Table 1 Physico-chemical characteristics and fed substrates of the four different biogas plants analysed in this study and optimal ranges of some of the parameters

pH

6.8–8.0

7.7

7.8

7.53

7.8

VOA (mg/l)

2050–6500

4876

5093

3391

3300

TIC (mgCaCO₃/l)

8500–15,000

11,040

15,928

14,714

11,600

VOA/TIC

0.11–0.6

0.45

0.32

0.23

0.28

NH4-N (g/kg)

1.2–4.0

1.9

2.32

3.15

n.d.

HAC-eq (g HAceq/l)^a

1.3–1.9

2.03

0.40

n.d.

0.57

Temperature (°C)

n.d.

40 (mesophilic)

40 (mesophilic)

40 (mesophilic)

54 (thermophilic)

Fed substrates (%)

n.d.

Maize silage (45), sugar beet (22), poultry manure (33)

Maize silage (50), grass (10), poultry/pig/cattle manure (40)

Maize silage (67), pig manure (33)

Maize silage (60), grass (30), pig manure (10)

Retention time (days)

n.d.

92

74

81

28

Biogas yield (l/kg oDM)

n.d.

609.87

644.5

528.5

658.11

% Methane

n.d.

49.60

52.24

52.4

56