1,721,061 research outputs found
Influence of denitrification reactor retention time distribution (RTD) on dissolved oxygen control and nitrogen removal efficiency
No full textLow concentrations of dissolved oxygen (DO) are usually found in biological anoxic pre-denitrification reactors, causing a reduction in nitrogen removal efficiency. Therefore, the reduction of DO in such reactors is fundamental for achieving good nutrient removal. The article shows the results of an experimental study carried out to evaluate the effect of the anoxic reactor hydrodynamic model on both residual DO concentration and nitrogen removal efficiency. In particular, two hydrodynamic models were considered: the single completely mixed reactor and a series of four reactors that resemble plug-flow behaviour. The latter prove to be more effective in oxygen consumption, allowing a lower residual DO concentration than the former. The series of reactors also achieves better specific denitrification rates and higher denitrification efficiency. Moreover, the denitrification food to microrganism (F:M) ratio (F:MDEN) demonstrates a relevant synergic action in both controlling residual DO and improving the denitrification performance
Characterization and management of wastes from automotive shredder residues - Gassification and combustion treatment
No full textEvaluation of automotive shredder residues (ASR) landfill behavior through lysimetric and traditional leaching tests
No full textWith regards to European waste catalog, automotive shredder residues (ASR) can be classified both as a hazardous or non-hazardous waste according to its hazardous properties (H1–H14). It is thus important to carry out an adequate chemical-physical characterization to identify the presence and concentration of those substances able to give, to this extremely heterogeneous material, the hazardousness character of. The issue of waste characterization, to identify the proper site for appropriate waste disposal, is based, according to the relevant laws, to the use of leaching tests. The analysis of the potential effects of landfilled waste in laboratory, however, run into several difficulties in reproducing phenomena depending both on the characteristics of small, heterogeneous quantity of waste and on the local boundary conditions. These difficulties are much more significant as the waste is heterogeneous at the small scale of the laboratory. This is one of the main problems often leading to scattered results even when starting from the same waste parcel. Present research aimed to overcome the above-mentioned difficulties deriving from waste heterogeneity and was based on a lysimetric simulation. Experimentation with lysimeter has shown it effectiveness in the comparison between leachate from the lysimeter and an ASR landfill leachate, from which similar distribution of metal mass ratios, close values for both BOD5 and COD, as well as the absence in both the fluids of organochlorinated compounds, emerge
A study on phosphorus flux from sediment in a shallow homogeneous lake
No full textA study on phosphorus release dynamics was conducted into a shallow homogeneus and mesotrophic lake. The purpose was to investigate physical- chemical factors which contribute to the nutrient release-adsorption from sediments. Water and sediment samples were analyzed under different conditions: aerobic and anoxic, static
and mixed. Results in both last cases (anoxic/aerobic conditions) show that the nutrient release- sorption dynamics are strictly linked to the iron- manganese
associated phosphorus contents within the sediments but the low overall phosphorus release is largely linked to the sediment’s calcareous nature (phosphorus precipitation
as hydroxyapatite and co-precipitation/adsorption with carbonates). In the mixed tests cases, as expected, the release is higher compared to static aerobic ones: the
sediments re-suspension allows for a higher contact surface area with water leading to a higher phosphorus desorption. In case of shallow lake the wind can therefore play an important role in influencing phosphorus balance in the waters. This aspect can be even more important when suspended fine clay particles are involved since they can be
considered a support for phosphorus forms. It follows that surficial sediments when re-suspended play a double role: they can redistribute phosphorus along the water column but they can re-adsorb it
nZVI mobility and transport: laboratory test and numerical model
Full text linkZerovalent iron nanoparticles (nZVI) are becoming one of the most widely recommended nanomaterials for soil and groundwater remediation. However, when nZVI are injected in the groundwater flow, the behavior (mobility, dispersion, distribution) is practically unknown. This fact generally results in the use of enormous quantities of them at the field scale. The uncertainties are on the effective volumes reached from the plume of nZVI because their tendency to aggregate and their weight can cause their settling and deposition. So, the mobility of nanoparticles is a real issue, which can often lead to inefficient or expensive soil remediation. Furthermore, there is another aspect that must be considered: the fate of these nZVI in the groundwater and their possible impact on the subsoil environment. All these considerations have led us to propose an application of nZVI simulating the permeation technique through a laboratory experience, finalized to have a better, or even simpler description of their real behavior when injected in a flow in the subsoil. A two-dimensional laboratory-scale tank was used to study the dispersion and transport of nZVI. A nZVI solution, with a concentration equal to 4.54 g/L, was injected into glass beads, utilized as porous medium. The laboratory experiment included a digital camera to acquire the images. The images were then used for calibrating a numerical model. The results of the mass balance confirm the validity of the proposed numerical model, obtaining values of velocity (5.41 x 10(-3) m/s) and mass (1.9 g) of the nZVI of the same order of those from the experimental tests. Several information were inferred from both experimental and numerical tests. Both demonstrate that nZVI plume does not behave as a solute dissolved in water, but as a mass showing its own mobility ruled mainly from the buoyancy force. A simple simulation of a tracer input and a nZVI plume are compared to evidence the large differences between their evolution in time and space. This means that commercial numerical models, if not corrected, cannot furnish a real forecast of the volume of influence of the injected nZVI. Further deductions can be found from the images and confirmed by means the numerical model where the detachment effect is much smaller than the attachment one (ratio k(d)/k(a) = 0.001). From what is reported, it is worthwhile to pay attention on the localization of the contaminants source/plume to reach an effective treatment and it is important to go further in the improvement of solution for the limiting the nanoparticles aggregation phenomenon
Removal and survival of fecal indicators in a constructed wetland after uasb pre-treatment
Full text linkThe experimentation plant, based on a sub-surface horizontal flow phytodepuration (SSHFP) unit with a pre-treatment by an upflow anaerobic sludge blanket (UASB) reactor, proved valuable in treating the sewage of a small rural community located in north Brazil. During a six-month trial, the plant achieved an average removal efficiency of 98.2% (1.74 log removal) for fecal coliforms (FC) and 96.0% (1.40 log removal) for Enterococci (EN), as well as 95.6% for BOD5, 91.0% for COD,00 and 95.4% for suspended solids (SS). The contribution of the UASB reactor to this overall performance was very significant as, alone, it achieved a yield of 62.7% for FC and 60% for EN, in addition to 65.2% for BOD5 and 65.0% for SS. EN was chosen, in addition to FC, because of its higher specificity and strong environmental persistence, leading to an increased risk to human health. In fact, the experimental results confirmed its lower removal efficiency compared to FC. The mechanical and biological mechanisms that led to such a removal efficiency of the two fecal indicators (FIs) are outlined in the article. The same mechanisms led to a good level of equivalence between the removal efficiency of the two FIs with the removal efficiency of SS and BOD5, for both the whole plant and the UASB reactor alone. The research demonstrated the close correlation between the concentrations of EN and FC for the plant effluent. This correlation can be explained by the following mathematical expression of the regression line Log EN = 0.2571 Log FC + 3.5301, with a coefficient of determination R-2 = 0.912. This implies that the concentration of the more specific indicator EN could be calculated, with acceptable approximation, from the simple analysis of FC and vice versa. The experimental plant brought important health benefits to the local population. In particular, there were no significant odor emissions; moreover, the risk of fecal pathogenic diseases was drastically reduced; finally, there was no proliferation of insects and other disease vectors, due to the absence of stagnant or semi-stagnant water exposed to the atmosphere
Murine erythroleukemia cell differentiation: possible involvement of a calcium dependent neutral proteinase.
No full textPartial Stabilization of Mo-Containing Hazardous Wastes Using a Ferrous Sulfate-Based Additive as a Redox Agent
No full textAbstract: Bottom and fly ashes from a hazardous waste incineration plant, which showed a high concentration of Mo in a leaching test, have been treated to decrease its leachability to below the limit set by the laws in force for admittance to a non-hazardous waste landfill. Both ashes have a basic pH, that is, of around 11–13, therefore most of the molybdenum species were expected to be in the form of molybdate ions (MoO42−), the most soluble molybdenum compound. The aim of the study was to immobilize the molybdate ions using the reducing properties of the Fe2+ ion, in compliance with specific pH and redox potential conditions, which resulted to be crucial for the partial stabilization and immobilization of Mo. The bottom ash was treated both by adding a cost-effective ferrous sulfate-based additive alone and by adding it together with calcium oxide. The fly ash was initially tested with the same ferrous sulfate-based additive; a mix of the former additive and a concentrated solution of sulfuric acid (96%) was then tested to increase the stabilization efficiency. The conducted experiments revealed that the molybdenum leaching behavior can be controlled efficiently by adding ferrous sulfate, under specific pH and redox potential conditions, thereby providing further insight into the sustainable chemical conditions necessary to partially stabilize Mo-containing hazardous waste. Graphic Abstract: [Figure not available: see fulltext.]
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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