| |
Daysa
|
R1
|
R2
|
R3
|
R4
|
R5
|
R6
|
|---|
|
Average specific biogas production (ml g−1VSsubstrate 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
|
- aDay 0–84: start-up phase; day 85: start of semi-continuous oleate feeding to R2, R3, R5, and R6; day 172: start of oleate pulse feeding; day 201: end of PASS and oleate feeding
- bCalculation of specific biogas production is based on the influent VS content of fresh substrate, does not include the recirculated VS
- cCumulative biogas production between days 201 and 255 after the PASS and oleate feeding was stopped
- dCumulative residual biogas production from oleate calculated by subtracting the cumulative biogas production in control digester, R1, from the values obtained for oleate-amended R2 and R3 and subtracting the cumulative biogas production of control digester with effluent recirculation, R4, from the values obtained for R5 and R6
