Open access peer-reviewed chapter

Global Fertilizer Contributions from Specific Biogas Coproduct

Written By

Sammy N. Aso, Simeon C. Achinewhu and Madu O. Iwe

Submitted: 06 October 2021 Reviewed: 08 November 2021 Published: 05 May 2022

DOI: 10.5772/intechopen.101543

From the Edited Volume

Biogas - Basics, Integrated Approaches, and Case Studies

Edited by Abd El-Fatah Abomohra and El-Sayed Salama

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The impact of Haber-Bosch process on modern agriculture is prodigious. Haber-Bosch process led to invention of chemical fertilizers that powered green revolution, minimized food scarcity, and improved human and animal nutrition. Haber–Bosch process facilitated agricultural productivity in many parts of the world, with up to 60% of crop yield increase attributed solely to nitrogen fertilizer. However, Haber-Bosch fertilizers are expensive, and their poor use efficiency exerts adverse external consequences. In European Union for example, the annual damage of up to € 320 (US$ 372.495) billion associated with chemical fertilizers outweighs their direct benefit to farmers, in terms of crops grown, of up to € 80 (US$ 93.124) billion. A substitute for chemical fertilizers is therefore needed. In this chapter, external costs of chemical fertilizers are highlighted. The capability of liquid fraction of cassava peeling residue digestate to supplant and mitigate pecuniary costs of chemical fertilizers required for production of cassava root is also analyzed and presented. Results indicate that about 25% of fund used to purchase chemical fertilizers required for cassava root production could be saved with the use of liquid fraction of cassava peeling residue digestate. The pecuniary value is estimated at US$ 0.141 (≈ € 0.121) billion for the 2019 global cassava root output. This saving excludes external costs associated with Haber-Bosch fertilizers such as ammonia air pollution, eutrophication, greenhouse gasses emissions, and contamination of potable water supply reserves. Consequently, liquid fraction digestate could reduce the cost of cassava root production, as well as minimize adverse health and environmental consequences attributed to chemical fertilizers.


  • anaerobic digestion
  • biogas
  • cassava peeling residue (CPR)
  • chemical fertilizer
  • circular economy
  • cost savings
  • digestate
  • eutrophication
  • Haber-Bosch process

1. Introduction

The impact of Haber-Bosch process on modern agriculture may not be overemphasized. It led to the invention of inorganic fertilizers that powered global green revolution, minimized food scarcity, and improved human and animal nutrition. In his noble lecture, Fritz Haber (The 1918 noble laureate for chemistry; for the Haber-Bosch process) alluded that his impetuses for creation of ammonia from the elements were to meet increasing human food requirements, and replenish soil nitrogen extracted by harvested crops when he concluded: “Let it suffice that in the meantime improved nitrogen fertilization of the soil brings new nutritive riches to mankind and that the chemical industry comes to the aid of the farmer who, in the good earth, changes stones into bread” [1]. Haber–Bosch process has facilitated agricultural productivity in many parts of the world, with up to 60% of crop yield increase attributed solely to nitrogen fertilizer [2]. It has been estimated that between 1908 and 2008, Haber–Bosch nitrogen enabled the number of humans sustained per hectare of arable land to increase from 1.9 to 4.3 persons [3]. However, poor nitrogen use efficiency (NUE) of the same fertilizer that laid the golden benefits has deposited unintended adverse consequences to environmental systems [4]. Impacts of poor NUE may manifest at local, regional, and global scales [5], thereby placing air, soil, and water quality and safety, as well as human and animal health in jeopardy. Environmental and ecosystem services disruptions due to fertilizer use in agriculture have been reported worldwide. These include impairments of eco-diversity, recreational use of freshwaters, lakefront property values, and drinking water supply sources [6, 7]; loss of tourism benefits to coastal communities, [8, 9]; greenhouse gas (GHG) emissions and climate perturbation [10]; as well as air quality degradation [11].

Ammonia (NH3) air pollution from animal husbandry, fertilizer production and application has also been documented and reported [12, 13, 14]. About 94% of NH3 emissions in Italy emanate from agricultural operations [15], and in 2013 and 2018, agriculture contributed 93% of all ammonia emissions in the European Union [16, 17]. In the United States, agricultural runoff and drainage accounts for 89% of the total nitrogen inputs into the Mississippi River [18], contributing to hypoxic zone of the Gulf of Mexico [19]. In France, about 89% of residual nitrogen contamination of water resources and marine environments is attributed to mineral fertilizer and animal manure [8]. Similarly, nitrate contamination of surface and ground water is associated with agricultural use of fertilizers and manures [7, 8, 20, 21, 22, 23]. Nitrous oxide (N2O) is a greenhouse gas that contributes to stratospheric ozone shield depletion and climate change [10]. Nitrogen fertilizer and manure contribute 92% of all N2O attributable to agriculture in the USA [24, 25]. In Italy and China, fertilizer accounts for about 68% of annual N2O emissions [15, 26]. Chemical fertilizer and manure are major contributors to external costs such as eutrophication and acidification of ecosystems [21, 27, 28, 29, 30]. Annually, up to € 320 (US$ 372.495) billion damage is associated with the use of nitrogen fertilizers in the European Union compared to direct economic benefit to farmers, in terms of crops grown, estimated at up to € 80 (US$ 93.124) billion [31]. Report currency, € 1.0 ≈ US$ 1.164 based on currency converter site: at Friday 22nd October 2021. Furthermore, inorganic fertilizers are not cheap, and may be used in large quantities. As at the second week of September 2021, the cost of 1 kg of nutrient fertilizer could range from ≈ US$ 0.375 for liquid nitrogen (as urea) to US$ 0.807 for dry phosphorus (as P2O5) [Ramsdell F&M Ltd. Brookings, SD USA]. In 2019, approximately 188.54 x 109 kg nutrient fertilizers (including 107.74 x 109 kg N, 43.41 x 109 kg P2O5, and 37.39 x 109 kg K2O) were consumed in agricultural production globally [32].

Due to outlined adverse effects and financial exigencies of chemical fertilizers, a more sustainable, environmentally benign, and cost-effective fertilizer system is desired. Digestate in the context of circular economy could play a prominent role. In this chapter, cost implications of using liquid fraction (LF) of cassava peeling residue (CPR) digestate, to supplement chemical fertilizers required for cassava root production are analyzed and presented (Figure 1).

Figure 1.

Graphical representation of the objectives and summary of this chapter.


2. Anaerobic digestion and digestate for circular economy

Circular economy is a credible intervention tool to minimize GHG emissions, limit global warming and ecosystem degradation. The circular economic model maximizes material and product conservation; prudent consumption; eco-friendly biorefinery; recyclability and reusability; green- smart mobility and renewable energy; systems thinking, innovative business models and policies; wasteless design and zero waste cities, as well as generation of useful products out of waste [33, 34, 35, 36, 37, 38, 39, 40]. Anaerobic digestion (AD) is a responsive technology that could rise to the occasion. In the context of biorefinery platform, sustainability, and circular economy, AD transforms organic matter to two major coproducts: biogas fuel and digestate [41]. Digestate has soil amendment and biofertilizer potentials.

Digestate enhances soil biological stability and enzymatic activities [42]; enriches microbial biomass [42, 43]; abates nutrients leaching and remediates metal contaminants [43, 44, 45]; conditions the soil and boosts plant nutrients, stimulates growth of beneficial microbes, improves buffering capacity, and physical properties such as texture, aeration, bulk density, hydraulic conductivity, and moisture retention capacity [46, 47, 48, 49]. In comparison to chemical fertilizers, digestate biofertilizers offer better ecosystem services, values, and life cycle assessment accounting [50]; including lower energy consumption [51, 52, 53], lower ammonia air pollution [15], lower GHG emissions [53, 54, 55], better soil carbon sequestration [54, 56], reduced soil erosion [54, 57, 58], and increased biodiversity [59].

To exploit these benefits and advantages, various organic substrates have been used for digestate creation via the AD process. At least 120 items have been identified in published scientific literature [41], but CPR is not one of them. Indeed, there is scarcity of information on nutrient content, speciation, agronomic properties and values of LF of digestates from AD of single feedstocks in general [60]; and LF of digestate derived from AD of CPR as single feedstock in particular [41, 61].


3. Nutrient content of liquid fraction (LF) of cassava peeling residue (CPR) digestate

The only information on primary macronutrients (i.e., nitrogen (N), phosphorus (P), and potassium (K)) content of LF digestate of CPR as sole feedstock found in literature is presented in Table 1. For perspective, the values are compared with LF of digestates derived from other feedstocks in Tables 24 respectively for N, P, and K. The values for each Table are presented in descending magnitude order. It can be seen that LF of CPR digestate is high in N and K, but low in P. Apart from livestock manure, most LF digestates with higher nutrient values are derived from AD of multiple feedstocks (Tables 24). Co-digestion of feedstocks may benefit from coactive effects.

S/NNutrientValue [mg/L]
1Total Kjeldahl nitrogen (N)573
2Total phosphorus (P)31
3Total Potassium (K)1066

Table 1.

Macronutrients (N, P, K) content of liquid fraction of CPR digestate [41].

S/NFeedstockN Value [mg/L]Reference
1Cow manure & slurry (70%), maize silage (20%) and grass silage (10%)5591[62]
2Dairy manure4723[63]
3Cattle & pig slurries (main feedstocks), various food wastes (co-substrates)4268–4507[64]
4Dairy cow slurry2800–4500[65]
5Organic waste (Kitchen garbage, spoilt food, etc.)3610–4120[66]
6Energy crops e.g., silage maize (92%) and pig slurry (8%)4035[67]
7Animal manure and energy crops4000[68]
9Sewage sludge2700–3800[70]
10Sewage sludge + Acid cheese whey2800–3750[70]
11Dairy manure3007[71]
12Biowaste and kitchen refuse1010–2780[72]
13Municipal wastewater2667[73]
14Maize silage and distillery stillage2620[74]
15Poultry litter1570–2473[75]
17Source separated household waste2200[77]
18Municipal solid waste1308–1569[78]
19Swine manure1135[79]
20Waste activated sludge and organic fraction of municipal solid waste425–850[80]
21Sewage sludge (half-synthetic)820[81]
22Piggery farm effluent774[82]
23Yeast production wastewater703[83]
24Cattle slurry and glycerin600[84]
25Municipal wastewater sludge280–590[85]
26Cassava peeling residue (CPR)573[41]
27Sewage sludge and organic fraction of municipal solid waste355–535[86]
28Municipal wastewater435–520[87]
29Swine wastewater460[88]
30Starch processing wastewater240–383[89]
31Starch processing wastewater265[90]
32Piggery wastewater139[91]

Table 2.

Comparison of nitrogen (N) content of liquid fraction of digestate derived from various feedstocks.

S/NFeedstockP Value [mg/L]Reference
1Pig slurry800–1700[65]
2Dairy cow slurry200–1000[65]
3Dairy manure802[63]
4Sewage sludge590–680[70]
5Sewage sludge + Acid cheese whey500–550[70]
6Pig manure492[92]
7Energy crops (92%) and pig slurry (8%)412[67]
8Municipal wastewater381[73]
10Cattle & pig slurries (main feedstocks), various food wastes (co-substrates)292–315[64]
11Maize silage and distillery stillage270[74]
12Fruit and vegetable food waste261[93]
13Source separated household waste230[77]
14Poultry litter154–214[75]
15Piggery wastewater185[91]
16Municipal wastewater sludge100–185[85]
17Organic waste (Kitchen garbage, spoilt food, etc.)58–167[66]
18Sewage sludge (half-synthetic)130[81]
19Sewage sludge and organic fraction of municipal solid waste29–120[86]
20Swine manure115[88]
21Waste activated sludge and organic fraction of municipal solid waste95[80]
22Municipal solid waste60–62[78]
24Municipal wastewater43[94]
25Starch processing wastewater23–40[89]
26Cassava peeling residue (CPR)31[41]
27Starch processing wastewater28[90]
28Swine manure25[79]
29Algal biomass (Tetraselmis sp.)7[95]
30Yeast production wastewater7[83]

Table 3.

Comparison of phosphorus (P) content of liquid fraction of digestate derived from various feedstocks.

S/NFeedstockK Value [mg/L]Reference
1Animal manure and energy crops3500[68]
2Pig manure3258[92]
3Cattle & pig slurries (main feedstocks), various food wastes (co-substrates)1337–2850[64]
4Organic fraction of municipal solid waste700–2216[96]
5Poultry litter1632–2100[75]
6Cattle slurry and 10% orange peel residue1200[84]
7Source separated household waste1130[77]
8Cattle slurry and 5% orange peel residue1100[84]
9Cassava peeling residue (CPR)1066[41]
10Baker’s yeast industry wastewater827[97]
11Swine manure809[79]
12Cattle slurry and glycerin800[84]
14Starch processing wastewater102–176[89]
15Starch processing wastewater174[90]
16Sewage sludge and organic fraction of municipal solid waste28–33[86]
17Waste activated sludge and organic fraction of municipal solid waste30[80]

Table 4.

Comparison of potassium (K) content of liquid fraction of digestate derived from various feedstocks.


4. Estimation of fertilizer credit for liquid fraction (LF) of cassava peeling residue (CPR) digestate derived from one metric ton (1000 kg) cassava root

The nutrient values presented in Table 1 are for digestate derived from 800 g CPR accumulated in the 3 L working volume of AD reactor [41, 61]. Therefore, total nutrient credits for the 800 g CPR are:

N = 573 mg/L × 3 L = 1719 mg (1.719 g).

P = 31 mg/L × 3 L = 93 mg (0.093 g).

K = 1066 mg/L × 3 L = 3198 mg (3.198 g).

With the nutrients credit for 800 g (0.8 kg) CPR established, estimation of corresponding nutrient credit for CPR generated from 1000 kg cassava root becomes possible. It has been reported that CPR constitutes about 19% mass fraction of fresh cassava root [98]. Consequently, 1000 kg cassava root would yield 190 kg CPR. Hence, N, P, and K fertilizer credits for CPR generated from 1000 kg cassava root are estimated as:

N = 190 kg/0.8 kg × 1.719 g.

P = 190 kg/0.8 kg × 0.093 g.

K = 190 kg/0.8 kg × 3.198 g.

The results are presented in Table 5

NutrientQuantity in LF of CPR digestate from 1000 kg cassava root
Nitrogen (N)408.26250.4082625
Phosphorus (P)22.08750.0220875
Potassium (K)759.5250.759525

Table 5.

Nutrient credit for LF of digestate of CPR derived from 1000 kg cassava root.


5. Capability of liquid fraction (LF) of cassava peeling residue (CPR) digestate to supplant chemical fertilizer in cassava root production

Cassava crop is forbearing of harsh growing conditions such as drought, acidic soil, marginal land, varied elevation, swings of temperature and rainfall [99, 100]. However, research has shown that cassava is also responsive to adequate soil fertility and fertilizer application [101, 102, 103]. The equivalent root productivities in response to three cases of chemical fertilizer input are presented in Table 6.

CaseFertilizer Input [kg/ha]Root Output [kg/ha]
Nitrogen (N)Phosphorus (P2O5)Potassium (K2O)

Table 6.

Nutrient requirements for cassava root production (Derived from ref. [102]).

From the atomic weights of P, K and O, the elemental nutrient equivalent of the oxide forms (P2O5 and K2O) could be computed with the equations:


Consequently, the total P and total K corresponding to the total N required for the three cases of cassava root production outlined in Table 6 are estimated and presented in Table 7.

CaseFertilizer Input [kg/ha]Root Output [kg/ha]
Nitrogen (N)Phosphorus (P)Potassium (K)

Table 7.

Elemental nutrient requirements for cassava root production (Derived from Table 6).

Based on nutrients required to produce one metric ton (1000 kg) of cassava root shown in Table 7, and the nutrient credit for LF of digestate of CPR generated from 1000 kg cassava root presented in Table 5, the capability of LF of CPR digestate to supplant chemical fertilizer in cassava root production is estimated and outlined in Table 8. The proportion of production nutrient substituted range from about 23–30% for nitrogen; 5–11% for phosphorus; and 21–40% for potassium.

CaseNutrientNutrient required for production of 1000 kg cassava root (From: Table 7) [kg]Nutrient credit for liquid fraction (LF) of digestate of CPR generated from 1000 kg cassava root (From: Table 5) [kg]Proportion of nutrient required for production of 1000 kg cassava root supplanted by LF of digestate of CPR generated from 1000 kg cassava root [%]
ANitrogen (N)1.780.40822.92
Phosphorus (P)0.1920.02211.46
Potassium (K)1.8920.76040.17
BNitrogen (N)1.810.40822.54
Phosphorus (P)0.4500.0224.89
Potassium (K)2.7390.76027.75
CNitrogen (N)1.380.40829.56
Phosphorus (P)0.2230.0229.87
Potassium (K)3.6350.76020.91
MeanNitrogen (N)1.65670.40824.63
Phosphorus (P)0.28840.0227.63
Potassium (K)2.75560.76027.58

Table 8.

Capability of liquid fraction of CPR digestate to supplant chemical fertilizers required for cassava root production (Estimate based on Tables 5 and 7).


6. Cost analysis

From the mean nutrient values in Table 8, about 25, 8, and 28% of N, P, and K respectively required for production of 1000 kg cassava root, and sourced from inorganic fertilizers are supplanted by liquid fraction of CPR digestate. The cost implications are analyzed and presented in Table 9. The analyses indicate that about 25% of the total financial cost of inorganic fertilizers is supplanted by liquid fraction of CPR digestate (Table 9).

Nitrogen (N)Phosphorus (P)Potassium (K)
Unit cost of nutrient*US$/kg1.343.952.33
Nutrient required for production of 1000 kg cassava rootkg1.65670.28842.7556
Cost of nutrient required for production of 1000 kg cassava rootUS$2.221.13926.42059.7797
Nutrient from liquid fraction of digestate of CPR generated from 1000 kg cassava rootkg0.4080.0220.760
Cost credit of nutrient from liquid fraction of digestate of CPR generated from 1000 kg cassava rootUS$0.54670.08691.77082.4044
Proportion of cost of nutrient required for production of 1000 kg cassava root saved by liquid fraction of CPR digestate%24.637.6327.5824.59

Table 9.

Cost implications of supplanting chemical fertilizers with liquid fraction of CPR digestate in cassava root production.

Unit cost of liquid fertilizer derived from price data supplied by Ramsdell F&M Ltd. Brookings, SD USA. (Price as at 13th September 2021).


7. Global fertilizer savings from liquid fraction (LF) of cassava peeling residue (CPR) digestate

In 2019, a total of 96 recorded countries/territories produced about 303.569 x 109 kg cassava root globally. The output ranged from 5000 kg for Maldives to 59.194 × 109 kg for Nigeria [104]. At 19% CPR mass fraction composition, 57.678 × 109 kg of CPR would be generated from the global root output. This quantity of CPR could be transformed to biogas and digestate via AD. Whole digestate could be separated into liquid and solid fractions using appropriate technologies [41]. The liquid fraction of CPR digestate could then be utilized to supplant inorganic fertilizers required for cassava root production. The cost data generated and presented in Table 9 are applied to estimate the pecuniary value of global fertilizer savings from liquid fraction of CPR digestate substitution of chemical fertilizers. The results for each of the 96 countries/territories that produced cassava root in 2019 are presented in Table 10. Total global cost savings is about US$ 141.019 (€ 121.130) million. The range is from US$ 2.323 (€ 1.995) for Maldives, to US$ 27.498 (€ 23.620) million for Nigeria.

S/NCountry2019 Cassava root output [x 109 kg]aCPR generated from 2019 root output @ 19% CPR mass fraction [x 109 kg]Cost of chemical fertilizer required for 2019 root output [x 106 US$]Potential savings from liquid fraction digestate derived from 2019 CPR output. (≈ 25% total fertilizer cost) [× 106 US$]
2Democratic Republic of the Congo40.0501127.6095212874.4188352618.60470882
8Viet Nam10.1052241.9199925618.776951244.69423781
10United Republic of Tanzania8.1840931.5549776715.207215123.80180378
13Côte d’Ivoire5.2382440.995266369.7334064212.433351605
16China, mainland4.9754720.945339689.2451384682.311284617
17Sierra Leone4.5886120.871836288.5262972682.131574317
26Lao People’s Democratic Republic2.2587020.429153384.196991311.049247828
36Central African Republic0.7303620.138768781.3571170380.339279259
37South Sudan0.5725310.108780891.063844470.265961117
41Venezuela (Bolivarian Republic of)0.421620.08010780.7834302520.195857563
45Sri Lanka0.2810750.053404250.5222775440.130569386
48Bolivia (Plurinational State of)0.2033270.038632130.3778106420.09445266
50Dominican Republic0.174690.03319110.3245990010.08114975
51Costa Rica0.1598610.030373590.2970445980.07426115
52Papua New Guinea0.1551450.029477550.2882815960.072070399
54Equatorial Guinea0.0796460.015132740.1479936570.036998414
61El Salvador0.0291480.005538120.0541611520.013540288
69China, Taiwan Province of0.0110850.002106150.0205975150.005149379
70Micronesia (Federated States of)0.008420.00159980.0156455640.003911391
73Cabo Verde0.0051240.000973560.0095211250.002380281
75Burkina Faso0.0040460.000768740.0075180470.001879512
76French Polynesia0.0039370.000748030.0073155090.001828877
77Brunei Darussalam0.0033820.000642580.006284240.00157106
78Solomon Islands0.0033810.000642390.0062823810.001570595
79Trinidad and Tobago0.0023550.000447450.0043759270.001093982
80Saint Lucia0.0014590.000277210.0027110310.000677758
81Sao Tome and Principe0.0013840.000262960.002571670.000642917
83New Caledonia0.0008320.000158080.0015459750.000386494
85Cook Islands0.0007180.000136420.0013341470.000333537
87Saint Vincent and the Grenadines0.0005860.000111340.0010888720.000272218
93Puerto Rico0.000170.00003230.0003158847.89711E-05
94Antigua and Barbuda0.0001590.000030210.0002954457.38612E-05
97World Total303.56881457.67807466564.0742668141.0185667

Table 10.

Global fertilizer savings from liquid fraction of CPR digestate.

Data source: (Ref. [104]).


8. Conclusion

Haber-Bosch process facilitated the existence of inorganic fertilizers that revolutionized crop yield, improved nutrition, and enhanced food security. However, external costs associated with the production and application of inorganic fertilizers in agriculture are prodigious. Air quality degradation, climate perturbation, eutrophication, harmful algal blooms, ocean dead zones, pollution of surface water bodies and groundwater aquifers used as potable water supply sources are notable examples. Anaerobic digestion in the context of circular economic paradigm could provide viable solution. Anaerobic digestion transforms organic wastes and residues to beneficial biogas fuel and digestate biofertilizer. This chapter analyzed and presented the cost implications of liquid fraction of cassava peeling residue (CPR) digestate to supplant chemical fertilizers required for cassava root production. About 25% of fund used to purchase the chemical fertilizers required for cassava root production could be saved with the use of liquid fraction of CPR digestate. The global pecuniary saving is estimated at US$ 0.141 (€ 0.121) billion for year 2019 cassava root output. Thus, exploitation of liquid fraction of CPR digestate would save 25% pecuniary cost of inorganic fertilizers required for cassava root production, as well as attenuate afore mentioned external costs correlated with the production and application of the inorganic fertilizers.

Perspectives: There is severe scarcity of data on the speciation of nutrients content of digestates derived from anaerobic digestion of CPR as single feedstock. The few studies reported in available literature focused on biogas potentials of CPR co-digested with other substrates such as animal manures. The reports did not indicate any data on generated digestate. For future perspectives, experimental questions could address systematic studies to characterize the nutrient speciation in digestates derived from CPR as mono feedstock. Findings may not only corroborate the fertilizer values of CPR digestate reported in this chapter, but also establish CPR’s nutrients influence and contribution when co-digested with other feedstocks. Furthermore, the work for this chapter searched, and could not find any study on the effects of CPR digestate on crop performance. Agronomic experiments designed with CPR digestate as bio-fertilizer, would provide valuable knowledge and insight on the suitability and practical impact of CPR digestate on yield and other performance indicators for cassava, and perhaps other crops.


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Written By

Sammy N. Aso, Simeon C. Achinewhu and Madu O. Iwe

Submitted: 06 October 2021 Reviewed: 08 November 2021 Published: 05 May 2022