A lab-scale set-up has been developed for studying the effects of boundary flow velocity and temperature on the sediment oxygen demand (SOD) of Shing-Mun River. The set-up was installed with upstream baffles to obtain even flow environment in the experimental study. It has been found that the correlation of the SOD with the flow velocity is approximately linear in the flow range of 0.035 m/s ~0.104 m/s at different temperature, while temperature effect on SOD rate is expressed as an exponential function of temperature in the range of 11°C to 35°C at different flow velocity. Therefore, temperature has a greater influence on the SOD than the flow velocity. A model for estimating the SOD rate has been developed in this study: SOD(gO₂ / m² / d) = 9.96U_se^0.076T _s ...[ Read more ]

A lab-scale set-up has been developed for studying the effects of boundary flow velocity and temperature on the sediment oxygen demand (SOD) of Shing-Mun River. The set-up was installed with upstream baffles to obtain even flow environment in the experimental study. It has been found that the correlation of the SOD with the flow velocity is approximately linear in the flow range of 0.035 m/s ~0.104 m/s at different temperature, while temperature effect on SOD rate is expressed as an exponential function of temperature in the range of 11°C to 35°C at different flow velocity. Therefore, temperature has a greater influence on the SOD than the flow velocity. A model for estimating the SOD rate has been developed in this study: SOD(gO₂ / m² / d) = 9.96U_se^0.076T

where : U_s = boundary flow velocity (m/s) T = temperature (degree C) The above model was generated from experimental data obtained under the following specific operation conditions: 1) flow velocity = 0.035 m/s ~ 0.104 m/s; 2) temperature = 11°C ~ 35°C; 3) initial DO concentration in overlying water = 6.4 ~ 7.0 mg/L; 4) COD concentration in overlying water = 23 ~ 28 mg/L 5) sediment thickness = 5 cm 6) organic content of sediment = 6 ~ 11% Through the overall mechanism study, it has been found that 62% of the SOD is from biological oxygen consumption within the sediment. Experimental data also implies that SOD should be mainly knited by oxygen mass transfer rate from the overlyingg water into the sediment.

Keywords: sediment oxygen demand, boundary flow velocity, temperature, Shing-Mun River