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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