Abstract
A physical model and a computational fluid dynamic (cfd) model (HYDRO-3D) have been developed to simulate the effects of novel maturation pond configurations, inlet and outlet positions, channels and critical environmental factors (wind speed and direction) on the hydraulic efficiency of maturation ponds at a small sewage treatment works in southern England. The ponds form the final, polishing stage of an otherwise conventional percolating filter treatment works. The final effluent of the plant joins a stream that discharges directly to a bathing beach. Thus the overall objective of the project is to maximise the efficiency of pathogen indicator removal and meet European bathing water standards. The specific aim of the study reported here was to calibrate the physical model and to assess its reliability as a tool for assessing and predicting hydraulic performance of ponds. Work focused on the comparison of simulation outputs from the cfd model and full scale system performance in order to increase the reliability of both models as design tools. The full scale ponds under study comprised three parallel, tertiary stage maturation ponds. A Geopacks flow meter was used to calibrate the ratio of water and wind velocities in the full scale pond channels and the model. Additionally floats and novel drogues were used to measure low flow velocities within the physical model. Initial tracer experiments using salt and rhodamine-WT were conducted to define the hydraulic retention time (HRT) of the physical model in still air and with top and bottom inlets and outlets. In the physical model the effect of back-mixing and dead zones can be readily observed and photographed, whereas this is more difficult to display in the outputs of computational models. Potential sources of disagreement are discussed in the thesis, but their concurrence suggests they both have a valuable role to play in the future design of ponds aimed at maximising hydraulic efficiency. The study also confirmed field observations which indicated that wind tends to be damaging rather than beneficial to pond performance. (Abstract shortened by ProQuest.).