Evaluation of baffles for optimisation of waste stabilisation ponds : a thesis presented in partial fulfilment of the requirements for the degree of Master of Engineering in Environmental Engineering at Massey University, Palmerston North, New Zealand

Abstract

Waste stabilisation ponds are a common form of treating wastewater throughout the world and they provide a reliable, low-cost, low-maintenance treatment system. A literature review undertaken highlighted the need for improved understanding of the hydraulics of such systems, and their upgrade. In particular, the application of baffles is not well understood beyond the use of longer, traditional baffles to increase the approximation to plug flow. The mechanisms and interactions behind baffles are not generally understood. The work involved the use of CFD modelling to assess various pond designs. In addition to this, traditional tracer studies were carried out on a physical laboratory model, and on a full-scale field pond. These traditional studies highlighted the success of the computer modelling approach. CFD modelling was used to model twenty pond designs, utilising various baffle lengths, number and position. These cases also studied inlet type and outlet position. In the second phase of the work, six of the CFD designs were tested in the laboratory setting. The final phase of work involved two tracer studies carried out on a field pond, utilising a modified inlet, then a combination of a modified inlet and the inclusion of a short (stub) baffle. CFD modelling has shown to be an effective investigative and design tool. The addition of results from laboratory and field studies further emphasises the benefits of the CFD modelling. The work has also provided an understanding of key flow mechanisms and interactions that have previously been attributed to other factors. Single baffles are not generally effective, and a minimum of two baffles will generally be required to achieve significant treatment improvements. The potential of short (stub) baffles has been shown, however they are sensitive to design changes and should be further researched. Previous research has looked at the pond using a 'black-box' approach, this work seeks to open and explain the flow patterns within that 'black-box'