Optimization of operational conditions for biodegradation of chlorophenols by laccase-polyacrilonitrile beads system

The oxidative biodegradation of 2- and 4-chlorophenol (CPs) catalyzed by immobilized laccase from Trametes versicolor was conducted in a bed reactor. The effects of reaction conditions (reaction time, dosage of immobilized enzyme, flow rate, pH value and temperature, initial concentration) on CPs removal efficiency (RE) were investigated. By using in the immobilization solution an enzyme dosage of 2.5mgfreeenzgcarrier-1, the maximum ratio of laccase to PAN-beads is resulted 0.25mgimmenzgcarrier-1. RE values greater than 70% were obtained when 40 mL of 1 mM substrate solution were circulated for 90 min at 75 mL min -1 in the bed reactor filled with 12 g of laccase-PAN beads. The optimal pH for CPs biodegradation was 5 and it was not related to substituent position on aromatic ring. Experiments with immobilized laccase demonstrated good removal at high initial substrate concentrations and high thermal stability. The affinity of 2-CP was higher than that of 4-CP. Finally, the 2-CP was also biodegraded as tertiary mixtures with 2,3,4,5- tetrachlorophenol (TCP) and pentachlorophenol (PCP). The presence of TCP and PCP decreased the removal efficiency of 2-CP. The order of the relative degrading capacity becomes TCP > PCP > 2-CP. © 2012 Elsevier B.V