Greenhouse gas (GHG) emissions related to composting of organic waste and use of compost was assessed from a waste management perspective. The GHG accounting for composting includes use of electricity and fuels, emissions of methane and nitrous oxide from the composting process, and savings obtained by the use of the compost. The GHG account depends on waste type and composition (kitchen organics, garden waste), technology type (open systems, closed systems, home composting), the efficiency of off-gas cleaning at enclosed composting systems, and the use of the compost. The latter is an important issue and is related to the long term binding of carbon in the soil, to related effects in terms of soil improvement and to what the compost substitutes; this could be fertilizer and peat for soil improvement or for growth media production. The overall Global Warming Factor (GWF) for composting therefore varies between significant savings (-900 kg CO 2 -equivalents tonne -1 wet waste (ww)) and a net load (300 kg CO 2 -equivalents tonne -1 ww). The major savings are obtained by use of compost as a substitute for peat in the production of growth media. However, it may be difficult for a specific composting plant to document how the compost is used and what it actually substitutes for. Two cases representing various technologies were assessed showing how GHGs accounting can be done when specific information and data are available.

Anaerobic digestion (AD) of source separated municipal solid waste (MSW) and use of the digestate is presented from a global warming (GW) point of view by providing ranges of greenhouse gas (GHG) emissions useful for calculation of global warming factors (GWFs), i.e. the contribution to GW measured in CO 2 -equivalents tonne -1 wet waste. The GHG accounting was done distinguishing between direct contributions at the AD plant and indirect upstream or downstream contributions. GHG accounting for a generic AD plant with either biogas utilization at the plant or upgrading of the gas for vehicle fuel -in both cases the digestate was used for fertilizer substitution -resulted in a GWF from -375 (a saving) to 111 (a load) kg CO 2 -eq. tonne -1 wet waste. This large range was a result of the variation found for a number of parameters. In descending order of importance these were: energy substitution by biogas, N 2 O-emission from digestate in soil, fugitive emission of methane, unburned methane, carbon bound in soil and fertilizer substitution. GWF for a specific AD plant was in the range -95 to 28 kg CO 2 -eq. tonne -1 of wet waste. The ranges of uncertainty, especially of fugitive losses of methane and carbon sequestration highly influenced this result. Compared to the few published GWFs for AD, the range of our data was much larger demonstrating the need to use a consistent and robust approach to GHG accounting and simultaneously accept that some key parameters are highly uncertain.

International audienceAs compost use in agriculture increases, there is an urgent need to evaluate the specific environmental benefits and impacts as compared with other types of fertilizers and soil amendments. While the environmental impacts associated with compost production have been successfully assessed in previous studies, the assessment of the benefits of compost on plant and soil has been only partially included in few published works. In the present study, we reviewed the recent progresses made in the quantification of the positive effects associated to biowaste compost use on land by using life cycle assessment (LCA). A total of nine environmental benefits were identified in an extensive literature review and quantitative figures for each benefit were drawn and classified into short-, mid-, and long-term. The major findings are the following: (1) for nutrient supply and carbon sequestration, the review showed that both quantification and impact assessment could be performed, meaning that these two benefits should be regularly included in LCA studies. (2) For pest and disease suppression, soil workability, biodiversity, crop nutritional quality, and crop yield, although the benefits were proved, quantitative figures could not be provided, either because of lack of data or because the benefits were highly variable and dependent on specific local conditions. (3) The benefits on soil erosion and soil moisture could be quantitatively addressed, but suitable impact assessment methodologies were not available. (4) Weed suppression was not proved. Different research efforts are required for a full assessment of the benefits, apart from nutrient supply and carbon sequestration; additional impact categories—dealing with phosphorus resources, biodiversity, soil losses, and water depletion—may be needed for a comprehensive assessment of compost application. Several of the natural mechanisms identified and the LCA procedures discussed in the paper could be extensible to other organic fertilizers and compost from other feedstocks

No abstract

Important greenhouse gas (GHG) emissions related to waste incineration and co-combustion of waste were identified and considered relative to critical aspects such as: the contents of biogenic and fossil carbon, N(2)O emissions, fuel and material consumptions at the plants, energy recovery, and solid residues generated. GHG contributions were categorized with respect to direct emissions from the combustion plant as well as indirect upstream contributions (e.g. provision of fuels and materials) and indirect downstream contributions (e.g. substitution of electricity and heat produced elsewhere). GHG accounting was done per tonne of waste received at the plant. The content of fossil carbon in the input waste, for example as plastic, was found to be critical for the overall level of the GHG emissions, but also the energy conversion efficiencies were essential. The emission factors for electricity provision (also substituted electricity) affected the indirect downstream emissions with a factor of 3-9 depending on the type of electricity generation assumed. Provision of auxiliary fuels, materials and resources corresponded to up to 40% of the direct emission from the plants (which were 347-371 kg CO(2)-eq. tonne( -1) of waste for incineration and 735-803 kg CO(2)-eq. tonne(-1) of waste for co-combustion). Indirect downstream savings were within the range of -480 to -1373 kg CO(2)eq. tonne(-1) of waste for incineration and within -181 to -2607 kg CO(2)-eq. tonne(- 1) of waste for co-combustion. N(2)O emissions and residue management did not appear to play significant roles.