Modeling California policy impacts on greenhouse gas emissions

This paper examines policy and technology scenarios in California, emphasizing greenhouse gas (GHG) emissions in 2020 and 2030. Using CALGAPS, a new, validated model simulating GHG and criteria pollutant emissions in California from 2010 to 2050, four scenarios were developed: Committed Policies (S1), Uncommitted Policies (S2), Potential Policy and Technology Futures (S3), and Counterfactual (S0), which omits all GHG policies. Forty-nine individual policies were represented. For S1–S3, GHG emissions fall below the AB 32 policy 2020 target [427 million metric tons CO₂ equivalent (MtCO₂e) yr⁻¹], indicating that committed policies may be sufficient to meet mandated reductions. In 2030, emissions span 211–428 MtCO₂e yr⁻¹, suggesting that policy choices made today can strongly affect outcomes over the next two decades. Long-term (2050) emissions were all well above the target set by Executive Order S-3-05 (85 MtCO₂e yr⁻¹); additional policies or technology development (beyond the study scope) are likely needed to achieve this objective. Cumulative emissions suggest a different outcome, however: due to early emissions reductions, S3 achieves lower cumulative emissions in 2050 than a pathway that linearly reduces emissions between 2020 and 2050 policy targets. Sensitivity analysis provided quantification of individual policy GHG emissions reduction benefits.     

Assessment of nitrogen fertilization for the CO2 balance during the production of poplar and rye

This study was designed to consider all nitrogen fertilizer-related effects on crop production and emission of greenhouse gases on loamy sandy soils in Germany over a period of nine years (1999–2007). In order to set up a CO₂ balance for the production of energy crops, different nitrogen pathways were investigated, such as direct N₂O emissions from the soil and indirect emissions related to NO₃ leaching and fertilizer production. Fluxes of N₂O were measured in an experimental field using closed chambers. Poplar (Populus maximowiczii × P. nigra) and rye (Secale cereale L.) as one perennial and one annual crop were fertilized at rates of 0 kg N ha^?1 yr^?1, 75 kg N ha^?1 yr^?1 and 150 kg N ha^?1 yr^?1. The mean N₂O emissions from the soil ranged between 0.5 kg N ha^?1 yr^?1 and 2.5 kg N ha^?1 yr^?1 depending on fertilization rate, crop variety and year. The CO₂ fixed in the biomass of energy crops is reduced by up to 16% if direct N₂O emissions from soil and indirect N₂O emissions from NO₃ leaching and fertilizer production are included. Taking into account the main greenhouse gas emissions, which derive from the production and the use of N fertilizer, the growth of poplar and rye may replace the global warming potential of fossil fuels by up to 17.7 t CO₂ ha^?1 yr^?1 and 12.1 t CO₂ ha^?1 yr^?1, respectively.     

Integrating livestock manure with a corn–soybean bioenergy cropping system improves short-term carbon sequestration rates and net global warming potential

Carbon cycling and the global warming potential (GWP) of bioenergy cropping systems with complete biomass removal are of agronomic and environmental concern. Corn growers who plan to remove corn stover as a feedstock for the emerging cellulosic ethanol industry will benefit from carbon amendments such as manure and compost, to replace carbon removed with the corn stover. The objective of this research was to determine the effect of beef cattle feedlot manure and composted dairy manure on short-term carbon sequestration rates and net global warming potential (GWP) in a corn–soybean rotation with complete corn-stover removal. Field experiments consisting of a corn–soybean rotation with whole-plant corn harvest, were conducted near East Lansing, MI over a three-year period beginning in 2002. Compost and manure amendments raised soil carbon (C) at a level sufficient to overcome the C debt associated with manure production, manure collection and storage, land application, and post-application field emissions. The net GWP in carbon dioxide equivalents for the manure and compost amended cropping systems was ?934 and ?784 g m^?2 y^?1, respectively, compared to 52 g m^?2 y^?1 for the non-manure amended synthetic fertilizer check. This work further substantiates the environmental benefits associated with renewable fuels and demonstrates that with proper management, the integration of livestock manures in biofuel cropping systems can enhance greenhouse gas (GHG) remediation.     

Environmental aspects of ethanol derived from no-tilled corn grain: nonrenewable energy consumption and greenhouse gas emissions

Nonrenewable energy consumption and greenhouse gas (GHG) emissions associated with ethanol (a liquid fuel) derived from corn grain produced in selected counties in Illinois, Indiana, Iowa, Michigan, Minnesota, Ohio, and Wisconsin are presented. Corn is cultivated under no-tillage practice (without plowing). The system boundaries include corn production, ethanol production, and the end use of ethanol as a fuel in a midsize passenger car. The environmental burdens in multi-output biorefinery processes (e.g., corn dry milling and wet milling) are allocated to the ethanol product and its various coproducts by the system expansion allocation approach.The nonrenewable energy requirement for producing 1 kg of ethanol is approximately 13.4–21.5 MJ (based on lower heating value), depending on corn milling technologies employed. Thus, the net energy value of ethanol is positive; the energy consumed in ethanol production is less than the energy content of the ethanol (26.8 MJ kg⁻¹).In the GHG emissions analysis, nitrous oxide (N₂O) emissions from soil and soil organic carbon levels under corn cultivation in each county are estimated by the DAYCENT model. Carbon sequestration rates range from 377 to 681 kg C ha⁻¹ year⁻¹ and N₂O emissions from soil are 0.5–2.8 kg N ha⁻¹ year⁻¹ under no-till conditions. The GHG emissions assigned to 1 kg of ethanol are 260–922 g CO₂ eq. under no-tillage. Using ethanol (E85) fuel in a midsize passenger vehicle can reduce GHG emissions by 41–61% km⁻¹ driven, compared to gasoline-fueled vehicles. Using ethanol as a vehicle fuel, therefore, has the potential to reduce nonrenewable energy consumption and GHG emissions.     

Economics of switchgrass and miscanthus relative to coal as feedstock for generating electricity

Switchgrass (Panicum virgatum) serves as a model dedicated energy crop in the U.S.A. Miscanthus (Miscanthus x giganteus) has served a similar role in Europe. This study was conducted to determine the most economical species, harvest frequency, and carbon tax required for either of the two candidate feedstocks to be an economically viable alternative for cofiring with coal for electricity generation. Biomass yield and energy content data were obtained from a field experiment conducted near Stillwater, Oklahoma, U.S.A., in which both grasses were established in 2002. Plots were split to enable two harvest treatments (once and twice yr^?1). The switchgrass variety ‘Alamo’, with a single annual post-senescence harvest, produced more biomass (15.87 Mg ha^?1 yr^?1) than miscanthus (12.39 Mg ha^?1 yr^?1) and more energy (249.6 million kJ ha^?1 yr^?1 versus 199.7 million kJ ha^?1 yr^?1 for miscanthus). For the average yields obtained, the estimated cost to produce and deliver biomass an average distance of 50 km was $43.9 Mg^?1 for switchgrass and $51.7 Mg^?1 for miscanthus. Given a delivered coal price of $39.76 Mg^?1 and average energy content, a carbon tax of $7 Mg^?1 CO₂ would be required for switchgrass to be economically competitive. For the location and the environmental conditions that prevailed during the experiment, switchgrass with one harvest per year produced greater yields at a lower cost than miscanthus. In the absence of government intervention such as requiring biomass use or instituting a carbon tax, biomass is not an economically competitive feedstock for electricity generation in the region studied.     

A comparison of avoided greenhouse gas emissions when using different kinds of wood energy

In this study, micro-level data from wood energy producers in Hedmark County were gathered and analysed. The aim was to find how much greenhouse gas (GHG) emissions various kinds of wood energy cause (not only CO₂, but also CH₄ and N₂O), which energy they substitute, their potential to reduce GHG emissions, and the major sources of uncertainty. The method was life cycle assessment. Six types of wood energy were studied: fuel wood, sawdust, pellets, briquettes, demolition wood, and bark.GHG emissions over the life cycle of the wood energy types in this study are 2–19% of the emissions from a comparable source of energy. The lowest figure is for demolition wood substituting oil in large combustion facilities, the highest for fuel wood used in dwellings to substitute electricity produced by coal-based power plants.Avoided GHG emissions per m³ wood used for energy were from 0.210 to 0.640 tonne CO₂-equivalents. Related to GWh energy produced, avoided GHG emissions were from 250 to 360 tonne CO₂-equivalents. Avoided GHG emissions per tonne CO₂ in the wood are 0.28–0.70 tonne CO₂-equivalents. The most important factors were technology used for combustion, which energy that is substituted, densities, and heating values. Inputs concerning harvest, transport, and production of the wood energy are not important.Overall, taking the uncertainties into account there is not much difference in avoided GHG emissions for the different kinds of wood energy.     

A shock tube study of the rate constants of HO2 and CH3 reactions

HO₂ and CH₃ are major intermediate species presented during the oxidation of natural gas at intermediate temperatures and high pressures. Previous theoretical calculations have identified several product channels for HO₂ and CH₃ reactions, with CH₃ + HO₂ → CH₃O + OH and CH₃ + HO₂ → CH₄ + O₂ being the dominant reaction pathways. Both reaction pathways play an important role in the kinetics of CH₄ oxidation as CH₃ + HO₂ → CH₃O + OH is a chain-branching reaction whereas CH₃ + HO₂ → CH₄ + O₂ a chain termination reaction.H₂O₂/CH₄/Ar mixtures were shock-heated to a temperature between 1054 and 1249 K near 3.5 atm to initiate the reaction. OH radicals yielded from H₂O₂ thermal decomposition react with H₂O₂ and CH₄ respectively to produce HO₂ and CH₃ in the reacting system. Using laser absorption spectroscopy, time-histories of H₂O, OH and HO₂ were measured behind reflected shock waves. The rate constant of reaction CH₃ + HO₂ → CH₃O + OH was determined to be 6.8 × 10¹² cm³ mol^?1 s^?1 with an uncertainty factor of 1.4. The rate constant of the competing CH₃ + HO₂ → CH₄ + O₂ reaction was determined to be 4.4 × 10¹² cm³ mol^?1 s^?1, with an uncertainty factor of 2.1. In addition, the rate constants of two other major reactions of the reacting system, H₂O₂ (+M) → 2OH (+M) and OH + CH₄ → CH₃O + OH, were found to have excellent agreement with values recommended in literature.     

Measures of the environmental footprint of the front end of the nuclear fuel cycle

Previous estimates of environmental impacts associated with the front end of the nuclear fuel cycle (FEFC) have focused primarily on energy consumption and CO₂ emissions. Results have varied widely. This work builds upon reports from operating facilities and other primary data sources to build a database of front end environmental impacts. This work also addresses land transformation and water withdrawals associated with the processes of the FEFC. These processes include uranium extraction, conversion, enrichment, fuel fabrication, depleted uranium disposition, and transportation.To allow summing the impacts across processes, all impacts were normalized per tonne of natural uranium mined as well as per MWh(e) of electricity produced, a more conventional unit for measuring environmental impacts that facilitates comparison with other studies. This conversion was based on mass balances and process efficiencies associated with the current once-through LWR fuel cycle.Total energy input is calculated at 8.7 × 10^− 3 GJ(e)/MWh(e) of electricity and 5.9 × 10^− 3 GJ(t)/MWh(e) of thermal energy. It is dominated by the energy required for uranium extraction, conversion to fluoride compound for subsequent enrichment, and enrichment. An estimate of the carbon footprint is made from the direct energy consumption at 1.7 kg CO₂/MWh(e). Water use is likewise dominated by requirements of uranium extraction, totaling 154 L/MWh(e). Land use is calculated at 8 × 10^− 3 m²/MWh(e), over 90% of which is due to uranium extraction. Quantified impacts are limited to those resulting from activities performed within the FEFC process facilities (i.e. within the plant gates). Energy embodied in material inputs such as process chemicals and fuel cladding is identified but not explicitly quantified in this study. Inclusion of indirect energy associated with embodied energy as well as construction and decommissioning of facilities could increase the FEFC energy intensity estimate by a factor of up to 2.     

A comparative analysis of woody biomass and coal for electricity generation under various CO2 emission reductions and taxes

Mitigating global climate change via CO₂ emission control and taxation is likely to enhance the economic potential of bioenergy production and utilization. This study investigated the cost competitiveness of woody biomass for electricity production in the US under alternative CO₂ emission reductions and taxes. We first simulated changes in the price of coal for electricity production due to CO₂ emission reductions and taxation using a computable general equilibrium model. Then, the costs of electricity generation fueled by energy crops (hybrid poplar), logging residues, and coal were estimated using the capital budgeting method. Our results indicate that logging residues would be competitive with coal if emissions were taxed at about US$25 Mg⁻¹ CO₂, while an emission tax US$100 Mg⁻¹ CO₂ or higher would be needed for hybrid poplar plantations at a yield of 11.21 dry Mg ha⁻¹ yr⁻¹ (5 dry tons ac⁻¹ yr⁻¹) to compete with coal in electricity production. Reaching the CO₂ emission targets committed under the Kyoto Protocol would only slightly increase the price of fossil fuels, generating little impact on the competitiveness of woody biomass. However, the price of coal used for electricity production would significantly increase if global CO₂ emissions were curtailed by 20% or more. Logging residues would become a competitive fuel source for electricity production if current global CO₂ emissions were cut by 20–30%. Hybrid poplar plantations would not be able to compete with coal until emissions were reduced by 40% or more.     

The effects of operating conditions on emissions from masonry heaters and sauna stoves

Emissions from masonry heaters and sauna stoves were studied. In the sauna stove the production of organic gaseous carbon (OGC) at 10 gC kg^?1 (per kilogram of fuel), carbon monoxide (CO) at 55 g kg^?1, fine particle mass (PM₁) at 5 g kg^?1 and number emissions (N) at 1.8 × 10¹⁵ kg^?1 was higher than in other measured appliances. In a modern technology masonry heater with a unique grate, the emissions were very low: 0.4 gC kg^?1 OGC, 14 g kg^?1 CO and 0.7 g kg^?1 PM₁. Conventional masonry heaters, using small logs, clearly produced higher emissions when compared to using large logs. Doubling the fuel load caused emission factors to increase by up to 4- times (OGC), except for the number emission, which decreased from 4.0 × 10¹⁴ to 2.0 × 10¹⁴ kg^?1. From the conventional masonry heater 90% of the PM was emitted during the firing phase. Its combustion process is different to that in stoves or conventional open fireplaces. The insufficient supply of air, due to too fast pyrolysis, and increased ash release, due to the high combustion temperature, are the main parameters which cause high particle and gas emissions in masonry heaters and sauna stoves.     

The economical and environmental performance of miscanthus and switchgrass production and supply chains in a European setting

The purpose of this study is to analyse the economical and environmental performance of switchgrass and miscanthus production and supply chains in the European Union (EU25), for the years 2004 and 2030. The environmental performance refers to the greenhouse gas (GHG) emissions, the primary fossil energy use and to the impact on fresh water reserves, soil erosion and biodiversity. Analyses are carried out for regions in five countries. The lowest costs of producing (including storing and transporting across 100 km) in the year 2004 are calculated for Poland, Hungary and Lithuania at 43–64 € per oven dry tonne (odt) or 2.4–3.6 € GJ^?1 higher heating value. This cost level is roughly equivalent to the price of natural gas (3.1 € GJ^?1) and lower than the price of crude oil (4.6 € GJ^?1) in 2004, but higher than the price of coal (1.7 € GJ^?1) in 2004. The costs of biomass in Italy and the United Kingdom are somewhat higher (65–105 € odt^?1 or 3.6–5.8 € GJ^?1). The doubling of the price of crude oil and natural gas that is projected for the period 2004–2030, combined with nearly stable biomass production costs, makes the production of perennial grasses competitive with natural gas and fossil oil. The results also show that the substitution of fossil fuels by biomass from perennial grasses is a robust strategy to reduce fossil energy use and curb GHG emissions, provided that perennial grasses are grown on agricultural land (cropland or pastures). However, in such case deep percolation and runoff of water are reduced, which can lead to overexploitation of fresh water reservoirs. This can be avoided by selecting suitable locations (away from direct accessible fresh water reservoirs) and by limiting the size of the plantations. The impacts on biodiversity are generally favourable compared to conventional crops, but the location of the plantation compared to other vegetation types and the size and harvesting regime of the plantation are important variables.     

LCA of domestic and centralized biomass combustion: The case of Lombardy (Italy)

This paper analyzes and compares the environmental impacts of biomass combustion in small appliances such as domestic open fireplaces and stoves, and in two types of centralized combined heat and power plants, feeding district heating networks. The analysis is carried out following a Life Cycle Assessment (LCA) approach. The expected savings of GHG (greenhouse gases) emissions due to the substitution of fossil fuels with biomass are quantified, as well as emissions of toxic pollutants and substances responsible for acidification and ozone formation.The LCA results show net savings of GHG emissions when using biomass instead of conventional fuels, varying from 0.08 to 1.08 t of CO₂ eq. per t of dry biomass in the different scenarios. Avoided GHG emissions thanks to biomass combustion in Lombardy are 1.32 Mt year^?1(1.5% of total regional GHG emissions). For the other impact categories, the use of biomass in district heating systems can again cause a consistent reduction of impacts, whereas biomass combustion in residential devices shows higher impacts than fossil fuels with a particular concern for PAH, VOC and particulate matter emissions. For example, in Lombardy, PM10 emissions from domestic devices are about 8100 t year^?1, corresponding to almost one third of the total particulate emissions in 2005.     

Exploration of regional and global cost–supply curves of biomass energy from short-rotation crops at abandoned cropland and rest land under four IPCC SRES land-use scenarios

We explored the production cost of energy crops at abandoned agricultural land and at rest land at a regional and a global level to the year 2050 using four different land-use scenarios. The estimations were based on grid cell data on the productivity of short-rotation crops on the available land over time and assumptions regarding the capital and the labour input required to reach these productivity levels. It was concluded that large amounts of grown biomass at abandoned agricultural land and rest land, 130–270 EJ yr^?1 (about 40–70% of the present energy consumption) may be produced at costs below $2 GJ^?1 by 2050 (present lower limit of cost of coal). Interesting regions because of their low production cost and significant potentials are the Former USSR, Oceania, Eastern and Western Africa and East Asia. Such low costs presume significant land productivity improvements over time and cost reductions due to learning and capital-labour substitution. An assessment of biomass fuel cost, using the primary biomass energy costs, showed that the future costs of biomass liquid fuels may be in the same order of the present diesel production costs, although this may change in the long term. Biomass-derived electricity costs are at present slightly higher than electricity baseload costs and may directly compete with estimated future production costs of fossil fuel electricity with CO₂ sequestration. The present world electricity consumption of around 20 PWh yr^?1 may be generated in 2050 at costs below $45 MWh^?1 in A1 and B1 and below $55 MWh^?1 in A2 and B2. At costs of $60 MWh^?1, about 18 (A2) to 53 (A1) PWh yr^?1 can be produced.     

National and regional generation of municipal residue biomass and the future potential for waste-to-energy implementation

Municipal residue biomass (MRB) in the municipal solid waste (MSW) stream is a potential year-round bioenergy feedstock. A method is developed to estimate the amount of residue biomass generated by the end-user at the scale of a country using a throughput approach. Given the trade balance of food and forestry products, the amount of MRB generated is calculated by estimating product lifetimes, discard rates, rates of access to MSW collection services, and biomass recovery rates. A wet tonne of MRB could be converted into about 8 GJ of energy and 640 kg of carbon dioxide (CO₂) emissions, or buried in a landfill where it would decompose into 1800 kg of CO₂ equivalent (in terms of global warming potential) methane (CH₄) and CO₂ emissions. It is estimated that approximately 1.5 Gt y^?1 of MRB are currently collected worldwide. The energy content of this biomass is approximately 12 EJ, but only a fraction is currently utilized. An integrated assessment model is used to project future MRB generation and its utilization for energy, with and without a hypothetical climate policy to stabilize atmospheric CO₂ concentrations. Given an anticipated price for biomass energy (and carbon under a policy scenario), by the end of the century, it is projected that nearly 60% of global MRB would be converted to about 8 EJ y^?1 of energy in a reference scenario, and nearly all of global MRB would be converted into 16 EJ y^?1 of energy by the end of the century under a climate policy scenario.     

Biomass yield and energy analysis of soybean production in relation to fertilizer-NPK and organic manure

The study attempts to quantify the root biomass and density, nodulation, crop biomass and grain yield of soybean, to analyze crop growth and energy (renewable and non-renewable) inputs in relation to fertilizer-NPK and organic manure. Observations were recorded from soybean grown with no fertilizer, NPK and NPK + FYM (farmyard manure). The root biomass (BM_root) increased significantly with NPK + FYM compared to NPK and control. The trend of BM_root was best fitted with a third order polynomial. Root length density was higher in NPK + FYM. Biomass of stem, petiole and leaf were significantly greater in NPK + FYM than other treatments, relative contribution to total biomass at physiological maturity were stem 29%, petiole 9%, leaf 17% and pod 46%; quadratic regression models best represented the stem, petiole and leaf biomass data. A maximum LAI of 4.88, total biomass of 633 g m^?2 at maturity, CGR of 18.4 g m^?2 d^?1 were recorded in NPK + FYM. Grain yields increased by 72.5 and 98.5%, and stover yields by 56.0 and 94.8% in NPK and NPK + FYM, respectively over control. Though the total energy input in NPK + FYM was greater than those in NPK and control, the share of renewable energy was much higher with greater net energy output and non-renewable energy productivity in NPK + FYM than NPK. The use efficiency of non-renewable energy was also higher in NPF + FYM. Thus, a combination of NPK-fertilizer and organic manure (FYM) could be the viable nutrient management option for soybean production.     

Anaerobic digestion of by-products of sugar beet and starch potato processing

Anaerobic digestion (AD) is a promising option for the environmentally friendly recycling of agricultural by-products. However, overloading of the digester with sugar, starch or protein might cause inhibition of the anaerobic processes. The aim of the present project was to investigate the AD of sugar beet, starch potato by-products and effect of pre-treatment by steam on methane yield of potatoes pulp. The investigated by-products have been: sugar beet pulp silage (SBP), sugar beet tail silage (SBT), potato pulp (PP), potato peel pulp (PPP) and potato fruit water (PFW). All by-products were digested in 1 l eudiometer-batch digesters at 37.5 °C during 28–38 days. The specific methane yields of SBP and SBT were 430 and 481 l_N kg^?1 volatile solids (VS), respectively. The specific methane yields of PP, PPP and PFW were 332, 377 and 323 l_N (kg VS)^?1. A steam pre-treatment significantly increased the specific methane yield of PP up to 373 l_N (kg VS)^?1.     

The influence of CO2 mitigation incentives on profitability of eucalyptus production on clay settling areas in Florida

Fast growing, short-rotation tree crops provide unique opportunities to sequester carbon on phosphate-mined lands in central Florida and, if used as a biofuel, can reduce CO₂ emissions associated with electricity generation. Base case land expectation values (LEVs) of phosphate-mined land under Eucalyptus amplifolia (EA) forestry range from 762 to 6507 $ ha^?1 assuming real discount rates of 10% and 4%, respectively. Assuming 5 $ Mg^?1 C, these LEVs increase from 3% to 24% with incentives for in situ carbon sequestration benefits, or 21% to 73% given in situ carbon sequestration with additional incentives for reducing CO₂ emissions through the use of EA as an energy feedstock. Potential benefits from below-ground C sequestration and mine land reclamation are estimated to be worth an additional 5642–11,056 $ ha^?1.     

Laboratory investigations on continuous bio-methanization of energy crops as mono-substrate without supplementation

Continuous bio-methanization of an energy crop, namely the beet silage, was investigated in this laboratory-scale work as mono-substrate, using a mesophilic biogas digester controlled by a fuzzy logic control (FLC) technique and without using any supplementing or buffering agent, despite the low pH of the substrate around 3.80. The temperature, pH, redox potential (ORP), daily biogas production and composition of digester biogas were continuously measured online. During the operation, the hydraulic retention time (HRT) varied between 24.8 and 9 days, as the organic loading rate (OLR) ranged from 2.6 to 4.7 g L^?1 d^?1. The average pH, specific gas production rate (spec. GPR) and volumetric gas production rate (vol. GPR) were determined to be 7.12, 0.31 L g VS^?1 d^?1 and 1.084 L L^?1 d^?1, respectively. The average methane (CH₄) content of digester biogas was about 56%. The FLC technique, which was developed at HAW Hamburg for anaerobic conversion of acidic energy crops to methane, determined the daily feeding volume (～ OLR/HRT) for the biogas digester, depending on the feedback from online pH and methane measurements, and on the calculation of the spec. GPR. The spec. GPR was calculated by the corrected daily biogas production. Through online monitoring of pH, biogas production rate and composition, and by use of the FLC technique, the acidic beet silage could continuously be converted to biogas, without using manure or any other kind of buffering or supplementing agent(s). The lab-scale anaerobic biogas digester performed stable and safe, without encountering any problems of instability, as indicated by an adequate amount of buffering capacity, a VFA content below 0.5 g L^?1 and a neutral pH range throughout the study.     

Anaerobic digestion of slaughterhouse by-products

Anaerobic digestion of animal by-products was investigated in batch and semi-continuously fed, reactor experiments at 55 °C and for some experiments also at 37 °C. Separate or mixed by-products from pigs were tested. The methane potential measured by batch assays for meat- and bone flour, fat, blood, hair, meat, ribs, raw waste were: 225, 497, 487, 561, 582, 575, 359, 619 dm³ kg^?1 respectively, corresponding to 50–100% of the calculated theoretical methane potential. Dilution of the by-products had a positive effect on the specific methane yield with the highest dilutions giving the best results. High concentrations of long-chain fatty acids and ammonia in the by-products were found to inhibit the biogas process at concentrations higher than 5 g lipids dm^?3 and 7 g N dm^?3 respectively. Pretreatment (pasteurization: 70 °C, sterilization: 133 °C, and alkali hydrolysis (NaOH) had no effect on achieved methane yields. Mesophilic digestion was more stable than thermophilic digestion, and higher methane yield was noticed at high waste concentrations. The lower yield at thermophilic temperature and high waste concentration was due to ammonia inhibition. Co-digestion of 5% pork by-products mixed with pig manure at 37 °C showed 40% higher methane production compared to digestion of manure alone.     

Modeling climate change mitigation from alternative methods of charcoal production in Kenya

Current carbon accounting methodologies do not accommodate activities that involve emissions reductions from both land-use change and energy production. This paper analyzes the climate change mitigation potential of charcoal production in East Africa by examining the impact of changing both land management and technology. Current production in a major charcoal producing region of Kenya where charcoal is made as a by-product of land clearance for commercial grain production is modeled as the “business-as-usual” scenario. Alternative production systems are proposed based on coppice management of native or exotic trees. Improved kilns are also considered. Changes in aboveground, belowground, and soil carbon are modeled and two distinct baseline assessments are analyzed: one is based on a fixed area of land and one is based on the quantity of non-renewable fuel that is displaced by project activities. The magnitude of carbon emissions reductions varies depending on land management as well as the choice of carbonization technology. However, these variations are smaller than the variations arising from the choice of baseline methodology. The fixed-land baseline yields annualized carbon emission reductions equivalent to 0.5–2.8 tons per year (t y^?1) with no change in production technology and 0.7–3.5 t y^?1 with improved kilns. In contrast, the baseline defined by the quantity of displaced non-renewable fuel is 2–6 times larger, yielding carbon emissions reductions of 1.4–12.9 t y^?1 with no change in production technology and 3.2–20.4 t y^?1 with improved kilns. The results demonstrate the choice of baseline, often a political rather than scientific decision, is critical in assessing carbon emissions reductions.