INTERACTION BETWEEN SULFATE-REDUCING BACTERIA AND METHANE-PRODUCING BACTERIA IN UASB REACTORS FED WITH LOW STRENGTH WASTES CONTAINING DIFFERENT LEVELS OF SULFATE

The mutual interaction between sulfate-reducing bacteria (SRB) and met hane-producing bacteria (MPB) in anaerobic sludge consortia was invest igated using three identical laboratory-scale UASB reactors. Reactors were fed in parallel with a synthetic low strength waste (starch and s ucrose, 500 mg COD l(-1)), but with different levels of Sulfate (30, 1 50, 600 mg SO42- l(-1), respectively). The mass balances of COD and su lfur over the experimental period of 180 days operation indicated that the higher the level of sulfate the less methane production caused si nce a greater electron flow was distributed to the SRB. Namely, at the last stage of the experiment in which the highest sulfate level was i mposed, 75% of the total COD removal was performed by SRB. The specifi c methanogenic activities (SMAs) of the respective sludges were evalua ted using the serum vial test using different substrates and by settin g different sulfate levels. SMA was not affected by the presence of su lfate in the vials when acetate was used as the vial substrate. In the case of glucose as the test substrate, SMA increased with an increase in sulfate level. On the other hand, SMA decreased with increasing su lfate level when hydrogen was employed as the test substrate. A large amount of propionate accumulation was observed during vial tests, in w hich glucose was fed to the sludge grown at higher levels of sulfate, when zero or low levels of sulfate were added to the vials. This resul t suggests that SRB played an important role in the breakdown of propi onate either through direct utilization or through a so-called intersp ecies hydrogen transfer.