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AGS from previously operated laboratory-scale SBRs was used to inoculate two 1.5-L SBRs (H/D = 2.5) after a 2.5-month storage period. The new reactors were operated for 315 days, comprising six experimental periods (A–F), characterized in Table 1. Filling was performed from the bottom of the reactors (Figure 1): as a plug-flow regimen in SBR2, allowing the feed to spread through the sludge bed; or at a peripheral site at the bottom of SBR1, the feed rapidly channeling across the settled biomass with no relevant contact between them. Both SBRs were operated in 6-h cycles including a 30-min static anaerobic feeding in SBR1 (no distribution of the feed through the sludge bed) and a 50-min static plug-flow feeding, through the sludge bed, in SBR2 (changed to 1.3-h in SBR2 from day 180 on), followed by a 1.5-h stirred anaerobic phase (changed to 1-h in SBR2 from day 180 on), 3.5-h aeration, 5-min settling, 1-min drain and idle. Mechanical mixing was provided by an anchor-like impeller at 70 rpm and by a 4-blade axial impeller at 280 rpm in SBR1 and SBR2, respectively, and aeration was supplied by air compressors via porous bottom diffusers (Figure 1).
Table 1

Summary of the operational conditions for SBR1 (static anaerobic feeding) and SBR2 (plug-flow feeding) along the experimental periods, regarding feed composition and anaerobic phase duration in SBR2 (E1 – Emsize; Ac – Acetate; AR14 – Acid Red 14)

PeriodDaysFeed composition (SBR1 and SBR2)
SBR2 anaerobic phase
F/M (gCOD gVSS−1 d−1)
Substrate (mg O2 L−1)AR14 (mg L−1)Filling (min)Stirring (min)SBR1SBR2
0–157 E1 - 1000 40 50 90 0.4 0.3 
158–164 E1 - 1000 120 0.5 0.4 
165–172 E1 - 3000 120 1.2 0.9 
A’ 173–179 E1 - 1000 40 0.6 0.5 
180–255 E1 - 1000 40 80 60 0.4 0.5 
256–291 50% E1 + 50% Ac - 1000 40 1.1 0.5 
292–315 Ac - 1000 40 1.8 1.0 
PeriodDaysFeed composition (SBR1 and SBR2)
SBR2 anaerobic phase
F/M (gCOD gVSS−1 d−1)
Substrate (mg O2 L−1)AR14 (mg L−1)Filling (min)Stirring (min)SBR1SBR2
0–157 E1 - 1000 40 50 90 0.4 0.3 
158–164 E1 - 1000 120 0.5 0.4 
165–172 E1 - 3000 120 1.2 0.9 
A’ 173–179 E1 - 1000 40 0.6 0.5 
180–255 E1 - 1000 40 80 60 0.4 0.5 
256–291 50% E1 + 50% Ac - 1000 40 1.1 0.5 
292–315 Ac - 1000 40 1.8 1.0 

The indicated food-to-microorganism ratio (F/M) was calculated for each period, taking into account the respective feed COD and average VSS.

Figure 1

Schematic representation of the SBRs used in this study employing two different feeding strategies: SBR1 had an anaerobic static feeding, followed by a stirred anaerobic phase and an aerobic stage; SBR2 had an anaerobic plug-flow feeding stage through the sludge bed, followed by a stirred anaerobic phase and an aerobic stage. The dashed arrows represent the feed flow pattern in each SBR.

Figure 1

Schematic representation of the SBRs used in this study employing two different feeding strategies: SBR1 had an anaerobic static feeding, followed by a stirred anaerobic phase and an aerobic stage; SBR2 had an anaerobic plug-flow feeding stage through the sludge bed, followed by a stirred anaerobic phase and an aerobic stage. The dashed arrows represent the feed flow pattern in each SBR.

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