A study on a combined process for the treatment of phenolic resin plant effluents

The removal of phenol and formaldehyde from phenolic resin plant effluents has been studied by using a combined process. In the first step, phenol was removed from effluent by solvent extraction. Special attention was paid to the effluent with a low content of phenol, which was treated by non-dispersive solvent extraction in hollow fibres. It was found that a single module of Liqui-Cel® 2.5 in. × 8 in. membrane contactor allowed processing ∼24 L/h of effluent with 0.4-0.7 g/L phenol and attaining values as low as 0.5 mg/L in the raffinate. Formaldehyde, which was left in phenolic resin plant effluent after the removal of phenol, has been treated with hydrogen peroxide in alkaline medium and also in acidic medium (Fenton process). In alkaline medium, formaldehyde was oxidized with hydrogen peroxide to formate ion, which was recovered by solvent extraction. The oxidation of formaldehyde with Fenton process was also studied under several operating conditions. It was found that a large amount of hydrogen peroxide (i.e. mole ratio H2O2:HCHO > 6) was necessary to mineralize more than 90% HCHO in 1-2 h, at atmospheric pressure and 25 °C. The combination of pressure and high temperature strongly increased the kinetics of the process and allowed achieving a very high overall efficiency of the treatment under moderate H2O2 dosage.