Processes for removing traces of formaldehyde from indoor air

Outline of reasons and objectives
In France, the number of workers exposed to formaldehyde totals 190,000 spread across over one hundred professions. The need to provide prevention solutions for reducing the exposure of workers exposed to formaldehyde, in particular in the tertiary sector – due to the composition of materials present in the workspaces – has been declared to be a priority by the French health authorities. The main objective of the work done is to study stand-alone purification systems, mobile or otherwise, placed in the workspace, as alternatives to ventilation and that would make it possible to reduce the health risk induced by exposure to formaldehyde.
Approach
The first step in this work was devoted to determining the kinetic relationships of the photocatalytic degradation of formaldehyde and toluene, identified as another major pollutant in indoor air. The second part of the study was focused on determining the kinetics of transfer of the formaldehyde contained in the air to an aqueous solution flowing in a contactor of the packed absorption column type. The experimental approach was supplemented by a modelling stage that incorporated the pairing made up of absorption and of photocatalytic degradation of formaldehyde. The model was then compared with the experiment conducted with a laboratory demonstrator. Alongside this laboratory work, an approach based on numerical simulation was conducted to assess the impact of operation of such a purification system on the formaldehyde concentration in a working environment.
Main results
The degradation of formaldehyde was studied in two different reactors. The results corresponding to this work highlight the influence of parameters such as temperature, agitation, and oxygen content on the photocatalytic decomposition of formaldehyde in solution. The influence of the initial pollutant concentration and of the irradiance on the photocatalytic degradation of formaldehyde was modelled satisfactorily. In addition, the use of numerical simulation made it possible to confirm the advantage of using a stand-alone purification system in a room for the purpose of removing formaldehyde. On the basis of the simulations performed, it is recommended to position the purification system away from the ventilation inlets and outlets in order to avoid short-circuits and in order to increase the flow of air in the room and the entrainment of the formaldehyde.
Discussion
Although not providing any information about this mechanism, this kinetic study does give information essential to engineers for designing an industrial photocatalytic process for treating effluent containing formaldehyde. Modelling the process could be developed by considering more complex kinetic models incorporating, for example, the presence of co-pollutants, the influence of pH or dissolved oxygen concentration. Finally, if the tests conducted in real situations are as conclusive as the tests resulting from the experimentation, the technology proposed here will constitute an advantageous alternative to general ventilation of workspaces. Designing and producing a demonstrator is being considered.