Abstract
A mathematical model for evaluating the effects of environmental condition. i.e., light condition, flow rate, water temperature, stream depth, etc., on the changes in water quality in a channel was constructed. Structure and parameter values in the model were determined from the results of experiments using artificial channels and the results of batch experiments using artificial substrata attached with river-bed biofilm.
Calculation results by the model showed the concentration of dissolved oxygen (DO) should be maintained high (about more than 4 mg·l-1) for the removal of pollutants, i.e., total organic carbon (TOC), total nitrogen (T-N), and total phosphorus (T-P). High temperature was desirable for T-N removal. On the contrary, low temperature was desirable for T-P removal because high temperature increased DO consumption rate with decomposition of organic matter and increased release rate of phosphorous from river-bed biofilm. Temperature was not an influential factor for TOC removal. Increase in the area of support media for attachment of biofilm would not improve the removal of T-N and T-P because DO concentration was tended to become low with the consumption of DO by increased biofilm area.
