The sediment oxygen demand (SODtT) can be assumed to be a 4-phase process as follows :
1. Oxidation of many unstable chemical substances (SODtC);2. Biochemical reaction for rapid assimilation of organic nutrients into bacterial cell. From the experimental data, this phase consists of a two-stage reaction (SODti1, and SODti2);3. And a subsequent slow oxidation of biological cell material through endogenous respiration (SODte).
Each reaction given above can mathematically be expressed by a first-order kinetics. These reactions contain no fewer than ten unknown parameters : four ultimate oxygen demands, four rate-constants, and two time-lags, but these parameters are determined by the modification of Lee's graphical method.
The sediment used is taken from three sea areas, including a drain pipe near sewage works, an oyster farm, and shido Bay.
In all sediments the rate-constants of the chemical oxidation, the bacterial growth phase, and the endogenous respiration are 2.2 day-1, 1.6 day-1, and 0.10 day-1, respectively. And a summary of other parameters is shown in Table 2.
The component curves of SODtT can mathematically be determined by using these results, and the course of SODtT is calculated by summing the four component curves.
Consequently, the calculated curve agrees well with the observed data.
