Resource Recovery and Conservation最新文献

Waste materials may be treated by incineration (burning) or by thermal processing in the absence of air or oxygen (pyrolysis), or, similarly, by thermal processing with a limited amount of air or oxygen (gasification).

Incineration gives waste reduction by weight and volume, a sterile residue, and the possibility of heat recovery as hot water and/or steam. Thermal processing gives waste reduction by weight and volume, a sterile residue, plus the following products and possibilities: (i) gas with a low to medium calorific value for use as a fuel or feedstock for chemical conversion; (ii) a solid or char which can be used as a fuel, or alternatively an ash; or (iii) liquid tars and/or heavy oils which may be used as a fuel oil substitute or as a feed for thermal cracking, accompanied by a volume of water containing dissolved organic materials. The latter may pose a considerable disposal problem.

The waste material used as a feed for thermal processing may be: raw refuse; sorted material in that the combustible portion has been separated or concentrated (termed refuse-derived fuel); sorted and prepared material in that most of the noncombustible portion has been removed and the combustible portion densified into a form meeting a specification as a fuel (termed densified refuse-derived fuel). The incineration of waste may yield steam or hot water which can be used to do work (e.g. generate electricity). Thermal processing may yield a storable, transportable fuel.

Some Dutch firms, together with TNO, have been operating a municipal refuse separating plant in the municipality of Haarlem since 1974. A brief description of this plant is given. Research into the application of products that can be obtained with this refuse separating plant are described. This research has been conducted at a scale of from 10 to 50 Mg of recovered products. These products, as input materials, are processed by different home and foreign potential users.

If the current rate of growth in electricity consumption continues unchecked, Norway will have utilized all of her economically feasible hydroelectric resources by the year 2000 at the very latest. If one of the popular conservation plans is chosen, this date will be pushed forward to 1990–1995. However, in the short run, conservation will have little adverse effect on the cost of electricity. Cost increases directly attributable to conservation will remain less than 20% within the next 15 to 20 years (1995–2000) or until other sources of electricity are required.

The floating freshwater macrophyte Eichhornia crassipes (water hyacinth) was fermented anaerobically to produce 0.4 1 of biogas/g volatile solids at 60% methane with a bioconversion efficiency of 47%. Both the liquid and solid digester residues were a rich source of nutrients that were recycled to produce additional biomass. An approximate balance of the nitrogen recycled through the culture—digester—culture system indicated that nitrogen was conserved within the digester. All of the nitrogen originally added to the digester in the form of shredded water hyacinths could be found in the liquid (48%) and solid (52%) residues; 64.5% of the nitrogen in these residues could be reassimilated by cultures of water hyacinths. This study indicated the potential of bioconversion of aquatic macrophytes to methane as a possible means of both producing and conserving energy.

Circumstances responsible for a specification approach to the control of residual elements are reviewed. For deleterious elements, response varies from insistence on 100% use of virgin materials, to setting maximum limits on a large number of residual elements, to specifying the relative quantities of two or more interactive species. For beneficial elements, minima must be set and testing techniques must assure that the desired element is present, not only in the proper amount but also in a state and location where its meliorating effects can be realized. Examples from both the alloy and ceramic fields are discussed.

Past, present and prospective uses of dredged silt in the construction industry are discussed as part of the current BRE research programme on the utilisation of waste materials. The annual dredging commitments and methods of silt disposal are tabulated for the major port authorities. Silt samples from a selection of these ports were compared by their physical properties, by the production of sintered aggregates, and by chemical and mineralogical analysis. Larger quantities of synthetic aggregate from dredged silt have been used to produce concrete suitable for structural work. It is concluded that the most promising possibility for a new use of dredged silt lies in the production of aggregates. The heat treatment proposed reduces the content of deleterious impurities to insignificant levels and the results may be relevant in countries short of clean aggregates.