ABB ortho-phosphate monitors help Severn Trent Water to meet tightening consent limits

The need for accurate measurement of ortho-phosphate levels in wastewater effluent has seen the recent installation of 120 Aztec 600 ortho-phosphate analysers in wastewater treatment plants throughout Severn Trent Water's operating area. Enabling continuous monitoring, the analysers are helping to ensure that the company keeps within consent limits set by the Environment Agency.

ABB ortho-phosphate monitors help Severn Trent Water to meet tightening consent limits

When present in watercourses, phosphate is a major contributor to eutrophication, where an environment becomes enriched with nutrients. In such environments, algae can flourish, consuming dissolved oxygen in the water, which is further depleted as other aquatic plants compete for the remaining oxygen. Known as aquatic hypoxia, this process can quickly result in the death of aquatic life.

A major by-product of wastewater treatment and agricultural processes in particular, phosphate needs to be closely monitored and controlled. Currently phosphate consents for sewage effluents are typically set at 1-2mg/l. In AMP6 and 7, this is likely to be further reduced to less than 0.5mg/l in some instances, which will require closer monitoring and control of phosphate levels.

The emphasis on minimising phosphate levels means that efforts are now shifting towards further reducing the phosphate load in water being discharged to rivers. In particular, the focus on outcomes rather than outputs encouraged by AMP6 will see greater attention being paid to monitoring and tackling the sources of phosphate within a catchment before it reaches the water treatment plant.

As part of its work to comply with effluent discharge standards, Severn Trent Water has installed ABB’s Aztec 600 ortho-phosphate analysers at all of its sewage treatment plants with total phosphate consent limits. Operating alongside ammonia analysers and turbidity monitors, the ortho-phosphate analysers have reduced the company’s reliance on manual sampling.

“Before ABB’s units were installed, we were totally reliant on manual spot sampling of effluent,” says Anthony Kyriacou, Proactive Network Control Manager for Severn Trent Water. “Although this enabled us to comply with Environment Agency requirements, it only gave us an indication of levels for a specific time and set of operating conditions, which was of limited value in helping us to find ways to optimise our effluent treatment processes.”

Connected to Severn Trent Water’s eSCADA system, the Aztec 600 ortho-phosphate monitors provide continuous real-time data including any alarms generated by issues such as high ortho-phosphate levels. By combining this data with data from other installed instruments measuring ammonia and turbidity, Severn Trent Water is able to obtain a detailed picture of effluent quality for any given moment.

“The ability to obtain real-time data on ortho-phosphate levels is vital in helping to ensure that we stay within our consented limits,” says Paul Duckett, Programme Engineer for Severn Trent Water. “Using this data enables us to better target future investments in our wastewater treatment plants to further optimise our effluent quality.”

The availability of real-time data will also enable Severn Trent Water to create a more proactive maintenance schedule matched to the actual needs of its treatment plants.

“Together, the data from our ortho-phosphate monitors and other instruments give us much greater visibility and knowledge of what’s going on at our treatment plants,” explains Paul. “We are now able to spot any potential malfunctions or issues before they can escalate, enabling us to be much more effective in the way that we deploy our maintenance teams.”

ABB’s Aztec 600 Phosphate colorimetric analyzer has been designed specifically for the measurement of ortho-phosphate in both potable water and municipal wastewater effluents. It offers reliable and accurate on-line analysis of phosphate up to 50 ppm PO4

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