Investigation of microbiological agents in vehicle washing facilities

Status:

completed 07/2003

Aims:

For both ecological and economic reasons, virtually all commercial and company vehicle washing facilities involve water-based systems. The vehicle wash water is recycled by means of physical, chemical and/or biological processes, and re-used. The chief purpose of processing is the removal of dirt particles, oil residue and other contaminants. The recycled water is classified as industrial water, or as non-drinkable water under DIN 4046, "Water-supply; terms; DVGW code of practice", and is thus inevitably subject to colonization by microorganisms. Since the risk cannot be excluded of the vehicle wash water also containing potential pathogens which might constitute a potential health risk to employees, if present in sufficiently high concentrations and with access to an intake route, the present research project was launched. The aim of the project was to measure the quantitative and qualitative microorganism load in the vehicle wash water and in the air, to assess this load as far as possible, and to identify suitable measures. The results of the research project are to be of value to the business operator as a guide for the performance of risk analyses in accordance with the Biostoffverordnung (BiostoffV), the German transposition of EU Directive 2000/54/EC on the protection of workers from risks related to exposure to biological agents at work.

Activities/Methods:

A total of 31 commercial and company vehicle washing facilities for passenger cars and commercial vehicles (heavy goods vehicles and buses) were studied. Owing to the technical design of vehicle washing facilities, only gantry-type facilities (n = 23, including one special design for trams) and drive-through washing facilities (n = 8) were employed for the studies. The most common types of equipment for recycling of the wash water were sand-filter systems with flocculation. 13 facilities were operated with disinfection measures (primarily ozone or hydrogen peroxide), 18 without. In nine facilities employing biological recycling measures, samples were taken in order to determine whether this form of recycling introduced further microorganisms into the system, or whether the disinfection measures which could not be employed in these facilities resulted in higher overall colony counts being detected in the wash water. Sampling and microbiological analysis were performed by a number of institutes: the BG Institute for Occupational Safety and Health (BIA) in Sankt Augustin, the Regional Centre for Occupational Health and Safety (LAfA) of North Rhine-Westphalia in Düsseldorf, and a number of laboratories to which the tasks were outsourced. In the summer of 2000, quantitative measurements of the microbial count (bacteria and mould fungi such as yeasts) were first performed on water samples taken from the reservoirs of a large number of gantry-type wash facilities for passenger and heavy goods vehicles prior to and following recycling. Air samples were taken as part of this series of measurements only in selected facilities, for the purpose of studying the measurement technique. Based upon the results from this series of measurements, both comparative studies involving air sampling with three different measurement systems, and qualitative and quantitative studies of water samples, were subsequently performed on a small number of selected vehicle wash facilities in July and August 2001. Results are available from qualitative studies of the fungal content of the air samples. The studies particularly focused on medicinally relevant pathogenic bacteria in Risk Category 2. Three different methods were employed for air sampling: filtration (GSP total dust sampling), impaction (MAS 100), and impingement (AGI-30). The total colony counts of bacteria, moulds and yeasts from water and air samples, and the colony counts of selected organism groups, were determined, depending upon the sampling method, by direct placing of the filter onto solid agar medium (GSP, direct method), plating-out of the (re-)suspended microorganisms (GSP, indirect method, AGI-30) on solid agar media, or incubation of the directly loaded, solid agar media (MAS 100) under defined laboratory conditions and counting of the established colonies. The colony counts were determined as the number of colony-forming units per aliquot of the medium under consideration (cfu/m³ air or cfu/ml). Performance of legionella analysis was contracted to another laboratory (cultural detection and serological differentiation). The abiotic parameters of temperature and pH value of the water samples were determined, and the appearance and odour evaluated. Both the temperature and relative atmospheric humidity of air samples were also measured.

Results:

Vehicle wash water is industrial water (recycling water) which neither is, nor is required to be, of bathing or drinking water quality. The results of the studies do not show any particular water treatment method to be superior to others. In the majority of cases, an improvement was observed in the odour and appearance of the wash water. This does not however enable any conclusions to be drawn with regard to microbial infestation; water without any conspicuous appearance or odour may still be microbially contaminated. Following processing of the wash water in vehicle washes, the total colony count for bacteria lay in the region of 10⁵ to 10⁶ CFU/ml. Moulds are not a significant factor for the microbial load in recycling water in vehicle wash systems, and yeasts only of limited significance. The microorganisms in the vehicle wash water were primarily bacteria (see above) assigned to Risk Groups 1 and 2. Salmonella and legionella, which owing to their potential health hazard are the critical microbes in aqueous systems in vehicle washes, were not detectable in any of the samples. The yeast Candida albicans was likewise not detected in any of the samples studied. The state of maintenance evidently has a significant influence upon the total microorganism count in the service water of a vehicle washing plant. Inadequately serviced filter systems, in particular, may lead to increased growth of microorganisms following water recycling. In facilities employing biological recycling (e.g. aeration, activated sludge tanks, contact beds), the colony count was unchanged by recycling, or was reduced slightly even in the absence of further measures for disinfection. Infestation of the wash water by further microorganisms did not occur. Whereas virtually no difference was noted in the total colony count for the mould fungi between the working area of the wash facility and the outside atmosphere, the total colony count for the bacteria was greater in the atmosphere of the working area than in the outside area by a factor of approximately ten. The working area of the wash facility thus exhibits substantial bacterial contamination of the breathing air. Based upon the results of atmospheric measurements, it may be assumed that the wash process principally results in bacteria from the wash water being transferred to the air in the form of bioaerosols, whereas the mould fungi found inside the facility are transferred for the most part from the outside atmosphere. The results of the study do not show any particular method of microbial reduction to be superior. The use of microbicide measures such as UV radiation, ozonization or the addition of H₂O₂ or preservatives does not necessarily bring about the desired reduction in the microorganism count. Under the BioStoffV, work performed in vehicle wash facilities (e.g. maintenance, repair and cleaning work) where contact exists with microbially contaminated wash water constitutes activity involving incidental contact with Risk Group 1 and 2 microorganisms. Activities associated with strong aerosol formation or performed in areas of strong formation of mist from industrial water are classified under Protective Level 2. All other activities relating to normal operation of the wash facility can be assigned to Protective Level 1.

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