- Thesis topic: The Potential of Transforming Agricultural Waste into Valuable Material by Atmospheric Pressure Microwave Plasma to support Circular Economy and reduce Carbon Emission

- Doi: https://doi.org/10.6840/cycu202201008

- Abstract: 

        Taiwan generates about 5 million metric tons of agricultural waste annually. However, about 30% of agricultural wastes are wasted and polluted due to poor utilization, causing excessive air pollution and little economic benefit. This study used atmospheric pressure microwave plasma in a nitrogen atmosphere at three individual flow rates of 7, 9, and 11 L/min to generate biochar for adsorbent and the composite catalyst by synthesizing biochar and TiO2 that were applied in visible light. Then product biochar was analyzed by benefit-cost ratio and its environmental impact compared with existing recycling methods. The high-quality biochars were successfully prepared via pyrolysis of rice straw, golden shower seed, and rice husk waste using The plasma pyrolysis technology could enhance a surface area about 1.91 - 6.05 times larger and 3 - 36 times faster than a conventional furnace. The golden shower seed biochar activated by plasma gas flowrate 11 L/min and rice straw biochar activated by plasma gas flowrate 7 L/min had the highest adsorption capacity among all biochars, 344.82 mg/g and 188.32 mg/g, respectively, which was 10.6 and 2.07 times higher than other golden shower and rice straw biochar from the previous research by much shorter pyrolysis duration of 24 and 48 times, respectively. The equilibrium data fit well with the Langmuir model, and the adsorption kinetics followed pseudo-second-order kinetics. For photocatalytic oxidation experiments, a composite catalyst with biochar produced by 9 L/min of plasma gas flow rate and ratio biochar/TiO2 1/1 exhibited the highest activity with a decolorization efficiency of 83.60, 69.51, and 50.87%. Based on the benefit-cost analysis, the recycling method by generating rice husk biochar using plasma technology showed profitability with a Benefit-Cost ratio > 1. The CO2eq of biochar generation by plasma system was 394.331 Kg CO2eq/ton biochar. This result is better than burying on-site, which resulted from previous research of about 1,260 Kg CO2eq/ton.

Keywords: Biochar, Adsorbent, Composite catalyst, Recycling method, Circular economy, Carbon emission reduction