|GATE - 1/93 - Solid Waste Management (GTZ GATE, 1993, 52 p.)|
Legal, Technical and Economic Aspects
by Hans Sutter
Over the last few years the basic concepts of industrial waste management have changed substantially, not only in its underlying philosophy, but in its technical and administrative aspects as well.
In the Federal Republic of Germany, the first waste management legislation was effected in 1972, which at the time dealt with organizational and planning requirements for the collection, treatment and final disposal of wastes and the necessary supervision. With some negligible exceptions, these regulative measures were limited to what takes place after "the end of the pipe".
Indicative of the intended progress towards source reduction, the Waste Disposal Act became the Waste Avoidance and Management Act coincidental with its 4th amendment in 1986. The basic tenets of this updated legislation specified the waste generation must be avoided as far as technically possible and economically acceptable and that waste must be recycled unless this is economically not feasable. Waste that can neither be avoided nor used with reasonable costs must be disposed of in an environmentally sound way. Therefore, one main objective of the new waste legislation is to give low-waste technologies priority over customary waste disposal.
In the context of this article, the term "low-waste technology" refers to industrial waste management and reduction and recycling intended to reduce the amount of waste requiring waste disposal capacity. It includes inplant measures (source reduction), as well as environmentally sound reuse in external plants.
The main reason for this new philosophy of eliminating hazardous waste at its source and using low-waste technologies lies in the shortcomings of the end-of-the-pipe technology concept to fight industrial pollution (Figure 1). The figure depicts an industrial process and the necessary end-of-pipe equipment for air pollution control, waste water treatment and waste disposal.
Industrial production and environmental pollution caused by industrial processes have much to do with material flows. According to the mass balance, the input materials are transformed into products and residues. The products are marketed, whereas the residues enter the environment through three different pathways: the air, water or hazardous waste path. In the air pollution control system, the contaminants are removed from the wasteair stream and transformed into waste water or solid waste. Only a residual stream that meets the legally established standards is emitted into the environment. In principle, the same happens in the waste water treatment system: the contaminants are removed from the waste water and transformed into a solid state and disposed of as waste.
Three waste streams enter the waste disposal system, one of which originates directly from the production process. These wastes are unwanted byproducts and therefore, often neglected in the design of the process, especially when there is the possibility of getting rid of them by emitting them into the environment. The other two waste streams stem from the air pollution control system and the waste water treatment system.
The waste disposal system itself is end-of-pipe technology and consists mainly of two parts (Figure 2):
- the pre-treatment system
- the final disposal in specially designed chemical landfills.
In the pre-treatment system, the wastes are converted from hazardous into less or non-harzadous materials, at the same time reducing the bulk of the waste and thus the landfill volume required. The methods used to accomplish these objectives can be classified into three major treatments: physical, chemical and thermal. A variety of technologies can be found in each of these groups. The most important pre-treatment method is incineration. The hazardous waste treatment system itself produces waste that must finally be disposed of on land. In addition, waste water and gaseous emissions result from these operations.
In the Federal Republic of Germany, the land disposal of many untreated hazardous wastes must be phased out according to the 1990 requirements of "Technical Instructions Hazardous Waste", an administrative ordinance the on ad implementing the new waste act. These regulations were to produce nationally applicable technical standards for the treatment and disposal of waste based on the latest advances in technology. However, relying solely on treatment and the establishment of strict controls on land disposal cannot fully solve hazardous waste problems. It is essential that the generation of hazardous waste is minimized by using low-waste technologies.
From an environmental point of view, a production system can be roughly explained as shown in Figure 3.
The input materials are transformed into products and residues. It is important to differentiate raw materials from auxiliary materials because they affect the development of low-waste technologies differently.
The raw materials consist of different components, among which the valuable part that goes into the product can be found. This might be, for instance, copper in a copper-containing ore. In the production of vinyl chloride, it is chlorine and ethylene. Beside these valuable parts, there are unwanted components like rocks in copper ores. As Figure 3 shows, only the valuable parts of the raw material end up in the product, whereas the other components create residue problems. The same happens with the so-called auxiliary materials. Their function is to enable production; they are not intended to be present in the product. Hence, all the auxiliary materials inputs result in residues. Examples of auxiliary materials are acids, chlorinated solvents, foundry sands or salts in smelting processes.
Developing low-waste technologies answers the question: What can be done with the residues as an alternative to their disposal? In the concepts shown in Figure 4, case "a" is a diagram representing an open production system, where all the residues are emitted directly into the environment. In case "b", the residues are reused as secondary raw materials in other production processes. If the waste stream consists only of auxiliary materials, then in principle, case "c", a closed-loop cycle, can be built up to avoid all waste. As Figure 3 indicates, substitution of raw materials or auxiliary materials is the third option to develop low-waste technologies.
In an open system, all the input materials are transformed into products and residues, which are emitted directly into the environment. The relationship between the input materials that end up in products and those which are left in the residues is dependent upon the particular process and can differ greatly from branch to branch. In chromium galvanizing, only 25 percent of the input material is used for the product, while 75 percent is transformed into residues that enter the environment via the waste path or as galvanic sludge.
A similar situation occurs with industrial spray-painting, where 25 percent of the input paint stays on the product and 75 percent is emitted into the environment by the air or solid waste path. In the Federal Republic of Germany, about 350,000 tons of non halogenated solvents are emitted and 250,000 tons of paint sludges have to be disposed of, which together have a raw material value of about one billion Marks per year. There are many other examples available of the poor usage of raw materials and high waste production. Clearly, these processes are good candidates for developing low-waste technologies because improving the waste situation results in better material usage and economic advantages over traditional processes.
The open system can be partially closed by reusing the residues as raw materials in other production processes. This depends on the composition of the residual stream and if it can be partially recycled internally (Figure 4) or if it must be reprocessed completely to produce a new product or a new intermediate product.
Principally, in cases where the waste stream consists only of auxiliary materials (and these cases are of great importance in the hazardous waste field), a closed loop cycle can be created to avoid the production of waste entirely.
Another approach in developing low-waste technologies lies in the substitution of those substances (raw or auxiliary materials) that create the waste problem. Normally, this approach requires a completely new process design. An example is the substitution of chlorinated solvents in metal cleaning by water-based systems.
As a result of the increased importance of low-waste technologies in solving hazardous waste problems, research and development projects for the avoidance and utilization of hazardous wastes in different industrial areas have been initiated. The results demonstrate that new solutions can be found if the product stream and the waste stream both are given research priority. New developments in low-waste technology already have led to reductions in hazardous waste generation, and will continue to do so.
The hopes for harmony between ecology and economy rely on the simple fact that reduced material input into the production process will result in reduced waste generation and in turn in reduced costs. Figure 5 suggests, as does Figure 3, such economic benefits for low-waste technologies. Processes with high waste production also consume a lot of input materials. The total amount of auxiliary materials can end up in the waste stream. If the process is not efficiently run, then a certain amount of the valuable part of the raw materials, which can be high, is transformed into waste and not into a product. Improving the efficiency of input material use means nothing less than minimizing waste. In other words: waste minimization means less material input and therefore less material costs and less disposal cost. This relationship is shown schematically in Figure 5.
The cost-savings of low-waste methods also must be considered in relation to other necessary processing costs such as energy and capital. Figure 6 assumes a progressive relationship between processing costs and reduced waste production. The total costs curve has a minimum at x(opt). This means that waste reduction begins to pay for itself somewhere between x(max) and x(opt). On the other hand, moving from x(opt) to x(min) leads to higher product costs because the cost savings of waste reduction methods are reduced by increased processing costs.
In recent years the management of industrial waste has undergone a change. Whereas the main thrust of activity was initially on developing methods for final treatment and disposal, the problem is now being tackled at the production stage. The emphasis is now on reducing, recycling and re-using the hazardous substances.
La gestion des dets industriels a connu une profonde lution au cours de ces dernis ann. Alors que la mise au point de procs de traitement et de stockage dnitifs occupaient auparavant une place de premier plan, on intervient aujourd'hui en amont, c'est-a-dire au niveau du processus de fabrication. Entre temps, l'accent est mis sur la rction, le recyclage et la des mataux dangereux employ
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