Process Engineering for Pollution Control and Waste Minimization_11 pptx

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 NO x , 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 NO x (nitrous oxide, N 2 O) 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 anthropogenic flows act physically, chemically, and biologically to produce real impacts on the biota (see Figure 8). This series of events is called the environmental mechanism. In the virtual reality of the environmental model, many assumptions and simplifications are made to yield indicators. Even the best current air dispersion models are accurate only within a factor of two to three, but the level of accuracy is getting better all the time. The principle methodological issue in life cycle impact assessment is the modeling management of often very complex, extended environmental mechanisms. A listing of all possible endpoint impacts is quite long and can look like the following suggested list. I. Toxicity issues A. Human health considerations 1. Acute human occupational 2. Chronic human by consumer 3. Chronic human by local population 4. Chronic human by occupational 5. Human health 6. Human toxicity by ingestion 7. Human toxicity by inhalation/dermal exposure 8. Inhalation toxicity B. Ecological considerations 1. Aquatic toxicity 2. Biodiversity decrease 3. Endangered species extinction 4. Environmental toxicity 5. Landfill leachate (aquatic) toxicity 6. Species change 7. Terrestrial toxicity 8. Eutrophication (aquatic and terrestrial) II. Global issues A. Atmospheric considerations 1. Acid deposition 2. Acidification potential 3. Global warming potential 4. Stratospheric ozone depletion potential 5. Photochemical oxidation potential 6. Tropospheric ozone B. Resource considerations 1. Energy use 2. Net water consumption 3. Nonrenewable resource depletion Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved. FIGURE 8 Midpoints versus endpoints (20). Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved. 4. Preconsumer waste recycle percent 5. Product disassembly potential 6. Product reuse 7. Recycle content 8. Recycle potential for postconsumer 9. Renewable resource depletion 10. Resource depletion 11. Resource renewability 12. Source reduction potential 13. Surrogate for energy/emissions to transport materials to recycler 14. Waste-to-energy value III. Local issues A. Waste considerations 1. Airborne emissions 2. Hazardous waste 3. Incineration ash residue 4. Material persistence 5. Particulates 6. Toxic content 7. Toxic material mobility after disposal 8. Solid waste generation rate 9. Solid waste landfill space 10. Waterborne effluents B. Public relation considerations 1. Esthetic (e.g., odor) 2. Habitat alteration 3. Heat 4. Industrial accidents 5. Noise 6. Radiation C. Environment considerations 1. Local land 2. Local water quality 3. Physical change to soil 4. Physical change to water 5. Regional climate change 6. Regional land 7. Regional water quality Clarifying the environmental mechanism can help determine when impacts may be additive or when they are independent and non-additive. Two illustrative examples are global climate change and stratospheric ozone depletion. Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved. Example 1: Global climate change. The conversion of various greenhouse gases into radiative equivalents is universally applicable based on a scientifically supported mechanism (once a judgment has been made to select a time frame for analysis.) Example 2: Stratospheric ozone depletion. Stratospheric ozone depletion is caused by the interaction of halogenated free radicals in the upper atmosphere directly reducing concentrations of ozone. However, many ozone-depleting agents are effective greenhouse gases as well. In addi- tion, recent research indicates that greenhouse effects on the lower atmosphere have led to trapping of energy near the earth, and consequent cooling of the upper atmosphere. The stratospheric cooling tends to exacerbate the effects of ozone depleters. Nevertheless, for the purposes of LCIA models, these two mecha- nisms are treated separately. This simplification helps develop an overall view of the environmental impacts of industrial systems at a first-order level. In fact, although LCIA modeling tends to be technically complex, one can view LCIAs as extended back-of-the-envelope calculations of realistic worst-case potential impacts. The goal in assigning LCI results to the impact indicator categories is to highlight environmental issues associated with each. Assignment of LCI results should: First assign results which are exclusive to an impact category and Then identify LCI results that relate to more than one impact category, including Distinguishing between parallel mechanisms (where a given molecule is “used up” in its actions), and serial mechanisms, where a molecule can act in one mechanism, and then in a second mechanism without losing its potency. SO x acts in parallel mechanisms of allocated be- tween human health and acidification, while NO x acts in a serial mech- anism as a catalyst in photochemical smog formation and then in acidification. Typically, in impact assessment a “nonthreshold” assumption is used. That is, inventory releases are modeled for their potential impact regardless of the total load to the receiving environment from all sources or consideration of the assimilation capacity of the environment. However, there is a trend, particularly in Europe, to consider thresholds in evaluating indicators. For example, ground- level ozone formation is often calculated as an indicator for photochemical smog. Background levels of ozone are about 20 ppb, while some vegetative damage has been observed at 40 ppb, and human health effects at 80 ppb. All these levels, as Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved. well as intermediate levels, have been used in determining indicators for photo- chemical smog. If LCI results are unavailable or of insufficient quality to achieve the goal of the study, then either iterative data collection or adjustment of the goal is required. The following sections offer descriptions of current approaches that are being applied to model some of the impact category indicators listed in Table 4. The most simplistic models are described in order to offer insight into the types of approaches that are being considered useful from both a practical aspect as well as least cost. Stratospheric Ozone Depletion. Ozone depletion is suspected to be the result of the release of man-made halocarbons, e.g., chlorofluorocarbons, that migrate to the stratosphere. For a substance to be considered as contributing to ozone depletion, it must (a) be a gas at normal atmospheric temperatures, (b) contain chlorine or bromine, and (c) be stable within the atmosphere for several years (21). The most important groups of ozone-depleting compounds (ODCs) are the CFCs (chlorofluorocarbons), HCFCs (hydrochlorofluorocarbons), halons, and methyl bromide. HFCs (hydroflourocarbons) are also halocarbons but contain fluorine instead of chlorine or bromine, and are therefore not regarded as contributors to ozone depletion. The ozone depletion potential (ODP) is calculated by multiplying the amount of the emission (Q) by the equivalency factor (EF) ODP = Q ⋅ EF Current status on reporting equivalency factors uses CFC11 as the reference substance. The equivalency factor is defined as EF ODP = contribution to stratospheric ozone depletion from n over # years contribution to stratospheric ozone depletion from CFC11 # years General LCA practice uses values that represent ODC’s full contribution, but Table 6 also shows factors for 5, 20, and 100 years for some gases. The ozone depletion potential (ODP) is calculated by multiplying a substance’s mass emis- sion (Q) by its equivalency factor. These individual potentials can then be summed to give an indication of projected total ODP for substances 1 through n in the life cycle inventory that contribute to ozone depletion: ODP = ∑ n 1 (Q ⋅ EF ODP ) Global Warming. The most significant impact on global warming has been attributed to the burning of fossil fuels, such as coal, oil, and natural gas. Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved. Several compounds, such as carbon dioxide (CO 2 ), nitrous oxide (N 2 O), methane (CH 4 ), and halocarbons, have been identified as substances that accumulate in the atmosphere, leading to an increased global warming effect. For a substance to be regarded as a global warmer, it must (a) be a gas at normal atmospheric temperatures, and (b) either be able to absorb infrared radiation and be stable in the atmosphere with a long residence time (in years) or be of fossil origin and converted to CO 2 in the atmosphere (21). Table 7 is a list of substances that are considered to contribute to global warming. Equivalency factors, based on carbon dioxide as 1, are shown for each substance over 20-, 100-, and 500-year spans. The choice of time scale can have considerable effect on how global warming potential is calculated. The 100-year time frame is often selected, unless reasons exist that indicate otherwise. EF GWP = contribution from n to global warming over # years contribution from CO 2 to global warming over # years TABLE 6 Equivalency Factors for Ozone Depletion (21) Substance Formula ODP g CFC11/g substance 5 years 20 years 100 years ∞ CFC11 CFCl 3 1 1 1 1 CFC12 CF 2 Cl 0.82 CFC113 CF 2 ClCFCl 2 0.55 0.59 0.78 0.90 CFC114 CF 2 ClCF 2 Cl 0.85 CFC115 CF 2 ClCF 3 0.40 Tetrachloromethane CCl 4 1.26 1.23 1.14 1.20 HCFC22 CHF 2 Cl 0.19 0.14 0.07 0.04 HCFC123 CF 3 CHCl 2 0.014 HCFC124 CF 3 CHFCl 0.03 HCFC141b CFCl 2 CH 3 0.54 0.33 0.13 0.10 HCFC142b CF 2 ClCH 3 0.17 0.14 0.08 0.05 HCFC225ca CF 3 CF 2 CHCl 2 0.02 HCFC225cb CF 2 ClCF 2 CHFCl 0.02 1,1,1,-Trichlorethane CH 3 CCl 3 1.03 0.45 0.15 0.12 Methyl chloride CH 3 Cl 0.02 Halon 1301 CF 3 Br 10.3 10.5 11.5 12 Halon 1211 CF 2 ClBr 11.3 9.0 4.9 5.1 Methyl bromide CH 3 Br 15.3 2.3 0.69 0.64 Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved. TABLE 7 Equivalency Factors for Global Warming (21) Substance Formula GWP g CO 2 /g substance 20 years 100 years 500 years Carbon dioxide CO 2 1 1 1 Methane CH 4 62 25 8 Nitrous oxide N 2 O 290 320 180 CFC11 CFCl 3 5000 4000 1400 CFC12 CF 2 Cl 2 7900 8500 4200 CFC113 CF 2 ClCFCl 2 5000 5000 2300 CFC114 CF 2 ClCF 2 Cl 6900 9300 8300 CFC115 CF 2 ClCF 3 6200 9300 13000 Tetrachloromethane CCl 4 2000 1400 500 HCFC22 CHF 2 Cl 4300 1700 520 HCFC123 CF 3 CHCl 2 300 93 29 HCFC124 CF 3 CHFCl 1500 480 150 HCFC141b CFCl 2 CH 3 1800 630 200 HCFC142b CF 2 ClCH 3 4200 2000 630 HCFC225ca CF 3 CF 2 CHCl 2 550 170 52 HCFC225cb CF 2 ClCF 2 CHFCl 1700 530 170 1,1,1-Trichloroethane CH 3 CCl 3 360 110 35 Chloroform CH 3 Cl 15 5 1 Methylene chloride CH 2 Cl 2 28 9 3 HFC 134a CH 2 FCF 3 3300 1300 420 HFC 152a CHF 2 CH 3 460 140 44 Halon 1301 CF 3 Br 6200 5600 2200 Carbon monoxide a CO 2 2 2 Hydrocarbons (NMHC) a Various 3 3 3 Partly oxidized hydrocarbons a Various 2 2 2 Partly halogenated hydrocarbons a Various 1 1 1 a Contributes indirectly due to conversion into CO 2 . Only compounds of petrochemical origin. Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved. The global warming potential (GWP) is calculated by multiplying a substance’s mass emission (Q) by its equivalency factor. These individual poten- tials can then be summed to give an indication of projected total GWP for substances 1 through n in the life cycle inventory that contribute to global warming: GWP = ∑ n 1 (Q ⋅ EF GWP ) Nonrenewable Resource Depletion. This impact category models resources that are nonrenewable, or depletable. The subcategories include: Fossil fuels Net non-fuel oil and gas Net mineral resources Net metal resources Some models also include the energy that is inherent in a product that is made from a petroleum feedstock in order to reflect the amount of stock that was diverted and is no longer available for use as an energy source. This category can also reflect land use as a resource. Land that has been disturbed directly due to physical or mechanical disturbance can be accounted for as a resource that is no longer available either for human use or for ecological benefit (such as providing habitat for a certain species). Other subcategories under the resource category include: Net marine resources depleted Net land area Net water resources Net wood resources Scientific Certification Systems (SCS) proposes the following approach in their Life-Cycle Stressor Effects Assessment (LCSEA) model for calculating net resource depletion (22). The LCSEA model is based on (a) the relative rates of depletion of the various resources and (b) the relative degree of sustainability of the resources. The model considers the key factors that affect resource depletion and includes consideration of recycled material as supplementing raw material inputs. It also takes into account materials that are part of the standing reserve base, i.e. materials, such as steel in a bridge, that will become available as a recovered reserve at some future time. Recycling of metals has great significance for the depletion calculation (see Figure 9). The elements to be considered in factoring resource depletion include: Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved. [...]... creation of pollutants and wastes at the source in order to reduce costs and to meet or exceed federal and state regulations on environmental discharges and emissions Over the years, significant work has been done by various government offices, universities, and industry to demonstrate pollution prevention techniques and effectively transfer this information to wider audiences for implementation A wealth... E I Pas, and P A Vesiland, Planning Hazardous Waste Reduction and Treatment Strategies: An Optimization Approach Waste Manage Res., vol.7, no 2, pp 153–163, 1989 Kenneth Humphreys and Paul Wellman, Basic Cost Engineering New York: Marcel Dekker, 1996 International Standards Organization, Environmental Management—Life Cycle Assessment—Principles and Framework, ISO 14040, 1997 International Standards... source Pollution prevention opportunity assessment The systematic process of identifying areas, processes, and activities which generate excessive waste streams or waste by-products for the purpose of substitution, alteration, or elimination of the waste POTW (Publicy Owned Treatment Works) Any device or system used to treat (including recycling and reclamation) municipal sewage or industrial wastes... potential; LANDUSE = land use for waste disposal bWater use was not reported as an impact because water availability is plentiful where CARC operations are located, and because water is typically treated and reused or released to the environment Copyright 2002 by Marcel Dekker, Inc All Rights Reserved After life cycle inventory data for the raw materials, painting, and disposal of the baseline CARC and alternative... (ed.), Industrial Pollution Prevention Handbook New York: McGraw-Hill, 1995 2 L Case, L Mendicino, and D Thomas, Developing and Maintaining a Pollution Prevention Program In Harry M Freeman (ed.), Industrial Pollution Prevention Handbook New York: McGraw-Hill, 1995 3 U.S Environmental Protection Agency, Facility Pollution Prevention Guide, EPA/ 600/R-92/088 Cincinnati, OH: Risk Reduction Engineering Laboratory,... excellent methodology for streamlined LCA with a matrix approach, yielding objective results, and explores the approaches used by major manufacturers in obtaining data for the matrices Others (2,3) present basic studies and applications, and there are many articles and texts available between basics and detailed methods The objective of this chapter is to explore the application of LCA for waste site remediation,... and regulatory constraints Key components for assessment in the material and energy balance approach are (a) the problem basis, (b) boundaries, (c) generation and accumulation, and (d) time These terms and their components must be consistent in analysis of, for example, technology comparisons in remediation or waste management methods for treatment of a process stream or contaminantmedia matrix In... study, and also to reflect the focus of the LCA being performed Equations may be written from this basic form for any process wherein boundaries can be determined, in either differential form or integral manner Further, those without accumulation terms are considered steady state, and of course, many processes have numerous streams to consider The matrix approach is typically utilized in such process. .. complexity found when processes are linked for a final solution, to ease algebra Herein we obtain the overall balances and individual component balances for overall matrix solutions Energy balances are handled in a similar fashion, incorporating thermodynamic properties and allowing for both open and closed systems, determined by the transfer of mass across a boundary A batch process would be considered... cost analysis/assessment and life cycle costing to emphasize that traditional approaches overlook important environmental costs (and potential cost savings and revenues) A firm’s cost accounting system traditionally serves as a way to Copyright 2002 by Marcel Dekker, Inc All Rights Reserved track and allocate costs to a product or process for operational budgeting, cost control, and pricing In life cycle . Factors for Ozone Depletion (21) Substance Formula ODP g CFC11/g substance 5 years 20 years 100 years ∞ CFC11 CFCl 3 1 1 1 1 CFC12 CF 2 Cl 0.82 CFC113 CF 2 ClCFCl 2 0.55 0.59 0.78 0.90 CFC114. biota potential; LANDUSE = land use for waste disposal. b Water use was not reported as an impact because water availability is plentiful where CARC operations are located, and because water. a product or process for operational budgeting, cost control, and pricing. In life cycle costing, accurate allocation serves to identify environmental impacts in order to achieve pollution prevention