Aanpak van industrieel afval Cementovens vergeleken met verbrandingsovens - Een milieuvergelijking

5. How are environmental impacts compared?

• 5.1 What steps are considered in this Life Cycle Assessment?
• 5.2 What environmental impacts categories are we concerned about?

5.1 What steps are considered in this Life Cycle Assessment?

The waste treatment options were evaluated by means of a Life Cycle Assessment (LCA), a method that compares the environmental performance of products or services, to enable an informed choice. The term 'life cycle' refers to the notion that a fair assessment must consider all steps from cradle to grave: raw material production, processing, use and disposal, and transportation.

The present Life Cycle Assessment compares two ways of treating industrial waste*: either in the Belgian cement clinker production where the wastes are used as fuel, or in specialised waste incinerators.

The assessment considers the following steps:

• Transportation of the waste to the different treatment sites
• Pre-treatment of the wastes (when necessary)
• Treatment of the waste in a cement kiln or incinerator
• Cleaning of flue gases and wastewater (if any)
• Disposal of remaining residues (if any)

For each of these steps the study takes into account possible emissions to air, water, or soil and the use of natural resources.

Moreover, when energy is produced by the burning of waste this avoids the use of other sources of energy which would have led to their own range of impacts on the environment. More...

5.2 What environmental impacts categories are we concerned about?

Emissions and resource use are then translated into a series of environmental impacts, in accordance with the CML assessment method.

The ten environmental impact categories considered are the following:

• Abiotic Depletion refers to the exhaustion of non-living natural resources such as minerals and fossil fuels. It takes into account the remaining reserves of minerals and fossil fuels used and the rate at which the resources are extracted. To make these different figures comparable, resource depletion is expressed measured in kg Antimony (Sb) equivalents, a reference case commonly used in Life Cycle Assessments.
• Global Warming is the impact of greenhouse gas emissions – notably CO₂ – on Earth’s temperature, which in turn affects human and ecosystem health. Greenhouse gas emissions are expressed in kg CO₂ equivalents. When CO₂ is released by the burning of waste that is not of fossil fuel origin but part of the carbon cycle, it is not considered a contributor to global warming in this assessment.
• Ozone layer depletion is the thinning of the ozone layer in the upper atmosphere, which protects life on Earth by filtering out the sun’s harmful ultraviolet radiation. This depletion has detrimental effects on humans and ecosystems. Chlorine and bromine contained in the waste can lead to the emission of ozone depleting substances. They are expressed in CFC-11 equivalents, since this substance has the highest ozone depleting potential.
• Toxicity refers to harmful effects of emissions on humans and ecosystems. Waste can contain many toxic substances such as heavy metals and organic chemicals that can potentially cause harmful effects if released to the environment. The assessment takes into account how these substances would behave in the environment and how living organisms would be affected by them in the very long term. For each toxic substance the toxicity is expressed using the reference unit, kg dichlorobenzene (1,4-DB) equivalents.
  
  
  • Human Toxicity includes the impacts on human health of toxic substances emitted to the environment.
  • Freshwater Aquatic Ecotoxicity refers to the impact of toxic substances on freshwater ecosystems.
  • Marine Aquatic Ecotoxicity refers to the impact of toxic substances on marine ecosystems.
  • Terrestrial Ecotoxicity refers to the impact of toxic substances on marine ecosystems.
• Photochemical Oxidation is the formation of smog (mainly ground-level ozone) by the action of sunlight on certain other air pollutants emitted directly from a source. Photochemical smog may be harmful to human health, ecosystems, materials, and crops. Impacts considered are mainly derived from NOx and volatile organic compounds (VOCS) such as released from solvents or paints. Emissions that lead to photochemical smog are measured in kg ethylene (C₂H₄) equivalents.
• Acidification (acid rain) is the result of the emission of air pollutants, such as SO₂ or NOx. Acid precipitations have negative impacts on soil, groundwater, surface waters, biological organisms, ecosystems and materials. Impacts considered mainly derive from the sulphur (S) contained in fossil fuels. Emissions that lead to acidification are measured in kg SO₂ equivalents.
• Eutrophication is the process by which a body of water becomes rich in dissolved nutrients, such as nitrogen and phosphorus. It can lead to a rapid excessive growth of algae that depletes the oxygen in the water and kills aquatic plants and animals. Impacts considered are mainly derived from emissions of NOx into air which in turn reach water bodies. Emissions that lead to eutrophication are expressed in kg phosphate (PO₄^3- ) equivalents.

Each emission to the environment, once quantified, is assigned to the suitable categories. For instance, CO₂ emissions measured in kg CO₂ equivalents are assigned to the global warming impact category. NOx emissions are assigned to the human toxicity, photochemical oxidation, acidification, and eutrophication impact categories. More...