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Table 1 Operating conditions of the laboratory stirred-tank anaerobic digesters (R1–R6)

From: Effluent solids recirculation to municipal sludge digesters enhances long-chain fatty acids degradation capacity

  Daysa R1 R2 R3 R4 R5 R6
PASS loading rate (gVS l−1 day−1) 0–200 1.3 ± 0.1 1.3 ± 0.1 1.3 ± 0.1 1.3 ± 0.1 1.3 ± 0.1 1.3 ± 0.1
201–255 0.0 0.0 0.0 0.0 0.0 0.0
Oleate loading rate (g l−1 day−1) 0–84 0.0 0.0 0.0 0.0 0.0 0.0
85–91 0.0 0.08 0.08 0.0 0.08 0.08
92–112 0.0 0.13 0.13 0.0 0.13 0.13
113–130 0.0 0.25 0.25 0.0 0.25 0.25
131–151 0.0 0.5 0.5 0.0 0.5 0.5
152–171 0.0 1.0 1.0 0.0 1.0 1.0
Pulse feedingb →  172–200 0.0 1.0 1.0 0.0 1.0 1.0
  201–255 0.0 0.0 0.0 0.0 0.0 0.0
Effluent solids recirculation rate (gTS l−1 day−1) 0–84 0.0 0.0 0.0 0.6 ± 0.0 0.5 ± 0.1 0.6 ± 0.1
85–171 0.0 0.0 0.0 0.8 ± 0.2 0.8 ± 0.1 0.9 ± 0.2
172–200 0.0 0.0 0.0 1.1 ± 0.1 1.2 ± 0.1 1.3 ± 0.1
201–255 0.0 0.0 0.0 0.0 0.0 0.0
Sulfide addition (mmol l−1 day−1) 0–200 0.0 0.0 20 0.0 0.0 20
201–255 0.0 0.0 0.0 0.0 0.0 0.0
  1. aDay 0–84: start-up phase; day 85: start of oleate addition to R2, R3, R5, and R6; day 172: start of oleate pulse feeding; day 201: end of PASS and oleate feeding
  2. bAddition of 2.0 g l−1 of oleate every second day is referred to as pulse feeding
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