Table 2 Operating parameters and performance variables (mean ± standard deviation) for the 8 anaerobic digesters during steady state
Parameter | Unit | Digesters | |||||||
|---|---|---|---|---|---|---|---|---|---|
DS1 | DS2 | DS3 | DS4 | ||||||
TDS1 | MDS1 | TDS2 | MDS2 | TDS3 | MDS3 | TDS4 | MDS4 | ||
HRT | Days | 3 | 17 | 3 | 17 | 3 | 10 | 3 | 10 |
Temperature |  °C | 55 | 37 | 65 | 37 | 55 | 37 | 65 | 37 |
Methane flow (3-day mean) | mL/day | 49 ± 5 | 3991 ± 307 | 32 ± 6 | 3665 ± 158 | 135 ± 49 | 7289 ± 1001 | 446 ± 134 | 6890 ± 921 |
Methane flow | mL/day | 93 ± 22 | 3889 ± 583 | 39 ± 17 | 3523 ± 284 | 191 ± 96 | 8019 ± 517 | 478 ± 150 | 7761 ± 579 |
CH4 | % | 4 ± 4 | 70 ± 2 | 2 ± 1 | 69 ± 2 | 9 ± 3 | 70 ± 1 | 28 ± 5 | 71 ± 1 |
pH |  | 5.69 ± 0.06 | 8.03 ± 0.06 | 5.55 ± 0.06 | 7.98 ± 0.09 | 5.74 ± 0.08 | 8.09 ± 0.11 | 6.22 ± 0.08 | 8.07 ± 0.09 |
Total ammonia nitrogen | mg/L | 121 ± 18 | 966 ± 84 | 101 ± 12 | 915 ± 88 | 170 ± 16 | 534 ± 27 | 256 ± 19 | 579 ± 25 |
Free NH3 | mg/L | 0.2 | 90.2 | 0.2 | 76.3 | 0.3 | 55.8 | 2.2 | 59.0 |
TCOD | g/L | 57.9 ± 30 | 15.7 ± 12.8 | 54.1 ± 33.4 | 16.3 ± 13.5 | 39.1 ± 1.4 | 10.5 ± 1.6 | 44.1 ± 3.9 | 13.4 ± 1.1 |
PCOD | g/L | 41.6 ± 30.1 | 14.2 ± 12.9 | 37.3 ± 33.5 | 14.8 ± 13.5 | 24.9 ± 3.1 | 8.8 ± 1.5 | 29.1 ± 5.3 | 11.7 ± 1 |
SCOD | g/L | 16.4 ± 0.6 | 1.5 ± 0.3 | 16.8 ± 1.5 | 1.5 ± 0.3 | 14.2 ± 2.8 | 1.7 ± 0.3 | 15 ± 2.7 | 1.7 ± 0.2 |
COD Conc. | g/L | 44.3 ± 16.2 | 10.5 ± 1.3 | 41.8 ± 16.7 | 10.7 ± 0.7 | 39.4 ± 1.1 | 10.9 ± 1.2 | 43.0 ± 1.9 | 13.1 ± 0.7 |
COD removal | % | 78.4 ± 3.8 | 77.6 ± 4.7 | 77.0 ± 3.3 | 71.0 ± 2.0 | ||||
Alkalinity | g/L as CaCO3 | 1.5 ± 0.4 | 6.1 ± 0.7 | 1.3 ± 0.2 | 6.2 ± 0.2 | 1.2 ± 0.4 | 4.7 ± 0.2 | 1.7 ± 0.2 | 5 ± 0.2 |
FOS/TAC |  | 3.25 ± 1.25 | 0.06 ± 0.07 | 3.8 ± 0.46 | 0.03 ± 0.05 | 4.65 ± 3.08 | ND | 2.08 ± 0.28 | ND |
Acetate |  mg/L | 2607.4 ± 177.9 | 19 ± 2.4 | 3744.1 ± 390 | 3.8 ± 1.7 | 2336.5 ± 95.2 | ND | 2724.7 ± 678.9 | ND |
Propionate |  mg/L | 143.4 ± 23.4 | 1.2 ± 3 | 32.3 ± 7.6 | 0.4 ± 0.9 | 244.4 ± 22.2 | ND | 237.7 ± 134.3 | ND |
Butyrate |  mg/L | 6161.2 ± 339.3 | ND | 6946.7 ± 641.1 | ND | 3351.1 ± 178.6 | ND | 1878.3 ± 1093.9 | ND |
Valerate | mg/L | 296.3 ± 56.9 | 8.9 ± 8.5 | 279.5 ± 197.6 | 13.1 ± 6.1 | ND | ND | ND | ND |
Volatile solids (VS) | g/L | 16.7 ± 1.5 | 6.3 ± 0.5 | 17.5 ± 1.6 | 6.8 ± 0.7 | 21.6 ± 4.2 | 7.2 ± 0.7 | 21.1 ± 2.2 | 8.3 ± 0.4 |
VS removal | % | 75.2 ± 1.7 | 74.1 ± 1.0 | 73.9 ± 2.4 | 70.1 ± 1.1 | ||||