Long-term competition between sulfate reducing and methanogenic bacteria in UASB reactors treating volatile fatty acids.
The competition between acetate utilizing methane-producing bacteria (MB) and sulfate-reducing bacteria (SRB) was studied in mesophilic (30 degrees C) upflow anaerobic sludge bed (UASB) reactors (upward velocity 1 m h-1; pH 8) treating volatile fatty acids and sulfate. The UASB reactors treated a VFA mixture (with an acetate:propionate:butyrate ratio of 5:3:2 on COD basis) or acetate as the sole substrate at different COD:sulfate ratios. The outcome of the competition was evaluated in terms of conversion rates and specific methanogenic and sulfidogenic activities. The COD:sulfate ratio was a key factor in the partitioning of acetate utilization between MB and SRB. In excess of sulfate (COD:sulfate ratio lower than 0.67), SRB became predominant over MB after prolonged reactor operation: 250 and 400 days were required to increase the amount of acetate used by SRB from 50 to 90% in the reactor treating, respectively, the VFA mixture or acetate as the sole substrate. The competition for acetate was further studied by dynamic simulations using a mathematical model based on the Monod kinetic parameters of acetate utilizing SRB and MB. The simulations confirmed the long term nature of the competition between these acetotrophs. A high reactor pH (+/-8), a short solid retention time (<150 days), and the presence of a substantial SRB population in the inoculum may considerably reduce the time required for acetate-utilising SRB to outcompete MB.
Omil
F
F
Department of Environmental Technology, Agricultural University of Wageningen, "Biotechnion," Bomenweg 2, P.O. Box 8129, 6700 EV Wageningen, The Netherlands.
Lens
P
P
Visser
A
A
Hulshoff Pol
L W
LW
Lettinga
G
G
D000085:Acetates / Q000378:metabolism; D000693:Anaerobiosis; D001673:Biodegradation, Environmental; D019149:Bioreactors; D003198:Computer Simulation; D005232:Fatty Acids, Volatile / Q000378:metabolism*; D008433:Mathematics; D019638:Methanomicrobiaceae / Q000378:metabolism*; D008954:Models, Biological; D013431:Sulfates / Q000378:metabolism*; D016999:Sulfur-Reducing Bacteria / Q000378:metabolism*
D000085:Acetates; D005232:Fatty Acids, Volatile; D013431:Sulfates