Investigation of micellar-enhanced ultrafiltration (MEUF) using rhamnolipid for heavy metal removal from desalter effluent

The removal of heavy metals from desalter effluent is an important issue due to the toxicity of these pollutants. In this study, micellar-enhanced ultrafiltration (MEUF) is applied for the removal of heavy metals from synthetic desalter effluent. MEUF is a process in which surfactants above their critical micellar concentration (CMC) form micelles. Micelles bind compounds with low molecular weight; then, these are rejected by a semi-permeable membrane. Rhamnolipid is an anionic biosurfactant that has advantages such as biodegradability and low CMC. Rhamnolipid complexation with synthetic desalter effluent demonstrates high efficiency for heavy metal removal. The highest overall removal efficiency was reached at a rhamnolipid concentration of 300 mg/L with 94.07%, 81.93%, 99.81%, 76.00%, and 41.91% for Zn+2, Mg+2, Cu+2, Mn+2, and Na+, respectively. Additionally, loading capacity on rhamnolipid micelles was evaluated to have better selectivity for Mn+2 > Cu+2 > Zn+2 > Mg+2 > Na+. Also, the results showed that phenol has a significant effect on heavy metal removal, decreasing CMC, which increases micelles. Finally, the permeate flux decreases after increasing the rhamnolipid concentration due to the formation of the gel layer, creating an additional resistance to the permeate flux that goes through the membrane. This work shows that MEUF with rhamnolipid is a reliable method for heavy metal removal from desalter effluent.