Advanced Hydraulic Studies on Enhancing Particle Removal

The removal of suspended solids and attached pollutants is one of the main treatment processes in wastewater treatment. This thesis presents studies on the hydraulic conditions of various particle removal facilities for possible ways to increase their treatment capacity and performance by utilizing and improving hydraulic conditions. Unlike most traditional theses which usually focus only on one particular subject of study, this thesis contains four relatively independent studies which cover the following topics: a newly proposed particle settling enhancement plate, the redesign of the inlet zone of a high-flow rate clarifier, identify the hydraulic problems of an old partially functioned CSO facility and investigate possible ways to entirely eliminate untreated CSO by improving its hydraulic capacity and performance. In order to be easily understood, each part includes its own abstract, introduction and conclusions as well as the study results. All studies were carried out with a combination of numerical model and measurements. In the first part of the thesis a new concept of using a vortex to increase particle removal from liquid was proposed and the new particle settling enhancement plates, Vortex Plate, were tested under various flows and settling conditions. Structure of the Vortex Plate consists of multiple long narrow parallel slots which are built on a flat plate. Vortices are generated by cross-flow passing the long narrow parallel slots. The Vortex Plate can be used in the same way as the widely used lamellar plates with cross flow configuration. However, the Vortex Plate takes advantage of high flows, which generate stronger vortices and entrainment of solids in the downward direction inside the slots, the sliding particles are protected from the strong incoming main flow field. The study results show that under the tested flow conditions and particles the new Vortex Plate outperforms the conventional lamellar plate, especially for higher inflow rates and smaller particle size. Part two presents a numerical approach to redesign of the inlet structure of a high-rate storm water clarifier. The inlet zone of an existing rectangular storm water clarifier was redesigned to improve the fluid flow conditions and reduce the hydraulic head loss in order to remove the lamellar plates and adapt the clarifier to the needs of high-rate clarification of storm water with flocculant addition. Conventional design methods based on surface loading rate, mean residence time and other parameters do not provide enough detailed hydraulic information to guide the improvement of the performance of the clarifier. This inconsistency in the traditional approach is discussed in the thesis. The redesign procedure was directed according to 3-dimensional flow and particle behavior as simulated with hydrodynamic and particle transport models under various configurations of the hydraulic structure.

In part 3, the performances of a combined sewer overflow (CSO) storage/treatment facility in North Toronto (NT), Ontario, Canada was investigated by conjunctive numerical and physical (hydraulic) modeling. The main objectives of the study were to assess the feasibility of increasing the hydraulic loading of the CSO facility without bypassing and major structural modification. Numerical simulations identified excessive local head losses and helped to select structural changes to reduce such losses. The analysis of the facility showed that with respect to hydraulic operation, the facility is a complex, highly non-linear hydraulic system. Within the existing constraints, a few structural changes examined by numerical simulation could increase the maximum treatment flow rate in the CSO storage/treatment facility by up to 31%. In the last part, the same CSO facility as studied in part 3 was re-investigated with both the numerical and physical models. In order to keep the self contained format and to be easily understood, some background introductions about the NT CSO facility may overlap with the content of part 3. The main goal of this study is to upgrade the hydraulic capacity of the facility to totally eliminate the untreated CSO overflow (not only the bypass as the study goal in the part 3). A new and more powerful CFD model was used in this project. The study started with verifying the new model against measured data from a physical model. Two possible scenarios of structural changes were proposed and examined in detail by both physical and numerical models. Even though the study was focused on a particular CSO facility, the hydraulic conditions in the facility should represent general flow conditions in a typical water treatment facility. The numerical modeling method used in the study could be applied to solve the wide ranges of hydraulic problems faced in environmental and hydraulic engineering. Obviously, traditional design methods based on many simplified assumptions would not predict the actual operational performance as well as the new method outlined in the thesis.