OXIDATION OF NONIONIC SURFACTANTS BY FENTON AND H₂O₂/UV PROCESSES

Abstract

The oxidation of 10 nonionic surfactants (6 alcohol ethoxylates and 4 alkylphenol ethoxylates) by Fenton and H₂O₂/UV processes was investigated in synthetic (deionized water) and real aqueous matrices, i.e. secondary effluent from municipal wastewater treatment plant and groundwater. Batch tests were carried out to assess the optimal dosages of reagents leading to the total removal of surfactants.

Regardless to the specific surfactant, both Fenton and H₂O₂/UV treatments of synthetic solutions containing one single surfactant (C₀=14 mg l⁻¹) always caused its rapid and quantitative removal (96–99%) with a corresponding very low (0–18%) TOC decrease.

Only for the Fenton treatment, linear relationships were found between the amounts of H₂O₂ and Fe²⁺ necessary for surfactant removal and the ethoxy chain length of each surfactant. Conversely, in the case of H₂O₂/UV treatment the H₂O₂ dosage causing the quantitative oxidation of the treated surfactant depended on the length of both chains: the ethoxy and the hydrophobic one.

Mixtures of the 10 surfactants (1.4 mg l⁻¹ each) were treated in both synthetic and real matrices. These latter were different in the case of Fenton (i.e. municipal secondary effluent) or H₂O₂/UV (i.e. real groundwater) treatments.

Fenton treatment of municipal secondary effluent containing the surfactants mixture led to its total removal when a molar ratio [Total surfactants]/[H₂O₂]/[Fe²⁺] equal to 1/17/12 was used. As for H₂O₂/UV treatment of real groundwater samples, quantitative removal of surfactants mixture was achieved with a molar ratio [Total surfactants]/ [H₂O₂] equal to 1/7.4.

Surfactants mixture removals, if compared in deionized water and in real matrices, showed the same matrix effect during both treatments, i.e. less amounts of reagents were always required in synthetic solutions.

Keywords:

• Advanced oxidation processes
• alcohol ethoxylates
• alkylphenol ethoxylates
• wastewater treatment
• groundwater pollution

ACKNOWLEDGEMENTS

The authors wish to acknowledge Mr. Vito Locaputo, Mr. Giuseppe Labellarte and Mrs. Nicoletta Rapanà for their assistance in carrying out the experimental work.