Determination of Ammonia Nitrogen in Landfill Leachate Using an Automated Kjeldahl Method

Landfill leachate is characterized by high concentrations of ammonia nitrogen and a highly complex matrix, making the Nessler’s reagent spectrophotometric method susceptible to significant interference. Therefore, an automated Kjeldahl method suitable for complex landfill leachate was established in this study. Leachate samples collected from Nanning and Fangchenggang were used to optimize distillation conditions and titration endpoints, and the method performance was evaluated in terms of the limit of quantification, precision, and recovery. A paired t -test was conducted to compare the results with those obtained by the Nessler method. The results showed that stable measurements were achieved at a distillation time of 240 s, with a practical limit of quantification (P-LOQ) of 1.0 mg/L. For actual samples, relative standard deviations were below 5.0%, and recoveries obtained by the Kjeldahl method ranged from 96% to 104%. No significant difference was observed between the two methods (P > 0.05), and recoveries by the Nessler method ranged from 87.7% to 105.2%. These results indicate that the automated Kjeldahl method is suitable for routine monitoring of ammonia nitrogen in landfill leachate.