Measuring NOM
Natural Organic Matter (NOM) is present in all surface waters and can greatly impact drinking water treatment. It influences coagulant usage, disinfection by-products (DBP) formation, and can interfere with corrosion control. Because of this, facilities rely on surrogate parameters to estimate the NOM present in water and how it will react during treatment.
A recent study from Charles University (Prague), published in the AWWA science journal compared two of the most used methods to measure NOM.
TOC and CODMn Measuring NOM
This is how these methods measure NOM:
- Total Organic Carbon (TOC) measures the total amount of organic carbon by fully oxidizing all organic compounds to CO2, and the amount of CO2 detected is proportional to the organic carbon in the sample.
- Permanganate Chemical Oxygen Demand (CODMn), on the other hand, measures only a fraction of NOM that reacts with potassium permanganate. As a result, CODMn reflects the oxidizability of organic compounds, not total concentration.
Challenges with CODMn and Traditional NOM Monitoring
CODMn is used in many jurisdictions worldwide, often interchangeably with TOC because of its inclusion in regulatory guidelines. However, the study aptly titled, “Why CODMn Is Not Suitable for Assessing NOM Concentration in Source Waters”, determined that CODMn can produce misleading results for NOM when source waters contain different NOM types.
Since permanganate only partially oxidizes specific organic compounds, CODMn tends to overestimate humic NOM and underestimate algal NOM. Without standardized modifications to improve this method of measuring, CODMn is unreliable for tracking true NOM concentration.
Additionally, traditional NOM monitoring metrics capture only a part of the picture:
- Total Organic Carbon (TOC): reflects the amount of carbon in a sample, but not how reactive NOM is.
- Ultraviolet Absorbance at 254 nm (UV254): provides some insight into aromatic, UV-absorbing fractions of NOM, which are linked to DBP formation. The drawback of this strategy involves NOM components being unable to absorb at this wavelength, so UV254 can miss important changes.
- Specific Ultraviolet Absorbance (SUVA): can estimate hydrophobicity, but is influenced by other substances, failing to reflect accurate NOM results.
Fortunately, not all hope is lost.
MANTECH’s PeCOD overcomes these limitations by providing a consistent, fully oxidizing, and sensitive measure of NOM reactivity in real time.
The PeCOD Solution
MANTECH’s PeCOD analyzers provide a modern alternative to traditional NOM monitoring by measuring how much oxygen is consumed when NOM is rapidly oxidized via photoelectrocatalytic oxidation. Therefore, making real‑time NOM reactivity monitoring accessible for everyday treatment operations, capturing what TOC misses. By delivering rapid, accurate measurements, they help operators:
- Track NOM changes from source to finished water.
- Measure oxidation of NOM within 5 minutes.
- Improve treatment responsiveness as water quality shifts.
- Support DBP mitigation strategies when paired with TOC and UV254.
This technology is available as a benchtop, autosampler or online autonomous solution to suit different requirements. With automated operation, safe chemistry, and modern data integration, MANTECH’s PeCOD systems help create a practical, efficient workflow for managing NOM in source waters.
