Streaming potential, definition

The definition of streaming potential was presented in the previous section. Here, we derive the relation between the streaming potential and the zeta potential and discuss some of the issues that must be considered in comparing zeta potentials obtained by different electrokinetic measurements. 

In order to maintain a definite contact area, soHd supports for the solvent membrane can be introduced (85). Those typically consist of hydrophobic polymeric films having pore sizes between 0.02 and 1 p.m. Figure 9c illustrates a hoUow fiber membrane where the feed solution flows around the fiber, the solvent—extractant phase is supported on the fiber wall, and the strip solution flows within the fiber. Supported membranes can also be used in conventional extraction where the supported phase is continuously fed and removed. This technique is known as dispersion-free solvent extraction (86,87). The level of research interest in membrane extraction is reflected by the fact that the 1990 International Solvent Extraction Conference (20) featured over 50 papers on this area, mainly as appHed to metals extraction. Pilot-scale studies of treatment of metal waste streams by Hquid membrane extraction have been reported (88). The developments in membrane technology have been reviewed (89). Despite the research interest and potential, membranes have yet to be appHed at an industrial production scale (90). 

Many nanoproducts either release ENMs into the wastewater stream during use (collected and treated) or release the bulk of the ENMs only during end-of-life-treatment. In this indirect release, ENMs are potentially removed in the effluent or discharge from treatment (waste incineration plant, wastewater treatment). One should, however, keep in mind that only carbonaceous materials can be definitively destroyed in treatment. Metals and metal oxides may be retained but will persist. Measures to prevent the entry of ENMs into the environment for products with indirect ENM release could be taken at the product design and manufacturing stage or at the treatment stage. 

Electrolytic treatment technologies have definite advantages over these more common treatment processes. The primary benefit is that chemical change in an electrochemical process is brought about by the ability to add or remove electrons from species to be treated. This eliminates the use of redox agents to treat wastes and also removes the need to treat spent redox streams. Other, equally important, benefits of electrochemical processes include close control of reactions through control of the applied potential or current lower operating temperatures and hence lower costs increased possibility of on-site treatment, especially in small-scale use possible simultaneous use of the anode and cathode for waste minimization and the ability to... 

---