Biodegradation of 4-chlorophenol by Bacillus timonensis strain 10403023: optimisation, kinetics and bioreactor design

This study investigates the aerobic biodegradation of 4-chlorophenol using Bacillus timonensis strain 10403023, emphasizing process optimization, kinetic modelling, and bioreactor applicability. Six operational variables (temperature, pH, inoculum size, incubation time, working volume, and initial 4-chlorophenol concentration) were optimized to maximize degradation efficiency. The highest degradation (99.62%) was achieved at 40 °C, pH 7.5, 24 h incubation, 500 mL working volume, 6% inoculum, and an initial concentration of 800 mg/L, with complete removal within 24 h. Biomass formation increased with substrate concentration, reaching a maximum OD600 of 1.095. Growth and degradation kinetics followed the integrated Haldane model with excellent agreement (R² = 0.9933 and 0.9999, respectively). Estimated kinetic parameters were μm = 0.024 h⁻¹, Ks = 26.54 mg/L, Ki = 124.65 mg/L, and Qs = 44.75 mg/L/h. The experimentally validated optimization and kinetic findings supported the conceptual design of an aerobic stirred-tank bioreactor. These results demonstrate the potential of B. timonensis strain 10403023 as an efficient and eco-friendly biocatalyst for treating high-strength 4-chlorophenol-contaminated pharmaceutical wastewater.