flumes

We often get calls from customers requesting quotes for part of a flow system – and they’re often surprised when we explain that it isn’t as simple as just selling them a flow meter.

In this article we explain why installing any MCERTS flow measurement system requires a holistic approach, and the importance of consulting the experts to ensure your system is not only cost-effective but fit for purpose.

The majority of businesses producing wastewater are required to carry out wastewater sampling to comply with their permit requirements.

Often this will be via self-monitoring, however companies may find themselves the subject of spot checks of their samples by the local water company to ascertain composition and volume of trade effluent produced. This supplied information is important as water companies use it to calculate final water treatment costs, using a method known as The Mogden Formula.

This rather complex-looking equation represents the key tool in calculating trade effluent charges.  Termed The Mogden Formula after first being adopted at the Mogden Water Works in London, it incorporates a number of variables such as contaminant and suspended solids levels that are used to calculate the final treatment cost per m3 of the effluent. 

The formula can be broken down as follows:

R = the charge from the water treatment works for receiving and conveying the effluent (in £/m3)

V = the charge from the water treatment works for the primary treatment* of the effluent *removal of material that will either float or readily settle out by gravity

(in £/m3)

Bv = the charge from the water treatment works for any biological* treatment (in £/m3) *breakdown/decomposition of organic contaminants from the wastewater

M = the charge from the water treatment works for the treatment and disposal of any effluent that must go out to sea (in £/m3)

B = the charge from the water treatment works for the biological oxidation* of any settled sewage (in £/m3) *B-stage, or bio-oxidation stage, where remaining organic material in low-loaded activated sludge is biodegraded

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

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

S = the charge from the water treatment works for the treatment and disposal of the primary sewage sludge (in £/kg)

St = the total of suspended solids of effluent at pH7 (in mg/litre)

Ss = the total of suspended solids of effluent (in mg/litre)

The Sewage Treatment Works was in need of an upgrade as demand on the site had increased in line with population growth in the area, estimated at some 19%.  The upgrade project had to identify solutions to the issues caused by increased flows and loads identified at the site and the related impacts on associated sewerage networks.  In addition to this, further work to tackle asset deterioration and ongoing pollution incidents due to sewer overflow was to be incorporated into the project. 

The design phase of the project, started in 2018, took an innovative “Off-site by Default” and DfMA (Design for Manufacture and Assembly) approach to build technology, an ethos that was mirrored throughout all phases of the project with the ongoing support of client Northumbrian Water.  The Sewage Treatment Works was consequently able to be built using off-site build methodology, a ground-breaking approach within the water industry. 

This method brought tangible and sizeable benefits to the project in terms of reduced costs, timelines and environmental impact; with some £1m pounds, 4 months and 34 man hours estimated to have been removed from the project initial budgets and timescales. 

Northumbrian Water now plans to adopt the new off-site build approach within their AMP7 framework, a real testament to the success of the project and the collaboration of partners and supply chain throughout.