The design of conventional settlement devices used for primary treatment at wastewater treatment works has traditionally been based on generalised loading criteria. These generalised loadings do not necessarily take into account the nature and settling characteristics of the suspended material in influent wastewater streams. The paper describes the practical use of wastewater characterisation, in the form of settling velocity distributions, for the design of primary sedimentation devices, such as the hydrodynamic separators used in the Swirl-FloTM process.

Results of settling velocity distributions for diverse wastewater sources (including municipal and industrial sources) are presented together with comparisons between steady-state model predictions with observed performance for waste streams at different sites. The observed differences in settling characteristics for the wastewater streams investigated, together with the implications these have for design and performance assessment, are used as basis for advocating the need to incorporate wastewater settling characteristics in the design process for wastewater sedimentation devices.

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