Enzymatic removal of phenol and chlorophenols using soybean seed hulls

Soybean peroxidase (SBP), (EC 1.11.1.7) can be readily extracted from soybean seed hulls. This study reports on the direct use of soybean seed-hull extracts for the bioremediation of phenolic wastes. The crude SBP extract from the hulls, like pure soybean peroxidase, is catalytically active in a broad range of pH and temperatures. As SBP is gradually released into the aqueous solution from seed hulls, the direct use of soybean seed hulls can reduce SBP inactivation by H2O2 and enhance the utilization efficiency of SBP through the slow release of the enzyme from the seed hulls. However, large doses of soybean seed hulls were found to be ineffective in phenol removal. Gradual additions of H2O2 in combination with the SBP released from the hulls were applied to optimize the bioremediation. Since the crude extract contains a mixture of multiple soybean proteins, soybean seed hull slurry required a higher concentration of H2O2 to remove the phenolic substrates than did the purified enzyme. Under the experimental conditions, 80 % of phenol (10.6 mM), 96 % of 2-chlorophenol (3.9 mM), 95 % of 2,4-dichlorophenol (3.1 mM), and 94 % of mixed phenol and chlorophenols were removed using soybean seed hulls in a single batch reactor. These results demonstrate that soybean seed hulls, compared to purified SBP, may be a more cost-effective alternative in the enzymatic removal of phenolic compounds through polymerization reactions.