Discharging your duties - chemical effluent sensors21 January 2021

Stage 1 of the Detectronic twin cone clarification system

Chemical sensors can highlight potential risks with discharged water and whether environmental standards are being met. How do these technologies work in practice and what are their limitations? By Brian Wall

Wherever standalone water discharge or groundwater activity occurs, there is a hefty onus on operators to ensure this is being carried out in compliance with environmental regulations. The Environment Agency will check that the terms of any permit are being fulfilled. Operating without one is breaking the law and failure to meet these obligations could result in a permit being revoked (www.is.gd/conuvo).

Ascertaining whether or not discharged water meets environmental standards for effluent isn’t something that can be done with the naked eye – hence the essential role that chemical sensors play in detecting questionable compounds and highlighting the potential risks they pose. But what criteria should be applied when assessing the performance of such sensors: should these be based purely on their ability to measure what is happening in real time, or is that too simplistic? There is also the question of cost. You might end up paying more for a real-time monitoring solution when near real-time monitoring is all that’s required – say, every 60 seconds, five minutes or even one-hour testing.

For Detectronic, which specialises in the design, manufacture and installation of ultrasonic wastewater flow, level and water quality monitoring equipment, the question of whether a manufacturer in the food, beverage or pharmaceutical industries, for instance, should be seeking out a solution that delivers near real-time monitoring misses the point.

Commercial director Dave Walker states: “The operations they carry out in those industries tend to be batch-processed, so you have to be very careful with how you manage the waste stream. If you’re proposing a monitoring cycle of, say, every fifteen minutes and batching takes place every two minutes, you could miss some vital issues in the interim. You always need to understand the manufacturing and processing cycles involved.”


By way of example, he references two large UK manufacturers who came to Detectronic recently to seek solutions to very different issues. He continues: “One was having problems with settleable content and needed to monitor that every five minutes, as the company was batch-processing goods to a really low volume over a 24-hour period, with batches every two to three hours. Installing a simple twin-cone clarification system and Orakel asset performance monitor [APM] has reduced the settled solid content to a level which is now within consent and is providing a safe buffer zone for those unpredicted events caused upstream in the manufacturing process.”

The other manufacturer saw production double during lockdown to 5m3 a day, which coincided with a surge in chemical oxygen demand [COD] in its effluent. Walker explains: “The high COD present in a particular type of food oil used in the production of a certain food meant the site was often exceeding the permitted COD level agreed in its consent with the regional sewage undertaker. So, we went back to the production centre to see what might be causing this,” says Walker.

“It was traced to in-house cleaning, which operated two different shifts. This was identified by the manufacturer hiring an online Orakel APM, which provided continuous instantaneous readings of COD, TSS [total suspended solids] and TDS [total dissolved solids]. Data was transferred remotely to the Detec Analytics web portal where data and shift patterns were compared. A common approach was devised to eliminate the issue.”


As the popularity of connected smart instrumentation rises, processes are ever more dependent on the data that it generates, observes Steve Tuck, technical sales engineer at Pollution & Process Monitoring (PPM). The correct instrument selection is therefore of paramount importance. “All the key factors affecting appropriate instrument selection should be considered before making a commitment that may otherwise turn a potential asset into a subsequent liability. Understanding the subtle design features that differentiate a product and its suitable application is really key to a successful installation.”

PPM primarily manufactures and distributes water quality measurement instrumentation, with particular expertise in continuous total organic carbon (TOC) and ammonia measurement. He adds: “Continuous analysis provides real-time measurement and control to minimise product loss and reduce waste, but typically requires careful selection of an appropriate sampling system. On-line TOC analysis is a good example of a technique that can be used to provide continuous measurement of upstream processes and help to maintain discharge compliance. With instrument response times from three minutes, proactive management is possible. Tests such as COD and biochemical oxygen demand (BOD) performed on discrete samples take two hours or five days respectively to complete.”

Ammonia is another critical effluent parameter. “On-site biological treatment processes can directly impact the quality of a trade discharge. Discrete sample analysis may not necessarily identify process failure or pollution events as they start to unfold. The ability to install real-time measurement systems with response times from less than 10 minutes allows for a much higher level of environmental compliance.”

Parameters such as pH and temperature are truly continuous and relatively low cost, so should certainly be measured in situ wherever applicable, advises Tuck. “What is also important is ensuring the measurements are representative. Taking a representative sample where processes may change rapidly and also maintaining sample integrity – preventing sample degradation prior to analysis, which often requires refrigeration during storage – may also be supportive of continuous on-line measurement.”

From PPM’s perspective, though, it is all about being proactive and responding to events as they occur. “It’s too late to react after something happens, such as a serious discharge into the water course. If tests have to be carried out off-site, it could be hours or even days before the analysis is completed. That is simply too long to be of real value.” Ultimately, though, the instrument used is only as good as the actual installation. A site survey to establish specific site requirements is often as important as instrument selection itself.


Siltbuster provides temporary water treatment systems. Any kind of lab analysis to monitor for water quality trends would be too slow to make sure organisations aren’t going to violate their discharge criteria, as the sites involved are constantly discharging.

“It’s commonplace for environmental advisors to be responsible for several project sites at any one time, all demanding the same level of attention,” says Richard D Coulton, general manager – construction at Siltbuster. “With fines becoming more prevalent for breaching environmental permits, advisors are often left with no choice but to delegate the supervision and maintenance of operational environmental protection systems to the project site managers. Irrespective of how diligent, thorough and environmentally aware the site manager is, they, too, are accountable for numerous daily tasks, resulting in continual supervision and monitoring of water treatment system discharge becoming seldom feasible.”

Developed to counter this challenge, Clarity by Siltbuster is a real-time water quality monitoring and reporting system that offers data logging of discharged water, but more significantly real-time alarm notifications – either via SMS (text message) or email – should the equipment detect non-compliant water passing the probes. “This enables immediate response procedures to be implemented, minimising the risk of a disastrous environmental pollution event and ensuring corporate responsibilities are met,” adds Coulton. “Using a purely data logging approach runs an inherent risk, as very often the data is downloaded at irregular intervals and typically, if breaches have occurred, it is only realised after the event and potentially because of regulatory investigation.”

Clarity is said to provide early warning that the system needs attention (shutting down the feed pumps, if so desired], in order to maintain compliance with any discharge criteria that might be in place. “Site managers and operatives can continue with their daily tasks without the need for constant supervision, in the knowledge that alerts will be issued, should the discharge water exceed predefined limits, but importantly before consent level has been breached, providing crucial time to rectify any issues and preventing a possible notifiable pollution event.”


Thermo Fisher Scientific initially approached Pollution & Process Monitoring (PPM) in May 2015 to supply analytical instrumentation to continuously measure trade discharge at its Basingstoke production facility in Hampshire.

The initial installation comprised a Proam ammonia monitor and Chemitec ortho-phosphate analyser. These instruments were pre-mounted by PPM onto PVC back-panels, to simplify the site installation. Sample preparation and reagent storage was also integrated. After several years of operation, the client asked PPM to scope a more comprehensive suite of instruments, covering key water quality parameters.

A purchase order for a new bespoke measurement system was placed in November 2017 and the installation was made the following spring. A large walk-in analyser kiosk, measuring 2.5 x2.5m with wet and dry sections, was equipped with a comprehensive array of instruments. Pre-installation included internal lighting, heating, sample pipework, electrical distribution and local isolation to each appliance. The analyser suite included continuous measurement of total organic carbon (TOC), ammonia, ortho-phosphate, sulphate, sulphide, and free chlorine.

A common controller continuously reporting pH, conductivity and turbidity was also installed to display and output the measurements from the individual sensors, mounted within a common sample break-tank.

Additionally, the client initially required the possibility to collect discrete samples to enable further laboratory investigation, so a refrigerated automatic sampler was also installed for this purpose.

Since the Basingstoke site manufactures cell culture media, the effluent stream associated with the associated production processes can be problematic for analytical measurement. Consequently, PPM installed its membrane filtration for sample preparation, removing biology and suspended solids, prior to analytical measurement. Additionally, automatic compressed air cleaning was integrated. The regular air blast system helps to strip biofilms off the membrane surface, reducing maintenance.

Instruction on operation and maintenance was given during commissioning to the relevant site engineers who would then perform simple duties such as changing reagents and periodically cleaning filters. Service engineers from PPM attend site on a monthly interval to perform more comprehensive maintenance, validate performance and ensure the suite of instruments continue to provide reliable measurement.

PPM also manages the supply of reagents and consumables using the company’s internal stock replenishing system.

The instrumentation has allowed Thermo Fisher Scientific to optimise the treatment plant, to improve the quality of its trade discharge and demonstrate compliance to the local water authority. All of the instrument signals are connected to a common signals terminal box, interrogated by the Siemens PLC system. Should the instruments detect any parameter falling outside compliant set points, the PLC control system can then operate a Rotork valve to divert the treated effluent for a second pass through the treatment plant. The measurement system also produces healthy status signals to provide additional assurance.

Since the organisation operates within the life science sector, manufacturing important culture media used for testing of pathogens such as COVID-19, the water quality monitoring installation has been deemed critical to site operations. PPM has therefore continued to attend site during the pandemic, observing social distancing measures to mitigate risk. With the instrumentation contained within a dedicated walk-in enclosure, this complete segregation from day to day operations has proved especially beneficial during the pandemic.

Brian Wall

Related Companies
Detectronic ltd
Pollution & Process Monitoring Ltd
Siltbuster Ltd

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