Open access peer-reviewed chapter

Cassava Residues Could Provide Sustainable Bioenergy for Cassava Producing Nations

Written By

Sammy N. Aso, Arthur A. Teixeira and Simeon C. Achinewhu

Submitted: 12 August 2017 Reviewed: 02 November 2017 Published: 17 January 2018

DOI: 10.5772/intechopen.72166

From the Edited Volume

Cassava

Edited by Viduranga Waisundara

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Abstract

Many cassava producing nations lack suitable energy availability and sufficiency. Just 10% of the population in Haiti receive power from the national electric grid. The proportion is 7% for Mozambique. In both countries, deforestation is extensive due to dependence on wood and charcoal for 70 and 85% of energy requirement respectively. In the case of Ghana, although biomass accounts for 64% of national energy supply, the dependence on primary biomass energy sources like wood and charcoal has led to increased loss of biodiversity, soil erosion and health problems. Prospects for the use of cassava peeling residues as a source of biomethane to mitigate these constraints have received little attention. In this chapter, the advantages and benefits of biomass energy, along with the potential for cassava as a feedstock and rationale for anaerobic digestion are highlighted. Depending on the quantity of cassava root processed by individual countries, the energy recovered from cassava peeling residues could satisfy up to 100% of national energy requirements.

Keywords

  • biomass
  • cassava residues
  • anaerobic digestion
  • biomethane
  • renewable energy

1. Introduction

In July 2015, world population was estimated at over 7.3 × 109 persons and will exceed 9.7 × 109 persons in July 2050 [1]. At the same time, planet earth’s capacity to sustain life is diminishing. Issues such as land use conflicts, rural poverty, food insecurity, energy insecurity and environmental pollution are posing serious threats to humanity. Global energy supply is dependent on fossil fuels, which account for over 78% of final energy consumption [2]. Fossil fuels are depleting non-renewables, and their use exacerbates anthropogenic forcing of environmental perturbations including carbon dioxide and other greenhouse gas emissions, acid rain, biodiversity and ozone layer depletions. Advancing global energy supply system toward renewable bioenergy could constrain these adverse impacts.

The poor economic development and progress in developing countries have been attributed in part to inadequate suitable energy supply. Mainly developing countries produce cassava. However, most of the production occurs in rural areas where fuel/electricity availability is limited. In Mozambique for instance, only 7% of households (1% in rural areas) has access to electricity [3], and 85% of total energy consumed comes from firewood and charcoal [4]. In Haiti, 10% of the population receive power from the national electric grid while wood and charcoal account for 70% of the nation’s energy use [5, 6]. These circumstances have led to extensive deforestation and soil erosion in both countries; with just 1.5% of land forested in Haiti [6], and 219,000 hectares of land deforested per year in Mozambique [4]. In the case of Ghana, although biomass accounts for 64% of national energy supply, the dependence on primary biomass energy sources like wood and charcoal has led to increased deforestation, land degradation, loss of biodiversity, soil erosion, and health problems [7]. Creative use of cassava as an energy crop would help to mitigate environmental degradation and energy paucity issues, as well as minimize the health problems associated with the combustion of firewood and charcoal in cassava producing nations.

Biomass energy should be of interest to developing and developed countries. This is because biomass alleviates reliance on limited fossil fuel sources, creates employment, and contributes to economic development and revitalization of rural communities. Biomass is a clean energy source that dramatically improves the environment by generating far less air emissions than fossil fuels, reduces the amount of waste sent to landfills, and decreases reliance on chemical fertilizer. Moreover, biomass energy is renewable and therefore sustainable. Renewable energy supplied 19% of global energy consumption in 2012 and in 2013, accounted for more than 56% of net additions to global power capacity with about 6.5 million people employed [2]. In 2015, renewable energy sales in Europe was 150 billion euros (≈ US$ 178 billion) [8].

These trends demonstrate the growing utility, benefits and advantages of renewable energy of which biomass energy is a major component. However, the use of edible biomass (food crops such as sugarcane, corn (maize), soybean, palm oil, etc.) for biofuel (bioethanol, biodiesel, etc.) production has raised ethical concerns about competition and diversion of land and food to fuel production. Perhaps a reasonable alternative is biofuel production from biomass originating from nonfood sources such as, agricultural residues, food processing residues, lignocelluloses, and microalgae. Nonfood cassava peeling residues (CPR) could come to the rescue.

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2. Potential of cassava as feedstock for bioenergy production

Cassava (Manihot esculenta Crantz) is a mostly vegetatively propagated perennial root crop that grows well in tropical climates. Nevertheless, the roots (main reason for growing cassava) are very perishable once taken from the soil and go to waste unless processed in some way soon after harvest. Most processing requires removal of peels (cortex and periderm), head, and tail ends. These components usually discarded as waste, engender environmental pollution. In this chapter, the components are referred to collectively as cassava peeling residues (CPR), and instead of being discarded as waste, would be put to bioenergy production function. The CPR is generated during production of numerous cassava root based food products like akpakpuru, attieke, casabe, chickwangue, farina (farinha de mandioca), fufu, fuku, gaplek, gari, ijapu, konkonte, lafun, landang, peujeum, and thundam [9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22]. Because more than 65% of global annual cassava output is processed for human consumption, enormous quantity of CPR is generated. This nonfood organic matter is potential good feedstock for anaerobic digestion (AD) processes that generate bioenergy.

There are numerous other reasons for the attraction of cassava crop as source of food and bioenergy.

  • Cassava provides economic and subsistence value for 800–1000 million people in more than 90 countries including Angola, Barbados, Brazil, Cambodia, China, Cook Islands, Democratic Republic of Congo, Dominica, Ghana, Haiti, India, Indonesia, Lao Peoples Democratic Republic, Mozambique, Nigeria, Suriname, Thailand, Uganda, United Republic of Tanzania, and Vietnam [23, 24, 25].

  • It is the fourth most important food crop in developing nations. Cassava is also world’s third largest source of food carbohydrates and the top food energy supplier for tropical and subtropical regions. About 30% of all calories consumed in Mozambique come from cassava [26]. In Zaire, cassava roots provide 60% of the daily caloric intake, while 20% of protein come from cassava leaves [27]. In addition, Cassava can be biofortified with vitamin A, iron and zinc to eliminate hidden hunger and improve the nutritional status of vulnerable groups.

  • Cassava presents numerous agro-climatic advantages and benefits as well. First, it has high biological efficiency as the edible root portion lies underground and does not require support from stems and branches. It is easily cultivated by stem cuttings for multiplication and planting purposes, and requires minimum agricultural inputs (fertilizers, pesticides, etc.). With the possible exception of sugarcane, cassava’s productivity in terms of calories per unit land area per unit of time is significantly higher than that of other staple food crops; and its production requires energy input that constitutes just 5–6% of the energy output of the entire cassava biomass [28].

  • Cassava can be planted most time of the year and is available all year long with more than 2 years harvest window. Cassava is adaptable to various farming systems. It can be intercropped with beans, yams, and other annual crops. It is tolerant of various climatic conditions (e.g., high drought; temperature: 8–33°C; rainfall: 500–6000 mm per annum; relative humidity: 15–90%; and elevation: sea level–2500 m). Cassava is also productive on soils with pH of 3–9.5. It can thus be cultivated on marginal lands where other crops such as corn, wheat, rice and sugarcane cannot be grown well [29, 30]. Cassava has high efficiency of photosynthetic CO2 assimilation. The photosynthetic rate of cassava is 40–50 μmol CO2 m−2 s−1 under high solar radiation. That of rice is around 20 μmol CO2 m−2 s−1 [31].

  • Cassava root is endowed with high starch content of excellent functional and structural qualities. The cassava starch can be transformed into products with huge industrial applications and is of major economic importance in Brazil, India, Indonesia, Philippines, China, Thailand, South East Asia, and in the tropical regions of the world.

  • Cassava is a major ingredient for livestock feeds.

  • Cassava is important in the provision of bioenergy such as bioethanol and biogas. For instance, the yield of bioethanol from cassava (6000 kg/ha) is higher than that of sugarcane (4900 kg/ha), carrot (4500 kg/ha), sweet sorghum (2800 kg/ha), Rice (2250 kg/ha), Maize (2050 kg/ha), and wheat (1560 kg/ha) [32]. A feasibility case study in Kenya using biogas engine for backup power generation showed ample savings over the use of diesel engine. Biogas engine saved 17 tons of carbon dioxide emissions, 18% reduction in net present cost, 20% reduction in levelized cost of electricity, and 30% reduction in capital cost [33].

Energy recycling from biomass residues and wastes is increasingly attractive because the sustainability of analyzed feedstock favors biomass waste flows over dedicatedly cultivated energy crops [34]. Therefore, utilization of nonfood cassava processing residues such as CPR in biomethane production via the anaerobic digestion technology is prudent and beneficial. Nevertheless, in order to properly assess and quantify the value and contribution of CPR to the energy mix of cassava producing nations, establishment of Biofuel Potential (BFP) of CPR is necessary. Relatively very few studies have been published on biomethane production from cassava feedstocks. Most of the studies utilized cassava starch extraction wastewater. Other cassava feedstocks used were stillage (wastewater) from cassava ethanol production; cassava stem residue; whole cassava root; effluent from cassava flour and meal industry; and cassava peeling residue (CPR). However, CPR constitutes about 19% fresh weight of the root and is perhaps the most abundant residue from cassava root processing. It is easy to generate and does not require water usage. Therefore, analyses of energy impact of cassava crop in this chapter will use CPR as the feedstock of choice in renewable biomethane production. Table 1 summarizes the biofuel potentials of CPR and other cassava feedstocks.

S/N Feed stock BFP yield BFP units References
1. Cassava peeling residue 377 L CH4/(kg VS) [47]
2. Cassava peeling residue 180–310 L CH4/(kg VS) [10]
3. Cassava peeling residue 280 L CH4/(kg VS) [48]
4. Cassava peeling residue 87.1 L biogas/(Total mass of slurry) [49]
5. Cassava peeling residue 68.7 L biogas/(Total mass of slurry) [50]
6. Cassava starch extraction wastewater 360 L biogas/(kg COD removed) [51]
7. Cassava starch extraction wastewater 130–325 L biogas/(kg dry matter) [52]
8. Cassava starch extraction wastewater 134–316 L CH4/(kg VSS Day) [53]
9. Cassava starch extraction wastewater 140 Nm3 per Mg dry mass of COD [54]
10. Cassava starch extraction wastewater 11.3 L CH4/(kg VSS Day) [55]
11. Cassava starch extraction wastewater 0.52–3.70 L biogas/(L wastewater Day) [51]
12. Cassava starch extraction wastewater 0.40–0.55 L CH4/(L effluent Day) [53]
13. Cassava stillage 215–380 L CH4/(kg VS) [56]
14. Cassava stillage 132–259 L CH4/(kg VS) [57]
15. Cassava stillage 249 L CH4/(kg VS) [58]
16. Cassava stillage 158–248 L CH4/(kg VS) [59]
17. Cassava stillage 220–230 L CH4/(kg COD added) [60]
18. Cassava tubers 660 L biogas/(kg VS) [48]
19. Cassava tubers 475–510 L biogas/(kg VS) [61]
20. Cassava stem residues after starch extraction 153 Nm3 per Mg dry mass of stem residues [54]
21. Cassava flour and meal industry effluent 14.5 L biogas/Day [62]

Table 1.

Biofuel potentials (BFP) of cassava feedstocks.

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3. Rationale for anaerobic digestion technology

Anaerobic digestion (AD) is a biochemical process that converts organic matter to biogas (a mixture of methane and carbon dioxide). This is achieved through the action of a mixed culture of naturally occurring microorganisms under near oxygen free ambient environmental conditions. The following attributes are among the numerous advantages and benefits of AD technology:

  1. Flexible technology; energy efficient; prevents emission of volatile hazardous compounds (air pollution control); biotransformation and biodegradation of xenobiotics; treatment of seasonal effluents (e.g., wastewaters from sugar and fish processing industries); system stability and minimal operational difficulties such as bulking and biomass washout; higher loading rates and concentrations operations, from 20 to 40 kg BOD removed/m2 per day; reduced mass and volume of waste sludge; high waste stabilization; and Low construction, treatment and maintenance costs are typical examples.

  2. AD can accommodate tighter restrictions on sludge disposal site location, air pollution, hazardous waste disposal, odor control, and other environmental regulations.

  3. AD is attractive as a means of generating alternative energy such as biogas used for electricity and heat production, and to feed gas networks.

  4. Among biofuel systems, AD is a highly energy positive process. AD generates energy as methane; with about 3.53 kWh/(kg COD) produced as biogas while aerobic treatment operations consume 0.5–2.0 kWh/(kg O2) [35].

  5. AD is used to produce hygienic digestate; a good source of soil organic amendment, compost and biofertilizer that can be sold for income generation.

  6. AD is a low cost, low technology energy source for developing countries. It can be used to achieve more sustainability and energy justice in society [36, 37].

  7. In addition, AD is versatile, with commercial equipment in varied types, shapes, sizes and operating modes. These include BIOCEL, Bioferm, GICON and SEBAC (sequential batch anaerobic composting); as well as the ABR (anaerobic baffled reactor), AF (anaerobic filter), CSTR (completely stirred tank reactor), EGSB (expanded granular sludge bed), UASB (upflow anaerobic sludge bed), fixed dome, floating cover, and balloon/tube digesters. Figure 1 highlights the operating principles of a simple floating cover anaerobic digester.

Figure 1.

Basic architecture and operating principles of the floating cover anaerobic digester. The sketch to the right was adapted with permission from Ref. [46].

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4. Technical feasibility of anaerobic digestion of CPR

Information obtained from available literature were analyzed to determine critical values relevant to CPR biogasification characteristics. Tables 2 and 3 summarize estimates and assumptions concluded from the analyses. These data and assumptions were also used to perform the mass balance computations presented in Figure 2.

S/N CPR mass fraction (%) References
1. 18 [10]
2. 18 [63]
3. 30 [47]
4. 16 [64]
5. 17 [65]
6. 17 [66]
Mean: ≈ 19

Table 2.

CPR mass fractions of fresh cassava root.

S/N Variable of interest Unit Value assumed Explanation/justification Source/references
1. CPR mass fraction of root (%) 19 Derived from literature data Table 2
2. CPR moisture content, wet basis (%) 67 Mean of four replications [10]
3. CPR methane capacity (L CH4/(kg VS)) 303 Derived from Table 1 [10, 47, 48]
4. Methane obtained from CPR generated by processing 1 tonne (1000 kg) of roots (kg) 12.55 Derived from 252 L CH4/(kg VS CPR) = 10.44 kg CH4 [10]
5. Proportion of cassava root output processed (%) 66 & 100 More than two–thirds of total production processed for human food [67]
6. Quantity of cassava root output processed (kg) Varies per country Based on 66 and 100% of individual country’s 2014 cassava output (see Table 4) [24, 67]

Table 3.

Values assumed for variable parameters used in analytical modeling.

Figure 2.

Mass balance for the anaerobic digestion of CPR from 1 tonne (1000 kg) of cassava root for biomethane production.

To compute the energy obtained from methane generated by AD of CPR, the following equations were used.

T me = M × HHV E1
E me = T me × ϵ = M × HHV × ϵ E2

where Tme = Thermal energy content of methane (MJ), M = Mass of methane (kg), HHV = Heat of combustion of methane (MJ/kg), Eme = Electrical energy equivalent of Tme (MWh), ϵ = Conversion efficiency; thermal energy to electrical energy (%), Note: This work used HHV = 55.53 MJ/kg, ϵ = 25% and 3600 MJ = 1 MWh.

Table 4 presents the 2014 cassava output and energy consumption patterns of cassava producing countries. Many of these countries are net energy importers; lacking in local energy capacity and sufficiency. However, in 2014, the global cassava output was over 268 million tonnes. Based on the equations, mass balances and analyses already posited in this chapter, 1 tonne of cassava root yielded 190 kg CPR. This CPR is transformed to 12.55 kg of methane; producing 697 MJ thermal energy or about 174 MJ electrical energy (≈ 0.0484 MWh). Therefore, the 268 million tonnes global cassava root output in 2014 would produce 51 million tonnes of CPR. This quantity of CPR would generate 3363.4 million kg of bio-methane which translates to 186.8 × 109 MJ of thermal energy; equivalent to 46.7 × 109 MJ of electrical energy (≈ 13 × 106 MWh). This is an enormous quantity of energy that could satisfy all the yearly energy needed by Slovenia or Turkmenistan. This energy should be recovered for the benefit and rescue of cassava producing nations. The foregoing analyses were applied to individual cassava producing nations to estimate the energy recoverable from their CPR. The results obtained are also presented in Table 4. It could be seen that the ability of recoverable energy from CPR to provide national energy requirement depends on the quantity or proportion of national cassava root output processed.

S/N Country 2014 Cassava output (×109 kg) b 2014 National energy consumption (MW.h/Y) c Energy from CPR if 100% of national cassava output was processed (MW.h/Y) Potential of CPR to provide national energy requirement if 100% national cassava output was processed (%) Energy from CPR if 66% of national cassava output was processed (MW.h/Y) Potential of CPR to provide national energy requirement if 66% national cassava output was processed (%)
1. Nigeria 54.8316 24,000,000 2653301.124 11.05542135 1751178.742 7.296578091
2. Thailand 30.022052 164,000,000 1452767.096 0.885833595 958826.2835 0.584650173
3. Indonesia 23.436384 195,000,000 1134086.622 0.581582883 748497.1704 0.383844703
4. Brazil 23.253514 518,000,000 1125237.542 0.217227325 742656.778 0.143370034
5. Ghana 16.524 9,200,000 799596.36 8.691264783 527733.5976 5.736234757
6. Dem. Rep. of Congo 14.683266 9,300,000 710523.2417 7.640034857 468945.3395 5.042423006
7. Viet Nam 10.209882 125,000,000 494056.19 0.395244952 326077.0854 0.260861668
8. Cambodia 8.325098 4,100,000 402851.4922 9.825646152 265881.9849 6.48492646
9. India 8.13943 1,001,191,000 393867.0177 0.039339848 259952.2317 0.0259643
10. Angola 7.63888 8,100,000 369645.4032 4.563523496 243965.9661 3.011925508
11. Mozambique 5.304188 12,000,000 256669.6573 2.138913811 169401.9738 1.411683115
12. Malawi 5.012763 2,100,000 242567.6016 11.55083817 160094.617 7.623553192
13. United Rep. of Tanzania 4.992759 5,000,000 241599.608 4.83199216 159455.7413 3.189114826
14. Cameroon 4.917544 6,100,000 237959.9542 3.900982855 157053.5697 2.574648684
15. China 4.659481 5,919,800,000 225472.2856 0.003808782 148811.7085 0.002513796
16. Côte d’Ivoire 4.239303 5,800,000 205139.8722 3.536894348 135392.3156 2.33435027
17. Sierra Leone 4.135064 200,000 200095.747 100.0478735 132063.193 66.0315965
18. Benin 4.066711 1,000,000 196788.1453 19.67881453 129880.1759 12.98801759
19. Rwanda 3.159551 500,000 152890.6729 30.57813458 100907.8441 20.18156882
20. Paraguay 3.06 9,700,000 148073.4 1.526529897 97728.444 1.007509732
21. Madagascar 2.929743 1,300,000 141770.2638 10.90540491 93568.37409 7.197567238
22. Uganda 2.812 2,700,000 136072.68 5.039728889 89807.9688 3.326221067
23. Philippines 2.540254 66,000,000 122922.8911 0.186246805 81129.1081 0.122922891
24. Burundi 2.242352 400,000 108507.4133 27.12685332 71614.89276 17.90372319
25. Colombia 2.186207 60,000,000 105790.5567 0.176317595 69821.76744 0.116369612
26. Lao People’s Dem. Rep. 1.629805 3,900,000 78866.26395 2.022211896 52051.73421 1.334659851
27. Congo 1.334881 900,000 64594.89159 7.177210177 42632.62845 4.736958717
28. Guinea 1.264078 900,000 61168.73442 6.796526047 40371.36472 4.485707191
29. Peru 1.195926 39,000,000 57870.85914 0.148386818 38194.76703 0.0979353
30. Togo 1.153109 1,100,000 55798.94451 5.072631319 36827.30338 3.347936671
31. Zambia 0.919497 11,000,000 44494.45983 0.404495089 29366.34349 0.266966759
32. Kenya 0.858461 7,600,000 41540.92779 0.546591155 27417.01234 0.360750162
33. Centr. Afric. Rep. 0.699764 200,000 33861.57996 16.93078998 22348.64277 11.17432139
34. Haiti 0.615 400,000 29759.85 7.4399625 19641.501 4.91037525
35. Liberia 0.534810 300,000 25879.4559 8.6264853 17080.44089 5.693480298
36. Myanmar 0.485 11,000,000 23469.15 0.213355909 15489.639 0.1408149
37. Cuba 0.435772 15,000,000 21087.00708 0.140580047 13917.42467 0.092782831
38. Venezuela (Boli. Rep.) 0.357876 78,000,000 17317.61964 0.022202076 11429.62896 0.01465337
39. Sri Lanka 0.301548 11,000,000 14591.90772 0.132653707 9630.659095 0.087551446
40. Senegal 0.257259 3,000,000 12448.76301 0.414958767 8216.183587 0.273872786
41. Gabon 0.247889 2,100,000 11995.34871 0.571207081 7916.930149 0.376996674
42. Bolivia (Plu. State of) 0.245808 7,500,000 11894.64912 0.158595322 7850.468419 0.104672912
43. Zimbabwe 0.235052 8,000,000 11374.16628 0.142177079 7506.949745 0.093836872
44. Nicaragua 0.231658 4,412,000 11209.93062 0.25407821 7398.554209 0.167691619
45. Argentina 0.186944 116,000,000 9046.22016 0.007798466 5970.505306 0.005146987
46. Dominican Republic 0.178327 15,140,000 8629.24353 0.056996325 5695.30073 0.037617574
47. Costa Rica 0.1755 9,200,000 8492.445 0.092309185 5605.0137 0.060924062
48. Chad 0.166888 200,000 8075.71032 4.03785516 5329.968811 2.664984406
49. Papua New Guinea 0.148213 3,000,000 7172.02707 0.239067569 4733.537866 0.157784596
50. Niger 0.133099 1,200,000 6440.66061 0.536721718 4250.836003 0.354236334
51. South Sudan 0.126244 694,100 6108.94716 0.880124933 4031.905126 0.580882456
52. Ecuador 0.111743 21,000,000 5407.24377 0.02574878 3568.780888 0.016994195
53. Somalia 0.090233 300,000 4366.37487 1.45545829 2881.807414 0.960602471
54. Fiji 0.075277 800,000 3642.65403 0.455331754 2404.15166 0.300518957
55. Equatorial Guinea 0.071673 91,140 3468.25647 3.805416359 2289.04927 2.511574797
56. Comoros 0.068733 40,920 3325.98987 8.128029985 2195.153314 5.36449979
57. Mali 0.052152 1,400,000 2523.63528 0.180259663 1665.599285 0.118971377
58. Malaysia 0.051911 131,000,000 2511.97329 0.001917537 1657.902371 0.001265574
59. Guinea-Bissau 0.045392 31,620 2196.51888 6.946612524 1449.702461 4.584764266
60. El Salvador 0.036026 5,700,000 1743.29814 0.030584178 1150.576772 0.020185557
61. French Guiana 0.029906 1447.15134 955.1198844
62. Timor-Leste 0.029485 125,300 1426.77915 1.138690463 941.674239 0.751535706
63. Honduras 0.025526 5,300,000 1235.20314 0.02330572 815.2340724 0.015381775
64. Panama 0.018802 7,800,000 909.82878 0.011664472 600.4869948 0.007698551
65. Mexico 0.018135 238,000,000 877.55265 0.00036872 579.184749 0.000243355
66. Guatemala 0.017498 8,915,000 846.72822 0.009497793 558.8406252 0.006268543
67. Jamaica 0.016549 2,800,000 800.80611 0.028600218 528.5320326 0.018876144
68. Taiwan, China Rep 0.013017 249,500,000 629.89263 0.000252462 415.7291358 0.000166625
69. Gambia 0.011555 300,000 559.14645 0.18638215 369.036657 0.123012219
70. Micronesia (Fed. States) 0.008891 178,000 430.23549 0.241705331 283.9554234 0.159525519
71. Tonga 0.007862 46,500 380.44218 0.818155226 251.0918388 0.539982449
72. Suriname 0.007127 1,900,000 344.87553 0.018151344 227.6178498 0.011979887
73. Guyana 0.006781 800,000 328.13259 0.041016574 216.5675094 0.027070939
74. Burkina Faso 0.004105 1,200,000 198.64095 0.016553413 131.103027 0.010925252
75. Cabo Verde 0.003847 300,000 186.15633 0.06205211 122.8631778 0.040954393
76. French Polynesia 0.003805 700,000 184.12395 0.026303421 121.521807 0.017360258
77. Trinidad and Tobago 0.003194 9,100,000 154.55766 0.001698436 102.0080556 0.001120968
78. Brunei Darussalam 0.00306 3,766,000 148.0734 0.003931848 97.728444 0.00259502
79. Solomon Islands 0.003025 79,050 146.37975 0.185173624 96.610635 0.122214592
80. Wallis and Futuna Islands 0.001874 90.68286 59.8506876
81. New Caledonia 0.001777 2,000,000 85.98903 0.004299452 56.7527598 0.002837638
82. Sao Tome and Principe 0.001349 65,100 65.27811 0.100273594 43.0835526 0.066180572
83. Guadeloupe 0.001235 59.76165 39.442689
84. Saint Lucia 0.001233 300,000 59.66487 0.01988829 39.3788142 0.013126271
85. Dominica 0.001217 90,210 58.89063 0.065281709 38.8678158 0.043085928
86. Bahamas 0.000938 1,600,000 45.38982 0.002836864 29.9572812 0.00187233
87. Belize 0.000927 400,000 44.85753 0.011214383 29.6059698 0.007401492
88. Cook Islands 0.000869 31,620 42.05091 0.13298833 27.7536006 0.087772298
89. St. Vin./Gren. 0.000721 100,000 34.88919 0.03488919 23.0268654 0.023026865
90. Barbados 0.000553 900,000 26.75967 0.002973297 17.6613822 0.001962376
91. Mauritius 0.000466 2,600,000 22.54974 0.000867298 14.8828284 0.000572416
92. Samoa 0.000424 100,000 20.51736 0.02051736 13.5414576 0.013541458
93. Puerto Rico 0.000377 19,000,000 18.24303 9.60159E-05 12.0403998 6.33705E-05
94. Mauritania 0.00025 800,000 12.0975 0.001512188 7.98435 0.000998044
95. Seychelles 0.000232 300,000 11.22648 0.00374216 7.4094768 0.002469826
96. Grenada 0.000217 200,000 10.50063 0.005250315 6.9304158 0.003465208
97. Antig./Barbuda 0.000127 300,000 6.14553 0.00204851 4.0560498 0.001352017
98. Ame. Samoa 0.000087 100,000 4.20993 0.00420993 2.7785538 0.002778554
99. Niue 0.000044 3720 2.12916 0.057235484 1.4052456 0.037775419
100. Réunion 0.000036 1.74204 1.1497464
101. Cay. Islands 0.000007 600,000 0.33873 0.000056455 0.2235618 3.72603E-05
102. Maldives 0.000006 300,000 0.29034 0.00009678 0.1916244 6.38748E-05
103. Singapore 0.000001 47,180,000 0.04839 1.02565E-07 0.0319374 6.76927E-08

Table 4.

Year 2014 cassava production output of nations, their energy consumption capacity and potential of CPR generated from cassava processing to provide national energy requirements a

Using HHV (heat of combustion) = 55.53 MJ/(kg CH4) and ϵ (conversion efficiency from thermal energy to electrical energy) = 25%.


Source: [24].


Source: [68, 69].


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5. Applications, utilizations and dividends of biomethane from CPR

The anaerobic digestion of CPR would generate biogas, which could be used as is or upgraded to obtain more efficient biomethane. The energy content of either fuel could be put to various applications and utilities. These include:

  • Fuel for stoves in cooking; boiling, frying, roasting, etc.

  • Fuel for lamps in lighting; illumination, reading, playing, etc.

  • Fuel for transportation; cars, trucks, sea vessels, etc.

  • Electrical power in processing operations; drying, grinding, heating, pumping, refrigeration, washing, etc.

  • The digester effluent (digestate) could be utilized for soil amendment and/or serve as biofertilizer for enhanced crop production. This was demonstrated to increase potato yield [38].

  • Perhaps the critical humane benefits are the reduction of drudgery and burden on the one hand and the improvement of health conditions on the other hand. This is due to reduced time spent on fetching firewood and charcoal for domestic fuel, and the reduced exposure to their combustion products.

    • Women and children may carry on their head 10 kg of firewood for distances up to 8 km, spending 5–6 hours per trip [39]; 2–6 hours per day [40].; or 5 hours per week [38]

    • Domestic combustion of the firewood releases health-impairing pollutants like carbon monoxide, hydrocarbons, smoke and other particulate matter. These combustion products may cause nausea, sneezing, eye and respiratory irritations [41]; pneumonia, lung cancer, and respiratory infections [42]; and reduced birth weight [43].

    • Biomethane utilization reduced firewood consumption by 74% in China [44] and 84% in Sri Lanka [45], thereby minimizing the drudgery, burden, and health hazards associated with use of firewood for domestic energy.

Figure 3 presents pathways of the production and utilization of biomethane from CPR and other renewable feedstocks.

Figure 3.

Schematics of biomethane production by anaerobic digestion of renewable feedstocks and pathways of the biomethane utilization. Adopted with permission from Ref. [46].

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6. Conclusions

Global energy security, sustainability and renewability could be enhanced by harnessing non-food biomass. The work presented in this chapter demonstrated that anaerobic digestion of cassava peeling residue (CPR) generated biomethane that could come to the energy rescue of cassava producing nations. Depending on the specific country and proportion of national cassava output processed, recovered biomethane from CPR could provide up to 7% national energy requirement in Haiti; 8% in Comoros; 10% in Cambodia; 11% in Nigeria; 31% in Rwanda; and 100% in Sierra Leone. The biomethane could be put to various applications and utilities that minimize the drudgery and burden of gathering wood and charcoal for domestic fuel. As additional dividends, use of the biomethane would prevent implications of the combustion products of these solid fuels that degrade air quality and impair human health. The time saved from fetching firewood may be put to economic, educational and social activities. Furthermore, the digester effluent (digestate) could be sold for soil amendment and as organic fertilizer, or applied to agricultural land for increased crop yield. Either way more revenue is generated for economic empowerment. Therefore, anaerobic digestion of CPR would help cassava producing nations to not only mitigate their energy insufficiency, but also address issues such as climate change, environmental degradation, poverty alleviation, rural development, and the sanitation and health hazards associated with the use of wood and charcoal as fuel.

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Written By

Sammy N. Aso, Arthur A. Teixeira and Simeon C. Achinewhu

Submitted: 12 August 2017 Reviewed: 02 November 2017 Published: 17 January 2018