In order to establish a regional material balance, engineers, scientists, and economists have to work together, develop a common language, collect data from most different sources, and combine these data to reveal regional fluxes. Such cooperation would be facilitated if the same systems analysis approach and a common terminology were used. It is an important future task to educate experts from various fields in the techniques of materials accounting.
The terms developed and the approach taken in this work are based on four steps. The basis - the first step - is a comprehensive systems analysis of the region, defining the region, the boundaries, the processes, and the link between processes by means of fluxes of goods and materials. This is followed by a rough assessment of the importance of the fluxes of goods, carried out with available or easily accessible information. On the basis of this estimation, those fluxes that have to be measured and assessed in more detail are selected. The last step consists in calculating and validating the regional material fluxes.
The Bünztal project has shown that this procedure is feasible if these four steps are taken as an iterative rather than as a consecutive process: the initial systems analysis may have to be expanded or reduced according to the first assessment of the fluxes, or because of the impossibility of balancing a process or process chain. The calculation of the final results may display a large deficit in a process, thus making it necessary to add supplementary measurements to the third step. Even with heavy expenditure, it may not be possible to balance a process (as in the case of lead in the process "river").
The experience in the Bünztal shows that methods have to be developed to take into account the uncertainty of the individual fluxes for regional material balances. These would allow one to quantify the probability that a deficit or a surplus in a regional balance is not an analytical artefact and that additional fluxes have to be looked for.
The most demanding task in regional materials accounting is to reduce the very many processes and fluxes of goods to a number that is small enough for analysis and still contains the gross of the fluxes of goods and materials. To achieve this, detailed knowledge of the region is necessary. Thus the cooperation of the region itself is important, and should include the public sector as well as private institutions.
The method applied in this study yields abundant information about the flux of goods through the various sectors and branches of a region. The data about these fluxes can easily be verified by comparing the output and input fluxes of consecutive processes, or entire process chains. The method also yields satisfactory results for materials if the concentration of materials in the goods used is known. This is often not the case. The assessment of the fluxes of Pb and P. as displayed in figs. 6 and 7, requires a detailed analysis of many processes (private households, detergent manufacturing, sewage treatment, waste management, car manufacturing, scrap processing, agricultural practice, and others) and involves laborious and costly investigations. But the main obstacle for regional materials accounting is the lack of information about the composition of today's intermediate and consumer goods. While the producer of the primary raw material still knows the composition of his raw iron, zinc, or ethylene, this information is soon lost on the way to the intermediate manufacturer, and particularly when it reaches the final consumer; end-users buy goods and not materials!
For future regional materials accounting, it is indispensable that the information about the material composition of a good should flow parallel to the information about, say, the price or the weight of a good. And this information should be passed from the process of origin to the next process of destination. This appears to be the only way to collect reliable information about the material make-up of today's complex goods, such as refrigerators, motor vehicles, or houses. Technically, with the data-bank management systems now available, it should pose no problem to carry such information from its origin, through the chain of processes, to the end-user.
Regional fluxes of goods and materials
Flux of goods
The overall anthropogenic flux of goods through the Bünztal is given in figure 8. The most important single good is water, which amounts to 69 per cent of the total flux and is mainly used to transport materials and energy in households and industrial processes. Air, utilized in combustion processes such as heating and motor vehicles, comes second with 15 per cent of the total flux. Construction materials account for 8 per cent, scrap iron and junk cars for 5 per cent, and other import goods for 3 per cent.
Of all aggregated processes, private households have the largest turnover, consuming more than one-third of all goods. The branch "production of chemicals" utilizes 29 per cent of the goods, "food and drink" 9 per cent, construction business 7 per cent, metal processing 6 per cent, and the remaining branches 10 per cent.
The fraction of goods which remains in the region is comparatively small and amounts to less than 10 per cent of the import. It consists chiefly of solids to build the matrix of the anthroposphere like construction materials, and goods from processes which are specific to the Bünztal, like solid wastes from the car-shredder and the metal processing plant. Still, this 10 per cent amounts annually to 20 t/c, or 10 kg/m², or 0.6 million tonnes, for the whole region. Thus, if the future fluxes of goods remain unchanged, the accumulation of goods in the next century might surpass the 1 t/m² range.
More than 90 per cent of the goods leaving the Bünztal region (export) are waste waters and offgases. The processes "waste-water treatment" and "offgas treatment" are thus of chief importance for the quality of the environment of the neighbouring regions. The water consumption in the Bünztal amounts to one-fifth of the water input into the region, and one-tenth of the water leaving the region; the dilution potential of the surface waters is low. The ratio of geogenic to anthropogenic fluxes is much higher for the good "air"; it is around 1:500,000, thus permitting a strong dilution of offgases.
The observed flux of goods through the regional anthroposphere supports the notion of the anthroposphere as a biological organism. An important difference from the metabolism of other living things is the large amount of water, which is used to transport the excrete (anthropogenic wastes) out of the region. The activity "to clean" seems to be organized less efficiently in the anthroposphere than in natural systems. In both the biota and the anthroposphere, food, fuel, and air are goods that are important in supporting energy metabolism.
Flux of materials
In this project, the main emphasis was put on the two materials phosphorus and lead. Figs. 5 and 6 and table 2 have shown how such fluxes were determined. In the following paragraphs, it is explained how the regional balance of these materials can be used for resource management and environmental protection.
LEAD. About 340 t/yr of Pb are imported, and about 280 t/yr are exported; the difference of 60 t/yr is stored in the region (see fig. 5). The main lead flux consists of Pb contained in used cars, which are shredded in a large shredder with a capacity of more than 100,000 cars per year. The lead flux through private households is two orders of magnitude smaller; it comprises 1.6 t of Pb in leaded gasoline (which can be easily measured with high accuracy), and 5.6 t Pb in household goods (which have been determined from the Pb concentration in MSW, and thus do not represent the actual consumption of lead in households).
Much of the lead from the car-shredder is processed in a steel mill within the region, which produces iron rods for construction, filter ash from a baghouse, and furnace slag. Owing to the chemical/ physical behaviour of lead, most of the lead (200 t/yr) is concentrated in the filter ash, and some is contained in the mild steel (70 t/yr). These goods are exported and re-used; thus about 80 per cent of the lead imported into the region leaves the region again. The nonmetallic shredder residue contains about 60 tons of lead; at present, this residue is landfilled.
RESOURCE MANAGEMENT. The landfill of the non-metallic shredder residue is the largest sink for lead in the region. It can be assumed that after a decade of landfilling this stock is the most important regional reservoir of lead. Therefore, the careful management of this stock is or will become extremely important. On the one hand, the lead in the landfill poses a threat to the hydrosphere. On the other hand, it may be an important resource for the future.
Following the goals introduced in the Introduction, the shredder residue should be transformed into a good which releases sustainable fluxes only. In addition, the objectives of resource conservation require that the material be in a concentrated and re-usable form. Unfortunately, the good "shredder residue" is far from attaining these two goals, since the lead is highly diluted with organic matter and may be mobilized during landfilling. A possible solution is to treat the shredder residue thermally, thus removing the organic matter and concentrating lead in the fly ash. Further treatment is required to render the fly ash immobile; since solidification with binders like cement dilutes the potential resource of lead and makes it more difficult to re-use, other techniques such as vitrification should be attempted. The final residue should preferably be disposed of in monofills, which contain one type of mixture of concentrated materials only. (Of course, if cars were designed with sustainable development in mind, direct recycling of single car parts might become possible, which would make the shredder in the region obsolete. Direct recycling, however, seems only to be a future option.)
ENVIRONMENTAL PROTECTION. The regional lead balance allows the setting of limits for the leaching of lead from the wastes as well as for emissions from the thermal treatment of wastes and goods. The largest regional sink of lead is the landfill. The good which contains the largest fraction of lead is the residue from the car-shredder. This waste does not yet have "final storage" quality; when it is landfilled, long-term biogeochemical reactions occur, which may mobilize the lead and other materials contained in the landfill. The geogenic flux of lead through the River Bünz is about 30 kg/yr. If the landfill releases about 1 kg/yr of lead, the geogenic flux will be changed less than by its natural variations. This means that, of the total content of about 1,000 tons of Pb in the landfill (corresponding to 10-20 years of landfilling), only about 1 ppm may be mobilized per year. Thus, the future regional goal for the treatment of shredder wastes can be defined as the production of a residue that releases not more than about 10 ppm of the mass of lead when landfilled. (Of course, other materials have to be considered as well).
One technical option for producing a residue with "final storage" quality would be incineration, followed by immobilization of the incineration residues. During thermal treatment, between 40 and 60 per cent of the lead is transferred to the flue gas. Air-pollution-control techniques allow the removal of most, but not all, of the lead from the gas stream. If the lead flux in the filtered flue gas is below 5 kg/yr, the incinerator emissions will not markedly change regional lead concentrations in the soil. A load of 5 kg Pb for 1,000 years in the soil reservoir of ~400 t equals an increase of about 1 per cent, if it is assumed that 80 per cent of the lead is retained in the soil. The flux of 5 kg/yr corresponds to 0.02 mg(Pb)/Nm³. Considering the lead in the raw gas as about 30 t/yr, a removal efficiency of more than 99.98 would be required - a value that can be achieved only if the best available airpollution-control technique is applied. (A similar calculation for lead fluxes from the incineration of municipal solid wastes demonstrates that the allowable emissions are about five times higher (0.1 mg(Pb)/Nm³). The reason for this is the lower overall flux of MSW and lead when compared to the shredder residue).
PHOSPHORUS. The main import goods for P in the Bünztal region are fertilizers and feedstock, the main internal P-fluxes are the agricultural cycle soil-plant-animal-soil, and the main export pathway is the River Bünz (see fig. 7). Most of the P-input into the process industry is from cereals, which are stored temporarily in a large industrial stock. The import flux (229 t/yr) surpasses the export flux (168 t/yr); thus, about 60 tons of P are accumulated annually in the region, and the stock of P in the soil of the region is increasing.
The amount of P in the River Bünz is mainly determined by three processes. The soil, as a result of surface run-off, erosion, and leaching, contributes ~17 t/yr, the sewage-treatment plant (STP) 19 t/yr, and unknown processes such as landfills or illegal effluents 10 t/ yr. In this study, the fluxes from the third category were not investigated. The River Bünz receives ~46 t P/yr, which is about 1.6 times more than the initial load when entering the region. If the elimination of P in the sewage-treatment plant were maximized, about 13 t/yr could easily be eliminated from the river. By contrast, it is not possible to influence the fluxes due to erosion and leaching from the soil in the short term; as long as the reservoir soil is increased, the flux from this process will increase even more. Owing to the high input of P from past and current agricultural practice, the flux of P to the surface waters also will remain high in the future.
The accumulation of P in the soil cannot be detected in the short term by soil analysis (this is true for heavy metals and trace substances in general): because of the heterogeneity of the soil, as well as the limited accuracy of sampling and laboratory analysis, a change in the soil concentration becomes significant only after decades. The material balance approach, however, allows the detection of a potential accumulation before large reservoirs have been developed, and thus can serve as an early-warning system. According to the values given in figure 7, the concentration of P in the soil of the Bünztal increases by about 1 per cent per year and thus will double within roughly 70 years. (In the past, the stock of lead in the soil grew annually by 0.5-1 per cent owing to the use of leaded gasoline.)
Regional materials accounting may be used as a powerful tool for soil protection: the most efficient means of decreasing the P-load of the soil can be assessed using figure 7. The flux of P is mainly due to the two activities "to nourish" and '`to clean." It was recognized several decades ago that P can be the limiting factor for the eutrophication of surface waters. In areas where eutrophication of lakes is a serious problem, the time-span between scientific recognition of its cause and preventative action was about two decades. Most actions concerned the replacement of phosphate-based detergents, that is, processes and goods involved in the activity "to clean." In the region investigated, the turnover of P resulting from the activity "to nourish" is nearly one order of magnitude larger than that from cleaning purposes (see table 2 and fig. 7). In future it will be of great importance to reduce in time the material fluxes for the activity "to nourish" to regionally balanced levels. This suggests that regional materials accounting should be applied as an early-warning tool, and that strategies should be developed which allow a decrease in the time-lag between the recognition of a problem and the implementation of measures to control it (table 6).
Table 6 Results and consequences
Source: Own design.
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