Give them credit‐the greenhouse gas performance of regional biogas systems

Anaerobic digestion to produce biogas is an important decentralised renewable energy technology. Production varies extensively between different countries and within countries, as biogas production is heavily dependent on local and regional feedstocks. In Germany, distinct regional differences can be observed. Therefore, understanding the kinds of biogas systems operating within a region is crucial to determine their greenhouse gas (GHG) mitigation potential and carbon neutrality. This is the first study to conduct an integrated life cycle assessment of biogas configurations in the landscape (biogas plants and their biomass catchments) for an entire region. RELCA a ‘REgional Life Cycle inventory Assessment’ approach was used to model the GHG mitigation potential of 425 biogas plants in the region of Central Germany (CG), aggregated to nine biogas clusters, based on feedstock mix (e.g. animal manures and energy crops) and installed capacity. GHG emission profiles were generated to compare and to identify the role of GHG credits and size of installed capacity on the mitigation performance of the regional biogas clusters. We found that smaller scaled slurry dominant clusters had significantly better GHG mitigation performance (?0.1 to ?0.2 kg CO_2eq kWh_el^?1), than larger energy crop dominant (EC_dom) clusters (0.04–0.16 kg CO_2eq kWh_el^?1), due to lower cultivation emissions and larger credits for avoided slurry storage. Thus, for the CG region larger EC_dom clusters should be targeted first, to support GHG mitigation improvements to the overall future electricity supplied by the regional biogas systems. With the addition of GHG credits, the CG region is producing biogas with GHG savings (?0.15 kg CO_2eq kWh_el^?1, interquartile range: 0.095 kg CO_2eq kWh_el^?1). This infers that biogas production, as a waste management strategy for animal manures, could have important ramifications for future policy setting and national inventory accounting.     

Life cycle environmental impacts of decommissioning Magnox nuclear power plants in the UK

Purpose

Full life cycle assessment (LCA) impacts from decommissioning have rarely been assessed, largely because few sites have been decommissioned so that the impacts of decommissioning are currently uncertain. This paper presents the results of an LCA study of the ongoing decommissioning of the Magnox power plant at Trawsfynydd in the UK. These results have been used to estimate the potential environmental impacts for the whole UK Magnox fleet of 11 reactors that will have to be decommissioned during this century.

Methods

The functional unit is defined as ‘decommissioning one Magnox power plant’. The system boundary considers all stages in the life cycle of decommissioning, including site management, waste retrieval, plant deconstruction, packaging and storage of intermediate- and low-level wastes (ILW and LLW). High-level waste, i.e. waste fuel is excluded as it was being removed from the site to be reprocessed at Sellafield. The environmental impacts have been estimated using the CML 2001 methodology. Primary data have been sourced from the Trawsfynydd site and the background from Ecoinvent.

Results and discussion

Most impacts from decommissioning are due to the plant deconstruction (25–75 %) and ILW storage and disposal (25–70 %). For the example of global warming potential (GWP), estimated at 241 kt CO₂ eq./functional unit, or 3.5 g CO₂ eq./kWh of electricity generated during the lifetime of the plant, 55 % of the impact is from plant deconstruction and 30 % from ILW disposal. The results for the whole UK Magnox fleet indicate that the impacts vary greatly for different sites. For example, the GWP ranges from 0.89 to 7.14 g CO₂ eq./kWh. If the impacts from storage of waste fuel at Sellafield are included in the estimates, the GWP increases on average by four times. Overall, decommissioning of the UK Magnox reactors would generate 2 Mt of CO₂ eq. without and 11 Mt of CO₂ eq. with the waste from Sellafield. This represents 0.4 and 2 % of the total UK annual emissions, respectively.

Conclusions

The impacts of decommissioning can vary greatly at different sites depending on the amount of waste and electricity generated by the plants. Delaying decommissioning to allow the energy system to decarbonise could reduce the environmental impacts, e.g. GWP could be reduced by 50 %. The impacts could also be reduced by reducing the volume of waste and increasing recycling of materials. For example, recycling 70 % of steel would reduce the impacts on average by 34 %.     

The effect of local climate and soil drainage on the environmental impact of grass-based milk production

Purpose

System modelling and life cycle assessment (LCA) were used to assess the climate change, acidification and eutrophication impacts of milk production using spring calving pasture-based system. The objective of the study was to evaluate the effect of climate and soil resources on the environmental impact per unit milk produced at the farm gate from low-cost, grass-based rotational-grazing dairy production.

Methods

A dairy system model, Dairy_sim, designed to identify optimum grass-based spring calving production systems considering the interaction between climate and soil resources was tested using the Irish National Dairy Blueprint and then used to assess regional differences of system management with well, moderately, mixed moderately-poorly and poorly drained soil resources available. Life cycle assessment was used to quantify environmental impacts of climate and soil drainage status. The Dairy_sim output was used as activity data for the LCA model.

Results and discussion

Differences were found in the management tactics influenced by climate and drainage resource. The impact of poor drainage reduced stocking rate, increased housing time and had greater need for later cut silage and more reliance on silage. Climate change, acidification and eutrophication impacts were greater for optimum management on poorly drained soil. The climate change ranged from 1.06 kg CO₂ eq./kg (well drained) to 1.18 kg CO₂ eq./kg (poorly drained) of energy corrected milk (ECM). The acidification and eutrophication ranged from 3.87 to 6.85 g SO₂ eq./kg ECM and 2.69 to 3.64 g PO₄ eq./kg ECM, respectively. Around 50% of poorly drained soil resource can be easily accommodated in dairy systems with little increase in environmental impact, where poor drained portion is utilised for silage.

Conclusions

LCA combined with a system optimization model revealed how dairy farm management practises constrained by poor land resource increased the environmental impact per unit product.

     

Conservation agriculture, increased organic carbon in the top-soil macro-aggregates and reduced soil CO2 emissions

Background and aims

Conservation agriculture, the combination of minimal soil movement (zero or reduced tillage), crop residue retention and crop rotation, might have the potential to increase soil organic C content and reduce emissions of CO₂.

Methods

Three management factors were analyzed: (1) tillage (zero tillage (ZT) or conventional tillage (CT)), (2) crop rotation (wheat monoculture (W), maize monoculture (M) and maize-wheat rotation (R)), and (3) residue management (with (+r), or without (?r) crop residues). Samples were taken from the 0–5 and 5–10?cm soil layers and separated in micro-aggregates (< 0.25?mm), small macro-aggregates (0.25 to 1?mm) and large macro-aggregates (1 to 8?mm). The carbon content of each aggregate fraction was determined.

Results

Zero tillage combined with crop rotation and crop residues retention resulted in a higher proportion of macro-aggregates. In the 0–5?cm layer, plots with a crop rotation and monoculture of maize and wheat in ZT+r had the greatest proportion of large stable macro-aggregates (40%) and highest mean weighted diameter (MWD) (1.7?mm). The plots with CT had the largest proportion of micro-aggregates (27%). In the 5–10?cm layer, plots with residue retention in both CT and ZT (maize 1?mm and wheat 1.5?mm) or with monoculture of wheat in plots under ZT without residues (1.4?mm) had the greatest MWD. The 0–10?cm soil layer had a greater proportion of small macroaggregates compared to large macro-aggregates and micro-aggregates. In the 0–10?cm layer of soil with residues retention and maize or wheat, the greatest C content was found in the small and large macro-aggregates. The small macro-aggregates contributed most C to the organic C of the sample. For soil cultivated with maize, the CT treatments had significantly higher CO₂ emissions than the ZT treatments. For soil cultivated with wheat, CTR-r had significantly higher CO₂ emissions than all other treatments.

Conclusion

Reduction in soil disturbance combined with residue retention increased the C retained in the small and large macro-aggregates of the top soil due to greater aggregate stability and reduced the emissions of CO₂ compared with conventional tillage without residues retention and maize monoculture (a cultivation system normally used in the central highlands of Mexico).     

Using a Crop Growth Model to Quantify Regional Biogas Potentials: an Example of the Model Region Biberach (South-West Germany)

Over the last decade, political framework conditions in the energy sector provoked a strong focus on biogas production in Germany. In this context, a sufficient and secure regional biomass supply is needed in order to run biogas plants economically. It is important to estimate which biomass amounts can be produced and are available for bioenergy production in a defined region. The present study focused on a model-based approach quantifying the biomass and, from this, the resulting biogas potential of the model region of Biberach (south-west Germany) using the process-oriented crop growth model DSSAT 4.0. Considering the regional soil and climate conditions of the model region, dry matter yields of maize, triticale, and a crop rotation system (CRS) of maize and triticale including different management systems (change in sowing and harvest date) were simulated. The results indicated an adequate model fit between simulated and measured yields. Dry matter yields of maize (14.7 t ha^?1), triticale (12.7 t ha^?1), and the CRS (18.1–19.2 t ha^?1) differed significantly, indicating that the chosen CRS provided the highest dry matter yields. The biomass potential of all crops was simulated considering different bioenergy scenarios depending on the available agricultural land used for bioenergy. The highest biomass potential was provided by the management system consisting of maize and triticale sown on 1 May and 15 October, respectively. Finally, an additional energy potential of 45,000 kW_el (bioenergy scenario 50/50 % of the agricultural land used for biogas production) and of 5,700 kW_el (bioenergy scenario 25/25 % of the agricultural land used for biogas production) was determined for the county of Biberach by implementing a CRS, which consisted of maize and triticale. It could be concluded that an additional biomass potential for biogas production exists in the county. Suitable areas for the location of biogas plants could be identified based on the available biomass potential.     

Life Cycle Assessment of Biomass‐based Combined Heat and Power Plants

Norway, like many countries, has realized the need to extensively plan its renewable energy future sooner rather than later. Combined heat and power (CHP) through gasification of forest residues is one technology that is expected to aid Norway in achieving a desired doubling of bioenergy production by 2020. To assess the environmental impacts to determine the most suitable CHP size, we performed a unit process‐based attributional life cycle assessment (LCA), in which we compared three scales of CHP over ten environmental impact categories—micro (0.1 megawatts electricity [MWe]), small (1 MWe), and medium (50 MWe) scale. The functional units used were 1 megajoule (MJ) of electricity and 1 MJ of district heating delivered to the end user (two functional units), and therefore, the environmental impacts from distribution of electricity and hot water to the consumer were also considered. This study focuses on a regional perspective situated in middle‐Norway's Nord‐ and Sør‐Trøndelag counties. Overall, the unit‐based environmental impacts between the scales of CHP were quite mixed and within the same magnitude. The results indicated that energy distribution from CHP plant to end user creates from less than 1% to nearly 90% of the total system impacts, depending on impact category and energy product. Also, an optimal small‐scale CHP plant may be the best environmental option. The CHP systems had a global warming potential ranging from 2.4 to 2.8 grams of carbon dioxide equivalent per megajoule of thermal (g CO₂‐eq/MJ_th) district heating and from 8.8 to 10.5 grams carbon dioxide equivalent per megajoule of electricity (g CO₂‐eq/MJ_el) to the end user.     

Quantifying greenhouse gases from the production,transportation and utilization of charcoal in developing countries: a case study of Kampala,Uganda

Purpose

This study aims to quantify greenhouse gases (GHGs) from the production, transportation and utilization of charcoal and to assess the possibilities of decreasing greenhouse gases (GHGs) from the charcoal industry in general in Uganda. It also aims to assess the emission intensity of the Ugandan “charcoal production” sector compared to that of some other major charcoal producing nations.

Methods

This work was done in accordance with ISO 14040 methodology for life-cycle assessment (LCA), using GABi 4.0—a software for life-cycle assessment. A cradle-to-grave study was conducted, excluding emissions arising from machinery use during biomass cultivation and harvesting. The distance from charcoal production locations to Kampala was estimated using ArcGIS 10.0 software and a GPS tool. Emission data from a modern charcoal production process (PYREG methane-free charcoal production equipment), which complies with the German air quality standards (TA-Luft), was compared with emissions from a traditional charcoal production process. Four coupled scenarios were modelled to account for differences in the quantity of greenhouse gases emitted from the “traditional charcoal production phase”, “improved charcoal production phase (biomass feedstock sourced sustainably and unsustainably)”, “transportation phase” and “utilization phase”. Data for this study was obtained via literature review and onsite measurements.

Results and discussion

The results showed that greenhouse gases emitted due to charcoal supply and use of traditional production technique in Kampala was 1,554,699 tCO₂eq, with the transportation phase accounting for approximately 0.15 % of total greenhouse gases emitted. The utilization phase (charcoal cookstoves) emitted 723,985 tCO₂eq (46.6 %), while the charcoal production phase emitted 828,316 tCO₂eq (53.3 %). Changing the charcoal production technology from a traditional method to an improved production method (PYREG charcoal process) resulted in greenhouse gases reductions for the city of 230,747 tCO₂eq; however, by using sustainably sourced biomass, this resulted in reductions of 801,817 tCO₂eq.

Conclusions

This study showcased and quantified possible GHG emission reduction scenarios for the charcoal industry in Uganda. The result of 3 tCO₂eq emitted per tonne of charcoal produced, using earth mound method, can be applied to other countries in Eastern Africa where similar charcoal production methods are used; this will allow for somewhat better regional estimates of the inventory of greenhouse gas emissions from the production of charcoal. The results of this study also suggests that the primary use of charcoal for cooking will lead to increases in GHG emissions and increases in deforestation on the long term, if legal frameworks are not made to ensure that biomass used for charcoal production is obtained via sustainable sources or if alternative cheap energy-generating technologies for cooking are not developed and deployed to the masses.     

Assessing environmental consequences of using co-products in animal feed

Purpose

The livestock sector has a major impact on the environment. This environmental impact may be reduced by feeding agricultural co-products (e.g. beet tails) to livestock, as this transforms inedible products for humans into edible products, e.g. pork or beef. Nevertheless, co-products have different applications such as bioenergy production. Based on a framework we developed, we assessed environmental consequences of using co-products in diets of livestock, including the alternative application of that co-product.

Methods

We performed a consequential life cycle assessment, regarding greenhouse gas emissions (including emissions related to land use change) and land use, for two case studies. Case 1 includes increasing the use of wheat middlings in diets of dairy cattle at the expense of using it in diets of pigs. The decreased use of wheat middlings in diets of pigs was substituted with barley, the marginal product. Case 2 includes increasing the use of beet tails in diets of dairy cattle at the expense of using it to produce bioenergy. During the production of biogas, electricity, heat and digestate (that is used as organic fertilizer) were produced. The decrease of electricity and heat was substituted with fossil fuel, and digestate was substituted with artificial fertilizer.

Results and discussion

Using wheat middlings in diets of dairy cattle instead of using it in diets of pigs resulted in a reduction of 329 kg CO₂ eq per ton wheat middlings and a decrease of 169 m² land. Using beet tails in diets of dairy cattle instead of using it as a substrate for anaerobic digestion resulted in a decrease of 239 kg CO₂ eq per ton beet tails and a decrease of 154 m² land. Emissions regarding land use change contributed significantly in both cases but had a high uncertainty factor, ±170 ton CO₂ ha^?1. Excluding emissions from land use change resulted in a decrease of 9 kg CO₂ eq for case 1 ‘wheat middlings’ and an increase of 50 kg CO₂ eq for case 2 ‘beet tails’.

Conclusions

Assessing the use of co-products in the livestock sector is of importance because shifting its application can reduce the environmental impact of the livestock sector. A correct assessment of the environmental consequences of using co-products in animal feed should also include potential changes in impacts outside the livestock sector, such as the impact in the bioenergy sector.     

Carbon footprint of spring barley in relation to preceding oilseeds and N fertilization

Purpose

Carbon footprint of field crops can be lowered through improved cropping practices. The objective of this study was to determine the carbon footprint of spring barley (Hordeum vulgare L.) in relation to various preceding oilseed crops that were fertilized at various rates of inorganic N the previous years. System boundary was from cradle-to-farm gate.

Materials and methods

Canola-quality mustard (Brassica juncea L.), canola (Brassica napus L.), sunflower (Helianthus annuus L.), and flax (Linum usitatissimum L.) were grown under the N fertilizer rates of 10, 30, 70, 90, 110, 150, and 200?kg?N?ha^?1 the previous year, and spring barley was grown on the field of standing oilseed stubble the following year. The study was conducted at six environmental sites; they were at Indian Head in 2005, 2006 and 2007, and at Swift Current in 2004, 2005 and 2006, Saskatchewan, Canada.

Results and discussion

On average, barley grown at humid Indian Head emitted greenhouse gases (GHGs) of 1,003?kg?CO₂eq?ha^?1, or 53% greater than that at the drier Swift Current site. Production and delivery of fertilizer N to farm gate accounted for 26% of the total GHG emissions, followed by direct and indirect emissions of 28% due to the application of N fertilizers to barley crop. Emissions due to N fertilization were 26.6 times the emission from the use of phosphorous, 5.2 times the emission from pesticides, and 4.2 times the emission from various farming operations. Decomposition of crop residues contributed emissions of 173?kg?CO₂eq?ha^?1, or 19% of the total emission. Indian Head-produced barley had significantly greater grain yield, resulting in about 11% lower carbon footprint than Swift Current-produced barley (0.28 vs. 0.32?kg?CO₂eq?kg^?1 of grain). Emissions in the barley production was a linear function of the rate of fertilizer N applied to the previous oilseed crops due to increased emissions from crop residue decomposition coupled with higher residual soil mineral N.

Conclusions

The key to lower the carbon footprint of barley is to increase grain yield, make a wise choice of crop types, reduce N inputs to crops grown in the previous and current growing seasons, and improved N use efficiency.     

Effect of biochar amendment on maize yield and greenhouse gas emissions from a soil organic carbon poor calcareous loamy soil from Central China Plain

Aims

A field experiment was conducted to investigate the effect of biochar on maize yield and greenhouse gases (GHGs) in a calcareous loamy soil poor in organic carbon from Henan, central great plain, China.

Methods

Biochar was applied at rates of 0, 20 and 40?t?ha^?1 with or without N fertilization. With N fertilization, urea was applied at 300?kg?N ha^?1, of which 60% was applied as basal fertilizer and 40% as supplementary fertilizer during crop growth. Soil emissions of CO₂, CH₄ and N₂O were monitored using closed chambers at 7?days intervals throughout the whole maize growing season (WMGS).

Results

Biochar amendments significantly increased maize production but decreased GHGs. Maize yield was increased by 15.8% and 7.3% without N fertilization, and by 8.8% and 12.1% with N fertilization under biochar amendment at 20?t?ha^?1 and 40?t?ha^?1, respectively. Total N₂O emission was decreased by 10.7% and by 41.8% under biochar amendment at 20?t?ha^?1 and 40?t?ha^?1 compared to no biochar amendment with N fertilization. The high rate of biochar (40?t?ha^?1) increased the total CO₂ emission by 12% without N fertilization. Overall, biochar amendments of 20?t?ha^?1 and 40?t?ha^?1 decreased the total global warming potential (GWP) of CH₄ and N₂O by 9.8% and by 41.5% without N fertilization, and by 23.8% and 47.6% with N fertilization, respectively. Biochar amendments also decreased soil bulk density and increased soil total N contents but had no effect on soil mineral N.

Conclusions

These results suggest that application of biochar to calcareous and infertile dry croplands poor in soil organic carbon will enhance crop productivity and reduce GHGs emissions.     

Development and characterization of wheat lines carrying stem rust resistance gene Sr43 derived from Thinopyrum ponticum

Key message

Wheat lines carrying Ug99-effective stem rust resistance gene Sr43 on shortened alien chromosome segments were produced using chromosome engineering, and molecular markers linked to Sr43 were identified for marker-assisted selection.

Abstract

Stem rust resistance gene Sr43, transferred into common wheat (Triticum aestivum) from Thinopyrum ponticum, is an effective gene against stem rust Ug99 races. However, this gene has not been used in wheat breeding because it is located on a large Th. ponticum 7el₂ chromosome segment, which also harbors genes for undesirable traits. The objective of this study was to eliminate excessive Th. ponticum chromatin surrounding Sr43 to make it usable in wheat breeding. The two original translocation lines KS10-2 and KS24-1 carrying Sr43 were first analyzed using simple sequence repeat (SSR) markers and florescent genomic in situ hybridization. Six SSR markers located on wheat chromosome arm 7DL were identified to be associated with the Th. ponticum chromatin in KS10-2 and KS24-1. The results confirmed that KS24-1 is a 7DS·7el₂L Robertsonian translocation as previously reported. However, KS10-2, which was previously designated as a 7el₂S·7el₂L-7DL translocation, was identified as a 7DS-7el₂S·7el₂L translocation. To reduce the Th. ponticum chromatin carrying Sr43, a BC₂F₁ population (Chinese Spring//Chinese Spring ph1bph1b*2/KS10-2) containing ph1b-induced homoeologous recombinants was developed, tested with stem rust, and genotyped with the six SSR markers identified above. Two new wheat lines (RWG33 and RWG34) carrying Sr43 on shortened alien chromosome segments (about 17.5 and 13.7 % of the translocation chromosomes, respectively) were obtained, and two molecular markers linked to Sr43 in these lines were identified. The new wheat lines with Sr43 and the closely linked markers provide new resources for improving resistance to Ug99 and other races of stem rust in wheat.     

Determination of the critical soil mineral nitrogen concentration for maximizing maize grain yield

Background and aims

A critical soil mineral nitrogen concentration (N_min) for guiding fertilizer application and maximizing maize grain yield is needed.

Methods

A three-year field experiment with three N regimes, unfertilized (N0), optimized N management (Opt.) and conventional N practice (Con.) was performed in maize.

Results

The mean soil N_min in 0–60 cm soil profile for N0, Opt. and Con. treatments was 2.0, 6.7 and 8.9 mg?kg^–1 at V8–VT growth stages and 2.2, 6.1 and 11.2 mg?kg^–1 on average over the whole growth season, respectively. Correspondingly, the soil N supplying capacity (soil N_min content?+?fertilizer N) of the three N treatments was smaller, identical or greater than the plant N accumulation at different growth stages. The Opt. treatment had significantly higher N use efficiency, N recovery efficiency and N partial factor productivity compared with the Con. treatment, while it did not cause maize yield loss.

Conclusions

Compared with the insensitivity of the critical shoot N dilution curve to excessive N application, soil N_min showed strong response to all treatments. We propose a minimum of soil N_min of 6.1 mg?kg^–1 at the sowing–V8, 6.7 mg?kg^–1 at the V8–VT, and 5.5 mg?kg^–1 at the VT–R6 growing stages with an average of about 6 mg?kg^–1 of soil N_min in the 0–60 soil depth for maximizing maize yield and N use efficiency in northern China. To maintain this critical N_min value over the whole growth period, N topdressing at V8 and V12 stages was recommended.     

Life cycle assessment of bio-based ethanol produced from different agricultural feedstocks

Purpose

Bio-based products are often considered sustainable due to their renewable nature. However, the environmental performance of products needs to be assessed considering a life cycle perspective to get a complete picture of potential benefits and trade-offs. We present a life cycle assessment of the global commodity ethanol, produced from different feedstock and geographical origin. The aim is to understand the main drivers for environmental impacts in the production of bio-based ethanol as well as its relative performance compared to a fossil-based alternative.

Methods

Ethanol production is assessed from cradle to gate; furthermore, end-of-life emissions are also included in order to allow a full comparison of greenhouse gas (GHG) emissions, assuming degradation of ethanol once emitted to air from household and personal care products. The functional unit is 1 kg ethanol, produced from maize grain in USA, maize stover in USA, sugarcane in North-East of Brazil and Centre-South of Brazil, and sugar beet and wheat in France. As a reference, ethanol produced from fossil ethylene in Western Europe is used. Six impact categories from the ReCiPe assessment method are considered, along with seven novel impact categories on biodiversity and ecosystem services (BES).

Results and discussion

GHG emissions per kilogram bio-based ethanol range from 0.7 to 1.5 kg CO₂ eq per kg ethanol and from 1.3 to 2 kg per kg if emissions at end-of-life are included. Fossil-based ethanol involves GHG emissions of 1.3 kg CO₂ eq per kg from cradle-to-gate and 3.7 kg CO₂ eq per kg if end-of-life is included. Maize stover in USA and sugar beet in France have the lowest impact from a GHG perspective, although when other impact categories are considered trade-offs are encountered. BES impact indicators show a clear preference for fossil-based ethanol. The sensitivity analyses showed how certain methodological choices (allocation rules, land use change accounting, land use biomes), as well as some scenario choices (sugarcane harvest method, maize drying) affect the environmental performance of bio-based ethanol. Also, the uncertainty assessment showed that results for the bio-based alternatives often overlap, making it difficult to tell whether they are significantly different.

Conclusions

Bio-based ethanol appears as a preferable option from a GHG perspective, but when other impacts are considered, especially those related to land use, fossil-based ethanol is preferable. A key methodological aspect that remains to be harmonised is the quantification of land use change, which has an outstanding influence in the results, especially on GHG emissions.     

Well-to-wheel analysis on greenhouse gas emission and energy use with natural gas in Korea

Purpose

In Korea, natural gas is widely used as city gas, fuel for electricity generation, and fuel for transportation (e.g., city bus). However, the environmental impact associated with the use of natural gas in Korea has not been paid much attention to. In this study, well-to-wheel (WTW) analysis on the greenhouse gas (GHG) emissions and energy uses associated with natural gas in Korea was performed by considering every step from feedstock recovery to final use in the vehicle operation.

Methods

The raw data used in the analysis were mainly provided by Korean natural gas industry and related associations. The additional information, especially for the processes in foreign countries, was also collected by literature survey. We adopted the GREET (Greenhouse Gases, Regulated Emissions, and Energy Use in Transportation) model as a base WTW analysis tool, which was developed by the U.S. Argonne National Laboratory. However, the WTW analysis on natural gas in Korea is far different from that of the U.S, because ~99 % of natural gas used in Korea is imported from the oversea countries in the form of liquefied natural gas (LNG). For this reason, detailed parameters in GREET were changed for Korean situation, and especially, significant modifications were made on liquefaction, LNG transportation and storage, and re-gasification processes.

Results and discussion

As a result of the analysis, the well-to-pump GHG emissions of city gas and compressed natural gas are calculated as 25,717–30,178 and 28,903–33,422 g CO₂ eq./GJ_{Fianl_fuel}, respectively. The WTW GHG emission of compressed-natural-gas-fueled city bus is calculated as 1,348–1,417 g CO₂ eq./km. These values are relatively larger than those of the U.S., because most of the natural gas used in the U.S. is transported by pipeline in a gaseous state, which typically takes less energy and associated GHG emissions, as compared to the import of LNG in Korea. Finally, sensitivity analysis is performed on the parameters, which have either range of values among various sources or uncertainties due to lack of accurate information.

Conclusions

The results show that further investigation on three parameters, i.e., CO₂ venting during natural gas processing, CH₄ leakage in Korea, and CH₄ leakage during recovery process, would be helpful to further improve overall accuracy of the analysis.     

Assessment of nitrate leaching loss on a yield-scaled basis from maize and wheat cropping systems

Background and aims

It is so far a gap in knowledge to assess nitrate (NO₃ ^?) leaching loss linking with crop yield for a given cereal cropping system.

Methods

We conducted a meta-analysis on 32 published studies reporting both NO₃ ^? leaching losses and crop yields in the maize (N?=?20) and wheat (N?=?12) systems.

Results

On average, 22 % and 15 % of applied fertilizer N to wheat and maize systems worldwide are leached in the form of NO₃ ^?, respectively. The average area-scaled NO₃ ^- leaching loss for maize (57.4 kg N ha^?1) was approx. two times higher than for wheat (29.0 kg N ha^?1). While, if scaled to crop yields, the average yield-scaled NO₃ ^? losses were comparable between maize (5.40 kg N Mg^?1) and wheat (5.41 kg N Mg^?1) systems. Across all sites, the lowest yield-scaled NO₃ ^? leaching losses were observed at slightly suboptimal fertilization rates, corresponding to 90 % and 96 % of maximum maize or wheat yields, respectively.

Conclusions

Our findings suggest that small adjustments of agricultural N management practices can effectively reduce yield-scaled NO₃ ^? leaching losses. However, further targeted field experiments are still needed to identify at regional scale best agricultural management practices for reducing yield-scaled NO₃ ^? leaching losses in maize and wheat systems.     

Mitigation of greenhouse gas emissions from reed canary grass in paludiculture: effect of groundwater level

Background and aims

Combination of rewetting and wetland crop cultivation (paludiculture) is pursued as a wider carbon dioxide (CO₂) mitigation option in drained peatland. However, information on the overall greenhouse gas (GHG) balance for paludiculture is lacking. We investigated the GHG balance of peatlands grown with reed canary grass (RCG) and rewetted to various extents.

Methods

Gas fluxes of CO₂, methane (CH₄) and nitrous oxide (N₂O) were measured with a static chamber technique for 10 months from mesocosms sown with RCG and manipulated to ground water levels (GWL) of 0, ?10, ?20, ?30 and ?40 cm below the soil surface. Gross primary production (GPP) was estimated from the above ground biomass yield.

Results

The mean dry biomass yield across all water table treatments was 6 Mg ha^?1 with no significant differences between the treatments. Raising the GWL to the surface decreased both the net ecosystem exchange (NEE) of CO₂ and N₂O emissions whereas CH₄ emissions increased. Total cumulative GHG emissions (for 10 months) corresponded to 0.08, 0.13, 0.61, 0.68 and 0.98 kg CO₂ equivalents m^?2 from the GWL treatments at 0, ?10, ?20, ?30 and ?40 cm below the soil surface, respectively.

Conclusions

The results showed that a reduction in total GHG emission can be achieved without losing the productivity of newly established RCG when GWL is maintained close to the surface. Further studies should address the practical constrains and long-term productivity of RCG cultivation in rewetted peatlands.     

Exploring variability in methods and data sensitivity in carbon footprints of feed ingredients

Purpose

Production of feed is an important contributor to life cycle greenhouse gas emissions, or carbon footprints (CFPs), of livestock products. Consequences of methodological choices and data sensitivity on CFPs of feed ingredients were explored to improve comparison and interpretation of CFP studies. Methods and data for emissions from cultivation and processing, land use (LU), and land use change (LUC) were analyzed.

Method

For six ingredients (maize, wheat, palm kernel expeller, rapeseed meal, soybean meal, and beet pulp), CFPs resulting from a single change in methods and data were compared with a reference CFP, i.e., based on IPCC Tier 1 methods, and data from literature.

Results and discussion

Results show that using more detailed methods to compute N₂O emissions from cultivation hardly affected reference CFPs, except for methods to determine $ \mathrm{NO}_3^{-} $ leaching (contributing to indirect N₂O emissions) in which the influence is about ?7 to +12 %. Overall, CFPs appeared most sensitive to changes in crop yield and applied synthetic fertilizer N. The inclusion of LULUC emissions can change CFPs considerably, i.e., up to 877 %. The level of LUC emissions per feed ingredient highly depends on the method chosen, as well as on assumptions on area of LUC, C stock levels (mainly aboveground C and soil C), and amortization period.

Conclusions

We concluded that variability in methods and data can significantly affect CFPs of feed ingredients and hence CFPs of livestock products. Transparency in methods and data is therefore required. For harmonization, focus should be on methods to calculate $ \mathrm{NO}_3^{-} $ leaching and emissions from LULUC. It is important to consider LUC in CFP studies of food, feed, and bioenergy products.     

Effects of nitrogen fertilization and root interaction on the agronomic traits of intercropped maize, and the quantity of microorganisms and activity of enzymes in the rhizosphere

Aims

To elucidate the mechanisms of the beneficial effects of below-ground root interactions in maize plus legume intercropping system,

Methods

A pot experiment was conducted using root separation techniques.

Results

It is shown that root interaction and nitrogen fertilization increased chlorophyll content and improved plant characteristics of maize, and the effect of root interaction was significant (p<0.05). Compared to a full root separation treatment, no root separation increased the leaf and grain nitrogen contents, and economic and biological yields per maize plant by 9.3? %, 6.0? %, 14.0? %, and 6.5? %, respectively. Root interaction and nitrogen fertilization enhanced the numbers of bacteria, fungi, actinomycetes and Azotobacteria and the activities of urease, invertase, acid-phosphatase and protease in soil. Correlation analyses revealed that the quantity of microorganisms and the activity of the aforementioned enzymes were all positively or significantly (p<0.05) positively correlated with chlorophyll content, plant height and economic and biological yields per maize plant.

Conclusions

The findings demonstrate that root interactions are important in improving the soil micro-ecological environment, increasing microbial quantity and enzyme activity in soil, and enhancing crop yield.     

Regional carbon footprint analysis of dairy feeds for milk production in the USA

Purpose

A greenhouse gas emissions analysis (carbon footprint) was conducted for cultivation, harvesting, and production of common dairy feeds used for the production of dairy milk in the USA. The goal was to determine the carbon footprint (grams CO₂ equivalents (gCO₂e)/kg of dry feed) in the USA on a regional basis, identify key inputs, and make recommendations for emissions reduction.

Methods

Commonly used dairy feeds in the USA, such as soybeans, alfalfa, corn, and others, were identified based on a recent literature review and information from dairy farm surveys. The following input data for the cultivation and harvesting of dairy feeds were collected for five US regions: crop production data, energy input, soil amendments, and crop protection chemicals. Life cycle inventory input data were mainly collected from the US Department of Agriculture National Agricultural Statistical Service on a state-by-state basis as well as from state extension services forage crop budget estimates. In addition to consulting other life cycle assessment studies and published articles and reports, this cradle-to-farm gate carbon footprint analysis was conducted using the Ecoinvent? unit processes in SimaPro version 7.1? (PRé Consultants 2009).

Results

The final carbon footprint results (gCO₂e/kg of dry dairy feed) varied regionally depending on a number of factors such as lime and fertilizer application rates. The average national US carbon footprint results of the main feeds were: corn grain (390), corn silage (200), dried distillers grains with solubles (910 dry mill, 670 wet mill), oats (850), soybeans (390), soybean meal (410), winter wheat (430), alfalfa hay (170), and forage mix (160).

Conclusions and recommendations

The southeast dairy region generally showed a relatively high level of carbon footprint for most feeds, and this is attributable to the higher application rates of both synthetic fertilizers and lime. The highest contributor to carbon footprint for most regions (apart from soybeans and soybean meal) was due to the application of inorganic nitrogen fertilizer. Efficient transfer of knowledge to farmers with regards to fertilizer best management practices such as precision application of farm nutrients may contribute significantly to reducing regional crop carbon footprints.