U.S.-FocUSed Biochar report - BioEnergy Lists

Benefits of Biofuels and Potential of BiocharThe net benefit of bioenergy production is discussed very controversially. Most evaluations assume a maximizationof biofuel production compromising soil fertility and carbon sequestration (Lal and Pimentel 2007; Tilmanet al. 2009; Vries et al. 2010) and competing with food production (Pimentel, Marklein et al. 2009; Searchingeret al. 2008). This applies particularly to bioenergy crops. Grain- and seed-based biofuels provide modest GHGmitigation benefits (Cherubini et al. 2009) and raise major nutritional and ethical concerns, as nearly 60% of theworld population is currently malnourished (Pimentel, Gardner et al. 2009). Others proposed maximizing carbonsequestration and waive benefits from renewable energy production and disregard the importance of SOC tomaintain soil fertility (Seifritz 1993; Strand and Benford 2009; Zeng 2008). Site-specific parameters and too manyuncertainties make it very difficult to provide values for greenhouse gas emissions and fossil fuel substitution ofbioenergy systems. Afforestation, reforestation or revegetation of degraded land, in combination with future bioenergyproduction has been described as a synergistic way to produce bioenergy and sequester carbon (Cherubiniet al. 2009). Biochar carbon sequestration may offer similar synergies with the greatest carbon sequestrationand economical potential if crop residues or waste biomass is used rather than purpose grown crops (Robertset al. 2010). Furthermore the revegetation of degraded land might require inputs such as biochar and fertilizers.Pyrolysis with biochar carbon sequestration allows cycling nutrients back into the agricultural soils and sequesteringcarbon in a recalcitrant form. A biorefinery processes biomass into a spectrum of marketable productsand energy. One such product could be biochar. However there is an opportunity cost attached to biochar carbonsequestration. This is the cost of energy still contained in the carbonized biomass. If pyrolysis gears for maximizingbiochar production (roughly 30 to 35% of the feedstock is converted to biochar), approximately 50% feedstockenergy is contained in the biochar. However, more than 60% of the emissions reductions of biochar productionwith energy co-generation are realized from C sequestration in the biochar (Roberts et al. 2010). Therefore theprice of carbon is critical to the cost-effectiveness of biochar projects (Pratt and Moran 2010; Roberts et al. 2010).However even the most expensive biochar projects revealed cost-effectiveness superior to other carbon negativetechnologies such as carbon capture and storage (Pratt and Moran 2010). Gaunt and Lehmann (2008) evaluateda sequestration cost of U.S. $9-16 Mg -1 CO 2 for biochar projects and concludes that potential revenues from Cemission trading alone can justify the maximization of a pyrolysis plant for biochar production. A strategy thatcombines pyrolysis for bioenergy production with biochar carbon sequestration is more effective than producingsolely bioenergy (Gaunt and Lehmann 2008; Roberts et al. 2010). About 30% more GHG emissions can bereduced when the biochar is applied to soil (-864 kg CO 2e Mg -1 dry corn stover) rather than combusted for energygeneration (Roberts et al. 2010). However if the corn stover is directly combusted (and not biochar) as a substitutionfor natural gas the result would be comparable in GHG reductions (Roberts et al. 2010). Nevertheless onlythe biochar option can address issues emerging from SOC depletion and carbon sequestered in soil actuallyremoves CO 2 from the atmosphere, whereas avoided fossil fuel consumption only reduces the speed of GHGconcentration increase. Avoided fossil fuel emissions today are not avoided forever, particularly when only partof the world undertakes carbon policy. Avoided emissions today, may mean higher emissions in the future, dueto a lower price path of fossil fuels (Herzog, Caldeira, and Reilly 2003).The capture of CO 2 and storage in depleted oil and gas fields or saline aquifers is an option which requires vastcapital inputs and large scale projects and would therefore be even more expensive for bioenergy projects due tothe lower energy and bulk density of biomass compared to coal. One of the main advantages of biochar carbonsequestration is that it can be implemented with or without additional energy production on a small scale (improvedkilns, stoves, gasifiers) as well as a large scale (e.g., biorefinery). This option would certainly expand thequantity of available biomass. Biomass from invasive species, dead trees or biomass generated from fuel reductiontreatments might be pyrolysed. It is estimated that 11 million ha (28 million acres) of forest could benefitfrom fuel reduction treatments in the western U.S. alone, with a total biomass treatment of 313 million Mg (345million dry tons) (USDA 2003). Vegetation treatments to regulate density and species mix, inhibit insect anddisease outbreaks, or reduce wildfire risk (Morgan, Johnson, and Piva 2009). Prescribed fires are the least expensiveoption, but limited by restrictions on air pollution, weather conditions and a lack of resources. From the 160million ha (400 million acres) surveyed in 2006, about 2.1 million ha (5.3 million acres) had tree mortality detectedBiochar in agricultural and forestry applications in:Biochar from Agricultural and Forestry Residues – A Complimentary Use of “Waste” Biomass7