Analysis Method for Total Nitrogen in Chlorinated Wastewater Containing Ammonium Nitrogen from Sewage Treatment Plant

The total nitrogen concentration in chlorinated wastewater from a sewage treatment plant included a large amount of ammonium nitrogen as determined by a measurement method established by the Water Pollution Prevention Act, but it was less than the concentration of dissolved inorganic nitrogen. The total nitrogen concentration may have been underestimated because some of the chloramines in the sample changed to nitrogen gas or nitrous oxide gas under alkaline conditions. Therefore, we evaluated a novel pretreatment method for total nitrogen analysis. The recovery rate of total nitrogen in a sample including 1 mg L-1 ammonium nitrogen and 1 mg L-1 available chlorine from sodium hypochlorite was enhanced to 98% by the addition of 50 mmol L-1 sodium sulfite solution, which accounted for at least 0.4 vol% of the sample. Additionally, a recovery test was carried out with some real samples. The recovery rates of total nitrogen in wastewater from the sewage treatment plant and in water from the environment around the plant were 100-104% after the addition of 50 mmol L-1 sodium sulfite solution.