Recovery and valorisation of agro-industrial waste through the development of hybrid materials for environmental applications

Management and reduction of waste, together with the resolution of water crisis are some of the major challenges of this century. The access to clean water is a right but nowadays pollutants are still released into the environment as a result of anthropic activities, therefore new integrated strategies and specific actions are required to ensure its availability to all human beings. Despite the many treatments that occur in plants, some kind of micropollutants cannot be completely removed and reach the receiving water bodies. Consequently, they can affect directly agricultural irrigation or aquaculture and indirectly human health by entering in the food chain. Therefore, the strengthening of the actual water treatment system is needed and may lead in the future to better-performing plants. At the same time a large quantity of agro-industrial wastes is continuously produced as a result of agriculture and food preparation and consumption and most of them are only partially recovered. They are often landfilled or burned, so contributing to increase environmental hazards. Nevertheless, crop residues should be considered as a potential raw material due to their high content in lignocellulosic biomass holding interesting functional groups that can be involved in complexation, chelation and adsorption processes. Furthermore, crops waste can also contain enzymes and other proteins not exploitable for food, but recoverable and usable for other purposes. This research project aims to adopt the circular economy approach in the context of the synthesis and development of bio-based materials. The main goal is to maximise the valorisation of soy processing residue, the seed hulls, through the recovery of soybean peroxidase (SBP) and cellulose and their exploitation in strategies for treatment of water, polluted by organic or inorganic contaminants, based on adsorption or biocatalysis. We tried to maintain the objective of circularity in the development, use and end-of-life of the prepared materials. At the same time, attention was also paid to the impacts reduction, focusing particularly on the initial biomass treatment. Indeed, alongside the classic acid-base multi-hydrolysis cellulose extraction, an alternative two-step hulls fractionation method assisted by microwaves has also been optimised. Subcritical water and diluted basic solution were employed as extraction solvents. Both strategies led to final samples enriched in cellulose and with comparable features, but the microwave-assisted process reduced cellulose isolation steps and avoided the use of acid treatments. In order to enhance the affinity towards specific contaminants, three chemical modifications have been carried out to introduce functional groups within the structure of cellulose. Hydrogels prepared with amine and thiol-functionalised cellulose or carboxymethyl cellulose showed good removal capabilities of potentially toxic elements from aqueous matrices not only in mono-elemental solutions but also in mixture. Moreover, the primary amino groups in the cellulose structure made it suitable for SBP immobilization allowing the development of biocatalysts for efficient organic contaminants’ oxidation. Preliminary studies on H2O2 photoproduction have been carried out with the aim of developing self-sustaining systems coupled with SBP that ensure organic compounds degradation avoiding an external H2O2 addition. Considerable attention was paid to evaluating the actual applicability of our strategies. Therefore, the materials’ performances have been tested also employing real aquaculture water as solvent for contaminants’ solutions preparation in order to evaluate the influence of pH, inorganic ions and dissolved organic matter on water treatments outcomes. Finally, regeneration test and biodegradation experiments were also carried out in order to extend the materials’ life-time and to close their life cycle by minimizing the impacts.