Definitions and abbreviations

Life Cycle Assessment of Biogas from Separated slurry

Ash. Ash is the remains after heating the dry matter (DM, see below) at 550°C for one hour. Typically, 20% of the dry matter is ash. Another term frequently used for ashes is “fixed solids” (FS).

DM - Dry matter. DM is the fraction of the manure that is left after water has been evaporated due to heating at 80°C to constant weight for typically 24 hours. It typically constitutes 1 – 10% of the slurry by mass (Sommer et al., 2008). In Danish: Tørstof (TS). It also consists of the total of volatile and fixed solids, and is frequently referred to as “total solids” (TS).

Ecoinvent. Ecoinvent database (v2.0) is a life cycle inventory database containing more than 4000 datasets in a wide variety of areas such as agriculture, energy supply, transport, bioenergy and biomaterials, chemicals, construction materials, packaging materials, metal processing, electronics, etc. These data are internationally recognised as high-quality data and are thoroughly documented with extensive background reports, including uncertainty assessment, and they have been independently reviewed.

LCA - Life Cycle Assessment. LCA is the assessment of the environmental impact of a product (or service) throughout its lifespan, i.e. “from cradle to grave”. The environmental impacts are followed through the whole product chain, typically from raw material extraction, through production and use, to final disposal or recycling. This methodology is standardised by the ISO standards ISO 14044 (ISO, 2006a) and ISO 14040 (ISO, 2006b).

Marginal data (marginal supply). Marginal data are used in consequential LCA. This represents the data from the marginal supply, i.e. the one responding to a minute change in demand on the market in question.

TAN - Total Available Nitrogen: TAN is the sum of NH₃-N + NH₄⁺-N. At pH 7.8 almost all the TAN is NH₄⁺(only around 1% is NH₃). TAN is often used as synonym for NH₄⁺ (assuming that the amount of NH₃ is insignificant), e.g. by Hansen et al. (2008) and by the Danish Norm Data (Poulsen et al. (2001), DJF (2008) and DJF (2008)), which use “NH₄⁺” and “TAN” for the same numbers. Strictly speaking, it does not totally cover the same – however, for practice use, they are used as synonyms – also in this study.

VS - Volatile solids. VS are the fraction of DM that volatilises when heating the DM at 550°C for one hour. This is the fraction lost during incineration (Sommer et al., 2008). The content of volatile solids is equal to the difference between the dry matter and ashes (VS = DM – ash). Typically, about 80% of DM is VS for slurry. In Danish: Askefrit tørstof eller glødetab.

VS – easily and heavily degradable. A distinction is made between two types of VS, the easily degradable VS (VS_ED) and the heavily (or slowly) degradable VS (VS_SD). As opposed to the easily degradable VS, the heavily (or slowly) degradable VS are recalcitrant to microbial degradation (and subsequent transformation to CH₄ and CO₂). Among the different components constituting the VS (e.g. lipid, protein, volatile fatty acids, carbohydrates), this distinction between easily and heavily VS concerns only the carbohydrates (the VS from lipid, protein and volatile fatty acids are considered to be easily degradable only). Sommer et al. (2009) define the heavily degradable VS (VS_SD) as the amount of VS in the crude fibre, i.e.: VD_SD=VS_{crude fibre}. The easily degradable VS (VS_ED) is defined as the remaining, from the whole VS content: VS_ED= VS – VS_SD.

Slurry: A mixture of all the faeces, urine and some bedding materials (straw, etc.) which is traditionally collected from the pit below the slatted floors. The dry matter content of slurry is typically 1-10% which is lower than for other types of manure, due to addition of washing water and little use of bedding materials.

Slurry “ex animal”: Slurry directly after its excretion from the animals (ex-excretion) and before undergoing any further transformation (i.e. losses or addition).

Slurry “ex housing”: Slurry leaving the slurry pits in the housing system.

Slurry “ex storage”: Slurry after a long time of outdoor storage.