Concentration of organic contaminants by ultrafiltration

The results of concentration experiments on model dye solutions containing anionic surfactant and mineral salts were reported. The objective of the study involved recovery of valuable substances and water reuse. The membrane efficiency as well as dye and surfactant rejections during concentration tests were evaluated. The Mollsep Fiber (Nadir) modules with membranes made of polyethersulfone (10 and 30 kDa) were used in the experiments. The anionic surface active agent (sodium dodecyl sulphate) and sodium chloride (NaCl) were added to the dye (Direct Black) solutions. The concentration experiments were conducted at 0.1 MPa. The effect of concentration factor on the volume flux of dye solutions, dye and surfactant rejection was studied. It was found that membrane permeability and dye separation factor was kept constant during concentration process for all experimental solutions. Surfactant retention was highly influenced by solution composition and subjected to great variations. Nevertheless, it was possible to receive two streams in UF process: concentrated dye solutions and water containing anionic surfactant (SDS).

(1) The Mollsep Fiber (Nadir) modules (10 and 30 kDa) yielded over 97% retention of organic dye (Direct Black) irrespective of the value of concentration factor and solution composition. Anionic surfactant (SDS) and mineral salt (NaCl) had a slight negative effect on permeate quality in the course on concentration process. (2) The module permeability was kept almost constant during concentration of aqueous mixtures of dye, surfactant and mineral salt. (3) The Mollsep Fiber (Nadir) modules (10 and 30 kDa) exhibited poor surfactant (SDS) retention — less than 60%. The content of SDS in permeate was highly influenced by solution composition and subjected to great variations in the course of concentration process. (4) It was possible to fractionate the dye-surfactant solution into two streams: concentrate — mostly rich in organic dye, containing a certain amount of SDS, and permeate — rich only in surfactant.