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51.
The present lab-scale experimental study presents the process of leaching waste printed circuit boards (WPCBs) in order to recover gold by thioureation. Preliminary tests have shown that copper adversely affects gold extraction; therefore an oxidative leaching pre-treatment was performed in order to remove base metals. The effects of sulfuric acid concentration, hydrogen peroxide volume and temperature on the metal extraction yield were studied by analysis of variance (ANOVA). The highest copper extraction yields were 76.12% for sample A and 18.29% for sample D, after leaching with 2 M H2SO4, 20 ml of 30% H2O2 at 30 °C for 3 h. In order to improve Cu removal, a second leaching was performed only on sample A, resulting in a Cu extraction yield of 90%. Other experiments have shown the negative effect of the stirring rate on copper dissolution. The conditions used for the process of gold extraction by thiourea were: 20 g/L thiourea, 6 g/L ferric ion, 10 g/L sulfuric acid, 600 rpm stirring rate. To study the influence of temperature and particle size, this process was tested on pins manually removed from computer central processing units (CPUs) and on waste CPU for 3½ h. A gold extraction yield of 69% was obtained after 75% of Cu was removed by a double oxidative leaching treatment of WPCBs with particle sizes smaller than 2 mm.  相似文献   
52.
The Mediterranean Region is a semi-arid area whose land is facing serious erosion, causing adverse impacts on agriculture. To improve the water availability, researchers have proposed the reclamation and reuse of treated wastewater. In this paper, we report the main findings of 10 years of research on the efficiencies of a conventional activated sludge process and a submerged membrane bioreactor, with particular emphasis on the removal of non-conventional pollutants. The studies showed that the membrane bioreactor produced a virtually solids-free, high-quality permeate: most nutrients, heavy metals, and persistent organic pollutants were removed, and in particular, dioxins, furans, and polychlorinated biphenyls were typically present at concentrations below the detection limit. Moreover, the total coliforms count decreased by 4–5 log and Escherichia coli was absent from the membrane bioreactor permeate. These results, combined with the continuing reduction of the capital and operating costs for this approach, suggest that membrane bioreactors are an increasingly cost-effective technology to produce treated effluents that are suitable for reuse.  相似文献   
53.
In corals where complex life history processes decoupling age from size (e.g., fragmentation, fusion, partial colony mortality) are rare or clearly detectable, individual age may be determined from size, and age-based growth and population dynamic models may be applied. One example is the solitary Mediterranean coral Leptopsammia pruvoti Lacaze-Duthiers 1897, whose population size and structure, and growth rates were determined at Calafuria (43°28′N and 10°20′E), Ligurian Sea, from December 2007 to June 2009. Growth rate decreased with increasing size. The growth curve derived from field measurements confirmed the one obtained by growth band analysis. The frequency of individuals decreased exponentially with age, indicating a steady state population. Turnover time was 2.3 years. Maximum life span was 13 years. Most reproductive output was from intermediate age classes (6 years), while older individuals (>7 years), although having higher fecundity, were rare and accounted for a minority of population reproductive output. In comparison with other solitary dendrophylliids, L. pruvoti life strategy was characterized by a reproduction with r-strategy correlates (high fecundity, short embryo incubation, small planula size, fast achievement of sexual maturity), and a rate of demographic renewal occurring halfway along the rK continuum (intermediate turnover time and maximum longevity).  相似文献   
54.
In this paper, we explore a range of concerns that arise in measuring short-term effects of ozone on health. In particular, we tackle the problem of measuring exposure using alternative daily measures of ozone derived from hourly concentrations. We adopt the exposure paradigm of Chiogna and Bellini (Environmetrics 13:55–69, 2002) extending it to ozone concentrations, and we compare its performances with respect to traditional exposure measures by exploiting model selection. To investigate the stability of model selection, we then apply the idea of bootstrapping the modelling process.  相似文献   
55.
Environmental Fluid Mechanics - The Eulerian–Lagrangian model ORSA2D_WT is employed for the simulation of uncongested wood transport, with reference to a field experiment that studied the...  相似文献   
56.
Sediment samples of different strata (0-3 and 12-15 cm) were collected between 1990 and 1992 during seasonal cruises in the Northern Adriatic Sea. A complete mapping of the Sr-90, Cs-137, Pu-238 and Pu-239(240) concentrations was obtained for samples covering a wide area, stretching from the Gulf of Trieste towards the Ancona shoreline. Sr-90 concentrations varied between 1.5 and 6.5 Bq kg-1 dw, Cs-137 was in the range 0.9-38.9 Bq kg-1 dw, Pu-239(240) in the range 0.08-1.5 Bq kg-1 dw and Pu-238 around 0.03 Bq kg-1 dw. Special reference was also put on the comparison between the off-shore environment and data obtained from samples collected inside the Po river delta. in spite of the major accumulation of Cs-137 inside the estuarine environment, higher concentrations of strontium and plutonium isotopes were detected in the offshore environment.  相似文献   
57.
ABSTRACT: Annual maximum daily rainfall data from nine stations throughout the southern slopes of the Eastern Italian Alps with record length of 67–68 years have been analyzed with the aim of verifying if their internal structure justifies the assumption of independence and identical distribution, or the “White noise hypothesis.” The approach is to consider the hypothesis H0 of white noise as the intersection of several sub-hypotheses, each concerning one of the characteristics of a white noise process. To this end the nine series were subjected to various statistical tests regarding randomness, independence, change-points, and predictability. The results are examined first individually and then globally. They indicate that in eight of the nine considered time series the “white noise hypothesis” was rejected.  相似文献   
58.
A coupled model of biological and settling phases aimed at optimal design of predenitrification systems is presented. Each unknown is obtained in explicit form, and is expressed as a function of the system's required performance. A model, taking into account both suspended and dissolved substrates, is adopted for the biological phase, while the limiting solid flux theory is assumed for the design of the settling phase. Finally, a relationship correlating the two phases is obtained expressing opportunely the sludge recycle flow and the sludge waste flow, without recourse to empirical parameters. The effect of different influent and effluent wastewater characteristics on the model's results is also analyzed.  相似文献   
59.
The feasibility of composting as disposal practice of husk mixed with olive mill wastewaters (OMW) was studied in the present research. The process was investigated with regards to some reliable and easy to be determined microbial activity parameters such as the ATP content, the activity of a pool of enzymes and the viable counts, keeping in mind the well known bias of this last technique. Two different composting technologies were compared: static pile and reactor by studying the cured composts obtained. Among the bioindicators tested, the composting process trend was described better by the ATP content and the activity of some enzymes. In fact, the ATP content showed an increase during the thermophilic phase in both the pile and the reactor, and decreased at the end of the process, it was also higher in the bioreactor-pile technology than in the pile. With regard to the enzymatic activity, with the reactor technology experiment, two peaks were evidenced in the thermophilic phase and during the curing phase in pile, and a drop during the transfer of material from the reactor to the pile. The quality of the cured product obtained using the reactor technology has been evaluated considering phytoxicity and hygienic features: the stabilised compost resulted to have neither phytoxical effect, nor faecal indicator contaminants.  相似文献   
60.
Mass balance of contaminants can provide useful information on the processes that influence their concentrations in various environmental compartments. The most important sources, sinks and the equilibrium or non-equilibrium state of the contaminant in individual environmental compartments can also be identified. Using the latest mercury speciation data, the results of numerical models and the results of recent studies on mercury transport and transformation processes in the marine environment, we have re-evaluated the total mercury (HgT) mass balance in the Mediterranean Sea. New calculations have been performed employing three distinct marine layers: the surface layer, the thermocline and the deep sea. New transport mechanisms, deep water formation and density-driven sinking and upwelling, were included in the mass balance calculations. The most recent data have even enabled the calculation of an approximate methylmercury (MeHg) mass balance. HgT is well balanced in the entire Mediterranean, and the discrepancies between inputs and outputs in individual layers do not exceed 20 %. The MeHg balance shows larger discrepancies between gains and losses due to measurement uncertainties and gaps in our knowledge of Hg species transformation processes. Nonetheless, the main sources and sinks of HgT (deposition and evasion) and MeHg (fluxes from sediment, outflow through the Gibraltar Strait) are in accordance with previous studies on mercury in the Mediterranean Basin. Mercury in the Mediterranean fish harvest is the second largest MeHg sink; about 300 kg of this toxic substance is consumed annually with sea food.  相似文献   
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