Much of the early initiative in pollution prevention focused on redesigning industrial processes to reduce the generation of process wastes. It is clear from the previous discussion that this cannot be the limit of our attempts to design environmental elegance into the system of provision of services. But it is certainly an important part of it. There is now a considerable body of experience and expertise in this important area. So it is worth while summarising briefly the key elements in industrial pollution prevention. Let us start out by looking at a few simple flow diagrams.
Figure 12 provides a simple schematic diagram of an industrial process. Like the service system depicted in Figure 9, the industrial process is represented in Figure 12 as a kind of black box. The main difference between Figure 9 and Figure 12 is that the functional output in Figure 12 is a material product rather than a service. These material products are manufactured from raw material inputs to the process. Only a proportion of the total material input is turned into useful product. The balance appears in the form of material wastes. Some materials are emitted to the air; others to the water; and some materials end up in the solid waste stream.
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Figure 12 Simple industrial material flows rf.ii ¡¡rrKitri
Figure 13 End-of-pipe treatment of air and water emissions
The mass balance principle discussed in Chapter 1 means that the total emissions to air, water and solid wastes are equal to the difference between the raw material inputs and the product outputs. And this mass balance principle applies both at the level of total mass, and also at the level of individual molecular contaminants.
End-of-pipe strategies (Figure 13) are usually aimed at reducing specific air emissions and waterborne effluents. They take out particular contaminants by adding filters, scrubbers and treatment plants on to the industrial process. Although they may be successful at reducing air and water emissions, what typically happens is that solid waste emissions increase. The simple mass balance equation makes it clear why this is the case. If the total raw material inputs are the same and the product output is constant, the balance between them must also remain unchanged. This unchanged balance constitutes the total waste emissions. If the air and water part of these total material emissions is reduced, then the solid waste emissions must increase to keep the total constant.
There are a number of variants on the end-of-pipe approach shown in Figure 13. For instance, some air-emission control technologies employ flue gas scrubbing, in which soluble flue gases are dissolved in jets of water. This process generates an increase in the aqueous emissions rather
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Figure 14 End-of-pipe treatment of solid wastes than in solid wastes, unless the water is subsequently treated and recycled. Another variant (Figure 14) exposes solid wastes to some kind of end-of-pipe treatment, such as incineration. Incineration reduces the total mass of solid wastes. But it does so at the expense of generating new air emissions.
The contrast between the prevention strategy and the end-of-pipe abatement strategy is illustrated by Figure 15. The mass balance principle is still observed. The product output has not changed. But now reduced material emissions correspond to reduced material inputs. If we were to represent the material efficiency of the process by the ratio of the product output to the material outputs, we could say that the material efficiency of the process in Figure 15 is improved over that of the processes in Figures 12 to 14.
Figures 12 to 15 still represent the industrial process itself as a more or less opaque black box. In reality, of course, it can be an immensely complicated network of material flows and technological conversion processes. And it is really only by delving into this network—which differs from process to process and from industrial sector to industrial sector—that we can realise the opportunities for industrial pollution prevention. It is only by making specific changes within the industrial process itself that we can improve material efficiencies and reduce the
Figure 15 Industrial pollution prevention—improved material efficiency
Figure 15 Industrial pollution prevention—improved material efficiency burden of material emissions. It is beyond the scope of this book, and probably beyond the power of any book, to present a detailed encyclopaedia of technological opportunities for pollution prevention in every industrial sector. Nevertheless, it is certainly worth outlining a few key strategies which lead to this kind of change, and illustrating these strategies with examples from real life.
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