Application of Phytoremediation Principles to Remediate Air Pollutants in the Climate Change Era

1. Introduction

Contamination of land and water resources is a growing contemporary era challenge particularly in the last 20 years (Nyika & Dinka, 2023 a, b). Conventional approaches used in remediating the involved pollutants are based on various thermal, chemical, and physical treatment technologies and engineering techniques, which hasten or slow down solute transport (Vasavi et al., 2010). However, the effectiveness of these technologies is pegged on their ability to withstand a wide range of osmotic potential, temperature, pH, pressure, and oxygen concentrations as well as their insensitivity to the heterogeneous nature of contaminants (Champagne, 2007; Nyika & Dinka, 2023b). These preconditions make the techniques expensive and explains their limited coverage as polluted areas with no remediation plans have increased in the last decade. In such areas, remediation coverage can be increased by adopting phytoremediation strategies that focus on ex-situ or in-situ use of plants to enhance the breakdown, removal or metabolism of contaminants using microorganisms within them. The technique is passive and works by degrading, sequestering and immobilising air, soil and water contaminants through plant-dependent physical, chemical and biological processes (Razzaq, 2017; Rivandra & Mor, 2022). The preference and continued use of this technique is due to its sustainability compared to conventional methods.

In the era of climate change, air pollutants mainly primary and secondary contaminants such as particulate matter (PM), inorganic pollutants (O₃, CO₂, SO₂, NO_x), volatile organic compound (VOCs) such as formaldehyde, poly aromatic hydrocarbons (PAHs), xylene, ethylbenzene, toluene, and benzene are a growing concern in the world (Rivandra & Mor, 2022). These pollutants are found indoors but often are in concentrated levels outdoors. They are associated with anthropic activities and known to accelerate the global warming and climate change effects (Manisalidis et al., 2020).

According to Weyens et al. (2015), the air pollutants have defied conventional pollutant abatement techniques as the environment still has them in high levels. The conventional removal methods include electrochemical (electrodialysis, electrocoagulation, electroflotation), physicochemical (membrane filtration, ion exchange, chemical precipitation) and adsorptive (carbon nanotubes and activated carbon) techniques, which in most cases are high-energy consuming, have sophisticated designs, and are engineering intensive, which makes them costly to maintain and prone to high failure rate (Nyika & Dinka, 2022). Each of the conventional techniques has diverse air pollutant removal efficacy and most do not completely eliminate some contaminants such as particulate matter. The conventional techniques also result to fouling and production of secondary pollutants.

The refractory nature of the air pollutants is exacerbating climate change effects even further. Phytoremediation is however a promising environmental-friendly approach to degrade and/ or detoxify such air pollutants through pollutant-scavenging plants. Such plants live in association with microbes such as bacteria and fungi, which support them cope with biotic and abiotic stress by producing antagonistic hormones, devising allelochemical inhibitory pathways and in facilitating food and nutrient uptake (Bulgarelli et al., 2013). Plant-microorganism interactions are shown to sequester pollutants and promote plant growth even when exposed to air pollutants. Berg et al. (2014) reported these findings in a study that showed plant growth indoors and outdoors increased air humidity but was not accompanied by an increase in air pollutants and colony forming units even when industrially produced devices were incorporated. This phenomenon was associated with the plants’ ability to release allelochemicals to the atmosphere, which inhibit the accumulation of air pollutants. This book chapter focuses on the mechanisms, types, applications, advantages, and disadvantages of phytoremediation of indoor and outdoor air pollutants. The significance of the chapter is to explore the potential application of the technique in air pollutant remediation considering its eco-friendly nature compared to conventional contaminant removal techniques.