Using Custom Sensors and Electrodes for Water Quality Monitoring

What is the Environment Act 2021 and what is Section 82?

The 2021 Environment Act is aimed at improving how water quality is measured, monitored, and managed in real-time, particularly in rivers, lakes, estuaries, and coastal waters. The Environment Act 2021 introduced several measures to improve environmental protections, and continuous water quality monitoring is a critical part of these efforts, especially for the management of wastewater and storm overflows. Section 82 of the Environment Act 2021 focuses on improving monitoring regarding water quality, specifically targeting how sewerage undertakers (i.e., water companies responsible for managing public sewer systems) handle wastewater discharges, including storm overflows, into rivers, streams, and coastal waters.

Sewerage undertakers are required to install and maintain monitoring equipment on storm overflows and combined sewer overflows to track how often they discharge untreated sewage into water bodies. Sewerage undertakers must ensure that any discharge from their sewer systems does not breach water quality standards, particularly in sensitive areas such as bathing waters and protected ecosystems.

The government guidance details the types of technologies and methodologies that sewerage undertakers should use to monitor water quality effectively. This includes specifications for:

• Flow meters and sensors for measuring discharge volumes.
• Water quality sensors for detecting pollutants (e.g., ammonia, pH, DO2, etc.).
• Data collection and management systems for storing and reporting monitoring data.

The legislation in place dictates that sewage undertakers must monitor their waste output upstream and downstream, of their asset being monitored, once per hour or every 15 minutes during a high-risk event. These changes are required to be rolled out as soon as practicably feasible and have started by 2025 with complete monitoring completed by 2035.

How can Sentek Help?

Electrochemical sensors play a significant role in supporting the Continuous Water Quality Monitoring Programme and compliance with the Environment Act 2021, particularly for sewerage undertakers in implementing Section 82. These sensors are designed to measure various chemical properties of water in real-time, offering precise and reliable data essential for maintaining water quality and detecting pollution. Sentek can provide a range of electrochemical sensors suitable for measuring common sewage works contaminants and key indicators of a water courses health:

• pH Levels
• Temperature
• Dissolved Oxygen
• Turbidity/Conductivity
• Ammonia – An increase in Ammonia is a common indicator of sewage contamination.
• Chlorine – Chlorine sensors can detect the presence of disinfectants that may be released from wastewater treatment plants.

Nitrate sensors help track nutrient levels, which can cause issues like eutrophication (excessive nutrient enrichment in water bodies leading to algal blooms and oxygen depletion).
As one of the leading UK sensor manufacturers, Sentek can support clients with design of custom electrochemical sensors, probes and sondes to meet their specific water quality monitoring requirements. These can be installed at combined sewer overflows and other wastewater discharge points to monitor when and how often untreated wastewater is being released into rivers or coastal waters. Sensors provide early detection of changes in water quality. For example, if a sensor detects a sudden rise in ammonia or a drop in dissolved oxygen, this could indicate a pollution event such as a sewage spill. Early detection allows companies to respond quickly and mitigate the environmental impact before it escalates.

Sentek electrochemical sensors have been used for long-term deployment across the globe, providing continuous monitoring that ensures companies remain compliant with the environmental regulations over time. By tracking trends and long-term changes in water quality, sewerage undertakers can identify problem areas, manage wastewater systems more effectively, and make informed decisions on infrastructure improvements.

Sensors from Sentek can be integrated with remote monitoring systems and data platforms, enabling seamless collection and transmission of water quality data. This integration is particularly useful for large-scale, continuous monitoring across multiple locations, such as river systems or coastal areas.

The sensors can also be incorporated into smart monitoring networks, where data is aggregated and analysed to provide insights into overall water quality trends and potential sources of pollution.

Sentek electrochemical sensors could significantly enhance water quality monitoring efforts by providing reliable, real-time data that helps sewerage undertakers meet their obligations under the Environment Act 2021 Section 82. These sensors enable proactive management of water resources, ensuring timely detection of pollution and helping to maintain high environmental standards.

Ammonia vs Ammonium

Ammonia is just one component in sewage that can be particularly harmful to aquatic life, it can be very challenging to monitor, particularly in the field. Ammonia ISE are available but presently are only practically useable in a lab-based setting.

Ammonia is only present as the deprotonated form NH3 in a basic pH greater than 7, below this it is mostly in the less harmful ammonium ion (NH4+). Ammonium is unable to cross cellular membranes so is therefore much less toxic than ammonia. As pH and temperature increases the proportion of ammonium being deprotonated to the smaller and more harmful ammonia increases so by monitoring NH4+, pH and temperature we can relatively accurately infer the ammonia concentration in the water. The table below shows the percentage of ammonia vs ammonium at varying pH and temperature.

This can be plotted onto a curve also shown here.

Schematic model of ammonium ion (NH4 + ) and neutral ammonia (NH3) proportions in function of the pH. At acidic and neutral pHs, NH4 + is the most abundant species. However, NH3 is dominant in highly alkaline solutions. Scientific Figure on ResearchGate. Available from: https://www.researchgate.net/figure/Schematic-model-of-ammonium-ion-NH4-and-neutral-ammonia-NH3-proportions-in_fig2_358973331

Calibration and Maintenance

Sensors or sondes can be pre calibrated prior to installing but will need periodic recalibration to maintain a high degree of accuracy. Over time the sensor will begin to drift away from the calibration point. Each sensor type will drift at a different rate as they age – the longer the sensors go without calibration the greater degree of uncertainty the measurement will have.

Regular maintenance will also be required to ensure that the sensors or sondes are working at their best, giving that monitoring a water way will naturally lead to an amount of biological fouling to the sensors. Contamination of the sensor junctions or plates will lead to increased resistance which in turn will skew measurements, so it is important that these are periodically cleaned off and recalibrated.

For more information on the Environment Act 2021 Section 82 and sensors used to measure chemical properties of water, contact a member of the team.