The study focuses on assessing the environmental impacts of producing biochar from agricultural residues such as rice straw, palm shells, corn stover, and mixed crop residues. Biochar is a carbon-rich material derived from the pyrolysis of biomass in low-oxygen environments. It has gained significant attention due to its potential for sustainable waste management, soil improvement, carbon sequestration, and renewable energy production.

Background and Objectives

The rapid growth of the global population has led to increasing food production, resulting in substantial agricultural waste generation, often mismanaged or left to decompose in fields, emitting harmful pollutants. Converting this waste into biochar offers a viable solution to these environmental challenges. The study aims to evaluate and compare the environmental impacts of biochar production using the life cycle assessment (LCA) methodology. A cradle-to-gate system boundary is applied, covering feedstock acquisition, transportation, pre-treatment, and production. The functional unit is 1 ton of biochar.

Methodology

The LCA was conducted based on ISO 14040/44 standards. Data on energy consumption, emissions, and other environmental factors were collected from databases such as Ecoinvent and prior studies. Four feedstocks—rice straw, palm shells, corn stover, and mixed crop residues—were analyzed. Environmental impacts were evaluated using the IMPACT 2002+ framework, which quantifies damage in four endpoint categories: human health, ecosystem quality, climate change, and resource depletion. Monte Carlo Simulation (MCS) was employed to address uncertainty in the results.

Key Findings

Environmental Impacts

1. Human Health Potential (HHP): Palm shell exhibited the highest HHP due to respiratory inorganics released during biochar production (4.889 kg PM2.5 eq per functional unit). Corn stover significantly contributed to carcinogenic and non-carcinogenic emissions due to the release of polycyclic aromatic hydrocarbons and arsenic.

2. Ecosystem Quality Potential (EQP): Palm shells caused severe ecosystem damage, mainly through terrestrial and aquatic acidification, while corn stover contributed to high aquatic and terrestrial ecotoxicity due to aluminum emissions.

3. Global Warming Potential (GWP): Mixed crop residues exhibited the highest GWP (281.884 kg CO2 eq per functional unit) primarily due to greenhouse gas emissions during production and pre-treatment processes. In contrast, corn stover had the lowest GWP due to lower energy consumption.

4. Resource Depletion Potential (RDP): Mixed crop residues consumed the most resources, accounting for 4,339.672 MJ per ton of biochar. Rice straw had the lowest resource consumption but still significantly impacted non-renewable energy use.

Normalization and Uncertainty Analysis

Normalization highlighted variations in the environmental impacts of different feedstocks. For instance, corn stover had low impacts on human health and ecosystem quality but moderate impacts on climate change and resource use. The Monte Carlo simulation revealed a coefficient of variation within ±10%, confirming the reliability of the findings.

Challenges and Limitations

The study acknowledges limitations, such as reliance on global databases that may not fully represent regional processes and exclusion of the utilization phase of biochar (a cradle-to-gate approach). The methodology also assumes static process conditions and uniform emission characterization factors, potentially oversimplifying temporal variations.

Implications and Future Directions

The study underscores the importance of feedstock selection in minimizing environmental impacts. It suggests prioritizing low-impact feedstocks like corn stover and rice straw for biochar production. Biochar’s potential to address agricultural waste challenges, enhance soil health, and sequester carbon aligns with principles of the circular economy and sustainable development. However, scaling biochar production technologies and optimizing processes to reduce emissions and energy use remain crucial.

Future research should explore biochar's long-term effects on soil health, crop productivity, and carbon dynamics. Integrating economic analyses and improving LCA methodologies could provide a more comprehensive understanding of biochar’s benefits. Regional studies are also essential to tailor biochar production strategies to specific environmental and agricultural contexts.

Conclusion

The research provides valuable insights into the environmental impacts of biochar production from agricultural residues. While biochar offers a sustainable solution for waste valorization and climate action, careful feedstock selection and process optimization are essential to maximize its environmental and economic benefits.