Recovery of iron (III) from aqueous streams by ultrafiltration

Biological wastewater treatment plants (BWWTP) are widely used to treat effluents from chemical process industry. However, there exist refractory substances, such as phenolic compounds, which require previous treatments. Advanced oxidation processes (AOP) are thoroughly being studied as pre-treatment to deal with such phenolic compounds before a BWWTP. Metal salts are widely used as homogeneous catalysts in AOP because they present higher activity than those heterogeneous. Unfortunately, to prevent subsequent environmental damage, they have to be recovered (and/or recycled) from the reactor effluent, which increases the treatment cost. Iron is often added as effective catalyst in the abovementioned AOP. In this study, a 5 kDa molecular weight cut-off (MWCO) ultrafiltration ceramic membrane (TAMI Industries, France) is tested to directly retain iron species from water. The influence of transmembrane pressure, solution pH, iron concentration and iron valence (Fe2+ and Fe3+) over iron retention at room temperature is investigated. The results indicate that there is a strong connection between iron speciation and recovery efficiency. When soluble charged iron hydroxide species are present in solution, high retention is attained, up to 99.9%. Thus, the retention mechanism involved could be the interaction between these metal hydroxides in solution and the membrane surface, forming a dynamic membrane.