Final Effluent Monitoring in a municipal wastewater treatment plant (Norfolk, England)

Background

Phosphorus is a leading contributor to freshwater eutrophication. For water utilities, it is a growing environmental challenge. Monitoring phosphate (PO₄-P) in treated effluent is critical to compliance, but remains technically complex, requiring wet chemistry rather than simpler spectral or ion-selective electrochemical technologies.

Anglian Water's Whitlingham STW, serving 300,000+ people, is a Bio-P removal plant using Enhanced Biological Phosphorus Removal (EBPR), which relies on effective Acetic Acid dosing. Discharge consent is 1 mg/L Total-P, tightening to 0.25 mg/L in AMP8 from April 2025. Whitlingham was selected as a pilot test site to explore if phosphate monitoring can provide insights for improving operational efficiency.

The Challenge

Phosphate is a critical pollutant to control and one of the hardest to monitor. It requires wet chemistry, making real-time measurement complex, costly, and until now, largely unavailable.

At Whitlingham STW, Anglian Water faced three key challenges:

Tightening Limits: Discharge permits were set to tighten from 1.0 mg/L to 0.25 mg/L under AMP8, demanding more efficient process control.

Data Gaps: Infrequent, delayed lab testing created blind spots, offering no early warning for process issues or compliance risks.

High Chemical Costs: With over £600,000 spent annually on acetic acid dosing, the lack of real-time data made optimisation difficult.

Without continuous monitoring, phosphate posed a regulatory risk, adding operational uncertainty and cost presssure.

The Solution

SouthWestSensor's DropletSens^TM PO₄ sensor is a compact, real-time phosphate monitoring solution that produces high-frequency, lab-quality data autonomously in the field.

Dissolved ortho-P levels in conjuction with turbidity may be used to estimate Total-P.

• Location: Fixed securely in the Final Effluent channel at Whitlingham STW.
• Power: Connected to mains electricity.
• Filtering: Fitted with a 0.45-micron inlet filter to prevent clogging.
• Data handling: Integrated with a UDLive logger, with seamless cloud data upload.

The Results

• Average PO₄-P Level: 0.1 mg/L
• Maximum Observed Spike: 0.8 mg/L (within permit limit)
• Data Points Logged: >750,000 over 3 months
• Lab Cross-Validation: Confirmed high sensor accuracy
• Opertional Efficiency Insights: 3 periods of higher P-levels observed; could benefit from dynamic adjustment of acetic acid dosing
• Outcome: Sensor permanently installed

Client Testimonials 

'SWS' sensor kit proved a key tool for our optimisation work, very easy & quick to install with readily available and continuous lab-quality data. Could lead to direct acetic acid dosing cost savings. Plus the sensors have much wider utility beyond P-optimisation.'

Alec Kimble, Managing Director, Bi-Zen Ltd

'The phosphate sensor is a game changer for us. It gives us constant eyes on critical P-levels versus normally conducted infrequent lab analysis, which is labour intensive and can miss key events; have now already ordered the SWS kit.'

Shaun Barker, Bioresources Operations Manager, Anglian Water

'Beyond P-monitoring as in Whitlingham, I can see much wider applicability of SWS sensors including the use of portable units to assist commissioning of new P-plants and for N-removal optimisation.'

Wilf Bourgeois, Senior Environmental Scientist, Anglian Water