Lens, Piet N. L.Gastesi Barasoain, RakelVergeldt, FrankVan Aelst, Adriaan C.Pisabarro de Lucas, GerardoVan As, Henk2019-01-102019-01-1020030099-2240 (Print)1098-5336 (Electronic)10.1128/aem.69.11.6644-6649.2003https://academica-e.unavarra.es/handle/2454/31952The 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.6 p.application/pdfeng© 2003, American Society for Microbiology. All Rights Reserved.Nuclear magnetic resonance (NMR)Diffusional propertiesMethanogenic granular sludgeinfo:eu-repo/semantics/articleinfo:eu-repo/semantics/openAccess