2018 Volume 41 Issue 6 Pages 193-203
To evaluate the properties indicated by biological oxygen demand (BOD) and chemical oxygen demand (COD) in lakes and rivers, we compared the BOD and COD with total organic carbon (TOC) in the waters of Lake Biwa, its inflowing river, and various discharge effluents. Biodegradation tests were also conducted to investigate the relationship between biodegradability, BOD, and COD. No correlation was observed between BOD and labile organic matter obtained by the 100-day biodegradation test. The BOD shows only a small part of biodegradable components. The BOD is strongly related to particulate organic matter, indicating that the initial biodegradation is largely due to the decomposition of particulate organic matter. Although the COD values in the lake and its inflowing river waters are roughly equivalent to half of TOC, COD and TOC data have high correlation and similar variance. The COD distribution reflects the fluctuations of organic matter in the lake and rivers. However, the COD detection includes 1) overestimation at low concentration, and 2) partial detection based on properties of organic matter. The different COD detection rates depending on the concentration and quality of the samples considerably affect the estimated amounts of organic matter in the lake and its watershed, particularly in the low concentration range.
