LIFE CYCLE ASSESSMENT OF ACTIVATED CARBON FROM WOODY BIOMASS

Activated carbon (AC) developed and marketed for water and gas purification is traditionally made from hard coals (fossil-based materials). However, increasing awareness of environmental impacts caused by fossil fuel consumption and fossil-based products has provided a market opportunity for renewable and low-impact biobased products as alternatives including AC. The huge volumes of woody biomass generated from forest management activities could be used as feedstocks for these new bioproducts. These new bioproducts require evaluation to determine if they are low impact. To aid in quantifying environmental impacts of a new bioproduct (such as AC), this study developed the cradle-to-gate life cycle inventory (LCI) data for the carbon activation of biochar in a rotary calciner by collecting operational and direct emission data while conforming to the internationally accepted life cycle assessment method. The LCI datawere then modeled to develop the life cycle impact assessment profile of biochar-based carbon activation and compared with commercial coal-based carbon activation. The results showed about 35% less cradle-to-product gate cumulative energy demand for the biochar AC system compared with the coal AC system. Consequentially, the greenhouse gas emissions for biochar AC production were less than half that of coal AC production (8.60 kg CO2 eq vs 18.28 kg CO2 eq per kg of AC produced). This was because of both lower energy consumption and the biogenic carbon benefit from using woody biomass for both feedstock and processing. To ensure substitution of the two ACs, the physical properties for the AC from biochar and coal were compared for their Brunauer-Emmett-Teller surface area and iodine number, which showed that both indicators were superior for biochar AC compared with coal AC. Therefore, biochar AC results from this study suggest a potential high-value market for woody biomass derived from forest restoration and wildfire suppression activities.