A new hydrodynamic treatment device is developed and tested in this study. The device contains two vertical concentric cylinders designed to intercept and retain sediments, oil and grease, and floatables from storm water runoff. This dissertation presents the findings on the performance of the device using simulated storm water. Removal characteristics are analyzed. This design provides good removal performance for suspended solids and oil and grease. Other advantages of this device are its compactness and flexibility for configuring in different modes.
Analyzing cost-benefits can provide a reference for engineers and researchers to estimate performance of best management practices (BMPs), conduct storm water management plans, and develop discharge regulations, etc. Two popular mathematical expressions are formulated and then utilized to illustrate the cost-benefit relationships. Cost-benefit relations for storm water BMPs are conceptually illustrated in a graph and discussed. Suspended solids removals via an ideal settling tank and via the hydrodynamic treatment device are used to illustrate the relationship and effectiveness calculation. Calculated effectiveness coefficients are higher for the hydrodynamic separator compared to an ideal settling tank.
A first order wash-off model is used to evaluate the significance of first flush. Assuming an exponentially decreasing concentration during a storm event, concentration is modeled as a function of a first flush coefficient (Cff), cumulative runoff depth, and initial pollutant concentration. Pollutant mitigation data from a wetland receiving runoff from a highway section in Ohio were obtained for the first flush analysis. It shows that the first order model and Cff provide a means to quantitatively evaluate the significance of first flush. Moreover, element models are established to analyze the first flush characteristics under complicated runoff situations, such as runoff from a large area, via a detention/retention device and when a constant pollutant source is present. Visual Basic programs are created to conduct the numerical analysis, and it is observed that the significance of first flush tends to be reduced under complicated conditions. This result matches well with the field data and some previous postulations.