Laboratory and field studies on a new sensor for dissolved N 2 O

Nitrous oxide (N O) is a strong greenhouse gas, whose atmospheric concentration has been continuously increasing for more than 200 years. One major source is wastewater treatment plants (WWTPs), where N O emissions should either be minimized or pushed to levels where exploitation in biogas combustion engines becomes efficient. Both these strategies require online control of the N O concentrations in the liquid as well as in the gas phase. For this purpose, we propose a system for membrane extraction of the gas from the liquid phase, which then allows for a subsequent gas-phase analysis, which we perform by photoacoustic spectroscopy. We compare different theoretical calculations of the extraction efficiency, based either on a straightforward mathematical model or on a finite element simulation. The comparison of results with measurements produced on a well-defined model system shows good accordance. Based on the outcome, a field probe was developed and tested on a WWTP, yielding results comparable to the one achieved by GC reference analysis. Graphical abstract Gas extraction from liquids, e.g. from a wastewater treatment plant, for online gas monitoring.