Type of seed sludge and experimental runtime — The outcome of the competition
between acetate utilizing bacteria depends on the length of the acclimation
period to high sulfate conditions (McCartney and Oleszkiewicz, 1991; Harada et
al., 1994). Visser et al. (1993d) found that 400 and 250 d were needed to increase
the share of acetate used by ASRB from 50 to 90% in UASB reactors fed,
respectively, acetate and a VFA mixture with an excess of sulfate. This can be
attributed to the long period of time needed to reach a steady state situation in
modern high rate anaerobic reactors, where the sludge retention time can be as high
as 0.5 to 1 year (Hulshoff Pol, 1989). Consequently, long time periods may be
needed for one type of bacterium to outcompete other species, especially if the
number of one of the competing species is very low compared with the other.
Computer simulations of the competition between SRB and MB for acetate underline
the importance of the initial number of bacteria and their growth kinetic
parameters on the time period needed to increase the share in the acetate degradation
of that particular population (Visser et al., 1993d). Hence, the choice of the
seed sludge is, in addition to the applied environmental conditions, of the utmost
importance for the outcome of the competition for acetate under sulfidogenic
conditions.
Type of seed sludge and experimental runtime — The outcome of the competition
between acetate utilizing bacteria depends on the length of the acclimation
period to high sulfate conditions (McCartney and Oleszkiewicz, 1991; Harada et
al., 1994). Visser et al. (1993d) found that 400 and 250 d were needed to increase
the share of acetate used by ASRB from 50 to 90% in UASB reactors fed,
respectively, acetate and a VFA mixture with an excess of sulfate. This can be
attributed to the long period of time needed to reach a steady state situation in
modern high rate anaerobic reactors, where the sludge retention time can be as high
as 0.5 to 1 year (Hulshoff Pol, 1989). Consequently, long time periods may be
needed for one type of bacterium to outcompete other species, especially if the
number of one of the competing species is very low compared with the other.
Computer simulations of the competition between SRB and MB for acetate underline
the importance of the initial number of bacteria and their growth kinetic
parameters on the time period needed to increase the share in the acetate degradation
of that particular population (Visser et al., 1993d). Hence, the choice of the
seed sludge is, in addition to the applied environmental conditions, of the utmost
importance for the outcome of the competition for acetate under sulfidogenic
conditions.
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