Dear Oliver, Microbiological ...

Dear Oliver,

Microbiological fouling in cooling systems is the result of abundant growth of bacteria on surfaces. Once-through and open or closed recirculating water systems may support microbial growth, A wide variety of bacteria can colonize cooling systems. Spherical, rod-shaped, spiral, and filamentous forms are common. Some produce spores to survive adverse environmental conditions such as dry periods or high temperatures. Both aerobic bacteria (which thrive in oxygenated waters) and anaerobic bacteria (which are inhibited or killed by oxygen) can be found in cooling systems.These bacteria are so strong and down the PH up to 6.0 and causing corrosion in piping system.These bacteria can choke the heat exchangers Tube.

Treatment of legionella bacteria

Biocide

At least two (2) types of biocides shall be used alternately on a weekly basis to prevent emergence of resistant strains of microorganisms.Chlorination is the best way to control bacteria.

Before setting up a biocidal water treatment programme, it shall be ensured that the system is clean.

1.  The ‘shot/slug dose’ method shall be implemented to prevent microbiological acclimatization. This involves the addition of the biocides, alternating them at suitable intervals, directly into the cooling tower basin using an automatic control system.

2. The biocide used to eliminate and control the growth of legionella bacteria shall comply with the following:

 (a) It shall not be a prohibited chemical in the Poisons Act for trade effluent discharge to a public sewer;

(b) It shall be effective against a wide range of micro-organisms (including all legionella bacteria) at the recommended dilutions, and its effectiveness supported by official independent reports.

(c.)It shall be proven to be effective when dosed in accordance to the manufacturer’s recommendations (frequency, dose strength, preparation);

(d) It shall have documentation available covering the safety and effectiveness of the product in recirculating systems;

(e) It shall not interfere with the method used for identification of legionella bacteria;

(f) It shall be chemically and physically compatible with processed water and neutral to piping materials.

The chemicals used and the subsequent end-products of the treatment programme shall be degradable with minimal hazards to the environment in the event of accidental spillage or through draining into effluent treatment plants.

Water sampling and bacteriological monitoring.

A regular testing programme for legionella bacteria (including total bacteria count) shall be carried out to check the efficacy of the water treatment regime at the following intervals:

Standard plate count - At least once a month.

Legionella bacteria count - At least once in every three months.

The water sample shall be taken before the dosing of biocide. If disinfection is carried out, the water sample shall be taken no less than 3 days after disinfection to ensure effectiveness of the treatment.