Automated dosing system blocks legionella

Like evaporation cooling systems and cooling towers, wet dust collectors can be the source of hazardous legionella. To eliminate such a risk for the respective personnel the 42nd BImSchV obliges the operators of such installations to maintain a high degree of transparency and to conduct regular, time consuming and costly controls. The dosing system RDS-pH from Rösler has proven to be a highly effective and cost-efficient alternative to these controls. In combination with a specially developed additive it automatically maintains the pH value of the process water above a level of 10 and, thus, prevents the formation of legionella.

The process water in cooling towers and evaporation cooling systems is an ideal breeding ground for legionella and other microorganisms. The same is true for wet dust collectors used for neutralizing the explosive dust created during shot blasting operations with work pieces made from aluminum and other non-ferrous metals. Since the water is sprayed, aerosols containing legionella can contaminate the environment around the equipment and become a health hazard for the personnel working nearby. With the 42nd administrative order regarding the federal emission protection law of Germany (42. BImSchV), in effect since August 2017, comprehensive and strict obligations for the operators of such systems were imposed. For example, their operation must be reported to the authorities, and the process water must be analyzed by an approved test lab during the startup phase.

Regular controls during operation
According to these regulations, an operating log must be maintained, in which the results of the required regular bi-weekly internal microbiological tests for the presence of legionella are documented. The results of tests conducted by an approved external test lab every three months must also be recorded. Compliance with these requirements can be quite costly! Violations of the 42nd BImSchV regulations and missed deadlines are punishable as legal infractions of the law.

Always on the safe side with an automatic dosing system
The BImSchV provisions also describe ways to avoid the complicated and costly controls. The regulations do not apply to operators who consistently maintain a pH value of 10 or higher in their process water. However, irrespective of this, an operator log must be maintained and kept up-to-date. For this purpose Rösler has developed the dosing unit RDS-pH 10 and additive RST-P1 allowing the automatic compliance with the BImSchV provisions. The dosing unit, maintaining the pH value of the process water in the required alkaline range, can be connected as stand-alone system to practically any wet dust collector regardless of the manufacturer. It is equipped with a measuring device that continuously monitors the pH value. As soon as the pH level falls below 10, a certain amount of additive is injected to increase the pH value. This prevents the formation of legionella consistently and reliably. The measured values are transferred from the dosing unit to a USB memory drive. The data can then be easily analyzed and visualized with a special Excel tool. This procedure is in full compliance with the requirement to maintain an operating log.

Improved safety and cost-efficiency
All these benefits convinced Emanuele Cassataro, manager of the die-casting department at the GSB Aluminium GmbH to install the dosing unit. This company, located in Wuppertal, Germany, is utilizing casting, forging and friction welding technologies to make aluminum components for various industries, such as automotive, machine building and medical engineering. About 80 percent of the die-castings made from a variety of aluminum alloys and weighing between five grams and eight kilograms undergo a shot blasting process. A side effect of this operation is the creation of explosive dust that is neutralized by a wet dust collector. Emanuele Cassataro explains: „Initially we had to replace the process water on a weekly basis to prevent the formation of legionella. Naturally, this was quite costly. Therefore, we looked for a simple and inexpensive solution to comply with the regulations of the 42nd BImSchV”. During his search the department manager found out that by increasing the pH level of the process water the formation of legionella can be prevented. Subsequently, the company chose the dosing system RDS-pH 10 from Rösler. Besides its excellent functionality and high cost-efficiency another decision factor for this dosing unit was that the shot blast machine and wet dust collector were also supplied by Rösler.
„We prepared a detailed documentation of the technical features of the dosing system for the authorities. For this reason we must no longer conduct internal measurements nor have external test labs conduct any controls”, reports Emanuele Cassataro. In the meantime the dosing system has been in operation for about 18 months. Since its installation the process water did not have to be replaced once. Fresh water is automatically added to offset losses due to evaporation and sludge discharge. The continuous pH measurements of the dosing system and the injection of a suitable amount of additive ensure that the pH value of the process water is always above 10. The department manager concludes: „I am very pleased with this solution. On the one hand the risk of legionella formation has been reliably eliminated. And on the other hand the entire shot blasting operation has become more economical because we no longer have to replace the process water and conduct costly controls. The system works so well that in September 2021 we purchased a second Rösler dosing unit for a wet dust collector from another supplier”.