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Clarification / Sedimentation

Clarification discharge Clarification discharge

Sedimentation has been the mainstay process for solid-liquid separation in the water and wastewater industry since its inception, based upon the simple fact that because solids are heavier than water, they will settle in a quiescent basin. This belies some of the complexities of the detailed design of settlement basins, be they clarifiers or thickeners, and the mechanisms required to ensure that they function correctly and reliably in the given application. Ovivo’s expertise and offering in this field is second to none. Our application experience covers: circular, rectangular, conical and flat bottom tanks. Various clarifier (scraper) bridges are available together with innovative designs to encourage settlement and mixing of coagulants when used.

Further Details

 A simple Stokes Law approach is often unsuitable, due to:

  • The impact of fats, oils and greases on grit and primary settlement
  • Coagulation and flocculation of colloidal particles
  • The essential requirement for rapid sludge removal after biological nutrient removal

Coupled with this, the actual areas of a clarifier or settlement tank have to be designed to optimize their function for overall effective operation, such as:

  • The inlet and feedwell configuration, to ensure effective distribution and to avoid short circuiting
  • The dewatering zone, the bottom slope and sludge removal configuration, to maximize sludge concentration, but avoid rat holing
  • Launder and weir design, which should ensure effective collection of clear water and to avoid sludge carry over
 

 

Tank Design

All of these issues have been addressed in those areas of the world that have been treating their water and sewage for many years, and certain customs, traditions and design norms have developed to capture this plethora of detailed design options; for example:

  • Rectangular or circular design bridge and drive design, center or peripheral
  • Echelon, logarithmic spiral or simple rake design
  • Inlet configuration: concrete feedwell, center column, peripheral pipe