Biodegradation of 4-chlorophenol by acclimated and unacclimated activated sludge— Evaluation of biokinetic coefficients

Unacclimated and acclimated activated sludges were examined for their ability to degrade 4-chlorophenol (4-CP) in aerobic batch reactors, both with and without a readily growing substrate. The objective was to investigate the biokinetic coefficients affected by varying concentrations of 4-CP on specific growth rate, yield coefficient, and specific substrate utilization rate. The results indicated a significant decrease in the toxicity of 4-CP upon acclimation, evidenced by an increase in IC50 from 130 mg/L to 218 mg/L. While the acclimated culture maintained COD removal efficiency even at 300 mg/L of 4-CP, the unacclimated culture showed a considerable decline in performance and did not achieve effective 4-CP removal. Through the application of the Haldane kinetic model, the biodegradation parameters were identified: maximum specific growth rate (qm) was 41.17 mg/(g MLVSSh), saturation constant (Ks) was 1.104 mg/L, and inhibition constant (Ki) was 194.4 mg/L. Partial degradation pathway analysis revealed complete degradation of 4-CP through a meta-cleavage route, forming 5-chloro-2-hydroxymuconic semialdehyde as an intermediate product.