Basic STP (Sewage Treatment Plant) Formula Sheet 1 Flow Rate Calculation Determines the volume of sewage entering the plant per day. Formula: Q = V / t Where Q = Flow rate (m³/day), V = Volume (m³), t = Time (days) 2 BOD Load Calculates the organic load based on Biochemical Oxygen Demand. Formula: BOD Load = Q × BOD Q = Flow rate (m³/day) BOD = mg/L 3 COD Load Estimates chemical oxygen demand for treatment sizing. Formula: COD Load = Q × COD COD = mg/L 4 MLSS Concentration Mixed Liquor Suspended Solids concentration in aeration tank. Formula: MLSS = (Weight of solids / Volume of sample) Expressed in mg/L 5 F/M Ratio Food to microorganism ratio for biological treatment efficiency. Formula: F/M = (Q × BOD) / (V × MLSS) Q = Flow rate, V = Aeration tank volume 6 Sludge Volume Index (SVI) Indicates settling characteristics of sludge. Formula: SVI = (Settled sludge volume in mL/L × 1000) / MLSS 7 Oxygen Requirement Calculates oxygen needed for biological oxidation. Formula: O₂ Required = BOD...
Basic STP (Sewage Treatment Plant) Formula Sheet
1 Flow Rate Calculation
Determines the volume of sewage entering the plant per day.
Formula: Q = V / t
Where Q = Flow rate (m³/day), V = Volume (m³), t = Time (days)
2 BOD Load
Calculates the organic load based on Biochemical Oxygen Demand.
Formula: BOD Load = Q × BOD
Q = Flow rate (m³/day)
BOD = mg/L
3 COD Load
Estimates chemical oxygen demand for treatment sizing.
Formula: COD Load = Q × COD
COD = mg/L
4 MLSS Concentration
Mixed Liquor Suspended Solids concentration in aeration tank.
Formula: MLSS = (Weight of solids / Volume of sample)
Expressed in mg/L
5 F/M Ratio
Food to microorganism ratio for biological treatment efficiency.
Formula: F/M = (Q × BOD) / (V × MLSS)
Q = Flow rate, V = Aeration tank volume
6 Sludge Volume Index (SVI)
Indicates settling characteristics of sludge.
Formula: SVI = (Settled sludge volume in mL/L × 1000) / MLSS
7 Oxygen Requirement
Calculates oxygen needed for biological oxidation.
Formula: O₂ Required = BOD Load × Oxygen Demand Factor
✅ Key Notes
Always measure flow rate (Q) accurately for reliable calculations.
BOD and COD loads determine the sizing of aeration and treatment units.
F/M ratio is critical for stable biological treatment.
SVI helps monitor sludge settling and clarifier performance.
Oxygen demand must be matched with blower and diffuser capacity.
A well-designed and efficiently operated Sewage Treatment Plant (STP) depends on accurate calculations and process control. This poster compiles the essential formulas and operating parameters used in wastewater treatment, making it a practical tool for engineers, operators, and students. 📌 Key highlights covered: • Flow & organic load calculations • Hydraulic Retention Time (HRT) & Organic Loading Rate (OLR) • F/M ratio, MLSS, and SVI fundamentals • Sludge age (SRT) and return sludge ratio (RAS) • BOD & COD removal efficiency calculations • Aeration and oxygen demand estimation • Clarifier design parameters (SOR & WLR) ⚙️ Designed for quick reference during plant operation, troubleshooting, and design validation, this sheet simplifies complex process calculations into an easy-to-use format. 💡 Whether you're managing daily STP performance or learning wastewater treatment, this guide helps ensure process stability, compliance, and efficiency.
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