Engineering Tool • Free to Use
Wastewater & Biogas Design Calculator
Size activated sludge tanks and clarifiers, estimate excess sludge and digester biogas yield, and run IPCC-style methane accounting — every formula below is cited to a primary engineering source, not a black box. See the full methodology and reference list at the bottom of this page.
Design Calculator
Four Tools, One Cited Model Set
Activated Sludge + Anaerobic Digestion Mass Balance
Sizes the aeration tank and clarifier, estimates excess biological + primary sludge production, and carries that sludge through to digester volume and biogas yield. Mirrors wastewater_models/mass_balance.py.
Design-manual-grade steady-state estimate (README §1–4). Not a substitute for a stamped detailed design — verify kinetic constants, CPHEEO Table 5.9 envelope, and site-specific conditions before construction.
Biogas Composition from Substrate Formula (Buswell Equation)
For a substrate of empirical formula CcHhOoNnSs, computes the stoichiometric maximum CH₄/CO₂/NH₃/H₂S yield (Buswell & Mueller, 1952 — README §3.1).
Stoichiometric ceiling assuming 100% conversion — real digesters fall short because some substrate is diverted to biomass synthesis and not all material is biodegradable.
IPCC Tier-1 Methane Emissions Estimate
GHG-inventory-style accounting equation (IPCC 2019 Refinement, Vol. 5, Ch. 6 — README §3.4): CH₄ emissions = organic load × B₀ × MCF.
Only the anaerobic-digester (0.8) and well-managed-aerobic (0) MCF values were cross-checked against more than one source this project — pull IPCC Table 6.3 directly for any other treatment/discharge pathway before regulatory use (see Methodology below).
Theoretical CH₄ Yield from COD Destroyed
Ideal-gas-law sanity check (README §3.2): every kg of COD converted to methane is fixed by CH₄'s stoichiometric oxygen demand (1 mol CH₄ ≡ 64 g COD).
Upper-bound reference only — real digester yields are always lower (biomass synthesis, incomplete biodegradation). At STP (0°C) this works out to ≈0.35 m³/kg COD, the figure widely cited throughout the anaerobic-digestion literature.
Engineering Reference
Methodology & References
This calculator is a browser-side port of a tested, cited model set. Every constant traces to a source below — the full derivations, nomenclature, and caveats live in the project README.
Where do these formulas come from?
Activated sludge kinetics and reactor/clarifier sizing follow Tchobanoglous et al., Wastewater Engineering: Treatment and Resource Recovery, 5th ed. (Metcalf & Eddy/AECOM, 2014), built on the SRT-based design approach of Lawrence & McCarty (1970). Indian design envelope cross-checked against the CPHEEO Manual on Sewerage and Sewage Treatment Systems, Part A (2013). Biogas stoichiometry follows Buswell & Mueller (1952). IPCC accounting follows the 2019 Refinement to the 2006 IPCC Guidelines, Volume 5, Chapter 6.
What's the scope, and what isn't included?
This is a steady-state, design-manual/Tier-1-grade model set for preliminary sizing and feasibility mass balances — not a dynamic, nutrient-resolved simulator. For time-resolved digester dynamics (VFA/pH, co-digestion transients) or nitrogen/phosphorus removal kinetics, the open-source tools QSDsan and PyADM1 implement the full ASM/ADM1 model families.
Full reference list & source code
The complete nomenclature, every equation's derivation, the numbered reference list (12 sources), and the tested Python implementation this calculator mirrors are in the repository at wastewater-models/ — see README.md for the full write-up.
Want a project-specific design, not just a sizing estimate?
This tool is for preliminary sizing only. For a stamped design, detailed mass balance, or site-specific ETP/STP/RO engineering, talk to our engineering team.