Tim Wilson explains how, in addition to providing visibility of water quality, ESNET final effluent monitors are also delivering substantial benefits for Scottish Water through enhanced process control. For example, ESNET units are dramatically reducing the use of dosing chemicals by introducing automatic monitoring and control.

Background

Typically, the mains-powered water quality analysers that are used for process monitoring at wastewater treatment works (WwTW) deliver accurate, high-quality data, but they have a significant footprint and are costly to install and operate. As a consequence, they only tend to be deployed at larger sites. However, in recent years it has become evident that final effluent can also be monitored with the same technologies that are used to monitor rivers. These ESNET systems are particularly advantageous for final effluent monitoring for a number of reasons. A single ESNET system, for example, is able to monitor multiple parameters simultaneously, providing almost real-time data from even the most remote sites. Importantly, in comparison with traditional final effluent monitors, ESNETs are quick, easy and low-cost to install and operate. However, as this article will explain, the connectivity of the ESNET units can be exploited to dramatically enhance process control.

ESNET deployments at Scottish Water

In 2021, Scottish Water started to install ESNET remote water quality monitors at some of its urban WwTWs. “The ESNET systems have dramatically improved our visibility of final effluent water quality data, without having to implement significant capital works,” explains Jamie Hesketh, Process Science Leader at Scottish Water. “Since 2021, we have installed 67 of the kiosk-based ESNET systems as final effluent monitors, and they have been so successful that we now plan to install around 113 more systems over the next few years.”

The kiosk-based systems have been installed at urban WwTW sites with a population equivalent of 2000 or above, but this may be expanded to PE>1000 as the rollout takes place. An automatic sampler was previously deployed at most of these sites, collecting final effluent samples that are stored and collected for subsequent analysis in a laboratory. The advantage of this method is that the samples can be tested for a wide variety of parameters, but the major disadvantage is the delay incurred by this procedure, which prevents automation and severely limits opportunities for process control. Consequently, processes such as dosing tend to operate 24/7 rather than on an ‘as required’ basis.

What is an ESNET?

Developed and manufactured by Meteor Communications, ESNET systems are complete, stand-alone, multi-parameter remote water quality monitors.  Originally designed for installation at sites with limited or no services, there are now hundreds of ESNET stations operating all over the UK, delivering almost real-time data from a wide range of diverse locations.

ESNETs are available in two formats – kiosk and portable. The kiosks are designed for permanent installation and the portable units are used for short-term deployment. Scottish Water, for example, have 7 portable ESNETS that are used primarily for process investigations.

Each of the Scottish Water ESNETs has a multiparameter water quality sonde fitted with sensors for measuring dissolved oxygen, temperature, pH, conductivity, turbidity and ammonium. Each sonde is located within an integrated flow chamber, through which sampled water is pumped. Water quality data is automatically transferred to the MeteorCloud® platform, which provides secure data visualisation, analysis and alarms.

One of the most important features of ESNETs is the ease with which they can be installed, usually requiring no capital works or pre-existing communications infrastructure. They are also designed to run with a very low power requirement, and are able to operate from a solar charged battery – even in Scotland.

Meteor Communications initially trained Scottish Water staff on how to install, service and calibrate ESNET systems, and this team of trained individuals now manages the network themselves. Their work involves routine visits to each site every 4-6 weeks to clean the pump and sample line, and to swap in a pre-calibrated sonde. Jamie’s team also log in to MeteorCloud every morning to check for any data anomalies that might mean swapping a sonde before its allotted date.

Enabling process efficiency

The wastewater process team at Scottish Water are able to log in to the MeteorCloud platform to view both historical and live water quality data, and to set up text alarms and email alerts to inform wastewater operations.

One of the most remarkable benefits to be gained from the ESNET systems is their ability to control dosing units. “We have started to hardwire some of the ESNETs to our dosing units, so that set points for, say, turbidity, can trigger coagulant dosing with PAC,” Jamie Hesketh explains. “In this example, the ESNET measures final effluent turbidity and transmits the data to MeteorCloud, and if the value is too high, MeteorCloud sends an instruction to the dosing unit via the ESNET. Similarly, when turbidity is low, dosing is unnecessary and therefore halted.”

The same mechanism is applied for other dosing mechanisms. For example, pH measurements are used to control the dosing of caustic soda (sodium hydroxide). It has been suggested that final effluent monitoring might be too late for dosing control, but in Jamie’s experience the key is the judicious selection of the set-point.

By automating dosing control, Scottish Water is negating the need for the installation and maintenance of additional process management hardware, all of which improves the sustainability of operations.

Looking forward

In addition to the water quality sonde, it is also possible to connect other sensors to ESNETs. For example, some users also connect water level or meteorological sensors. In addition, a multitude of different data feeds can be connected to ESNET systems, including analogue, digital and serial protocols. This lowers data infrastructure costs and reduces the need for manual checks.

Scottish Water has exploited the ESNET’s connectivity by attaching traditional final effluent ammonia monitors at some locations. “This has enabled us to compare the data from ESNET sondes with that from their (much more expensive) predecessors,” Jamie says. “The results have been very pleasantly surprising, because we have found that the data from the two different instruments trend in similar ways. However, there is still a justification for deploying a dedicated ammonia analyser where levels are particularly low.”

The program of ESNET installations is progressing well, delivering real-time multiparameter final effluent water quality data to enable prompt process management. Initial work to connect dosing units to the ESNETS has shown enormous potential to reduce the volume and cost of dosing chemicals, so Scottish Water plans to expand this capability across the whole country, with concurrent environmental and cost benefits.

The ESNET-based automatic dosing control mechanisms have only recently commenced operation, so it is probably too soon to draw any firm conclusions. Nevertheless, early indications are showing savings in chemical costs of around 20%. The Scottish Water wastewater process team is therefore optimistic about potential future improvements.