water cooling tower is controlled by reducing the amount of light available for the algae to photosyn­ thesize. The light available for photosynthesis is reduced by incorporating a dye into the water in the water cooling system. Thus the dye absorbs the light necessary for photosynthesis and in turn prevents algae growth. Preferably fluorescein at a concen­ tration of 0.2 to 800 parts per million is incorpo­ rated into the water in the water cooling system. Other dyes can be selected depending on the particular algae.

Description: Open water systems most notably water cooling towers have a severe problem with algae. The portion of the system which is exposed to sunlight can easily develop algae growths. Carbon dioxide in the air and the light from the sunlight provide the necessary elements for photosynthesis and thus algae growth. Algae growth can retard the heat exchange in the cooling system by reducing water flow rates through the cooling tower and can also provide a severe source of dispersed solids within the system. These can eventually foul a system to the extent that it is almost totally inoperative or that an over-flow of the tower deck results. There are various algacides and algastats which are typically added to water systems to control algae growth. These chemicals are generally complex chemicals such as quaternary ammonium compounds which may or may not be totally effective. Even with these compositions some water cooling towers become fouled with algae. This may require a shut down of the system and physical removal of the algae using various dangerous chemicals. The chemicals, physical labour and shut down time are exceptionally costly. Algae growth is a problem only in systems where the water is exposed to sunlight. Sunlight is present because these systems by definition are open systems and require exposure to the environment for heat exchange purposes. Covering the system would prevent algae growth but would also reduce the efficiency of the system. German Patent Application No. 3135194 describes a process for preventing the formation or growth of algae and slime-forming bacteria in open industrial water systems. The process comprises adding to the system on aqueous solution of methylene blue. The methylene blue acts in two ways, firstly it turns the water opaque and this prevents algae growth due to the reduced amount of light available for the algae to photosynthesize. Secondly the algae already present concentrates the methylene blue in itself which will essentially cause it to die. However methylene blue is only slightly light sensitive and any overspray from the system will cause staining of adjacent areas. In accordance with the invention, a method of retarding algae growth in a circulating water system comprises establishing a concentration of a dye in the water; the dye being a photodegradable water soluble dye which absorbs light at a wavelength required by the algae to photosynthesize, the concentration being established at an amount effective to substantially retard photosynthesis by algae characterised in that the dye is fluorescein, Rhodamine B of Rhodamine WT. By this method, algae growth in an open water system is substantially reduced or eliminated by shielding the algae from the light necessary for photosynthesis. Preferably, the dye is such as to absorb 10% and preferably 50% or more of various wave lengths of light needed by the algae for photosynthesis over a .25-6 inch (6.5-150 mm) path. This will substantially reduce algae growth in water cooling towers. The dye is a photodegradable dye which will therefore not foul the environment. In particular, spray from the water cooling tower will not permanently discolor any nearby surface. A preferred embodiment involves maintaining a concentration of fluorescein in the water system at from about .2 parts per million up to several hundred parts per million. This has been found to reduce effectively algae growth. The invention will now be further described by the way of example with reference to the accompanying drawings in which: Figure 1 is a graph of the action spectrum for green algae; Figure 2 is a graph depicting the transmittance of fluorescein at 500 nm relative to concentration level. According to the present invention, a dye is added to the water in an open water system. By open water system we mean any water system in which any part of the water in the system is exposed to sunlight. Generally these will be recirculating water systems, i.e., cooling towers and evaporating towers. Primarily these systems will be water cooling towers use for building air conditioners. Such systems require a cooling tower where water is pumped to a distribution pan and passes over the tower fill down to a collection pan. The distribution pan will have a water depth of generally from about .25 to about 6 inches (6.5 to about 150 mm) and generally 2-3 inches (50-75 mm). Algae generally grows on the bottom surface of the distribution pan. The dye must absorb visible light specifically the light required for photosynthesis by algae. There are various types of algae including brown algae, red algae, blue green algae, filamentous algae and green algae. The method can be employed with all of these types of algae but is primarily useful with green and blue green algae which photosynthesize using chlorophyll. Red algae absorbs blue light using a carotonoid pigment but also relies on chlorophyll. As shown in Fig. 1, the action spectrum of green algae peaks from about 400 to about 520 nm. Thus, chlorophyll is absorbing light between 400 and 520 nm referred to as photo system 1. There is a second peak between about 650 and 700 nm referred to as photo system 2. Thus, to retard green algae growth, the dye should absorb light between 400 and 520 nm or between 600 and 700 nm. Red algae has a peak on its action spectrum between 460 and 680 nm corresponding to the absorbtion spectrum of phycoerythrin. In an exposed water system, troublesome algae generally adhere to the bottom surface of the exposed portion of the water system. Thus, in a water cooling tower algae growth is noted most prominently in the bottom of the distribution pan. As indicated these distribution pans typically have .25 to 6 inches (6.5 to 150 mm) of water generally 2-3 inches (50-75 mm). Thus, in order to be effective the concentration of the dye should be such that a substantial amount of the light required for photosynthesis is absorbed through the water in the distribution pan. Thus, it is preferred that the water in the distribution pan have an absorbance of 10% preferably at least about 50% at a wavelength between 420-520 nm. More preferable the absorbance should be 50%-100%. Algae growth cycles vary depending on algae type and environment including pH, temperature, available light, and nutrients. To effectively retard algae growth, the fluorescein should be maintained at effective levels for a continuous period during system operation. Generally seven days continuous application will retard most algae. However, shorter intermittent periods of time should cause some detectable algae retardation. Of course, preferably the effective concentration should be maintained continuously. Suitable dyes include fluorescein, Rhodamine B or Rhodamine WT. These dyes absorb light either in the red area of the spectrum toward 700 nm or as with fluorescein in the green sector of the spectrum at about 490; 510 nm. Additionally, two dyes may be used which absorb at different wave lengths preferably one in photo-system 1 and the other in photo-system 2. The absorbance of fluorescein versus concentration is shown in Fig. 2. As,can be seen, at about 800 parts per million fluorescein absorbance approaches 100%. For algae control, the concentration of fluorescein is preferably from about .2 part per million to about 800 parts per million and preferably at least 1 ppm. Anything is excess of 800 ppm would be wasted. At a concentration of 3 part per million, the fluorescein will absorb approximately 60% of the light transmitted at 500 nm 1 inch (25 mm) of the dye containing water. Thus, for a collection pan that is from 2 to 4 inches (50 to 100 mm) in depth a very substantial portion of that wave length of light is absorbed which in turn prevents or retards growth. This presents a unique opportunity. Fluorescein as referred to herein is actually the water soluble salt of fluorescein generally sodium fluorescein. This is a reaction product of phthalic anhydride with sodium hydroxide. It is also referred to as resorcinolphthlalein sodium, uranine, uranine yellow, CI acid yellow, CI145350. The dye for use in the method is one which is photodegradable by natural sunlight. A dye is photodegradable if at use concentrations after exposure to sunlight in a petrie dish (.25-.5 inches, 6.5-13 mm) for a period of about 3 hours the dye will no longer absorb visible light. Thus, the dye if blown from the exposed portion of the water system onto another surface will not permanently discolor the surface. Again fluorescein is the preferred dye for this purpose since it is photodegradable. This is also beneficial since the water from these cooling towers are continually bled off and discarded in the sewage system. Thus this will have no permanent effect on the water system. Since fluorescein is photodegradable it will not maintain its concentration in a system indefinitely. Further the water in the system is periodically bled off. Therefore to insure that an effective concentration of fluorescein is present, the concentration of the fluorescein should be monitored using preferably a colorimeter. The method is further advantageous because it can be used in combination with other algacides and algastats. The dyes used are inert, do not absorb on solids or suspended matter and therefore do not interfere with the activity of other water treatment agents. Accordingly, these can be used in combination with any currently used algacide or algastat. These include: 2,2-dibromo-3-nitrilopropionamide, poly[oxyethylene-(dimethyliminio) ethylene(dimethyliminio)-ethylene dichloride, 5-chlor-2-methyl-4-isothiazolin-3-one, 2-methyl-4-iosthiazolin-3-one, 2-(thiocyanomenthylthio)benzothiazole and generally the class of linear alkyl substituted quaternary chloride compounds including, but not limited to the following: dioctyl dimethyl ammonium chloride, dimethyl benzyl ammonium chloride, didecyl dimethyl ammonium chloride. There is thus provided a method of retarding or in certain cases stopping algae growth in open water systems which is compatible with other water treatment methods and compositions excluding oxidants and therefore has a very substantial range of potential applications.

Claims: 1. A method of retarding algae growth in water in a circulating open water system, comprising establishing a concentration of a dye in the water; the dye being a photodegradable, water soluble dye which absorbs light at a wavelength required by the algae to photosynthesize, the concentration being established at an amount effective to substantially retard photosynthesis by algae characterised in that the dye is fluorescein, Rhodamine B or Rhodamine WT. 2. A method as claimed in Claim 1 wherein the concentration is effective to absorb 10% of a wavelength of light at from 400 to about 520 nm through water exposed to sunlight in the system. 3. A method as claimed in either Claim 1 or Claim 2 wherein the open water system is an open recirculating cooling tower. 4. A method as claimed in any of the preceding claims wherein a second algacide is added to the water. 5. A method as claimed in any of Claims 1 to 3 wherein a second dye is added to the water, the second dye comprising a water soluble dye which absorbs light at a wavelength required by the algae to photosynthesize. 6. A method as claimed in any of the preceding claims wherein the dye is fluorescein. 7. A method as claimed in Claim 6 wherein the concentration of fluorescein in the water system is established at about .2 to about 800 parts per million. 8. A method as claimed in Claim 7 wherein the concentration of fluorescein is from about 1 to about 800 ppm. 9. A method as claimed in Claim 8 wherein the concentration of fluorescein is about 3 to about 50 ppm.

Inventors: BAKER, GARY L, CHRISTENSEN, RONALD J.
Applicants: DIVERSEY CORPORATION
Application year: 1988
Main classification: C02F1
IPC codes: A01N25, A01N43, C02F1, C02F3