Analysis of flux decline during rhamnolipid based micellar-enhanced ultrafiltration for simultaneous removal of Cd+2 and crystal violet from aqueous solution

Abstract

Micellar enhanced ultrafiltration (MEUF) experiments were carried out with rhamnolipid (RHL) biosurfactant in a stirred cell for removal of Cd+2 and crystal violet (CV), simultaneously from aqueous solution. The influence of various operating conditions on the transient profiles of permeate flux and observed rejections were investigated. Experimental results revealed that for the treatment of aqueous feed under optimal conditions (RHL: 1730 × 10−3 kg. m−3; Cd+2: 30 × 10−3 kg. m−3; CV: 15 × 10−3 kg. m−3; NaCl: 5 kg.m−3; pH:7.8), the process condition (414 kPa, 600 rpm and 40 °C) was found to be the most suitable to achieve the permeate flux of (75 ± 1.5) L.m-2. h-1 at volume concentration ratio of 2 with more than (98 ± 0.1)% rejections of both the pollutants (Cd+2 and CV) and minimum surfactant loss (<3 %) to the permeate. The rapid decline in permeate flux at the earlier stage of filtration was attributed to adsorption-pore blocking followed by gradual decline at the later stage due to the growth of a cake layer of RHL-pollutant aggregates on the membrane surface. The transition of fouling mechanism occurred in the range of 200−390 s depending on the operating conditions. A combined model based on resistance-in-series theory coupled with Hermia’s constant pressure cake-filtration model was developed to analyze the profiles of flux decline and observed rejections of Cd+2, CV and RHL. The predicted results showed a good agreement with the experimental data. The developed model was successfully tested to other MEUF studies. The estimated model parameters in this study would help in design and scaling up of such MEUF process.