Nanofiltration and Fenton's process over iron shavings for surfactants removal.

The presence of surfactants in wastewater composition tends to jeopardize the efficiency of the traditional aerobic treatment processes. In this regard, the application of Fenton's reaction and nanofiltration as single processes and integrated (nanofiltration followed by Fenton's process) was investigated on the abatement of a solution containing two surfactants usually found in effluents coming from detergent industry (dodecylbenzene--DDB and sodium lauryl ether sulphate--SLES). The potential of a solid waste (iron shavings) as catalyst in the Fenton's process was evaluated and the reaction system was optimized regarding the key operating parameters (iron and hydrogen peroxide concentration and pH). The highest chemical oxygen demand (COD) degradation (66%) was attained for pH 3, [H2O2] = 32 mM and 50 g/L of iron shavings. Besides, it was concluded that oxidation was due to hydroxyl radicals adsorbed on the metal surface even if bulk interaction between hydrogen peroxide and dissolved iron cannot be neglected. The main variables ruling nanofiltration were evaluated (pH, temperature and cross-flow rate). Eighty-four percent of COD rejection was determined at pH 7.5, cross-flow 14.4 cm3 s(-1), 20 degrees C and 15 bar of pressure drop. Finally, nanofiltration followed by Fenton's process under the best conditions was integrated; however, no significant improvement was attained with 85% of COD being globally removed.