Long term monitoring of constructed wetlands using an NMR sensor

Subsurface flow wetlands have become a popular technology for the treatment of waste water all over the world. These systems become clogged over time, and must be renovated at great expense. We present a nuclear magnetic resonance sensor which is sufficiently small and inexpensive that several of them could be embedded in a constructed wetland to allow spatially resolved long term continual monitoring of the clogging process. We demonstrate the suitability of this sensor by first measuring NMR of sludge from an operational wetland, and secondly by monitoring the evolution of the fluid´s NMR spin lattice relaxation time (T₁) during clogging in a model wetland. Measurement of clogging rates in two locations are made and found to be 10.7×10^-2 min^-1 and 4.9×10^-3 min^-1 for regions near the inlet and the centre respectively.