GB2084560A - Disinfection of Aqueous Media - Google Patents

Abstract

A composition for the disinfection of aqueous media, particularly bacteria-containing aqueous effluents, comprises a combination of hydrogen peroxide, a soluble copper sat and a low molecular weight aliphatic alcohol.

Description

SPECIFICATION Disinfection of Aqueous Media The present invention relates to processes and compositions for the disinfection of aqueous media.

Aqueous effluents in the untreated state can often contain high concentrations of bacteria, so that it is highly desirable that they be treated before being discharged into lakes and water-ways, the more so because such inland waters are being used for recreactional purposes to an increasing extent.

Chlorine has been employed as a bactericide, but there appears to be a risk that chlorine reacts to some extent with organic impurities in the treated water forming carcinogens such as chloroform.

Since water commonly passes through the public supply after purification several times, there is naturally a desire not to introduce carcinogen-forming compounds with the result that alternatives to chlorine are being sought.

Hydrogen peroxide has been proposed as a bactericide/bacteristat and advantageously, when it decomposes, it yields oxygen and water, but it suffers from the disadvantage that by itself it is relatively inefficient. Its use in conjunction with copper has also been proposed in order to enhance bactericidal activity and it has now been found that activity can be enhanced further by introduction of readily available organic compounds.

According to the present invention there is provided a process for the disinfection of a bacteria containing aqueous medium comprising the step of introducing into the aqueous medium hydrogen peroxide to provide a concentration selected in the range of from 2.5x1 O-BM to 3x 1 0-3M, a soluble copper salt in a concentration in the range of from 1 xl O-6M to 2 x10-5M and a low molecular weight aliphatic alcohol in a concentration in the range of from 2.5 xl 0-5M to 2 xl 0-3M.

Desirably the components of the combination are present in a mole ratio of hydrogen peroxide: copper in the range of 1:1 to 150:1. and in many embodiments the hydrogen peroxide:copper mole ratio is in the range of from 5:1 and to 60:1, and preferably at least 10:1 hydrogen peroxide to copper.

If less than the preferred range of peroxide:copper ratio is employed the effectiveness of the disinfectant is impaired whereas if significantly more than the preferred range of peroxide:copper ratio is employed the cost effectiveness can be impaired.

The weight ratio of hydrogen peroxide to alcohol is preferably in the range of 5:1 to 1:5, and frequency from 2:1 to 1:2.

The pH of the treated medium is suitably from pH5 to pH9, and frequency from pH6 to pH7.5.

Preferably sufficient hydrogen peroxide is introduced to provide a concentration in the aqueous medium of at least 2.5x 1 0-5M and in practice is unlikely to be greater than 2.5x 1 0-3M. Frequently, its concentration is at least 1 x10-4M and often no more than 7.5x 1 0-4M. Desirably the copper is present in a concentration of at least 3 x 1 0-6M and usually in practice, not substantially more than 1.75 x 1 0-5M. The alcohol is desirably present at a concentration of at least 5x 1 0-5M and preferably up to 5 x 1 0-4M. The concentrations of the components within their ranges are selected in combination to obtain mole ratios falling within the above-mentioned ranges.

The soluble copper salt is conveniently copper sulphate but can be any other salt having a solubility sufficient to provide the aforementioned desired concentration of copper and preferable such that the copper dose can be obtained by adding a small amount of a preformed aqueous solution to the aqueous medium. As a guide any salt having a solubility of at least 5 gpl such as cupric acetate, chloride and nitrate has substantially greater than the minimum solubility.

The low molecular weight alcohol can be any aliphatic alcohol having a molecular weight of below 80, including methanol, ethanol, n- and isopropanol, allyl alcohol and t-butanol, and in many embodiments the alcohol is either ethanol or n-propanol. Mixtures of any two or more of the aforementioned alcohols may be used, and for example, in practice, it will be recognised that industrial ethanol usually contains a small proportion of methanol.

Desirably, each of the components of the combination can be introduced into aqueous medium in aqueous solution. One convenient method is to preform a concentrated solution containing all these components in the desired mole ratios of the components shortly before their introduction into the aqueous medium to be disinfected. However, during prolonged storage to avoid loss of reagents, it is preferred to separate the hydrogen peroxide and copper. The alcohol, being liquid, can be added in undiluted form or diluted beforehand with water to any desired extent. The concentrations of the various components in the aqueous solution introduced into the aqueous medium can be readily calculated to provide the desired mole ratio of components in the aqueous medium.By way of illustration, a mixture of two volumes of 35% w/w hydrogen peroxide and six volumes of a solution containing 1 Sgpl copper sulphate (as CuSO4) together with one volume of ethanol has a mole ratio of approximately 40:1:30 of H2O2:Cu:alcohol. If such a mixture were employed at a rate of 1 litre of mixture per 9,000 litres oi aqueous medium, the dosage would be approximately 1 Oppm hydrogen peroxide and corresponding amounts of the other components, Cu just below 0.5ppm and about 1 Oppm ethanol.Naturally, if desired, the hydrogen peroxide solution can be subjected to an intermediate dilution before use in order to facilitate more accurate metering, especially when it is desired to employ it in a low mole ratio to the other components, for example less than 10:1:6. It will therefore be realised that commercially available hydrogen peroxide solutions containing from 5 to 80% hydrogen peroxide can be employed either as such or diluted and that in view of the large dilution that occurs upon use, there is no need to use the more concentrated solutions. As an alternative to using separate solutions, an alcoholic hydrogen peroxide can be used or the two other components can be dissolved in appropriate amounts in the hydrogen peroxide solution, preferably without prolonged storage before use, or in any water used to dilute the hydrogen peroxide solution.

The combination of components forming the disinfectant of the present invention can suitably be applied to any aqueous effluent containing bacteria, especially Enterobacteriaceae and Staphylococeae and has particular application in a tertiary treatment of municipal sewage, i.e. a treatment subsequent to a secondary treatment of the activated sludge of trickling filter types and prior to discharge into water courses or reservoirs. Alternatively, the disinfectant can be employed on the effluents in the paper and food processing industries. Advantageously, since the disinfectant is often employed to treat effluent having a pH in the range of 6 to 9, and especially in the range pH 6.5 to 8, the treated effluent can be discharged without any further adjustment to the pH.Conveniently, the process according to the present invention can be effected at the natural temperature of the aqueous medium, which will be, in many cases, at a slightly higher than ambient. In practice the aqueous effluent is often retained in holding tanks prior to being discharged, the average residence time in the tanks being usually in the range of from 1 5 minutes to 2 hours, although lower residence times may be used if desired. Mainly the temperature of the aqueous medium during the treatment according to the present invention will be in the range of ambient to 500C.

Where the aqueous medium initially has a pH outside the preferred range of pH6 to 7.5, its pH can be adjusted to within that range by known methods such as with acid or alkali as is appropriate.

It will be recognised that the hydrogen peroxide can be generated in situ, if desired, by the use of such adducts as sodium percarbonate or sodium perborate. Alternatively, the hydrogen peroxide can either be replaced by a peroxyacid such as peroxyacetic or perphthalic acid or salt e.g.

diperoxyisophthalic acid or employed in combination with an activator, i.e. a compound such as an anhydride or an N-acyl compound such as TAED i.e. tetra acetyl ethylene diamine which reacts with hydrogen peroxide to generate in situ a peroxyacid. Such activators have been disclosed particularly with respect to peroxyacid formation in aqueous low temperature washing or bleaching of fabrics.

When the hydrogen peroxide is employed to generate peroxyacid or is replaced by it, the preferred mole ratio of active-oxygen-containing compound to copper in the combination tends to be lower than when hydrogen peroxide without activator is employed, and is often in the range of 1:5 to 25:1 moles especially 1:5 to 5:1 moles peroxyacid per mole of copper.

Various embodiments of the present invention will now be described more fully by way of Example.

In each of the Examples and Comparisons the aqueous medium to be disinfected was a sample of effluent withdrawn after the secondary treatment of municipal sewage which contained initially a mixture of the following microorganisms to a total count in the region of 104 to 105 per ml: Enterobacteriaceae, coliforms, faecal coliforms, D-Streptococcae, Staphyloccae, Micrococcae and aerobic and anaerobic spore-forming organisms such as Clostridium perfringens. The total count was obtained by innoculating plates of Tryptone Soya Agar with known volumes of sample, diluted when necessary, and incubating the plates at 370C for 48 hours. Unless otherwise stated, as in Examples 1 6 to 25 the effluent was treated at its natural pH which was within the range of pH 6.5 to 7.3.

A 1 00ml sample of the effluent was dosed at ambient temperature with sufficient of each of the components of the disinfectant combination to provide the concentrations of the components specified in the Tables hereinafter. The copper salt was copper sulphate and the alcohol was again as specified in the Tables. After a contact time of an hour, or as otherwise stated the total bacteria count in the disinfected water was again determined as before, using the method described above. In the Table 1 the term reduction in bacteria count is the % of bacteria surviving obtained by comparing the bacteria counts before and after the treatment, and the term contact time refers to the time at which the second bacteria count is made, i.e. the period during which the disinfectant system has been permitted to work.

Since each group of results were carried out on different batches of micro-organism-containing effluent comparisons within each group can be made fairly whereas between groups cannot be so made. The respective groups are C 1 C to Ex1, C2C to Ex2, C3C to Ex3, C4C to Ex7, Ex8 to Ex1 1, Ex12 to Vex1 5, Exl 6 to Ex25 and C26C to Ex45.

Table 1 Reduction (Disinfection system used) Contact in H202 Copper time in bacteria ppm ppm Alcohol ppm mins count(%) C1C 10 0.5 60 90.7 ClA n-propanol 10 60 15.1 Ex1 10 0.5 n-propanol 10 60 93.6 C2C 10 0.5 60 92.7 C2A iso-propanol 10 60 3.2 Ex2 10 0.5 iso-propanol 10 60 94.3 C3C 10 0.5 60 97.5 C3A 2-propenol 10 60 32.6 Ex3 10 0.5 2-propenol 10 60 98.6 C4C 10 0.5 60 72.6 Ex4 10 0.5 n-propanol 25 60 86.4 Ex5 10 0.5 iso-propanol 25 60 83.6 Ex6 10 0.5 2-propenol 25 60 81.9 Ex7 10 0.5 methanol 25 60 78.7 Ex8 10 0.5 ethanol 10 10 82.1 Ex9 10 0.5 ethanol 10 30 90.7 Ex10 10 0.5 ethanol 10 60 99.1 Ex11 10 0.5 ethanol 10 120 99.6 Ex12 10 0.1 ethanol 10 10 63.8 Vex 13 10 0.1 ethanol 10 30 90.3 Vex14 10 0.1 ethanol 10 60 92.7 Ex15 10 0.1 ethanol 10 120 98.7 In Examples 16 to 25 the pH of the aqueous media to be treated were adjusted to the points given in Table 2. In each Example, the disinfectant system used was 1 Oppm hydrogen peroxide, 0.5ppm copper (present from copper sulphate) and 1 Oppm alcohol, and the contact time of the disinfectant was again 60 minutes.

Table 2 Reduction In Bacteria Count ExNo Alcohol pH {%) 16 methanol 6 98.5 17 methanol 6.5 98.5 18 methanol 7 99.2 19 methanol 7.5 98.8 20 methanol 8 96.3 21 ethanol 6 98.8 22 ethanol 6.5 98.8 23 ethanol 7 99.2 24 ethanol 7.5 98.0 25 ethanol 8 97.5 From Table 2 it can be seen that there is a tendency for the reduction in bacterial count to be higher in the pH range of 6 to 7.5.

In Examples 26 to 45, the disinfectant system used was 1 Oppm hydrogen peroxide, 0.5ppm copper and alcohol in the amount specified in Table 3, all on samples of the same effluent, and again using a contact time of an hour at the natural pH of the aqueous medium.

Table 3 Reduction In Example Bacterial Count No Alcohol ppm (%) C26C 96.8 Ex26 methanol 5 97.7 Ex27 methanol 10 98.0 Ex28 methanol 20 99.1 Ex29 methanol 50 98.1 Ex30 ethanol 5 98.5 Ex31 ethanol 10 98.2 Table 3 Reduction In Example Bacterial Count No Alcohol ppm (%) Ex32 ethanol 20 97.0 Ex33 ethanol 50 96.9 Ex34 n-propanol 5 98.2 Ex35 n-propanol 10 98.5 Ex36 n-propanol 20 97.7 Ex37 n-propanol 50 98.3 Ex38 isopropanol 5 97.3 Ex39 isopropanol 10 97.7 Ex40 isopropanol 20 96.1 Ex41 isopropanol 50 96.6 Ex42 t-butanol 5 97.6 Ex43 t-butanol 10 97.9 Ex44 t-butanol 20 98.4 Ex45 t-butanol 50 98.7 From Table 3, it can be seen that in general the addition of alcohol increased the extent to which the bacterial count was reduced, the exceptions being when 20ppm and 50ppm isopropanol was used.

Moreover, it was in general found that the disinfectant was often very effective at even about 5 to 10ppm added alcohol achieving similar or sometimes better results than at a higher added amount.

Claims (10)

Claims

1. A process for the disinfection of a bacteria containing aqueous medium comprising the step of introducing into the aqueous medium hydrogen peroxide to provide a concentration selected in the range of from 2.5 x 10-6M to 3 x10-3M, a soluble copper salt in a concentration in the range of from 1 x 10-6M to 2 x 10-5M and a low molecular weight aliphatic alcohol in a concentration in the range of from 2.5x 10-5M to 2 x 10-3M.

2. A process according to claim 1 in which the hydrogen peroxide:copper mole ratio is within the range of 5.1 to 60:1.

3. A process according to claim 1 or 2 in which the hydrogen peroxide: alcohol weight ratio is in the range 2:1 to 1:2.

4. A process according to any preceding claim in which the concentration of hydrogen peroxide is from 10-4M, the concentration of copper is from 3x10-6M to 1.75x10-5M and the concentration of the alcohol is from 5x10-5M to 5x 10-4M.

5. A process.according to any preceding claim in which the alcohol is ethanol or n-propanol.

6. A process~according to any preceding claim in which the hydrogen peroxide is employed in conjunction with an O-acyl or N-acyl compound which interacts therewith to generate from the acyl group a peroxyacid, or the peroxyacid is employed instead of the hydrogen peroxide.

7. A process according to claim 1 in which the aqueous medium is effluent from an activated sludge or trickling filter secondary treatment of municipal sewage, or effluent from paper or food processing industries.

8. A process for disinfecting a bacteria containing aqueous medium substantially as described herein with respect to any of Examples 1 to 45 excluding any comparison.

9. A process for disinfecting an aqueous medium employing any novel feature disclosed herein, either alone or in combination with any other novel feature or known feature disclosed herein.

10. Disinfected water whenever obtained by a process as claimed in any preceding claim.