Removal and bioconversion of phenol in wastewater by a thermostable β-tyrosinase

Abstract

This study explores an enzymatic method for removing phenol from the wastewater created during the manufacture of phenolic resin. The enzyme used was a thermostable β-tyrosinase catalyzing the synthesis of L-tyrosine from phenol, pyruvate, and ammonia. As the reaction proceeds, L-tyrosine precipitates as insoluble aggregates because L-tyrosine is barely soluble in water. The enzymatic removal of phenol was effective at pH values ranging from 6.5-9.0 and temperatures below 70°C. The optimal concentration of each substrate was determined as 60 mM phenol, 0.1 M pyruvate, and 0.4 M ammonia. When the enzyme was used in an intact cell or acetone-dried cell state instead of the cell-free extract, the optimal concentration of phenol was increased up to 120 mM. By treating wastewater containing 100 mM phenol with acetone-dried cells at 37°C, we could reduce the concentration of phenol to 8 mM within 24h.