Pulsed field gradient nuclear magnetic resonance (NMR) techniques have been applied to study diffusion and flow in a sulfidogenic granular sludge bed. When sulfidogenic granular sludge is exposed to a 20 MHz magnetic field, a multi-exponential spin-spin relaxation (T2) with at least 5 populations is observed. One of these populations (T2 ≈ 30 ms) is intracellular water. Diffusion measurements at 22°C with 1H-water as tracer indicated that sulfidogenic granular sludge contains a distribution of diffusion coefficients between 1.0 × 10−9 m2/s and 2.1 × 10−9 m2/s. Analysing the data set using a monoexponential fit gives a general parameter that can be used to describe the apparent diffusion coefficient in granular sludge. This approach showed that sulfidogenic granular sludge cultivated in different reactor configurations (UASB, USSB and baffled reactors) has comparable diffusional characteristics. Finally, the use of flow and imaging measurements in sulfidogenic granular sludge beds is discussed.

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