In anaerobic wastewater treatment, Upflow Anaerobic Sludge Blanket (UAS reactors operating under sulphidogenic conditions (COD/SO42- < 1) are an emerging reactor technology for the treatment of sulfate rich wastewater. Unlike methanogenic reactors, few gaseous end products are formed, resulting in inferior mass transfer rates compared to methanogenic UASB reactors.
The aim of this research proposal is to study possible improvement of t treatment efficiency of such sulphidogenic bioreactors by improved mass transfer. Three ways to accelerate mass transfer will be studied: (i) upflow velocity in the reactor, (ii) mixing by gas evolution and (iii) the 'breathing' granule principle. The latter consists of alternate compression and expansion of granules.
The effect of these operational strategies will be evaluated in laboratory scale reactors using specially developed NMR-techniques, i.e. pulsed gradient spin echo-NMR (PGSE-NMR) imaging, PGSE-NMR spectroscopy and chemical shift imaging. NMR was chosen as this non invasive technique provides information inaccessible compared to ex vivo techniques like microelectrodes or confocal microscopy. However, to assess the accuracy and reproducibility of the developed NMR protocols, the effective diffusion and mass transfer coefficients obtained by NMR will be compared to those obtained by microelectrode measurements.
The insight in mass transfer phenomena given by the NMR techniques, in combination with the operation of laboratory scale bioreactors will contribute to the optimisation of the process efficiency of UASB reactors operating under fully sulphidogenic conditions.