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What is wastewater analysis?

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What is wastewater analysis?

Wastewater sampling: what is measured and why?

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.

Wastewater analytes

What is being measured?

The full spectrum of analytes covered by MCERTS is listed in the Environment Agency standard Performance Standard for Organisations Undertaking Sampling and Chemical Testing of Water.

This is the standard businesses should refer to when implementing their effluent sampling processes as it details business requirements for the sampling and testing of trade effluent.

The most common analytes businesses are required to test by MCERTS are:

Physical properties

Physical properties analysed during wastewater testing include:

  • Temperature – Discharged consents are sometimes waived when the temperature drops below 4ºC so it’s important to conduct accurate temperature monitoring to avoid regulatory issues
  • pH – Monitoring acid/alkaline levels in water is important to ensure there is no impact on aquatic life. Even small changes to pH levels can have catastrophic results
  • Electrical conductivity (salinity) – Conductivity measures the ion capacity of liquids to carry electrical current. The reason we measure this is because higher conductivity generally means there is a higher ion concentration from dissolved salts
  • Turbidity – Turbidity refers to the clarity of the effluent. Although it is technically a measure of how cloudy the liquid is, often the particles are invisible to the naked eye which is why specialist equipment is required
  • Colour/odour – Hazen colour and odour checks can be an important verification tool to check against other physical properties  
BOD & COD

Dissolved oxygen (DO) in water is essential to the survival of aquatic life.

In wastewater sampling, the BOD (biochemical oxygen demand) and COD (chemical oxygen demand) of effluent are measured to ensure water course DO levels will not be impacted by its discharge.

 

BOD measures the biological oxygen demand over a five-day period and equals the amount of dissolved oxygen required by organisms for aerobic decomposition of organic matter present in the water.

 

COD refers to the mass concentration of oxygen equivalent to a specified oxidant consumed by dissolved or suspended matter when a water sample is treated with that oxidant under defined conditions.

Solids

The level of solids in wastewater affect its quality and how it needs to be treated going forward.

Solids measurement differs from turbidity in that TSS measures the actual physical particles in the water (e.g. sediment) whereas turbidity measures the effect on light caused by particles. Solid measurement is split into:

 

  • TSS (total suspended solids) measures the dry weight of particles suspended (undissolved) in the sample. A high level of TSS allows water to absorb more light, increasing water temperature and reducing dissolved oxygen (DO), which can have a negative impact on aquatic life

  • TDS (total dissolved solids) – effluent with a high level of TDS can contain high concentrations of salts, making it unsuitable for irrigation or industrial reuse
Nutrients

An excess of nutrients in water contributes to algae overgrowth. 

Nutrient measurement is important as too much algae in water uses high amounts of nitrogen and phosphorus and results in the production of neurotoxins that are harmful to animals and may contaminate future drinking water.

Typically measured nutrients include:

Metals

Trade effluent from industrial processes is a primary source of heavy metal contamination.

Industries including textile, paper/pulp and metal finishing are all contributors, producing effluent that contains the “top four” toxic heavy metals arsenic (metalloid), cadmium, lead and mercury as well as chromium, nickel and zinc which are also toxic to humans and animals.

what is wastewater analysis sampler picture
What is wastewater analysis?

Solutions

Next steps

The above list is not exhaustive, but contains some of the common analytes permit holders are required to be measured on. It may seem like an overwhelming task, but a good automatic wastewater sampler and associated monitors provide an accurate and user-friendly solution.

SIRIS offer a comprehensive range of MCERTS-approved wastewater samplers and analytical measurement tools designed to simplify the wastewater analysis process.  

WE CAN HELP

For any queries or assistance with your trade effluent sampling or flow measurement, please contact our expert installations project team, who are set to help with any effluent challenge.

CONTACT US

What is the Mogden Formula and why does it matter for trade effluent?

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The Mogden Formula

Calculating Trade Effluent Charges

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)

what is the mogden formula

The more contaminants and suspended solids in the wastewater or effluent, the more expensive it will be to treat and dispose of.  This is known as The Trade Effluent Charge and is charged by the local water company to cover costs associated with the transportation, treatment and disposal of the effluent.

 

Many companies use water as part of their processing, such as produce cleaning or cooling, and understanding your Mogden formula can help identify areas to reduce wastewater processing charges.  Essentially there are two ways to do this:

 

–       Reduce the levels of contaminants/solids within the effluent

–       Reduce the volume of effluent

Water companies will issue licences of “Consent to discharge trade effluent” to those companies producing effluent for public disposal, which will outline specific conditions and charges for your licence.  The consent licence will stipulate how the wastewater must be monitored (or measured).  Sometimes this will be through self-monitoring but the water company may also routinely monitor flow and composition of the effluent to ensure compliance and estimate charges.   Water companies may vary in their application of the Mogden formula, but this information will be publicly displayed on their website, in line with the OFWAT regulator. 

 

Having an accurate and reliable picture of your effluent data is therefore key in ensuring the correct charges are being paid, as well as understanding where costs are coming from within the variables.  This is done via two primary methods – wastewater sampling and wastewater flow measurement. 

A Siris Effluent Sampler
THE MOGDEN FORMULA IN PRACTICE

Role of Effluent Sampling

An accurate base for calculations

Effluent sampling ensures the accurate measurement of those variables used within the Mogden formula.  Without them, calculations may be based on estimates, which could be bringing unnecessary additional charges to the business.

Investing in an approved, on-site wastewater sampling system gives more comprehensive and ongoing accurate data that can be used to monitor the quality of the wastewater discharge on a continual basis, using composite samples to provide data to the EA and local water authorities that can reduce charge liabilities and business costs.

 

At SIRIS we offer a range of MCERTS-accredited wastewater samplers that suit both open channel and closed pipe applications, providing robust and long-lasting sampling solutions for a range of industrial and commercial businesses.  We offer automatic, composite, refrigerated sampling, which ensures regular samples of your effluent at key times e.g. high loads/low loads.  Factors such as this are important and carefully considered in the design and specification of your effluent monitoring system by the SIRIS team.  For example, water company spot samples may focus on times of high contaminant concentration, giving an inaccurate picture of the average effluent strength level and causing unnecessary charges.  The refrigerated element of our samplers ensures that samples do not degrade.,

ACCURATE VOLUME OF FLOW

Role of Flow Measurement

Ensure a true picture of volume of effluent

 

Measurement of volume of flow is another critical data point in which to ensure accuracy.  Again, on-the-spot water company measurements can give biased flow volumes, for example if these were taken only during high production points on the plant. 

 

Our solutions ensure an accurate picture of flow volume over time.  Depending on the specific business type and requirements, effluent flow may be measured on either an instantaneous or continuous basis, each of which requires careful specification of equipment. At SIRIS, our experienced approach to effluent flow measurement allows us to specify and develop robust and reliable measurement systems.

Learn how we saved one client over £170,000 through accurate effluent monitoring

WE CAN HELP

For any queries or assistance with your trade effluent sampling or flow measurement, please contact our expert installations project team, who are set to help with any effluent challenge.

CONTACT US

Proud to be supply chain partner of award-winning Wolsingham Sewage Treatment Works Growth Improvement Project

SIRIS proud to be supply chain partner of award-winning Wolsingham Sewage Treatment Works Growth Improvement Project

The whole projects team at SIRIS is proud to have been a recognised supply chain partner in the award-winning Wolsingham Sewage Treatment Works (STW) Growth Improvement Project.  Completed in 2021 during the height of the pandemic, the £6m project has been awarded Civils Project of the Year in the Constructing Excellence in the North East Awards.

Led by Tilbury Douglas (contractor) and Wood (designer) for client Northumbrian Water, the project was recognised for its use of new technology, implementation of off-site, sustainable construction methods and best-in-class collaboration between all project stakeholders

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The Project

An upgrade to tackle increased flows and asset deterioration

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. 

Picture courtesy of Tilbury Douglas
Early phase drawing of the inlet flume design The inlet flume, manufactured off-site and installed into the inlet works Picture courtesy of Wood https://www.woodplc.com/
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SIRIS FLOW INLET FLUME & WEIR INSTALLATION

Off-site Build Concepts

Working under the brief of design partners, Wood, SIRIS was able to develop off-site build concepts for the inlet of the works, using a prefabricated, above-ground approach.  The inlet-flume design was built offsite within the SIRIS on-site factory, using non-standard GRP-reinforced, welded PVE construction materials to give the increased accuracy and sensitive tolerances expected for MCERTS certification.  The materials also benefited from a service life of up to 50 years.    

Transported in two sections, the inlet flume was installed readily into the SWT without problem, showing the potential for future off-site build methods for installations of this type.

 

 

“The off-site construction nature of this project represented a new approach in the water industry.  With our on-site factory and engineering team, we were able to quickly integrate into the adopted working methods by providing a fully constructed inlet flume and weir system, then transported to and installed on the works site directly.  Our team collaborated fearlessly with the project team to achieve all requirements and we are proud to have been involved in such an innovative development.”

SIMON RICHARDSON
DIRECTOR, SIRIS
Here at SIRIS we are able to work with our clients flexibly and in line with individual project requirements.

Working with varying client types, including water companies and trade customers, we design, construct and install reliable and accurate flow measurement and sampling installations for use with trade effluent and wastewater.