Polyurethane wastes conversion into a plant biostimulant via ozonolytic attack: An innovative strategy for waste management and sustainable agriculture

Abstract

A novel, non-toxic plant biostimulant has been developed through the depolymerization of polyurethane (PU) foams via an aqueous ozonolysis process. This method yields a water-based extract rich in small, soluble molecules, referred to as oxidized liquid extract (OLE), which acts as a growth-promoting substrate for pepper plants (Capsicum annuum). This approach not only enables the conversion of PU waste into plant biomass but also represents an innovative model for circular economy implementation. When applied at low concentrations (diluted 1:5 and 1:10), OLE elicits a hormetic response, enhancing photosynthetic performance, protein content, and photosynthetic pigment levels. Additionally, it stimulates the accumulation of industrially relevant secondary metabolites such as terpenoids and capsaicinoids an effect likely linked to the extract's high nitrate content. Although short-chain polyols were detected in the fruits of plants treated with the 1:5 dilution, these compounds are biodegradable and widely used in pharmaceutical and cosmetic applications. Moreover, OLE induces favorable shifts in rhizospheric microbial communities, promoting the enrichment of biofertilizing bacterial genera capable of transforming extract derived compounds and enhancing the adsorption of biomolecules secreted by plant roots. This sequential chemical and biological transformation facilitates the complete valorization of a highly recalcitrant polymeric waste, resulting in a bioactive extract that supports plant growth and development. Taken together, this strategy offers a promising and sustainable solution that integrates waste management with agricultural productivity, aligning with the core principles of the circular bioeconomy.

Keywords: Circular economy; Ozone; Plant Growth Promoting bacteria; Polyurethane; Recycling.