Page 9 - Guide to Managing Trade Effluent - 2023

Calculating Effluent Charges Drivers for Investing in
Modgen Formula
Under Section 142 of the Water Industry Act 1991, the Effluent Treatment
sewage undertaker is allowed to make a charge for the
discharge of effluent into his sewer. There are five main reasons why a company should consider investing in its effluent treatment
The calculation charge is calculated using the Modgen system. These are:
Formula. C = total charge per cubic meter of trade
In a simplified form the Modgen Formula can be expressed effluent Achieving Compliance: Failure to ensure that the quality of the effluent achieves the conditions
as: set out within the Trade Effluent Consent may result in Court action and subsequent fines. Where
R= One third of the amount determined severe non-compliance or prolonged non-compliance issues occur; the Sewerage Undertaker
Cost = Volume x Strength by the Sewage Undertaker as the has the ability to prevent further discharges into his sewerage system occurring.
average cost to the Sewage Undertaker
for the year of charge of receiving into its
sewers and conveying one cubic meter of Increased Capacity: Plans for increasing the factories production capacity may increase the
• The more concentrated (stronger) the effluent the higher the sewage to the sewage treatment works
charge. volume of effluent that is produced. Increasing the capacity of the sites effluent treatment plant
• Even diluted effluent will be subject to a charge eg clean V=The amount determined by the may give rise to a need to upgrade or modify the factories the existing effluent treatment plant.
water. sewage undertaker as the average
• Dilution will not reduce the total cost payable. cost for the year of charge of primary Reducing Operating Costs: Modernisation of the effluent treatment plant may reduce electricity
treatment and other volumetric treatment usage, reduce consumables, and or reduce the amount of waste generated. These benefits may
costs in the treatment of one cubic meter
A reduction in the overall cost of disposal will only be of sewage at the treatment works reduce the cost of treating the effluent, reducing the facilities operating costs. In addition, the
achieved by reducing the strength of the effluent and/or improvements may also reduce the amount of waste generated, again reducing the facilities
reducing the volume of effluent that is disposed. Ot =The Chemical Oxygen Demand operating costs.
(COD) of the trade effluent in mg/l after
one hour quiescent settlement
Changes In Effluent Quality: Both the volume and composition of the effluent generated by the
Os=The estimated average Chemical facility is a function of the operating processes undertaken at the facility. Where changes to the
Oxygen Demand (COD) of settled sites production is made, this may change the composition of the effluent that is delivered into the
sewage in mg/l at the sewage treatment
works as determined by the Sewerage sites effluent treatment plant. Any changes in the nature of the effluent which is produced may
Undertaker for the purposes of the year of necessitate a need to alter the sites existing effluent treatment capabilities.
charge.
More Stringent Discharge Targets: There is a continuing drive to reduce the amount of pollution
B= The amount determined by the
sewerage undertaker as the average cost that enters our inland waterways. Sewage undertakers are being put under increasing pressure to
to the sewerage undertaker for the year reduce the concentration of pollutants present within the discharge from the sewage treatment
of charge of biological treatment of one works. This in turn sees the undertaker imposing tighter limits on the quality of the effluent that is
cubic metre of sewage at the sewage discharged into his network; making a need to upgrade the sites effluent treatment plant.
treatment works.
St= The total suspend solids in the trade
effluent in mg/l at the pH of the trade
effluent.

Ss= The estimated average amount of
suspended solids in mg/l determined on
a shaken sample, in sewage received
for treatment as the sewage treatment
works as determined by the sewerage
Undertaker for the purposes of the year of
charge

S= The amount determined by the
Sewerage Undertaker as the average
cost to the Sewerage Undertaker for
the year of charge, of primary sludge
treatment and disposal of one cubic
meter of sewage at the sewage
treatment works

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