A study on the relationship between BOD₅ and COD in a coastal seawater environment with a rapid BOD measurement system

The dual objectives of this study are to: (1) examine the relationship between COD and BOD in seawater environment with a rapid but reliable method for the measurement of BOD in seawater, and (2) establish the relationship model between BOD₅ and COD in the firth of Dongbao River to predict the values of BOD₅. The first objective is met by the successful development of a technique utilizing bacteria-immobilized membrane flow cell for biodegradation process, coupled with fibre optic fluorescence detection for oxygen depletion quantitation. The technique has been applied to coastal seawater samples collected in the coastal area of Shenzhen, China. The BOD₅ and COD values for the samples are acquired and the results show that there is no apparent linear relationship existing between BOD₅ and COD in relatively clean seawater samples away from the shore. However, in estuary water samples containing relatively high concentration of sewage contamination, a linear correlation does exist between BOD₅ and COD. The linear relationship between the two parameters allows for the calculation of BOD₅ values based on COD data which can be measured more readily and precisely.