Bioregeneration of activated carbon and activated rice husk loaded with phenolic compounds: Kinetic modeling

A kinetic model consisting of first-order desorption and biodegradation processes was developed to describe the bioregeneration of phenol- and p-nitrophenol-loaded powdered activated carbon (PAC) and pyrolyzed rice husk (PRH), respectively. Different dosages of PAC and PRH were loaded with phenol or p-nitrophenol by contacting with the respective phenolic compound at various concentrations. The kinetic model was used to fit the phenol or p-nitrophenol concentration data in the bulk solution during the bioregeneration process to determine the rate constants of desorption, kd, and biodegradation, k. The results showed that the kinetic model fitted relatively well (R2 > 0.9) to the experimental data for the phenol- and p-nitrophenol-loaded PAC as well as p-nitrophenol-loaded PRH. Comparison of the values of kd and k shows that k is much greater than kd. This indicates clearly that the desorption process is the rate-determining step in bioregeneration and kd can be used to characterize the rate of bioregeneration. The trend of the variation of the kd values with the dosages of PAC or PRH used suggests that higher rate of bioregeneration can be achieved under non-excess adsorbent dosage condition.