Energy Balance and Emissions Associated with Biochar Sequestration and Pyrolysis Bioenergy Production

Abstract

The implications for greenhouse gas emissions of optimizing a slow pyrolysis-based bioenergy system for biochar and energy production rather than solely for energy production were assessed. Scenarios for feedstock production were examined using a life-cycle approach. We considered both purpose grown bioenergy crops (BEC) and the use of crop wastes (CW) as feedstocks. The BEC scenarios involved a change from growing winter wheat to purpose grown miscanthus, switchgrass, and corn as bioenergy crops. The CW scenarios consider both corn stover and winter wheat straw as feedstocks. Our findings show that the avoided emissions are between 2 and 5 times greater when biochar is applied to agricultural land (2--19 Mg CO2 ha(-1) y(-1)) than used solely for fossil energy offsets. 41--64% of these emission reductions are related to the retention of C in biochar, the rest to offsetting fossil fuel use for energy, fertilizer savings, and avoided soil emissions other than CO2. Despite a reduction in energy output of approximately 30% where the slow pyrolysis technology is optimized to produce biochar for land application, the energy produced per unit energy input at 2--7 MJ/MJ is greater than that of comparable technologies such as ethanol from corn. The C emissions per MWh of electricity production range from 91-360 kg CO2 MWh(-1), before accounting for C offset due to the use of biochar are considerably below the lifecycle emissions associated with fossil fuel use for electricity generation (600-900 kg CO2 MWh(-1)). Low-temperature slow pyrolysis offers an energetically efficient strategy for bioenergy production, and the land application of biochar reduces greenhouse emissions to a greater extent than when the biochar is used to offset fossil fuel emissions.

Biochar for Soil Improvement: Evaluation of Biochar from Gasification and Slow Pyrolysis

“…All show the potential of biochar to improve resource efficiency. Focusing on the value of CO2 reductions, Gaunt and Lehmann [56] determined that biochar application to agricultural land would provide greater GHG emission reductions than using the char for electricity generation, assuming (1) a fertilizer reduction of 10%, which would result in a reduction in N2O emissions of 50% compared to a case without any treatment and (2) the effect of biochar would remain for 10 years after application. If the cost of CO2 emissions is also considered not only the environmental balance but also the economic balance will become considerably attractive in favor of biochar co-production [57].…”

Impact of Biochar on Organic Contaminants in Soil: A Tool for Mitigating Risk?

“…The increased research and development on strategies to improve and produce bioenergy from renewable energy sources to contribute to the energy needs of developing and developed societies will contribute to the deposition of biochar-like products into the environment [72]. Additionally, it may be produced as a result of uncontrolled bush burning or wild fires and then deposited onto soil [73], and it has been reported that biochar-amended soils have the ability to retain moisture, increase cation exchange capacity (CEC), increase adsorptive capacity and increase pH [74].…”

Influence of Active Charcoal and Plant Position on Some Morphological Parameters of a Local Variety of Okra (<i>Abelmoschus caillei</i>)

“…Generally, activated charcoal is alkaline, but may have a pH of 4 to 12 depending on the conditions surrounding the manufacturing process [10] [11]. Its use in cropping systems contributes to the reduction of greenhouse gas emissions [12]. The incorporation of activated charcoal on the soil modifies its water state and influences the root development of plants as well as the fauna of the soil [13].…”