Magnetic removal of surfactants from wastewater using micrometric iron oxide powders

The aim of this paper is the study of a sustainable process for the treatment of urban wastewater able to reduce surfactant concentrations close to the back-ground levels or, at least, lower than the values allowed by law for a reuse in agriculture. The considered process is based on the adsorption of surfactants (water diluted) on commercial iron oxide powders and their removal in a magnetic filtration system. The powders of hematite and magnetite used have a diameter of 0.5 µm, 1 µm. 5 µm, respectively; they are non-toxic for humans and the environment and they have a relatively low cost. The removal of surfactants on a laboratory scale at concentrations in the wastewater range (0.2 mg/l - 4.2 mg/l) was studied applying the treatment on pure surfactants, mixtures of pure surfactants and detergents. With regard to the adsorption on magnetite, despite the large quantity of powder required (17-51 g/l), the tests led to positive results for cationic surfactants (up to 90% of removal) and relatively good for the anionic (up to 20%) and non ionic ones (up to 40%). Adsorption on hematite has shown encouraging results with regard to all surfactants (from 50% to higher than 90% of removal) with a much lower amount of powder required (1-17 g/l). In all cases the adsorption took 10 minutes and the magnetic separation of the iron oxides was fully achieved after 10 minutes of filtration.