Electrolytic Clarification of Vegetable Washing Water : Fundamentals of the Electrolytic Process

Abstract

For the clarification of washing water from potato- and vegetable washing, the electro-chemical method proves superior to conventional sedimentation techniques because, after the necessary amount of electric energy has been ex- pended, the wastewater is clear within a short time and requires a reduced ba- sin surface for sedimentation. The present report describes the procedural prin- ciple of electrolysis, as well as its operational and performance parameters ba- sed on experimental studies during which standardized model washing water is subject to electrolytic clarification in a batch reactor. Appropriate setting of the parameters allows the electrolytic clarification of ve- getable washing water to be influenced: there is a direct connection between the electrolytic current and the process time required for electrolysis. The product of both parameters releases a defined quantity of electrode material for the pre- cipitation of a certain pollutant load (Faraday´s law). The amount of electroly- tic current also depends on the set electrolytic voltage, the properties and the size of the electrolytic unit, and the conductibility of the liquid to be treated. High electrolytic tensions, which result in very short process times for clarifi- cation, cause the development of large quantities of gas so that the amount of electricity employed cannot entirely be converted into chemical precipitation material. Therefore, the cost of electric work increases disproportionately. At low tensions, electrolytic treatment is more cost-efficient. Longer process times result in improved clarification performance. For the reduction of the COD, however, which is present in a dissolved form, even significantly prolonged cla- rification periods do not provide substantial improvement. The electrode com- bination aluminium/chromium steel (Al/XSt) allowed for high current densities and led to the best clarification results with regard to COD reduction.