HK1054519B - Method for flushing particle-bearing filter beds, to sterilise and decontaminate the same - Google Patents

Description

Flushing method for sterilization and purification of particle-containing filter beds

Technical Field

The invention relates to a washing method for sterilizing and purifying a particle-containing filter bed in a circulating water treatment device or a linear water treatment device.

Background

Filtration of water in the water treatment process of a circulating water treatment plant or a linear water treatment plant is an important and essential method step. In this case, the unfiltered water is first filtered off of the solid matter with a filter bed. The filter bed is usually made of materials such as gravel, sand, silica, zeolite or carbonaceous materials, and solid materials or agglomerated materials are filtered out in or between the filter beds. Such devices require periodic cleaning of the filter bed. Water is usually pumped through the filter bed in the opposite direction to the flow of the water to be filtered during the filtration process, but not all systems are cleaned. This process is referred to as flushing or filter bed flushing. Air and water-air-water mixtures, either alone or in combination with one another, can also be used for flushing.

In addition to the formation of organic or inorganic deposits, with increasing operating time of the filter bed, there is often contamination of the filter material by microorganisms, which may even be pathogenic bacteria. Tests have shown that about 80-90% of the filter material, in particular in the lower region of the filter material layer, has a high content of bacteria and biological deposits (biofilm). In addition to the filter material, bacteria and biological deposits are also found on the surface of the filtrate chamber and on the walls of the filter nozzle and flush water reservoir. This can cause serious hygiene problems in, for example, swimming pool and tub waters, i.e. although the bather is only in direct contact with the bath water at this time, there is a serious risk of contamination of the filters with microorganisms, since, for example, a large number of bacteria flowing out of the affected filters can enter the bath water in a very short time at a sudden drop in the sterilization capacity of the bath water.

DE-a-3233857 describes a method and a device for cleaning a cleaning filter element, in which a mixture of water and a pre-pressurized gas is used. Where possible, a wetting agent may be added to the gas in the mixture to reduce the surface tension of the water, so that a uniform mixture of the rinsing agent is obtained.

DE-3229219 describes surface-active substances as rinsing agents for rinsing particulate-containing and flushable filter beds for water treatment in basin water, drinking water and wastewater treatment plants. However, the cleaning of solid deposits by this method is not very good, especially for filters contaminated with microorganisms and biological deposits. Furthermore, high concentrations of surface-active substances must be used, which leads to high costs and large amounts of waste water.

Disclosure of Invention

It is therefore an object of the present invention to provide a method which avoids the above-mentioned disadvantages. In particular, the method according to the invention should, in addition to having a high cleaning action against organic and inorganic solid deposits in the filter bed, also be able to effectively remove microbial and biological deposit contamination over the entire filter, while being cost-effective and producing only small amounts of waste water.

According to the invention, this object is solved as follows: the chlorine oxide and/or the halogen-containing and/or peroxide-containing aqueous solution is allowed to act on the deposits in the granular filter bed, and the reaction products produced under the above-mentioned process conditions and the residual chlorine oxide or halogen or peroxide are then removed by flushing with water or an aqueous medium.

The important features of the method according to the invention are the following two steps. In a first step, the filters are charged with an aqueous solution of chlorine oxide and/or halogen-containing and/or peroxide-containing, and these solutions are then allowed to act on the filter material. The filter is then rinsed with water or an aqueous medium in a second step.

The method according to the invention is particularly suitable for use in circulating water treatment plants, such as swimming pool circulating water, cooling water circulating water, industrial water circulating water treatment plants, and linear water treatment plants, such as drinking water and wastewater treatment plants.

Detailed Description

It has proven most preferred that the oxychloride and/or the aqueous halogen-containing and/or peroxide-containing solution reacts with the deposits on the particulate filter bed for about 1 to 3 hours. Under certain conditions, a shorter time may be sufficient or a longer time may be required.

Oxychloride is particularly preferred not only for functional effects but also for workability reasons, so the chlorine oxide-containing solution used in the process according to the invention is preferably an aqueous chlorine oxide-containing solution. Tests have shown that the oxidizing properties of the oxychloride give rise to a high action effect of the process according to the invention. Since oxychloride is a chemically unstable and difficult to handle material, most of it is desirable that it is not present in the solution in free form, but in a combined form of chemical species from which it can be continuously produced. One such material is tetrachlorodecaoxo dianion [ Cl ]₄O₁₀]^2-The substance is numbered ELINCS-Nr.420-970-2 in the literature. Since the tetrachlorodecaoxoanion and the oxychloride exist in the same weight, the solution of the tetrachlorodecaoxoanion always contains a predetermined amount of the oxychloride, and the oxychloride is produced at the time of use.

In a preferred embodiment, therefore, the divalent anion [ Cl ] is tetrachlorodecaoxy complexed in the aqueous oxychloride solution₄O₁₀]^2-。

The solution containing tetrachlorodecaoxygen complex dianions and chlorine dioxide is advantageously obtained as follows: an aqueous solution containing sulfate ions having a pH of 3 or less and a stable peroxygen compound is prepared, and then the solution is mixed with an aqueous alkaline chlorite solution. The aqueous solution containing sulfate ions is preferably reacted with an amount of a stable peroxy compound such that the concentration of peroxy compound in the final product is from about 0.001 to about 0.01 mole. Tests have shown that it is particularly advantageous to react an aqueous solution containing sulphate ions with a stable peroxygen compound, subsequently mix this solution with a quantity of an aqueous alkaline chlorite solution and adjust the pH to above 7.0, in particular to 7.5-8.0,

the method of the present invention can employ various concentrations of the solution containing the above-mentioned tetrachlorodecaoxy complex dianion and chlorine dioxide depending on the degree of contamination of the filter and/or bacterial contamination. In a preferred embodiment, this solution is allowed to react with the deposit on the particulate filter bed at a concentration corresponding to an initial concentration of chlorite of about 5 to 20 mmol/l.

Tests have shown that hydrogen peroxide, persulfates, percarbonates, perborates or inorganic peroxo compounds of alkali metals or alkaline earth metals are particularly advantageous as peroxy compounds. Alkali metal chlorites or alkaline earth metal chlorites are preferably used as chlorite. Particularly good results are obtained when the pH of the aqueous solution containing sulfate ions is adjusted to a value of 1 or less.

If the starting aqueous solution used exhibits only a small carbonate hardness or is prepared from demineralized water, it is advantageous to work under an inert gas atmosphere, since, without a protective gas layer, an explosive air/chlorine dioxide mixture is formed between the small amount of evaporated chlorine dioxide and the air. At a ratio of air to chlorine dioxide of about 10: 1, the chlorine dioxide in the air/chlorine dioxide mixture tends to explosively decompose into chlorine and oxygen. For aqueous starting solutions of medium or high carbonate hardness (> about 7 degrees or > about 1.3mmol/l carbonate hardness), it is generally not necessary to add an inert gas because it forms a carbon dioxide shielding gas layer. Therefore, in order to prepare an aqueous solution containing sulfate ions, the aqueous solution can be used to prepare a solution containing tetrachlorodecaoxometallate dianions and chlorine dioxide, preferably using mineralized water.

The solution containing tetrachlorodecaoxometallate dianions and chlorine dioxide preferably contains water soluble phosphates, since the amount of peroxy compounds can be reduced if small amounts of water soluble phosphates, such as sodium metaphosphate, are present in the finished solution.

The method according to the invention is suitable for sterilization and cleaning rinse of different types of particle-containing filter beds in circulating and linear water treatment plants. There is no fundamental limitation on the type, size and configuration of the filter bed. The particle-containing filter bed is preferably a filter layer/layers comprising filter material consisting of quartz, gravel and/or sand and/or porous filter material, such as silica, zeolites and/or carbonaceous materials, such as activated carbon, lignite and Antrazithkohle. If chlorine and/or chlorine dioxide is to be removed particularly thoroughly in the second step, an aqueous thiosulfate (e.g. sodium thiosulfate) solution can be used for rinsing where the water is to be rinsed. Preferably, about 5.3g of thiosulfate per gram of chlorine is used, and about 3.0g of thiosulfate per gram of chlorine dioxide is used.

In summary, it was established that the method according to the invention makes it possible to sterilize and decontaminate the filter beds containing particles in circulating water treatment plants and linear water treatment plants, which method gives better results than the prior art. Therefore, the cleaning effect on solid organic and inorganic deposits is remarkably improved. A particularly significant advantage is the cleaning effect on contamination due to microorganisms and biological deposits (biofilms). Here, the cleaning methods described in the prior art show only a weak cleaning effect. Tests have surprisingly shown that the process according to the invention not only largely removes contamination on the filter bed to be treated, which is attacked by microorganisms and biological deposits, but also achieves a strong preventive effect, in particular with porous filter materials. This may be due to the following reasons: by destroying all pathogenic bacteria and simultaneously removing all contaminants that promote microbial growth, for example as a nutrient source for the microorganisms, the spread of the microorganisms is prevented for a longer period of time after this treatment due to the removal of the contaminants. The method according to the invention is therefore regarded as and serves as a preventive measure. The method according to the invention is of course also suitable as an "emergency measure" for the "sterilization" of the filter material. Furthermore, the process according to the invention is very cost-effective and does not produce large amounts of waste water.

The invention is explained more clearly below with reference to some examples.

Example 1: preparation of solutions containing tetrachlorodecaoxygen complex dianions and chlorine dioxide

To 1 liter of sulfate-containing water (carbonate hardness: 18 ℃ or 3.2mmol/l) having a pH value of 0.5, 0.5g of a 30% by weight hydrogen peroxide solution was added. To this solution 0.9 liters of a commercial sodium chlorite solution (about 300g sodium chlorite/liter) was added with stirring. The solution is brown in color and turns bright green with a pH value of more than 7 after the stabilization reaction. The pH of the solution at this point was 7.5.

Example 2: the method according to the invention treats purified swimming pool and tub waters with a multi-layer filter with carbon material

The filter used in this example is a typical filter used to purify pool water in open and indoor swimming pool areas. This filter has the following characteristic values:

high: 2.5m

Diameter: 2.1m

Volume of the filter bed: 5.2m³

Filter housing material: glass fiber reinforced plastic

Filter material filled in the filter: 4 quartz sand layers with upward gradually reduced particles

And an uppermost layer composed of a granular carbon material

The rinsing method according to the invention is applied in the filter described above as follows:

the filter is first conventionally rinsed with water and the filter container is then emptied of water. 6.7 liters of the solution containing tetrachlorodecaoxo dianions and chlorine dioxide described in example 1 were then added to the filter starting from the bottom with a dosing pump. The filter is then completely filled from the bottom with water. After the filter was completely filled, the reaction was allowed to proceed for 1.5 hours. After the action, the filter was rinsed with water for about 10 minutes at a rinsing water flow rate of about 40 m/h.

Claims (14)

1. A method for sterilizing and cleaning particle-containing filter beds in a washing circuit or linear water treatment plant, characterized in that an aqueous solution containing oxychloride and/or halogen and/or peroxide is introduced into the filter, the aqueous solution is allowed to react with the deposits in the particle-containing filter beds for 1 to 3 hours, and then the reaction products produced under the above-mentioned process conditions and the residual oxychloride or halogen or peroxide are removed by washing with water or an aqueous medium, wherein the particle-containing filter bed is a single-layer/multi-layer filter bed and the filter material is quartz, gravel and/or sand and/or a porous filter material and/or a carbonaceous material.

2. The method according to claim 1, characterized in that the porous filter material is silica and/or zeolite and the carbonaceous material is activated carbon, lignite and/or anthracite.

3. The method of claim 1, wherein the aqueous solution containing chlorine oxide is an aqueous solution containing chlorine dioxide.

4. A process according to claim 3, characterized in that the chlorine dioxide-containing aqueous solution contains the tetrachlorodecaoxo-complex dianion [ Cl ]₄O₁₀]^2-。

5. A process according to claim 3, characterized in that the aqueous solution having a pH of 3 or less and containing sulfate ions is reacted with a peroxide compound stabilized therein, and subsequently the solution is mixed with an aqueous alkaline solution of chlorite, whereby an aqueous solution containing chlorine dioxide is obtained.

6. A process according to claim 5, characterized in that the sulphate ion-containing aqueous solution is reacted with a stable peroxide in an amount such that the peroxide concentration in the final product is between 0.001 and 0.01 mol.

7. A process according to claim 5, characterized in that the aqueous solution containing sulphate ions is reacted with the peroxide compound stabilized therein, whereafter the solution is mixed with an amount of an aqueous alkaline solution of chlorite and the pH is adjusted to above 7.0.

8. A method according to claim 7, characterized in that the pH is adjusted to between 7.5 and 8.0.

9. A method according to claim 5, characterized in that the chlorine dioxide-containing aqueous solution is allowed to react with the deposits in the granular filter bed in a concentration corresponding to an initial concentration of chlorite in the range of 5-20 mmol/l.

10. Process according to one of claims 5 to 9, characterized in that hydrogen peroxide, persulfates, percarbonates, perborates or peroxo compounds of alkali metals or alkaline earth metals are used as peroxy compound.

11. Process according to one of claims 5 to 9, characterized in that alkali metal and/or alkaline earth metal chlorite is used as chlorite.

12. The process as claimed in claim 5, wherein the aqueous solution containing sulfate ions has a pH of 1 or less.

13. A method according to any of claims 5-9, characterized in that mineralized water is used to prepare the sulfate ion-containing aqueous solution.

14. A method according to any one of claims 5-9, characterized in that the aqueous solution containing chlorine dioxide contains a water-soluble phosphate.