Biomass - Using Anaerobic Digestion

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Glossary of Terms

  1. Anaerobic digestion (AD): the process by which bacteria that act only in airless (anaerobic) conditions decompose organic matter with the concurrent production of biogas.

  2. Bacteria: Microscopic single celled organisms, which break down the organic matter of the feedstock.

  3. Bioenergy: Energy, in the form of heat, electricity or motion produced from biomass.

  4. Biofuel: Liquid fuels produced from biomass sources; biomass is any mass of biological material.

  5. Biogas: Gas produced by the anaerobic digestion process, which is typically 60% methane (CH4), 40% carbon dioxide (CO2), with other trace compounds.

  6. Biomass: Any organic matter on the Earth’s surface, which has inherent chemical energy content.

  7. Biodegradable Municipal Waste (BMW): Waste from households that is capable of undergoing anaerobic or aerobic decomposition.

  8. BOD: Biological Oxygen Demand.

  9. Centralised Anaerobic Digester(CAD): digester which imports feedstocks from a variety of sources.

  10. Carbon Dioxide (CO2): Gas naturally produced by animals during respiration and through decay of biomass.

  11. Carbon Dioxide Equivalent (CO2e): A metric measure used to compare the emissions from various greenhouse gases based upon their global warming potential.

  12. Combined Heat and Power (CHP) : In normal mode of a generator, the major sources of heat, engine cooling water and exhaust system, are normally discharged to atmosphere; CHP recovers this heat via heat exchangers, increasing the efficiency of the fuel source.

  13. C:N ratio: Percentage of carbon to that of nitrogen in organic materials.

  14. COSHH: Control of Substances Hazardous to Health,Regulations 1994.

  15. Decommissioning: Closing and removing the facility after its useful life.

  16. DEFRA: Department for Environment Food and Rural Affairs.

  17. Digestate: The digested output from the AD process, consisting of fibre and liquor.

  18. Digester : The closed container in which anaerobic digestion takes place.

  19. Dry solids: The residue remaining when water is evaporated away from the residue and dried under heat.

  20. DTI: Department of Trade & Industry.

  21. EA : Environmental Assessment.

  22. Energy balance: Comparison of energy going into a process (inputs), to energy coming out of the process (outputs).

  23. Energy crop: Crops, which are produced specifically for their fuel value.

  24. EU: European Union.

  25. Feedstock: The material fed to the digester.

  26. Fibre: The coarse solids, which have been mechanically separated from the liquid portion of the digestate.

  27. Fossil fuel: Any energy source derived from finite fossil sources eg coal and oil.

  28. Leachate: Water, which flows through the soil or ground and ends up in the watercourse, causing pollution.

  29. Greenhouse Effect: Warming of the atmosphere due to the reduction in outgoing solar radiation resulting from concentrations of greenhouse gases.

  30. Greenhouse Gases (GHG’s): One of six gases (carbon dioxide, methane, nitrous oxide, hydrofluorocarbons, perfluorocarbons and sulphur hexafluoride) that contribute to the natural greenhouse effect.

  31. Hydraulic Retention Time (HRT): The average number of days the fluid is kept within a digester. HRT = Vessel volume/volumetric flowrate.

  32. Input buffer tank: Storage tank for feedstock prior to digestion.

  33. Internal rate of return (IRR): A comparative indication of the profitability of alternative investment options. The Internal Rate of Return is that rate of interest, which makes the present day value of future cash flows equal, in total, to the present day cost of the project.

  34. Liquor: The liquid fertiliser that has been mechanically separated from the coarse fibre portion of the digestate.

  35. Mesophilic digestion: Digestion involving microorganisms with a growth optimum around 20-45oC.

  36. Methane (CH4): Gas produced by anaerobic digestion. Can be used as a fuel source but is between 20 and 25 times as potent CO2 as a greenhouse gas.

  37. Municipal Solid Waste (MSW): Waste from households.

  38. Non-Fossil Fuel Obligation(NFFO): Obligation requiring Regional Electricity Companies to purchase a certain amount of electricity from non-fossil fuel sources.

  39. Nitrate Vulnerable Zone (NVZ): Catchment areas where water quality standards for nitrates at risk of being exceeded.

  40. Pathogens: Organisms that can cause disease.

  41. PH value: A numerical scale for expressing the acidity or alkalinity of a liquid, ranging from 0 for strong acids to 14 for strong alkalis, with 7 representing the neutrality point. The ideal pH range in an anaerobic digester should be 6.8 – 8.

  42. Profitability Index: An index used to evaluate proposals for which net present values have been determined. The profitability index is determined by dividing the present value of each proposal by its initial investment. An index value greater than 0 is acceptable and the higher the number, the more financially attractive the proposal.

  43. Renewables Obligation Scotland (ROS): ROS requires licensed electricity suppliers to source at least part of their electricity from renewable generation.

  44. Planning conditions: Conditions relating to the construction and operation of a development imposed as part of the granting of planning permission.

  45. SEPA: Scottish Environmental Protection Agency, which provides an integrated environmental protection system for Scotland.

  46. Soil conditioner: A material, which improves the soil (eg peat, garden compost or fibre from AD); soil conditioners may or may not contain nutrients.

  47. Solid Retention Time (SRT): The average number of days the solid feed remains in the vessel. Can be different from HRT if not fully mixed in vessel.

  48. Short Rotation Crops (SRC): High-yielding variety of either willow or poplar, which is commonly used as an energy crop

  49. Sustainable development: Development that meets the needs of the present without compromising the ability of future generations to meet their own needs.

  50. Tessellation: A regular tightly fitted pattern, made up of polygons. Used to estimate tanker movement and transport costs.

  51. Thermophilic digestion: Digestion involving microorganisms that grow above 40oC, typically kept at about 55oC.

  52. VGF: Vegetable, garden and fruit waste.

  53. Volatile Suspended Solids (VSS): Those solids in the feedstocks which are volatile (ie will convert into gases when heated) and which are therefore digestible.

  54. Watercourse: Any natural or artificial channel that conveys surface water.