Determination of ortho- and total phosphate phosphorus in water

Importance of the Topic

Efficient removal of phosphorus from wastewater is essential to protect aquatic ecosystems from eutrophication. Monitoring both bioavailable orthophosphate (o-PO4-P) for biological treatment and total phosphate phosphorus (TP) for regulatory compliance ensures optimized treatment strategies and environmental safety.

Objectives and Overview

This study evaluates the Metrohm 2035 TP Analyzer for continuous online determination of o-PO4-P and TP in water according to EN ISO 6878. The goal is to provide round-the-clock data to guide biological nutrient removal and chemical dosing processes.

Methodology

The analyzer applies a colorimetric method based on EN ISO 6878. For o-PO4-P, a direct reaction with ammonium molybdate and potassium antimonyl tartrate forms phosphomolybdic acid, which is reduced by ascorbic acid to produce molybdenum blue, measured photometrically at 875 nm. TP determination includes a preliminary digestion step in a cuvette using heat, an oxidizing agent, and acid to convert all phosphate species to orthophosphate before the same colorimetric measurement.

Instrumentation Used

• Metrohm 2035 Process Analyzer with compact digestion cuvette photometer module
• Measurement options: thermostated cuvette system or fiber-optic immersion probe
• Integrated stirring and temperature control for consistent reaction conditions

Main Results and Discussion

The system supports three TP measurement ranges:

• Low TP: 0–150 µg/L PO4-P (detection limit 5 µg/L)
• Standard TP: 0–5 mg/L PO4-P (detection limit 50 µg/L)
• High TP: 0–100 mg/L PO4-P (detection limit 1 mg/L)

Continuous monitoring allows precise adjustments to reagent dosing and early detection of influent spikes, enhancing both biological and chemical treatment efficiency.

Benefits and Practical Applications

• 24/7 process data reduces reliance on slow, manual lab tests
• Automated alarms inform operators of out-of-specification events, minimizing downtime
• Optimized reagent consumption lowers operational costs and environmental impact

Future Trends and Opportunities

Integration with digital control systems and cloud-based analytics will support predictive maintenance and advanced process control. Emerging sensor technologies and multiplexed analyzers may enable simultaneous monitoring of multiple nutrients for comprehensive wastewater management.

Conclusion

The Metrohm 2035 TP Analyzer delivers reliable, continuous analysis of o-PO4-P and TP, meeting EN ISO 6878 standards. Its flexible instrumentation and real-time reporting facilitate improved treatment performance, cost savings, and regulatory compliance.

References

• Brochure: Environmental Testing Industry I – Online Analyzers for Municipal Wastewater Analysis
• Phosphor Species in Process Water
• Wastewater Treatment Plants: Nitrogen Removal – Simultaneous Analysis of Ammonia, Nitrate, and Nitrite