Comparison of percolation to batch and sequential leaching tests: Theory and data

Leaching tests are becoming more relevant in assessing solid waste material, particularly with respect to groundwater risks. In the field, water infiltration is the dominant leaching mechanism, which is simulated in the lab with batch and column tests. In this study, we compared percolation, through analytical solutions of the advection–dispersion equation, to laboratory batch and sequential leaching tests. The analytical solutions are supported with comprehensive data from various field and laboratory leaching of different solutes from waste materials and soils collected in long-term joint research projects funded by the German Federal Ministry for Education and Research and the Federal Environment Agency. The comparison of theory and data is facilitated if concentrations and cumulative release are plotted versus the liquid–solid ratios (LS). Both theory and data indicate that leaching behaviour is independent of duration and physical dimensions of the leaching tests. This holds even if field lysimeters are compared to laboratory columns of different size, different flow velocities as well as different contact times. In general, laboratory batch tests over predict effluent concentrations (for LS < K_d). Leaching of solutes from solid samples of certain materials (e.g. chloride from incineration ashes or sulphate from demolition waste) in column and lysimeter tests compares very well and agrees with the analytical solutions. Overall, reproducibility and agreement with theory of column tests are better than batch tests, presumably because the latter are prone to artefacts (e.g. in liquid–solid separation steps). Theory and data fit surprisingly well, despite the fact that the theory is based on the local equilibrium assumption; non-linear sorption and chemical reactions in the solid waste materials are not considered.     

Continuous in-line gasification/vitrification process for thermal waste treatment: process technology and current status of projects

The Thermoselect High Temperature Recycling process has been developed in order to make available a thermal waste treatment technology avoiding major problems as known from traditional techniques like landfills or ashes, filter dust and emission producing processes. It combines slow degassing with fixed bed oxygen blown gasification and mineral and metal residue melting in a closed loop system. Municipal, industrial and other kinds of waste are compacted to less than one fifth of their original volume by means of an armored hydraulic press, and then periodically pushed into an indirectly heated degasification channel. As the waste plugs are pushed down the channel in an oxygen-free environment, waste humidity is evaporated and the organic components in the refuse are partially degasified and to a certain extent converted into a carbon-like product as the temperature increases. This flaky product and the enclosed inorganic components such as metals and minerals are continuously fed into a high-temperature reactor (HTR). Pure oxygen is added in controlled quantities and reacts with the material following exothermic oxidisation reactions. Due to overall under-stoichiometric conditions, gasification products form a combustible synthesis gas. The heat of reaction leading to temperatures up to about 2000°C in the core of the lower HTR section acts to also smelt the metal and mineral components of the waste. Chlorinated hydrocarbons such as dioxins and furans are reliably destroyed along with other organic compounds in the gaseous and the liquid phase. Material conversion equilibria are assured due to high temperatures and sufficient residence times. The synthesis gas is purified before use as combustible or primary material. After long term operation of the industrial scale demonstration plant in northern Italy, recent orders of differently sized Thermoselect plants can be announced and are illustrated on the basis of three cases out of five [with Herten 225,000 Mg/a and Berlin 300,000 Mg/a] in Germany: (1) Karlsruhe plant, 3 lines, 225,000 Mg/a, under construction; (2) Ansbach plant, 1 line, 75,000 Mg/a, completely purchased in July 1997; (3) Hanau plant, 2 lines, 90,000 Mg/a, partially purchased in October 1997. The technical concepts of these projects are illustrated with special emphasis on the flexibility of tailor-made energy recovery solutions.     

An advanced study on the hydrometallurgical processing of waste computer printed circuit boards to extract their valuable content of metals

This study refers to two chemical leaching systems for the base and precious metals extraction from waste printed circuit boards (WPCBs); sulfuric acid with hydrogen peroxide have been used for the first group of metals, meantime thiourea with the ferric ion in sulfuric acid medium were employed for the second one. The cementation process with zinc, copper and iron metal powders was attempted for solutions purification. The effects of hydrogen peroxide volume in rapport with sulfuric acid concentration and temperature were evaluated for oxidative leaching process. 2 M H₂SO₄ (98% w/v), 5% H₂O_2, 25 °C, 1/10 S/L ratio and 200 rpm were founded as optimal conditions for Cu extraction. Thiourea acid leaching process, performed on the solid filtrate obtained after three oxidative leaching steps, was carried out with 20 g/L of CS(NH₂)₂, 6 g/L of Fe³⁺, 0.5 M H₂SO₄, The cross-leaching method was applied by reusing of thiourea liquid suspension and immersing 5 g/L of this reagent for each other experiment material of leaching. This procedure has lead to the doubling and, respectively, tripling, of gold and silver concentrations into solution. These results reveal a very efficient, promising and environmental friendly method for WPCBs processing.     

Ecological benefits of the alley cropping agroforestry system in sensitive regions of Europe

Alley cropping is an agroforestry system that offers a promising land use alternative for the temperate zone. On the same field, the sustainable production of food and biomass is possible, while simultaneously, especially in marginal areas, the ecological function of the landscape can be improved. Thus, alley cropping corresponds with the increasing demand for renewable energy resources and for a specific adaptation to the predicted changes of climatic conditions within Central Europe.However, presently, little knowledge exists regarding the effects of alley cropping on the environment. In this study a literature survey was undertaken to provide an overview of the different ecological benefits arising from alley cropping systems within temperate Europe. Abiotic factors (nutrient cycle, microclimate), biotic factors (biodiversity) and the effects on the carbon cycle are discussed in detail.Summarising, the results showed that alley cropping may be an ecologically advantageous land use system for sustainable food and biomass production in comparison with conventional agricultural practices. As a very flexible, but low-input system, alley cropping can supply biomass resources in a sustainable way and at the same time provide ecological benefits.     

Biomolecules preserved in ca. 168 million year old fossil conifer wood

Biomarkers are widely known to occur in the fossil record, but the unaltered biomolecules are rarely reported from sediments older than Paleogene. Polar terpenoids, the natural products most resistant to degradation processes, were reported mainly from the Tertiary conifers, and the oldest known are Cretaceous in age. In this paper, we report the occurrence of relatively high concentrations of ferruginol derivatives and other polar diterpenoids, as well as their diagenetic products, in a conifer wood Protopodocarpoxylon from the Middle Jurassic of Poland. Thus, the natural product terpenoids reported in this paper are definitely the oldest polar biomolecules detected in geological samples. The extracted phenolic abietanes like ferruginol and its derivatives (6,7-dehydroferruginol, sugiol, 11,14-dioxopisiferic acid) are produced only by distinct conifer families (Cupressaceae s. l., Podocarpaceae and Araucariaceae), to which Protopodocarpoxylon could belong based on anatomical characteristics. Therefore, the natural product terpenoids are of great advantage in systematics of fossil plant remains older than Paleogene and lacking suitable anatomical preservation.     

Defining and achieving sustainable development

SUMMARY

This paper analyses the fundamental problems of defining and achieving sustainable development. A common core of the various definitions of sustainability circulating is identified. Economic and scientific approaches to operationalize sustainability generally lead to management rules, which — if obeyed — should guarantee sustainability. Since it is not possible to precisely predict the future, this scientific—technical—economic route to sustainability may fail. A second, ethical way, to sustainability which interprets sustainability as an ideal for fair play is introduced. How the two different ways may complement one another with a three-step hierarchy of political goals is elucidated.     

Regio- and stereoselective isomerization of hexabromocyclododecanes (HBCDs): kinetics and mechanism of beta-HBCD racemization

Hexabromocyclododecanes (HBCDs) are high production volume chemicals currently produced in quantities exceeding 20000ty(-1). They are used as flame retardants for plastics and textiles. HBCDs are thermally labile compounds, rapidly decomposing at temperatures above 250 degrees C to form bromine radicals, which scavenge other radicals formed during pyrolysis. But certain HBCD stereoisomers must reach the environment without decomposition, because their levels in soils, sediments, and biota are increasing worldwide. The fate of individual HBCD stereoisomers during production, product use, disposal, and transformation in the environment remains unclear. Herein we report on the thermally induced, highly selective isomerization of (+) and (-)beta-HBCD. Regio- and stereoselective migration of only two of the six bromine atoms resulted in the racemization of both beta-HBCDs. First order rate constants (k(rac)) increased from 0.005, 0.011, 0.021, to 0.055min(-1) at 130, 140, 150, and 160 degrees C, corresponding to half life times tau(1/2) of 143, 63, 29, and 14min, respectively. From the deduced kinetic model, we conclude that any thermal treatment of enantiomerically enriched beta-HBCDs in the range of 100-160 degrees C will result in a loss of most optical activity within few hours. The simultaneous inversion of two asymmetric centers occurred with perfect stereocontrol. Selectively, vicinal dibromides with the RR- and the SS-configurations migrated at these temperatures. An intramolecular reaction mechanism with a four-center transition state is postulated, based on the obtained stereoisomer pattern and the observed reaction kinetics. Crystal structure analysis revealed that all vicinal dibromides in beta-HBCDs prefer synclinal (gauche) conformations. However, an antiperiplanar (staggered) conformation is assumed to facilitate the concerted 1.2-shifts of both bromine atoms, resulting in an inversion of both neighboring carbon atoms. First experiments with other HBCD stereoisomers suggest that the presented isomerization mechanism is of relevance for those stereoisomers as well.