Technology and nature together to improve indoor air quality

There are three possible strategies to combat pollution and improve indoor air quality: (1) control of pollutants at source, (2) ventilation, and (3) air purification.

Control at source is the smartest strategy, as it is based on prevention and aims to avoid the problem at source. This is one of INEGI's strategies which, through its Indoor Air Quality Laboratory, supports the industrial development of "clean" materials and has the ability to assess dozens of contaminants, by determining the concentration of volatile organic compounds (VOCs) and volatile substances (COMVs) and low molecular weight aldehydes (formaldehyde, acetaldehyde, among others) in air samples collected in service buildings and housing. This strategy, however, may not be applicable in some cases, due to restrictions related to construction materials or ongoing activities.

Natural ventilation is a simple and preventive measure that also allows to lower concentrations of compounds dangerous to human health and prevent infections. However, in highly polluted environments outside, as is the case in certain cities, ventilation of interior spaces is not effective to achieve air with the required quality. On the other hand, mechanical ventilation requires energy and implies emissions to the ambient air, both locally and globally.

For these reasons it is important to consider new strategies to ensure healthy indoor air, with reduced cost and high energy efficiency. The use of technologies for air purification is a possible strategy. In conventional processes solid adsorbents for VOCs, filtration for particulate matter (PM) and disinfection for bio aerosols and microorganisms are used. These can be combined with advanced treatment processes such as photocatalytic oxidation of VOCs, bipolar air ionization to agglomerate PM and ultraviolet disinfection to inactivate bioaerosols [3].

Despite their high applicability, these processes have some disadvantages. For example, to remove particles by filtration, frequent replacement of filters is necessary and, in the case of electrostatic precipitation, there is a high risk of generating ozone. UV photocatalytic oxidation appears to be a promising technology, but there are still aspects to be resolved before it can be used safely in buildings, such as the generation of formaldehyde and acetaldehyde from the partial oxidation of ubiquitous VOCs, such as alcohols [4]. ]. In addition, the high cost of these technologies is also an aspect to consider.

Natural-based solutions represent an interesting alternative. This is an emerging research area, which is based on existing solutions in nature to respond to human needs, following the precepts of biomimetics, theorized in 1997 by Janine Benyus [5]. The approach has been used in architecture for the construction of buildings with greater energy efficiency and autonomy, reducing their environmental footprint.

Another innovative and promising hypothesis is the creation of buildings, and potentially cities, powered by microalgae. This approach would contribute to the development of ecologically more sustainable cities with greater biodiversity. This solution, proposed by a group of researchers from INEGI with other research centers [6], idealizes the use of microalgae to clean indoor air, based on the concept of circular economy, reducing the use of resources and maximizing benefits. Integrating microalgae production systems into buildings would potentially improve indoor air quality, making it better than outdoor air. At the same time, this type of solution allows for thermal regulation and new architectural features.

In the proposed system, exhaust air from rooms or other building spaces, such as classrooms, is injected directly into the microalgae production system with multiple photo bioreactors (PBR) cultivation, providing a source of CO2 for the cultures. of microalgae [6]. In each PBR, microalgae convert CO2 into O2 during their photosynthetic and metabolic activity, producing microalgae biomass. The O2-rich air leaving the microalgae production system is connected to air treatment systems (AHS), instead of (or supplementing) the outside atmospheric air, to be filtered and corrected for temperature and humidity levels and , then admitted, via a pipeline, into the rooms for ventilation purposes using and transforming the current heating, ventilation and air conditioning (HVAC) system.