0191 5131313 | hello@siris.co.uk
0191 5131313 | hello@siris.co.uk


What is Event Duration Monitoring (EDM)?

Event Duration Monitoring (EDM) helps ensure sewage treatment works (STW) are sticking to their permitted discharge limits. When combined with flow to full treatment monitoring it provides an accurate picture of where flow is going when a STW is at full capacity. In this guide we explain what it means, why it’s important and how to implement it. 


What is Event Duration Monitoring and why is it important?

When we talk about an “event” in flow measurement terms, we’re referring to an adverse weather event, typically a storm, that increases the amount of flow going through a sewage treatment works.


In simple terms, Event Duration Monitoring allows a treatment works to monitor whether or not an event is happening, and how long it lasts.


This is important because an STW has a maximum limit it is permitted to treat, known as flow to full treatment (FFT). This is based on a calculation, normally three times the maximum dry weather flow (DWF). Anything exceeding this amount when storm event occurs is permitted to overflow to storm management systems, or be discharged to a river.


The problem arises when a works discharges to storm management before its maximum limit is reached, as this is a breach of its permit and illegal.


The Environment Agency’s U_MON3 driver requires water companies to install EDM monitoring by 2025, and more recently the Government announced further measures to ensure STWs are not relying on storm overflows outside of storm events.


What does the Environment Agency say?

In 2018, the Environment Agency announced a series of measures designed to better monitor flow to full treatment, which included mention of Event Duration Monitoring:


“Install EDM on WwTW overflows to storm tanks at those WwTW where we can’t use existing monitors to be confident that the permitted FFT setting is being complied with.” U_MON3 Driver


In a recent report, the EA said it had installed 12,000 monitors by the end of 2020, with installations on remaining sites expected to be completed by 2023.


The EA says EDM will give them an accurate picture of how water companies are using their storm overflows and allow them to identify where improvements can be made, take enforcement action where necessary, and ultimately improve water quality.


Best practice with Event Duration Monitoring

The EDM device is usually situated immediately upstream of the FFT meter so if any excess flow goes into stream it can record it.


Traditionally, the most common way of conducting Event Duration Monitoring is by using a flow measurement device with probes. However, as they are fundamentally contact devices this can cause problems if the probes become damaged or dirty. Careful installation is essential for this type of device because it can be very difficult to reference them against the low point of the weir.


A better solution is a non-contact device such as an ultrasonic or radar, installed on a fixed robust bracket that includes a calibration reference point and correctly referenced against the spill height. With care, this should be able to be undertaken within +/- 2mm.


As with any flow measurement device, EDM needs to be set up and calibrated by a qualified MCERTS inspector to ensure it doesn’t trigger too early or not at all.


Talk to us about Event Duration Monitoring

To find out more about EDM and how we can help, get in touch with our friendly and professional team.


Additional resources:

What does Bulletin 27 mean for AV?

The CSA Group*, the provider of the Environment Agency’s MCERTS scheme, recently released Bulletin 27, an update on how area velocity (AV) flow measurement systems should be installed and used.


The use of AV technology can cause confusion – particularly as new rules on flow to full treatment (FFT) are due to come into force. Our guide aims to help you make a more informed decision when choosing your wastewater system. 


What does AV mean?

Area velocity (AV) flow meters are used for measuring flow without a flume or weir. They operate on the “area velocity principle” – a probe is inserted into the water and continuously transmits ultrasonic pulses.  when particles pass through it registers the shift in area velocity and uses this to calculate the flow.


AV meters are popular because they are quick and easy to install – simply fitting them to a pipe or open-channel. They also tend to be more affordable than alternatives, such as electromagnetic flow meters.


However, a downside to AV meters is that it is difficult during MCERTS inspections to verify the accuracy of the results they are producing.   This means that although they may seem like a cost-effective solutions, in reality they can often end up costing more in the long run.   As MCERTS inspectors we would only recommend AV meters over other meters in certain situations, such as a temporary option or where other solutions aren’t viable.


Soon, the Environment Agency will require wastewater treatment works to comply with new regulations in the way they measure flow to full treatment (FFT).   This may mean that many sites will opt for AV meters as a quick and affordable solution to meet requirements, but it is important that you make yourself aware of potential limitations before committing.   In all instances you should seek the advice of MCERTS-qualified advisors.


What is Bulletin 27?

The CSA Group occasionally shares updates and additional guidance relating to the existing Environment Agency MCERTS guidelines, known as bulletins.


Bulletin 27 – “Installation and use of area-velocity flowmeters in free surface flows.” is the most recent update and provides guidance on how area velocity flow meters should be used in order to pass MCERTS inspections.


The key things it covers are:

  • Location and installation
  • Maintenance
  • Verification


What does Bulletin 27 mean for AV?

Bulletin 27 clarifies some areas of concern raised on how the accuracy of area velocity flow meters can be verified.


One of the key things it confirms is that there must be a “defined measurement section”. This is described as:


“a straight, stable length of channel or pipe with a constant cross section and with a length which is sufficient to create a fully developed flow profile at all expected flowrates.



Note: This will normally require at least 20 channel widths/pipe diameters upstream and 5 channel widths/pipe diameters downstream of the flowmeter.”


The additional note is important – although it acts as a recommendation it gives important guidance as to how we can accurately verify the results the area velocity flow meter provides. Bulletin 27 also explains that if these conditions can’t be met the site can still be MCERTS certified, so long as the inspector “is satisfied that that the flow measurement uncertainty conforms to the MCERTS requirements at all expected flow rates”. 


Another important issue addressed is maintenance. Area velocity flow meters measure the area of the channel – and that means that any build-up of material within the channel will skew the results. It states that “the sensors and the measurement section shall be kept free from sediment and other fouling material.” In other words, the channel needs to be kept cleaned and well-maintained in order to confirm accuracy of results.


Our view

Area velocity technology should be carefully considered as a long term solution, weighing up issues of potential accuracy and verification before focusing on cost and speed of installation.  Despite the relatively low initial outlay for an AV meter, inaccurate results and the issues presented by them over a long period could ultimately cost businesses and water companies more money. Electromagnetic flow meters or flumes can remove the typical issues found with AV meters and their data accuracy and, even though more costly for initial installation, can prove more cost-effective in the longer term.


It is encouraging to see further clarification on the use of AV meters from CSA Group and we believe that if these guidelines are followed – particularly the recommended installation location – then it will go some way in improving the accuracy of this technology.


Talk to the experts

To discuss your requirements, get in touch with our friendly team on 0191 5131313, or email hello@siris.co.uk.


*Confused about the role of the CSA Group? Read our guide to the key wastewater industry players.

Case study: Ensuring MCERTS compliance for food manufacturer

As producers of trade effluent, food and beverage manufacturers are required to take part in the Environment Agency’s MCERTS scheme. However, many manufacturers simply don’t realise that they could save money by investing in a new wastewaster monitoring system. We worked with our supplier Pulsar Process Measurement to ensure MCERTS compliance for food manufacturer Premier Foods, in Newport.




The project

The site’s existing wastewater monitoring system wasn’t fit for purpose – an older weir tank was installed but it was undersized for the capacity required and was costing the food manufacturer money and making it difficult for them to measure accurately.


We assessed the site and worked with Pulsar and the client to understand the options available to them. We recommended installing a much larger weir tank – utilising space the factory had close to the existing tank.


A larger tank results in smoother, more tranquil flow which allows for greater accuracy in measurement.


As accuracy was such a key consideration for this site, we designed and installed the system to work alongside Pulsar’s DUET flow meter. Unlike a standard ultrasonic flow meter, which operates using a single transducer, the DUET’s unique design utilises two transducers to provide highly accurate results.


Money saving

By installing a fully-compliant system that was tailored to the client’s requirements, we were able to help the company make substantial savings.


Discharging more or less trade effluent than is stipulated in the conditions of a company’s consent to discharge permit can prove costly.


A food manufacturer discharging too much trade effluent can result in fines from the Environment Agency – and the company will also be required to apply for a new permit at a further cost. However, discharging less than expected also has cost implications as the company will be paying to discharge more than it actually is!


Correct and accurate monitoring that meets MCERTS requirements and uses MCERTS-certified equipment is the only way to ensure a manufacturer is paying the correct amount.


MCERTS guarantee

We offer an MCERTS guarantee, meaning that any system we design, install and maintain will be fully MCERTS-compliant. MCERTS compliance for a food manufacturer is vital, as it ensures that their system is performing at a high level of accuracy and providing cost-effective results, while remaining within the limits of their consent to discharge permit.

What are MCERTS approved products?

As well as providing MCERTS inspection services, we also stock a range of MCERTS approved products, including flow meters and wastewater samplers.


But what are MCERTS approved products, and why do you still need MCERTS inspections if you already use certified products as part of your wastewater monitoring system? Our guide answers these questions.


CSA Group is the awarding body for MCERTS


What is MCERTS?

A quick refresher if you’re new to the world of MCERTS:

MCERTS refers to the Environment Agency’s Monitoring Certification Scheme (MCERTS), which provides a framework of standards for the safe monitoring of liquid flow, such as trade or sewage effluent. Compliance with MCERTS ensures that everybody involved in the measurement of liquid flow is working towards the same standards and is providing accurate emissions information to the Environment Agency. The regulation covers areas such as product and personnel certification, as well as the quality of inspections.


If you want to learn more about MCERTS, check out some of our other guides.


Who certifies MCERTS approved products?

The CSA Group is responsible for certification standards across a range of areas and operate internationally across a wealth of countries. Within the UK, among many other areas of certification, it delivers the MCERTS scheme, under the SIRA name.


According to CSA, the MCERTS product certification scheme provides the mechanism for the certification of products according to Environment Agency performance standards, which are based on relevant CEN, ISO and national standards.


MCERTS is a mark of quality, giving consumers the confidence that the products they are using are fully compliant with Environment Agency standards.


So why do I still need inspections if my equipment is MCERTS approved?

Ensuring the equipment you are using is MCERTS certified is just one part of complying with the Environment Agency’s standards. In fact, MCERTS covers everything from equipment performance standards, the level your staff must be qualified to and accreditations of the people carrying out your site inspections.


Your wastewater monitoring equipment must meet the required standard, however it is still your responsibility to choose an appropriate monitoring system and ensure it is installed correctly. Sites with consent to discharge permits are required to host regular inspections (at least every five years) to make sure their monitoring system is performing within the stipulations of their permit.


As qualified MCERTS inspectors, we can take responsibility for this entire process – from specifying a flow measurement system that best suits your requirements and is compliant with your consent to discharge permit and installing it to Environment Agency standards, to carrying out regular site inspections to ensure ongoing compliance.


Talk to the experts

We know the world of MCERTS can be confusing – which is why we pride ourselves on offering a “one-stop-shop” solution to our customers. To find out how we can help you, get in touch with our friendly team on 0191 5131313 or email hello@siris.co.uk


What is trade effluent?

If you’re new to the world of wastewater monitoring, it’s likely one of the first terms you have come across is “trade effluent”. But what is it and what does it mean for your business? We’ve put together a quick guide to explain. 



What is effluent?

As a broad term, effluent includes any liquid waste entering a water body such as rivers or the sea. Most commonly we think of effluent as being sewage, however this is not always the case. Sewage is a form of effluent but not all effluent is sewage!



What is trade effluent?

Trade effluent is wastewater being produced by a business during the course of industrial activity which is potentially harmful to the environment. It can be confusing as not all wastewater produced by businesses is classed as “trade effluent”.


Typically, any wastewater produced by factories, chemical processing and engineering plants, car washes, laundrettes and swimming pools counts, whereas that produced by hairdressers, restaurants/takeaways/pubs/hotels, medical practices, residential homes (e.g. care homes), grocers and office buildings, doesn’t. This is because water companies don’t consider its content high risk enough to complicate processing at water treatment works.


What are the legal requirements for my business?

It is illegal to discharge trade effluent to a public sewer without consent from your water authority. This is because water companies need to know about factors such as its strength, content and volume to make sure their treatment plants can process it correctly, as well as manage potential risks to people or the environment.


To find out more about consent to discharge and applying for a permit, read our guide. You will also be required to monitor your effluent under the government’s MCERTS scheme.


We can help you understand your trade effluent requirements and advise you on your next steps. Get in touch with our team of MCERTS experts today.

Is SIRA test and certification the same as MCERTS?

If you’ve been researching your effluent discharge permit requirements, you’ve probably come across the terms “SIRA Test and Certification”, CSA Group, Environment Agency and SCS, among others. But what are all of these terms and what do they have to do with MCERTS?

Who are SIRA?

SIRA originally started within the British optics industry in 1918, offering services within scientific research. The full company name is SIRA Certification Service (or SCS for short) but most of those in the industry simply reference SIRA.

In 2009, SIRA was acquired by the CSA Group and, in May 2015 the group merged SIRA with another company to form CSA Group Testing UK Ltd.

So, does SIRA Test and Certification not exist any more?

SIRA does still exist and is the EU notified body (No. 0518) related to ATEX* activities, as well as IECEx CB & ExTL for IECEx approvals and covers, among other certifications, MCERTS.   So, you can think of SIRA as the parent company that manages and issues MCERTS accreditation, but SIRA itself is owned and managed by the CSA Group.  You will still see the SIRA name used widely within the industry and the CSA Group readily states that many of its client companies still request SIRA certification marks and logos in order to use them within their product labelling and literature.

*ATEX stands for “atmosphères explosibles”, which is an EU Directive covering “equipment and protective systems intended for use in potentially explosive atmospheres.”

What part does the CSA Group play?

The CSA Group (which was initially known as the Canadian Standards Association) is responsible for certification standards across a range of areas and operate internationally across a wealth of countries. Within the UK, among many other areas of certification, it is the provider of the MCERTS environmental certification scheme, under the SIRA name.

To complicate things even a little more (!) MCERTS is actually the Environment Agency’s Monitoring Certification Scheme for equipment, personnel and organisations, but the CSA Group is the body approved to manage the MCERTS scheme, through its UKAS-accredited SIRA arm, and according to the ISO/IEC 17000 series of conformity assessment standards.

What does MCERTS certification cover?

MCERTS is a UK scheme that ensures compliance with the EU directives regulating emissions, monitoring data, equipment and employees. It provides a robust framework to ensure consistent and safe standards for monitoring liquid flow, such as commercial or water authority effluent. MCERTS compliance goes a long way to ensuring that there is consistency of standards and accuracy of information to the Environment agency with regards to the measurement and sampling of this liquid flow.

You can view the status of your certification from SIRA, including MCERTS through its Certificate Database that shows whether a certificate is still current or has been withdrawn or suspended.

MCERTS covers areas such as product and personnel certification, as well as the quality of inspections.

Briefly, the MCERTS scheme covers a range of monitoring, sampling and inspection activities including:

  • MCERTS product certification
  • MCERTS personnel certification
  • MCERTS for the self monitoring of flow

You can read full information about MCERTS and how SIRIS can help ensure your site’s compliance with the scheme here.


Our Sira test and certification MCERTS qualified team

What is the Environment Agency?

Since 1996, the Environment Agency has been the UK authority responsible for protecting and improving the environment of England. It is both a licensing and a regulatory authority, issuing permits within specified thresholds and monitoring requirements, and also inspecting and regulating the conditions of these permits. It has the power to prosecute those who fail to comply with the conditions of their Environmental Permits.

If you would like to know more about the Environment Agency’s standards, permits and conditions, or to view more information about the MCERTS scheme, or to download the Environment Agency’s performance standards and requirements, please view EA Mcerts Monitoring Emissions.

What is the CSA Group?

If you’ve been researching your trade effluent discharge requirements, you’ll likely have come across the CSA Group. But what does the CSA Group actually do and how can it help you?

CSA Group (formerly Canadian Standards Association) develops certification compliance standards in a range of areas. It provides a number of services worldwide and is the UK’s provider of the MCERTS environmental certification scheme under SCS (Sira Certification Service).

What’s the difference between CSA and SCS?

SCS, more commonly known as Sira, is the EU Notified Body for ATEX approvals, IECEx and MCERTS certification. CSA acquired SCS in 2009. The two entities became fully integrated in 2015 when they formed CSA Group Testing UK Ltd.

How can the CSA Group help you with MCERTS?

CSA Group is the awarding body for MCERTS

CSA (under SCS) is the UK’s only MCERTS certification awarding body and issues certificates to businesses which are required to be compliant by the Environment Agency.

SIRIS is one of the few UK companies appointed by CSA to deliver MCERTS services under the guidelines laid out in the Environment Agency’s minimum requirements for the self-monitoring of flow.

Our CSA certified inspectors are qualified to carry out site inspections and system audits. Once these checks have been successfully completed you will receive MCERTS certificate which is valid for five years.

CSA also provides MCERTS certification for waste water monitoring products. We guarantee that any system we design and install will meet these standards.

Guide to: Consent to discharge trade effluent

Do you think your business might need consent to discharge trade effluent?

Navigating your responsibilities can be confusing. Our guide answers some frequently asked questions about consent to discharge and the steps your business needs to take.


What is trade effluent?

Trade effluent is any liquid waste your business discharges to the UK’s water ways or sewers which could be harmful to the environment.

The Water Industry Act 1991 defines it as “any liquid, either with or without particles of matter in suspension in the liquid, which is wholly or partly produced in the course of any trade or industry carried on at a trade premises.” 

This means if your business discharges any liquids to the public sewer system that is not considered domestic waste (e.g. toilets) or rainwater (e.g. roof drainage) then you are producing trade effluent and you may need a permit from your local authority.


Which businesses need consent to discharge trade effluent?

The majority of businesses which produce liquid waste require permission – but there are exceptions which are considered ‘low risk’.

  • Swimming pools
  • Food/drink manufacturers
  • Car washes
  • Laundrettes
  • Chemical processing plants
  • Engineering plants
  • Hairdressers
  • Food service (e.g. restaurants, takeaways, pubs and hotels)
  • GP surgeries/dental and veterinary practices
  • Residential homes (e.g. care homes)
  • Grocery retailers (e.g. butchers, fishmongers and supermarkets)
  • Office buildings


Why is consent important?

Domestic waste discharged to our sewer systems is usually fairly easy to monitor. This is because water authorities can be confident what the strength, volume and content of this waste will be.

However, because trade effluent can come from so many different sources, it is difficult to predict what it contains and the harm it can do to people, the network and the environment. Above all, water authorities need to be confident that their treatment works will be able to process the effluent effectively and won’t be overloaded by the volume.

Water authorities reserve the right to refuse to accept any trade effluent they believe will cause undue harm to the environment, damage their sewerage systems or treatment processes, or have an impact on the health and safety of the general public or authority staff.

It is a criminal offence to discharge trade effluent to a public sewer system or waterway without consent, consequently it’s essential to obtain a permit before doing so. If you discharge without consent you could receive a fine of up to £5,000 in a Magistrates court, while more serious cases can be referred to Crown Court where fines are unlimited.


How do I apply for consent?

If you think your business requires consent to discharge trade effluent you will need to make an application via your retailer, who will complete a Trade Effluent Notice (G/02 Form).

What will my consent include?

Your consent will include several limits and conditions including:

  • Maximum discharge and daily volume rates
  • Solid particulate/organic matter concentration limits
  • pH level restrictions – normally this is between 6 and 10

Substances which could produce flammable or toxic vapours which could be harmful to people or the environment are not allowed and you will also be banned from discharging any liquid with a temperature higher than 43.3°C. Additionally, depending on the nature of your trade effluent, your local water authority may also impose additional conditions if required by the Environment Agency.


How can I be sure my business is being compliant?

Your consent to discharge trade effluent permit will include monitoring stipulations set out by your local water authority. Your permit may also include a requirement to comply with the Environment Agency’s Monitoring Certification Scheme (MCERTS). You may be required to conduct regular sampling of your trade effluent or monitor it on an ongoing basis.

Compliance with MCERTS ensures that your business is providing accurate emissions information to the Environment Agency. You can read more about MCERTS requirements here.

How can SIRIS help?

We offer an MCERTS compliance guarantee to ensure your business is fulfilling its consent to discharge permit. This gives you peace of mind that you are meeting your certification requirements. Get in touch with our friendly team to find out more.