Novel Hybrid ‘powdered Activated Carbon – Fenton Oxidation’ Processes for Water Treatment

This paper reports on the development of hybrid water treatment technologies that take advantage of the attributes of activated carbon adsorption and Fenton oxidation through the development of novel hybrid process schemes: i) a continuous Powdered Activated Carbon (PAC) – Fenton process using a dilute suspension of PAC in a well-mixed reactor vessel connected to a submerged ultrafiltration (UF) membrane module for the continuous production of purified water, with no reject stream, in combination with the in-situ electrosynthesis of hydrogen peroxide (PAC-EF-UF), ii) a PAC-EF-UF process coupled with ultraviolet light irradiation for treatment performance enhancement leading to the Photo-Electro-Fenton process (PAC-PEF-UF). Preliminary results are presented herein of the PAC-Fenton process efficiency for degradation of diclofenac; the latter is a widely used non-steroidal anti-inflammatory drug and one of the most frequently detected pharmaceutically active compounds in surface waters (rivers, lakes). The adsorption characteristics of diclofenac and the regeneration capacity of PAC was investigated under homogeneous and heterogeneous Fenton reactions. Specifically, batch experiments were carried out using iron (II) sulfate heptahydrate as a precursor salt in the PAC solution (homogeneous system) and Fe-loaded PAC (heterogeneous system), both in combination with the external addition of H2O2. Emphasis was given on the optimization of the composite PAC/Fe material in terms of diclofenac adsorption and regeneration capability. In the case of the classic homogeneous Fenton treatment of PAC at acidic pH (~3), a significant loss of the adsorption capacity was observed (~60%), regardless the concentration of the Fenton reagent (H2O2/Fe salt) used. Diclofenac treatment with the optimum composite PAC/Fe adsorbent resulted to slight increase of solute adsorption (from 197.4 mg/gPAC to 203 mg/gPAC/Fe), and a smaller loss of the adsorption property (~25%) after the regeneration (heterogeneous Fenton) at neutral pH. Research is ongoing regarding the optimization of PAC regeneration through the synthesis of effective PAC/Fe materials for their subsequent testing in the novel PAC-(P)EF-UF system developed in the laboratory.