IWA Standard Models

Process Models

IWA ASM1, ASM2d, and ADM1 simulators with configured ODE integration and explicit convergence evidence.

ASM1 Biokinetic Simulator

IWA Activated Sludge Model No. 1 — solver and convergence evidence reported with every run

Load example

IWA ASM1 convergence-checked run for a typical municipal activated-sludge reactor with default kinetic parameters at 20 °C.

Save this scenario

Influent Characteristics

Wastewater Source

Project ASM1 fractionation required

The domestic SI/SS/XI/XS partition is a scoped literature default. Enter the project-specific fSND/fXND organic-N split; no primary source supports the historical pair as a silent default.

Organic-N is split by project fSND:fXND; measured NH₄-N is used directly by this simulator.

fSND

fXND

The domestic ASM1 COD partition has scoped literature support, but no defensible fSND/fXND default has been verified. Enter this project's organic-N split before running the simulation. Missing: fSND, fXND.

Flow Rate(m³/d)

COD(mg/L)

BOD₅(mg/L)

TSS(mg/L)

TKN(mg/L)

NH₄-N(mg/L)

Alkalinity(mg/L as CaCO₃)

Reactor Configuration

Volume(m³)

HRT(hours)

SRT(days)

Temperature(°C)

Target DO(mg/L)

RAS Ratio

Simulation Mode

Convergence tolerance (relative change)

User-declared stopping criterion; smaller values require tighter numerical convergence.

What-If Tuning

Live recalculation (steady state)

SRT(days)15

330

Temperature(°C)25

1035

Influent COD(mg/L)500

1002000

Drag a slider to explore sensitivity. With live recalculation on, steady-state results update automatically; use Run for a full dynamic time series.

Based on IWA Activated Sludge Model No. 1 (Henze et al., 1987). Parameters at 20°C with Arrhenius temperature correction.

8 biological processes • 13 state variables • RK4 solver with explicit convergence evidence

ASM1 Features

Heterotrophic growth (aerobic & anoxic)
Autotrophic nitrification
Decay of biomass
Hydrolysis of particulate matter
Ammonification

Applications

Conventional activated sludge
Extended aeration
Nitrification systems
Pre-denitrification

References

ASM1: Henze, M., et al. (1987). Activated Sludge Model No.1. IAWPRC Scientific and Technical Report No. 1.

ASM2d: Henze, M., et al. (1999). Activated Sludge Models ASM1, ASM2, ASM2d and ASM3. IWA Scientific and Technical Report No. 9.

ADM1: Batstone, D.J., et al. (2002). Anaerobic Digestion Model No.1 (ADM1). IWA Scientific and Technical Report No. 13.

IWA biokinetic simulators: ASM1 (carbon + nitrogen), ASM2d (biological P removal) and ADM1 (anaerobic digestion / biogas), using RK4 integration with a user-declared tolerance and convergence evidence.

แบบจำลองชีวจลนศาสตร์ตาม IWA: ASM1 (คาร์บอน+ไนโตรเจน), ASM2d (กำจัดฟอสฟอรัสทางชีวภาพ) และ ADM1 (ย่อยไร้อากาศ/ไบโอแก๊ส) ใช้ RK4 พร้อม tolerance ที่ผู้ใช้กำหนดและหลักฐานการลู่เข้า

When to use

Predicting effluent N/P from an activated-sludge configuration
Exploring SRT / temperature sensitivity of nitrification
Estimating biogas / methane yield from anaerobic digestion

How to use

1Select the model (ASM1 / ASM2d / ADM1).
2Set influent fractions, kinetic/stoichiometric parameters and SRT/HRT.
3Run the model, verify the convergence evidence, then inspect state variables and effluent quality only when convergence is reached.

Key formulas

Monod growth

µ = µ_max · S / (K_s + S)

S = substrate; K_s = half-saturation constant

Biomass balance

dX/dt = (µ − b) · X

b = endogenous decay rate (1/d)

Process rates (Gujer matrix)

dCᵢ/dt = Σⱼ νᵢⱼ · ρⱼ

νᵢⱼ = stoichiometry; ρⱼ = process rate

Nitrification vs SRT

Temperature: 20 °C
µ_max (autotrophs): 0.8 /d

Minimum aerobic SRT ≈ 1/(µ_max − b) ⇒ design SRT ≥ ~4–10 d for full nitrification

References

• Henze et al. (2000), Activated Sludge Models ASM1/2/2d/3, IWA STR No. 9
• Batstone et al. (2002), Anaerobic Digestion Model No. 1 (ADM1), IWA

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