Comparison and evaluation of methods for the measurement of total nitrogen in wastewater

The measurement methods for total nitrogen in wastewater containing a high concentration of nitrogen were evaluated. (1) The UV spectrophotometry, (2) reduction-distillation Kjeldahl, (3) total Kjeldahl nitrogen, and (4) ion chromatography methods were applied. The experimental procedure of the UV spectrophotometric method was simple, but it produced large errors deriving from the dilution of samples and calibration standards. While, the reduction-distillation Kjeldahl method didn't need dilution, but the amount of Devarda's alloy and NaOH lead to large errors up to 50 mg/L. The levels of total nitrogen measured by each method were as follows: reduction-distillation Kjeldahl (568.6 +/- 38.7 mg/L) > UV spectrophotometry (527.3 +/- 9.6 mg/L) > total Kjeldahl nitrogen method (494.7 +/- 21.4 mg/L) > ion chromatography method (417.9 +/- 7.3 mg/L). Therefore, the reduction-distillation Kjeldahl method is preferred for wastewater with the high concentration of nitrogen. Optimal conditions for each experimental procedure, however, are needed to be confirmed, and the Standard Operation Procedure (SOP) for total nitrogen is required for reliable measurements.