Electrochemical conversion of ammonia to nitrogen in non-chlorinated aqueous solution by controlling pH value

The conversion of ammonia to nitrogen at Ti/PbO2 anode in non-chlorinated solution by controlling the pH value was discussed in detail in this work. The results showed the pH value made a great effect on the conversion of ammonia to nitrogen during electrolysis. Ammonia was converted to nitrogen primarily by direct oxidation in alkaline solution, whereas it was oxidized by OH radicals in acidic solution. The 80-min electrolysis at 15 mA/cm2 showed that the conversion rates of ammonia increased about 3.5 times as pH from 3.0 to 5.0 and 2.0 times from 9.0 to 11.0. High pH value caused the accumulation of NO3− with electrolysis time. The accumulation rate was 9.61 mg-N/(L ⋅ h) at pH 11.0, about six times of that at pH 9.0. For actual wastewater with the pH of 5.0, the ammonia oxidation rate was 41 mg-N/(L ⋅ h), 95% of removed ammonia converted to N2 and only 4.83% to NO3− within the electrolysis time of 120 min.