Optimisation of soybean peroxidase treatment of 2, 4-dichlorophenol

Abstract

In the presence of hydrogen peroxide (H2O2), peroxidase enzymes (PE) catalyse the oxidation of various chlorinated phenols to free radicals, which then combine to form insoluble polymers that precipitate out of solution. This study systematically characterises the treatment of 2, 4-dichlorophenol (2, 4-DCP) using soybean peroxidase (SBP) as an oxidising catalyst. The effects of pH, SBP concentration, polyethylene glycol (PEG) additive and initial chlorophenol concentration on 2, 4-DCP treatments are reported. Optimum pH for removal of 2, 4-DCP without PEG was pH 8.2. The pH operating range of SBP was from 2.5 to 9.4 which is wider than reported for horseradish peroxidase (HRP). A general equation is presented that describes the units of SBP required (without PEG) to treat a given amount of 2, 4-DCP at the optimum pH of 8.2. Addition of PEG increased the effectiveness of SBP by factors of 10 and 50 for PEG-3350 and PEG-8000 respectively. A new pH optimum of 6.2 was also found when SBP was used with PEG. Batch and semi -batch enzyme delivery has also been identified as a crucial parameter for the SBP treatment process. The most effective addition scheme was based on five equal concentrations of SBP and H2O2 over 15 min and 30 min intervals respectively compared to a single batch addition. This protocol was the most effective as it took advantage of limiting the amount of SBP and H2O2 available at each step. This reduces the possible chance of SBP inactivation by excessive H2O2 when using a single batch concentration. Average 2, 4-DCP removals achieved were 83.5%, 75.5% and 71.5% for 100, 200 and 300 mg/l 2, 4-DCP concentrations respectively compared to 62%, 52% and 58% for the single batch addition control.


WaterSA Vol.28(2) 2002: 149-158