Table 2 Parameters monitored during operation of the laboratory stirred-tank anaerobic digesters (R1–R6)

Average specific biogas production (ml g⁻¹VS_substrate day⁻¹)^b

0–84

510 ± 95

590 ± 100

570 ± 110

610 ± 100

610 ± 90

570 ± 90

85–171

510 ± 75

590 ± 80

590 ± 80

525 ± 85

940 ± 310

950 ± 310

172–200

515 ± 65

745 ± 400

821 ± 480

590 ± 80

1540 ± 175

1315 ± 310

Cumulative residual biogas (ml)^c

201–255

16,340

108,930

85,240

25,280

73,360

97,130

Cumulative residual biogas from oleate (ml)^d

201–255

0

92,590

68,900

0

48,080

71,850

Methane (% of biogas)

0–84

61 ± 2

60 ± 2

64 ± 1

60 ± 1

61 ± 1

64 ± 1

85–171

61 ± 1

62 ± 3

64 ± 1

60 ± 1

61 ± 2

66 ± 1

172–200

61 ± 2

63 ± 1

65 ± 1

60 ± 2

64 ± 3

66 ± 2

Gaseous H₂S (ppm)

0–84

< 20

< 20

50 ± 35

< 20

 < 20

50 ± 30

85–171

< 20

< 20

190 ± 80

< 20

 < 20

70 ± 20

172–200

< 20

< 20

320 ± 200

< 20

 < 20

150 ± 15

pH

0–200

7.4 ± 0.1

7.4 ± 0.1

7.5 ± 0.1

7.6 ± 0.2

7.6 ± 0.2

7.7 ± 0.2

Total solids (% of total weight)

0–84

2.1 ± 0.3

1.9 ± 0.3

2.4 ± 0.1

2.6 ± 0.2

2.4 ± 0.5

2.8 ± 0.4

85–171

2.0 ± 0.4

2.3 ± 0.4

2.9 ± 0.4

3.5 ± 0.7

3.6 ± 0.4

4.1 ± 0.7

172–200

2.3 ± 0.4

3.5 ± 0.2

3.9 ± 0.8

4.6 ± 0.2

5.0 ± 0.5

5.5 ± 0.3

Volatile solids (% of TS)

0–84

56 ± 2

58 ± 2

53 ± 2

56 ± 2

56 ± 2

53 ± 3

85–171

53 ± 2

54 ± 3

50 ± 2

47 ± 4

48 ± 3

45 ± 3

172–200

50 ± 1

61 ± 5

61 ± 6

43 ± 1

48 ± 2

43 ± 2