Cell agglomeration in acidogenic, mixed, and methanogenic cultures at different loading and mixing conditions

Cell agglomeration studies were conducted in anaerobic fluidized bed reactors without any external support. Granulation was studied at different combinations of loading and mixing conditions utilizing synthetic wastewater. Both single-stage and two-stage biomethanation processes were studied. Reactors of volume 0.55, 10, and 16 l were operated with height to diameter ratio of 7-8. It was found that the acidogens were more liable to form granules among mixed culture of anaerobes, while the methanogens were capable of forming cell agglomerates in the form of flocs. In acidogenic granules, rod shaped bacteria were dominating, while in case of methanogens, there were more cocci. It was found that for an upflow liquid linear velocity upto 2.0 m h(-1), acidogens showed very good granulation but at relatively higher values of upflow liquid linear velocities granulation was affected adversely, causing breakage and dissociation of granules. In the case of methanogens and mixed process, it was found that upflow liquid linear velocities up to 4.0 m h(-1) were suitable and biomass flocs were actively growing. The maximum organic loadings applied were 39.0 and 54.4 kg COD m(-3) d(-1) (at 27.3 and 35.36 kg COD m(-3) d(-1) degradation respectively) for single-stage and two-stage biomethanation respectively.