Wastewater Flows & Loads Calculator
Estimate the design flow, organic load and population equivalent (PE) for your site. Based on PPU design flows and loads. Always design for 100% occupancy.
Estimated daily loading
Design PE governs on the most demanding parameter — flow, organic load (BOD) or ammonia — not just the head count. Grease separators are required for all catering uses, surface water must be excluded from the treatment system, and laundry flow should stay below 30% of the total for effective treatment.
Quick minimum population (P) sizing for single dwellings and small groups. Group discounts are applied automatically to the combined total.
Group factors: 13–25 P total ×0.9 · 26–50 P total ×0.8 · over 50 P should be sized from a full flow & load analysis (use the Site tab or contact us).
Key definitions & design notes
- Population (P / PE)
- The number of people (or population equivalent) the system is designed to serve. 1 PE = 150 L/day, 60 g/day BOD₅, 8 g/day ammonia.
- Flow
- Sewage volume generated per person or activity per day, in litres.
- BOD₅
- Biochemical Oxygen Demand — mass of oxygen consumed over 5 days at 20°C; the standard measure of organic load.
- Ammonia (as N)
- Ammonia / ammonium expressed as nitrogen content, in grams per day.
- Occupancy
- Always design for 100% occupancy, never average expected usage.
- Grease separators
- Required for all catering applications upstream of biological treatment.
- Surface water
- Rainwater and surface run-off must be excluded from the treatment system.
- Waste disposal units
- Increase the biological load — allow for this if fitted.
- Laundry
- Should not exceed 30% of total flow for effective treatment.
- Part-time staff
- Assessed on a 4-hour shift basis.
Indicative figures for early-stage sizing only, based on PPU design flows and loads. Final design must be confirmed by a qualified engineer against site-specific conditions and the discharge consent. ClearFox® is a registered brand of PPU Umwelttechnik GmbH.