From Waste to Resource: Valorization of Lignocellulosic Agri-Food Residues through Engineered Hydrochar and Biochar for Environmental and Clean Energy Applications-A Comprehensive Review.

Agri-food residues or by-products have increased their contribution to the global tally of unsustainably generated waste. These residues, characterized by their inherent physicochemical properties and rich in lignocellulosic composition, are progressively being recognized as valuable products that align with the principles of zero waste and circular economy advocated for by different government entities. Consequently, they are utilized as raw materials in other industrial sectors, such as the notable case of environmental remediation. This review highlights the substantial potential of thermochemical valorized agri-food residues, transformed into biochar and hydrochar, as versatile adsorbents in wastewater treatment and as promising alternatives in various environmental and energy-related applications. These materials, with their enhanced properties achieved through tailored engineering techniques, offer competent solutions with cost-effective and satisfactory results in applications in various environmental contexts such as removing pollutants from wastewater or green energy generation. This sustainable approach not only addresses environmental concerns but also paves the way for a more eco-friendly and resource-efficient future, making it an exciting prospect for diverse applications.

An approach towards Zero-Waste wastewater technology: Fluoxetine adsorption on biochar and removal by the sulfate radical.

The appearance of pharmaceuticals in the aquatic environments has become a serious problem because of their hazardous effect on the biota. Therefore, great efforts are focussed in the removal to these pollutants from wastewaters. In this study, an innovative technology based on the principles of Zero-Waste for the management of wastewater streams is presented. Hence, adsorption of fluoxetine (FLX), selected as a model pollutant, in an eco-friendly adsorbent, biochar, was followed by an in situ removal of the pharmaceutical in the solid matrix by the action of sulfate radicals. Initially, an in-depth characterisation of the adsorbent and the adsorption process was carried out. The pseudo-second order kinetic and Freundlich isotherm described well the process, and the electrostatic attractions were revealed as the primary adsorption mechanism. Later, the removal of the FLX was studied by the sulfate radicals, in the presence of activators (Fe2+ and citric acid), in liquid and onto the biochar medium. It was concluded that in order to enhance the pollutant removal it is necessary the presence of both activators in liquid media. However, in in situ removal onto biochar, it was not necessary the Fe2+ presence and only the addition of complexing agents was required as a result of biochar's mineral content. Finally, the applicability of the proposed approach was studied in fixed-bed column assays where the adsorption and the removal of the pollutant were efficiently accomplished. This fact confirms the suitability of the developed process as a viable alternative in the treatment of wastewaters.