Tube Settler Coverage in a Circular Clarifier

Tube settler coverage is the minimum required area tube settlers must cover to obtain the desired treatment. By nature of the shape, the calculations for circular clarifiers are a bit more complicated. However, the variables in the equation are standard measurements. To calculate in English units, all you need to know is basin flow in MGD, overflow rate in gpm/ft2, and clarifier diameter in ft.

(# MGD) / (# gpm/ft2) / (1440 min/day) = Minimum Required Area
Tank Diameter / 2 = Clarifier Radius
Pi * R2 = Clarifier AreaClarifier Area – Minimum Required Area = Uncovered Area
SqRt(Uncovered Area/Pi) = Uncovered RadiusClarifier Radius – Uncovered Radius = Tube Settler CoverageTube settler coverage is the width of the ring of tube settlers around the outer edge of the clarifier. We were recently asked to calculate the coverage for a customer. Here is the example:

Tube Settler Coverage

Clarifier Details:
6 MGD Basin Flow
2 gpm/ftOverflow Rate
103.5-ft Clarifier Diameter

(6 MGD) / (2 gpm/ft2) / (1440 min/day) = 2083.3 ft2 Minimum Required Area

(103.5 ft) / 2 = 51.75 ft Clarifier Radius
Pi * (51.75 ft)2 = 8,413.4 ft2 Clarifier Area

(8,413.4 ft2) – (2,083.3 ft2) = 6,330.1 ft2 Uncovered Area
SqRt[(6,330.1 ft2) / Pi] = 44.9 ft Uncovered Radius

(51.75 ft) – (44.9 ft) = 6.85 ft Tube Settler Coverage > Round up to 7 ft

This meets the Minimum Required Area as the 7-ft ring of tube settlers has a coverage area of 2,122.1 ft2.

2 responses to “Tube Settler Coverage in a Circular Clarifier”

    • Hi Brian – Our experience in municipal wastewater secondary clarifiers is limited. We currently have two successful installations, one in the USA and one in Canada. A controlled pilot study at the Canada site has indicated even after increasing plant flow by three to four times, improved effluent quality was achieved after installation of Brentwood tube settlers.

      As there are no design standards in the industry regarding solids loading rates for tube settler applications in wastewater, a pilot study is recommended. The pilot study will provide information on: coverage area; solids loading requirement; effluent quality at specific hydraulic and associated solids loading rate for a given MLSS level; and biological growth, which will also assist the end user to make adjustments to clarifier operation factors such as RAS ratio, WAS ratio and pumping/piping system at increased treatment capacity.