UnitWorks: WWTP Unit Process Design Tools (Excel + Web + Manual)

Size a whole wastewater treatment plant in an afternoon, and show every step of the working.

UnitWorks is a set of process design tools for engineers who design, check or upgrade treatment plants. Size each unit on its own, or link them into a complete plant. Inlet works, BNR, MBR, clarifiers, disinfection, digestion and dewatering are all included, with the return liquors closed back to the inlet. Every result is checked against typical design criteria. When a check fails, it tells you what to change.

Watch the 70-second demo above to see the web tool and Plant designer in action.

What's in the download

• Design workbook (Excel): 34 unit-process modules, one sheet each, from design flows to sludge dewatering. Yellow cells are inputs, and every formula is visible and protected.
• Linked plant workbook (Excel): a complete 20 ML/d BNR plant built from the modules and linked by formulas, with a live flowsheet and the return liquors resolved by iteration.
• Web tool with Plant designer: all 34 modules in your browser, plus a designer that links them into a plant. It works offline, with nothing to install.
• 85-page user manual (PDF): step-by-step use of both Excel workbooks and the web tool; for every module, the method, inputs, results and checks, with a worked example. It also has design criteria tables and a fully worked 20 ML/d plant.

The Plant designer

• Choose the train: MLE, A2O bio-P, nitrification only, oxidation ditch, MBR or SBR, with or without primary settling, chemical P trim, UV or chlorination, and the sludge line.
• Enter population, per-person loads, temperatures and effluent targets. Every unit is sized from the one upstream.
• You get a drawn flowsheet with every tank shown, effluent quality against your targets, the water and nitrogen balances, and every design check in one place.
• Click any unit to open its full linked calculation and fine-tune it.
• Four example plants are ready to explore: a 20 ML/d MLE, a 20 ML/d A2O, a 4.5 ML/d oxidation ditch and a 10 ML/d MBR.

34 design modules

Design flows and loads; bar and fine screens; aerated and horizontal-flow grit; primary clarifiers; lamella settlers; activated sludge for BOD removal and nitrification; MLE denitrification; biological P removal; oxidation ditch; SBR; MBR with feed and permeate pumps and scour air; secondary clarifiers with state point analysis; RAS and WAS pumping; aeration and blowers; tertiary denitrification with methanol; trickling filters; MBBR for BOD, nitrification and denitrification; facultative ponds and aerated lagoons; chemical P removal; metal hydroxide precipitation; DAF; chlorination; UV; plant solids mass balance; gravity and mechanical thickening; anaerobic and aerobic digestion; centrifuge and belt press dewatering; UASB; septic tank and soil absorption.

Why engineers like it

• No black boxes: every step is shown with its symbol, unit and typical range, so you can follow it, check it and put it in a report.
• Built-in design checks: results are flagged OK, CHECK, HIGH or LOW against typical criteria, and each flag comes with a short note on what to change.
• Schematics for every unit, labelled with your live results, including a plan view of every tank.
• Tested: every module has worked examples, and the Excel and web versions give identical results.
• Fast to use: invalid inputs are highlighted, a glossary explains every term, and one click copies the results for your report.

Details

• SI units. No macros or add-ins.
• Excel workbooks: Microsoft 365, Excel 2019 or later, and Excel for Mac. The plant workbook uses Excel's iterative calculation.
• Web tool: any modern browser, works offline.
• Instant download after purchase, delivered as one zip file.
• Support: hello@wwtpplus.com

UnitWorks is a design aid. Results depend on the inputs and coefficients you choose. Check every design against your local regulations, standards and supplier data, and have it reviewed by a qualified engineer. Licensed to the purchaser for their own projects, including client projects. Not for resale or redistribution. © 2026 WWTP Plus.