Process Engineering for Pollution Control and Waste Minimization_11

Việc lựa chọn loại tác động và các chỉ số thể loại và các mô hình có thể ổ đĩa tập hợp các dữ liệu kiểm kê. Ví dụ, người ta có thể chọn để đánh giá khoáng sản chỉ có dự trữ được dự đoán bị cạn kiệt trong vòng 100 năm, hoặc một số khung thời gian hợp lý khác.
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Process Engineering for Pollution Control and Waste Minimization_11 linkage between the inventory results and effects in the environment. Others (e.g., habitat modification) are known to play a critical role in environmental impacts of products (e.g., agricultural products), but are difficult to model quantitatively. Life cycle impact assessment practice is moving more and more toward using sophisticated fate and transport models to evaluate indicators of environmental impacts. The choice of impact categories and category indicators and models can drive the collection of inventory data. For example, one might choose to evaluate only minerals whose reserves are predicted to be depleted within 100 years, or some other reasonable time frame. This would eliminate the need to gather data on such materials as bauxite, clay, or iron ore, and would decrease the cost of inventory collection and management. To date, no “standardized” listing of impact categories to be used in LCA has been established, but several categories are employed in common practice, as shown in Table 5. The Classification Step. Inventory data need to be classified into the relevant impact categories for modeling. Some emissions have influence on more than one environmental mechanism and must be classified into more than one category. The classic example oif this is oxides of nitrogen, or NOx, which acts as catalyst in the formation of ground-level ozone (smog), but also is a source of acid precipitation. These substances must be characterized into both categories. One form of NOx (nitrous oxide, N2O) is also active as a greenhouse gas. The classification rules for any LCIA must be clearly reported, so that readers of a study understand what exactly was done to the inventory data. The Characterization Step The goal of life cycle impact assessment is to convert collected inventory inputs and outputs into indicators for each cate- gory (aggregates can be system-wide, by life cycle stage, or by unit operation). TABLE 5 Typical Impact Categories 1. Stratospheric ozone depletion 2. Global warming 3. Human health 4. Ecological health 5. Smog formation 6. Nonrenewable resource depletion 7. Land use/habitat alteration 8. Acidification 9. Eutrophication 10. Energy: processing/transportation Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved. These indicators do not represent actual impacts, because the indicator does not measure actual damage, such as loss of biodiversity. However, together, they do constitute an ecoprofile for a product or service. While there is no universally accepted “right” list of impact categories or indicators, basic objectives have been set by the Society of Toxicology and Chemistry (SETAC) that help define categories: 1. Category definition begins with a specific relevant endpoint. Ideally, the endpoint can actually be observed or measured in the natural environment. 2. Inventory data are correctly identified for collection. In principle, those inventory inputs and outputs which relate to the particular impact are identified. 3. An indicator describes the aggregated loading or resource use for each individual category. The indicator is then a representation of the aggregation of the inventory data. Figure 7 compares the real-world causes and effects (the environmen- tal mechanism) with the modeled world of LCIA. There are many differences between the two. In an LCI, for example, the inventory information is typi- cally modeled as a constant and continuous flow, while in the real world, emissions typically occur in a discontinuous fashion, varying from minute to minute. FIGURE 7 Comparison of “real-world” endpoints to LCIA indicators. Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved. Both natural and anthropog ...