Method for eliminating legionellae from water of a cooling circuit, which is loaded with organic substances and inorganic particles

Abstract

A method for eliminating legionellae from water of a cooling circuit of industrial plants, in particular of a hot rolling mill, is disclosed. The water is loaded with organic substances and inorganic particles. In a further aspect, the use of bacteria for eliminating legionellae from a water of a cooling circuit of an industrial plant is disclosed.

Claims

1.-8. (canceled)

9. A method for eliminating legionellae from water of a cooling circuit of an industrial plant (2), the water being loaded with organic substances and inorganic particles, the method comprising: passing the water in a cooling circuit (3) through a separation device (5) for separating the organic substances and/or the inorganic particles from the water; cooling the water by passing the water through an open cooling tower (11) arranged downstream of the separation device (5); adding bacteria to the water, the bacteria being suitable for degrading the organic substances present in the water; and thereby forming a biological purification stage within the cooling circuit (3), such that, in a steady state, a legionellae limit value in the water of the cooling circuit of less than 100 CFU/ml is achieved.

10. The method of claim 9, wherein the industrial plant (2) is a hot rolling mill.

11. The method of claim 9, wherein the achieved legionellae limit value in the water of the cooling circuit is less than 70 CFU/ml.

12. The method of claim 9, wherein the achieved legionellae limit value in the water of the cooling circuit is less than 40 CFU/ml.

13. The method of claim 9, wherein the achieved legionellae limit value in the water of the cooling circuit is less than 10 CFU/ml.

14. The method of claim 9, wherein the achieved legionellae limit value in the water of the cooling circuit is less than 1 CFU/ml.

15. The method according to claim 9, wherein the bacteria are added to the water of the cooling circuit upstream of and/or within the separation device (5), and/or upstream of the cooling tower (11).

16. The method according to claim 9, further comprising: adding nutrients to the water of the cooling circuit upstream of the separation device (5) and/or upstream of the cooling tower (11) to promote growth of the added bacteria.

17. The method according to claim 16, further comprising: reducing a ratio of added bacteria to added nutrients over time.

18. The method according to claim 16, wherein the bacteria and/or the nutrients are provided in form of a granulate and/or a suspension and/or are added to the water of the cooling circuit in form of an aqueous solution.

19. The method according to claim 16, wherein the bacteria and/or the nutrients are provided in form of a granulate and/or a suspension, and wherein the bacteria in the granulate and/or the suspension are lyophilized bacteria.

20. The method according to claim 9, further comprising passing the water within the separation device (5) through a settling basin (6), a clarifying basin (7) and/or a filtration purification device (8).

21. The method according to claim 9, wherein the bacteria have different milieu requirements, namely anaerobic, anoxic and/or aerobic.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0027] FIG. 1 is a schematic illustration of a plant for eliminating legionellae from water of a cooling circuit loaded with organic substances and inorganic particles in one embodiment.

DETAILED DESCRIPTION

[0028] In the embodiment shown here, the plant 1 shown in FIG. 1 comprises a hot rolling mill 2 that is adjoined by a cooling circuit 3. The cooling circuit 3 comprises a plurality of aggregates, each of which is fluidically interconnected and will be explained in more detail below.

[0029] As shown, the hot rolling mill 2 is initially coupled to the cooling circuit 3, such that water of a cooling circuit loaded in the hot rolling mill 2 with organic substances, such as oils and greases, along with inorganic particles, such as scale in particular, is treated by the aggregates arranged in the cooling circuit 3 to such an extent that it can be fed directly back to the hot rolling mill 2. If the quantity of water of the cooling circuit should fall below a specific volume, additional fresh water can be added to the cooling circuit 3 via a fresh water inlet 4.

[0030] The plant 1 shown in FIG. 1 initially comprises a separation device 5 for separating the organic substances and the inorganic particles from the water of the cooling circuit of the hot rolling mill 2, such that a pre-purified water of the cooling circuit is obtained. As can be seen from FIG. 1, the separation device 5 comprises a plurality of components connected in series.

[0031] In the present embodiment, the separation device 5 comprises a settling basin 6 for separating a coarse fraction of a mixture of organic substances and inorganic particles, a clarifying basin 7 for separating an average size of the mixture of organic substances and inorganic particles and for sucking away free oil from the surface, and finally a filtration device 8, which generally comprises a plurality of filtration units.

[0032] It should be noted that, in the present embodiment, only two filtering units 9, 10 of the plurality of filtering units of the filtering device 8 connected in parallel are shown as examples. In the filtration device 8, a fine fraction of the mixture of organic substances and inorganic particles is separated. Both filtration units 9, 10 of the filtration device 8 are designed to be able to be backflushed and are connected to a gravel filter sludge buffer 14. In the present case, the filtration units 9, 10 are designed in the form of a gravel filter.

[0033] Furthermore, the plant 1 shown in FIG. 1 comprises an open cooling tower 11, via which the pre-cleaned water of the cooling circuit can be cooled. In the cooling tower 11, the pre-cleaned water from the cooling circuit is sprayed such that, among other things, water droplets are formed, which partly evaporate, then condense and cool down in the process. The cooled pre-cleaned water from the cooling circuit then obtained is returned to the hot rolling mill 2 via a main line 12.

[0034] Within the cooling circuit 3, the plant 1 further comprises a dosing device 13 for adding bacteria that are suitable for degrading the organic matter present in the water of the cooling circuit. In the present case, the bacteria are formed as lyophilized bacteria. The dosing device 13 can be arranged upstream of the separation device 5, as shown. Alternatively, the dosing device 13 can also be arranged within the separation device 5 upstream of the settling basin 6, upstream of the clarifying basin 7 and/or upstream of the filtration device 8 (not shown).

[0035] Nutrients that promote the growth of the added bacteria are also added to the cooling circuit 3 via the dosing device 13. The added nutrients promote the formation of a biocenosis by the bacteria and further favor their long-term existence.

[0036] Furthermore, it has proven advantageous if the bacteria are also added to the gravel filter sludge buffer 14, in which the fine scale is collected (not shown), via a further dosing device.

EXAMPLE

[0037] The bacteria used were pure cultures of specially oil-degrading and fat-degrading species with different milieu requirements (anaerobic, anoxic, aerobic), which are available from the applicant under the product name “Oilco-Bacteria.”

[0038] Bacteria present in the form of granules were dissolved in water. The granules consist of 1% by weight of the bacteria and 99% by weight of nutrients. The water was initially heated to a temperature comparable to the water of the cooling circuit. Then, the granules were added according to the instructions and the solution was prepared. After a maturing time of 3 to 6 h, the inoculation solution was added to the cooling circuit 3 in a distributed manner via the dosing device 13.

[0039] The bacteria added to the water of the cooling circuit have different environmental requirements. The settling basin 6 is anaerobic, the clarifying basin 7 is anaerobic, the filtration device 8 is anoxic aerobic and the cooling tower 11 is aerobic.

[0040] Due to the addition of the bacteria, a biocenosis formed in the entire cooling circuit 3 over the course of 2 to 8 weeks. After such incubation period, the biofilms were visibly reduced, which was reflected in the decrease of the legionellae bacterial count from originally over 100 CFU/ml to below 1 CFU/ml.

[0041] After the incubation period, to maintain the formed biocenosis, the nutrient concentration was increased and the concentration of newly added bacteria was decreased.

[0042] After an additional 6 weeks, a steady state condition was established, such that no resistant biofilms were detected in the cooling circuit 3, which is the breeding ground for legionellae. After an analysis of the water of the cooling circuit according to DIN EN 13098:2018, no legionellae bacterial count could be detected.

[0043] The hot rolling mill in which the method was tested produces approximately 1,400 t/a of sludge. Approximately 1,200 t/a of scale was dredged from the settling basin 6 and approximately 200 t/a of fine scale sludge was produced.

[0044] The COD content in the supernatant water of the settling basin 6 decreased from the original 60 mg/l to 30 mg/l and in the clarifying basin 7 from 48 mg/l to 6 mg/l.

[0045] The organic content of the coarse scale decreased from 280 mg/l to 35 mg/kg. In the fine scale sludge, the organic content amounted to 37% by weight and decreased to 6%.

[0046] A phosphate, nitrite, ammonium and nitrate content could not be detected in the water of the cooling circuit due to the detection limit. The pH value decreased due to anaerobic acid formation. As a result, the CaCO3 concentration was reduced, such that hardness, conductivity and salinity decreased. In the settling basin 6, there was a sight depth of approximately 1 m, which did not exist prior to dosing. The cleaning of the filtration units 9, 10, which was carried out regularly prior to dosing, usually monthly, was no longer necessary.

LIST OF REFERENCE SIGNS

[0047] 1 Plant [0048] 2 Industrial plant/hot rolling mill [0049] 3 Cooling circuit [0050] 4 Fresh water inlet [0051] 5 Separation device [0052] 6 Settling basin [0053] 7 Clarifying basin [0054] 8 Filtration device [0055] 9 Filtration unit [0056] 10 Filtration unit [0057] 11 Cooling tower [0058] 12 Main line [0059] 13 Dosing device [0060] 14 Gravel filter sludge buffer