Resources and Conservation最新文献

Agricultural irrigation is considered to be the most economical way to dispose of municipal wastewater in a sanitary manner in Israel. Due to the location of the irrigated areas, energy expenses for effluent transport cannot be reduced significantly. This paper presents a study which prepares the ground for energy savings at the treatment plants themselves.

The study consisted of two parts: a survey of different types of treatment plants and a more detailed analysis of an activated-sludge and an aerated lagoons plant. Results show that energy utilization ranges from 140 to 800 W h/m³ and a properly managed activated-sludge plant can spend less energy than an aerated-lagoon plant. A possible reduction of 20% in plant energy utilization may bring about up to 8% reduction in effluent cost and promote its agricultural application.

The present work is concerned with the utilization of wood as energy source in the existing wood stoves and cook stoves in Chile, focused on determining which changes in the operation of real stoves could lead to substantial energy savings. A survey was made all over the country to determine the models presently being used, and also for estimating the fuel wood consumption per family. An adiabatic chamber was designed and built in order to determine experimentally the average efficiency of the most common appliances and also the possible efficiency increases by variation of the operating conditions. The average total efficiency was found to be approximately 25% and 40% for stoves and cook stoves, respectively and the efficiency improvement, with respect to these values, due to changes in the operating conditions was found to be approximately up to 100% and 12% for stoves and cook stoves, respectively. Finally an estimation was made of the possible wood savings that may be obtained according to the optimal, experimentally obtained efficiency for the appliances and the possible wood savings resulting from the eventual introduction of more efficient modern wood-burning stoves. These savings were economically evaluated at different fuel prices.

Considerable damage due to corrosion occurred at the landfill gas utilization plants of Gerolsheim and Braunschweig. In these cases the landfill gas contains high contents of hydrogen sulphide and aliphatic chlorohydrocarbons respectively. Purification will be necessary to remove these undesirable trace components before utilization. Hydrogen sulphide removal is to be achieved by an activated carbon adsorption process. The activated carbon adsorption method and a heterogeneous-catalytic dehalogenation process were practicable to remove halogenated hydrocarbons. The suitabilities of all processes were proven by operating pilot plants. High elimination rates were achieved.

Based on the application of activated carbon, and a special carbon molecular sieve CMSC adsorption processes for the purification of landfill gases and subsequent recovery of substitute natural gas have been developed. By using different activated carbons trace contaminations (e.g. hydrogen sulfide, ammonia, mercury, halogenated hydrocarbons, higher alkanes and aromatics) are removed from landfill gas. The cleaned gas can then be processed by means of a pressure-swing adsorption process using molecular sieve CMSC into natural gas.

The adsorption processes can not only be applied to landfill gases but also waste water treatment plants and bioreactors. The processes are dry and almost maintenance-free. At the moment several pilot and demonstration plants are in operation in the Federal Republic of Germany and the Netherlands. Now several industrial-scale plants with gas flows of up to 1,500 m³/h (STP) are under consideration for various Dutch landfill sites and waste water treatment plants.

Compared to the competing scrubbing and diaphragm processes the pressure-swing adsorption process using the carbon molecular sieve CMSC has some essential advantages and technical realization can be expected in the near future.

Since 1974 the glass recycling in Germany, Switzerland and the Netherlands has grown from less than 10% to almost 50% of the one-way produced glass. With the increased tonnage of collected glass the demands on the quality of the produced glass cullet by the glass recycling industry have changed. These quality changes in the cullet feed of the glass production process were necessary to guarantee the same high quality product of bottles of the glassworks as before.

The purpose of this paper is to provide a focus for discussion on future developments in hazardous waste management. From an examination of present practice and trends in various countries, particularly in Western Europe, North America and Japan, six major directions for the next 5–10 years have been highlighted, together with a number of consequent challenges. The various directions may be summarized:

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  o less emphasis on drawing up legislation with more on making it work in practice (A major challenge is how to encourage compliance, so that regulations can be enforced);

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  o a general move away from both land and sea disposal. Challenges include the provision of adequate treatment and disposal capacity for hazardous wastes, ensuring that it is used and developing new treatment methods for the future;

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  o increased emphasis on preventing waste, on producing wastes that are less hazardous and on recycling;

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  o a continuation of the current trend to focus more attention on the long-term care of waste disposal facilities;

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  o increased public awareness of, and hostility to, hazardous wastes; and

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  o the gradual extension of controls over hazardous wastes to other industrialised countries and to the newly industrialising countries in the developing world.

Sludge from sewage treatment plants can accumulate significant amounts of heavy metals, organic toxins and pathogenic micro organisms. Traditional use of sludge in agriculture as a fertiliser is increasingly frustrated by the presence of these impurities. Alternatives for agricultural use have been studied and compared using technical feasibility, total costs and ecological consequences as criteria. From the results it can be concluded that an increasing proportion of the sludge will have to be combusted.

Three alternative process scemes are discussed, consisting of the following components: —filtration —heat recovery —drying —fluidized bed combustion — flue gas purification. The three schemes differ in the way the heat recovery is carried out: —by direct heat transfer between flue gas and the combustion air, —by drying the filtered sludge in a fluidized bed dryer heated by the flue gasses and —by multiple effect drying of the filtered sludge in a set of fluidized bed dryers operated at different pressures.

In an automated computer procedure, the physical dimensions of the equipment components are calculated. By a similar method the capital investments, capital costs, running costs and consequently the integral costs of treatment are calculated.

The results indicate that heat recovery is an important means to decrease the total costs of combustion. As direct heat transfer between the flue gas and the combustion air allows only a limited fraction of the heat of combustion to be recycled, this option is always more expensive. On the other hand, the application of multiple effect drying requires large investments and its costs are somewhat higher than those for an installation which uses only one stage drying.

This paper gives an evaluation of combustion trials of various types of refuse-derived fuels (RDF) tested at several different furnaces. Also, the energy parameters and the content of harmful matter of diverse kinds of RDF are surveyed. Special attention is paid to the post-combustion remnents of hazardous materials which are to be found in RDF. The proportion of these which is released and emitted is greater than the amount allowed under existing and future laws in West Germany. Thus, it is and will not be possible to incinerate RDF in West Germany without intensive gas cleaning.

Thermal hydrogenation of organic chlorine compounds is advanced as an alternative to incineration and as an environmentally sound process for conversion/ detoxification of industrial organic wastes.

The chemical reactions proceed at ca. 600–900° C and lead to HCl (and analogous derivatives of non-hydrocarbon functional groups) and a mixture of hydrocarbons, especially CH₄, C₂′s and benzene. There is little or no tar or soot formation. Toxins such as chlorinated dioxins are also effectively converted; the resulting products can be considered as a fuel. The requisite hydrogen can be supplied or made (in situ) from a source like methanol.