Removal of Cr(VI) from tanning wastewater using chitosan-SDS complexes in PEUF: Optimization and analysis via response surface methodology

In this study, we addressed the removal of hexavalent chromium (Cr(VI)), a highly toxic and soluble anionic heavy metal, using enhanced ultrafiltration (UF). The objective was to eliminate Cr(VI) species with molecular weights beyond the retention capability of standard UF membranes and achieve their retention through the incorporation of polymers and polymer-surfactant complexes within the UF membrane. Chitosan, a cationic polymer, and sodium lauryl sulfate (SDS), an anionic surfactant, were used in this context. The Cr(VI) solution was subjected to ultrafiltration in a laboratory-scale membrane cell, and its removal was assessed spectrophotometrically. Polymer and surfactant structures were characterized using turbidity, electrical conductivity, SEMEDX, and FTIR analyses. Experimental studies were conducted using the face-centered central composite design (CCD) of the response surface methodology (RSM) to determine optimal removal and permeate flux values, as well as to unveil the relationships between the studied factors and the resulting responses. The results revealed that 100 % of the Cr(VI) species were removed from wastewater in the chitosan-based polymer-enhanced ultrafiltration (PEUF) study. With the chitosan-SDS complex, a removal efficiency of 98.33 % was achieved in synthetic wastewater. The PEUF study employing chitosan and the chitosan-SDS complex yielded permeate flux values of 30.73 L/h/m2 and 53.89 L/h/m2, respectively. The optimized conditions obtained from the models were then applied to real wastewater obtained from a leather industry tanning process. In the case of chitosan and the chitosan-SDS complex, the Cr(VI) removal efficiencies in the real wastewater were 4.40 % and 98.33 %, respectively.