# A Spreadsheet to Calculate Oxygen Requirement Activated Sludge Process

## Oxygen Requirement Activated Sludge Background

The theoretical oxygen requirement for BOD removal can be approximated as ranging from  0.90 lb O2/lb BOD removed at an SRT of 5 days to 1.3 lb O2/lb BOD removed at an SRT of 20 days.  This leads to the equation:

O2 requirement in lb/day  =  0.90  +  [(SRT – 5)/(20 – 5)](1.3 – 0.9)(lb/day BOD removed)

A design increase factor (safety factor) is typically multiplied times the calculated oxygen requirement to get the design oxygen transfer rate.  The design oxygen transfer efficiency and the air density at design conditions can then be used to calculate the design air flow rate.  The blower horsepower can then be calculated from the following equation:

Blower hp  =  (Qair)(ΔP)/(229*η)

Where:

• Qair is the air flow rate in cfm to be delivered by the blower
• ΔP is the pressure rise across the blower in psi  = outlet pressure – inlet pressure
• η is the blower efficiency

If oxygen is to be provided for nitrification as well as BOD removal, then additional calculations are needed to estimate the oxygen requirement for nitrification.

## Example Spreadsheet to Calculate Oxygen Requirement Activated Sludge Process

A spreadsheet to Calculate oxygen requirement activated sludge process is partially shown in the image below.  It can be used to calculate the oxygen requirement and blower specifications for an activated sludge wastewater treatment system.  This Excel spreadsheet, as well as others for wastewater treatment calculations, is available in either U.S. or S.I. units for a very reasonable price in our spreadsheet store.

References:

1.  Bengtson, Harlan H., “Activated Sludge Oxygen Requirement,”  an online blog article.
2. Bengtson, Harlan H., “Activated Sludge Calculations Spreadsheet: Aeration Tank Calculations,”  an Amazon Kindle e-book.
3. Bengtson, Harlan H., “Biological Wastewater Treatment Process Design Calculations,”  available as a paperback book or Amazon Kindle e-book

# Sequencing Batch Reactor Design Calculation Spreadsheet

## Sequencing Batch Reactor Design Calculation Background

A typical activated sludge wastewater treatment process operates as a continuous flow process, with incoming wastewater flow coming into a primary clarifier and treated effluent continuously coming off from the secondary clarifier.  A sequencing batch reactor wastewater treatment system, on the other hand, operates as a batch system.  Two or more tanks are required.  While one tank is receiving influent wastewater (the “fill” part of the cycle), another tank is undergoing aeration (the “react” part of the cycle), settling (the “settle” part of the cycle) and decanting of treated effluent (the “decant” part of the cycle).  This is illustrated in the diagram below.

## Sequencing Batch Reactor Design Calculation Applications

A sequencing batch reactor wastewater treatment system has a great deal of flexibility.  It can be used for traditional BOD removal and nitrification using the four cycle components shown above.  In that case there may be aeration for at least part of the fill cycle.  If denitrification is to be accomplished also, then there should be no aeration during the fill cycle.  If the SBR wastewater treatment system is to be designed for biological phosphorus removal as well, then an anaerobic react period is needed after the fill portion of the cycle, and an anoxic react is needed after the aerobic react part of the cycle, as shown in the diagram below.

## Example Sequencing Batch Reactor Design Calculation Excel Spreadsheet

The Sequencing Batch Reactor Design Calculation excel spreadsheet partially shown in the image below can be used to make a variety of design calculations for an SBR wastewater treatment system.  Based on input information about the wastewater flow rate and characteristics, as well as the treatment objectives, the spreadsheet leads the user through calculations for deciding on times for each part of the SBR cycle, tank number and size, and checks on the adequacy of the design.  This Excel spreadsheet, as well as others for wastewater treatment calculations, is available in either U.S. or S.I. units for a very reasonable price in our spreadsheet store.

## Reference:

Bengtson, Harlan H.,  “SBR Wastewater Treatment Plant Design Spreadsheet,” an online blog article.