Diffusional properties of methanogenic granular sludge: 1H NMR characterization.
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 degrees 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 H(2)O 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 H(2)O 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 degrees C) temperatures than in aggregates cultivated in nutrient-poor conditions or at low (10 degrees C) temperatures. Exposure of aggregates to 2.5% glutaraldehyde or heat (70 or 90 degrees C for 30 min) modified the diffusional transport up to 20%. In contrast, deactivation of aggregates by HgCl(2) did not affect the H(2)O 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.
Lens
Piet N L
PN
Laboratory of Biophysics, University of Wageningen, 6700 EV Wageningen, The Netherlands. piet.lens@wur.nl
Gastesi
Rakel
R
Vergeldt
Frank
F
van Aelst
Adriaan C
AC
Pisabarro
Antonio G
AG
Van As
Henk
H
D000693:Anaerobiosis; D001422:Bacterial Adhesion; D018533:Biomass; D019149:Bioreactors; D004058:Diffusion; D009682:Magnetic Resonance Spectroscopy / Q000379:methods*; D008697:Methane / Q000378:metabolism*; D011522:Protons; D012722:Sewage / Q000737:chemistry* / Q000382:microbiology*; D014865:Waste Disposal, Fluid
D011522:Protons; D012722:Sewage; D008697:Methane