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Use of rhamnolipid to remove heavy metals from aqueous streams via micellar enhanced ultrafiltration

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Abstract

In this research, the rhamnolipid biosurfactant was utilized in micellar-enhanced ultrafiltration (MEUF) of heavy metals from contaminated waters. The effects of different major operating conditions on the (MEUF) system performance were investigated for copper, zinc, nickel and cadmium using two membranes. The optimal conditions were successfully applied to treat six contaminated wastewaters from metal refining industries and three contaminated groundwaters using the two membranes (> 99% rejection ratio). To efficiently choose the most influential factors to the MEUF system, optimization by the response surface methodology approach was utilized and data quality was examined. Three studies were performed in order to investigate the mechanism and the interactions between the heavy metal ions and the rhamnolipid micelles in the rhamnolipid-based UF system. The first study successfully investigated the applicability of Gouy-Chapman approach for binding of heavy metal ions to rhamnolipid biosurfactant in the MEUF system and the mechanism via electrostatic attraction was suggested. The second study efficiently evaluated binding behavior of the four heavy metal ions individually and collectively onto the rhamnolipid. The order was Cu 2+ > Cd 2+ > Zn 2+ > Ni 2+ .The third study analyzed the equilibrium data using Langmuir, Freundlich, and linear adsorption models. The Freundlich model fitted the data better and the K F values were from 1.3 to 6.1. In addition, solidification/stabilization (S/S) technology was successfully used to stabilize solid wastes contaminated with heavy metal. Furthermore, preliminary trials were performed to examine the recovery of the rhamnolipid from the retentates for possible reuse. The amounts recovered ranged from 12 ± 1% to 18 ± 1% of the rhamnolipid concentration initially present in the retentate. Similarly, preliminary trials to reuse water from the retentates were investigated. The total portions recovered ranged from about 81.0 ± 0.34% to 82.3 ± 0.46$% of the total feed water. This work may be used as preliminary investigations for further detailed pilot and/or large-scale studies to treat contaminated groundwater and industrial wastewater.

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