**6. Biochar applications**

Biochar is considered as a multifunctional material related to carbon sequestration, contaminant immobilization by adsorption, greenhouse gas reduction, soil fertilization, and waste-water and industrial effluent treatments. Biochar is widely used in heat and power generation, in soil fertility enhancement to improve the physical properties of soil, especially in soils with bad soil structure or high bulk density [3, 47, 50], in adsorption and filtration processes in different industrial effluent treatments [3] and in catalysis or as a catalyst support [51].

Biochar is an economical adsorbent [10] removing various organic contaminants such as agrochemicals, antibiotics, polycyclic aromatic hydrocarbons, polychlorinated biphenyls, volatile organic compounds, and various inorganic contaminants like heavy metals, ammonia, nitrate, phosphate, sulfide, etc. The high adsorption capacity, high specific surface area, microporosity, and ion exchange capacity of biochar are important characteristics for its applications. The feedstock types and pyrolysis conditions used during the biochar production greatly change its physicochemical properties such as surface area, polarity, atomic ratio, elemental composition and pH, giving the overall surface property of the biochar [8, 9]. These varieties in biochar qualities have significant implications on its suitability and efficacy in the remediation of targeted pollutants. Applications of biochar in soil improves the physicochemical and biological properties of the soils [5], which contribute to soil carbon sequestration and greenhouse gas emission reduction.

Biochar produced at low temperatures may be suitable for controlling fertilizer nutrients release, while high temperatures would yield material similar to activated carbon [52]. Because of the high aromaticity, the carbon in biochar is highly recalcitrant in soils with very long residence times. Thus, biochar incorporated in soil represents a potential terrestrial carbon sink and also a means of mitigating CO2 emissions. In addition, biochar has a significant potential to mitigate greenhouse gas emissions from agriculture, both by storing carbon in soils and through mitigating N2O emissions [48]. Furthermore, biochar can reduce the amount of fertilizer required and the emission of N2O and CH4 from the soil, thus the amount of carbon emissions prevented by biochar can be significant [27, 34]. Biochar application significantly reduced the leaching of applied N fertilizers. Biochar would not only enhance soil fertility but also sequester carbon from the atmosphere further research findings revealed that biochar has an affinity for organic compounds and may sorb toxic by-products from the wastewater treatment process. DAP (diammonia phosphate)-based fertilizer is used and studies have shown a large proportion (>85%) of N applied as NH4 + , N was lost through NH3 volatilization within one week after application [53]. Therefore biochar application can increase nutrient retention capacity and N use efficiency [48, 54, 55]. Several researchers demonstrated the benefits of biochar for soil, for example, wood biochar applied into a Colombian savanna Oxisol increased available Ca and Mg concentrations and pH, and reduced toxicity of Al [56, 57], moreover, biochar improved soil structure [58], created a carbon sink in soil [59], and reduced CH4 emissions [60].

In addition to being used as a soil conditioner and carbon sequestration regent, biochar has attracted much attention in wastewater treatment fields. Recent works of literature show biochar as a highly efficient, environmentally friendly, and lowcost adsorbent [61–63]. Biochar characteristic or quality plays a critical role in contaminant removal, which is usually governed by pyrolysis temperature and feedstock type. Fully carbonized biochar produced at a higher pyrolysis temperature (>500 °C) has higher affinity for organic contaminants due to high surface area [20], microporosity, hydrophobicity carbon-to-nitrogen (C/N) ratio [17, 31, 38], and pH [9, 15, 33, 37, 38, 40]. Partially carbonized biochars that are produced at lower pyrolysis temperatures have higher content of O-bearing functional groups like hydroxyl and carboxyl compounds and lower porosity making them more appropriate for removal of inorganic pollutants [9].

Biochar is used as an electrode as well for various electrochemical devices, including lithium-ion and Li-S batteries [64], supercapacitors [65], and microbial fuel cells [66], etc. Such biochar, namely activated biochar, are found to ne more sustainable than their fuel-based counterparts owing to its high surface area and porosity, efficient electrical and thermal conductivity, high stability, low economical cost, and availability [66, 67].

The unique chemical structure of biochar with a large surface area and tailored surface functional groups can be easily prepared by activation or functionalization and shows great potential to be used as a versatile catalyst or catalyst support in many chemical processes [51, 68–70].

### **7. Conclusion**

Biochar is considered as a multifunctional material related to carbon sequestration, contaminant immobilization by adsorption, greenhouse gas reduction, soil fertilization, and waste-water and industrial effluent treatments. The most promising feature of biochar is the fact that it represents a low cost and sustainable products with a spectrum of applications. Biochars have a tremendous range of

*Recent Perspectives in Biochar Production, Characterization and Applications DOI: http://dx.doi.org/10.5772/intechopen.99788*

physical and chemical properties, which greatly affect their wide applications. The feedstock and the method by which the biochar is produced has a significant impact on biochar characteristics, including concentrations of elemental constituents, density, porosity, and pH, which collectively impact the suitability of the biochar for various applications. This chapter examines in detail the production and characteristics of biochar resulting from slow pyrolysis process, including the effect of feedstock type and different pyrolysis process parameters on the properties and yield of biochar has been thoroughly studied. The selection of a specific type of feedstock is to a great extent determined by its in a place where the biochar is likely to be produced, as this reduces the cost of transport while decreasing the carbon footprint of the biochar technology. The pyrolysis temperature affects the biochar quality, higher carbon contents of biochars can be obtained at higher temperature while volatiles and molar ratios of O/C, H/C and N/C decrease with pyrolysis temperature. Biochars of higher carbon contents are preferable for most applications. Biochars produced at low pyrolysis temperature are suitable for controlling fertilizer nutrients release, while high temperatures would yield material similar to activated carbon. The pH of biochar is also another important parameter that determines its application. More basic, higher pH, biochar is preferred for soil application usually to correct soil acidity. Neutral pH biochar is also most preferable for adsorption processes for the removal of pollutants and contaminants from industrial effluents. Biochars produced at higher pyrolysis temperature have high affinity for organic pollutants due to high surface areas. In addition, neutral pH biochar is used as energy sources because acidic biochars cause corrosion and basic biochars cause fouling problems. Thus, the pyrolysis temperature should be selected as per the final application of the biochar.
