Flow Rate (Q)

Formula:

Q=A×V

Where: ( Q ) = flow rate (e.g., m³/s), ( A ) = cross-sectional area (m²), ( V ) = velocity (m/s)

Used to determine the volume of wastewater moving through a system.

Biochemical Oxygen Demand (BOD) Removal Efficiency

Formula:

Efficiency (%)=BODin−BODout/BODin x 100

Where: BODin=influent BOD (mg/L), BODout=effluent BOD (mg/L)

Chemical Oxygen Demand (COD) to BOD Ratio

Formula:

COD:BOD; COD/BOD

Where: COD = chemical oxygen demand (mg/L), BOD = biochemical oxygen demand (mg/L)

Sludge Volume Index (SVI)

Formula:

SVI=SSV30/MLSS×1000

Where: SSV30=settled sludge volume after 30 minutes (mL/L), MLSS = mixed liquor suspended solids (mg/L)

Food to Microorganism Ratio (F/M)

Formula:F/M=BODin x Q/MLSS x V

Where: (Q)=Flow Rate (meters cubed per day), (V)=aeration tank volume (meters cubed)

Hydraulic Retention Time (HRT)

Formula: HRT=V/Q

Where: (V) = tank volume (meters cubed), (Q) = flow rate (meters cubed per day)

Solids Retention Time (SRT)

Formula:SRT=V×MLSS/Qw×WASSS+Qe×ESS

Where:Qw=waste sludge flow rate (m³/day), WASSS = waste activated sludge suspended solids (mg/L)

Qe = effluent flow rate (meters cubed per day) , ESS = effluent suspended solids (mg/L)

Organic Loading Rate (OLR)

Formula:OLR= BODin x Q/V

Units: kg BOD/m³·day

Chlorine Dosage

Dose: Cl2Demand+Residual/Efficiancy

Where:

Cl2 Demand = chlorine required to oxidize contaminants (mg/L),

Residual = desired chlorine residual (mg/L),

Efficiency= application efficiency (decimal)

Settling Velocity (v)

Formula: V=Q/A

Where: ( Q ) = flow rate (m³/s), ( A ) = surface area of settling tank (m²)

Total Suspended Solids (TSS) Removal

Formula: Removal (%)=TSSin−TSSout/TSSin x 100

Where: TSSin = influent TSS (mg/L), TSSout = effluent TSS (mg/L)

Power Requirement for Aeration

Formula: P= O2 Demand×Q/O2 Transfer Efficiency

Where: ( P ) = power (kW), O2 Demand = oxygen required (kg/day), ( Q ) = flow rate (m³/day)