Cooling Water Test Program Setup
The rapid and accurate feedback provided by LuminUltra’s 2nd generation ATP analyses make it an ideal tool for optimizing biocide treatment in a cooling water system. By monitoring ATP before and after biocide treatment, you can observe the effectiveness of the biocide as it kills the cells in a contaminated system.
Since industrial biocides kill microorganisms by a variety of mechanisms, the effect on ATP concentration may range from minutes to hours, depending on the type of biocide and its dosage. The main variables in a biocide treatment program are:
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Type of biocide – Active ingredients are sometimes alternated to minimize the chances of development of resistant microorganisms. For example, an oxidizing biocide may be used routinely with a weekly shock treatment of non-oxidizing biocide.
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Application frequency – Some systems treat using a slug feed approach while others treat continuously.
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Biocide dosage – This depends on factors such as the size of the system, the degree of microbial content present, and the type and application frequency as described above.
By changing these variables and observing the effect on ATP, the optimum program can be defined. Here are some guidelines for effective microbial growth control using ATP monitoring:
| Process |
Parameter |
Good Control |
Preventative Action Required |
Corrective Action Required |
| Drinking Water |
cATP (pg/mL) |
< 0.5 |
0.5 to 10 |
> 10 |
| Cooling Water (Non-Oxidizing Biocide) |
cATP (pg/mL) |
< 100 |
100 to 1,000 |
> 1,000 |
| Cooling Water (Non-Oxidizing Biocide) |
cATP (pg/mL) |
< 10 |
10 to 100 |
> 100 |
| Fresh or Reuse Water |
cATP (pg/mL) |
< 5 |
5 to 100 |
> 100 |
NOTE: The reason why different targets are suggested for oxidizing and non-oxidizing biocides is because oxidizing biocides tend to achieve a better kill but frequency dosing is required. Non-oxidizing biocides maintain a residual for longer periods, but it is rarely feasible to attempt the same level of disinfection as oxidizing biocides achieve.
Sampling Locations
The figure below shows a process flow diagram of a typical cooling system as well as the sampling locations where ATP monitoring can be applied:
If the make-up water to the cooling system has a high microbiological content, it can provide major problems from the onset. Often, biocide can be added at this point to treat incoming water and subsequently decreasing the microbial load on downstream components.
If possible, sample from a point just prior to when the hot water is discharged to the cooling stage. Comparing feed water results to this point will show the accumulation of microbial growth throughout the system.
If water is being cooled by being spread over surfaces, pathogen growth may occur on the surfaces of the media. Mists that are produced at this point are a significant health risk (i.e. Legionella) if not closely monitored and controlled.
Cooling water collected in the basin is usually at its warmest and therefore holds the highest risk for pathogen growth. It is also the location that best depicts how microbial growth has propagated through the cooling system from start to finish.
Continuous Feed Systems
Routine monitoring of cooling water at various points in a continuous-feed biocide treatment program should reveal if the dosage used is sufficient to keep microbial growth under control. In industrial cooling systems, biofouling problems (e.g. microbially influenced corrosion, loss of heat exchange efficiency, plugging) typically occur when ATP levels rise above 1000pg/ml, although some systems may experience problems at lower biomass concentrations. Based on the correlation between ATP and successful operation, an index can be derived that should not be exceeded for successful operation.
Shock Feed systems
The rate of biocide decay depends on a number of factors, including:
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Hydraulic retention time of the system
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Inherent biocide stability in the application environment
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Biocide reaction tendencies with other chemical components
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Biocide kill efficiency
When the concentration decreases to a critical level, it no is longer effective as a biocide and may even act as food for the surviving microorganisms. Therefore, an important aspect of optimizing a biocide treatment program is determining the effective life of the biocide after its addition to the system. This can be effectively determined using ATP monitoring.
For an overview of how to simulate a shock feed scenario and determine biocide treatment requirements, click below.
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Take a cooling water sample and test for ATP, then add biocide. Refrigerate this sample.
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Take samples at various time periods following biocide treatment.
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Add a portion of sample from step (1) to the samples in step (2) to a concentration of ~5% of total volume and incubate at room temperature. Incubating at 28-30°C is preferable. Ideally, the incubation temperature would be at the same temperature as the process from which the samples are taken.
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After a suitable period to allow the surviving microorganisms to multiply, test the inoculated samples for ATP. If biocide is still active, ATP should not increase during the incubation period.
NOTE: Usually several days of incubation is required for low nutrient environments. Adding a spike of 100-200 mg/L sterilized yeast extract may be useful to ensure multiplication of the microorganisms.
This strategy may be done in several vessels using various biocide dosages.
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Test Program Setup 
