Mogden formula

In the sewage treatment, the Mogden formula is a pricing strategy used to estimate the difficulty in treating industrial wastewater. It is named after Mogden Sewage Treatment Works.^[1]

The Mogden formula calculates cost as a combination (empirical coefficients) of volume, strength in terms of normal treatment oxidation demand and the suspended solids proportion.^[1] Applicable to the whole works, it also approximates the cost for tested industrial waste water that may, if treatable, be lawfully sent to a regular sewage works.^[1][2][3][4]

The Mogden formula is:

C = R + [(V + Bv) or M] + B(Ot/Os) + S(St/Ss)

where:

C = charge per volume of effluent (£/m³)

R = reception and conveyance charge [£/m³]

V = primary treatment (volumetric) charge [£/m³]

Bv = additional volume charge for biological treatment [£/m³]

M = treatment and disposal charge where effluent goes to sea outfall [£/m³]

B = biological oxidation of settled sewage charge [£/m³]

Ot = chemical oxygen demand (COD) of effluent after one hour of quiescent settlements at pH 7 [mg/litre]

Os = chemical oxygen demand (COD) of effluent after one hour of quiescent settlement [mg/litre]

S = treatment and disposal of primary sewage sludge charge [£/m³ or £/kg]

St = total suspended solids of effluent at pH 7 [mg/litre]

Ss = total suspended solids of effluent [mg/litre]

Thus the less biologically friendly the effluent (see wastewater quality indicators including pH), and more solid-laden, the higher the charge should be for treating the lawful effluent.^[5]