COMPARISON OF ROD-TYPE VERSUS FILAMENT-TYPE METHANOGENIC GRANULES - MICROBIAL-POPULATION AND REACTOR PERFORMANCE

Two types of methanogenic granules capable of high chemical oxygen dem and removal rates were developed in laboratory-scale upflow reactors a t 35-degrees-C. One granule type (R-granules) had a rod-type Methanoth rix-like species as the predominant species whereas the other (F-granu les) had a filament-type M. soehngenii-like acetate-utilizer as the pr edominant species. These two types of granules were compared in terms of operational performance, physical-chemical characteristics and micr obial population. The R-granules had a higher density [65-70 vs 39-43 g suspended solids (SS)/l], specific gravity (1.03 vs 1.01) and specif ic volumetric methane production rate (180 vs 120 1 CH4/l granules per day) than the F-granules. Acetate, propionate and butyrate degraders in both types of granules had similar specific growth rates. The most probable number enumeration indicated that both types of granule had t he same population levels (cells/g SS) in terms of methanogens (H2-CO2 -, formate- and acetate-utilizing) and syntrophic acetogens. Hydrolyti c-fermentative bacteria were present in greater number in the F-granul es than in the R-granules. The R-granules had a higher cell density th an the F-granules. The differences in operational performance were due mainly to their different microbial composition, especially the predo minant acetate-utilizing methanogens in the granules. The long-filamen tous M. soehngenii-like rods in the F-granules appeared to be responsi ble for their lower density and large-sized granules.