Parasitic current minimization

Since the electrical resistance of the effiuent and parasitic currents are minimal at high level of impurities, specihc interest in electrically assisted membrane processes could increase due to more strict laws and legislation around effluents. The depletion of freshwater resources and the necessity to process brackish or seawater to produce potable water could promote the use of electrically assisted membrane processes in the future. Electrodialysis will have to compete with pressure-driven membrane processes such as reverse osmosis. The growing awareness of the unique cleaning ability of electrically ionized water (EIW) [47], a byproduct of electrodialysis, may be a factor to consider in the choice between ED and RO systems. NMR relaxation measurements were used to determine the water cluster size of electrically ionized water EIW. It is known that the water cluster size of EIW is signihcantly smaller than that of tap water. The smaller water cluster size is believed to enhance the penetration and extractive properties of EIW. Recently, EIW has been produced and used in several cleaning processes [47] in industry. 

Another source of inefficiency are the shunt currents arising in all series-connected systems with a common electrolyte. In the EDA system, these parasitic currents are minimized to some (model computed) 5% power loss by maximizing the hydraulic resistance. 

Current efficiency is defined as the fraction of the total current participating in the desired reaction. The portion of the current that produces undesired products is usually a function of the current density generally, parasitic reactions are more likely to be favored at higher current densities. Overall energy efficiency is the product of the voltage efficiency times the current efficiency. In an optimization it is useful to examine the magnitudes of the losses from the various sources and to determine whether the major losses can be minimized. 

The Lever oscillator [39], Fig. 16, allows the application of series resonance configurations with one-side quartz electrode grounding. Since the effect of parasitic capacitance is minimized and simple shielding is possible, this circuit configuration is especially suited for under-liquid QCM. Besides the series resonance frequency, the series resonance resistance Rs can be measured. For this purpose the Lever oscillator allows a largely transistor current gain-independent measurement of the resistance. An automatic level control provides a signal proportional to Rs. 

The major efficiency loss arises from the recombination of (e cB) with either unreacted h" or adsorbed OH. This is minimized in PEC by applying a constant current or anodic potential to a semiconductor-based thin film anode subjected to UV/Vis illumination. Since the photoinduced electrons are continuously extracted from the anode through the external electrical circuit, parasitic reactions are inhibited, and the production of h" from reaction (14) and OH from reaction (16) is accelerated. The coupling of PEC with either EF or PEF is much more effective, due to the synergistic oxidative action of the photoanode and OH formed in the bulk via Fenton s reaction (1). PEC has been performed with planar or annular semiconductor photoanodes and three-dimensional nanotube arrays, being mainly qiplied to decolor-ization of dyes. 

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