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CHAPTER 1
Material metabolism through society and environment: a new view on waste management
Henri C. Moll
1.1 INTRODUCTION
An environmental science university course book (McKinney and Schoch 2003) describes three very different approaches for waste management: the "disperse and dilute" strategy, the "concentrate and contain" strategy, and the "resource recovery" strategy. In the course book description of these strategies, the "disperse and dilute" strategy is characterised to be historical (till the early industrial age). The "concentrate and contain" strategy was introduced in the beginning of the 20th century and has been dominant during this whole century. Presently the "resource recovery" strategy is getting increasingly attention and is expected to be the dominant approach for sustainable waste management in the next few decades.
The concept eco-efficiency draws highly the attention in modern business circles and is seen as an important principle to elaborate sustainable business solutions for the society and the environment. Eco-efficiency means (see DeSimone and Popoff 1997): less energy intensity, less material intensity and lower levels of environmental toxicity and risk. Eco-efficiency implies to go further than the pollution control approach (the so-called end-of-pipe approach) and to work on process integration, and further on higher scale levels on integral facility planning, industrial ecology on industrial sites, and on sustainable regions.
The quotations mentioned above demonstrate that waste management strategies have become interrelated with the material strategies in the production sectors. The outputs (i.e. waste) of the economic system should be related to the inputs (i.e. resources) of the economic system (see Ayres and Ayres 1998, 1999). Considering resources, materials, products and waste as parts of an integrated system enables to research the potential of the waste management strategy "resource recovery" as well as the material efficiency approach advocated presently in industry. In such a system, waste management and efficient material use may become the two sides of one valuable coin.
The quotations demonstrate also the importance of considering the history of waste management and material use. Analysis of past practice may give insight in the long-term effects of some waste handling practices and some past behaviour may give inspiring examples for the future. Also important lessons are derived from analysis of differences in the economic system and in the environmental conditions between present modern society and societies and cultures in the past.
In this chapter waste management is discussed from an environmental system analysis perspective. In this perspective substances are part of a cycle. Some cycles are mainly driven by natural processes, and some other cycles are driven mostly (or fully) by human activities. Each cycle has phases within the economic system as well as within environmental systems. Material use and waste management are both related to one or more phases of one or more substance cycles. New ways to manage waste and new approaches to recover resources from waste imply minor or possibly major changes in substance cycles and should be evaluated on their effects in the whole substance cycle involved. The overall cycle of a substance is named in this chapter the material metabolism of a substance.
The material metabolism patterns of the various substances differ mutually. Partly these differences are related to inherent properties of the substance itself, but also some differences are determined by the societal use of a substance. Effective waste management and resource recovery strategies should deal with the differences of the inherent substance properties and should also address or even change the usage characteristics of substances.
This chapter begins in Section 1.2 with a discussion on the history of waste and waste management, starting some millennia ago. In Section 1.3 the present-day status is discussed of waste treatment technologies and waste management approaches. In these sections all kinds of materials are considered with some specific focus on organic solid waste and organic wastewater. In Section 1.4 waste management is studied from the environmental system analysis perspective. Some substance cycles are discussed as well as the anthropogenic influence on these cycles. The elaboration of the cycle concept results in the identification of some environmentally sound waste management principles. These principles may form also the base of sustainable material and waste management, the issue addressed in Section 1.5. Especially increasing the use of resources recovered from consumer waste puts a high challenge to the present production and consumption system. In Section 1.6 some cases of material quality management, involving also changes in the usage characteristics, are reviewed. The road to sustainable waste management is examined in Section 1.7. In Section 1.8 the final conclusions are presented.
1.2 A BRIEF HISTORY OF WASTE MANAGEMENT
The generation of waste by humans is a very natural thing. As each living being man requires food to stay alive and produces urine and excrements to remove the digested remnants of food consumption. The generation of waste is also related to the structure and functioning of the society. Waste flows originate from the production, use and disposal of goods that are required to be an accepted member of a society. Although human waste generation has been omnipresent in history, waste management has not been always considered to be necessary. Two conditions should be met for the development of waste management approaches in a society: first, waste itself should be considered to be a problem, and second means should be available to manage this problem.
1.2.1 Waste in rural societies
In rural societies using mostly resources of biological origin harvested from the surrounding environment, the waste problem did not exist. Rest flows of agriculture, hunting and food preparation were used for other purposes like feeding domestic animals, clothing, construction, and fuelling fire. The excrements of humans and animals were used in many cases for fertilising agricultural land and pastures. Even when such flows became definite waste and were dumped in the close environment, these flows were decomposed quickly by natural processes. Materials like stone, sand and clay extracted from the surrounding environment used for building and the manufacture of goods like pottery, were reused often before they became waste disposed in the environment. After disposal aboveground or underground such waste generally did not cause environmental problems, because of its chemical and biological innocuous nature.
The substitution of resources derived directly from nature by mineral resources and fossil energy sources extracted from the (deep) underground has been a new cause of waste problems. The extraction and the processing of materials out of mineral resources generate often solid, fluid and gaseous substance flows, which may injure the local environment. Also when these materials become waste after their use in products, they may cause environmental damage. These substances and materials are not a part of the natural cycles of biological production and decomposition and may therefore interfere in a detrimental way with the functioning of natural systems.
1.2.2 Waste management in cities
The development of cities has become a source of waste problems (see Ponting 1992 for a discussion about the development of cities and the related environmental problems). Within a city a large number of people live closely together. Many of the resources and goods required to live within a city are not found and produced in the close surrounding of the city. So provision of materials and goods requires trade and transport. The generation of waste - human excrements, food waste and disposed goods - in the city causes problems. Neglecting the organisation of the removal and handling of city waste results in deterioration of the living conditions in the city: stench, polluted water and related illnesses and health problems.
Processing of natural and mineral resources and the production of goods has often taken place within the cities or in the close neighbourhood of cities. In preindustrial times mostly on small scale, and since the start of industrialisation the average scale of process industry and manufacture enlarged substantially. Processing resources and the production of goods generate also waste flows that are not treated on the location of the industrial activity itself. These waste flows are transported and sometimes reused elsewhere but often also disposed into the water and soil resulting in environmental problems.
The large amounts of city waste generated by households as well as by industrial plants have created a strong pressure to develop management systems for city waste. City waste management systems are based on the collection of some waste flows, the transport of waste outside the city and some handling afterwards such as dumping or combusting the collected waste. Such systems were developed in most cases by the city authorities. Next to these removal-oriented systems also commercial systems developed based on the collection of specific waste flows with economic value because of their potential for reuse and material recovery.
1.3 PRESENT-DAY TECHNOLOGIES FOR WASTE MANAGEMENT
The increasing level of concentration of industrial production and consumption in the 20th century has increased the necessity of waste management. The technological development of the last century has enabled the possibility of efficient and effective waste management. The main waste handling technologies presently used are still based on practices applied already in the past: waste separation, landfilling, combustion or incineration, biological treatment, and recovery for use in agriculture and in industry. The present-day status of these technologies is discussed (see Stessel 1996 for an overview of waste processing technologies).
1.3.1 Some general waste handling practices
An element of all waste handling systems for specific kinds of materials is waste separation in order to obtain "pure" material flows in the waste handling system. Waste separation improves the efficiency of the following processes and increases the quality of the resulting material. Separation of waste in pure material flows can be performed at the source of waste i.e. the household or the industrial plant. Instruction is required to realise successful separation at the source and the people involved should develop deliberate and consistent separation behaviour. Households are commonly able to produce pure material fraction for glass, paper and also organic waste. Also technology is available to separate waste in different material flows after collection. The material flows produced by separation after collection are generally more physically and chemically contaminated than the flows produced by separation at the source. But that does not pose problems for materials like metals that are easily cleaned afterwards.
Landfilling waste aboveground or underground at disposal sites has remained a very common practice to handle waste. But, the area occupied and the amount of waste stored on dumping sites is presently enormously larger than some centuries ago. Due to the possible contents of reactive and toxic substances in dumped waste, control technologies are being applied on modern waste deposit sites. The flow of rainwater and ground water through the deposed waste is limited by covering above and by application around with impermeable foils. Also waste deposit water treatment is applied regularly. The methane emitted by waste sites, which contain a large amount of organic digestible materials, is captured and mostly used as fuel to save energy. Sometimes restrictions are set on the types of waste that are disposed. For example, in many European countries it is not allowed anymore to dump on waste deposit site materials that are combustible or digestible.
At the beginning of the 21st century waste incineration plants demonstrate a large scale of operation (several hundred thousands tons of waste per year) and a high level of technological sophistication is available to recover useful energy and to remove substances that may cause air pollution, like dioxin, small size particulates (fly ash), sulphur oxide and nitrous oxides.
1.3.2 Treatment of organic waste: decomposition and incineration with potential of resource recovery
A variety of technologies are applied to treat the fluid waste flows of biological nature and to extract in some cases useful substances or materials from these flows. Some fluid organic waste flows like human excrements put in the sewage system are brought to sewage water treatment plants. In most cases the sewage water is treated aerobically with removal of nitrate and sometimes also of phosphate. Sewage water can also be treated anaerobically using bacterial methano-genesis, resulting in the production of biogas, usable for energy purposes. Sewage water cleaning results in the production of large amounts of sewage sludge potentially useful for agriculture. But in practice because of pollution by toxic substances from the sewage water, the sewage sludge is often too polluted for agricultural applications. Therefore sewage sludge is considered mostly as waste that should be treated further. Finally sewage sludge is disposed in specific depots or incinerated after a drying step to remove the largest part of water from the sludge. Also in industry many fluid organic process flows are generated that were in the past considered as waste and were emitted to surface water causing environmental problems like eutrophication and stench. Presently the content of these flows are mostly recovered and are converted to useful products. Sometimes aerobic and anaerobic wastewater treatment processes are also used in industry to remove the organic compounds from the wastewater flows.
Solid food waste flows occurring in food industry and in households are incinerated in some cases together with other waste flows despite its adverse effects on energy efficiency because of the substantial water content of solid food waste. Often food waste flows are treated together with private and public garden waste in specific processes. In large-scale plants these waste flows are composted in a few weeks under controlled aerobic circumstances. Depending on the (chemical) purity of the organic waste the quality of the compost is high enough for further use in agriculture and horticulture. Because of the large amount of compost produced presently in the Netherlands, problems exist to find sufficient markets for these amounts. Another way to treat these waste flows is anaerobic digestion. Digestion results in the production of methane containing biogas and sludge, comparable with the sludge produced in anaerobic wastewater treatment.
Solid organic waste flows like paper, wood and polymers produced from fossil energy sources are mostly treated in waste incineration plants or are directly fed in electricity production plants. Presently some other methods to handle these waste flows are also relevant. Gasification (at high temperature) and pyrolysis (at moderate temperature) of solid organic waste produce gaseous hydrocarbons that after clean up of these gases - can be used for chemical synthesis purposes and very efficient electricity production in gas turbines. An important other application of these solid organic flows is reuse and recycling. Presently half (or more) of discarded paper is used as input in paper and cardboard production as substitute for virgin wood based pulp. Discarded wood is partly used for the production of chipboard and fibreboard. Discarded polymers are sometimes reused in the polymer production and the production of polymer products.
1.3.3 Treatment of mineral waste: reuse, recycling and landfilling
After the use phase, materials produced from mineral resources like metals, concrete, ceramics, bricks and stone are often disposed in waste dumping sites. Incineration of these materials does not result in a substantial reduction of the waste volume and requires energy instead of generating useful energy. Instead of becoming waste these materials are also often reused as secondary materials. Metals like steel, aluminium, copper and zinc are recycled after melting and purification in comparable applications as these metals in primary (i.e. gained from mineral resources) form. Materials like concrete, bricks, asphalt and stone regained from demolition of buildings and roads may also be reused to substitute new construction materials.
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Excerpted from "Resource Recovery and Reuse in Organic Solid Waste Management"
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