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Mogden Formula
Mogden Formula

Mogden Formula

Modgen Formula helps you stop putting money down the drain with your waste water treatmentMost companies in the UK pay for their industrial effluent to be treated by their local water authority under a scheme called the Mogden Formula. The formula was initially introduced to cover the costs of taking the effluent from a site to a local sewage treatment works and treating it before it could be discharged safely.

However as the scheme has developed some water authorities have introduced additional ‘add-ons’ to meet local requirements, so besides working to a core value, now some companies have to ensure their own treatment takes out pollutants such as Phosphates, Anionics and Sulphates, putting more pressure and cost onto companies.

For a company there are 3 main factors that can be controlled, Volume, Chemical Oxygen Demand (COD) and Suspended Solids (SS). By inference pollutants such as those highlighted above, (Phosphates etc.,) should be taken out by an adequate chemical effluent treatment programme.

Monitoring of Mogden charging is controlled by the OFWAT and they publish the standard charges for each water authority on an annual basis. All local water authorities also have to publish their charges, although it is sometimes hard to find them on their websites. A link to the OFWAT section is provided below;

As mentioned above there are really only 3 main factors that a company can address, if we look at the Mogden Formula you can see where these are

Charge per unit of effluent = R + [(V + Bv) or M] + B(Ot/Os) + S(St/Ss)7

R = reception and conveyance charge [p/m3]

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

Bv = additional volume charge if there is biological treatment [p/m3]

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

B = biological oxidation of settled sewage charge [p/kg]

Ot = Chemical oxygen demand (COD) of effluent after one hour quiescent settlement at pH 7

Os = Chemical oxygen demand (COD) of crude sewage one hour quiescent settlement

S = treatment and disposal of primary sewage sludge charge [p/kg]

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

Ss = total suspended solids of crude sewage [mg/litre]

So a Company can look at Volume (V), Chemical Oxygen Demand (COD)(Ot) and Suspended Solids (SS) (St)

Volume initially is fairly easy, ensuring hosepipes and taps are not left running are easy examples, but after a while a site might have save so much in these areas that the concentration strength of the effluent goes up and the other factors (COD & SS) rise as a result.

Effluent Treatment to reduce Mogden Charges

The simplest first stage is to have an interceptor, for low volume sites this is usually enough, and normally sites install a pH monitor and control to ensure that the pH is correct before leaving site. It is important to ensure that if an interceptor is installed that it does not become anaerobic with fats settling out on top causing a crust so that no oxygen can get to the effluent. Regular emptying by gully-suckers is the normal route for controlling this, although a simple air-line and bacteria/enzymes are also effective. Interceptors are particularly good at taking out Suspended Solids (SS) if designed correctly.

For larger sites and for this the volumes are usually over 10cum3/day then there is normally a more structured effluent treatment. This can be physical treatment, or a combination of physical and chemical treatment. This is normally termed primary treatment and is a start to taking out COD and SS from an effluent.

To assist site B&V Effluent Services will undertake testing on site and provide a report of the cost of a treatment programme so that site can evaluate which treatment system to install. The range of systems is vast; to assist B&V do provide a list of some companies who provide some effluent treatment systems.

To find more out about how B & V Effluent Services can help you implement systems and plant to reduce your costs please visit our waste water treatment plant page.

Some of the criteria to consider when thinking about an effluent treatment system are:

Cost – There may not be a return on investment (ROI) with effluent treatment, especially if the driver for installing equipment is a local water authority, or your customers

Foot-print – Most sites are built for production, areas such as car parking and effluent treatment are not factored in. Some companies are now providing small foot-print systems and also containerised systems, particularly useful if near residential areas, or site is likely to expand/move

Customer Requirements – If producing goods for most of the supermarket chains they will expect to see effluent treatment as part of the environmental audit. They may also dictate whether or not the chemical effluent treatment programme is organic or inorganic

Build for the Future – A lot of companies are driven by cost and may put in the cheapest tender, many times this back-fire, examples being,

  1. where companies expand the effluent treatment system, is not considered into sites expansion and can no longer cope with the loading,
  2. sadly unlike production investment in effluent treatment is minimal
  3. company who puts the system in goes bust and you can’t find replacement parts  
  4. What do you need to achieve, does site require an all singing all dancing fancy lights system or will something more robust and practical be sufficient
  5. Seek help and advice. If your company is considering putting in an effluent treatment system, B&V Effluent Services are available to offer you impartial advice, on which system to install, contact details can be found via our website.



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