抄録
Chemical Oxygen Demand (COD) of subsurface brine of water-soluble natural gas is higher than that of sea water. We investigated why the brine has higher value than sea water.
We adopted as samples both Narutoh gas field water and artificial brines. The latter samples contained inorganic ions such as NH4+, HCO3-, Br-, I- etc. These ions are more concentrated in those samples both in Narutoh field water and in the artificial brines than in sea water.
COD of these samples were determined adopting acidic KMnO4 method at 100°C.
As most ions tested, except halides, hardly misled the determination, they could not virtually influence on COD value.
3 halide ions interfered COD determination, leading to higher value than usual. As bromide ion as well as chloride ion could be masked with silver salt in JIS method, COD value could not be misdetermined by both ions.
To get net COD value, it was necessary to exclude iodide ion as silver iodide from the reaction system, because iodide ion was unmasked with silver salt.
Some of organic compound dissolved in the brine was considered to be another oxygen scavenger.
