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The Role of Organic Substrates on Anaerobic Sludge Granulation, Microbial Community and Activity Under Saline Conditions
Group: Wageningen University
Promotor: prof. dr HHM Rijnaarts & prof. dr ir G Zeeman
Co-promotor: dr ir BG Temmink
Around 5% of globally produced wastewater is saline. Anaerobic biological treatment of wastewaters has been proven to be a cost-effective approach to remove organic pollutants from waste streams. One of the most widely applied high rate anaerobic treatment systems is upflow anaerobic sludge blanket (UASB), which relies on formation of microbial aggregates (granules) within the reactor, thus allowing for high loading capacities, high concentrations of active biomass and decoupling of hydraulic and sludge retention times. Therefore formation of granular biomass is a core to success of this system.
However, treatment of highly saline wastewaters with means of UASB process is challenging due to osmotic toxicity of high salinity towards microbial biomass, which leads to inhibition and lysis of microbial cells and disintegration of granules. Naturally occurring salt tolerant microorganisms have two strategies for osmoadaptation: i)”salt in” strategy, where potassium is accumulated within the cell to balance out the osmotic pressure; ii) accumulation of small organic molecules (osmolites) to counteract the osmotic pressure without need to adapt cell’s enzyme machinery. Microbial granulation is believed to be dependent on the presence of multivalent cations, such as Ca2+, which are binding together the polymeric substances present within granular bioaggregates. This research will be focused on the possibility and mechanisms of microbial granule formation under saline conditions by means of using either metal ions, osmolites or combination of both to stimulate the process and to assess the treatment capacity of the formed granules. Our hypothesis is, that multivalent cations can promote granulation, whereas potassium and/or osmolites can prevent loss of microbial activity, thus allowing for the process under saline conditions. Parameters to be monitored within bioreactors are: microbial activity, COD balances, granular size, granule strength, exopolysaccharides and proteins within granules, microbial population within granules, microbial activity of biomass, organics/metals distribution within granules, TSS/VSS balances.