Removal of heavy metals by surfactant-enhanced ultrafiltration from wastewaters

This study examines the effects of cationic and anionic surfactants on the performance of surfactant-enhanced ultrafiltration process. In particular, the separated removal of lead and arsenic from wastewater is investigated by using dodecylbenzenesulfonic acid (DSA) as anionic surfactant and dodecylamine as cationic surfactant. The ultrafiltration process is performed by means of a monotubular ceramic membrane of nominal pore size 20 nm (molecular weight cut-off: 210 kDa). Pb and As ions are removed from the water flow one at a time using both DSA and dodecylamine. Metals and surfactants are added in a biologically treated wastewater from a municipal wastewater treatment plant and then ultrafiltered. Concentrations of lead and arsenic introduced in the water vary from 4.4 to 7.6 mg/l, while DSA and dodecylamine concentrations are equal to 10–5 M and 10–6 M, respectively, both of them below their critical micelle concentration. The results show a quantitative removal of lead ions >99% in the Pb/DSA and Pb/dodecylamine systems, while it was observed a decrease of arsenate ions in both of systems of about 19%. The almost complete retention of lead cannot be due only to surfactants, but also to its bioabsorption by the abundant organic matter present in solution, while AsO4- ions, being very toxic, are not adsorbed by microorganisms, therefore the removal is very low. The rejection of other main constituents found in wastewaters is already presented.