Electrochemical waste water treatment using high overvoltage anodes Part 11 : Anode performance and applications

I wi Brou t t Bowrr. Corporare Rescwc-li CRB. CH-.The performance of highly doped SnO, anodes for the oxidative treatment of biologically refractory ~ a s t e water was compared with PbO, and Pt. The oxidation of a wide range of organic compounds proceeds with a n efficiency which is about 5 times higher than with platinum anodes. The oxidation efficiency was found to be independent of the pH of the wgter. In chloride containing media, SnO, anodes produce less chlorine gas than platinum anodes and hence show less potential to form hazardous chlorinated organic by-products. The design of a simple plate-and-frame reactor with undivided cells for waste water treatment using SnO, anodes was based on two experimental findings: (a) no interference of the cathode with the oxidation has been found: (b) the rate of oxidation is not limited by tnass transfer, indicating the participation of homogeneous reactions in the overall oxidation. The new anode material reduces the specific energy requirement of electrochemical oxidation of organics in waste water to 30 to 50 kWh kg-' of COD removed. This makes the process an interesting alternative to chemical oxidation using oxidants such as ozone and hydrogen peroxide, or \let oxidation using oxygen a t elevated temperature and pressure. Biological treatment of waste water has become the m o b t important process controlling the pollution of the aquatic environment by organic chemicals from municipal and industrial sources. The degradability of organic chemicals in a sewage plant depends strongly on the nature of the chemical compounds involved. Some of the chemicals that get into the waste water from industrial processes are degradable to such a bmall extent that they pass through the municipal sewage plants and accumulate in the environment. Legal practice in most countries has been to define a percentage of the chemical oxygen demand (COD) of a given waste stream which has to be removed by the biological treatment. In Germany for example, this ratio has been at 75%. in Switzerland 85%. It is most likely that the regulations will be tightened in the near future and that, as a consequence either industrial production will have to be changed and/or the treatment of industrial was 11 need addi'tional processes in order to co he legal requirements. Electrochemical oxidation as a pre-treatment of biologically refractory water contents before discharge to a bioloSical/mechanical sewage plant has been proposed among other competing …