Impact of Starch from Cassava Peel on Biogas Produced through the Anaerobic Digestion Process
Abstract
:1. Introduction
2. Material and Methods
2.1. Substrates and Sludge
2.2. Response Surface Methodology (RSM)
2.3. Beating Pre-Treatment
2.4. Total Solid and Volatile Solid
2.5. Anaerobic Digestion (AD)
2.6. Energy Balance
3. Results and Discussion
3.1. General Results
3.2. CP Results
3.3. Model Estimation
3.3.1. Biogas
3.3.2. Biogas g−1-VS
3.3.3. CH4%
3.3.4. CO2%
3.3.5. CH4 g−1-VS
3.3.6. Digestate
3.4. Optimisation and Energy Evaluation
3.4.1. The optimisation
3.4.2. Energy Evaluation
4. Conclusions
Author Contributions
Funding
Acknowledgments
Conflicts of Interest
Nomenclature
AD | Anaerobic digestion |
N | Nitrogen |
P | Phosphorous |
K | Potassium |
DOE | Design of experiment |
RSM | Response surface methodology |
Significance level | |
CP | Cassava peel |
VS | Volatile Solid |
TS | Total solid |
MS | Moisture content |
SQ | Sludge quantity |
ANOVA | Analysis of variance |
BBD | Box-Behnken design |
Pred. R2 | Predicted R2 |
Adj. R2 | Adjusted R2 |
Adeq. Precision | Adequate Precision |
Cor total | Total sum of the squares corrected for the mean |
df | Degree of freedom |
Bs | The energy content of biogas produced by CP in [kW h/m3] |
9.67 | The energy content of 1 Nm3 (Normal cubic meter) of biogas. |
Ep | The energy gained from a gram of volatile solid of CP from the biogas produced in [Wh g−1-VS] |
Bp | The biogas volume produced from each gram of volatile solid of CP. |
Ec | The energy consumed by the water bath to digest the gram volatile solid of CP in [Wh g−1-VS]. |
Ept | The electric energy consumed in the digestion process, which was measured by a prodigit kilowatt-hour meter. |
VSm | The total amount of volatile solid in the water bath |
Net Ep | The net energy produced by a gram of volatile solid of treated CP in [Wh g−1-VS] |
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Factors and Their Codes | Unit | Lower Level | Centre Point | Upper Level |
---|---|---|---|---|
Temperature (A) | °C | 34 | 37 | 40 |
Volatile Solid (B) | g-VS | 1.1 | 2.65 | 4.2 |
Sludge Quantity (C) | % | 25 | 37.5 | 50 |
Sample No. | Factor 1 | Factor 2 | Factor 3 |
---|---|---|---|
A: Temperature | B: Volatile Solid | C: Sludge Quantity | |
°C | g-VS | % | |
1 | 34 | 4.0 | 50 |
2 | 37 | 4.0 | 50 |
3 | 40 | 4.0 | 50 |
Std. | Run | Factor 1 | Factor 2 | Factor 3 | Resp.1 | Resp.2 | Resp.3 | Resp. 4 | Resp.5 |
---|---|---|---|---|---|---|---|---|---|
A | B | C | Biogas | Biogas g−1-VS | CH4 | CO2 | CH4g−1-VS | ||
°C | g-VS | % | cc | cc g−1-VS | % | % | cc g−1-VS | ||
1 | 10 | 34 | 1.1 | 37.5 | 831 | 755.4 | 56.8 | 19.6 | 428.8 |
2 | 7 | 40 | 1.1 | 37.5 | 1587 | 1442.5 | 54.5 | 21 | 786.7 |
3 | 9 | 34 | 4.2 | 37.5 | 2275 | 541.7 | 39.7 | 36.1 | 214.9 |
4 | 1 | 40 | 4.2 | 37.5 | 3367 | 801.6 | 42.5 | 33.7 | 340.9 |
5 | 12 | 34 | 2.65 | 25 | 1271 | 479.7 | 45.8 | 29.2 | 219.8 |
6 | 4 | 40 | 2.65 | 25 | 1844 | 695.8 | 47.1 | 28.3 | 327.7 |
7 | 8 | 34 | 2.65 | 50 | 1870 | 705.7 | 54.7 | 22.5 | 386.3 |
8 | 5 | 40 | 2.65 | 50 | 2562 | 966.9 | 57.8 | 20.4 | 559.2 |
9 | 6 | 37 | 1.1 | 25 | 1096 | 996 | 43.6 | 32 | 434.2 |
10 | 14 | 37 | 4.2 | 25 | 3064 | 729.5 | 33.8 | 37.8 | 246.6 |
11 | 16 | 37 | 1.1 | 50 | 1552 | 1411 | 60.3 | 15.9 | 850.8 |
12 | 17 | 37 | 4.2 | 50 | 3830 | 911.9 | 39.3 | 35.7 | 358.7 |
13 | 11 | 37 | 2.65 | 37.5 | 2390 | 928.2 | 58.3 | 23.4 | 540.8 |
14 | 3 | 37 | 2.65 | 37.5 | 2169 | 818.6 | 59.8 | 22.9 | 489.8 |
15 | 15 | 37 | 2.65 | 37.5 | 2210 | 833.8 | 61.8 | 22.7 | 515 |
16 | 2 | 37 | 2.65 | 37.5 | 2255 | 851 | 58.5 | 24.6 | 497.5 |
17 | 13 | 37 | 2.65 | 37.5 | 2225 | 839.5 | 57.2 | 22.5 | 480.4 |
Resp. | Control Samples | Predicted Value | ||||||||
---|---|---|---|---|---|---|---|---|---|---|
Biogas | Biogas g−1-VS | CH4 | CO2 | CH4 g−1-VS | Biogas | Biogas g−1-VS | CH4 | CO2 | CH4 g−1-VS | |
Unit | cc | cc g−1-VS | % | % | cc g−1-VS | cc | cc g−1-VS | % | % | cc g−1-VS |
1 | 2766.1 | 691.5 | 40.5 | 35.0 | 280.1 | 2727.7 | 667.3 | 40.2 | 35.2 | 243.0 |
2 | 3558.7 | 889.7 | 42.9 | 33.3 | 381.4 | 3479.2 | 882.8 | 42.7 | 33.9 | 365.2 |
3 | 3630.5 | 907.6 | 41.7 | 32.3 | 378.8 | 3505.9 | 837.3 | 41.5 | 32.6 | 333.2 |
Source | Sum of Squares | df | Mean Square | F-Value | p-Value | |
---|---|---|---|---|---|---|
Model | 9.539 × 106 | 4 | 2.385 × 106 | 86.14 | <0.0001 | Significant |
A-Temperature | 1.211 × 106 | 1 | 1.211 × 106 | 43.76 | <0.0001 | |
B-Volatile Solid | 6.975 × 106 | 1 | 6.975 × 106 | 251.97 | <0.0001 | |
C-Sludge Quantity | 8.058 × 105 | 1 | 8.058 × 105 | 29.11 | 0.0002 | |
A2 | 5.466 × 105 | 1 | 5.466 × 105 | 19.74 | 0.0008 | |
Residual | 3.322 × 105 | 12 | 27,682.67 | |||
Lack of Fit | 3.038 × 105 | 8 | 37,972.65 | 5.35 | 0.0614 | Not significant |
Pure Error | 28,410.80 | 4 | 7102.70 | |||
Cor Total | 9.871 × 106 | 16 | ||||
Adequacy measuring tools | R2 = 0.9663 | Adjusted R2 = 0.9551 | Predicted R2 = 0.9212 |
Source | Sum of Squares | df | Mean Square | F-Value | p-Value | |
---|---|---|---|---|---|---|
Model | 9.592 × 105 | 6 | 1.599 × 105 | 31.05 | <0.0001 | Significant |
A-Temperature | 2.536 × 105 | 1 | 2.536 × 105 | 49.24 | <0.0001 | |
B-Volatile Solid | 3.281 × 105 | 1 | 3.281 × 105 | 63.72 | <0.0001 | |
C-Sludge Quantity | 1.497 × 105 | 1 | 1.497 × 105 | 29.08 | 0.0003 | |
AB | 45,624.96 | 1 | 45,624.96 | 8.86 | 0.0139 | |
A2 | 76,839.04 | 1 | 76,839.04 | 14.92 | 0.0031 | |
B2 | 1.152 × 105 | 1 | 1.152 × 105 | 22.37 | 0.0008 | |
Residual | 51,494.42 | 10 | 5149.44 | |||
Lack of Fit | 44,108.57 | 6 | 7351.43 | 3.98 | 0.1011 | Not significant |
Pure Error | 7385.85 | 4 | 1846.46 | |||
Cor Total | 1.011 × 106 | 16 | ||||
Adequacy measuring tools | R2 = 0.9491 | Adjusted R2 = 0.9185 | Predicted R2 = 0.7554 |
Source | Sum of Squares | df | Mean Square | F-Value | p-Value | |
---|---|---|---|---|---|---|
Model | 1240.05 | 7 | 177.15 | 69.90 | <0.0001 | Significant |
A-Temperature | 3.00 | 1 | 3.00 | 1.18 | 0.3048 | |
B-Volatile Solid | 448.50 | 1 | 448.50 | 176.98 | <0.0001 | |
C-Sludge Quantity | 218.40 | 1 | 218.40 | 86.18 | <0.0001 | |
BC | 31.36 | 1 | 31.36 | 12.37 | 0.0065 | |
A2 | 13.99 | 1 | 13.99 | 5.52 | 0.0434 | |
B2 | 335.20 | 1 | 335.20 | 132.27 | <0.0001 | |
C2 | 148.94 | 1 | 148.94 | 58.77 | <0.0001 | |
Residual | 22.81 | 9 | 2.53 | |||
Lack of Fit | 10.42 | 5 | 2.08 | 0.6729 | 0.6674 | Not significant |
Pure Error | 12.39 | 4 | 3.10 | |||
Cor Total | 1262.86 | 16 | ||||
Adequacy measuring tools | R2 = 0.9819 | Adjusted R2 = 0.9679 | Predicted R2 = 0.9459 |
Source | Sum of Squares | df | Mean Square | F-Value | p-Value | |
---|---|---|---|---|---|---|
Model | 689.15 | 7 | 98.45 | 114.70 | <0.0001 | Significant |
A-Temperature | 2.00 | 1 | 2.00 | 2.33 | 0.1612 | |
B-Volatile Solid | 375.38 | 1 | 375.38 | 437.35 | <0.0001 | |
C-Sludge Quantity | 134.48 | 1 | 134.48 | 156.68 | <0.0001 | |
AB | 3.61 | 1 | 3.61 | 4.21 | 0.0705 | |
BC | 49.00 | 1 | 49.00 | 57.09 | <0.0001 | |
B2 | 96.96 | 1 | 96.96 | 112.97 | <0.0001 | |
C2 | 22.18 | 1 | 22.18 | 25.84 | 0.0007 | |
Residual | 7.72 | 9 | 0.8583 | |||
Lack of Fit | 4.90 | 5 | 0.9793 | 1.39 | 0.3873 | Not significant |
Pure Error | 2.83 | 4 | 0.7070 | |||
Cor Total | 696.88 | 16 | ||||
Adequacy measuring tools | R2 = 0.9889 | Adjusted R2 = 0.9803 | Predicted R2 = 0.942 |
Source | Sum of Squares | df | Mean Square | F-Value | p-Value | |
---|---|---|---|---|---|---|
Model | 4.806 × 105 | 7 | 68,651.47 | 50.86 | <0.0001 | Significant |
A-Temperature | 73,095.76 | 1 | 73,095.76 | 54.16 | <0.0001 | |
B-Volatile Solid | 2.242 × 105 | 1 | 2.242 × 105 | 166.14 | <0.0001 | |
C-Sludge Quantity | 1.073 × 105 | 1 | 1.073 × 105 | 79.53 | <0.0001 | |
AB | 13,444.40 | 1 | 13,444.40 | 9.96 | 0.0116 | |
BC | 23,180.06 | 1 | 23,180.06 | 17.17 | 0.0025 | |
A2 | 26,762.41 | 1 | 26,762.41 | 19.83 | 0.0016 | |
C2 | 10,498.41 | 1 | 10,498.41 | 7.78 | 0.0211 | |
Residual | 12,147.72 | 9 | 1349.75 | |||
Lack of Fit | 9874.08 | 5 | 1974.82 | 3.47 | 0.1256 | Not significant |
Pure Error | 2273.64 | 4 | 568.41 | |||
Cor Total | 4.927 × 105 | 16 | ||||
Adequacy measuring tools | R2 = 0.9753 | Adjusted R2 = 0.9562 | Predicted R2 = 0.8693 |
Test | Unit | Result |
---|---|---|
Total phosphorous | mg/kg | 632 |
Potassium | mg/kg | 526 |
Total nitrogen | g/100g | 3886 |
Dry matter | mg/kg | 2.7 |
Factors and Responses | 1st Criteria | 2nd Criteria | 3rd Criteria | |||
---|---|---|---|---|---|---|
Goal | Importance | Goal | Importance | Goal | Importance | |
A: Temperature | In range | 3 | Minimise | 3 | Minimise | 3 |
B: Volatile Solid | In range | 3 | Maximise | 3 | Maximise | 3 |
C: Sludge Quantity | In range | 3 | Minimise | 3 | In range | 3 |
Biogas | In range | 3 | In range | 3 | In range | 3 |
Biogas g−1VS | Maximise | 3 | Maximise | 3 | Maximise | 3 |
CH4 | Maximise | 5 | Maximise | 5 | Maximise | 5 |
CO2 | Minimise | 3 | Minimise | 3 | Minimise | 3 |
CH4 g−1VS | Maximise | 3 | Maximise | 3 | Maximise | 3 |
Criterion | A: °C | B: g-VS | C: % | Biogas cc | Biogas cc g−1-VS | CH4 % | CO2 % | CH4 g−1VS cc g−1-VS |
---|---|---|---|---|---|---|---|---|
1st | 38.6 | 1.2 | 50.0 | 1831 | 1448.1 | 59.8 | 15.9 | 871.5 |
2nd | 36.8 | 2.1 | 39.4 | 2012 | 939.7 | 61.4 | 20.6 | 578.9 |
3rd | 36.5 | 2.0 | 50.0 | 2195.4 | 1053.2 | 60.9 | 17.9 | 652.4 |
Criterion | Energy Nonsumed, kWh | VolAtile Solid Weight, g | Bs, kWh/m3 | Ep, kWh g−1-VS | Ec, kWh g−1-VS | Net Ep, kWh g−1-VS | Energy Balance,% |
---|---|---|---|---|---|---|---|
1st | 70.6 | 1.15 | 5.78 | 0.62 | 0.82 | −0.20 | −23.27% |
2nd | 56.2 | 2.13 | 5.93 | 0.41 | 0.35 | 0.07 | 18.93% |
3rd | 56.2 | 2.05 | 5.89 | 0.47 | 0.37 | 0.10 | 27.26% |
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Alrefai, A.M.; Alrefai, R.; Benyounis, K.Y.; Stokes, J. Impact of Starch from Cassava Peel on Biogas Produced through the Anaerobic Digestion Process. Energies 2020, 13, 2713. https://doi.org/10.3390/en13112713
Alrefai AM, Alrefai R, Benyounis KY, Stokes J. Impact of Starch from Cassava Peel on Biogas Produced through the Anaerobic Digestion Process. Energies. 2020; 13(11):2713. https://doi.org/10.3390/en13112713
Chicago/Turabian StyleAlrefai, Alla Mohammed, Raid Alrefai, Khaled Younis Benyounis, and Joseph Stokes. 2020. "Impact of Starch from Cassava Peel on Biogas Produced through the Anaerobic Digestion Process" Energies 13, no. 11: 2713. https://doi.org/10.3390/en13112713