Journal of Water and Environment Technology
Online ISSN : 1348-2165
ISSN-L : 1348-2165
Original Articles
Feasibility of Mercury-free Chemical Oxygen Demand (COD) Test with Excessive Addition of Silver Sulfate
Naoyuki KishimotoMasashi Okumura
ジャーナル フリー

2018 年 16 巻 6 号 p. 221-232


The conventional chemical oxygen demand (COD) test requires mercuric sulfate (HgSO4) for masking chlorides (Cl) in a sample. Since the use of mercury (Hg) will be strictly restricted under the Minamata Convention on Mercury, the feasibility of Hg-free COD test by closed reflux, colorimetric method with excessive addition of silver sulfate (Ag2SO4) was discussed in this research. Although Cl contamination tended to increase the dichromate consumption even in the conventional COD test, the Ag2SO4 dose in sulfuric acid reagent not less than 10.3 g/kg-H2SO4 successfully masked Cl not more than 500 mg-Cl/L. As a result of applying to 14 organic compounds with theoretical oxygen demand of 90 mg-O2/L, the Hg-free COD test tended to output slightly higher COD than the conventional one; the average degradation efficiency of 96% in the Hg-free test and 94% in the conventional test. The average accuracy for the Hg-free COD test was superior to the conventional one. In the economical viewpoint, the Hg-free COD test successfully cut off the chemical cost of Ag2SO4 and HgSO4 from 13,459 to 7,831 JPY/1,000 samples. Consequently, the Hg-free COD test was thought to be feasible for water samples containing Cl not more than 500 mg-Cl/L.

© 2018 Japan Society on Water Environment