Mitigating greenhouse gas emissions and enhancing composting efficiency using biochar, used oil, and compost inoculum...

This study aimed to evaluate the effectiveness of combining biochar, used cooking oil, and compost inoculum as amendments to improve the composting process of agricultural residues (broccoli and pepper waste) and manure. The objective was to enhance compost maturation, microbial safety, and environmental performance, particularly in terms of greenhouse gas emissions. Six treatments were tested: 50% manure + 50% agricultural residues (T_1-1, control), 60% manure + 40% agricultural residues (T_1- 2, control), 50% manure + 50% agricultural residues + 20 ml used cooking oil (T_2-1), 60% manure + 40% agricultural residues + 20 ml used cooking oil (T_2-2), 50% manure + 50% agricultural residues + 20% inoculum compost (T_3-1), and 60% manure + 40% agricultural residues + 20% inoculum compost (T_3-2), Then the first experiment was conducted to produce compost without adding biochar. After the first experiment was completed, a second experiment was conducted with the addition of 10% biochar at the same proportions as in the first experiment. The resulting mixture was composted in a controlled reactor with aeration and mixing. Results showed that the combination of used cooking oil and biochar significantly increased temperature, prolonged the thermophilic phase, and reduced the composting period to 10 days. This combination also decreased GHG emissions by 27-33% and eliminated methane emissions. Pathogenic bacteria (E. coli and Salmonella) were fully removed within one week. The findings suggest that integrating these amendments can accelerate composting, improve hygienic quality, and reduce environmental impacts.