Synergistic Removal of 4-Chloroaniline from Contaminated Water via Biochar-enhanced Microbial Degradation and Adsorption Using Carbonized Wood Waste

4-chloroaniline (4-CA) is a widely used aromatic amine, resulting in contamination in aquatic environments. Due to its high toxicity and persistence, 4-CA has been designated as a priority pollutant. This study aims to investigate 4-CA removal using an integrated system of biochar (carbonized wood waste) and Bacillus subtilis GRSW2-B1 (GRSW2-B1). The study consists of three parts: 1) evaluation of 4-CA removal by biochar, GRSW2-B1, and biochar and GRSW2-B1 combination, 2) investigation of 4-CA degradation kinetics, and 3) examination of the role of biochar in 4-CA removal. The result showed that biochar provided good 4-CA adsorption, following the Langmuir model, with a maximum capacity of 4.9 mg/g. The combined system of biochar and microbial cells (designated as BC-G1) achieved a removal efficiency of up to 73%, while microorganism alone (G1) yielded a value of 45%. For the 4-CA degradation kinetics, both G1 and BC-G1 systems followed the Andrews model, with an inhibition concentration of 65 mg/L. Field-emission scanning electron microscopy (FE-SEM), Fourier transform infrared (FTIR) spectroscopy, and fluorescence excitation-emission matrix (EEM) spectroscopy revealed that biochar enhanced 4-CA removal via: 1) adsorption on the biochar surface and stimulation of extracellular polymeric substance (EPS) production, and 2) enhancing biodegradation by facilitating redox-related electron transfer. The EPS-related functional groups, aromatic proteins, and fulvic and humic acid-like compounds showed increased levels in BC-G1, which is associated with electron shuttling and mediation processes. Overall, the integration of biochar and microbial cells significantly improved 4-CA removal, highlighting a promising, sustainable approach for the remediation of emerging toxic contaminants.