Design parameters for dissolved air flotation in South Africa

Dissolved air flotation has been used in South Africa for more than 25 years in the field of water and waste-water treatment, with practically all the development and verification done locally. This substantial body of knowledge and experience was recently condensed into a document titled A South African Design Guide for Dissolved Air Flotation. A general literature survey was combined with a detailed survey of 26 dissolved air flotation plants operating in Southern Africa, to arrive at suggested design parameters. Two broad categories of applications were covered in the guidelines - those of water clarification, and of activated sludge thickening. A clear trend emerged from the data collected. Drinking water clarification plants were generally designed within a fairly narrow range of the most design parameters, and the perception of operators and managers was that these clarification plants performed very efficiently. Sludge thickening plants, on the other hand, showed considerable variability in terms of most design parameters, and the general perception of its efficiency consequently varied from highly positive to negative. The paper includes summaries of the ranges of the actually surveyed design parameters, the suggested design values and a comparison with typical design values available from other countries.