Adsorption and Desorption of Emerging Pollutants with Engineered Biochar Adsorbents
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.