Anaerobic biodegradation of phenols inhibition kinetics and system stability

The Haldane inhibition model was used to describe the anaerobic microbial biodegradation of phenol. Experimental data on the biodegradation of phenol obtained from a continuous flow anaerobic fermenter and a series of closed batch reactors were analyzed. Phenol was found to have a very low half velocity coefficient, K_s, value of 0.03 mg/L. Other kinetic parameters included a maximum specific utilization rate, k, of 0.027 hr⁻¹, a haldane inhibition constant, K_i, of 363 mg/L, a biomass yield factor, Y, of 0.16 mg VSS/mg phenol, and a biomass decay coefficient, b, of 0.0008 hr⁻¹. Analytical system stability studies on the continuous flow fermenter operating at steady state were theoretically simulated using the phenol kinetic parameters. Pulse and step increases in phenol influent feed concentration were simulated and the response of the fermenter was analyzed using a computer program. Conditional and unconditional recovery regions from a pulse feed input were identified. For each influent phenol concentration of less than 1,650 mg/L, there exists a critical hydraulic detention time, θ_cr, above which fermenter recovery is insured for any pulse increase in the phenol feed concentration. When operated under steady state feed concentration of 4,000 mg/L phenol and a hydraulic detention time of 30 days, the anaerobic fermenter was able to recover from step increases in phenol feed concentration of up to 8,500 mg/L. Under the same steady state conditions, however, a step increase to 10,000 mg/L phenol feed concentration led to complete system failure.