There is a more general potential difficulty associated with any strategy of substitution. How do we know that we have substituted something which is better (from an environmental point of view) for something which is worse? How do we ensure that we do not simply substitute one environmental hazard for another? We have already seen that the range of materials which cause environmental concern is very wide. We have also seen how easy it is for an abatement measure simply to transfer pollution from one place to another. But we should not assume that this problem simply disappears when we are talking about preventive measures.
For instance, suppose that a particular factory reduces its use of a particular toxic compound by an internal recycling measure. We know from thermodynamics that energy is required to close a material cycle. This means that the factory is likely to be using more energy as a result of the measure than it was before. Suppose that this energy is provided by electricity. The toxic emissions from the factory itself will certainly be
Figure 17 System effects of pollution prevention measures
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Figure 17 System effects of pollution prevention measures reduced by the recycling measure, but more electricity is needed to close the cycle. So, in a sense, we could say that we have substituted electricity for the toxic compound in question within the industrial process. Since we know that the generation of electricity is a polluting activity, we could also say that we have substituted toxic pollution with sulphur pollution and carbon pollution (if it is a coal-fired electricity generation plant, for instance).
This is not the end of the story, however, because by recycling the toxic compound we have reduced the material input requirements. Since energy is required to provide these raw material inputs, the internal recycling measure can also be said to have reduced the energy requirements on the raw material side.6 What I am drawing attention to here is that each industrial process is a part of a larger system. What we described simply as the 'input side' of the industrial process in Figure 12, turns out (Figure 17) to be a complex interrelated system of material interactions, each involving different raw material requirements and different kinds of environmental emissions. The question of whether there is an overall increase or an overall decrease in environmental emissions can only be resolved by looking at the wider system of which the industrial process is a part.
This system aspect of industrial production is just one of the factors which makes it difficult to decide whether a particular substitution
Life-Cycle Assessment (LCA) is a process of evaluating the environmental burdens associated with a product, process or activity by identifying and quantifying energy and materials used and wastes released to the environment; of assessing the impact of those energy and material uses and releases to the environment; and of identifying and evaluating opportunities of effecting environmental improvements.
LCA has the following five stages:
1 GOAL DEFINITION
• define the system under consideration
• identify the system boundary
• identify the purpose of the assessment (policy, engineering, economic)
• identify and quantify resource requirements
• identify and quantify environmental emissions
• assess the contribution of resource requirements to resource depletion
• assess the contribution of environmental emissions to environmental burdens
• assess the relative importance of environmental burdens and resource demands
• assess the reliability of results and sensitivity to key parameters
• use the results of the exercise to identify environmental improvements, use of new technologies, or changes in practice makes us better off or worse off in environmental terms. Another factor is the difficulty which we are likely to encounter in evaluating trade-offs between different kinds of environmental emissions. Is the environmental benefit associated with a decrease in toxic emissions greater or smaller than the environmental burden associated with increased carbon dioxide emissions from an electrical plant? How can we measure the relative environmental impacts of different kinds of emissions? A considerable amount of effort is now being dedicated to the development of life-cycle assessment methodologies (Box 2) which attempt to quantify and assess the environmental burdens associated with different technologies and processes. But even using such techniques, none of these questions is very easy to answer.
The whole issue becomes much easier when we can say unequivocally that a particular pollution prevention action has reduced all of the material inputs—as well as all the waste emissions—associated with the system in which the industrial process is embedded. In this case, of course, we are really talking about overall material efficiency improvements again. And the only caveat we need to be aware of is that there are thermodynamic limits to such improvements. These limitations arise because of the second law. Materials and energy are degraded during transformation. In order to return them as useful inputs to further transformations they must be upgraded and this can only be done by supplying more high-quality energy.
At the moment, in the existing industrial system, we are still a long way from thermodynamic limits. Improvements are possible in all kinds of industries and processes. Many of the most obvious efficiency improvements relate to the use of energy. The possibilities for saving energy in industry (for instance in process heating applications and in motive power) are now well-documented.7 But I hope it is clear from the preceding discussion that we still need to make a careful assessment of the impacts of each process modification, each new design concept, and each substitution.
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