**2.2 Production process**

Thermochemical conversion technologies are more popular than biochemical conversion technologies in case of biochar production as the rate of hydrogen production and yield are quite lower in the later. The former can further be divided into combustion, pyrolysis and gasification. Different thermochemical processes involved in biochar production are shown in **Figure 1**. Biochar which is obtained by slow pyrolysis from biomass waste (agricultural, municipal, animal, or industrial sources), is highly porous, fine-grained, carbon dominant product rich in paramagnetic centres having both organic and inorganic nature, with large surface area possessing oxygen functional groups and aromatic surfaces [9] with the primary goal of soil improvement. The pyrolysis temperatures generally employed ranges from 300 to 1000°C. Different types of pyrolysis along with their operating conditions are summarized in **Table 1**. In the absence of oxygen, Pyrolysis rapidly heats biomass, driving off carbon monoxide and hydrogen and turning the residue into biochar, a carbon rich solid. In this process, a mixture of volatile gases is released which can be captured and condensed into an energydense liquid called bio-oil. Further it can be refined into diesel and other hydrocarbon products. Recently, it has been reported that biochar obtained from the carbonization of organic wastes can be a substitute that not only influences the sequestration of soil carbon but also modifies its physicochemical and biological properties [15].

*Biochar: A Sustainable Approach for Improving Soil Health and Environment DOI: http://dx.doi.org/10.5772/intechopen.97136*

#### **Figure 1.**

*Different thermochemical processes for biochar production.*


#### **Table 1.**

*Types of pyrolysis and their operating conditions for biochar production.*

#### **2.3 Factors associated with biochar quality**

Specifically, the quality of biochar depends on several factors, such as the type of soil, metal, and the raw material used for carbonization, the pyrolysis conditions, and the amount of biochar applied to the soil (**Figure 2**).

The tendency of the surface functional groups to attract positive charges enhances the cation exchange capacity, which is an important property of biochar for remediation of metal-contaminated soils. The advantages of biochar with various physiochemical properties are shown in **Figure 3** [16].

The physical properties of biochar play significant role to its function as a tool for managing the environment. Research has been shown that biochar, when used as a soil amendment, improves soil quality and boosts soil fertility by increasing the

**Figure 2.**

*Schematic diagram of factors affecting the quality of biochar.*

**Figure 3.** *Physicochemical properties of biochar.*

moisture retaining capacity, soil pH, cation exchange capacity, attracting more beneficial fungi and other microbes, and preserving the nutrients in the soil. Biochar increases soil aeration and cation-exchange capacity, reduces soil hardening and soil density and changes the soil structure and consistency by changing the physical and chemical properties. In drought prone areas, the effects of drought on crop productivity can be reduced by addition of biochar due to its moisture-retention capacity. It has also been reported that it eliminates soil constraints that limit the growth of plants, and neutralizes acidic soil because of its basic nature [17].

As far as its chemical properties are concerned, biochar reduces soil acidity by increasing the pH (also called the liming effect) and helps the soil to retain nutrients and fertilizers. The application of biochar improves soil fertility through two mechanisms: adding nutrients to the soil (such as K, to a limited extent P, and many micronutrients) or retaining nutrients from other sources, including nutrients from the soil itself. However, the main advantage is to retain nutrients from other sources.
