Table 2.
Average performance parameters of the digesters during operational periods 1, 2 and 3 (days 0–110, 111–220 and 221–320, respectively)
| Digester | Period | Spec. methane production (N L/gVS day) | Av. methane content of the gas (%) | Degree of degradation (%)a | VFA (g/L)b | |||
|---|---|---|---|---|---|---|---|---|
| Prop | Ace | Val | But | |||||
| D37 | 1 | 0.22 ± 0.02 | 57 ± 2 | 69 | 5.6 ± 1.1 | 2.8 ± 0.6 | 2.6 ± 0.3 | 0.4 ± 0.2 |
| 2 | 0.25 ± 0.02 | 62 ± 2 | 68 | 3.4 ± 0.8 | 3.4 ± 0.3 | 2.8 ± 0.6 | 0.9 ± 0.6 | |
| 3 | 0.23 ± 0.01 | 60 ± 2 | 72 | 4.2 ± 0.8 | 2.9 ± 0.5 | 2.2 ± 0.4 | 0.3 ± 0.1 | |
| D42 | 1 | 0.23 ± 0.02 | 57 ± 3 | 69 | 6.3 ± 0.7 | 1.5 ± 0.5 | 1.7 ± 0.8 | – |
| 2 | 0.24 ± 0.02 | 61 ± 3 | 66 | 6.1 ± 2.0 | 2.3 ± 0.7 | 2.0 ± 0.6 | – | |
| 3 | 0.25 ± 0.01 | 60 ± 1 | 73 | 6.2 ± 2.0 | 1.7 ± 0.3 | 1.8 ± 0.5 | – | |
| DTE37 | 1 | 0.31 ± 0.02 | 59 ± 2 | 84 | 1.0 ± 1.8 | – | – | – |
| 2 | 0.33 ± 0.02 | 61 ± 1 | 82 | – | – | – | – | |
| 3 | 0.33 ± 0.03 | 62 ± 2 | 89 | – | – | – | – | |
| DTE42 | 1 | 0.26 ± 0.02 | 59 ± 2 | 78 | 4.0 ± 1.3 | 0.2 ± 0.1 | – | – |
| 2 | 0.30 ± 0.01 | 62 ± 1 | 74 | 0.4 ± 0.4 | 0.3 ± 0.3 | – | – | |
| 3 | 0.30 ± 0.03 | 61 ± 2 | 88 | 0.1 ± 0.1 | 0.1 ± 0.1 | – | – | |
aA rough estimation method [62] was included in the calculation to compensate for VFA losses in the determination of dry matter. The standard deviations in the triplicate analyses in each period were >0.001
b–, below detection limit (<0.1 g/L); Prop, propionate; Ace, acetate, Val, isovalerate; But, isobutyrate