Resources and Conservation最新文献

A review is presented of progress made in the period between roughly 1980 and 1985 in treating wastewaters that contain heavy metals ions. The review concentrates on wastewaters from the metalplating industry. The applicability of electrodeposition has been greatly improved through the development of large surface area electrodes. Electrodeposition now appears to be a promising treatment method, especially for wastewaters that contain heavy metals ions in fairly high concentrations together with chelating agents. Water evaporation techniques and adsorption on insoluble starch xanthate are promising developments that merit attention. Heavy metals sulfide precipitation by adding compounds like FeS and CaS seems to be an improvement in comparison to older methods in which soluble sulfides were added. Ways to separate different species of heavy metals ions from each other by means of combined ion exchange and hydrometallurgical extraction may be of interest in situations were the wastewaters from many firms are treated in one central processing plant. Progress in membrane processes is to be expected as the quality of membranes steadily improves. Several other novel and interesting removal methods have been proposed such as e.g. electroprecipitation and the reduction of chromates with sulfides and ferrous ions.

Chemical analysis of household waste and measuring of pollutants emitted by waste treatment processes are both supplying fundamental data necessary for planning and operating of waste disposal systems, as well as for the development of strategies to reduce the dissipation of anthropogenic substances into the environment. The large variety of natural and man made products ending up as household waste contributes significantly to the extreme heterogeneous composition of the material under investigation. Thus, sampling and sample preparation may be considered to be the crucial step of any analysis of waste. To meet the statistical requirements as well as the existing possibilities of the investigating laboratory, a practicable approach has to be found. It is shown that the reported preparation technique, including sorting and classifying of the bulk sample into material categories followed by a three step crushing and grinding procedure, is a reasonable solution. Frequently used analyses methods for heavy metals, such as atomic absorption spectrometry (AAS) and X-ray fluorescence spectrometry (XRF) are reported after the description of wet decomposition techniques as well as plasma dry-ashing of the sample. For the determination of chlorine, fluorine and sulphur in waste, the Wickbold oxygen-hydrogen-flame decomposition technique is recommend in combination with ionchromatography. Additionally, basic principles and methods for emissions measurements are summarized. To illustrate the broad range of analytical tools applied, a newly developed dust emission monitor is reported as well as the use of IR-LASER-spectrometry for continuous measuring of HF in the flue gas. Finally, the determination of polychlorinated dioxins (PCDD) in fly ash is mentioned as a prominent example of complex ultra trace analysis.

For economical and product specific requirements the possibility of an extra treatment and exploitation of components with high heating values was followed, especially in connection with large units specialized to recover material components from municipal and domestic waste.

Components for fuel production can be seen in household-waste separated light fractions (RDF), fibres coming from seperated waste collections like waste paper of inferior quality, and production residues from agriculture and forestry.

Between different concepts of waste fuel densification, pelleting as a process of fuel production has been put into the limelight. Even if pelleting can be seen as a more expensive method, compared to baling press systems or container pressing, it offers some advantages concerning combustion characteristics such as diameter, shape, density and by this a better handling of the products during transport, storing, oven charging, etc..

Success of pelleting and results of pressing are dependent on a large number of material- and process determined parameters, by whose control economy as well as pellet quality can be extensively influenced.

For the realisation of the RDF densification concept, one should not only see its technical and economical production, but also place high importance on the storability. This point especially is to be retained because the production of fuel and its later use can vary in respect to space and time.

Latest trends observed in the municipal solid waste management and recycling in Japan are discussed along with the relevant legal and societal backgrounds. An economic incentive system for the pre-collection group recycling, and latest developments in materials recovery at processing plants and energy recovery at incineration facilities are specifically detailed. Some newer progresses made in thermal treatment technology other than incineration are also followed. Situations in landfilling and land reclamation are briefly mentioned in the context of land contamination and difficulty felt in newer siting. Some trends in the field of hazardous substances of municipal solid waste are discussed by citing the recent public concerns about the disposal of dry battery cells and the detection of dioxins in the ashes of incinerators.

Since April 1982 the city of Zeist in the Netherlands offers subsidized compost containers to its citizens. After about one and a half year 504 households that have a garden near their house have purchased the container. Households that have purchased the container (1), households that have not purchased the container but that compost vegetable, fruit and garden waste in another way (2), and households that haven't bought the container and that do not compost are compared on a number of aspects: sociodemographic characteristics, ecology-consciousness, and on the perceived costs and benefits of buying and using the compost container. The results show that the groups differ largely on the selected aspects. Some conclusions are drawn, and recommendations are made for the design of information campaigns accompanying subsidization programs and, in general, for the design of programs aimed at reducing the amount of waste for disposal.

“Black Points” are contaminated sites, which stem from former malpractices in waste management. Methodical campaigns have been launched to obtain an inventory of such sites. The strategies and techniques of prospection and investigation are reviewed and the parameters affecting risk evaluation are analysed.

Numerous factors have to be considered when preparing a remedial action. Depending on the forms of contamination more or less extensive safety precautions should be taken. Contaminated earth and buried wastes may have to be excavated and treated, prior to disposal. The most prominent methods, which recently were developed for the cleaning of earth are reviewed.

A major problem during the sanitation of most sites is the management of groundwater, leachate, and liquid wastes. In one strategy the contaminated site is completely isolated from the environment, in another it is hydraulically isolated by adjusting pumping rates from a series of wells and creating supplemental barriers. Also the problem of the treatment of leachates is briefly adressed.

For aiding and optimizing the recycling of residue materials (post-consumer recycling) it is necessary that the products are designed in a recycling-conform way, i.e. that they are prepared for the eventual reutilisation of the materials after the end of the product use. From the analysis of the recycling system and of the design process, guide-lines for a recycling-conform product design are derived and explained by examples; the chances are discussed whether they can be carried out in practice.

The Wet Air Oxidation process can be used for cleaning up high energy containing solid-water mixtures as well as low energy containing toxic effluents. Conversion of reaction enthalpy to mechanical energy, thus attaining a selfsustaining steady state W.A.O. process, can become a possibility under certain conditions.

This paper discusses the potential feasability of a relatively simple energy recovery system. The system is simulated on a microcomputer after development of a mathematical model describing the W.A.O. reactor and utilities. Simulations point out, that the system becomes thermally self-sustaining when ΔCOD values are above 1O–20 g/kg, the mean operating temperature being 275°C at a reactor pressure of 1O3 bar. Even at very high mechanical efficiencies of the compressor no excess mechanical energy is produced with the recovery system used in the present study. The results of predicted influences of other independent variables such as reactor pressure, oxygen use efficiency and heat loss show satisfying agreement with those of other authors. Assumed utility efficiencies appear to be of major importance in calculating maximum attainable relative excess mechanical energy.

The combined need for new energy sources and better waste disposal techniques has led to the development of an efficient energy and soil improver recovery system. The Envermeu Plant (France) is using this household refuse treatment line combining the SILORCO process to produce RDF (Refuse-Derived Fuel) in the form of pellets and the SILODA process to produce high quality compost through both forced aeration and windrowing. This facility is described with emphasis on the technical principles and main advantages.