Screening and Quantitation of Micro-pollutants from Sewage Water in the Process of Bank Filtration Using UHPLC-HRAM

Significance of the Topic

Bank filtration converts surface water influenced by treated sewage effluent into a safer raw water source for drinking water production. Understanding the fate of trace organic micro-pollutants during this natural filtration process is crucial for water utilities aiming to close the water cycle and ensure compliance with health and safety standards.

Objectives and Study Overview

This study evaluated the barrier function of bank filtration at a transect near Lake Tegeler See in Berlin. Multiple groundwater sampling points between the lake shore and a production well were analyzed to identify and quantify a broad range of known and unknown micro-pollutants, assess their degradation under varying redox conditions, and investigate the formation of transformation products.

Methodology and Sample Preparation

Samples from different bank filtration sites and the production well were injected directly into an online solid-phase extraction (SPE) system. Pre-concentration used a C18 SPE column, followed by separation on a narrow-bore C18 UHPLC column with a fast methanol–water gradient containing formic acid. Total cycle time including re-concentration was 15 minutes.

Used Instrumentation

• Online SPE system coupled to UHPLC
• C18 pre-concentration column, 2.1 × 20 mm, 12 μm
• C18 analytical column, 2.1 × 50 mm, 1.8 μm
• Thermo Scientific Q Exactive Focus hybrid quadrupole-Orbitrap mass spectrometer
• TraceFinder software for target screening and quantitation
• Compound Discoverer software for non-target and transformation product analysis

Main Results and Discussion

Suspect screening of full-scan data yielded 260 candidates, of which 94 were confirmed and 58 quantified using reference standards. Concentrations of 31 compounds remained above 0.1 μg/L in the production well. Degradation patterns fell into three redox zones:

• Aerobic (nitrate-reducing) zone: rapid removal of compounds such as amisulpride and venlafaxine
• Manganese-reducing zone: moderate degradation of carbamazepine and sucralose
• Iron-reducing zone: persistence of gabapentin, primidone, and valsartan acid

Unknown screening of the top 20 peaks confirmed eight additional compounds not covered in the suspect list. Transformation product search identified key metabolites such as gabapentin lactam (dehydration product) and phenazone acetylation derivatives. High-resolution full-scan and fragment ion matching via FISh scoring provided unambiguous confirmation.

Benefits and Practical Applications

• Rapid, automated combined screening and quantitation reduces analytical effort
• Comprehensive coverage of both target and non-target compounds supports risk assessment
• Redox-based degradation profiling aids optimization of bank filtration design and monitoring
• Transformation product detection highlights potential secondary contaminants requiring further treatment

Future Trends and Potential Applications

Advances in data-independent acquisition and machine learning-driven non-target workflows will expand the range of detectable contaminants. Coupling online SPE-UHPLC-HRMS with real-time data processing will enable continuous monitoring of bank filtration performance. Integration of bioanalytical effect assays alongside chemical screening can improve safety assessment of transformation products.

Conclusion

This work demonstrates that bank filtration significantly attenuates many urban micro-pollutants under varying redox conditions, though some persistent compounds still pass through. The described online SPE-UHPLC-HRMS workflow provides a powerful, efficient tool for comprehensive water quality monitoring and supports the implementation of sustainable water reuse strategies.

Reference

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