Your trade effluent charges
and the Mogden Formula tool
What is trade effluent?
Trade effluent

Trade effluent is any liquid waste (effluent) that is discharged from premises being
used for a business, trade or industry.

Trade effluent can be discharged from both large and small premises, including
businesses such as car washes and launderettes.

You must always get a trade effluent consent or enter into a trade effluent agreement
with your water and sewerage company before you discharge trade effluent to a
public foul sewer. For further information visit the following business websites:
England - Business Link: Environment and efficiency
Northern Ireland - NIBusinessInfo: Environment and efficiency
Scotland - Business Gateway: Environment and efficiency
Wales - Business.Wales.gov.uk: Environment and efficiency
Trade effluent
Trade effluent is wastewater which may be contaminated with
materials such as:
 heavy metal rinses
 fats, oils and greases
 solids
 chemicals
 food wastes
 detergents
The only liquid wastes which are not classed as trade effluent are:
 domestic sewage
 clean, uncontaminated surface water, i.e. clean rainwater which
has not been contaminated when running over your site.
How are trade effluent
charges calculated?
Trade effluent charges

Trade effluent charges are based on the Mogden Formula.
Your trade effluent service provider uses the Mogden Formula
to recover the cost of carriage to and treatment of your trade
effluent at their treatment plant (sewage works).

The scale of your effluent charge depends on factors such as
its ‘strength’ and volume.

Component costs are revised each year in April. Check your
trade effluent bill to see what charges apply.
Trade effluent charges

Trade effluent volume may be metered or based on
calculations (i.e. your water use less your non-return to sewer
allowance).

Non-return to sewer allowances include ‘losses’, e.g. from nonrecovered steam, evaporative losses from cooling towers and
water used as product make-up.

For further information refer to leaflet
EN664 Understanding water and wastewater bills
which you will find in the Module Resources section.
The Mogden Formula
Charge (p/m3) = (R + V + Bv + M + B x Ot + S x St) x volume
Os
Ss
R = reception and conveyance
V
= primary treatment
8.77 - 62.9 p/m3
10.76 - 52.68 p/m3
Bv = additional biological treatment (p/m3)
M = marine (where effluent goes to sea) (p/m3)
B
= BOD of settled sewage
10.94 - 92.75 p/m3
S
= treatment and disposal of primary sludge
9.37 - 55.42 p/m3
Os = COD of crude sludge after 1 hour at pH 7
345 - 852 mg/litre
Ss = suspended solids after 1 hour
160 - 512 mg/litre
Ot = COD of trade effluent (mg/litre)
St = TSS of trade effluent at pH 7 (mg/litre)
Reducing trade effluent charges
The first step in reducing your charges is to ensure the volume
figure on your bill is correct:
 Check the non-return to sewer allowance is correct for your
site, e.g. is any lost in steam?
 Check for leaks on your site, not only will you be charged for
incoming water, but also outgoing sewerage/ trade effluent,
even if it is not going to sewer.
 Review your water use on-site to see if any is suitable to
discharge to groundwater, e.g. cooling water. Ensure your
service provider is informed.
Reducing trade effluent charges
 If the COD or suspended solids concentration are significant
take steps to reduce these by preventing product or material
entering the effluent stream unnecessarily.
 The Mogden Formula tool can be used to identify how much
you could save if you reduced the volume and/or strength of
your effluent.
 Use this information to consider further actions. For example,
is it cost effective to install a biological treatment process to
reduce the effluent strength?
What is the Mogden Formula tool?
Mogden Formula tool
The Mogden Formula tool, is a Microsoft® Excel-based tool. It
can be downloaded from:
www.wrap.org.uk/mogden
You can use the tool to:
 check your trade effluent bill
 investigate the impact of modifying specific aspects of your
effluent on the cost to discharge, e.g. the volume and strength
(COD and TSS).
Mogden Formula Tool

The tool uses water companies' standard tariffs, but if you are
a large water user there is an 'other tariffs' option which allows
you to enter industrial tariffs.

The Mogden Formula tool is updated each year to include
trade effluent charges that are applied by the water companies
(and sewerage undertakers) in England and Wales, Northern
Ireland and Scotland. The tool also includes data from the
previous year so that comparisons can be made between
water companies' charging tariffs.
Why use the Mogden Formula tool?
 To check your trade effluent bills.
 To gain a better understanding of the impact of individual
components within your effluent on the cost of its discharge.
 To calculate the cost of modifying specific aspects of your effluent,
for example:
– a reduction in effluent volume
– a reduction in COD or suspended solids concentration.
 To support the development of a cost benefit analysis or to calculate
the cost effectiveness of preliminary treatment measures.
How to use the
Mogden Formula tool
On opening the spreadsheet an information box will appear. The
Mogden Formula tool is not appropriate for all sectors. If it is not
relevant for your company sector, speak to your sewerage
undertaker, otherwise click on ‘continue’.
The main menu screen is shown below. Select the most
appropriate regional option.
From the drop down options, select your ‘Sewerage undertaker’
and the relevant billing ‘year’.
Then click on ‘Charging components.’
Use the information on your trade effluent bill to check your
charges. An example bill is shown below.
A pop-up box will appear displaying the treatments your sewage
undertaker offers. Select the appropriate treatment used for
your effluent, and click on ‘Continue.’
Your service provider’s Mogden Formula charging components
are shown. Click on ‘Enter your data’ to continue.
Enter your data and compare the charge on your bill with the
figure calculated by the Mogden Formula tool.
Using the Mogden Formula Tool to
identify savings
Identifying savings
 The Mogden Formula tool enables you to see what the
cost impacts are if you change your trade effluent ‘makeup’.
 This will help you decide on the most cost effective
actions to take, for example, whether it is cost effective
to install a biological treatment process to reduce the
effluent strength.
Start by changing one component to see what effect this
would have on the cost of effluent disposal, e.g. reducing
effluent volume.
What would the potential cost savings be if you
reduced the effluent volume by 10%?
What would be the potential cost savings if you reduce
each component by 10%? Click on ‘Reduce more than one
parameter’.
Enter the percentage change for each parameter.
Summary
Use the Mogden Formula Tool to:

check your trade effluent bill

investigate the potential savings associated with reducing
the volume or strength (COD and TSS) of your effluent.
Access the Mogden Formula tool at:
www.wrap.org.uk/mogden
WRAP Resource Efficiency helpline
0808 100 2040