The proposed electrochemical method is focused on the removal of nitrate and nitrite from wastewaters, which contain toxic organic compounds, heavy metals, high concentration of nitrate or other salts and extremely high or low pH values. An example of such wastewaters are the low level nuclear wastes (LLW), which are characterised by low radioactivity and contain about 1.6-2.2 M NaNO3, 0.4-0.6 M NaNO2 and 1.1-1.5 M NaOH. Low level nuclear wastes constitute 99 % of overall nuclear wastes. The destruction of nitrate and nitrite is necessary in order to eliminate possible groundwater contamination that could occur from the leaching of these species.
This electrochemical system exhibits high rate and high selectivity of conversion of nitrate and nitrite to nitrogen, low operation cost and broad range of applications, regardless of the solution composition. According to this method, nitrate can be converted to the non-toxic nitrogen and nitrous oxide with a yield of about 92%. The high yield is accompanied with high reaction rate of about 300-400 mA cm-2. The by-products are hydrogen gas and ammonia (yield ~ 8%). In addition, the removal of nitrate is not affected by the presence of salts, toxic compounds and heavy metals. The current efficiency in this case is 100% at the first electrolysis steps and then it drops to 75% as the concentration of nitrate decreases to zero. The energy consumption is 0.1 KWh/gN and it can be significantly reduced to about 0.02 kWh/gN by a better design of the electrochemical reactor.