(American Society for Microbiology, 2003) Lens, Piet N. L.; Gastesi Barasoain, Rakel; Vergeldt, Frank; Van Aelst, Adriaan C.; Pisabarro de Lucas, Gerardo; Van As, Henk; Producción Agraria; Nekazaritza Ekoizpena
The diffusive properties of anaerobic methanogenic and sulfidogenic aggregates present in wastewater
treatment bioreactors were studied using diffusion analysis by relaxation time-separated pulsed-field gradient
nuclear magnetic resonance (NMR) spectroscopy and NMR imaging. NMR spectroscopy measurements were
performed at 22°C with 10 ml of granular sludge at a magnetic field strength of 0.5 T (20 MHz resonance
frequency for protons). Self-diffusion coefficients of H2O in the investigated series of mesophilic aggregates
were found to be 51 to 78% lower than the self-diffusion coefficient of free water. Interestingly, self-diffusion
coefficients of H2O were independent of the aggregate size for the size fractions investigated. Diffusional
transport occurred faster in aggregates growing under nutrient-rich conditions (e.g., the bottom of a reactor)
or at high (55°C) temperatures than in aggregates cultivated in nutrient-poor conditions or at low (10°C)
temperatures. Exposure of aggregates to 2.5% glutaraldehyde or heat (70 or 90°C for 30 min) modified the
diffusional transport up to 20%. In contrast, deactivation of aggregates by HgCl2 did not affect the H2O
self-diffusion coefficient in aggregates. Analysis of NMR images of a single aggregate shows that methanogenic
aggregates possess a spin-spin relaxation time and self-diffusion coefficient distribution, which are due to both
physical (porosity) and chemical (metal sulfide precipitates) factors.
