Introduction to Biochar

Biochar: Thermally treated biomass that consists primarily of carbon. Biochar, commonly known as black carbon, is produced from organic materials high in carbon (C) and is frequently discovered in soils in extremely stable solid forms, such as deposits. Bio-chars can last for thousands of years in the soil at various depths.

Charcoal, which is made from wood, is the most typical example. Bio char, its nature, and its properties have been the subject of extensive research in recent years in order to assess its potential benefits and negative consequences, especially for use in agriculture as soil amendments.

Characteristics of Biochar

Carbon Content: Typically contains 50–80% carbon.
Physical Properties: Lightweight, highly porous, dark-colored, and offers a large surface area.
Chemical Properties: Usually alkaline, with high cation exchange capacity (CEC), enabling effective nutrient retention.
Feedstock Sources: Wood chips, crop residues (corn stover, straw), poultry litter, sewage sludge, nutshells, and more.
Mineral Composition: May contain potassium, phosphorus, calcium, and magnesium depending on the source.

Synthetic Protocols for Biochar Production

The breakdown of organic biomass produces biochar, a carbon-rich substance with a porous structure.
Different biochars were made using different feedstocks and manufacturing methods, and the biochar’s physicochemical and surface characteristics were used to determine its quality.
The char product is divided into three categories: charcoal, biochar, and hydrochar.
The creation of biochar through pyrolysis, torrefaction, gasification, hydrothermal liquefaction, and other methods is covered in depth.

1. Pyrolysis

In the absence of oxygen, pyrolysis is a thermal process that breaks down biomass to create biochar (pyrochar), bio-oil, and gases.
It is divided into thermal, solar, infrared, and microwave heat sources, as well as into slow, fast, and intermediate pyrolysis operating conditions, and it takes place at temperatures exceeding 300°C.
Depending on the kind of biomass—typically cellulose, hemicellulose, and lignin—the process entails intricate processes like depolymerisation, dehydration, and aromatization.
Biochar that works well as fuel comes from lignocellulosic biomass, whereas nonlignocellulosic biomass is better for soil modifications.
Nutrient content is improved by copyrolysis (e.g., seaweed and corn straw).
The output of microwave pyrolysis ranges from 12% to 75%, and it provides quicker, more effective heating and produces high-quality biochar with a larger surface area and pore volume.
Pyrolysis is a common method for creating biochar, which has many uses in energy production, soil enhancement, and heavy metal adsorption.

2. Hydrothermal Liquefaction (HTL)

Wet biomass, such as sewage sludge, municipal garbage, algal residue, and lignocellulosic materials, is transformed into bio-oil, gas, and hydrochar in water by hydrothermal liquefaction (HTL), a thermochemical process that occurs at high temperature and pressure.
Hydrothermal carbonization (HTC) under subcritical circumstances produces hydrochar, which has distinct characteristics from biochar.
In a complex, interconnected network, the process involves reactions like hydrolysis, dehydration, decarboxylation, and aromatization.
Hydrochar has been shown by research to be useful for soil modification, solid fuels, supercapacitors, and metal adsorption.
Hydrochar produced from industrial wastewater, for example, demonstrated increased soil application quality, and whereas hydrochar made from sunflower stalks and beech wood was utilized in water purification and energy storage. Depending on the feedstock and process parameters, yields usually fall between 30 and 60%.

3. Gasification

The thermochemical process of gasification involves heating biomass, such wood, crop leftovers, and agricultural waste, in a low-oxygen environment to produce syngas (a mixture of gases) and a tiny amount of biochar.
It is an environmental friendly way to manufacture chemicals and renewable energy while lowering greenhouse gas emissions.
Although there isn’t much of it, the biochar produced is rich in ash and minerals, making it ideal for soil improvement, CO2 sequestration, and use as a catalyst support.
Its application in enhancing water retention and soil fertility has also been demonstrated by research.
In comparison to traditional methods, microwave-assisted gasification may reduce reaction temperatures by 200°C.

4. Torrefaction

To reduce moisture and volatile components in biomass, torrefaction is a low-temperature pyrolysis procedure carried out in an oxygen-free atmosphere at 200–350 °C.
It improves gasoline qualities such energy density, grindability, and hydrophobicity while lowering biological activity.
The biomass’s carbon content increases as a result of the significant degradation of elements such hemicellulose throughout the process.
The majority of the torrefied biochar is used for heat and power generation. Compared to traditional torrefaction, microwave-induced torrefaction is a more effective technique that yields a higher oxygen-to-carbon ratio.

Uses of Biochar

1. Reducing Climate Change

The ability of biochar to trap carbon in the soil is a major benefit. The addition of biochar to soil traps carbon, lowers greenhouse gas emissions, and lessens the effects of climate change.
The byproducts of pyrolysis can also be used to produce clean energy. Fossil fuels can be replaced by capturing and processing the heat and syngas.
Here are other ways that bio char may help the environment: Groundwater pollutants, such as heavy metals, are adsorbed.
Lower the amount of biomass trash by boosting its water-holding capacity and enhancing its stability, lessen soil erosion.

2. Soil Health Improvement

Due to its porous structure, biochar applications to the soil have been demonstrated by several researches to improve soil health.
These minute pores have the ability to hold water and absorb and retain vital elements.
Farmers are able to withstand hardships such as droughts and increasing fertilizer prices thanks to this significant increase in the soil’s water retention capacity.
The porous nature of bio char also serves as a habitat for advantageous microorganisms that aid in nutrient cycling, organic matter breakdown, and disease prevention. Ultimately, all of this will result in higher crop yields and guarantee food security.

3. Soil pH Neutralization and Stabilization

Biochar typically has a high pH value because it is alkaline. It can help neutralize acidity when added to acidic soils, making them more conducive to plant development.
Biochar can also serve as a buffer, which aids in maintaining a consistent soil pH. As a result, the soil is protected from becoming overly acidic or alkaline by its ability to withstand pH variations.

4. Mine Site Remediation

Biochar is also employed in the rehabilitation of mine sites, where heavy metals or harmful leftovers have frequently poisoned soils and depleted their nutrients.
Biochar’s chemical characteristics and porous structure enable it to absorb and immobilize these harmful compounds, lowering their bioavailability and mobility in the soil. This aids in limiting pollution and starts the gradual process of ecological restoration.

5. Wastewater Treatment

Adsorbs contaminants (heavy metals, dyes, pharmaceuticals).
Alternative to activated carbon.
Used in sludge dewatering, nutrient removal, and pollutant degradation.

Techniques for Analysis

1. Infrared Spectroscopy by Fourier Transform (FTIR)

For examining the functional groups on the surface of biochar, Fourier Transform Infrared (FTIR) spectroscopy is a useful technique.
As the temperature rises, studies have revealed considerable variations in the makeup of bio char in a mixture.
The best way to monitor these changes is with a non-destructive FTIR device. Usually, the analysis shows a decline in aromatic groups at higher temperatures (between 650 and 800°C).

2. Raman Spectroscopy

A well-known method for analyzing the structure of carbon-based materials like biochar is Raman spectroscopy.
Researchers have used Raman spectroscopy extensively to learn more about the structure and characteristics of bio char. Because of its clear resolution, high sensitivity, low sample preparation needs, and ability to analyze samples without harm, it is a popular choice.
This method works well for identifying bio char made from different agricultural waste products, like rice husk, sugarcane bagasse, and pine wood.
Changes in the structure of biochar with increasing pyrolysis temperature can be detected using Raman spectroscopy.
This method detects variations in the Raman band’s position and width, which suggests a more organized carbon structure at higher temperatures. Keep in mind that the chemical composition of bio char is strongly influenced by its source material.
There has been a consistent trend in research showing that the degrees of carbon order in biochar increases with pyrolysis temperature.

3. Scanning Electron Microscopy (SEM)

Scanning Electron Microscopy (SEM) is a useful method for studying the surface morphology and structure of Biochar.
It demonstrates how the size and shape of biochar particles are greatly influenced by temperature and processing techniques.
Increasing pyrolysis temperature has been shown to improve the pore characteristics of biochar in a number of researches.
The distribution and features of pores inside biochar particles are described in detail using the SEM method.
Using SEM, the surface morphology of biochar can be predicted both before and after it absorbs pollutants.
In addition, researchers may examine the makeup and characteristics of biochar’s surface by combining SEM with Energy Dispersive X-ray (EDX) analysis.

4. Nuclear Magnetic Resonance (NMR) Spectroscopy

Nuclear Magnetic Resonance (NMR) spectroscopy analyzes the resonance of specific atomic nuclei within biochar when exposed to radiofrequency waves.
Solid-state NMR is commonly employed to study the non-liquid, carbon-rich structure of biochar.
Structural Insights Provided by NMR:
- Identifies carbon functional groups present in biochar.
- Determines the degree of aromaticity—how many stable aromatic ring structures are present.
- Analyzes the ratio of aromatic to aliphatic hydrocarbons, providing insight into chemical composition.
- Helps evaluate the degree of carbonization, which influences the stability and longevity of biochar in soil.
Used to compare biochar produced under different pyrolysis temperatures.
Assesses structural changes in biochar over time or after environmental exposure.
Offers molecular-level understanding for tailoring biochar for specific applications (e.g., soil amendment, pollutant adsorption).
Limitations of NMR Spectroscopy in Biochar Analysis:
- Presence of ferromagnetic minerals (like iron oxides) in biochar can interfere with the NMR signal, complicating data interpretation.
- High-temperature pyrolyzed biochars often yield low signal-to-noise ratios, making it harder to obtain clear, accurate spectra.
- Solid-state NMR is a costly and time-consuming technique compared to other analytical methods.

5. X-Ray Diffraction (XRD)

The crystallinity and microstructure of bio char are often examined using x ray Diffraction (XRD). The creation of Nano crystals inside the bio char is indicated by the existence of clear and well-defined peaks in the XRD pattern. Surprisingly, studies reveal that the size of these Nano crystals grows with time.

6. Thermo gravimetric Analysis (TGA)

TGA is a thermal analysis technique used to measure changes in a material’s mass as a function of temperature or time under a controlled atmosphere.
Evaluates the thermal stability and decomposition behavior of biochar and biomass.
Helps determine the rate of mass loss during pyrolysis, the process of heating biomass in limited or no oxygen.
Working Principle:
- The sample is gradually heated, and mass loss is recorded continuously.
- Different temperature ranges indicate the breakdown of different biomass components:
  - Moisture loss at low temperatures (~100°C)
  - Hemicellulose and cellulose decomposition at mid-range temperatures
  - Lignin degradation and carbonization at higher temperatures
Quick, straightforward, and reliable technique for analyzing thermal properties.
Offers insights into the volatile matter content, residual carbon, and ash content of the material.
Optimizing pyrolysis conditions by analyzing thermal degradation stages.
Characterizing biochar for fuel quality, stability, and reactivity.
Distinguishing between feedstocks based on thermal behavior.
TGA helps predict how biochar will perform under field conditions.
Useful for quality control and standardization in large-scale biochar production.

Applications of Biochar

1. Climate change

Biochar functions as a steady carbon sink, which is essential for reducing the effects of climate change.
A significant amount of carbon is trapped in a stable, non-decomposable form that lasts for hundreds or even thousands of years when biomass is pyrolyzed into biochar. This inhibits the release of CO2 that would result from combustion or natural decay.
Furthermore, biochar has the potential to lower nitrous oxide and methane emissions from soils, two powerful greenhouse gases.
Biochar integration into agricultural practices results in soil carbon sequestration, which supports climate change adaptation and mitigation strategies and contributes to negative emissions.

2. Wastewater treatment

Biochar is being used more and more for wastewater treatment due to its high porosity, large surface area, and high adsorption capability.
It successfully eliminates pollutants from industrial and municipal wastewater, including heavy metals (such lead, cadmium, and arsenic), organic contaminants, dyes, pharmaceuticals, and excess nutrients (nitrogen and phosphorus).
Biochar is a cost-effective and environmentally friendly replacement for traditional activated carbon because its surface functional groups attach pollutants via ion exchange, complexation, and physical adsorption.
Biochars that have been altered or engineered are extremely efficient and are being researched for use in removing particular pollutants from water and sludge treatment systems.

3. Soil health

Biochar greatly increases soil health by enhancing its physical, chemical, and biological characteristics.
Because of its porous structure, it improves soil aeration and water retention, which is particularly advantageous for sandy or degraded soils.
Because of its high cation exchange capacity, biochar increases nutrient retention, which decreases nutrient leaching and boosts plant absorption.
Additionally, it aids in the development of healthy soil microorganisms, which enhances soil fertility and agricultural yield.
In addition, biochar can immobilize hazardous compounds such as heavy metals and pesticides, as well as buffer soil pH, increasing the safety and productivity of soils over time.

4. Energy Generation

Biomass pyrolysis, a thermochemical process that produces biochar as well as bio-oil and syngas, both of which may be utilized as renewable energy sources, is a valuable coproduct of biochar production.
Bio-oil may be processed into liquid fuels, while the syngas produced can be used to create electricity or heat.
The incorporation of biochar manufacture into energy systems makes for a more environmentally friendly energy cycle by turning organic waste into usable energy while also producing a stable, carbon-rich product.
Biochar production is a viable approach for low-emission, distributed energy generation in both rural and urban environments due to this.

Benefits of Using Biochar

Improves soil fertility by increasing nutrient retention and microbial activity.
Improves soil water holding capacity, particularly in dry or sandy regions.
Reduces greenhouse gas emissions and stores carbon in the soil.
Adsorbs contaminants such as heavy metals and pesticides from soil and water.
Increases crop productivity by enhancing soil structure and health.
Supports climate change mitigation by storing carbon long-term.
Provides a use for agricultural waste by converting it into valuable materials.
Reduces nutrient leaching and protects groundwater from pollution.
Enhances compost quality when used as an additive.
It can be utilized for water treatment to clean wastewater and eliminate toxins.

Conclusion

Biochar offers a multi-functional solution for environmental sustainability, agricultural productivity, and waste management. Its role in climate change mitigation, soil improvement, and clean energy makes it an indispensable tool for a greener future. Continued research and technological advancements will further optimize its applications across diverse sectors.

Biochar: Properties, Production, and Applications