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Production of advanced adsorptive materials based on biochar

Regouzas Panagiotis

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Summary

Climate change along with the need of CO2 emissions reduction towards a sustainable way of living in the future has led to the need of reconsidering the linear model that has been followed by humanity so far, thus making a transition into a circular model of resources and waste management. Biochar is a product that is derived from biomass pyrolysis and shows several favourable physicochemical properties, which makes it a good candidate for several applications in different fields. Any type of organic solid waste can be feedstock for biochar production, such as agronomic waste, municipal solid waste, sewage sludge, animal manure, along with other organic industrial wastes. Converting these wastes into biochar changes their initial declaration as “waste” and converts it into resources for new material production. Biochar finds a range of applications, such as soil amendment, adsorptive material, constructed wetland substrate, composting enhancer, energy storage, production of sustainable building materials and solid fuel applications.This PhD thesis focuses on biochar application as an adsorbent, with the goal to utilize biochar technology to create new advanced and application-targeted adsorptive materials that could be significantly more effective than the conventional ones and can provide a sustainable alternative in difficult-to-manage waste treatment, such as the removal of Emerging Micro-Contaminants from water and wastewater. The produced materials are in total agreement with the principles of circular economy, since a previously consider waste resource is used to create a new material that will be further applied for decontamination purposes. To achieve that, three experimental cycles were implemented to investigate different parameters towards the production of the most effective advanced adsorbent. In the beginning, six different biomasses of agronomic or human derived origin were investigated as feedstocks for biochar production at two pyrolytic temperatures, in order to thoroughly characterize them physicochemically and evaluate their potential for different agronomic and environmental applications. The results of this work showed that higher pyrolytic temperature was more suitable for environmental application of biochar, by providing better carbon stability and more porous structure. Rice Husks was selected as a representative of agronomic waste and Sewage Sludge was selected as a human waste originated biomass to proceed to the next experimental cycle. That involved the production of the nanomaterial Graphene Oxide, which would be further implemented into the two biomasses, in two doses, prior to pyrolysis, resulting to the production of advanced sorptive materials named biochar nanocomposites. The produced samples were physicochemically characterized, followed by the application of both biochar and biochar nanocomposites as adsorbents for the removal of six Emerging Micro-Contaminants from water and wastewater. Results showed that some biochar nanocomposites could reduce the required amount of adsorption contact time from 60min to 30min, compared to conventional biochar samples, but higher adsorption efficiency was still required, leading to the implementation of the last experimental cycle. That included the implementation of commercially available Carbon NanoTubes into the selected biomasses, leading to the production of CNT-doped biochar nanocomposites. The results concerning the adsorption of the same contaminants from water and wastewater showed that these adsorbents could effectively remove >80% of the pollutants after 5min of contact time, which makes them perfect candidates for filter substrate, used for tertiary water or wastewater decontamination.

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