**3. Environmental usefulness of biochar**

## **3.1 Biochar from biomass as a fertilizer and a soil conditioner**

The use of biochar from plant biomass as a soil fertilizer or conditioner has received significant attention in the recent past [12]. Formerly, extractions from the fermentation of bioethanol and flavonoids as well as recoveries from chemicals have also been applied as organic soil fertilizers [22]. However, the residues from

**127**

**Table 2.**

feedstocks.

*Biochar Potential in Improving Agricultural Production in East Africa*

organic carbon while minimizing greenhouse gas (GHG) emissions [2].

**3.2 The potential of biochar in carbon sequestration**

*Biochar nutrients proportion from various biomass feedstocks (in g kg<sup>−</sup><sup>1</sup>*

fermentation processes have short lifespans. They are uneconomical to use as fertilizer because of their high moisture content. Thus, the need to develop alternative products from sustainable thermal conversion ways has put the use of biochar into perspective [23]. This is key since the conventional method of leaving raw biomass wastes on the soil to degrade naturally has remarkable risks primarily due to high bulk density, high moisture content, and the hygroscopic nature. Further, the biomasses contribute to air and water pollution and greenhouse effects via smoke resulting from burning. On the other hand, the use of biochar has been cited as a viable way of stabilizing soil

Biochar has been identified as a carbon-neutral bioenergy resource capable of enhancing soil conditions for better agriculture. It can also aid in curbing greenhouse emission effects and global warming [24]. Biochar as a carbon sequester can significantly contribute to agricultural productivity through the improvement of soil fertility and controlled pollution of rivers and groundwater, which are threatened by continued unsustainable agrarian practices [25]. Besides influencing carbon content in the soil, fresh biochar is instrumental in immobilization of nitrogen, improvement of soil pH and soil structure [1]. Further, soils affected by continuous leaching due to herbicides application, research has shown that biochar can curb the leaching process and assist in reigniting microbial activity in the soil [24, 26]. The following biomass feedstocks have been used for biochar production to utilize it as a fertilizer: microalgae [24], eucalyptus crop residues, castor meal, coconut pericarp, sugarcane bagasse [27], water hyacinth [28], and banana wastes [29]. **Table 2** illustrates the biochar nutrient contents of various biomass

The potential of biochar as a viable tool to carbon sequestration has recently been centered on the common discourse of climate change. Biochar has been pointed out to enhance carbon sinks, especially in dry regions [32]. However, the degree with which biochar achieves carbon sequestration depends on various factors. Most importantly, it depends on the desired soil carbon content and the rate of carbon dioxide removal from the atmosphere [3]. There are considerable large sizes of arable lands (estimated at 6% of the earth's surface); thus, they require relatively high amounts of biochar to be incorporated therein. Ideally, up to 90 tons of biochar per hectare should be incorporated into the farms compared to the current recommendations of 50 tons of biochar in a hectare [1] to help in reducing the level of carbon dioxide in the atmosphere. Since it takes long to sequester carbon dioxide

**Residue N P K C Ca Mg** Wheat straw 0.21 2.90 18.29 7.70 4.30 Maize cob 10.8 0.45 9.40 429 0.18 1.70 Maize stalk 8.1 2.10 0.03 427 4.70 5.90 Forest residue 1.6 0.29 0.11 39 130 19.0 Peanut 15.0 2.4 — 429 — — Soybean 23.8 0.9 — 441 — — Rice husk 0.3 0.16 0.48 36 1.63 —

*) [27, 30, 31].*

*DOI: http://dx.doi.org/10.5772/intechopen.92195*

### *Biochar Potential in Improving Agricultural Production in East Africa DOI: http://dx.doi.org/10.5772/intechopen.92195*

*Applications of Biochar for Environmental Safety*

**Temperature range (°C)**

Fast pyrolysis 500–1250 Very fast

Hydropyrolysis 500–1000 Very fast in

Slow pyrolysis 350–800 Slow (<10°C/min) Atmospheric Hours–

Vacuum pyrolysis 450–600 Slow Low (0.05–

Gasification 700–1500 Moderate–very fast Atmospheric-

(10–200°C/sec)

hydrogen

Torrefaction 200–300 Slow (<10°C/min) Atmospheric Minutes–

Flash pyrolysis 900–1200 Fast Elevated 0.1–1 s Biocarbon/

**Thermochemical process**

Intermediate pyrolysis

*Source: Omulo [17].*

**Table 1.**

*products.*

The lower heating rates and longer retention time enable vapor formed from

*Thermochemical processes, their representative reaction conditions, particle residence times, and primary* 

**2.3 Slow pyrolysis versus traditional charcoal making**

**3. Environmental usefulness of biochar**

**3.1 Biochar from biomass as a fertilizer and a soil conditioner**

The use of biochar from plant biomass as a soil fertilizer or conditioner has received significant attention in the recent past [12]. Formerly, extractions from the fermentation of bioethanol and flavonoids as well as recoveries from chemicals have also been applied as organic soil fertilizers [22]. However, the residues from

complete secondary reactions to be eliminated, thus forming the solid carbonaceous

**Heating rate Pressure Residence** 

Vacuum– atmospheric

0.20 MPa)

High (5–20 MPa)

elevated

500–650 0.1–10°C/sec Low (0.1 MPa) 5–35 min Bio-oil/

**time**

days

hours

Seconds– minutes

10–20 s Bio-oil

Hours Biochar

10–20 s Bio-oil

**Primary product**

Biochar

char

biochar

Stabilized, friable biomass

Syngas/ producer gas

Charcoal has been used as a perennial fuel for domestic heating. In practice, charcoal is made by slow burning of wood in the absence of oxygen at mild to high temperatures [22]. Even though the charcoal making process can be referred as slow pyrolysis, the initial heat required to ignite the reaction is generated by burning part of the wood or the feedstock making it hard to achieve inert environment. For a typical slow pyrolysis process, the heat needed to decompose the feedstock thermally is supplied externally via an indirect heating medium. In contrast to the charcoal making process, the feedstock remains in airtight vessels or reactors [8]. Thus, the goal of slow pyrolysis is to yield a biochar product with high energy and carbon content. This is besides other by-products like pyroligneous acid or wood tar and non-combustible or syngas.

**126**

biochar [10, 11, 19–21].

fermentation processes have short lifespans. They are uneconomical to use as fertilizer because of their high moisture content. Thus, the need to develop alternative products from sustainable thermal conversion ways has put the use of biochar into perspective [23]. This is key since the conventional method of leaving raw biomass wastes on the soil to degrade naturally has remarkable risks primarily due to high bulk density, high moisture content, and the hygroscopic nature. Further, the biomasses contribute to air and water pollution and greenhouse effects via smoke resulting from burning. On the other hand, the use of biochar has been cited as a viable way of stabilizing soil organic carbon while minimizing greenhouse gas (GHG) emissions [2].

Biochar has been identified as a carbon-neutral bioenergy resource capable of enhancing soil conditions for better agriculture. It can also aid in curbing greenhouse emission effects and global warming [24]. Biochar as a carbon sequester can significantly contribute to agricultural productivity through the improvement of soil fertility and controlled pollution of rivers and groundwater, which are threatened by continued unsustainable agrarian practices [25]. Besides influencing carbon content in the soil, fresh biochar is instrumental in immobilization of nitrogen, improvement of soil pH and soil structure [1]. Further, soils affected by continuous leaching due to herbicides application, research has shown that biochar can curb the leaching process and assist in reigniting microbial activity in the soil [24, 26]. The following biomass feedstocks have been used for biochar production to utilize it as a fertilizer: microalgae [24], eucalyptus crop residues, castor meal, coconut pericarp, sugarcane bagasse [27], water hyacinth [28], and banana wastes [29]. **Table 2** illustrates the biochar nutrient contents of various biomass feedstocks.

### **3.2 The potential of biochar in carbon sequestration**

The potential of biochar as a viable tool to carbon sequestration has recently been centered on the common discourse of climate change. Biochar has been pointed out to enhance carbon sinks, especially in dry regions [32]. However, the degree with which biochar achieves carbon sequestration depends on various factors. Most importantly, it depends on the desired soil carbon content and the rate of carbon dioxide removal from the atmosphere [3]. There are considerable large sizes of arable lands (estimated at 6% of the earth's surface); thus, they require relatively high amounts of biochar to be incorporated therein. Ideally, up to 90 tons of biochar per hectare should be incorporated into the farms compared to the current recommendations of 50 tons of biochar in a hectare [1] to help in reducing the level of carbon dioxide in the atmosphere. Since it takes long to sequester carbon dioxide


### **Table 2.**

*Biochar nutrients proportion from various biomass feedstocks (in g kg<sup>−</sup><sup>1</sup> ) [27, 30, 31].* from the atmosphere, the predisposition asserted by industrial activities makes the process even longer. This means that even though biochar has the potential to sequester carbon, sustainable land use change and pollution control are indispensable. With improved and cheaper innovations like pyrolysis techniques, biochar productions potentially depend on biomass availability [3, 17, 27]. **Table 3** highlights the average agricultural wastes across East African countries generated from the major food crops [33].
