## SCIENTIFIC COMMUNICATION

# Ecologic index of Ecological Charcoal Based on Mix *Prosopis juliflora* *Eichhornia crassipes* and their carbon sequestration potential

Alexis Dzokom<fnref n="1" />, Roger Djoudé Darman<fnref n="2" />

### ABSTRACT

The objective of this study is to evaluate the ecological quality of charcoal based on *Prosopis juliflora* linked to *Eichhornia crassipes* and to determine its index ecological value. The collection and preparation of 1.05±0.32 Ton of mixed dry biomass of *Prosopis juliflora* and *Eichhornia crassipes*, made it possible to obtain on average 0.918±0.234 Ton of ecological charcoal without binder and 1.267±0.342 Ton ecological coal with binder. The local combustion of ecological coal for energy use releases on average approximately 0.193±0.011 Ton CO2/day, or 1194.31±1512.21 Ton CO2/year, inducing an average environmental compensation of 155.72±20.01 at 196.59±31.09 plants/Ha/month, or between [467.16±60.03; 598.50±93.27] plants/Ha/year to be planted during the good season. The Ecological Value Index of carbonized and ground *Prosopis juliflora* (100/0%) (3.759) is less than that of carbonized and ground *Eichhornia crassipes* (100/0%) (71.284). The most interesting Ecological Value Index of *Prosopis juliflora* linked to carbonized and ground *Eichhornia crassipes* (75/25%) is 48.971, which makes it ecologically viable for the production of ecological charcoal, following *Prosopis juliflora*.

Keys words: Ecological Value Index; Charcoal; Environmental compensation; *Eichhornia crassipes*; *Prosopis juliflora*

### INTRODUCTION

*Prosopis juliflora* in the Cameroonian Sahel, is present in the majority of humid and semi-arid zones and helps to stop desertification, control deforestation and can help alleviate wood energy shortages. In the Cameroonian Lake Chad area, *Prosopis juliflora* is one of the invasive plants and *Prosopis juliflora* firewood provides 45% of the energy needs of rural areas due to the fact that it is considered to be a wood whose smoke is irritating for the eyes in kitchens [30]. Studies show that in arid and semi-arid regions of India, *Prosopis juliflora* accounts for up to 70% [29] or 80-90% [1] of all domestic fuel needs of rural populations.

On the energy front, the overexploitation of wood energy, which represents one of the major environmental problems [2], [3], [4], has caused a widening of the circle of deforestation around the Sahelian towns of Maroua and Garoua, leading to erosion and a decline in agricultural productivity [5], [6]. In the areas supplying the Sahelian town of Maroua with fuelwood (Madjina, Songonyé, Ngambarou and Kinguériwa) the decline of the bush is clear [5]. Wood energy thus remains one of the most used forms of energy per capita in Cameroon with 586 kg/inhabitant [5]. However, this consumption does not specify the location, the forms, or the consumers of this energy source; which cannot facilitate planning of this energy

source [7]. Furthermore, it was estimated that the charcoal production activity would employ 150,000 people in 1991 and generate more than 50 million US dollars by contributing only 6% to the energy needs in Haiti [8]. In India, forest service's produce and market 3 million tons of *Prosopis juliflora* charcoal per year, creating on average 55,500 days of employment per man per year [9], while between 3,000 and 16,000 tons /year *Prosopis juliflora* charcoal is produced in northern Peru [10]. However, charcoal is mainly consumed in urban areas and is often produced at considerable distances from the point of consumption and approximately 3 to 6 kg of *Prosopis juliflora* or *Prosopis pallida* wood is required to produce 1 kg of charcoal depending on the method used [11].

The production of ecological charcoal based on aquatic invasive plants such as *Eichhornia Crassipes* in Lake Chad requires an operational and functional choice of available and free binder in order to meet the needs of poor populations in arid and semi-arid zones [12]. The objective of this study is to evaluate the ecological quality of ecological charcoal based on *Prosopis juliflora* linked to *Eichhornia crassipes* and to determine its index ecological value. The binder, in the context of this study, is clay. At the end of this study, it is expected to produce large quantities of high quality ecological charcoal with a very high energy capacity,

<footnote n="1">¹Department of Environmental Sciences, National Advanced School of Engineering, University of Maroua, Cameroon</footnote>

<footnote n="2">²Department of Agriculture Animal Husbandry and By-Products, National Advanced School of Engineering, University of Maroua, Cameroon</footnote>
close to that of firewood.

# I- MATERIALS AND METHOD

## I-1)- Study sites

The study was carried out in the Lake Chad area, in the Far North of Cameroon, around 10 sites, including 5 sites which are affected by the invasion of water by *Eichhornia Crassipes* and 5 other sites on dry land which are concerned by the invasion by *Prosopis juliflora*.

<figure><img src="image_1.png" /><figcaption>Figure 1: Map of the Study Area</figcaption></figure>

## I-2)- Sampling of biomass and preparation of ecological coal samples

The dry dead biomasses of *Prosopis juliflora* and *Eichhornia crassipes* were collected in bulk in nature. Then, via a manual selective sorting process described by [2]. They were separated then arranged into dry dead biomasses on the one hand and into living biomasses on the other hand.

Using the methodologies developed by [13], [2], [3], [4], the very selective sorting of the raw material is preferably done manually, using individual protective equipment (nose covers, gloves, etc.). The fork, the pickaxe, the rakes, the garbage excavations, the shovels were used to dig and separate the raw material from the organic deposits. Wheelbarrows and bags are tools that made it possible to collect, transport and store this raw material [2], [3], [4].

### I-2-1) Carbonization process

The carbonization was carried out following the methodology developed by [4]. It consisted of carbonizing the dry biomass in a carbonizer at a temperature between 400-600°C.

### I-2-2) Mass yield taken from biomass

The mass yield makes it possible to estimate the carbon production of equipment based on the mass of the product to be carbonized processed. It is defined as the mass of ecological coal produced relative to the mass of carbonized biomass. Determining this ratio requires the following operations described by [13]. For the mass yield before carbonization we have:

* Weigh all of the biomass put into the oven (Wi);

* Determine the raw humidity (H%) of the biomass;

* Mass of biomass whose raw humidity is greater than 50% (H>50%) (MBO (H>50%));

* Determine the mass of the biomass (MB), by calculation, from the initial total mass (Wi), according to the formula :

$$MB = Wi \times (MBO(H > 50\%) - \frac{H\%}{100}) \quad (1)$$

For the mass yield after carbonization we have:

* Sorting and weighing any unburned products resulting from carbonization (MI);

* Immediate weighing of all the coal (MC).

The mass yield on anhydrous (R) expressed as a percentage is given by the formula :

$$R = 100 \times (\frac{MC}{MB-MI}) \quad (2)$$

If this fuel is wood, the quantity of anhydrous wood (AW) introduced into the system must be assessed in the same way as above. The formula for mass yield then becomes:

$$Rnet = 100 \times (\frac{MC}{MB-MI+AW}) \quad (3)$$

If this fuel is not wood, the quantity of ant energy can also be taken into account, and the following formula makes it possible to calculate the equivalent of anhydrous wood (AW) such that:

$$AW = \frac{\text{Combustible anhydrous mass} \times \text{Combustible anhydrous LCV}}{\text{LCV anhydrous carbonized wood}} \quad (4)$$

The samples of the Coal obtained were prepared according to the method used by [2], where each one was subdivided into triplicates, marked and weighed, and taken for laboratory analysis. Moisture levels, density and calorific value were determined as described in the following sections.

### I-2-3) Density (D) of the Coal obtained

Density was determined as the ratio of kiln dry weight (gr) to volume (cm³) using equation 3. The procedure followed the technique described in [14] whereby the volume of the wood is d first determined by immersing the samples in water for 5 days (120 h) to reach total saturation, allowing them to drain for 5 min, and measuring their diameters using a caliper. The volume was calculated using equation 2:

$$Volume = \frac{\pi \times D^2 \times L}{4} \quad (5)$$

Where D = average diameter of the sample and L = length of the sample.

The samples were dried again at 100°C until reaching a constant weight. The density (D) was then calculated according to equation 3:

$$Density = \frac{\text{Dry weight of Charcoal}}{\text{Sample volume}} \quad (6)$$

Where the dry weight of the coal is in grams and the volume of the ecological coal sample is in cm³

## I-4) Physico-chemical characterization of fuel samples based on *Prosopis juliflora* linked to *Eichhornia crassipes*

### I-4-1)- Clay Binder

The preparation of the clay consisted of crushing the clay, then sieving it through three meshes

<figure><img src="image_2.png" /></figure>

<figure><img src="image_3.png" /></figure>

<figure><img src="image_4.png" /></figure>

<figure><img src="image_5.png" /></figure>
(0.25mm/mm, 1mm/mm and 2mm/mm). We
then obtain particles of different sizes.

<figure><img src="image_6.png" /><figcaption>**Photo 1:** a) Clay after crushing and ready to be sifted; b) Clays of different particle sizes (0.25mm, 1mm and 2mm)</figcaption></figure>

### I-4-2) Moisture content of fuel samples based on *Eichhornia crassipes*

As part of this work, the determination of the humidity level was inspired by the methodological measurement processes developed by [18]. The humidity level expresses the water content and strongly influences the calorific value and the ignition capacity of the briquettes. The humidity level is obtained by the following formula:

$$W(\%) = \frac{\text{Wet matter} - \text{Dry matter}}{\text{Wet matter}} \times 100 \quad (7)$$

With: W: humidity level; M wet: mass of the sample; M dry: mass obtained after heating to 105°C in the oven.

### I-4-3) Surface/volume ratio of fuel samples based on *Eichhornia crassipes*

Determining the dimensions of ecological charcoal involves determining the length, width (or diameter for cylindrical briquettes) and height. Thanks to the determination of dimensions and the simple calculation of surfaces and volumes, in order to determine the size of the likely particles and to produce the best ecological coals for combustion, we have determined their surface area and their volume.

$$\text{Area} = \text{Length} \times \text{Width} = 2 \times \text{Radius}^2 \times \pi \ (\text{mm}^2)(8)$$

$$\text{Volume} = \text{Area} \times \text{Height} = \text{Radius}^2 \times \text{Height} \times \pi \ (\text{mm}^3)(9)$$

The samples of ecological charcoal being carbonized plants, and the combustion of plants is very dependent on their surface/volume ratio [23], we determined:

$$\text{Surface/volume ratio} = \frac{\text{Surface (mm}^2)}{\text{Volume (mm}^3)} (\text{mm}^{-1}) (10)$$

### I-4-4) Density of fuel samples based on *Eichhornia crassipes*

The skeletal density ($\rho_{sq}$) of the crushed materials is determined using laboratory measurements. The average skeletal densities obtained during the tests were calculated according to the formula [15], [2], [16]:

$$\rho_{sq} = \frac{m \text{ crushed biomass}}{v_{\text{total}} - v_{\text{ethanol}}} (\text{gr/ml}) \quad (11)$$

The apparent density of the crushed materials is measured in the laboratory. The ratio between mass and volume gives the apparent density ($\rho_{app}$), the averages of which are calculated using Excel software.

### I-4-5) Porosity of fuel samples based on *Eichhornia crassipes*

Determining the porosity of the briquettes, carried out in the laboratory, consists of determining the ratio between the volume of air present in the crushed materials (Skeletal volume - Apparent volume of briquette) and the skeletal volume of the fuel briquette. Its formula is given by the relation:

$$\alpha_b = 1 - \frac{p_{app}}{\rho_{sq}} \quad (12)$$

With $\alpha_b$: porosity; $\rho_{app}$: apparent density; $\rho_{sq}$: skeletal density

### I-4-6) Resistance index of fuel samples based on *Eichhornia crassipes*

The Impact Resistance Index (IRC) or Stability Test of ecological coal is determined by the compression tests undergone by ecological coal. The compressive force of ecological coal in its cylindrical position is determined by the appearance of faults during its compression [20].

<figure><img src="image_7.png" /><figcaption>**Figure 2:** a)-Test of the compression force of the briquettes and condition for the appearance of cleavages; b) -Test of the axial compression force of the briquettes and condition for the appearance of cleavages [2].</figcaption></figure>

### I-4-7) Moisture recovery content of fuel samples based on *Eichhornia crassipes*

The moisture recovery test via a simple immersion test that the ecological combustible coal is subjected to makes it possible to characterize their potential for resistance to thermal and environmental hazards of the storage location. It consists of measuring the diameter of the fuel before and after immersion in order to determine the difference in water imbibition and the percentage of inclusion of materials in the ecological coal briquette [26]. It is expressed in cubic centimeters (cm³) [15].

### I-4-8) Volatile matter content

The BS EN 14.774-1 protocol for determining the volatile matter of a fuel consists of weighing the dry sample then heating it under nitrogen, at a temperature between 890° and 910°C for 7 minutes in a crucible with lid and weigh it again. The formula developed by the standard method [21] makes it possible to calculate the rate of volatile matter:

$$M.O.V. = \frac{(M850^{\circ}\text{C} - M899^{\circ}\text{C}) \times 100}{\text{M dry}} \quad (13)$$

With: MOV: Rate of volatile matter, M895°C: Mass obtained after heating to 895°C, M899°C: mass obtained after heating to 899°C

### I-4-9) Ash content

In the context of this work, the ash rate is the quantity of very small mineral materials contained in a fuel and released after complete combustion, under the effect of heat at high temperatures. The result is obtained by applying the formula developed by the standard methods [22] and [23]:
$$A(\%) = \frac{M850^{\circ}C \times 100}{M \text{ dry}} \quad (14)$$

With: A, M 850°C: mass of the powder obtained after incineration at 850°C, M dry: dry mass of the sample.

### I-4-10) Fixed carbon content

To determine fixed carbon, the BS EN 14.774-1 protocol was used. Two parts, each weighing 1 gram, were made from the combustible briquettes, then they were introduced into an oven for calcination. One part was calcined for 10 minutes at a temperature of 550°C, while the other part was calcined for 10 minutes at a temperature of 850°C. The fixed carbon rate developed by the standard method [23] allows it to be calculated using the following formula:

$$Cf(\%) = 100 - (H \text{ dry} + Mce850^{\circ}C + Mv550^{\circ}C) \quad (15)$$

### I-5) Combustion tests

The combustion test allowed us to determine:

- the ease of lighting fuels;

- the duration of combustion of fuels;

- energy efficiency of fuels.

### I-5-1) Determination of the ease of ignition of fuels

The ignition test consists of determining the ease of ignition of fuels in 5 minutes. It consists of measuring, using a thermocouple, the temperature of the fire of an incandescent sample (T°al). The ignition of the fuel lasts 1 minute and the temperature of the incandescent part of the fuel is measured at 25 seconds (T°t) and at 300 seconds (T°t'). Ease of ignition is written by Formula 1[24].

$$T^{\circ}\text{al} = T^{\circ}\text{t}'' - T^{\circ}\text{t}' \quad (16)$$

T° al: ignition temperature, T° t: temperature at t equal to 5 min, T° t': temperature at t equal to 25 s.

### I-5-2) Determination of the combustion duration of fuels

The combustion time (DC) test consists of determining the total combustion time of 600 g of fuels introduced into an improved fireplace with a clay combustion chamber. It begins with lighting until ashes are obtained. The combustion duration is written according to Formula 2.

$$\Delta t = tf - ti \quad (17)$$

Δt: time it takes for fuels to burn; tf: end of fuel combustion time; ti: sample combustion start time

## I-8) Ecological Value Index of Ecological Coal (EVI Coal)

### I-8-1) Rate of CO₂ sequestered by ecological coal

The data collected is entered into the Microsoft Excel 2013 spreadsheet. The biovolume, the distribution of trunks and stems by height and diameter classes of the raw materials are adjusted according to the distribution parameters: Aboveground biomass, underground biomass, total biomass, Carbon Stock and Carbon Equivalent [25].

The aboveground biomass (BA) is calculated according to the classic allometric equations applicable to the study area [27]. The calculation of the

**Table1:** Floristic composition of invasive plants on the sites

underground biomass was based on the relationship in [26]. Statistical analyzes were carried out using Excel 2013 and SPSS® software. The variables were calculated according to the formulas:

- Density of species on a given surface (D):

$$D = \frac{Ni}{si} \times 0,0001 \quad (18)$$

- Average diameter of trunks and stems of species (Dm): $D = \frac{\sum di}{Ni}$ (15)

- Basal area covered by the species (G): $G = \sum \frac{Ci^2}{4\pi}$ (19)

- Volume of species biomass (V): $V = \sum (\frac{Ci^2}{4\pi} \times Hi)$ (20)

With, Ni = number of individuals in group i, si = surface area of group i, di = diameter of individual i, Ci = circumference of individual i and Hi = height of individual i.

The distribution histograms were established by diameter class of 10 cm and by height class of 2 m to reflect the demographic structure of woody populations on the basis of probability density.

➤ Probability density:

$$f(x) = \frac{c}{b} \times \left(\frac{x-a}{b}\right)^{c-1} e^{\left(x-\frac{a}{b}\right)^{c}} \quad (21)$$

➤ Aerial biomass of species (BA):

$$BA = e^{(-2,187+0,916\ln(\rho HD^2))} \quad (22)$$

➤ Belowground biomass of species (BS):

$$BS = e^{(-1,0587+0,8836 \times \ln(BA))} \quad (23)$$

The total biomass of each tree (BT) is the sum of its aboveground biomass and its belowground biomass. From where:

Total species biomass: $BT = BA + BS$ (24)

Carbon stock of species (SC): $SC = BT \times CF$ (25)

With, CF = 0.47 = default carbon ratio of all species combined [28]

The following formula to evaluate the rate of CO₂ sequestered in ecological coal makes it possible to better determine the quality of the coal produced:

$$\frac{\text{Rate of CO2 sequestered from ecological coal}}{\text{Weight of dry ecological coal produced (kg) \times Fixed carbon rate(\%)}} = \text{Biomass harvesting area (Ha)} \quad (26)$$

## II-1) RESULTS

### II-1)- Invasive floristic composition of the sites

On average, a total of 73.87±7.24 individuals/Hectare distributed into 7.56±1.67 genera/Hectare, 5.17±1.09 species/Hectare and 3.11±0.58 families/Hectare was recorded in the ten study sites (Table 2). The distribution according to species on dry land shows a clear dominance of *Prosopis juliflora* (i.e. 29.16±1.67 individuals/hectare) followed by *Eichhornia crassipes* on water (98,509.06±68.68 individuals/hectare). These two species alone cover 81.59% of the vegetation studied. The most represented families are those of Mimosaceae (4 species), followed by Moraceae (3 species). Caesalpineaceae, Meliaceae, Rhamnaceae, Palmoeae, Sapotaceae, Annonaceae, Sterculiaceae and Bombaceae have only one species. The Shannon index reveals a low diversity of the site (0.6 bits), the Pielou fairness being equal to 0.41. This index reflects the uneven distribution of inventoried species dominated by the two species *Prosopis juliflora* and *Eichhornia crassipes*

<figure><img src="image_8.png" /></figure>

<figure><img src="image_9.png" /></figure>

<figure><img src="image_10.png" /></figure>

<figure><img src="image_11.png" /></figure>
<table><thead><tr><th rowspan="2">Species</th><th rowspan="2">Emission factor (grams CO<sub>2</sub>eq/Kg)</th><th colspan="4">Density (Plants / km<sup>2</sup> / saison)</th><th rowspan="2">Frequency (%)</th><th rowspan="2">Ecological footprint (ha/person)</th></tr><tr><th>rainy season</th><th>Max. rainy season</th><th>dry season</th><th>Min. dry season</th></tr></thead><tbody><tr><td><em>Prosopis juliflora</em></td><td>0.094</td><td>17.981±0.614<sup>f</sup></td><td>18.742±0.594<sup>a, b</sup></td><td>15.007±0.553<sup>c</sup></td><td>5.459±0.067<sup>e</sup></td><td>43.50±1.04<sup>d</sup></td><td>0.476×10<sup>-4</sup><sup>d</sup></td></tr><tr><td><em>Eichhornia crassipes</em></td><td>0.743</td><td>842.375±14.118<sup>a</sup></td><td>1038.009±7.186<sup>a</sup></td><td>151.573±21.171<sup>d</sup></td><td>38.735±7.116<sup>c</sup></td><td>37.56±2.07<sup>e</sup></td><td>0.012±0.004<sup>a</sup></td></tr></tbody></table>

The average density of *Prosopis juliflora* on dry land within the study sites is 17.981±0.614 plants/km² during the rainy season (May to October), with the highest peak (18.742±0.594 plants/km²) in the month of August while during the dry season (from November to April), this density is 15.007±0.553 plants/Km² with a weak peak (5.459±0.067 plants/Km²) in the month of March. The emission factor of *Prosopis juliflora* during carbonization before the manufacture of ecological charcoal is 0.0937±0.007 grams CO₂eq/Kilogram, while this emission factor after manufacture of ecological charcoal (carbonized *Prosopis juliflora* linked to clay) is 0.011±0.003 gram CO₂eq/Kilogram. The removal of 3572.286±1.428 plants of *Prosopis juliflora*, or approximately 1000 kilograms of raw material, followed by their carbonization could result in a total of 937.367±1.967 grams CO₂eq/kilograms of the ecological charcoal produced, with an ecological footprint of 0.476×10⁻⁴ha/person having been impacted during the activities to make available 735.117±6.154 Kilograms of ecological coal (Table 1). The average density of *Eichhornia crassipes* on the water surface during the rainy season (May to October) is 842.375±14.118 plants/m², with the highest peak (1038.009±7.186 plants/m²) at month of August while

during the dry season (November to April) is 151.573±21.171 plants/m² with a low peak (38.735±7.116 plants/m²) in the month of March. The emission factor of *Eichhornia crassipes* during carbonization before the manufacture of ecological charcoal is 0.743±0.072 gram CO₂eq/Kilogram while this emission factor after manufacture of ecological charcoal is 0.0012±0.0001 gram CO₂eq/Kilogram. The cleaning of the 3900 Kilograms followed by their carbonization results in a total emission of 1768.7 grams CO₂eq (i.e. 1.7687 kilograms CO₂eq) with an ecological footprint of 0.012±0.004 ha/person having been impacted during the charcoal production activities ecological (Table 1).

## II-2)- The role of soils in CO₂ sequestration

The center of our study area is occupied by villages (continuous and discontinuous urban fabric) located not far from Lake Chad, made up of residential areas, collective facilities and activity zones. At the edge, a large area is covered by arable land, agricultural plots, meadows, as well as some natural spaces (steppe and woods).

<figure><img src="image_12.png" /><figcaption>**Figure 3:** Distribution of land use by invasive plants</figcaption></figure>

The soils near the lake are 70% clay and constitute natural carbon reservoirs, which absorb carbon from the atmosphere and therefore help to reduce the concentration of atmospheric CO₂. The photosynthesis of *Eichhornia crassipes* in the waters of Lake Chad is the main driver of CO₂ sequestration, which allows the extraction of terrestrial carbon and storage in the root system which constitutes a carbon sink. This natural mechanism governs the growth of *Eichhornia crassipes* by ensuring the synthesis of biomolecules and the release of O₂ using the light energy received from the sun and from CO₂, H₂O and mineral elements (N, P, K, etc.). On dry land, the soils covered by *Prosopis juliflora* are also the basis for the development of photo-autotrophic organisms that consume CO₂ more or less resistant to drought and which thus play a very important role in the

carbon cycle and for the balance of atmospheric concentrations in Sahelian environments.

The plant areas of our study area, directly involved in the sequestration of atmospheric CO₂, occupy an area of approximately 152 km², or 30.4% of our study area. In order to determine the net sequestration of CO₂ by these plant areas, it is necessary to distinguish between agricultural soils and areas occupied by invasive plants, because these classes have different biological activities and thus a potential for specific surface carbon sequestration. The impact of land use changes is also presented.

## II-2)- Sampling of biomass and preparation of ecological coal samples

## II-2-1)- Living biomass and assessment of net sequestration of CO₂ stock linked to *Prosopis juliflora* and *Eichhornia crassipes*

<figure><img src="image_13.png" /></figure>
In the study sites, the average diameter of the trunks and stems of the species studied varies. The average diameter of the main trunks of *Prosopis juliflora* is 23,404±5,253 cm. The basal area covered by the *Prosopis juliflora* taken into account in the context of this study (trunk diameter ≥20 cm) is 3,978±1,391 m²/Ha

with a coverage of 955.8±1,391m²/Ha and a volume of biomass of 7.956±0.512 m³.

The average diameter of the main stems of *Eichhornia crassipes* is 5.914±0.893 cm with a covered basal area of 2.872±0.449 m²/Ha and a biomass volume of 1.436±0.603 m³ (Table 2).

<table><caption>Table 2: Determination of aboveground biomass (BA)</caption><thead><tr><th>Species</th><th>Average diameter of the main trunks (and stems) of the species (cm)</th><th>Basal area covered by the species (m²/Ha)</th><th>Density (Ind. No./Km²)</th><th>Volume of species biomass (m³)</th></tr></thead><tbody><tr><td><i>Prosopis juliflora</i></td><td>23.404±5.253<sup>a,g</sup></td><td>3.978±1.391<sup>d</sup></td><td>16.507±1.768<sup>a</sup></td><td>7.956±0.512<sup>e,f</sup></td></tr><tr><td><i>Eichhornia crassipes</i></td><td>5.914±0.893<sup>e</sup></td><td>2.872±0.449<sup>e</sup></td><td>151.573±21.171<sup>b</sup></td><td>1.436±0.603<sup>d</sup></td></tr></tbody></table>

The total average biomass of *Prosopis juliflora* and *Eichhornia crassipes* studied is variable. However, the total average biomass of *Prosopis juliflora* is 16.80±1.54 T/Ha/year, lower than the total average biomass of *Eichhornia crassipes* which is 197.77±0.79 T/Ha/year. The average carbon stock by *Prosopis juliflora* is

7.896±0.183 T C/Ha/year with an average Carbon Equivalent of 15.06±0.35 T C/Ha/year while the average carbon stock by *Eichhornia crassipes* is 92.952±1.547 T C/Ha/year with an average Carbon Equivalent of 22.36±0.13 T C/Ha (Table 3).

<table><caption>Table 3: Total living biomass and carbon stock of each species</caption><thead><tr><th>Species</th><th>Aboveground biomass of species (BA,T/Ha)</th><th>Belowground biomass of species (BS,T/Ha)</th><th>Total biomass of species (BT,T/Ha)</th><th>Stock of sequestered CO<sub>2</sub>/species (SC, T CO<sub>2</sub>/Ha/year)</th><th>Carbon equivalent (EqC, T/Ha)</th></tr></thead><tbody><tr><td><i>Prosopis juliflora</i></td><td>2.65±0.71<sup>a</sup></td><td>14.15±0.83<sup>a</sup></td><td>16.80±1.54<sup>a</sup></td><td>7.896±0.183<sup>f</sup></td><td>15.06±0.35<sup>d</sup></td></tr><tr><td><i>Eichhornia crassipes</i></td><td>67.15±0.03<sup>c</sup></td><td>130.62±0.76<sup>b</sup></td><td>197.77±0.79<sup>a</sup></td><td>92.952±1.547<sup>a</sup></td><td>22.36±0.13<sup>e</sup></td></tr></tbody></table>

The calculation of CO₂ absorption by type of gasoline is presented in the following table. In total, the net sequestration linked to *Prosopis juliflora* and *Eichhornia crassipes* is estimated at approximately 100.85±1.73 T CO₂/year over an area of 65,200 Ha in 2024.

<table><caption>Table 4: Calculation of net surface sequestration linked to *Prosopis juliflora* and *Eichhornia crassipes*</caption><thead><tr><th>Sequestration</th><th>Carbon Storage coefficient (T C/m³)</th><th>Carbon surface storage (T C/ha/year)</th><th>CO₂ surface storage (T CO₂/ha/year)</th><th>Surface area (Ha)</th></tr></thead><tbody><tr><td><i>Prosopis juliflora</i></td><td>0.98±0.07<sup>a</sup></td><td>7.367±0.667<sup>a</sup></td><td>5.543±0.232<sup>f</sup></td><td>15200</td></tr><tr><td><i>Eichhornia crassipes</i></td><td>0.26±0.56<sup>c</sup></td><td>90.654±0.982<sup>c</sup></td><td>87.443±0.764<sup>a</sup></td><td>50000</td></tr></tbody></table>

## II-2-2)- Dry dead biomass and raw material preparation

The average weight of the trunk of the dry dead biomass of *Prosopis juliflora* is 17.02±3.00 kg/m² while its average weight is 58.27±4.56 kg/m². The average

LCV of the dry dead biomass of *Prosopis juliflora* is 17.92±0.02MJ/kg with its average dry stock is 75.29±6.18 kg/m² and the average stock of its bioenergy is 1.35±0.101 GJ/m². These values are distributed in the table below:

<table><caption>Table 5: Dry dead biomass and bioenergy stock</caption><thead><tr><th>Site</th><th>Species</th><th>Trunk weight (kg/m²)</th><th>Plant weight (kg/m²)</th><th>LCV (MJ/kg)</th><th>Biomass stock (kg/m²)</th><th>Bioenergy stock (GJ/m²)</th></tr></thead><tbody><tr><td rowspan="2">Koussérie</td><td><i>Prosopis juliflora</i></td><td>16.27±0.65<sup>a</sup></td><td>53.16±1.44<sup>a</sup></td><td>17.957±1.042<sup>b,h</sup></td><td>69.43±1.04<sup>a</sup></td><td>1.246±0.754<sup>d</sup></td></tr><tr><td><i>Eichhornia crassipes</i></td><td>11.05±0.63<sup>c</sup></td><td>51.69±0.98<sup>a</sup></td><td>18.543±7.767<sup>i</sup></td><td>62.74±0.80<sup>g</sup></td><td>1.163±0.387<sup>a</sup></td></tr><tr><td rowspan="2">Makary</td><td><i>Prosopis juliflora</i></td><td>17.89±0.27<sup>a</sup></td><td>61.86±1.56<sup>a</sup></td><td>17.952±1.088<sup>d</sup></td><td>79.75±0.91<sup>a,b</sup></td><td>1.431±0.672<sup>c</sup></td></tr><tr><td><i>Eichhornia crassipes</i></td><td>11.15±0.23<sup>c</sup></td><td>57.96±0.69<sup>a</sup></td><td>18.521±7.605<sup>a</sup></td><td>69.11±0.46<sup>d</sup></td><td>1.279±0.986<sup>f</sup></td></tr><tr><td rowspan="2">Hilé Alifa</td><td><i>Prosopis juliflora</i></td><td>12.65±0.71<sup>a</sup></td><td>58.16±1.31<sup>a</sup></td><td>17.959±0.057<sup>f</sup></td><td>70.81±1.01<sup>e</sup></td><td>1.271±0.676<sup>d</sup></td></tr><tr><td><i>Eichhornia crassipes</i></td><td>16.15±0.03<sup>c</sup></td><td>57.77±0.79<sup>a</sup></td><td>18.508±7.764<sup>c</sup></td><td>73.92±0.41<sup>g</sup></td><td>1.368±0.111<sup>a</sup></td></tr><tr><td rowspan="2">Blangoua</td><td><i>Prosopis juliflora</i></td><td>19.65±0.34<sup>a</sup></td><td>61.89±1.71<sup>a</sup></td><td>17.898±1.091<sup>b</sup></td><td>81.54±1.02<sup>e</sup></td><td>1.459±0.653<sup>g</sup></td></tr><tr><td><i>Eichhornia crassipes</i></td><td>16.15±0.13<sup>c</sup></td><td>57.77±0.79<sup>a</sup></td><td>18.558±7.955<sup>a</sup></td><td>73.92±0.46<sup>h</sup></td><td>1.371±0.807<sup>b</sup></td></tr><tr><td rowspan="2">Darack</td><td><i>Prosopis juliflora</i></td><td>18.65±0.73<sup>a</sup></td><td>56.27±1.11<sup>a</sup></td><td>17.892±1.049<sup>c</sup></td><td>74.92±0.92<sup>a</sup></td><td>1.340±0.468<sup>c</sup></td></tr><tr><td><i>Eichhornia crassipes</i></td><td>16.15±0.59<sup>c</sup></td><td>47.17±0.79<sup>a</sup></td><td>18.498±7.785<sup>d</sup></td><td>63.32±0.69<sup>d</sup></td><td>1.171±0.293<sup>h</sup></td></tr></tbody></table>

<figure><img src="image_14.png" /></figure>

<figure><img src="image_15.png" /></figure>

<figure><img src="image_16.png" /></figure>

<figure><img src="image_17.png" /></figure>
The average weight of the stems of the dry dead biomass of *Eichhornia crassipes* is 14.13±3.50 kg/m² while its average weight is 54.47±4.06 kg/m². The average LCV of the dry dead biomass of *Eichhornia crassipes* is 18.52±0.02MJ/kg with its average dry stock is 72.22±6.19 kg/m² and the average stock of its

bioenergy is 1.31±0.103 GJ/m². These values are distributed in the table below:

A total of 5.78 kilograms of dry dead biomass was obtained from the carbonization of a total of 15.42 kilograms of wet dead biomass, distributed as follows:

<table><caption>**Table 6: Preparation of raw materials**</caption><thead><tr><td>Raw material</td><td>Weight before drying (Kg)</td><td>Weight after drying (Kg)</td></tr></thead><tbody><tr><td>Dry dead biomass of Prosopis juliflora</td><td>7.71</td><td>4.24</td></tr><tr><td>Dry dead biomass of Eichhornia crassipes</td><td>7.71</td><td>1.54</td></tr></tbody></table>

The total amount of carbonized raw material used in this study was adjusted to 5 kilograms, consisting of the dry dead biomass of carbonized *Prosopis juliflora* (2.50 kilograms) and the dry dead biomass of

carbonized *Eichhornia crassipes* (2.50 kilograms). The overall preparation process was carried out according to the following diagram:

<figure><img src="image_18.png" /><figcaption>**Figure 2: Raw material processing diagram**</figcaption></figure>

## II-2) Carbonization and preparation of the raw material

### II-2-1) Carbonization process and proportion of binder added

The diagram of the carbonization process of *Prosopis juliflora* and *Eichhornia crassipes* in this study is as follows.

<figure><img src="image_19.png" /><figcaption>**Figure 3: Scheme for producing ecological charcoal based on *Prosopis juliflora* and *Eichhornia crassipes***</figcaption></figure>

The clay binder sifted through the 0.25mm/mm mesh was used and represents 8% of the biomass used to mold

### II-2-2) Mass yield taken from biomass

The carbonization test was carried out 10 times. Each time, the mass yields were evaluated. The mass yield

made it possible to estimate the potential carbon production of the dry dead biomasses of *Prosopis juliflora* and the dry dead biomasses of *Eichhornia crassipes* to be carbonized treated. The determination of the mass yields was recorded in the following table 7:

<table><caption>**Table 7: Mass yield before and after carbonization of raw materials**</caption><thead><tr><td>Raw material</td><td>Weight after carbonization (Kg)</td><td>Mass yield before carbonization (%)</td><td>Mass yield after carbonization (%)</td><td>Net coal mass yield (%)</td></tr></thead><tbody><tr><td>Dry dead biomass of Prosopis juliflora</td><td>1.03</td><td>36.57±2.62</td><td>25.91±0.76</td><td>91.75±3.78</td></tr><tr><td>Dry dead biomass of Eichhornia crassipes</td><td>1.01</td><td>16.02±1.59</td><td>94.35±0.84</td><td>98.42±4.95</td></tr></tbody></table>

The mass yield before carbonization of biomasses whose raw humidity is greater than 50% (H>50%) is 26.29±2.10% while the mass yield after carbonization of biomasses is 60.13±0.80%

Concerning the dry dead biomasses of *Prosopis juliflora*, the quantity of wood introduced into the metal carbonizer made it possible to obtain the net carbonization mass yield of 91.75±3.78% while for the

dry dead biomasses of *Eichhornia crassipes* the quantity of ant energy to the metal carbonizer made it possible to obtain the net mass carbonization yield of 98.42±4.95%.

### II-2-3) Density (D) of the Coal obtained

Then, 15 samples of ecological charcoal of three types of dimensions were made for each of the two species,

<figure><img src="image_20.png" /></figure>

<figure><img src="image_21.png" /></figure>

<figure><img src="image_22.png" /></figure>

<figure><img src="image_23.png" /></figure>
and composite samples of ecological charcoal based on *Prosopis juliflora* linked to *Eichhornia crassipes* were made and presented in Table 8.:

<table><caption>**Table 8:** Sized samples of ecological coal</caption><thead><tr><th rowspan="2">Raw material</th><th colspan="6">Samples of Ecological Coal</th></tr><tr><th>L: 5.3±0.9 cm</th><th>D: 2.7±0.5 cm</th><th>L: 7.4 ±0.3 cm</th><th>D: 2.7±0.5 cm</th><th>L: 10.6±0.7 cm</th><th>D: 2.7±0.5 cm</th></tr></thead><tbody><tr><td>Dry dead biomass of <i>Prosopis juliflora</i></td><td>3</td><td></td><td>3</td><td></td><td>3</td><td></td></tr><tr><td>Dry dead biomass of <i>Eichhornia crassipes</i></td><td>3</td><td></td><td>3</td><td></td><td>3</td><td></td></tr><tr><td>Dry dead biomass of <i>Prosopis juliflora</i> (25%) + <i>Eichhornia crassipes</i> (75%)</td><td>3</td><td></td><td>3</td><td></td><td>3</td><td></td></tr><tr><td>Dry dead biomass of <i>Prosopis juliflora</i> (50%) + <i>Eichhornia crassipes</i> (50%)</td><td>3</td><td></td><td>3</td><td></td><td>3</td><td></td></tr><tr><td>Dry dead biomass of <i>Prosopis juliflora</i> (75%) + <i>Eichhornia crassipes</i> (25%)</td><td>3</td><td></td><td>3</td><td></td><td>3</td><td></td></tr></tbody></table>

With L= Length of the sample in centimeter (cm) and D= Diameter of the sample in centimeter (cm))

These samples were prepared according to the method used by Dzokom (2021), where each was subdivided into triplicates, marked and weighed, and taken for laboratory analysis. Moisture levels, density and

calorific value were determined as described in the following sections. The clay binder was added in the following proportions:

<table><caption>**Table 9:** Proportion of raw material-binder mixed</caption><thead><tr><th>Proportion of clay binder (%)</th><th>2</th><th>5</th><th>8</th><th>10</th></tr></thead><tbody><tr><td>Carbonized and ground <i>Prosopis juliflora</i> (%)</td><td>100/0</td><td>100/0</td><td>100/0</td><td>100/0</td></tr><tr><td><i>Eichhornia crassipes</i> carbonized and ground (%)</td><td>100/0</td><td>100/0</td><td>100/0</td><td>100/0</td></tr><tr><td rowspan="3"><i>Prosopis juliflora</i> and <i>Eichhornia crassipes</i> carbonized and ground (%)</td><td>25/75</td><td>25/75</td><td>25/75</td><td>25/75</td></tr><tr><td>50/50</td><td>50/50</td><td>50/50</td><td>50/50</td></tr><tr><td>75/25</td><td>75/25</td><td>75/25</td><td>75/25</td></tr></tbody></table>

The variation between 0.372±0.053 g/cm³ and 0.405±0.094 g/cm³ indicates that there is significantly a variation in level p<0.05 (F (df=9) =11.528, p=0.0001) for the density. The density of the charcoal obtained from *Prosopis juliflora* (50≤%) and *Eichhornia crassipes* (50≥%) carbonized and ground is

0.395±0.037g/cm³ while the density of the charcoal obtained from *Prosopis juliflora* (50≥%) and *Eichhornia crassipes* (50≤%) carbonized and ground is 0.385±0.083g/cm³. The charcoal based on *Prosopis juliflora* (50%) and *Eichhornia crassipes* (50%) carbonized and ground (% linked to % clay) is 0.391±0.095 g/cm³

<table><caption>**Table 10:** Density of ecological charcoal based on carbonized and ground *Prosopis juliflora* and *Eichhornia crassipes* bound to clay</caption><thead><tr><th>Sample of ecological coal</th><th>Length (L in cm)</th><th>Diameter (D in cm)</th><th>Volume (cm³)</th><th>Weight of dry coal sample (g)</th><th>Density (g/cm³)</th></tr></thead><tbody><tr><td><i>Prosopis juliflora</i> charred and ground (100/0%)</td><td>5.343±0.932</td><td>2,678±0.345</td><td>30.329±3.049</td><td>11.226±3.054</td><td>0.372±0.053</td></tr><tr><td><i>Eichhornia crassipes</i> carbonized and ground (100/0%)</td><td>5.273±0.798</td><td>2,734±0.495</td><td>30.327±3.047</td><td>11.838±3.056</td><td>0.396±0.061</td></tr><tr><td><i>Prosopis juliflora</i> and <i>Eichhornia crassipes</i> carbonized and ground (25/75%)</td><td>7.417±0.283</td><td>2,677±0.385</td><td>42.351±2.809</td><td>16.945±1.842</td><td>0.405±0.094</td></tr><tr><td><i>Prosopis juliflora</i> and <i>Eichhornia crassipes</i> carbonized and ground (50/50%)</td><td>7.394±0.276</td><td>2,667±0.485</td><td>42.352±2.808</td><td>16.515±1.843</td><td>0.397±0.091</td></tr><tr><td><i>Prosopis juliflora</i> and <i>Eichhornia crassipes</i> carbonized and ground (75/25%)</td><td>10.611±0.647</td><td>2,657±0.485</td><td>60.659±1.957</td><td>23.051±2.914</td><td>0.382±0.026</td></tr></tbody></table>

### II-3) Physico-chemical characterization of fuel samples based on *Prosopis juliflora* linked to *Eichhornia crassipes*

The average humidity level before drying (48.89±14.03%) induces low average surface/volume

ratios of ecological coal of 23.20±0.48 mm⁻¹, low porosity (0.17±0.01) and a low average impact resistance index of coal (69.37±5.93%).

<table><caption>**Table 11:** Physico-chemical characteristics</caption><thead><tr><th>Settings</th><th><i>Prosopis juliflora</i> carbonized and ground (100/0%)</th><th><i>Eichhornia crassipes</i> carbonized and ground (100/0%)</th><th><i>Prosopis juliflora</i> and <i>Eichhornia crassipes</i> carbonized and ground</th><th><i>Prosopis juliflora</i> and <i>Eichhornia crassipes</i> carbonized</th><th><i>Prosopis juliflora</i> and <i>Eichhornia crassipes</i> carbonized</th></tr></thead></table>

<figure><img src="image_24.png" /></figure>

<figure><img src="image_25.png" /></figure>

<figure><img src="image_26.png" /></figure>

<figure><img src="image_27.png" /></figure>
<table><thead><tr><th></th><th></th><th></th><th>ground<br>(25/75%)</th><th>and ground<br>(50/50%)</th><th>and ground<br>(75/25%)</th></tr></thead><tbody><tr><td colspan="2">Moisture content before drying (%)</td><td>42.73±0.06</td><td>73.92±0.54</td><td>43.85±0.07</td><td>41.17±0.72</td><td>42.76±0.16</td></tr><tr><td colspan="2">Coal surface/volume ratio (mm-1)</td><td>22.68 ± 3.97</td><td>23.55±2.51</td><td>22.68±1.64</td><td>23.53±1.76</td><td>23.57±3.07</td></tr><tr><td rowspan="2">Density of<br>coal (gr/ml)</td><td>Skeletal (psq)</td><td>354.48±203.65</td><td>350.57±250.71</td><td>356.83±100.07</td><td>351.03±110.09</td><td>350.27±80.37</td></tr><tr><td>Apparent (gapp)</td><td>438.50±32.60</td><td>423.29±20.85</td><td>427.36±05.65</td><td>427.18±58.72</td><td>422.94±30.61</td></tr><tr><td colspan="2">Porosity</td><td>0.63</td><td>0.74</td><td>-0.29</td><td>-0.58</td><td>-0.67</td></tr><tr><td colspan="2">Coal impact resistance index (%)</td><td>76.53±4.11</td><td>74.66±2.73</td><td>64.26±0.65</td><td>63.65±0.87</td><td>67.73±0.46</td></tr><tr><td colspan="2">Coal moisture recovery rate (%)</td><td>1.34±0.67</td><td>1.65±0.14</td><td>1.76±0.36</td><td>1.49±0.52</td><td>1.55±0.72</td></tr><tr><td colspan="2">Coal volatile matter rate (%)</td><td>76.97±1.63</td><td>26.87±1.43</td><td>49.25±0.53</td><td>62.74±0.39</td><td>72.79±0.84</td></tr><tr><td colspan="2">Fixed carbon rate of coal (%)</td><td>19.39±1.82</td><td>84.43±1.29</td><td>52.55±1.76</td><td>64.86±1.26</td><td>69.98±1.79</td></tr></tbody></table>

The average rate of fixed carbon (58.24±24.54%) and the average rate of volatile matter in the coal II-4) Combustion tests

(57.72±20.29%) induce a low average rate of moisture recovery in the coal (1, 56±0.16%) after storage. The average ignition temperature is 120.4±1.14°C, useful for an average coal combustion duration of 20.4±1.15 minutes.

<table><caption>Table 12: Combustion tests</caption><thead><tr><th>Settings</th><th>Prosopis juliflora<br>carbonized<br>and ground<br>(100/0%)</th><th>Eichhornia crassipes<br>carbonized<br>and ground<br>(100/0%)</th><th>Prosopis juliflora<br>and Eichhornia<br>crassipes<br>carbonized<br>and ground<br>(25/75%)</th><th>Prosopis juliflora<br>and Eichhornia<br>crassipes<br>carbonized<br>and ground<br>(50/50%)</th><th>Prosopis juliflora<br>and Eichhornia<br>crassipes<br>carbonized<br>and ground<br>(75/25%)</th></tr></thead><tbody><tr><td>Ignition temperature/Ease of<br>ignition of coal (T°al in °C)</td><td>122±3.46</td><td>120±2.08</td><td>121±8.05</td><td>120±3.72</td><td>119±8.97</td></tr><tr><td>Coal burning time (minute)</td><td>19±4.47</td><td>22±0.08</td><td>20±0.43</td><td>21±0.56</td><td>20±0.32</td></tr></tbody></table>

## II-5) Water boiling tests

During the water boiling test with fuels based on carbonized and ground *Prosopis juliflora* and *Eichhornia crassipes*, the average start of boiling was observed from 11.39±0.38 minutes with a duration of boiling time of

103±3.39 minutes. These times were observed during the boiling test of 1000 milliliters of water, at the end of which an average of 174.8±14.20 milliliters remained when 825.2±14.20 milliliters remained

<table><caption>Table 13: Water boiling tests</caption><thead><tr><th>Water Boiling Test Parameters with Fuels</th><th>Prosopis juliflora<br>carbonized<br>and ground<br>(100/0%)</th><th>Eichhornia crassipes<br>carbonized<br>and ground<br>(100/0%)</th><th>Prosopis juliflora and<br>Eichhornia<br>crassipes<br>carbonized and<br>ground<br>(25/75%)</th><th>Prosopis juliflora and<br>Eichhornia<br>crassipes<br>carbonized<br>and ground<br>(50/50%)</th><th>Prosopis juliflora<br>and Eichhornia<br>crassipes<br>carbonized<br>and ground<br>(75/25%)</th></tr></thead><tbody><tr><td>Start of boiling (min)</td><td>11.22±4.36</td><td>12.06±0.82</td><td>11.21±0.85</td><td>11.26±2.37</td><td>11.19±0.27</td></tr><tr><td>Boiling time (min)</td><td>109±2.06</td><td>102±0.28</td><td>101±0.58</td><td>102±2.37</td><td>101±2.91</td></tr><tr><td>Amount of water remaining (milliliter)</td><td>159±4.36</td><td>168±2.68</td><td>172±5.08</td><td>178±2.37</td><td>197±4.82</td></tr><tr><td>Quantity of water evaporated (milliliter)</td><td>841±0.49</td><td>832±0.86</td><td>828±0.93</td><td>822±0.88</td><td>803±0.36</td></tr></tbody></table>

## II-5) Energy efficiency of fuels

With an average calorific value of ecological coal of 17.56±0.96 kJ/kg, the specific heat capacity of ecological coal is 0.596±0.004 kJ/kg/K. The average

conversion efficiency of plants into ecological coal is 1.585±0.807% with an energy production during the combustion of coal of 8360 Joules.

<table><caption>Table 14: Fuel energy efficiency tests</caption><thead><tr><th>Water boiling test<br>parameters with these fuels</th><th>Prosopis<br>juliflora<br>carbonized<br>and ground<br>(100/0%)</th><th>Eichhornia<br>crassipes<br>carbonized<br>and ground<br>(100/0%)</th><th>Prosopis juliflora<br>and Eichhornia<br>crassipes<br>carbonized and<br>ground (25/75%)</th><th>Prosopis juliflora<br>and Eichhornia<br>crassipes<br>carbonized and<br>ground (50/50%)</th><th>Prosopis juliflora<br>and Eichhornia<br>crassipes<br>carbonized and<br>ground (75/25%)</th></tr></thead><tbody><tr><td>Calorific value of coal<br>(kJ/kg)</td><td>17.987±0.208</td><td>15.876±0.759</td><td>17.794±0.123</td><td>17.845±0.283</td><td>18.311±0.357</td></tr><tr><td>Specific heat capacity of<br>coal (kJ/kg/K)</td><td>0.603±0.082</td><td>0.595±0.095</td><td>0.599±0.079</td><td>0.595±0.059</td><td>0.591±0.053</td></tr><tr><td>Energy of combustion of<br>coal fuels (Joules)</td><td>8360±350.7</td><td>4180±649.5</td><td>4180±507.3</td><td>4180±570.5</td><td>12540±735.0</td></tr></tbody></table>

<figure><img src="image_28.png" /></figure>

<figure><img src="image_29.png" /></figure>

<figure><img src="image_30.png" /></figure>

<figure><img src="image_31.png" /></figure>
<table><tr><td>Conversion yield of plants into coal (%)</td><td>1.007±0.043</td><td>2.957±0.064</td><td>1.585±0.052</td><td>1.239±0.075</td><td>1.065±0.006</td></tr></table>

## II-4)- Evaluation of net carbon destocking linked to the quantity of ecological coal consumed in households on site

Depending on the size of households, the average ecological coal consumed is 241.328±93.974 kg/Households/year with an average carbon released of 13.598±5.637 kg CO₂/Households/year. These quantities are distributed as follows:

<table><caption>Table 15: Assessment of carbon destocking by household size</caption><thead><tr><th>Size of households (No. of inhabitants)</th><th>Ecological coal consumed (kg/Households/year)</th><th>Carbon released (kg CO₂/Households/year)</th></tr></thead><tbody><tr><td>[0-5]</td><td>136.65±5.90</td><td>07.584±0.225</td></tr><tr><td>[5-10]</td><td>185.36±6.98</td><td>10.795±3.637</td></tr><tr><td>[10-15]</td><td>235.59±5.32</td><td>13.721±2.453</td></tr><tr><td>[15-20]</td><td>260.82±5.62</td><td>15.191±3.644</td></tr><tr><td>[20-25]</td><td>388.22±5.63</td><td>22.609±2.653</td></tr></tbody></table>

Depending on the age group and gender, the average of ecological carbon consumed by women (125.976±111.745kg/Households/year) is higher than by men (18.879±9.980kg/Households/year) with an average of carbon destocked by activities carried out by women (9.321±3.724kg CO₂/Households/year) higher than by activities carried out by men (1.130±0.449kg CO₂/Households/year). The age group that uses ecological coal the most is [25-45]years while the age group that uses the least ecological coal is [0-5]years (Table). These quantities are distributed as follows:

<table><caption>Table 16: Assessment of carbon destocking by age group and sex</caption><thead><tr><th rowspan="2">Age (years)</th><th colspan="2">Ecological coal consumed (kg/year)</th><th colspan="2">Carbon released (kg CO₂/year)</th></tr><tr><th>Man</th><th>Woman</th><th>Man</th><th>Woman</th></tr></thead><tbody><tr><td>[0-5]</td><td>6.13±0.65</td><td>6.13±0.65</td><td>0.92±0.05</td><td>7.58±0.97</td></tr><tr><td>[5-25]</td><td>24.84±0.85</td><td>205.36±0.90</td><td>1.31±0.74</td><td>10.79±0.65</td></tr><tr><td>[25-45]</td><td>28.50±0.63</td><td>235.59±8.62</td><td>1.66±0.45</td><td>13.72±0.71</td></tr><tr><td>45 years and over</td><td>16.02±0.52</td><td>56.82±3.72</td><td>0.63±0.08</td><td>5.19±0.16</td></tr></tbody></table>

In the study site, the average ecological coal consumed is 59.208±12.032 kg/inhabitant/year with an average carbon released of 3.209±0.130kg CO₂/inhabitant/year. Ecological coal is consumed more by the inhabitants of Koussérie (71.35kg/inhabitant/year) and less consumed by the inhabitants of Darack (44.14kg/inhabitant/year). These quantities are distributed as follows:

<table><caption>Table 17: Evaluation of carbon destocking by study sites</caption><thead><tr><th>Study sites</th><th>Ecological coal consumed (kg/year)</th><th>Carbon released (kg CO₂/year)</th></tr></thead><tbody><tr><td>Koussérie</td><td>71.35±4.46</td><td>3.43±0.01</td></tr><tr><td>Makary</td><td>67.01±2.87</td><td>3.13±0.73</td></tr><tr><td>Hile Alifa</td><td>48.65±1.48</td><td>3.22±0.85</td></tr><tr><td>Blangoua</td><td>64.89±2.29</td><td>3.13±0.74</td></tr><tr><td>Darack</td><td>44.14±1.77</td><td>3.12±0.86</td></tr></tbody></table>

## II-5)- Evaluation of net sequestration linked to households using mixed energy in the study sites

It is interesting to put into perspective the net sequestration of CO₂ linked to households using mixed energy in the study sites with regard to the carbon reduction generated by the local consumption of biomass through the energy use of cooking. The evaluation carried out here thus presents the carbon impact of the current level of exploitation of vegetation for wood energy use in the study area.

<figure><img src="image_32.png" /><figcaption>Table 18: Evaluation of net sequestration linked to households using mixed energy</figcaption></figure>

<figure><img src="image_33.png" /></figure>

<figure><img src="image_34.png" /></figure>

<figure><img src="image_35.png" /></figure>
<table><thead><tr><th>Study sites</th><th>Ecological coal consumed (kg/inhabitant/year)</th><th>Other forms of energy (wood energy) consumed (kg/inhabitant/year)</th><th>Carbon released when using ecological coal (kg CO<sub>2</sub>/inhabitant/year)</th><th>Carbon released when using ecological coal use of other forms of energy (wood energy) (kgCO<sub>2</sub>/inhabitant/year)</th><th>Conversion factors</th></tr></thead><tbody><tr><td>Kousserie</td><td>5.880±0.813</td><td>583.412±56.612</td><td>3.413±0.767</td><td>110.848±05.534</td><td>0.992±0.321</td></tr><tr><td>Makary</td><td>5.343±0.018</td><td>513.03±76.518</td><td>3.133±0.829</td><td>97.476±4.902</td><td>0.960±0.566</td></tr><tr><td>Hile Alifa</td><td>5.536±0.871</td><td>532.23±35.287</td><td>3.223±0.014</td><td>101.124±02.546</td><td>0.961±0.030</td></tr><tr><td>Blangoua</td><td>5.363±0.602</td><td>513.26±29.248</td><td>3.126±0.652</td><td>97.519±0.097</td><td>0.957±0.554</td></tr><tr><td>Darack</td><td>5.897±0.703</td><td>534.31±87.535</td><td>3.431±0.032</td><td>101.519±0.072</td><td>0.907±0.076</td></tr></tbody></table>

The average harvest of wood for energy use on each site was estimated at approximately 535,248±28,751 kg/inhabitant/year, the carbon released during the use of other forms of energy (wood energy) (kgCO₂/inhabitant/year) for the year 2023. This estimate comes from a surface ratio of the wood harvest on the scale of the Logone and Chari area, the source data of which is extracted from the analysis report of the wood sector published by the environmental NGO SAHEL NATURE CONSULTING in May 2024. By this calculation, a rate of surface exploitation of forests in Sahelian territories similar to that of the Logone and Chari area, in Diamaré and Mayo Tsanaga was considered. Considering the conversion factors of 0.955±0.030 tons of chips/m³ of round wood from the Logone and Chari zone as well as an average humidity rate of the chips at 35.4%, the wood energy harvest has generated 101.697±5.462 kgCO₂/inhabitant/year during combustion. These CO₂ emissions correspond to 9.78% of the CO₂ storage provided by the forest cover.

The effects of substituting wood energy with ecological coal has enabled the development of the use of products and cooking energies from invasive plants valued thanks to the following orders of magnitude proposed by SAHEL NATURE CONSULTING (2023):

* 1.05 ton of *Prosopis juliflora* wood products can produce on average 0.233 ton of raw anhydrous charcoal;

* 1.05 ton of dry biomass of *Prosopis juliflora* makes it possible to obtain on average 0.971 ton of ecological charcoal without binder and 1.271 ton of ecological charcoal with binder;

* 1.05 ton of dry *Prosopis juliflora* biomass transformed into ecological charcoal and used in the form of cooking energy releases 0.199 ton CO₂/year of Carbon while wood.

* 1.05 ton of dry biomass of *Eichhornia crassipes* makes it possible to obtain on average 0.989 ton of ecological coal without binder and 1.243 ton of ecological coal with binder;

* 1.05 ton of dry *Eichhornia crassipes* biomass transformed into ecological charcoal and used in the form of cooking energy releases 0.087 Ton of CO₂/year of Carbon.

* 1.05 ton of the mixture of dry biomass of *Prosopis juliflora* and *Eichhornia crassipes*, all proportions combined, makes it possible to obtain on average 0.918 ton of ecological charcoal without binder and 1.267 ton of ecological charcoal with binder and used in the form of cooking energy destocked on average 0.193 ton CO₂/year of Carbon.

## II-6) Index of the Ecological Value of Ecological Coal (IVEcoC)

For an average weight of dry ecological coal produced (46.44±23.49 ton/year), harvested previously on an area of 0.6±0.2 Ha, the average rate of fixed carbon is 58.24±24.54%. 1194.31±1512.21 ton/year of CO₂ sequestered by ecological coal in 2024 induces an average environmental compensation of 155.72±72.96 plants/Ha to be planted

<table><caption>Table 19: Ecological Value Index of Ecological Coal</caption><thead><tr><th>Water Boiling Test Parameters with Fuels</th><th><em>Prosopis juliflora</em> carbonized and ground (100/0%)</th><th><em>Eichhornia crassipes</em> carbonized and ground (100/0%)</th><th><em>Prosopis juliflora</em> and <em>Eichhornia crassipes</em> carbonized and ground (25/75%)</th><th><em>Prosopis juliflora</em> and <em>Eichhornia crassipes</em> carbonized and ground (50/50%)</th><th><em>Prosopis juliflora</em> and <em>Eichhornia crassipes</em> carbonized and ground (75/25%)</th></tr></thead><tbody><tr><td>Weight of dry ecological coal produced (kg)</td><td>50±0.2</td><td>5±0.1</td><td>59.7±2.4</td><td>58.9±3.3</td><td>58.6±4.9</td></tr><tr><td>Fixed carbon rate (%)</td><td>19.39±1.82</td><td>84.43±1.29</td><td>52.55±1.76</td><td>64.86±1.26</td><td>69.98±1.79</td></tr><tr><td>Biomass harvesting area (Ha)</td><td>0.25</td><td>0.50</td><td>0.75</td><td>0.75</td><td>0.75</td></tr><tr><td>Quantity of CO<sub>2</sub> sequestered by ecological coal (T/year)</td><td>3878±0.55</td><td>844.30±0.65</td><td>4182.98±0.87</td><td>5093.67±0.34</td><td>5467.77±0.38</td></tr><tr><td>Quantity of carbon released from ecological charcoal during cooking (T/year)</td><td>751.94±43.55</td><td>712.84±08.40</td><td>2198.15±06.87</td><td>3303.75±30.23</td><td>3826.34±60.59</td></tr><tr><td>Environmental compensation (Number of plants/Ha/month)</td><td>155.12±04.35</td><td>33.72±06.89</td><td>167.32±08.43</td><td>203.75±09.54</td><td>218.71±07.34</td></tr></tbody></table>

<figure><img src="image_36.png" /></figure>

<figure><img src="image_37.png" /></figure>

<figure><img src="image_38.png" /></figure>

<figure><img src="image_39.png" /></figure>
<table><tr><td>Ecological Value Index of Ecological Coal</td><td>3.759</td><td>71.284</td><td>27.614</td><td>42.068</td><td>48.971</td></tr></table>

The Ecological Value Index of carbonized and ground *Prosopis juliflora* (100/0%) less (3.759) than that of carbonized and ground *Eichhornia crassipes* (100/0%) (71.284).

<figure><img src="image_40.png" /><figcaption>Photo4: *Prosopis juliflora* wood</figcaption></figure>

The Ecological Value Index of *Prosopis juliflora* linked to carbonized and ground *Eichhornia crassipes* (75/25%) is 48.971, which makes it ecologically viable for the production of ecological charcoal, following *Prosopis juliflora*.

## DISCUSSION

The Intergovernmental Panel on Climate Change (IPCC) and other scientific committees estimate that up to 25% of CO₂ absorption from the atmosphere comes from forests [28]. Therefore, the Ecological Value Index of *Prosopis juliflora* linked to carbonized and ground *Eichhornia crassipes* (25/75%) is 47.46, while that of *Prosopis juliflora* is higher at 80.62. This indicates that there is a high carbon stock in carbonized and ground *Eichhornia crassipes*-related *Prosopis juliflora* (25/75%).

The local combustion of ecological coal for energy use releases on average approximately 0.193±0.011 Ton CO₂/inhabitant/year, i.e. a total of approximately 322.463±408.296 Kg Carbon/inhabitant/year and 1194.31±1512.21 TCO₂/year in the locality, inducing an average environmental compensation between 155.72±20.01 and 196.59±31.09 plants/Ha/month, or between 467.16±60.03 and 598.50±93.27 plants/Ha/year to be planted during the good season. Carbon stock sequestration is estimated at 16.39 tC/Ha for Agroforests, 12.64 tC/Ha for dense semi-deciduous forests/forest galleries and 6.44 tC/Ha for tree/shrub savannahs in the plant formations of the Akposso Plateau (Togo) [25]. Considering overall that a mature tree sequesters at least on average 167 kg of CO₂/year [2], the recovery of 10,509 kg of the dead biomass of *Prosopis juliflora* linked to carbonized and ground *Eichhornia crassipes* makes it possible to preserve on average around 218.71±07.34 *Azadirachta indica* trees/Ha/month, the most resilient ornamental plants adapted to the climatic contexts of the Sahelian city of Maroua. Thus, it is possible to fix on average 5467.77±0.38 kg of CO₂/hectare/year (i.e. 14.98±1.04 CO₂/hectare/day of aerial biomass only), putting the potential for release of the carbon of ecological coal during cooking at 3826.34±60.59 tons/year of carbon, or approximately 10.48±0.16 tons of carbon/day [2]. The carbon balance allows us to conclude that the carbon sequestration potential from ecological coal is

significantly greater than the carbon release potential of ecological coal, which is an ecological indicator that is very beneficial for the environment.

## CONCLUSION

In the Sahel in general and the Cameroonian Lake Chad area in particular, *Prosopis juliflora* is one of the invasive plants and the firewood of *Prosopis juliflora* provides 45% of the energy needs of rural areas due to the fact that it is considered to be a wood whose smoke is irritating to the eyes in kitchens. On average, a total of 73.87±7.24 individuals/Hectare was recorded in the ten study sites. The main objective of this study was to evaluate the ecological quality of charcoal produced from *Prosopis juliflora* linked to *Eichhornia crassipes* and to determine its ecological index value. The collection and preparation of samples of ecological charcoal based on dry dead biomasses of *Prosopis juliflora* and *Eichhornia crassipes* made it possible to collect in bulk in nature 16.80±1.54 T/Ha of *Prosopis juliflora* and on average 197.77±0.79 T/Ha of *Eichhornia crassipes*. For an average weight of 46.44±23.49 kg of the dry ecological coal produced, previously harvested on an area of 0.6±0.2 Ha, an average weighted mass yield of ecological coal of 90.096±1 was observed. 5136%, with an average fixed carbon rate of 58.24±24.54%. The eco-friendly coal was produced by carbonization at 450°C and characterized for analysis and immediate use. The density of the charcoal obtained from *Prosopis juliflora* (50≤%) and *Eichhornia crassipes* (50≥%) carbonized and ground is 0.395±0.037g/cm³ while the density of the charcoal obtained from *Prosopis juliflora* (50≥%) and *Eichhornia crassipes* (50≤%) carbonized and ground is 0.385±0.083g/cm³. The density of charcoal based on carbonized and ground *Prosopis juliflora* (50%) and *Eichhornia crassipes* (50%) (% bound to % clay) is 0.391±0.095 g/cm³. The Ecological Value Index of carbonized and ground *Prosopis juliflora* (100/0%) higher (80.62) than that of carbonized and ground *Eichhornia crassipes* (100/0%) (15.58). The Ecological Value Index of *Prosopis juliflora* linked to carbonized and ground *Eichhornia crassipes* (25/75%) is 47.46, which makes it ecologically viable for the production of ecological charcoal, following *Prosopis juliflora*. The physicochemical characterization of fuel samples based on *Prosopis juliflora* linked to *Eichhornia crassipes* made it possible to obtain an average humidity level before drying (48.89±14.03%), a low porosity (0.17±0.01) and a low average impact resistance index of coal (69.37±5.93%). The average rate of fixed carbon (58.24±24.54%) and the average rate of volatile matter in the coal (57.72±20.29%) induce a low average rate of moisture recovery in the coal (1.56±0.16%) after storage.

The collection and preparation of 1.05±0.32 Tons of the mixture of dry and dead biomass of *Prosopis juliflora* and *Eichhornia crassipes*, made it possible to obtain on average 0.918±0.234 Tons of ecological carbon without binder and 1.267±0.342 Ton of ecological

<figure><img src="image_41.png" /></figure>
coal with binder. The local combustion of ecological coal for energy use releases on average approximately 0.193±0.011 Ton CO2/day, or 1194.31±1512.21 Ton CO2/year, inducing an average environmental compensation of 155.72±20.01 at 196.59±31.09 plants/Ha/month, or between [467.16±60.03; 598.50±93.27] plants/Ha/year to be planted during the good season.

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