Enrichment set-up
The same bioreactor, pH, and temperature as used for the inoculum
cultivation was used for the subsequent three enrichments. Similar
mineral composition as in (J. Tamis et al., 2015) was used and the
glucose concentration in the influent was 6 g·L-1
(influent volume: 1.25 L). For all three enrichments the settling time
was set to 60 minutes ensuring biomass retention. The cycle length was 6
hours and the HRT was 12 hours. A cycle length consisted out of the
following phases: Settling phase (60 min), effluent phase (6 min),
nutrient feeding phase (5 min), acclimization phase (10 min), glucose
feeding phase (3 min) and finally a reaction phase (276 min). The first
SRT investigated was uncontrolled SRT, for this SRT no sludge was
manually removed. Hence, the SRT was determined by the biomass washout
via the effluent. The other SRT investigated were 1-2 d and 10-20 d SRT.
In these systems biomass, besides the biomass washout via the effleuent
sludge was manually removed at the end of the reaction time when the
reactor was completely mixed. The reactor was mixed by recycling the
produced biogas from the culture, and anaerobic conditions were
maintained by two water-locks connected to the bioreactor in serie. The
second water-lock was connected to the outside environment and sparged
with N2 gas keeping the bottle anaerobic.