Carbothermal Shock Derived Electrochemical Regeneration of Spent Biochar for Remediation of Ciprofloxacine Contaminated Water
Authors: Hong Hye-Jin , Lee Gyubin , Jeong Hyeon SU 
Published: December 2024

Biochar, derived from waste biomass, is a potent material for carbon dioxide sequestration, owing to its stable, non-degradable aromatic structure [1]. Biochar is found to have advantageous characteristics, such as a unique pore structure, large specific surface area, complex surface-active functional groups, and stable chemical properties. These properties make biochar as a high potential biosorbent for removal of pollutants from water [2]. Meanwhile, the escalating use of pharmaceuticals has led to pervasive environmental residues, posing public health risks. Specifically, antibiotic contamination risks augmenting antibiotic resistance, underscoring the need for efficient wastewater treatment methods [3]. However, current wastewater treatment plant(WWTP) based on biological treatment was not effectively eliminate this types of waste in the water and it is necessary to investigate efficient method for removal of antibiotics from wastewater.
This study explores the use of biochar for ciprofloxacin (CIP) removal from water and introduces a novel electrochemical biochar regeneration technique. We utilized sludge from chemical plants to produce biochar through standard and alkali-activated pyrolysis, yielding CB (normal pyrolysis) and CAB (alkali activated pyrolysis) types with distinct physicochemical properties. CAB, with an exceptionally high surface area (~2330 m²/g) and carbon purity (95.4%), demonstrated superior CIP adsorption capacity (~550 mg/g). We investigated the CIP adsorption isotherm, kinetics and thermodynamics to elucidate the underlying mechanisms, which appear dominated by π-π and electrostatic interactions facilitated by the high pyrolysis temperatures reducing oxygen-containing groups on the biochar. After the biochar became saturated with CIP, we regenerated it using joule heating in Ar atmosphere, employing the carbothermal shock method for rapid, short-duration temperature increases [4]. In contrast to traditional CTS which can sometimes lead to structural damage by directly heating the material on the carbon substrate [5], we used radiant heat from the CTS process to ensure controlled temperature elevation. This modified approach maintains the structural integrity of the biochar by avoiding direct contact between the biochar and the carbon substrate while facilitating the regeneration process. Additionally, this method facilitates the physical separation of the biochar from the carbon substrate, enhancing the recovery and reuse of biochar. Such an approach contributes to the efficient regeneration of biochar and environmentally friendly processing. We examined parameters such as distance from the substrate and duration to optimize the regeneration conditions. Ultimately, we assessed the efficacy of the CIP adsorption by the regenerated biochar. Traditional thermal treatments for biochar regeneration are energy-intensive and time-consuming. We propose an innovative approach using joule heating under a nitrogen atmosphere, employing carbothermal shock for rapid, efficient regeneration. By optimizing parameters such as voltage and duration, we identified ideal conditions for regenerating biochar, significantly enhancing its CIP adsorption efficacy. This study not only highlights the potential of biochar in environmental remediation but also introduces an energy-efficient regeneration method, contributing to sustainable pollution management solutions.

References

[1] J. Lehmann, A. Cowie, C.A. Masiello, C. Kammann, D. Woolf, J.E. Ammonette, M.L.Cayuela, M.C-Arbestain, T. Whitman, Biochar in climate change mitigation, Nature Geoscience (2021) 14, 883
[2] B. Qui, Y. Tao, H. Wang, W. Li, X. Ding, H. Chu, Biochar as a low-cost adsorbent for aqueous heavy metal removal: A review, Journal of Analytical and Applied pyrolysis (2021) 155, 105081
[3] M. B. Ahmed, J. L. Zhou, H. H. Ngo, W. Guo, Adsorptive removal of antibiotics from water and wastewater: Progress and challenges (2015) 532, 112
[4] Y. Yao, Z. Huang, P. Xie, S. Lacey, R. Jacob, H. Xie, F. Chen, A. Nie, T. Pu, M. Rehwoldt, D. Yu, M. R. Zachariah, C. Wang, R. Shahbazian-Yassar, J. Li, L. Hu, Carbothermal shock synthesis of high-entropy-alloy nanoparticles. Science (2018) 359, 1489
[5] C. Kim, J.-Y. Song, C. Choi, J. P. Ha, W. Lee, Y. T. Nam, D. Lee, G. Kim, I. G., W.-B. Jung, H. Lee, Y., H. Jeong, H.-T. Jung, Atomic-Scale Homogeneous Ru-Cu Alloy Nanoparticles for Highly Efficient Electrocatalytic Nitrogen Reduction, Advanced Materials (2022) 34, 2205270

Figure 1