Legionella Control Programs

Effective Legionella Control Requires an Effective Biofilm Control Program

Outbreaks in Legionnaires’ Disease such as the one in the South Bronx in August 2015 highlight the importance of having an effective Legionella Control Program. Legionella bacteria grow in biofilms in building water systems, where they are protected from the disinfecting action of oxidizing and non-oxidizing biocides.

The importance of biofilm control is highlighted in the following excerpt from Biofilms: The Stronghold of Legionella Pneumophila by M. Adbel-Nour, C. Duncan, D.E. Low and C. Guyard (Toronto); Int. J. Mol. Sci. 2013, 14, 21660-21675.


The evidence from decades of scientific research is very clear. Legionella pneumophila resides primarily in biofilms in building and industrial water systems.

Priscilla Declerck’s article, Biofilms: the environmental playground of Legionella pneumophila (Society for Applied Microbiology and Blackwell Publishing Ltd, Environmental Microbiology, 12, 557-566) summarizes several research studies involved with the mechanisms and factors that affect the biofilm life cycle of L. pneumophia. Declerck notes:

For further reading on Legionella in biofilms see “Replication of Legionella pneumophila in Biofilms of Water Distribution Pipes”, by Priscilla Declerck, Jonas Behets, Anca Margineanu, Vincent van Hoef, Brenda DeKeersmaecker, and Frans Ollevier. Microbiological Research 164 (2009) 593-603.

These articles illustrate that in order to deliver effective Legionella control, it is absolutely essential that your biocide program effectively controls biofilms!

AMSA’s BCP 1015 (DTEA II®) is a field-proven organic deposit penetrant/dispersant which has been used with oxidizing and non-oxidizing biocide programs for more than 18 years to provide an effective Biofilm Control Program in industrial water systems.

BCP® 1015 has been used effectively in the hyper-halogenation Wisconsin Emergency Protocol for Legionella cleanup and control, and can be used subsequent to cleanup and disinfection in an ongoing maintenance program with biocides to control biofilm buildup throughout the cooling system. See Legionella case study.


ASHRAE Standard 188-2015: Legionellosis: Risk Management for Building Water Systems

A key document from ASHRAE that establishes minimum Legionellosis risk management requirements for building water systems was published in June of 2015 (ANSI/ASHRAE 188-2015). Many government buildings and municipalities concerned with Legionella control are mandating building managers follow the guidelines outlined in this document.


Four important documents cite the importance of using a “dispersant” in conjunction with biocides for clean-up and control of Legionella.
Cooling Tower Institute (CTI) WTB-148 (2008)
Legionellosis Guideline: Best Practices for Control of Legionella

“Legionella pneumophila grows within biofilms and within protozoa acting to shield L. pneumophila from concentrations of biocides that would otherwise kill or inhibit L. pneumophila when freely suspended in water.”

“Emergency Disinfection Procedure:

  1. Add a biocide sufficient to achieve 25 to 50 ppm of free residual halogen.
  2. Add an appropriate biodispersant (and antifoam if needed).
  3. Maintain 10 ppm free residual halogen for 24 hours…
  4. Drain the system…
  5. Refill the system and repeat (the treatment)…
  6. Inspect after the second drain-off.
  7. If a biofilm is evident, repeat the procedure.
  8. When no biofilm is obvious, mechanically clean the tower fill, tower supports, cell partitions, and sump.”
OSHA Technical Manual, Section III Chapter 7
Section III, Chapter 7. Legionnaires Disease

Clean and disinfect the entire cooling system including attached chillers and/or storage tanks (sumps) following the “Wisconsin (Emergency) Protocol” , as follows:

  1. “Shock” treat cooling tower water at 50 ppm free residual chlorine.
  2. Add dispersant.
  3. Maintain 10 ppm chlorine for 24 hours.
  4. Drain system.
  5. Refill and repeat steps a through d.
  6. Inspect system for visual evidence of biofilm. If found, repeat steps a through d.
CDC Procedure for Cleaning Towers infected with Legionella
  1. Add fast-release, chlorine-containing disinfectant in pellet, granular, or liquid form, … to achieve initial free residual chlorine of 50 mg/L
  2. Add dispersant simultaneously with or within 15 minutes of adding disinfectant.
  3. After adding disinfectant and dispersant, continue circulating the water through the system. Add chlorine as needed to maintain FRC at > or = 10 mg/L for 24
  4. Drain the system. Refill system with water and repeat procedure
Legionella and the Prevention of Legionellosis (2007)
  1. Add fast-release, chlorine-containing disinfectant in pellet, granular, or liquid form, … to achieve initial free residual chlorine of 50 mg/L
  2. Add dispersant simultaneously with or within 15 minutes of adding disinfectant.
  3. After adding disinfectant and dispersant, continue circulating the water through the system. Add chlorine as needed to maintain FRC at > or = 10 mg/L for 24
  4. Drain the system. Refill system with water and repeat procedure

Geothermal Electric Power

BCP® 5000 Series Products offer a solution to sulfur deposition issues that often plague geothermal cooling towers in electric power plants

Geothermal energy systems experience a number of unique operational problems. Fluids produced from geothermal reservoirs include steam, brine and a variety of non-condensable gasses (CO2, H2S, CH3, N2, etc.). In water cooled systems with direct contact condensers, elemental sulfur fouling in the cooling system can be a significant problem.

Source: http://www.energy.gov

The pictures below illustrate geothermal power plants with severe sulfur deposition that causes frequent shut-downs for cleaning.  This severe sulfur deposition reduces system efficiency resulting in reduced mega-watt output from the plant.

Sulfur deposit accumulation in flowlines.
Sulfur deposition in nozzle orifice and on diffusion ring causes poor water distribution across cooling tower fill.
Sulfur accumulates in damaged fill beneath fouled spray nozzles.
Sulfur deposits in stainless steel steam scrubber system.

Sulfur deposits in direct contact condensers reduce efficiency of the geothermal steam condensation process.

Sulfur deposits released from flowlines (left) and expelled from spray nozzles (right) following BCP® 5000 series chemistry.

BCP® 5000 Series Products (containing DTEA II®) are well known as organic deposit penetrants and dispersants. In rigorous testing in large geothermal plants in Mexico and the Philippines, DTEA II® has been shown to be the only chemistry effective in removing pre-existing hard elemental sulfur deposits, and in preventing the formation of new elemental sulfur deposits.

IR Thermography clearly shows better hot & cold temperature water mixing in a geothermal electric power plant cooling tower located in Mexico.

Click here, or on the images below, to read more about what is shown using Infra-red Thermography in the images.

Comfort Cooling

AMSA BCP® products keep comfort cooling water systems working efficiently

BCP® 1000 and 2000 Series liquid products work within a complete chemical treatment program to maintain clean comfort cooling water systems that operate at peak cooling efficiency.  Used in conjunction with a registered biocide, AMSA BCP® chemistry controls microbial biofilms and minimizes the risk of the presence of pathogens in cooling systems.

 Cooling tower before DTEA II®

Cooling towers that provide air conditioning to buildings need scheduled cleaning and regular maintenance.  In fact, Legionella outbreaks have been reported in cooling towers that service industrial and commercial buildings.  AMSA BCP® liquid products make cooling tower disinfection programs more effective.  The addition of BCP 1015BCP 2430, or BCP 2175 before dosing with an oxidzing or non-oxidizing biocide help the biocide penetrate biofilm and better disinfect cooling towers during cleaning procedures.  When AMSA BCP products in liquid or solid form are used regularly in a cooling tower maintenance treatment program, the cooling water systems are kept clean and biological control is more easily achieved.

Cooling Tower after DTEA II® Clean-up

DTEA II® tablets are specifically designed for maintaining small and medium sized cooling systems.  These tablets are ideal for treating systems on a monthly service plan.  They are also more convenient than liquid chemicals for treating roof-top cooling towers.

AMSA BCP® liquid 1000 and 2000 series products are well suited to clean up fouled comfort cooling towers.  The before and after pictures above highlight a comfort cooling tower in Las Vegas that was cleaned with DTEA II® (BCP® 1015).

AMSA BCP® Liquid and DTEA II Solid Slow Release Tablets are perfect solutions to maintain small, hard to reach comfort cooling towers, such as building towers located on a rooftop.

Small comfort cooling towers in hard-to-treat areas need maintenance too!

Process Cooling

Large or Small Process Cooling Water Applications are Perfect for AMSA BCP® Chemistry

AMSA BCP® 1000, 2000, & 3000 series products have been successfully used to provide penetration and dispersion of organic deposits in order to clean and maintain clean surfaces in large and small process cooling systems.  BCP® chemistry in liquid formulations can be slug dosed, pumped semi-continuously, or added to an all-in-one drum formulation.  Solid slow release DTEA II® tablets provide continuous treatment to control fouling, corrosion and scale in small and medium sized systems.

SubstanceThermal Conductivity
(W m-1K-1)
CaCO32.6
CaSO42.3
Ca3(PO4)22.6
Fe22.9
Analcite1.3
Biofilm0.6

The impacts of biofilm on heat exchanger efficiency are dramatic.  The following excerpt from the Influence of Fouling biofilim on Heat Transfer clearly explain the negative impact biofouling has on heat exchanger efficiency.

“Bacterial biofilms may also foul heat exchange equipment, especially after a process leak or influx of nutrient. The sudden increase in nutrient in a previously nutrient-limited environment will send bacterial populations into an accelerated, logarithmic growth phase. The biofilms that develop will then interfere with heat transfer efficiency. Table 1 demonstrates the thermal conductivity of a variety of deposit-forming compounds compared to biofilm. A lower number indicates a greater resistance to heat transfer (Characklis, W.J. and Marshall, K. C., Biofilms, John Wiley and Sons, 1990, pp. 316.).”


Cooling Tower Clean-up

An 800 ton CT at a detergent plant was allowed to become severely fouled.  The approach temperature was 4 times above normal.

165 ppm of BCP® 2175 was applied in a slug dose into the sump. In 11 minutes a field technician took this video.

By the end of the second day of the clean-up procedure approach temperatures returned to normal at 3.5 degrees Farenheit!

Video of Cooling Tower Clean-up taken 11 minutes after BCP® 2175 was dosed into a heavily fouled system.

Keeping a Chiller Clean

A Midwest plastic injection molding plant used small mobile chillers to produce low temperature chill water to chill the molding process.

Biofilm formation on the heat exchange surfaces in the chiller caused poor cooling and led to numerous production problems.

BCP® 1015 was dosed at 12 ppm once per week along with a few ppm of biocide.  Downtime due to condenser fouling was eliminated!

Chiller surface coated with biofilm.
Chiller surface kept clean with BCP® 1015.