Typically, 80% to 90% of consumed water is converted into sewage. Formula:
Designing a Sewage Treatment Plant (STP) involves a systematic series of calculations to determine the plant's required capacity, unit sizes, and operational parameters. The core goal is to ensure the facility can handle peak hydraulic loads while achieving the desired level of contaminant removal. 1. Calculate Sewage Generation
This is where biological treatment occurs. Sizing depends on the Food-to-Microorganism (F/M) ratio and Mixed Liquor Suspended Solids (MLSS). Volume Formula: Volume = (Flow × Retention Time) . stp design calculation
$$V = \fracBOD_in \times ADFL \times t$$
Standard Parameters: Retention time is typically 6–8 hours with MLSS levels maintained between 2,000 and 3,500 mg/l. 3. Secondary Clarification and Sludge Management Typically, 80% to 90% of consumed water is
To handle surges (e.g., morning showers), a "Peak Factor" (often between 1.5 and 2.5) is applied to the average flow. Formula: Peak Flow = Average Daily Flow × Peak Factor .
| Parameter | Unit | Example Value | |-----------|------|----------------| | Population Equivalent (PE) | persons | 1000 | | Per capita water supply | LPCD | 135 | | Sewage generation factor | % of supply | 80% | | Influent BOD | mg/L | 300 | | Influent COD | mg/L | 600 | | Influent TSS | mg/L | 350 | | Required effluent BOD | mg/L | ≤ 20 | | Required effluent TSS | mg/L | ≤ 30 | Volume Formula: Volume = (Flow × Retention Time)
Sizing Rule: Usually of the total daily flow, providing an HRT of 8 to 12 hours.
Surface Overflow Rate (SOR) = 20–30 m³/m²/day Area (m²) = Avg. Daily Flow / SOR Diameter (m) = √(4 × Area / π)