This work deals with fouling and successive cleaning of RO membrane fouled by an organic foulant, sodium alginate using a laboratory-scale cross flow test unit. First, spiral-wound RO membrane was fouled with sodium alginate solution up to 10% and 15%, respectively at an applied pressure of 1380 kPa with flow rate of 10 lit/min. An anionic surfactant, sodium dodecyl sulfate (SDS) was used as a chemical cleaning agent for cleaning of RO membrane. The effect of cleaning chemical dose and cross-flow velocity on the membrane chemical cleaning duration to achieve 100% cleaning efficiency (i.e., to get original water flux) was also investigated. As the SDS concentration increases, the membrane chemical cleaning time decreases due to increase in the solubility of the foulant (when the surface tension decreases by an increase in the SDS concentration). Furthermore, the membrane chemical cleaning time decreases with increasing cross-flow velocity of the cleaning chemical solution (SDS). Higher cross-flow velocity enhances the turbulence at the fouling layer and hence the mass transfer of the foulant from the fouling layer to the bulk solution is improved, then the SDS has weakened the structural integrity of the fouling layer. It is observed that better cleaning is occurred with higher concentration of SDS and flow rate. The obtained results clearly reveal that SDS cleaning is proved to be an efficient cleaning method for RO membranes fouled with organic foulant.

This work focuses on the membrane ultrafiltration technique to separate humic acids from aqueous solution. An unstirred dead end ultrafiltration of synthetic aqueous humic acids solutions of 50, 150 and 250 mg L -1 was performed with Polyethersulfone membrane. To observe the effects of applied transmembrane pressure (TMP) drops during separation, the experiments were carried out at 207, 276, 345 and 414 kPa with 50 kDa molecular weight cutoff (MWCO) membrane. The performance of this process is expressed in terms of volume reduction factor (VRF). To analyze flux decline and pore blocking behavior, Hermia's fouling mechanism models, namely, complete, standard, intermediate and cake filtration models have been studied in search of best fittings in flux decline system. After completion of the experiment with 50 mg L -1 feed solution, the concentration of Humic acids in permeate was 2.9 mg L -1 , revealing 94% rejection during the membrane ultrafiltration. Keywords: