Development of guidelines for improved hydraulic design of waste stabilisation ponds

Abstract

Pond hydraulic behaviour is influenced by the inlet/outlet configuration, baffles and wind, but design information relating to these factors is still very limited. This paper reviews the development of "Guidelines for the Improved Hydraulic Design of Waste Stabilisation Ponds" and summarises some of the key findings and recommendations. This work was based on review of previous research, laboratory experimentation, field studies and mathematical modelling using computational fluid dynamics. The inlet design can have a significant influence on the flow regime in a pond. Poorly considered positioning of the inlet and the outlet can create hydraulic short-circuiting problems. As an example of the nature of the work undertaken in this project, the use of a small horizontal inlet pipe was compared against a vertical inlet design. A practical method of assessing the relative significance of wind versus inlet power input was presented. The application of this analysis may allow engineers to size inlet pipes to help control the flow patterns in ponds for efficient performance. Extensive testing has been undertaken on a wide range of baffle configurations. An example of this research showed how short stub baffles could provide similar improvements to longer "traditional" baffle designs, potentially offering significant savings in construction costs. For traditional baffle designs a minimum of two baffles is recommended. For the pond modelled in this work, it was found that any more than four baffles gave only marginal improvements.