Towards real-time kinetic monitoring of wastewater treatment: A case study of sunlight and ozone treatment of unconcentrated wastewater using flow NMR

Wastewater contains complex organic signatures whose components can be harmful to both environmental and human health. Nuclear Magnetic Resonance (NMR) spectroscopy is an excellent tool for molecular monitoring, with the ability to follow total organics, subcategories (aromatics, aliphatic etc.) and, resolution permitting, even individual compounds. However, due to the relatively low sensitivity of NMR, studies of wastewater to date have involved pre-concentration (often many liters) before analysis. This proof of concept study asks, Is NMR sensitive enough for on-line wastewater monitoring without pre-concentration? Here, a continuous flow 500 MHz NMR system, coupled with a sunlight simulator and ozone generator, was used on unaltered and unconcentrated wastewater to assess the potential of on-line NMR for understanding wastewater treatment processes. Wastewater from 3 different treatment stages were analyzed. In general, combined ozone and sunlight was more effective at removing organics, while differences in behavior of the same molecules within different wastewater fractions suggest that the chemistry is more complex than just the action of reactants (light, ozone) on the target chemicals, and to some extent, involves other components in the wastewater. As such, the nature of the effluent itself could also have important impacts on the rate and completion of its degradation. In summary, online NMR of wastewater treatment could be carried out without pre-concentration of the wastewater, in line with important future applications for understanding wastewater treatment processes at the molecular level. Over the last decade, there has been considerable development in low field, low footprint, low cost, NMR spectrometers. Portable versions of those systems could potentially, in the future, be applied for on-site, on-line monitoring of waste streams at water treatment plants, as described here.

Automated summary

Nuclear Magnetic Resonance (NMR) spectroscopy is a valuable tool for monitoring complex organic compounds in wastewater. This study demonstrates the potential of online NMR for understanding wastewater treatment processes without the need for pre-concentration. The research suggests that a combination of ozone and sunlight is effective in removing organics from wastewater, and highlights the complexity of chemical reactions involved in wastewater treatment.