Why is Measuring NOM Important for Drinking Water Treatment Process Optimization?
Drinking water plants are increasingly focused on measuring NOM (natural organic material) as rising concentrations create new treatment challenges. Factors such as climate change, land-use shifts, and recovery from acid rain have all contributed to the rise of NOM levels, leading to the widespread of “brownification” in surface waters.
While NOM is not harmful on its own, it introduces several treatment challenges, including increased coagulant usage, taste and odor changes, disinfection by-product (DBP) formation, and interference with corrosion control. These challenges become more apparent when NOM levels increase, and facilities lack the effective tools to monitor it.
The Challenges That Come with Measuring NOM
Traditional NOM monitoring metrics capture only a part of the picture.
- Total Organic Carbon (TOC): reflects the amount of total carbon in a sample, but not the reactive NOM fraction.
- Ultraviolet Absorbance at 254 nm (UV254): provides some insight into aromatic, UV-absorbing fractions of NOM, some of which are linked to DBP formation. The drawback of this strategy involves straight chain NOM components being unable to absorb at this wavelength, thus UV254 will miss important changes.
- Specific Ultraviolet Absorbance (SUVA): can estimate hydrophobicity, but is influenced by other substances, failing to reflect accurate NOM results.
- Advanced Tools (EEMs, EDC): fluorescence spectroscopy and electron donating capacity can get a better read on NOM but are more complex and are not designed for routine monitoring.
Case Study
A study published in the AWWA Water science journal evaluated how PeCOD measurements correlate with conventional NOM metrics such as TOC and UV254. The research took place across nine drinking water treatment facilities in Atlantic Canada and the United Kingdom. The objective was to determine whether PeCOD could better detect changes in NOM reactivity, specifically where partial oxidation occurs. PeCOD readings were compared directly with TOC and UV254 across multiple treatment stages including biofiltration, oxidation, and advanced oxidation processes. This allowed researchers to assess sensitivity to NOM degradation.
Results
The results showed that PeCOD displayed only moderate correlations with TOC and UV254. However, it consistently captured treatment-related changes that traditional methods often missed. Figure 1 highlights how PeCOD method responds more sensitively to treatment processes than SUVA alone. While SUVA shows minimal variation across the treatment steps, both the mean oxidative state of carbon (Cos) and the PeCOD:TOC ratio decrease as NOM is oxidized or removed. This demonstrates the PeCOD’s ability to detect changes in NOM reactivity that traditional methods overlook.
Furthermore, recent research from Charles University demonstrated that the permanganate index method (CODMn) can give misleading results because it oxidizes different NOM types to varying degrees. As a result, CODMn often overestimates humic-rich NOM and underestimates algae-derived NOM, making it unreliable for tracking true NOM concentration. 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 make real‑time NOM reactivity monitoring accessible for everyday treatment operations. By delivering rapid, accurate measurements, they help operators:
- Track NOM changes from source to finished water
- Measure oxidation of NOM within 5 minutes
- Measure the reactive fraction of TOC
- Improve treatment responsiveness as water quality shifts
- Support DBP mitigation strategies when paired with TOC and UV254
PeCOD provides a modern alternative to traditional NOM monitoring by measuring how much oxygen is consumed when NOM is rapidly oxidized via photoelectrocatalytic oxidation. With automated operation, safe chemistry, and modern data integration, MANTECH’s PeCOD systems provide a practical, efficient workflow for managing NOM in source waters.
