Use of a focused microwave system for the determination of Kjeldahl nitrogen in industrial wastewaters

This paper demonstrates the use of a focused microwave method involving chemical digestion in two steps, mineralization and oxidation with H 2O2, for the determination of Kjeldahl nitrogen in industrial wastewaters. The most influential variables of the process (viz., microwave power, mineralization time, and oxidation time) were optimized by using an experimental design in conjunction with acetanilide as the reference substance. Tests revealed microwave power to have little effect on the extent of digestion in the range studied. The optimum mineralization time and oxidation time were both in the region of 10 min. However, the latter two must be adjusted as a function of the concentration and ease of degradation of the Kjeldahl nitrogen present in each sample. The proposed method was applied to industrial waste-waters of variable origin and found to provide results on a par with those of the standard method for this purpose, with digestion times shorter than this by a factor ranging from 6 to 60 depending on the ease of degradation of the particular sample. Copyright © Taylor & Francis, Inc.