# Dissolved Air Flotation Design Calculations Spreadsheet

## Background for Dissolved Air Flotation Design Calculations

Dissolved air flotation is an alternative to clarification for removal of fine suspended mater from a water or wastewater stream. It is especially good for fine suspended matter that doesn’t settle out well with regular clarification. The air-solids ratio, A/S, is typically calculated with the following equation:Where:  sa is the air solubility, f is an efficiency factor, P is the recycle pressure, R is the recycle flow rate, Sa is the influent suspended solids concentration, and Q is the influent flow rate.  The required DAF area can be calculated based on a design value for DAF hydraulic loading rate or based on a design value for DAF solids loading rate.

## Example Dissolved Air Flotation Design Calculations Spreadsheet

An example dissolved air flotation design calculations spreadsheet is partially shown in the image below.  This Excel spreadsheet can be used to calculate A/S, the needed air to solids ratio, and the required DAF area based on user input information on influent design flow and characteristics.  This Excel spreadsheet, as well as others for wastewater treatment process design calculations, is available in either U.S. or S.I. units for a very reasonable price in our spreadsheet store.

References:

1. Metcalf & Eddy, Inc, (Revised by Tchobanoglous, G, Burton, F.L, Stensel, H.D.), Wastewater Engineering, Treatment and Reuse, 4th Ed., New York, NY, 2003.

2. Bengtson, Harlan, “DAF Design Calculations Spreadsheet,” an online blog article

# Activated Sludge Secondary Clarifier Design Spreadsheets

## Where to Find Activated Sludge Secondary Clarifier Design Spreadsheets

For an Excel spreadsheet for activated sludge secondary clarifier design calculations, click here to visit our spreadsheet store.  Obtain a convenient, easy to use primary and secondary clarifier design spreadsheets for only \$11.95.  Read on for information about the use of an Excel spreadsheet for activated sludge secondary clarifier design calculations.

## Activated Sludge Secondary Clarifier Design Parameters

The parameters typically used for activated sludge secondary clarifier design are the surface overflow rate (SOR), solids loading rate (SLR), and weir overflow rate (WOR).  Activated sludge parameters are shown in the flow diagram at the right.  The equations defining these three parameters are:

SOR = Qo/A,  SLR = (Qo + Qr)X/A, and  WOR = Qo/L,  where:

• Qo = primary effluent flow rate in MGD (U.S.) or m3/d (S.I.)
• A = total surface area for secondary clarifier(s) in ft2 (U.S.) or m2 (S.I.)
• Qr = recycle activated sludge flow rate in MGD (U.S.) or m3/d (S.I.)
• X = mixed liquor activated sludge solids concentration in mg/L (U.S. or S.I.)
• L = length of secondary clarifier effluent weir in ft (U.S.) or m (S.I.)

Typical values of surface overflow rate and solids overflow rate for activated sludge secondary clarifier design are shown in the tables below:

## Calculation of Activated Sludge Secondary Clarifier Surface Area

The equation for calculating the needed activated sludge secondary clarifier surface area from a design SOR value with units as shown above is:  A = Qo*106/SOR

The formula for calculating activated sludge secondary clarifier surface area from a design value of SLR with parameter units as shown above is:  A = (Qo + Qr)*8.34*X/SLR

## An Excel Spreadsheet as an Activated Sludge Secondary Clarifier Design Calculator

The Excel spreadsheet template shown below can be used to carry out the activated sludge secondary clarifier design calculations described above.   Why bother to make these calculations by hand?  This Excel spreadsheet can handle primary and secondary clarifier surface area calculations and determine diameter for circular clarifier(s) or length and width for rectangular clarifier(s) and is available in either U.S. or S.I. units at a very low cost (only \$11.95)  in our spreadsheet store.  These spreadsheets also make weir overflow calculations to aid in effluent weir design.

Reference

1. Metcalf & Eddy, Inc, (revised by Tchobanoglous, G, Burton, F.L., Stensel, H.D., Wastewater Engineering Treatment and Reuse, 4th Edition, New York, NY, 2003.