OPTIMIZATION OF THE REACTION CONDITIONS FOR ENZYMATIC REMOVAL OF PHENOL FROM WASTE-WATER IN THE PRESENCE OF POLYETHYLENE-GLYCOL

The effect of the additive, polyethylene glycol (PEG), on the horseradish peroxidase (HRP) catalysed removal of phenol from wastewater has been studied over the phenol concentration range of 1-10 mM (0.1-1.0 g/l). The optimum pH, HRP concentration, PEG concentration and the molar ratio of hydrogen peroxide and phenol have been investigated in the presence of PEG at room temperature in order to achieve the maximum phenol removal efficiency with the minimum cost. The effect of concentrations of HRP and PEG on reaction time was also investigated. Experimental results showed that the addition of PEG had significant protective effect on the activity of HRP. The amount of peroxidase required was reduced 40- and 75-fold less than that required without PEG for 1 and 10 mM phenol solutions, respectively. The higher the phenol concentration, the more effective was the addition of PEG. In the presence of PEG, the optimum pH is 8.0 and the optimum molar ratio of hydrogen peroxide and phenol is around 1.0. The minimum doses of HRP and PEG required for at least 95% removal were determined for several phenol concentrations and two empirical models are proposed to predict the minimum HRP and PEG doses required for 95% removal over the entire phenol concentration range of 1-10 mM. Under the optimum reaction conditions described above, the reaction times for at least 95% removal from 1 and 10 mM phenol solutions were 5 and 3h, respectively. An increase in HRP concentration significantly reduced the reaction time; however, an increase in PEG concentration showed negligible influence.