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Thesis Format

Monograph

Degree

Doctor of Philosophy

Program

Chemical and Biochemical Engineering

Supervisor

Berruti, Franco

2nd Supervisor

Fiore, Silvia

Affiliation

Politecnico di Torino

Joint Supervisor

Abstract

The rapid increase in industrial development and chemical usage has escalated environmental pollution, particularly in water bodies, necessitating advanced pollutant removal methods. This research investigated biochar – a carbon-rich material derived from the pyrolytic conversion of renewable sources, typically wastes and residues – as a sustainable and cost-effective alternative adsorbent to commercial activated carbon. A comprehensive systematic literature review was conducted to explore the adsorption of emerging pollutants on carbon-based adsorbents (biochar, char, and commercial activated carbon). Various feedstocks, such as agricultural and industrial wastes, woody biomass, sludge, and others were evaluated for adsorbent production and performance. The review highlighted production methods, activation techniques, adsorption mechanisms, and adsorbents’ reusability, providing insights into the factors influencing adsorption capacities and the adsorbent regeneration.

The experimental work began with the pyrolytic conversion of cup waste into value-added products, optimizing yield and quality by varying temperatures and heating rates. Advanced characterization techniques, including Brunauer-Emmett-Teller (B.E.T) analysis, Fourier-transform infrared (FTIR) spectroscopy, elemental analysis, and chemical composition characterization determined the physicochemical properties of the pyrolysis products. Potential applications were suggested based on the analyses. The char derived from paper cup waste underwent subsequent activation under varying conditions to optimize the activation process.

Based on the optimized activation conditions, biochars were produced from different cellulosic biomasses, specifically birchwood pellets and miscanthus. Adsorption experiments were conducted to assess the performance of these biochars in removing representative emerging pollutants, such as dyes and pharmaceuticals, including methyl orange, methylene blue, acetaminophen, ibuprofen, amoxicillin, and tetracycline under different conditions. The adsorption mechanisms were elucidated through kinetic and isotherm models, revealing insights into the interactions between adsorbates and adsorbent.

Furthermore, the study investigated spent adsorbent regeneration using solvent extraction and supercritical fluid extraction. The findings demonstrated these regeneration processes were effective, enabling the reuse of the adsorbents. This approach extends the functional life of the adsorbents and significantly reduces the overall cost and environmental impact associated with the adsorption process. In particular, the utilization of supercritical CO2 was investigated as a proof-of-concept for its ability to avoid any residue after desorption, offering a sustainable solution for adsorbent regeneration and recovery of pure adsorbates.

Overall, this thesis provides a comprehensive understanding of the production and characterization of biochar products derived from a variety of wastes, the adsorption of emerging pollutants using such biochars, and the regeneration of spent adsorbents with the recovery of potentially valuable adsorbates or adsorbate molecules that may require further treatments before disposal, contributing to the advancement of sustainable water treatment technologies.

Summary for Lay Audience

Environmental pollution, especially in water systems, has become a significant problem due to rapid industrial growth and increased chemical use. This pollution poses risks to both the environment and human health, making it crucial to find effective methods to clean contaminated water. This research explores the use of biochar – a carbon-rich material made from renewable sources – as a sustainable and cost-effective alternative to commercial activated carbon for removing pollutants from water.

Biochar is produced from various waste materials like agricultural and industrial waste, woody biomass, and even sewage sludge through a process called pyrolysis, which involves heating these materials in the absence of oxygen. This research began by converting paper cup waste into valuable products, optimizing the yield and quality by varying production conditions. Advanced techniques were used to analyze the properties of these pyrolysis products and suggest potential applications. The char derived from paper cup waste was further treated with various conditions to enhance its ability to capture pollutants.

Based on the optimized conditions, biochars were produced from different plant-based materials. These biochars were tested for their effectiveness in removing various pollutants including dyes and pharmaceuticals from water. The study used theoretical models to understand how these pollutants interact with the biochar.

An important part of the research was figuring out how to reuse biochar after it has been used to clean water. This study tested methods like solvent treatments and supercritical fluid extraction, which uses high-pressure carbon dioxide, to regenerate the biochar. These methods proved to be effective, allowing the biochar to be reused, significantly reducing costs and environmental impact. In particular, the use of supercritical CO2 was highlighted for its ability to avoid residue production, making it a sustainable solution.

Overall, this research demonstrates that biochar is a promising, sustainable, and cost-effective solution for treating polluted water. By providing a detailed understanding of how to produce, enhance, and reuse biochar, this study contributes to the development of better and more environmentally friendly water treatment technologies.

Creative Commons License

Creative Commons Attribution 4.0 License
This work is licensed under a Creative Commons Attribution 4.0 License.

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