The impact of industrial waste on the environment in Flanders: Methodology

The objective of the study was to work out a methodology for determining the relative significance of the environmental impact of industrial waste. As the various aspects of the environmental impact are not readily measurable as a single whole unit, it is proposed to base the methodology on the principle of multi-criteria analysis (MCA). This method was applied for industrial wastes in Flanders produced in 2000. The result thus obtained is intended to provide input for the determination of the "priority industrial wastes". The policy will be focused on these categories in order to reduce the environmental impact during the processing of the wastes. This reduction can be realised both by waste prevention and by control over the waste handling procedures to reduce the specific environmental impact during the processing of 1 kg of waste. This is one of the objectives of the Flemish Environmental Plan 2003-2007. The instrument can further be used for the purpose of evaluation. The results for the year 2000 may then be counted as a zero measurement.

Scope

A list of 'priority industrial wastes' was drawn up on the basis of the environmental impact that they cause during their processing. This means that:

  1. the environmental impact during the production process of the products (before consuming) is not counted; this environmental impact can - however - be very significant in comparison with the environmental impact during the processing of the wastes.
  2. the environmental impact during the use of recycled products generated from the wastes is counted with regard for the avoided energy and raw materials. Nonetheless, other aspects connected to the use of recycled products can in turn have their own environmental impact. This, however, is not counted.

In addition, the ranking on the basis of one single final score provides a picture of the environmental impact as an aggregate of all the various environmental aspects. When the policy is focused on separate environmental aspects, the ranking needs to be looked at on the basis of those particular environmental aspects rather than the final ranking based on all environmental aspects.
Finally, the list does not reflect at all if it is possible to reduce the environmental impact of the wastes. For it is entirely possible that attempts have already been made to reduce the volume of wastes and that it is not possible or recommended to adapt the processing methods.

The methodology

The following environmental aspects have been included for the determination of the industrial wastes with the largest environmental impact:

  • emission into the atmosphere (greenhouse gasses, substances with a harmful effect on the ozone layer, smog-generating substances, eco-toxic substances, toxic substances for human populations and eutrophic substances)
  • emissions into water (eco-toxic substances, toxic substances for human populations and eutrophic substances)
  • emissions into the soil
  • water consumption, fossil energy sources and raw materials and pressure on public space
  • local nuisance (noise and vibrations, odours, dust, mobility, visual nuisance)
  • risks of major environmental damage through illegal disposal and through incidental discharge
  • special occurrences (risk of radio-activity in the wastes)
  • avoidance of environmental impact because of recovery (avoidance of use of fossil energy sources and of use of raw materials)

Not all of these environmental aspects could be expressed in quantitative terms. For that reason, it was decided to give in quantitative terms (ratio-scale) only the criteria under the criterion groupings emissions into the atmosphere (except for substances harmful to the ozone layer), emissions into water, water consumption, auxiliary and raw materials and pressure on public space and the avoided environmental impacts. For a number of criteria (emissions of substances harmful to the ozone layer, emissions into the soil), only a check was made to determine whether or not there exists an environmental impact (binary scale). For a final group of criteria, (nuisance and hazard factors), a ranking was defined (ordinal scale). This means that the result only reflects whether the category of waste substances scores better or worse for those defined criteria, rather than how much better or worse.

The quantitative criteria were standardized following the linear method, between the value 0 and the value 1. The maximum value for standardization was set higher than the maximum score achieved and was determined on the basis of the relative importance of the waste processing sector for the respective environmental aspects within the total environmental impact in Flanders (impact of industry, transport, population).

Finally, each of the criteria was assigned a weight, in accordance with the degree of importance attached to those criteria. The weighing was carried out in a workshop with experts from the administration, the university, and the industry, by making a paired comparison for each criterion pair within the same hierarchical level.

To carry out the classification, the Evamix method was used. This method offers the advantage that quantitative scores are being processed in a quantitative way and qualitative scores in a qualitative way before their being combined. In addition, the method offers the possibility to assign weights to the criteria, to standardize the criteria (in accordance with standardization curves of choice) and to carry out sensitivity and uncertainty analyses on the result achieved. The result of the method is a classification of the industrial waste categories whereby the distance between the final scores represents a yardstick for the difference in environmental impact during the processing of the waste.

Filling in the scores

A multi-criteria analysis combines scores for different criteria into one final score. A first step in the implementation of the method consisted in filling in the score table. For each of the 62 studied industrial waste categories, scores were filled in for 25 criteria. The scores were a combination of separate scores for each of the processing options and sub-flows. When no figures were available, standard scores were used (for instance, for the incinerating or landfilling of waste), or an estimate was made on the basis of the procedure in the processing option that has the largest environmental impact (for instance, the use of electricity or heat).
The result of this phase in the study consisted of two score tables: one for the analysis wherein the wastes were compared on the basis of the environmental impact generated per kg of waste processed, and a second for the analysis wherein the wastes were compared on the basis of the total environmental impact generated during the processing of the waste.

The results

In order to define the priorities for the policy (which industrial wastes generate the largest environmental impact ?), especially the total environmental impact is of prime importance. However, this total environmental impact is a result of two factors: The annually produced quantity of waste, on the one hand, and the environmental impact per unit of weight, on the other.

Thus, as already mentioned, two analyses were carried out: one analysis on the basis of the environmental impact per kg of waste, and an analysis on the basis of the total environmental impact. The combination of the results of both analyses makes it possible to draw conclusions (albeit cautiously).

In the classification on the basis of environmental impact per kg, the following industrial waste categories create the most impact on the environment:

  • used oil;
  • used chemical catalysts;
  • carpet and textile wastes.

These three categories are characterized by high scores for atmospheric emissions, whether or not as a result of large energy consumption during the processing of the wastes.

Nonetheless, also for these categories, recycling and recovery is important: used oil is primarily utilized as alternative fuel; used chemical catalysts are being cleaned up for re-use, and textile waste products (mainly carpet waste) are likewise used as alternative fuel or a recycling of materials is carried out (nylon).

When drafting the policy for reducing the environmental impact, one must take care that the reduction of the 'negative' environmental impact (for instance, by shifting processing methods) is not coupled to a (stronger) reduction of the 'positive' environmental impact.
In the classification on the basis of the total environmental impact, the industrial waste categories with the highest impact on the environment are always waste materials of large or very large quantity:

  • sewage sludge;
  • animal wastes;
  • diverse mineral wastes;
  • mixed wastes;
  • carpet and textile wastes.

Other very substantial waste categories (for instance, construction and demolition waste, waste from power stations) do not score badly (or even score very highly) in the classification since the avoided environmental impact is quite large in comparison with the other waste categories. Becuase of their very small quantity, a number of waste categories logically score very well in the classification (tannery effluent, residuals from chemical reactions, waste consisting of cyanide and cyanate elements, etc.).

With the exception of a number of categories, it may be held that the final score for the total environmental impact is to a significant degree dependent on the quantity produced. This cannot be claimed for the environmental impact per kg. No relationship is found between the final score for the total environmental impact and the final score for the environmental impact per kg.

Conclusions

A "top 20" list of priority industrial wastes was drawn up on the basis of both the position in the classification for the environmental impact per kg and the total environmental impact. Industrial waste products with both a high total environmental impact and a high environmental impact per kg are the most likely candidates to appear on this list.

  1. Sewage sludge
  2. Animal wastes
  3. Used oil
  4. Textile wastes
  5. Spent chemical catalysts
  6. Mixed and unsorted waste
  7. Sorted fractions of a sorting installation
  8. Wood waste
  9. Industrial waste water purification sludge
  10. Separation residue
  11. Diverse mineral waste
  12. Bio-degradable sludge from the treatment of other waste water
  13. Industrial sludge - not further specified
  14. Acids and bases
  15. Sludge from the surface treatment of metals
  16. Metal-containing sludge of ferrous and non-ferrous metallurgy
  17. Laboratory waste
  18. Non-specified hazardous wastes
    (primarily mercury and mercury compounds)
  19. Packaging (contaminated packaging)
  20. Waste from flue gas cleaning (fly ashes)
Greater priority

Examples of categories with both a large environmental impact per kg and a large total environmental impact are: sewage sludge, animal wastes, and carpet and textile wastes. For these industrial waste categories, both a reduction in quantity and a reduction in the environmental impact per kg is relevant.

Other industrial waste categories are especially priority elements because of their elevated total environmental impact: sorted fractions, mixed wastes and diverse mineral waste. The reduction of the environmental impact per kg (if still possible) will have major consequences for the total environmental impact, in view of the quantity of these waste categories. Taking measures to deal with the quantity of wastes for these waste categories is also relevant.

Finally, a number of categories have been included in the Top 20 list that are primarily characterized by their substantial environmental impact per kg: used oil, used chemical catalysts.

The other categories combine a fairly large environmental impact per kg with a moderate total environmental impact or, vice-versa, a fairly large total environmental impact with a moderate environmental impact per kg.

A reduction of the total environmental impact during the processing of the waste categories can always be achieved through waste prevention. Less waste leads to a reduced environmental impact. Reduction of the environmental impact per kg of waste can be achieved by a shift of the relative importance of the processing options (for instance, greater re-use as secondary raw material) or by making the processing procedures more efficient (for instance, reduced energy consumption per unit of product). If the policy is aimed at reducing the emission of pollutants into the atmosphere, other wastes need to be considered than when the policy is concentrated on the reduction of the localized nuisance factor caused by waste processing. The ranking order per environmental aspect (criterion group) gives here an indication.

Recycling or re-use of waste, following the methodology employed here, does not automatically lead to a lower score for the environmental impact than incineration or landfilling. The absolute environmental impact caused by landfilling is - in theory - often smaller than the impact caused by (pre-treatment for) recycling or re-use. Waste incineration, in spite of its high rating for emissions into the atmosphere, etc., scores moderately well since the avoidance of using fossil energy (either by using the waste as alternative fuel or by energy recovery in the waste incinerator). This, however, does not mean that there ought to be more incineration or landfilling of waste. There are other important considerations as well in the choice of certain processing techniques.

The study "Methodology for determining the relative significance of the environmental impact of industrial waste in Flanders" was carried out by the research and consulting agency Resource Analysis in association with the BECO-group, on behalf of the Public Waste Agency of Flanders (OVAM).

The study was guided by an internal supervisory group, composed of the following persons: Anne Vandeputte, Anne Adriaens, Anne D'Haese, Mike Van Acoleyen, Koen Smeets, Herman Gobel, Hugo Geerts, Luk Vanacker, Guy Haemels, Peter Van Acker.