HISTOLOGICAL ANALYSIS OF MICROSTRUCTURE OF UASB GRANULES

A histological method was demonstrated for the microscopic analysis of granules from upflow-anaerobic-sludge-blanket (UASB) reactors. Granul es were first fixed with formaldehyde and embedded in paraffin, before being sectioned by a microtome to a thickness of 3-5 mum. The section was then mounted on a glass slide for microscopic examination using p hase contrast and epi-fluorescent excitation. Using this simple method , the microstructure of the granules and the distribution of methanoge nic bacteria could be analyzed. Over 100 granules from UASB reactors t reating sucrose wastewaters were examined. Microscopic photos showed t hat the granules had a surface layer comprised of hydrogen-consuming m ethanogenic cocci and bacilli, and a loosely packed interior, mainly c omprised of acetotrophic Methanothrix. This simple method provides eng ineers with a practical tool for studying the microstructure of the gr anules, the mechanisms of their formation, and kinetic modeling.