FREE ENGINEERING TOOLSET · SOUTHEAST ASIA

Municipal Wastewater Treatment Design Manual

Engineering calculators and full calculation sheets for every unit of the treatment train — calibrated to tropical conditions (26–34 °C), Vietnam QCVN 14:2025 / QCVN 40:2025 and Indonesia PERMENLHK 68. Every constant traces to a cited source. Free to use; nothing is uploaded.

⚠ Screening values only. Every calculator on this page returns engineering screening estimates from simplified first-principle models — not a substitute for detailed design. Final equipment sizing, and any construction or permit submission, must be confirmed against the manufacturer's verified performance curves and the applicable local regulation (e.g., Vietnam QCVN 14 / QCVN 40, Indonesia PERMENLHK 68).

38live calculators
11process-chain groups
38calculation sheets (PDF / MD)
21English engineering notes
0emails sent automatically

The treatment train ALL LIVE

01 · Influent
Headworks & equalisation
5 tools
02 · Primary
Sedimentation
3 tools
03 · Biological
BOD / N removal
8 tools
04 · Secondary
Solid–liquid
3 tools
05 · Nutrient
Chemical P & carbon
1 tool
06 · Disinfection
Cl₂ · UV · O₃
3 tools
07 · Sludge
Thicken & digest
3 tools
08 · Tertiary
Polish & reuse
4 tools
09 · Compliance
Permit monitoring
1 tool
10 · I&C
Manual, 5 units
5 tools
11 · Balance of plant
Piping & dosing
1 tool
Run them in order: the biological unit feeds the clarifier, the clarifier feeds the sludge train, and the tertiary units close the reuse loop. Every tool ends with an instrumentation list you can quote at factory-direct price, and every tool hands its results to the next one — no re-typing the duty.

Start here — the core chain

If you only open four tools, open these. They carry the design and they hand their numbers to everything downstream. Each ends with "Get this calculation (PDF)" — instant download of your inputs, results and sources; no email is ever sent automatically.

Aeration Oxygen Demand

Sludge age → sludge production → AOR → SOR → air flow → blower power, with tropical temperature and elevation correction (APHA saturation, Benson & Krause).
Feeds: biological sludge · alkalinity · effluent TN
Instrument list: DO · MLSS · air flow · blowers

A²/O Biological N & P Removal

Anaerobic–anoxic–oxic zone volumes, SRT, bio-P capacity vs the chemical-polish shortfall, internal-recycle sizing — the skeleton that joins aeration and chemical-P into one design chain.
Feeds: clarifier · chemical tool · sludge train
Instrument list: DO · MLSS · ORP · flow

Secondary Clarifier

Four-way SOR/SLR envelope sizing for new tanks, or a capacity check of existing ones — with the RAS-concentration-vs-SVI limit that quietly decides whether a BNR clarifier actually works.
Takes: MLSS & RAS from A²/O
Instrument list: RAS flow · MLSS · turbidity · ORP

Chemical P & Carbon Dosing

Alum / ferric / ferrous dose by target effluent TP (Me:P interpolation), alkalinity make-up (nitrification + chemical), sludge increment — plus external carbon to hit your TN limit.
Feeds: chemical sludge · sludge train
Instrument list: dosing pumps · pH/ORP · flow

10 Instrumentation & control manual — 5 units COMPLETE

A standalone manual, in order. Start at Unit 1 if you are wiring a transmitter; start at Unit 5 if you are building a panel and need a point count.

Unit 1 · 4–20 mA loop & cable sizing

Voltage budget for two-wire transmitters, load-capability check, the HART 230–600 Ω window and IS-barrier budget, with tropical cable derating.

→ Open Unit 1

Two-wire and HART loop voltage drop, maximum cable length, and the exact cable size that still leaves headroom.

Unit 2 · RS-485 Modbus bus

Length-versus-baud field limits with a propagation-delay check, daisy-chain and stub rules, 120 Ω termination, unit loads and IEC 61643-21 surge protection.

→ Open Unit 2

How far you can run at 9600 or 115200 baud, and where the surge protector goes per cable entry.

Unit 3 · Range & accuracy selector

Operating point as %FS, the 40–70 % golden band, the %FS trap, a control-versus-compliance verdict and the exact catalogue model to order.

→ Open Unit 3

Turn a process range into a real error figure and a purchasable model number.

Unit 4 · Monitoring-station UPS

Tick the analysers, set the hold-up time: UPS VA and battery Ah with lead-acid depth of discharge, C-rate and tropical temperature.

→ Open Unit 4

Why a monitoring station is a battery-sizing problem, not a power-sizing one.

Unit 5 · I/O schedule builder

4–20 mA or RS-485 per device → AI / AO / DI / DO / Modbus point count, PLC module sizing with 20 % spare, field-wiring pair estimate.

→ Open Unit 5

The one-page deliverable for the panel builder; rolls up Units 1 to 4.

Engineering notes — what the calculators taught us

Your A²/O Bio-P May Not Work at 30 °C

Above 28 °C, glycogen-accumulating organisms outcompete phosphorus-removing bacteria for the VFA they live on. Why tropical bio-P fails quietly, how to spot it, and how to price the chemical hedge.
Reads with: A²/O BNR · UCT · Chemical P & carbon

Over-Sized Tanks — and Why Aeration Barely Moves

Designing a 30 °C plant with a 20 °C manual changes oxygen demand by ~0 % but inflates the tank volume ~50 %. Where the tropics really save you, and what the smaller tank then demands.
Reads with: Aeration · CAS · Oxidation ditch

Your Alkalinity Deficit Is Inevitable

Nitrification eats 7.14 mg CaCO₃ per mg N — on tropical high-ammonia feed that alone can exceed the influent alkalinity. The full make-up equation, and why the alkali skid belongs in the P&ID from day one.
Reads with: Chemical P & carbon · UCT · Aeration

Sludge Bulking Halves Your Clarifier Capacity

SVI 120 → 200 cuts the attainable RAS concentration by ~40 % — a clarifier that passes every SOR/SLR check can still fail in a warm climate. SVI is the hidden design parameter.
Reads with: Secondary clarifier · Rectangular secondary · A²/O
Browse all 21 engineering notes →

Coverage & roadmap

GroupUnits coveredStatusNotes on what is deliberately out of scope
01 InfluentBar screen · fine / drum screen · vortex grit · aerated grit · equalisation5 LIVEComminutors and septage receiving not modelled
02 PrimaryCircular · rectangular · lamella / inclined plate3 LIVEImhoff tanks and septic primary not modelled (legacy)
03 BiologicalCAS · A²/O · UCT/MUCT · oxidation ditch · SBR · MBBR · MBR · trickling filter8 LIVETwo-stage and temperature-phased BNR not modelled
04 SecondaryCircular · rectangular · lamella retrofit3 LIVEFlotation clarification of activated sludge not modelled
05 NutrientChemical P · external carbon · alkalinity make-up1 LIVECrystallisation (struvite) recovery not modelled
06 DisinfectionChlorine / CT · UV dose · ozone with bromate risk3 LIVEPeracetic acid and chlorine dioxide not modelled
07 SludgeGravity/mechanical thickening & dewatering · DAF · anaerobic digestion3 LIVEDrying beds, lime stabilisation, composting and thermal drying not modelled
08 TertiaryMedia filtration · UF/MF · GAC · RO for reuse4 LIVETwo-pass RO, brine concentrators and ion exchange not modelled
09 CompliancePermit-driven monitoring list per standard1 LIVESampling and laboratory QA/QC procedures not covered
10 I&C manualLoop · bus · range · UPS · I/O schedule5 LIVEManual complete at Unit 5 of 5
11 Balance of plantPipe and dosing-line sizing1 LIVEPump curves and network hydraulics not modelled
Every unit ships as: interactive calculator → full calculation sheet (formulas, coefficient ranges, worked example, source codes) → instrumentation list mapped to our catalogue → English technical article for organic search. 38 tools are live and regression-tested, and the 21 engineering notes above each read with the tools that back them. The right-hand column is the honest list of what these tools will not do for you — we would rather you knew before you relied on one.
Why we give these away. Every calculation closes with the instruments that duty needs — and we quote them at the manufacturer's ex-works price with no mark-up (our margin is the export tax rebate, not a spread on the device). A designer who has just sized a blower, a clarifier or a carbon bed already knows what to ask for; the tool simply makes the list precise. If you only need the export paperwork, we run receiving, customs and rebate for a fixed service fee.

Need a unit designed — or the instruments quoted?

Send your raw influent data and effluent target. We run the full design chain for you and respond with a sized instrument list at factory-direct price — typically within 24 hours.

Request a design & quote
Response within 24 hours · Instruments at factory ex-works price · Export handled for a fixed fee if preferred
Questions about a duty, a specification, or transparent sourcing? Contact our application engineers →
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