Design Calculations Overview

Sizing and verification calculations for process units

Introduction

ErgoPlanner provides comprehensive design calculations based on industry standards and best practices. Use these tools to size equipment, verify capacity, and check design margins.

Calculation Categories

By Process

Category	Units Covered
Preliminary	Screens, grit chambers
Primary	Clarifiers, settlers
Biological	Reactors, biofilm systems
Secondary	Final clarifiers, DAF
Tertiary	Filters, UV, membranes
Sludge	Thickeners, digesters

By Method

Method	Description
Sizing	Determine equipment dimensions
Verification	Check existing equipment capacity
Optimization	Improve performance parameters

Design Standards

UK Water Industry

ErgoPlanner incorporates UK water company design criteria:

Parameter	Typical Criteria
Primary retention	2-3 hours at DWF
Secondary SOR	<1.0 m³/m²·h at 3DWF
Biofilter loading	0.15-0.3 kg BOD/m³·d
Humus tank SOR	1.2-2.0 m³/m²·h

International Standards

Standard	Coverage
WEF MOP 8	Clarifier design
Ten States	US design standards
ATV-DVWK	German standards
ISO	Quality systems

Detailed Guides

Primary Treatment

• Primary Tanks - Clarifier sizing
• Lamella settlers
• Imhoff tanks

Biological Treatment

• Biofilters - Trickling filter design
• Activated sludge sizing
• MBBR media calculations

Secondary Treatment

• Humus Tanks - Post-biofilter settling
• Secondary clarifier design
• DAF sizing

Chemical Systems

• Chemical Dosing - Dose calculations
• Storage tank sizing
• Mixing requirements

Key Design Parameters

Hydraulic Parameters

Parameter	Symbol	Unit
Surface Overflow Rate	SOR	m³/m²·h
Hydraulic Loading Rate	HLR	m³/m²·d
Hydraulic Retention Time	HRT	hours
Weir Loading	WL	m³/m·h

Organic Parameters

Parameter	Symbol	Unit
Organic Loading Rate	OLR	kg BOD/m³·d
Food/Mass Ratio	F/M	kg/kg·d
Sludge Loading Rate	SLR	kg MLSS/m²·h
Solids Retention Time	SRT	days

Design Workflow

Sizing New Units

graph TD
    A[Define Design Flow] --> B[Calculate Loads]
    B --> C[Select Unit Type]
    C --> D[Apply Design Criteria]
    D --> E[Size Equipment]
    E --> F[Verify Capacity]
    F --> G{Acceptable?}
    G -->|No| D
    G -->|Yes| H[Document Design]

Verification

1. Input existing equipment data
2. Define current/future loads
3. Calculate utilization
4. Identify bottlenecks
5. Recommend upgrades

Where the calculation forms are

You do not need a simulation run to open a sizing form. The forms take an influent you enter and work it through in the browser, and the runs you save from them are kept against a project or a drawing — never against a simulation run.

There are two places to open them, and they are the same forms in both:

Where	How to get there
Project detail page	Open the project → Calculations tab → Process calculations
Simulation editor	Bottom data panel → Calculation tab → Process calculations

Pick a module from the Calculation module box — type to search it — and its form opens underneath. Ten modules are offered: flow and load, primary tanks, biofilters, humus tanks, chemical dosing, alkalinity balance, sludge production, ballasted precipitation (CoMag), the headroom report, and mass balance.

The project mount is the one to use for design work that has no model yet, and it shows the runs saved against that project. The editor mount is convenient while you are in a model, and lists every saved run for the module.

Sharing a link to a form

Whichever module you have open is written into the address bar, so the link in your browser is already a link to it:

/admin/projects/<project-id>?tab=calculations&calc=process&module=coMag

Send that and your colleague lands on the same module. Reloading the page keeps you there too.

The editor's other surface, Unit sizing, is the one that does need a run — it reads flows and loads off a converged model for whichever unit is selected on the canvas. If no model has been run it says so, and points you at the Process calculations tab.

Using ErgoPlanner

Design Mode

1. Select unit type
2. Click Design Wizard
3. Enter design criteria
4. Review calculated dimensions
5. Accept or modify

Verification Mode

1. Enter existing dimensions
2. Specify loading conditions
3. View capacity analysis
4. Export design report

Example: Primary Clarifier

Design Inputs

Parameter	Value
Design flow	10,000 m³/d
Peak flow	30,000 m³/d
Influent TSS	250 mg/L
Target removal	60%

Design Criteria

Parameter	Criterion
HRT at DWF	>2 hours
SOR at 3×DWF	<1.5 m³/m²·h
Depth	3.0-4.5 m
Weir loading	<10 m³/m·h

Calculated Results

Parameter	Value
Required area	833 m²
Diameter	33 m
Depth	3.5 m
Volume	2,917 m³
HRT at DWF	7.0 h
SOR at 3×DWF	1.5 m³/m²·h

Design Reports

ErgoPlanner generates comprehensive design reports:

• Equipment schedule
• Design calculations
• Drawing references
• Specification notes

Report Sections

1. Design basis - Flows, loads, criteria
2. Calculations - Step-by-step sizing
3. Results - Final dimensions
4. Verification - Capacity check
5. Notes - Assumptions, references

Best Practices

1. Apply safety factors - 1.2-1.5 for design
2. Consider future loads - 20-year horizon
3. Check all conditions - DWF, PWF, peak
4. Document assumptions - For future reference
5. Peer review - Independent check

Related Topics

• Process Units
• Running Simulations
• Design Standards
• Templates

References

1. Metcalf & Eddy "Wastewater Engineering"
2. WEF Manual of Practice No. 8
3. UKWIR Design Guidelines
4. Ten States Standards