A thousand and one ways to enhance the value of willow!

Author: Mélanie Trudel, researcher at Innofibre

 

In Quebec, there are more than forty species of native willows. The cultivation of shrub willows has gained popularity in recent years due to its many advantages. Some species are known for their resistance to abiotic stress and their rapid growth. These willows can be harvested after just three years of growth. During harvesting, the base of the trunk and the roots are left in place so that the branches can regenerate for the next harvest. The biomass produced can be used for various purposes, ranging from bioenergy to material production.

 

Treating wastewater with willow

Willow can absorb contaminants from the soil through its roots. In 2022, an article on the research of Ph.D. candidate Eszter Sas was published in Québec Science. Ms. Sas conducts her research under the supervision of Frédéric Pitre, a professor in the Department of Biological Sciences at the University of Montreal and a member of the Plant Biology Research Institute (IRBV). According to this publication, it is possible to treat 20 million liters of wastewater per hectare of planted willows, equivalent to 16,000 willows. The wastewater is absorbed by the plant roots, and contaminants are sequestered in the biomass. This process, known as phytoremediation, could significantly reduce the number of contaminants escaping current wastewater treatment systems and entering water bodies.

Willows can accumulate high levels of nitrogen, phosphorus, and heavy metals, as well as reduce the amount of organic matter found in wastewater. According to an article published in Le Devoir in 2017, a phytoremediation process developed in Quebec could absorb up to 98% of the nitrogen contained in wastewater and up to 40% of the phosphorus. These two elements serve as nutrients for plant growth.

However, a phenomenon called eutrophication can occur if excessive amounts of nitrogen and phosphorus reach water bodies. Eutrophication is characterized by excessive growth of aquatic plants and algae, which, following their life cycle, will absorb large amounts of oxygen. As a result, the integrity of the aquatic ecosystem is threatened since it no longer receives the oxygen necessary for its survival.

 

The many uses of willow

Mature willows are used in various ways, including as wood chips for bioenergy or horticultural mulch. Willow branches can also be used to create noise barriers and fences. Finally, value-added products can be developed by extracting specialized metabolites synthesized by willows. Some natural extracts from willow bark are currently marketed as natural products (Figure 1).

 

Figure 1. Current valorization pathways for willow

 

 

Currently, this valorization pathway remains underexploited. However, scientific literature demonstrates that willow bark contains several bioactive metabolites with anti-inflammatory (e.g., organic acids), antioxidant (e.g., lignans), antimicrobial (e.g., phenols, terpenes), and anticancer (e.g., flavonoids) activities.

Although some companies in the cosmetics industry distribute various willow extracts—for example, for sebum regulation—further research is still needed to develop this sector and thus maximize the valorization of our resources.

 

Interest and advances at Innofibre

Innofibre has state-of-the-art equipment for biomass conditioning and the extraction of value-added molecules, both at pilot and laboratory scales. Recently, the center focused on studying willow extracts for use in animal health, thanks to funding from the Programme d’Aide à la Recherche et au Transfert (PART) of the ministère de l’Enseignement supérieur (MES).

Willow bark-based extracts were produced to validate their antimicrobial effects against strains responsible for mastitis and lameness in farm animals (Staphylococcus aureus, Escherichia coli, and Streptococcus agalactiae). From dried and ground biomass, an accelerated water extraction process was carried out to extract phenolic compounds. A portion of this extract was then fractionated using an organic solvent to concentrate the molecules of interest. The fractionated extract showed strong antimicrobial potential. When dissolved in a solution at a concentration of 1.7% (w/w), it reduced the number of E. coli bacteria in a culture broth by 97.8% after a contact time of three minutes. Further optimization of extraction parameters (temperature, pressure, etc.) will be necessary to enhance its antimicrobial efficacy.

 

What’s next?

The numerous characteristics of willow suggest that this biomass deserves to be further explored. The increasing societal awareness of environmental issues encourages the use of locally sourced, bio-based products to reduce our ecological footprint. Innofibre’s promising results indicate that willow extract could serve as an effective antimicrobial agent. The center will continue its research to develop new willow extract-based products for use in various sectors, including disinfectant, cosmetic, pharmaceutical and food products.