Processes for purifying workplace air that is contaminated with microorganisms: an investigative preparatory study on the technical solutions of separation and disinfection

Outline of reasons and objectives
Exposure to bioaerosols (bacteria, moulds, and sub-products or fragments of micro-organisms) present in the air at workstations has been established in numerous occupational sectors. In certain employees, inhaling airborne biological agents has been associated with occurrence of respiratory disorders. Technical solutions have been proposed for preventing such biological risks, in particular air treatment systems designed to reduce the levels of bioaerosol concentration in the workshops or at the workstations. And yet, knowledge about the efficacy of such systems, their harmlessness and their consistency with biological risk prevention is not yet stabilised and does not make it possible to put forward specific recommendations. Such expertise is however necessary in order to be efficient in answering questions from companies or CARSATs (Regional Occupational Health and Pension Insurance Funds) who are faced with significant exposures. In order to study the air treatment solutions that are most appropriate for the bioaerosols that can be generated in workplace air, an preliminary study was launched. The objectives were to acquire the necessary knowledge and a critical assessment of the conceivable treatment processes for treating atmospheres contaminated by bioaerosols, and to determine the test means for supplementing that knowledge.

Approach
The study comprised two parts conducted in parallel:
a bibliographic study aiming to document the separation/inactivation techniques and to identify the most appropriate processes;
a pre-study conducted on the basis of two purification processes deemed relevant during the bibliographic search: filtration using a granular bed, and filtration using a metal fibre filter media, the filtration being coupled with thermal inactivation.

Main results
The bibliographic search (> 300 articles) made it possible to identify and to document all of the air treatment processes that aim to remove micro-organisms, all activities considered together. A distinction was made between processes based on direct inactivation of bioaerosols in the air without prior collection, and processes leading to prior separation and collection of the biological particles and to their inactivation by means of different modes of treatment. The step consisting in separating the particles out, when such a step exists, takes place exclusively by means of fibre filter media. Thermal inactivation offers numerous advantages compared with the other techniques
due to it being easy to implement and to it guaranteeing that the micro-organisms are completely destroyed. It does not generate any toxic sub-products, which can conversely be generated by oxidation processes and certain chemical treatments.

Discussion
The summarised results of the bibliographic search on the processes for separating/inactivating the microbiological agents constitute an initial foundation of knowledge on the treatment processes conceivable for treating atmospheres contaminated with bioaerosols. It also makes it possible to answer questions from companies or CARSATs, and, where applicable, to give elements of expert appraisal of commercially available processes that some manufacturers propose. However, the data collected do not make it possible to propose a technical prevention solution capable of reducing, with known efficacy, the bioaerosol concentration levels in workshops or at workstations.
The experimental phase made it possible to show that both technologies were capable of presenting high separation efficacies and of allowing a sufficient thermal load to destroy the most resistant micro-organisms, such as fungal entities, for example. These solutions look promising. Additional work will be necessary to validate these techniques with biological particles, and to enable them to be dimensioned for possible industrial application.
Finally, an inventory was taken of the action and prevention means currently available to the French Prevention Network (Reseau Prevention) for improving working conditions and for reducing biological risks in companies. The INRS guides and brochures, and the feedback from the CARSATs may contribute to actions for improving working situations when it is established that employees are exposed to bioaerosols.