Table 1 Biogas production and sludge characteristics

Days

116

74

100

21

29

OLR

g Spirulina (L_R day)⁻¹

1.0

2.0

3.0

4.0

5.0

Daily biogas production

mL biogas day⁻¹

470 ± 69

986 ± 176

1487 ± 252

2096 ± 118

2210 ± 325

Daily methane production

mL CH₄ day⁻¹

327 ± 49

648 ± 117

972 ± 190

1397 ± 79

1399 ± 260

CH₄

%

69 ± 5

69 ± 2

70 ± 13

68 ± 1

62 ± 4

_CO2

%

30 ± 5

30 ± 2

25 ± 10

31 ± 1

37 ± 4

N₂;O₂

%

1 ± 1

1 ± 1

5 ± 16

1 ± 1

1 ± 1

H₂S

%

<1.0

<1.0

<1.0

<1.0

<1.0

SBP-VS added

mL_biogas (day g VS)⁻¹

354 ± 52

369 ± 66

372 ± 63

393 ± 22

334 ± 47

SBP-g Spirulina added

mL_biogas (day g Spirulina)⁻¹

313 ± 46

329 ± 58

330 ± 55

349 ± 19

297 ± 42

SMP-VS added

mL_methane (day g VS)⁻¹

246 ± 37

243 ± 44

243 ± 47

262 ± 14

211 ± 39

SMP-g Spirulina added

mL_methane (day g Spirulina)⁻¹

218 ± 33

216 ± 39

216 ± 42

233 ± 13

188 ± 34

pH

7.5 ± 0.3

7.9 ± 0.1

8.5 ± 0.1

8.6 ± 0.1

8.6 ± 0.1

Alkalinity

g CaCO₃ L⁻¹

8.6 ± 0.7

11.4 ± 0.8

16.5 ± 3.1

20.8 ± 1.2

25.4 ± 2.4

Total Solids

g Kg⁻¹

17.6 ± 1.3

21.7 ± 1.2

26.6 ± 2.6

29.3 ± 1.4

38.2 ± 5.0

Volatile Solids

g Kg⁻¹

10.2 ± 1.0

13.7 ± 1.2

18.9 ± 2.5

21.1 ± 1.2

29.1 ± 4.6

COD_T

g O₂ L⁻¹

17.2 ± 1.0

24.1 ± 3.5

33.2 ± 2.5

36.6 ± 3.8

54.8 ± 8.34

CODs

g O₂ L⁻¹

3.9 ± 1.0

5.5 ± 0.5

8.6 ± 2.9

7.2 ± 0.1

19.3 ± 6.5

BOD₅

g O₂ L⁻¹

2.0 ± 0.6

3.3 ± 1.1

4.4 ± 0.1

4.9 ± 0.1

12.9 ± 0.1

Total Nitrogen

g ^L-1

3.2 ± 0.3

4.5 ± 0.6

5.8 ± 0.3

6.7 ± 0.6

8.0 ± 0.8

NH₄ ⁺-N

g ^L-1

2.2 ± 0.2

2.9 ± 0.2

2.8 ± 0.2

3.0 ± 0.2

3.7 ± 0.4

NH₃-N

g ^L-1

0.1 ± 0.1

0.3 ± 0.1

1.1 ± 0.2

1.4 ± 0.2

1.6 ± 0.3

Acetic acid

mg L-1

376 ± 301

646 ± 168

1647 ± 858

1836 ± 919

3117 ± 1526

Propionic acid

mg L-1

35 ± 10

173 ± 66

629 ± 614

713 ± 623

1582 ± 521