| The free energy change for conversion of propionate to acetate and hydrogen is positive under standard conditions. The hydrogen partial pressure, therefore, must be maintained at an extremely low level to enable favorable thermodynamic conditions for continuous and efficient propionate conversion. The sufficiently low hydrogen levels can be achieved by increasing the biological hydrogen removal capacity and/or the physical hydrogen removal capacity.;For the increase in the biological hydrogen removal capacity, hydrogen-producing and hydrogen-consuming species are required to be in close proximity to each other. On the other hand, for the increase in the physical hydrogen removal capacity, a gas phase washout system is required to accompany the removal of hydrogen from the reactor.;The proximity between two species was facilitated by processes in which granular sludge develop. The gas phase washout was facilitated by two-staged systems connected in series. Therefore, this study focused on the examination of individual and synergistic effects of the two factors through different process configurations. The proximity effect by granular sludge systems, the gas phase washout effects by two-staged systems, and the synergistic effects by granular sludge/two-staged systems showed 40-50%, 10-40%, and 98-810% increase in process efficiency compared to non-granular sludge systems and non-staged systems, respectively.;Anaerobic studies with halogenated aliphatic compounds (HAC's) have shown that many of these compounds are biodegradable. The conversion of propionate to methane requires the combined activity of three bacterial groups. These three groups have different inhibition tolerance and different biodegradation potential for the HAC's.;In this study, the inhibition effect, the fate, and the biodegradation potential of five HAC's (methylene chloride, chloroform, carbon tetrachloride, 1,1,1-trichloroethane, and trichloroethylene) were addressed in three enrichment cultures (H;In all cases of the five selected HAC's, H... |
