The practical application of computational fluid dynamics to dissolved air flotation, water treatment plant operation, design and development

Computational fluid dynamics (CFD) can be applied to the advancement of dissolved air flotation (DAF) plant design. The use of CFD in design and predictive analysis, in particular here with reference to the upgrading of an existing DAF plant from 30 to 60 Ml/d and associated diagnostics, while still developing, helped by the emergence of ever more powerful computational systems, can be regarded as an established tool providing beneficial and useful data, although on occasions care may be required in the interpretation of results. The initial CFD studies were undertaken using the existing and upgraded works flows and structures at both ‘low’ and ‘high’ temperatures, i.e. 2 and 20°C, while the modelling results are reported using graphical representations of ‘contours of flow velocity’ and ‘velocity vectors’. In addition the degree of short circuiting based on T₁₀ together with other retention parameters T₅₀ and T₅₀/m are reported. Further modifications were also considered: how changes to the incline baffle and tank depth can impact on the predicted distribution, vorticity and in practice on the actual subnatant water quality measured in terms of turbidity. Finally applying CFD to DAF plant design is shown to be a beneficial tool for the designer.