In a major step forward for emissions monitoring, researchers have developed a powerful spectroscopy system that can measure multiple greenhouse gases in real time across large open areas.
Study: Ultra-broadband coherent open-path spectroscopy for multi-gas monitoring in wastewater treatment. Image Credit: wasanajai/Shutterstock.com
Designed for complex environments like wastewater treatment plants (WWTPs), this system offers a significant upgrade over traditional point-based methods that often miss fast-changing or spatially varied emissions.
Why Wastewater Emissions Are So Challenging to Track
Greenhouse gas (GHG) emissions from WWTPs aren’t static—they shift constantly based on biological processes such as nitrification, denitrification, and organic matter degradation. Among these gases, nitrous oxide (N2O) is especially potent, with a global warming potential far higher than carbon dioxide (CO2). Its emission levels depend on how well nitrogen is converted in the treatment process—something that’s influenced by oxygen levels, aeration timing, and incoming wastewater composition.
Historically, most monitoring has relied on point-based gas analyzers. These instruments provide accurate readings, but only from a specific location. They struggle to capture the bigger picture: how emissions vary across a treatment basin or spike during short operational changes. As a result, they can miss key dynamics critical to mitigation and regulation.
Open-path spectroscopy, where gas is measured along a beam path across open air, has been proposed as a better alternative. It offers broader spatial coverage and the ability to track fluctuations over time. But previous systems have typically been limited to detecting a few gases, lacked sensitivity, or required complex calibration to separate overlapping signals—making them difficult to deploy in WWTP settings.
The Breakthrough: A Broadband, Real-Time Multi-Gas Monitoring System
In a new study published in Environmental Science and Ecotechnology, researchers have introduced an ultra-broadband coherent open-path spectroscopy (COPS) system specifically designed for industrial-scale environmental monitoring.
This system combines Fourier transform spectroscopy with a high-powered mid-infrared light source that spans from 2 to 11.5 micrometers, allowing it to pick up the absorption fingerprints of a wide range of gases, all at once.
The setup is simple but powerful: the light source and detector are positioned above an aeration tank, and a retroreflector 60 meters away bounces the beam back to form a long, open path across the emission zone. Every 40 seconds, the system collects a new spectrum of data, offering near real-time monitoring of the gases present.
To analyze the data, the team used advanced fitting algorithms that match observed spectra against known reference signatures from the HITRAN database. These algorithms correct for common issues like spectral interference and etalon effects to ensure reliable gas identification and quantification.
To validate the system, researchers ran it alongside high-precision point instruments—including cavity-enhanced laser systems and photoacoustic analyzers—to measure methane (CH4), CO2, N2O, ammonia (NH3), and carbon monoxide (CO).
What the Data Revealed
The COPS system successfully detected and distinguished multiple gases in real time. The spectral fits were clean, with minimal residuals, confirming that the system could reliably resolve complex absorption patterns even in a variable WWTP environment.
Methane and CO2 concentrations fluctuated with operational activity, such as changes in aeration and wastewater loading. For example, during periods of high ammonium input, the system observed increased methane levels, likely due to biogenic activity in low-oxygen zones. CO2 emissions rose during active aeration, corresponding with increased microbial respiration.
N2O levels were more stable but clearly tracked total nitrogen loading and denitrification activity, mirroring the trends captured by the point-based analyzers. Ammonia levels also shifted as expected, reinforcing the system’s ability to capture the real-time impact of process changes.
Crucially, the system also detected short-lived emission events—brief spikes and dips in gas concentrations that would likely go unnoticed by less frequent, localized sampling. This kind of temporal resolution is essential for capturing the true variability of emissions and understanding their underlying causes.
Why This Matters
The ultra-broadband COPS system represents a practical and scientifically robust solution to a long-standing challenge in environmental monitoring. Its ability to continuously and accurately track multiple gases over extended distances opens the door to much deeper insights into how, when, and why emissions occur at wastewater facilities.
Unlike traditional systems that offer only snapshots in time and space, this platform paints a fuller picture, capturing the nuances of emission dynamics as they unfold. With better data, operators can optimize plant performance, identify inefficiencies, and reduce greenhouse gas output more effectively.
In a regulatory and climate landscape that increasingly demands precision and accountability, tools like this can help close critical gaps in emissions inventories and support smarter, science-backed mitigation strategies.
Journal Reference
Krebbers R., van Kempen K., et al. (2025). Ultra-broadband coherent open-path spectroscopy for multi-gas monitoring in wastewater treatment. Environmental Science and Ecotechnology. DOI: 10.1016/j.ese.2025.100554, https://www.sciencedirect.com/science/article/pii/S2666498425000328?via%3Dihub