Effect of degradation kinetics on the microstructure of anaerobic biogranules

The microstructure of anaerobic biogranules treating a wide variety of wastewaters was investigated using light and scanning electron microscopies. Biogranules were sampled from upflow anaerobic sludge blanket (UASB) reactors treating wastewater individually containing formate, acetate, propionate, butyrate, peptone, sucrose, starch, benzoate, brewery and monosodium glutamate. Results indicated that the microstructure of the biogranules was strongly dependent on the degradation kinetics of substrates. Anaerobic degradation is a multi-step process, involving fermentation/acidogenesis, acetogenesis and methanogenesis. For substrates, such as carbohydrates, of which the initial step of degradation was considerably faster than the subsequent degradation of intermediates, biogranules developed a layered microstructure. On the other hand, for substrates, such as proteins, of which the initial step of degradation was rate-limiting, a uniform microstructure would be developed. These findings are of significance for the development of kinetic models for biogranule and biofilm.