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 methane-producing bacteria (MPB) in anaerobic sludge consortia was investigated using three identical laboratory-scale UASB reactors. Reactors were fed in parallel with a synthetic low strength waste (starch and sucrose, 500 mg COD l(-1)), but with different levels of Sulfate (30, 150, 600 mg SO42- l(-1), respectively). The mass balances of COD and sulfur over the experimental period of 180 days operation indicated that the higher the level of sulfate the less methane production caused since a greater electron flow was distributed to the SRB. Namely, at the last stage of the experiment in which the highest sulfate level was imposed, 75% of the total COD removal was performed by SRB. The specific methanogenic activities (SMAs) of the respective sludges were evaluated using the serum vial test using different substrates and by setting different sulfate levels. SMA was not affected by the presence of sulfate 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 sulfate level when hydrogen was employed as the test substrate. A large amount of propionate accumulation was observed during vial tests, in which 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 result suggests that SRB played an important role in the breakdown of propionate either through direct utilization or through a so-called interspecies hydrogen transfer.