Turning Herbal Waste into Clean Energy and Pollution Filters

Jenn Hoskins
17th February, 2024

Turning Herbal Waste into Clean Energy and Pollution Filters

Nettle (Urtica gracilis), one of the plant species used in the study as a biochar source.

Photo adapted from: Lynn / CC BY (Source)
Biochar, a carbon-rich material created by heating biomass (organic matter) in an environment with limited oxygen, is gaining attention for its potential in various applications, from improving soil health to cleaning up pollutants. The source of the biomass used to create biochar significantly impacts its properties and effectiveness. Researchers at Maria Curie-Sklodowska University[1] recently investigated biochars produced from common herbs – nettle, sage, mint, and lemon balm – to understand how their chemical makeup influences the resulting biochar’s characteristics and its ability to absorb specific polymers. The core problem this study addresses is the need to understand how different plant materials translate into biochar properties. While biochar production is becoming more widespread, detailed knowledge about the relationship between the original plant source and the final biochar product remains limited. This is crucial because biochar’s effectiveness depends heavily on its physical and chemical features. As highlighted in earlier research[2], the cost and greenhouse gas balance of biochar production vary considerably depending on the technology and feedstock used. Understanding which plants yield biochars with desirable properties can help optimize production for specific applications. The study focused on analyzing the physicochemical properties of biochars created from each herb. These properties included surface area, porosity, pH, the types of chemical functional groups present, and importantly, the energy content – specifically, the higher heating value (HHV), which indicates how much energy is released when the biochar is burned. The researchers found that the mineral content of the original herbs strongly influenced the surface area of the resulting biochar, while the amount of hemicellulose (a component of plant cell walls) affected the number of functional groups on the surface. Lemon balm biochar stood out, exhibiting the highest HHV at 20.36 MJ/kg, comparable to typical energy sources. Beyond characterizing the biochars, the researchers tested their ability to adsorb, or bind to their surface, two types of ionic polymers: polyethylenimine and polyacrylic acid. These polymers are used in various industrial processes and can be pollutants if released into the environment. The study revealed that while the amount of polymer adsorbed wasn’t exceptionally high, the presence of one polymer actually enhanced the adsorption of the other. This suggests a synergistic effect, where the polymers interact with each other on the biochar surface, improving overall removal efficiency. This research builds upon previous work demonstrating the importance of biochar production technology in determining final product characteristics[3]. The study’s focus on herbaceous plants is a novel approach, as much prior research has concentrated on woodier biomass sources. The findings align with the general principle that biochar properties are intimately linked to the feedstock material and processing conditions[4], but provide specific insights into the unique contributions of different herb components. The study’s method involved pyrolysis, a specific type of thermochemical conversion where biomass is heated in the absence of oxygen. This process breaks down the organic matter, leaving behind the stable carbon-rich biochar. The researchers then used various analytical techniques to characterize the biochar, including measurements of surface area and porosity using gas adsorption, and identification of functional groups using spectroscopy. Polymer adsorption experiments were conducted in controlled laboratory settings, carefully measuring the amount of each polymer bound to the biochar under different conditions. The observation that lemon balm produces a biochar with high energy content is particularly interesting. This suggests that biochars from this herb could potentially be used not only for environmental applications but also as a renewable energy source. Furthermore, the synergistic polymer adsorption effect opens up possibilities for using these biochars in water treatment or industrial separation processes. The findings also support the broader trend towards “engineered biochar”[5], where biochar is modified or tailored to enhance specific properties for targeted applications.

HerbsSustainabilityBiotech

References

Main Study

1) Preparation of biochars by conventional pyrolysis of herbal waste and their potential application for adsorption and energy purposes.

Published 16th February, 2024

https://doi.org/10.1002/cphc.202300507

Related Studies

2) Technical, economical, and climate-related aspects of biochar production technologies: a literature review.

https://doi.org/10.1021/es201792c

3) Biochar production and applications in agro and forestry systems: A review.

https://doi.org/10.1016/j.scitotenv.2020.137775

4) Mechanisms of metal sorption by biochars: Biochar characteristics and modifications.

https://doi.org/10.1016/j.chemosphere.2017.03.072

5) Engineered biochar: A multifunctional material for energy and environment.

https://doi.org/10.1016/j.envpol.2022.118831


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