# 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.

## Where to get Wastewater Lagoon Design Spreadsheets

For wastewater lagoon design spreadsheets in either U.S. or S.I. units, click here to visit our spreadsheet store.  Obtain convenient, easy to use spreadsheets for wastewater lagoon design calculations at reasonable prices. Read on for information about the use of Excel spreadsheets for wastewater lagoon design.  Three types of wastewater lagoons that will be discussed next are the anaerobic lagoon, the facultative lagoon, and the maturation pond.

## Anaerobic Wastewater Lagoon Design

Anaerobic lagoons are most useful for incoming wastewater with a high BOD content.  If present, an anaerobic lagoon would typically be the first type of treatment, often followed by facultative and or maturation ponds.  Anaerobic lagoons are deeper than facultative or maturation ponds, usually 8 to 15 ft.  Anaerobic wastewater lagoon Design is usually based on volumetric loading (kg BOD/day/m3 or  lb BOD/day/1000 ft3).  A specified minimum hydraulic retention time may also be used.

## Facultative Wastewater Lagoon Design

The classic type wastewater treatment lagoon is the facultative pond.  It is aerobic at the  top with an anaerobic sediment layer at the bottom.  Algae growing in the lagoon are important for maintaining dissolved oxygen in the pond.  There are often one or more primary facultative ponds and one or more secondary ponds.  A typical three cell layout for two primary cells and one secondary cell is shown in the diagram below.  A well designed and operated facultative lagoon system can provide secondary level treatment if algae are removed from the effluent.  Facultative wastewater lagoon design is typically based on surface loading (kg BOD/day/ha or lb BOD/day/acre).  A specified minimum hydraulic detention time is often used as a design factor also.

## Maturation Wastewater Lagoon Design

A maturation pond will typically be the last type of pond in a wastewater lagoon system if it is present.  There is usually little additional BOD removal in a maturation pond.  Its primary function is disinfection/reduction in bacterial content.  Maturation pond design is often based on required reduction in coliform bacteria with perhaps a minimum hydraulic retention time.

## A Screenshot for a Wastewater Lagoon Design Spreadsheet

For a wastewater lagoon design spreadsheet with calculations in S.I. or U.S. units, or for other spreadsheets for activated sludge wastewater treatment calculations, see: www.engineeringexceltemplates.com

The Excel spreadsheet screenshot below shows part of a spreadsheet for wastewater lagoon design calculations, available  at our spreadsheet store in either U.S. or S.I. units at a very reasonable price.

References

1.  USEPA, Principles of Design and Operations of Wastewater Treatment Pond Systems for Plant Operators, Engineers, and Managers, EPA/600/R-11/088, August 2011.

2. Mara, D. & Pearson, H., Design Manual for Waste Stabilization Ponds in Mediterranean Countries, Lagoon Technology International Ltd, 1998.

# Activated Sludge Calculations in a Solids Mass Balance Spreadsheet

## Where to Find a Solids Mass Balance Spreadsheet for Activated Sludge Calculations

For Excel solids mass balance spreadsheets to make activated sludge calculations calculations, click here to visit our spreadsheet store.  Obtain a convenient, easy to use spreadsheet for solids mass balance activated sludge calculations for only \$22.95. Read on for information about the use of an Excel spreadsheet for estimating the effect of recycle flow, BOD and TSS through solids mass balance activated sludge calculations.

## Solids Mass Balance Background for Activated Sludge Calculations

Several streams from sludge treatment processes are typically recycled back into the wastewater treatment plant inflow.  Examples are sludge thickener overflow, anaerobic digester supernatant, aerobic digester supernatant, centrate from centrifuge dewatering, and filtrate from filtration dewatering.  The liquid flow, BOD load, and TSS load in these recycled streams contribute to the wastewater flow to be handled by the mainstream wastewater treatment processes.

An iterative solids mass balance is an organized procedure for estimating the total flow rate, BOD load, and TSS load in the recycled flows from sludge treatment and handling processes.  This type of calculation is illustrated in an eight page example in Metcalf and Eddy (Reference #1).  The flow diagram below shows a typical set of sludge treatment processes and recycle flows for an activated sludge plant.

## Activated Sludge Calculations Influent and Effluent Inputs for Spreadsheet

General information about the wastewater influent flow and characteristics will need to be input to the spreadsheet along with information about target effluent characteristics.  The screenshot below shows typical influent and effluent inputs needed.

Solids Mass Balance Activated Sludge Calculations for Each Treatment Process

The next step is solids mass balance calculations for each of the treatment processes, leading to estimates of the recycle flow rate, BOD load and TSS load for each recycle stream.  For a wastewater treatment plant with the flow diagram shown above, there would need to be solids mass balance calculations for the primary clarifier, the aeration tank/secondary clarifier, the sludge thickener, the anaerobic digester, and the sludge dewatering process.  The screenshot below shows typical inputs and outputs for a solids mass balance over a sludge thickener.

Similar calculations would be made for each of the wastewater treatment and sludge treatment/management processes, leading to information about recycle flow rate, BOD load, and TSS load, for each recycle stream as shown in the summary tables in the next section.  After completion of the first iteration, the recycle flowrate, BOD load and TSS load are added to values for those parameters for the incoming wastewater and all of the solids mass balance calculations are repeated in a second iteration.

Summary Tables

The screenshot below shows a set of tables summarizing the results of the calculated recycles flows from the first three iterations of the activated sludge calculations.   Spreadsheets are available to make this type of solids mass balance calculations in either U.S. or S.I. units at a very low cost (only \$22.95) in our spreadsheet store.  These spreadsheets are set up to make the solids mass balance calculations for four iterations.

References

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.

2. Bengtson, Harlan H.,  “Activated Sludge Solids Mass Balance Spreadsheet,”  an online blog article.

# Activated Sludge Secondary Clarifier Design Spreadsheets

## 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.

# Activated Sludge Aeration Tank Design with Excel Spreadsheets

## Where to Find Spreadsheets for Activated  Sludge Aeration Tank Design

For Excel spreadsheets to use for activated sludge aeration tank design or operation calculations, click here to visit our spreadsheet store.  Get an easy to use spreadsheet to make a variety of activated sludge aeration tank design calculations for a very reasonable price. Read on for information about activated sludge aeration tank design and operation calculations.

The activated sludge process is widely used for biological wastewater treatment all over the world.  This method of biological wastewater treatment was invented in England in about 1914.  An activated sludge wastewater treatment system always has an aeration tank and secondary clarifier, which function as a unit to remove biodegradable organic matter (biochemical oxygen demand or BOD) and suspended solids from the wastewater and keep the aerobic microorganisms that carry out the treatment in the system.  Most types of activated sludge processes also have a primary clarifier that removes settleable solids from the incoming wastewater before it goes to the aeration tank.  A flow diagram for a typical activated sludge wastewater treatment plant is shown in the diagram below.  The diagram shows the typical flow pattern through the primary clarifier, aeration tank and secondary clarifier mentioned above, plus initial preliminary treatment (screening, flow measurement and grit removal) and disinfection, which is usually the final step in wastewater treatment.

This article will emphasize the equations, parameters, and calculations for design and operation of the aeration tank/secondary clarifier of an activated sludge plant.

## Parameters for Activated Sludge Aeration Tank Design Calculations

The diagram at the left shows a typical flow pattern for a conventional activated sludge aeration tank and secondary clarifier.  Some of the parameters that are typically used in activated sludge aeration tank design calculations are shown for the primary effluent, secondary effluent, waste activated sludge, and recycle activated sludge. The following list shows those parameters, along with some others that are used for activated sludge calculations, with their U.S. and S.I. units.

• primary effluent flow rate, Qo,  (MGD – U.S. or m3/day – S.I.)
• primary effluent biochemical oxygen demand (BOD) concentration, So, (mg/L – U.S. or g/m3 – S.I.)
• primary effluent suspended solids conc., Xo, (mg/L – U.S. or g/m3 – S.I.)
• aeration tank volume, V, (ft3 – U.S. or m3 – S.I.)
• aeration tank MLSS (suspended solids conc.), X, (mg/L – U.S. or g/m3 – S.I.)
• secondary effluent flow rate, Qe,  (MGD – U.S. or m3/day – S.I.)
• secondary effluent susp.solids conc., Xe, (mg/L – U.S. or g/m3 – S.I.)
• secondary effluent biochemical oxygen demand (BOD) concentration, Se, (mg/L – U.S. or g/m3 – S.I.)
• waste activated sludge flow rate, Qw, (MGD – U.S. or m3/day – S.I.)
• waste activated sludge biochemical oxygen demand (BOD) conc., Sw, (mg/L – U.S. or g/m3 – S.I.)
• waste activated sludge susp. solids conc., Xw (mg/L – U.S. or g/m3 – S.I.)
• recycle activated sludge flow rate, Qr, (MGD – U.S. or m3/day – S.I.)
• Food to Microorganism ratio, F:M, (lb BOD/day/lb MLVSS – U.S. or kg BOD/day/kg MLVSS – S.I.)
• Hydraulic retention time, HRT, (hours for U.S or S.I.)
• Sludge retention time (also called sludge age), SRT, (days for U.S. or S.I.)
• Volumetric loading, VL, (lb BOD/day/1000 ft3 – U.S. or kg BOD/day/m3 – S.I.)
• % volatile solids in the aeration tank mixed liquor suspended solids, %Vol.

## Activated Sludge Aeration Tank Design Calculations with Excel Spreadsheets

The table below shows the typical range of values for three commonly used activated sludge aeration tank design parameters: volumetric loading, hydraulic retention time, and food to microorganism ratio. The table includes design information for three activated sludge variations: conventional plug flow, complete mix, and extended aeration activated sludge plants.

The spreadsheet image below uses Excel formulas to calculate the required aeration tank volume based on values provided for the input parameters shown in the spreadsheet: primary effluent flow rate, Qo; primary effluent biochemical oxygen demand (BOD), So; Aeration tank MLSS, X; design volumetric loading, VL; and % volatile solids in the aeration tank, %Vol.  The Excel spreadsheet uses the input data to calculate the design value of aeration tank volume, V, and values for two other design parameters that are sometimes used to size the aeration tank, hydraulic retention time in the aeration tank, HRT, and food to microorganism ratio, F:M, using the following equations.

• V = [ (8.34*So*Qo)/VL ] (1000)
• VMGV*7.48/1,000,000
• HRT = 24*VMG/Qo
• F:M = (8.34*So*Qo)/(8.34*%Vol*X*VMG)  =  (So*Qo)/(%Vol*X*VMG)

For Excel spreadsheets to make a variety of activated sludge aeration tank design and operation calculations in either U.S. or S.I. units for a very reasonable price, click here to visit our spreadsheet store.

## Activated Sludge Aeration Tank Operational Calculations with Excel Spreadsheets

The table below shows typical ranges for several commonly used operational activated sludge waste water treatment process parameters. Note that the values for all of these parameters remain the same for U.S. or S.I. units.  MLSS concentration will have the S.I. unit of g/m3, which is numerically equal to the U.S. units of mg/L. SRT will have units of days for either the U.S. or S.I. system.  F:M will have the S.I. unit of kg BOD/day/kg MLVSS, which is numerically equal to the U.S. unit of lb BOD/day/lb MLVSS. The % unit for Qr/Qo remains the same for U.S. or S.I. units.

The Excel spreadsheet image shown below uses the input values to calculate the activated sludge operational parameters shown.  The input parameters required are: primary effluent information (flow rate, Qo; BOD, So; and TSS, Xo); TSS in the waste and recycle activated sludge streams, Xw; the aeration tank volume, V; aeration tank MLSS, X; % volatile solids in the MLSS, %Vol; and sludge retention time, SRT.

The activated sludge operational parameters calculated by the Excel formulas in the spreadsheet are: recycle activated sludge flow rate, Qr; waste activated sludge flow rate, Qw, and aeration tank food to microorganism ratio, F:M. The equations used are as follows:

• Qr = (X – Xo)/(Xw – X)
• VMGV*7.48/1,000,000
• Qw = (8.34*VMG*X)/(8.34*SRT*Xw)  =  (VMG*X)/(SRT*Xw)
• F:M = (8.34*So*Qo)/(8.34*%Vol*X*VMG)  =  (So*Qo)/(%Vol*X*VMG)

For Excel spreadsheets to make a variety of activated sludge aeration tank design and operation calculations in either U.S. or S.I. units at a very reasonable price, click here to visit our spreadsheet store.

## References

References for Further Information:

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.

2. Vesilind, P.A. and Morgan, S.M., Introduction to Environmental Engineering, 2nd Edition, Belmont, CA, Brooks/Cole, 2004.

3. Grady, C.P.L., Daigger, G.T., Lim, H.C., Biological Wastewater Treatment, 2nd Edition, New York, NY, Marcel Dekker, Inc., 1999.

4. Bengtson, Harlan H. “Biological Wastewater Treatment Process Design Calculations,” available as an Amazon Kindle e-book and as a paperback.

5. Bengtson, Harlan H., “Activated Sludge Calculations Spreadsheet: Aeration Tank Calculations,” an Amazon Kindle e-book.