Laboratory and online TOC measurement in paper production

Significance of the Topic

Monitoring organic load in paper mill process waters is essential for environmental compliance, process optimization and reliable wastewater treatment. Total Organic Carbon (TOC) analysis provides a faster, non‐toxic and automation‐friendly alternative to Chemical Oxygen Demand (COD), enabling real‐time insight into organic pollution levels.

Objectives and Overview of the Study

The study describes the implementation of laboratory and online TOC monitoring at the UPM-Kymmene paper mill in Schwedt, Germany. Goals included replacing COD measurements, improving sampling reliability and meeting evolving environmental regulations for wastewater discharge.

Methodology and Instrumentation

Process waters from wastepaper dissolution, pre‐flotation, post‐flotation, filtration stages and fresh or well water were sampled continuously and in the laboratory. The approach combined sample cooling, constant‐pressure introduction and automated acid rinsing to prevent biofilm formation and ensure reproducible results.

Used Instrumentation

• Shimadzu TOC-VCPH analyzer with cooled PTV Injector Optic 3 for laboratory TOC measurements
• SSM-5000A solid‐state autosampler module for high‐throughput analysis of liquid and solid samples
• Shimadzu TOC-4100 online TOC analyzer, installed adjacent to the aerobic treatment tanks
• Optional µ-vials for direct analysis of thermally labile or high‐boiling compounds via DTD/DMI modes

Main Results and Discussion

TOC concentrations and COD/TOC ratios were tracked through each stage:

• Pre-flotation stage showed highest organic loads, reduced significantly after post‐flotation and filtration.
• Process waters exhibited COD/TOC ratios close to the stoichiometric factor of 2.67, confirming consistency with theoretical oxidation requirements.
• Well and fresh water displayed elevated ratios due to oxidizable metal ions (Fe, Mn), highlighting matrix effects on COD measurements.
• Implementation of online TOC monitoring improved detection of reduced sulfur species and other compounds not captured by COD assays.

Benefits and Practical Applications of the Method

• Elimination of toxic reagents (dichromate, mercury) used in COD analysis
• Analysis time reduced by an order of magnitude, enabling near real‐time process control
• Improved accuracy for complex matrices and reduced interference from inorganic species
• Facilitated compliance with ISO 9001, ISO 14001 and EMAS II standards

Future Trends and Potential Applications

• Regulatory shift from COD to TOC monitoring for paper, carton and cardboard wastewater
• Advances in online analyzer design (e.g. TOC-4110) for enhanced sensitivity and automated maintenance
• Extension of TOC‐based surveillance to other industrial effluents and biological treatment systems

Conclusion

The adoption of TOC analysis at the UPM-Kymmene Schwedt mill demonstrated significant advantages over traditional COD methods, offering rapid, accurate and environmentally friendly monitoring. This approach supports robust process control, regulatory compliance and sustainable wastewater management.