High-carbon-content biochar from chemical manufacturing plant sludge for effective removal of ciprofloxacin from aqueous media

Abstract

Biochar is considered a promising biosorbent for harmful organic pollutants in aqueous media. However, only a limited number of biochars derived from industrial sludges have been utilized due to their problematic high ash content and heavy metal leaching. In this study, a highly effective biochar was prepared as a superabsorbent for ciprofloxacin (CIP) from chemical manufacturing plant sludge via K2CO3-activated pyrolysis, and its CIP removal behavior was evaluated. Unlike sewage sludge, chemical manufacturing plant sludge contains low SiO2, resulting in an ultra-pure carbon (95.4%) based biochar with almost negligible ash content. As the pyrolysis temperature increased from 400 to 800 °C, the ordered graphitic carbon structure transformed into an amorphous carbon phase, and most oxygen-containing groups disappeared. However, the pore size significantly decreased to ∼4.5 nm due to the corrosive carbon volatilization caused by K2CO3, resulting in an extremely large surface area of 2331.8 m2/g. Based on its large surface area and porous carbon structure, the activated biochar at 800 °C (CAB-800) exhibited an outstanding CIP adsorption capacity of 555.56 mg/g. The CIP adsorption isotherm, kinetic, and thermodynamic studies were systematically investigated. The CIP adsorption on CAB-800 was mainly attributed to π-π interactions and hydrogen bond formation, with electrostatic interactions partially contributing to the adsorption reaction. From pH 2 to 12, CAB-800 showed an excellent CIP adsorption capacity of over 316.7 mg/g, with adsorption favored under acidic conditions. Except for HCO3− and CO32−, the presence of anions and humic acids did not significantly affect CIP adsorption capacity. These results demonstrate that biochar produced from chemical manufacturing industry sludge via K2CO3 activation is a highly feasible material for the removal of CIP from aqueous media.