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HyBRid photocatalyitic air filtEr for rEmoving pollutants and odours from aircraft cabin ZonE

Periodic Reporting for period 3 - BREEZE (HyBRid photocatalyitic air filtEr for rEmoving pollutants and odours from aircraft cabin ZonE)

Reporting period: 2020-06-01 to 2020-11-30

An aircraft cabin is a unique environment due to the extremely high density of occupation and the limited available air volume. Typically, half of the air is exhausted and the other half is mixed with outside air (in most aircraft, supplied through the engine -bleed air-) and re-circulated into the passenger cabin, with a complete cabin air exchange every 2–3 min. This situation leads to the dispersion of germs and viruses and the accumulation of pollutants. Among them, Volatile Organic Compounds (VOCs) include not only internal pollutants (e.g. from materials present in the cabin or related to the presence of passengers) but also outdoor pollutants which can be present on the ground at very low altitudes (including gases from reactors and auxiliary power units).

In the majority of aircraft, the recirculated air passes through High Efficiency Particulate Air (HEPA) filters to trap contaminants suspended in the air (particles, bio-contaminants). However, these systems are not able to remove chemical pollutants (i.e. VOCs, ozone) and, since bio-contaminants (such as bacteria, viruses or fungi) are not inactivated, they can remain in the filter or even grow, thus representing a possible health risk. Only a small proportion of aircraft currently in service have implemented air treatment systems for VOCs/odour removal such as adsorbers. Moreover, these systems usually have high weight and cost, short life span (saturation) and septic conditions due to growth of microbial matter such as fungi and bacteria. Other technologies include electrostatic passive filters/precipitators based on the use of wires to remove pollutants, but the high voltage usually generates ozone. UVC lamps can also be used for air treatment and disinfection, but their efficiency for chemical pollutant removal is usually limited and they can also generate ozone. There is a great need for new alternative and innovative solutions that can surpass these limitations in current air treatment systems, capable of removing pollutants and bio-contaminants under aircraft environmental conditions while fulfilling constraints imposed by the size, weight and energy consumption.

To surpass those limitations, Breeze project propose to develop a new air purifier, connectable to the environmental control system ECS of aircraft to treat the recirculated air. The solution investigated is based on a composite filter that combines adsorption and photocatalytic technologies. The R&D program includes the design of the reactor and its testing for VOC, ozone and microorganism removal. Moreover, constraint regarding the incorporation of the prototype in real environment (TRL 6) is taken into account. In this regard, the tests are conducted at aircraft conditions (high flow rate and low humidity), and pressure loss of the system is monitored. The main objective is to achieve at least 85% VOCs removal without generating harmful by-product with a filter span life of at least 3000 hours of flight.

At the end of the project, a reactor compatible with the current ECS system, combining a low pressure drop HEPA filter for particle removal with a photocatalyst coated activated carbon filter was delivered. The adsorption properties allowed to achieve the objective of VOC removal with a filter’s span life evaluated around 4500 flight hours. However, the photocatalytic activity of the filtering media tested was not significant under experimental conditions representative of the ECS system.
The execution of BREEZE has started by defining the specifications of the air purifier: (1) the selection of the target compounds to be reduce, (2) the determination of the constraints for the implementation of the air purifier into the real environment regarding size, weight, pressure drop and characteristics of the air to be treated (pressure, humidity and temperature).

A report on the state of the art on technologies and standards applicable to cabin air quality was written. A screening of the different air filter technologies was done with an emphasis on adsorption and photocatalysis. It was found that the association of the two technologies can lead to a synergetic effect by improving the contact time available for photocatalytic reaction. As a result, the degradation of VOCs and ozone is enhanced in comparison of the two technologies tested alone.

Considering the information collected during the tasks described above, construction of the prototype with different geometries and different purification media have been carried out and tested for VOC removal and pressure drop. Experimental setups were designed and assembled in the laboratory to allow the testing of the reactor close to aircraft conditions defined at the beginning of the project. The solutions studied consisted of a 2 filtration stages composed of a photocatalytic filter followed by an adsorption stage or consisted of a 1 filtration stage in the form of activated carbon pellets coated with TiO2. The former showed significant photocatalytic activities (on VOC and bacteria) that might enhance the span life of the adsorption stage by reducing the amount of pollutant at the inlet and then, delaying its saturation. The latter (composite materials) showed a high adsorption of VOC without generation of by-products and was combined with a HEPA filter and integrated in a reactor compatible with the aircraft’s ECS system. This material was chosen for its better integration (composite material) and availability. The characterization of the performance during ageing tests estimated the lifetime of the filter to be around 4500 flight hours and confirmed the VOC removal performance obtained in the laboratory. However, photocatalysis had neither a significant effect on the removal of VOC after breakthrough of the adsorbent nor on the regeneration of the adsorbent using experimental condition close to the real ones. Moreover, the insufficient photocatalytic performances were confirmed by the evaluation of the biocide effect.

Communication and dissemination activities included the participation in international air quality conferences, the publication of articles on blogs, the creation of a video and the organisation of a workshop on indoor air quality.
To the best of our knowledge, the Breeze project is the first attempt to applied composite adsorbent/photocatalysis air filter activated by UVA-LED to improve aircraft cabin air quality.

The combination of the two techniques can lead to a synergetic effect where the pollutant firstly trapped on the adsorbent is transferred on the photocatalyst, where the degradation takes place. It is expected to obtain higher degradation rates increase and to slow down the saturation of the filter in comparison of standalone adsorption or photocatalysis. The reactor will be designed to achieve at least 3000 hours flight of span life, while respecting the integration constraint into the final environment.

This environment imposes to develop a system adaptable to the existing environmental control system of the aircraft that provide air to passenger at high flow rate and low humidity.

The BREEZE reactor will improve the air quality in the cockpit, increasing the safety of staff and passengers by reducing the amount of VOC and biocontaminants. It will also remove ozone at low temperature which will enable the system to be used in the bleedless E-ECS system.
Logo of BREEZE project