Influence of operating conditions on the ammonia electro-oxidation rate in wastewaters from power plants (ELONITA™ technique)

Power plants, like many other industries, are confronted with the need to reduce the nitrogen content of their wastewaters. Indirect electro-oxidation, through hypochlorite formation, is a possible answer to an ammonia–nitrogen problem, through converting it into gaseous nitrogen. Several parameters affect the ammonia oxidation rate: current density, chloride concentration and the presence of oxygen-containing anions, mainly SO42−, CO32− and PO43−. pH values between 5.5 and 10 have been found to have no effect on the ammonia oxidation rate. However, at higher pH values (above 11), the oxidation slows down and chlorate ions appear. A model can be fitted from the experiments to predict the ammonia oxidation rate based on four main parameters: pH, current density, sulfate concentration and chloride concentration. The average difference between the predicted oxidation rates and the experimental measures is only 6.5%. This model confirms that the optimal operating conditions are a high chloride concentration (7 g l−1), no sulfate and a high current density (1200 A m−2).