Key messages

  • Cooling tower model operational programs include several elements that must be included.
  • Elements are a maintenance program, a chemical program, bacterial testing, service frequency, tower cleaning and service reports.
  • The Public Health and Wellbeing Regulations 2009 specify requirements for many of these elements.

Scope of work

The maintenance program includes:

  • treatment of the cooling tower system for control of corrosion, scale formation and fouling, and to minimise microbiological growth (ensuring that it remains at safe levels)
  • testing of the water for heterotrophic colony count (HCC) (also called total bacteria or total plate count)
  • testing of the water for Legionella
  • monitoring of the cooling tower system structure itself to ensure that the cooling tower equipment is operating effectively, and that the cooling tower system is safe and free from hazards.

Chemical program

The chemical program must incorporate use of:

  • a corrosion and scale inhibitor
  • at least one biocide (preferably two, used in rotation)
  • a biodispersant to help remove any biofilm in the system.

Bacterial testing

Bacterial testing is required as follows.

Heterotrophic colony count

  • Sampling for HCC in accordance with AS/NZS 3666.3 for sample collection, and AS 2031 for selection of containers and preservation of water samples for microbiological testing.
  • Analysis of water samples for HCC in accordance with AS 4276.3 by a laboratory accredited by the National Association of Testing Authorities.
  • Analysis commenced within 24 hours of the sample being taken (101).

Legionella


  • Sampling for Legionella in accordance with AS/NZS 3666.3 for sample collection, and AS 2031 for selection of containers and preservation of water samples for microbiological testing.
  • Transport of the samples to the laboratory as soon as possible.
  • Testing for Legionella by a laboratory in accordance with AS/NZS 3896 (Waters – Examination for Legionella spp. including Legionella pneumophila) by a laboratory accredited by the National Association of Testing Authorities.

Reporting

Reporting of all results must include:

  • for any results that exceed the limits set by legislation or this contract (whichever is more stringent), immediate notification by fax or email (102), and a follow-up telephone call to confirm receipt
  • emailing of a copy of all results (103)
  • availability to discuss results, either by telephone or on-site, as appropriate.

The Public Health and Wellbeing Regulations 2009104 specify the following with regard to HCC:
1. Within 24 hours of receiving a report from a laboratory that any sample of water taken from the cooling tower system has a heterotrophic colony count exceeding 200,000 colony forming units per millilitre, the responsible person must ensure that the following procedure is implemented:
a. the water of the system must be manually treated with additional quantities of biocide or with an alternative biocide; and

b. the water treatment program, tower operation and maintenance program of the system must be reviewed; and

c. any faults must be corrected; and d. any changes necessary to prevent a re-occurrence of those faults must be implemented.

2. Between 2 and 7 days after the water has been treated under subregulation (1), the responsible person must ensure that a further sample of the recirculating water of the system is taken and is delivered to a laboratory for testing and reporting on for heterotrophic colony count.

3. Within 24 hours of receiving a report from a laboratory that a sample taken in accordance with subregulation (2) has a heterotrophic colony count exceeding 200,000 colony forming units per millilitre, the responsible person must ensure that the water of the cooling tower system is disinfected.

4. Between 2 and 7 days after the water has been disinfected under subregulation (3), the responsible person must ensure that a further sample of the recirculating water of the cooling tower system is taken and is deliv-ered to a laboratory for testing and reporting on for heterotrophic colony count.

5. If, after following the procedure in subregulations (1), (2), (3) and (4), the heterotrophic colony count still exceeds 200,000 colony forming units per millilitre, the responsible person must:

a. ensure that the steps in subregulations (3) and (4) are repeated until the heterotrophic colony count does not exceed 200,000 colony forming units per millilitre in 2 consecutive water samples taken approximately one week apart; or

b. close the cooling tower system until the problem has been remedied.

These Regulations are summarised in Figure A1.

Figure A1: Flowchart describing actions to be taken if the HCC is more or less than 200,000 CFU/ml at the monthly sample. If more, a disinfection protocol and retesting is required. This is repeated until the HCC is less than 200,000 CFU/ml.Figure A2: Flowchart describing alternative actions to take if the HCC is more or less than 200,000 CFU/ml at the monthly sample. The protocol is similar to that described in Figure A1, except that the water is treated with a biocide immediately after taking a sample.Figure A3: Flowchart describing actions to take after Legionella sampling, which is done quarterly. If Legionella is detected, the system must be disinfected and resampled. The department must be notified of three consecutive Legionella detections.

Figure A1: Standard HCC sampling and response

The Regulations further state:

1. The responsible person is not required to comply with subregulations (1) to (5) if:

a. during the period between the sample being taken for the purpose of regulation 56(2) and the receipt of a report from a laboratory indicating that the cooling tower system has a heterotrophic colony count exceeding 200,000 colony forming units per millilitre, the system was manually treated with additional quantities of biocide or an alternative biocide; and

b. within 72 hours of receiving the report that any sample of water taken from the cooling tower system has a heterotrophic colony count exceeding 200,000 colony forming units per millilitre, the responsible person–

  • reviews the water treatment program, tower, operation and maintenance program; and
  • corrects any faults and makes changes necessary to prevent a re-occurrence of those faults; and

c. within 7 days of receiving the report in subregulation (6)(b), the responsible person ensures that a further sample of the recirculating water of the system is taken and is delivered to a laboratory for testing and re-porting on for heterotrophic colony count;

d. within 24 hours of receiving a report that a sample taken in accordance with subregulation (6)(c) has a heterotrophic colony count exceeding 200,000 colony forming units per millilitre, the responsible person –

  • ensures the water in the cooling tower system is disinfected; and
  • between 2 and 7 days after the water has been disinfected in accordance with paragraph (i), ensures that a further sample of the recirculating water of the system is taken and is delivered to a laboratory for testing and reporting on for heterotrophic colony count;

e. after following the procedure in subregulation (6)(d) the heterotrophic colony count continues to exceed 200,000 colony forming units per millilitre, the responsible person –

  • ensures the steps in subregualtion (6)(d) are repeated until the heterotrophic colony count does not exceed 200,000 colony forming units per millilitre in 2 consecutive water samples taken approximately one week apart; or
  • closes the cooling tower system until the problem has been remedied.

These Regulations are summarised in Figure A2.

Figure A2

 
 
 
 
 
 
 
 

 

Figure A2: Alternative HCC sampling and response


The Public Health and Wellbeing Regulations 2009105 specify the following with regard to Legionella:

1. Within 24 hours of receiving a report that Legionella has been detected in a water sample taken from a cooling tower system, the responsible person must ensure that the following procedure is implemented :

a. the cooling tower system must be disinfected; and

b. the water treatment program, tower operation and maintenance programs of the system must be reviewed; and

c. any faults must be corrected and any changes necessary to prevent a re-occurrence of those faults must be implemented.

2. Between 2 and 7 days after the disinfection required by subregulation (1)(a) has been completed, the responsible person must ensure that a further sample of the recirculating water of the system is taken and is delivered to a laboratory for testing and reporting on for Legionella.

3. Within 24 hours of receiving a report that Legionella has been detected in a sample taken in accordance with subregulation (2), the responsible person must ensure that the water of the cooling tower system is disinfected, cleaned and re-disinfected.106

4. Between 2 and 7 days after the disinfection required by subregulation (3) has been completed, the responsible person must ensure that a further sample of the recirculating water of the system is taken and is delivered to a laboratory for testing and reporting on for Legionella.

5. If, after following the procedure in subregulations (1), (2), (3) and (4), Legionella is still detected, the responsible person must:

a. ensure that the steps in subregulations (3) and (4) are repeated until Legionella is not detected in 2 consecutive water samples taken approximately one week apart; or

b. close the cooling tower system until the problem has been remedied.

These Regulations are summarised in Figure A3.

1. If, while following the procedure in this regulation Legionella is detected in 3 consecutive water samples taken from the same system, the responsible person must notify the Secretary of the detection of the presence of that organism:

a. immediately by telephone; and

b. by notice in writing within 3 days.

 Figure A3

Figure A3: Legionella sampling and response


Service frequency

The service frequency shall be as specified in the operational plan.

The service shall ensure that:

  • water quality is checked
  • chemical dosing tanks are refilled
  • empty tanks are removed from the site
  • dosing and control equipment is checked, and is operating correctly; if problems are observed, remedial action will be taken to fix the problem
  • the wetted components will be inspected, and the general integrity of the system (including cleanliness) will be checked; action will be taken to remedy any problems (107).

In addition to the service frequency, the corrosion coupons (metal test plates) will be checked every 3 months for signs of corrosion. The corrosion coupons must be of the same types of metal as those used in the cooling tower system, and are to be immersed in the system water and checked as above (108).

All samples of water to be taken for bacterial testing (HCC and/or Legionella) must be taken before any addition of chemicals.

Tower cleaning

Tower cleaning shall be in accordance with the operational program (109).

The tower cleaning process should be as follows:

  1. Thoroughly clean the internal shell, fill and tower sump by brushing and/or hosing all surfaces.
  2. Remove all debris.
  3. Thoroughly clean internally and externally all water filters, strainers, separators, water nozzles and fittings associated with the water distribution system.

Service report

A service report must be completed at the time of each visit, detailing all test results, observations and actions taken, including repairs, maintenance and testing work. The information to be provided as a minimum following each visit is shown in Appendix 6.

A copy of the service report (110) is to be provided to the responsible person, and any points of significance are to be discussed with the contract manager.

Footnotes

101. In some remote areas, it is not always possible to achieve this objective, but analysis must still take place in the shortest practicable time. Contact should be made with the testing laboratory to determine the best transport option.

102. Where the sampling and maintenance have been outsourced to one company that then subcontracts to another company for microbiological analysis, it is important that you obtain a copy of the testing laboratory’s results rather than a report from the maintenance contractor.

103. Where available

104. Regulation 57

105. Regulation 58

106. A chlorine-compatible biodispersant must be added to the recirculating water, and the system must then be disinfected by dosing the water with a chlorine-based biocide, equivalent to 10 mg/L of free chlorine for at least 1 hour, while maintaining a pH of between 7.0 and 7.6. A bromine-based compound may be used equivalent to at least 20 mg/L of free bromine for at least 1 hour, while maintaining the pH of the water between 7.0 and 8.5.

107. Insert other requirements

108. You may need to seek independent specialist advice about the risk of corrosion in your system and the best ways to control and monitor it.

109. Insert desired cleaning frequency (e.g. 6-monthly).

110. The Public Health and Wellbeing Regulations require the responsible person for the cooling tower system to keep records of all microbiological test results, as well as maintenance and corrective activities undertaken in relation to the system during the preceding 12 months. These records must be produced for inspection at the request of authorised officers from the department. Electronic record keeping is becoming more popular, and the department considers this to meet the requirement of the Regulations, provided that these records can be produced on request.