STP & ETP Calculators

An STP (Sewage Treatment Plant) treats predominantly domestic municipal wastewater, while an ETP (Effluent Treatment Plant) treats industrial or process effluent with site-specific contaminants. Many design equations overlap — flow, detention time, clarifier loading, and sludge mass balances — but ETPs often need tighter pretreatment and chemical dosing.

Yes. Every calculator linked from this hub is free, runs in your browser, and does not require registration. Inputs are not stored on our servers.

Engineering calculators on this hub primarily use SI units: m³/h, m³/d, mg/L, kg/d, m², and kW. Some tools also report L/min, m³/s, or HP for convenience.

Use them for preliminary design, academic work, and operational estimates. Regulatory submissions typically require licensed engineer stamps, site-specific pilot data, and local code checks beyond any online calculator.

Common approaches include detention time (HRT), F/M ratio loading, or SRT targets. Start with design flow and influent BOD, pick a target MLSS, then use the aeration basin volume and oxygen calculators in the Biological Treatment section to iterate.

Secondary clarifiers for activated sludge often target roughly 0.5–1.0 m³/m²·h at average flow, with lower rates for bulking-prone sludge. Always confirm against local design standards and settleability (SVI) data.

Sludge production combines removed TSS, biological yield from BOD removal, and any chemical solids from coagulation or precipitation. The Sludge Production calculator on this hub walks through dry solids and wet volume at different concentrations.

They compute deterministic formula results from your inputs. Apply your own peak factors, turndown margins, and equipment safety factors before procurement — typically 10–25% for pumps and blowers in wastewater service.

Yes. The hub is useful for environmental, civil, and chemical engineering coursework. Cite the specific calculator methodology and verify assumptions with your course design brief or textbook.

High-impact engineering calculators display a last-reviewed date on their pages. We align methods with standard wastewater texts and EPA design guidance, but you should confirm critical designs with current local standards.

Begin with flow characterization, then Hydraulic Retention Time and Equalization Tank Volume. Move to biological loading (F/M, SRT), clarifier overflow rate, and sludge production before detailed mechanical and chemical sizing.

Yes. Chemical dosing, pH correction, clarifier sizing, sludge handling, and hydraulic tools apply to industrial ETP trains. Add pretreatment steps and contaminant-specific treatment beyond the generic biological models where needed.