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Technology and nature together to improve indoor air quality

04 February 2022
Photo @Allmicroalgae - Natural Products, S.A

Article by Teresa Mata, researcher in the area of ​​environment and sustainability, and Gabriela Ventura, researcher in the area of ​​air quality at INEGI.

The urban lifestyle that characterizes contemporary society is often synonymous with spending 90% of our time indoors - home, offices, classrooms, restaurants, shops, and public transport - and this has consequences for our health.

The quality of the air we breathe and our health are intertwined. This link is so strong that the World Health Organization has recognized air pollution as one of the greatest challenges to public health worldwide [1].

All air contaminants are at stake: not just the tiny particles that enter the lungs and cardiovascular system and cause us illness, but also biological pollutants, and more than 400 different organic and inorganic chemical compounds whose concentrations depend on various factors linked to the indoor and outdoor environment [2].

In indoor air, some contaminants can reach concentrations about 10 times higher than in outdoor air. For example, we are talking about formaldehyde, whose sources are usually furniture and cleaning agents.

There are several ways to reduce exposure to pollution

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.

Microalgae may be a solution to "cleanse” the air we breathe

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.


1. WHO. Ambient air pollution: a global assessment of exposure and burden of disease; World Health Organization. Department of Public Health, Environmental and Social Health Organization: Geneve, Switzerland, 2016; pp. 1–121;. 
2. González-Martín, J.; Kraakman, N.J.R.; Pérez, C.; Lebrero, R.; Muñoz, R. A state–of–the-art review on indoor air pollution and strategies for indoor air pollution control. Chemosphere 2021, 262, doi:10.1016/j.chemosphere.2020.128376.
3. Daniels, S.L. On the qualities of the air as affected by radiant energies (photocatalytic ionization processes for remediation of indoor environments). J. Environ. Eng. Sci. 2007, 6, 329–342, doi:10.1139/S06-072.
4. Hodgson, A.T.; Destaillats, H.; Sullivan, D.P.; Fisk, W.J. Performance of ultraviolet photocatalytic oxidation for indoor air cleaning applications. Indoor Air 2007, 17, 305–316, doi:10.1111/j.1600-0668.2007.00479.x.
5. Benyus, J.M. Biomimicry: Innovation Inspired by Nature; HarperCollins Publishers: California, USA, 2009;
6. Mata, T.M.; Oliveira, G.M.; Monteiro, H.; Silva, G.V.; Caetano, N.S.; Martins, A.A. Indoor Air Quality Improvement Using Nature-Based Solutions: Design Proposals to Greener Cities. Int. J. Environ. Res. Public Health 2021, 18, 8472, doi:10.3390/ijerph18168472.

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