Anaerobic digestion is a technology with large application for the treatment of domestic sewage and industrial wastewater. However, under stressing conditions, such as shock loading and toxic materials input, disequilibrium can occur due to kinetic and thermodynamic limitations, especially of methanogens. Through the provision of more favorable conditions for each group of microorganism, two-stage anaerobic reactors (acidogenic-methanogenic) provides a greater control and stability to the process. In addition, other potential advantages include the possibility of increasing bioenergy production through the recovery of hydrogen from acidogenic reactors, and also the reduction of viscosity and suspended biomass in methanogenic reactors, which may implies in achievement of higher fluxes when they are coupled to membranes (AnMBR). In the present thesis, four acidogenic reactor designs - granular UASB, flocculent UASB, conventional fixed-bed reactor and completed mixed fixed-bed reactor - will be evaluated regarding the acidification degree, hydrogen production and reduction of hydraulic retention time. After choosing the better configuration amongst those studied, the acidogenic reactor will be followed by a fixed-bed methanogenic reactor. A single-stage fixed-bed reactor will be operated in parallel. The performance of the single- and two-stage anaerobic reactors under increasing organic loads will be compared, especially regarding the potential for bioenergy production (hydrogen and methane). Finally, experiments with single- and two-stage anaerobic membrane bioreactors will be performed in order to indicate the changes in sludge properties due to effluent acidification in a previous step and their impact on membrane filtration performance.
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