2,124 research outputs found

    School Resources and Educational Outcomes in Developing Countries: A Review of the Literature from 1990 to 2010

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    Developing countries spend hundreds of billions of dollars each year on schools, educational materials and teachers, but relatively little is known about how effective these expenditures are at increasing students’ years of completed schooling and, more importantly, the skills that they learn while in school. This paper examines studies published between 1990 and 2010, in both the education literature and the economics literature, to investigate which specific school and teacher characteristics, if any, appear to have strong positive impacts on learning and time in school. Starting with over 9,000 studies, 79 are selected as being of sufficient quality. Then an even higher bar is set in terms of econometric methods used, leaving 43 “high quality” studies. Finally, results are also shown separately for 13 randomized trials. The estimated impacts on time in school and learning of most school and teacher characteristics are statistically insignificant, especially when the evidence is limited to the “high quality” studies. The few variables that do have significant effects – e.g. availability of desks, teacher knowledge of the subjects they teach, and teacher absence – are not particularly surprising and thus provide little guidance for future policies and programs.

    VARIABILITY of EMISSION RATE DEFINITION in REGULATORY ODOUR DISPERSION MODELLING from CIVIL WASTEWATER TREATMENT PLANTS

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    The analysis of odour impacts in civil wastewater treatment plants (WWTPs) is a challenging task. Odour regulations still present a lack of standardization, that bring inherent levels of uncertainty to the analysis procedure. Dispersion models can provide support towards the characterization and reduction of odour nuisances. The application of dispersion models requires an adapt setting and a detailed characterization of the emission sources, in terms of emission rate. In this study odour dispersion of a large WWTP in northern Italy was considered. Simulations were carried out with the CALPUFF model. The study focused on the selection of the open field correction method for wind velocity used in the calculation of odour emission rates (OERs). Three different relationships were considered: the power law, the logarithmic law and the Deaves–Harris (D–H) law. The area underlying the 1 OU/m3, 3 OU/m3, and 5 OU/m3 concentration isopleths was considered as indicator. The results showed that OERs and impact area varied depending on the selected method. Taking the power law as the reference, the average variability of the impact area was between –33% and –48% if the logarithmic law was applied, and –83% and –94% if the D–H law was applied. The present study provides knowledge towards a better alignment of the concept of the odour impact criteria

    Sustainable energy management benchmark at wastewater treatment plant

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    Urban wastewater effluents bring large amounts of nutrients, organic matter, and organic microcontaminants into freshwater ecosystems. Ensuring the quality of wastewater treatment (WWT) is one of the main challenges facing the management of wastewater treatment plants (WWTPs). How-ever, achievement of high-quality standards leads towards significant energy consumption: usually the more intensive WWT process requires additional energies. Energy efficiency at WWTP is actual mainstream on the current sustainable development agenda. The WWTP processes and methods can be considered from the standpoint of material and energy flows according to circular economy paradigm, which offers great possibilities to reuse waste originating from WWT in order to receive renewable energy. The correlation between energy and quality issues to evaluate WWTP efficiency is of a great scientific and practical interest. The main goal of the paper is to check the dependency between these two main issues in WWTP management\u2014WWT quality and energy efficiency\u2014and to determine possible limits of such relation. The municipal sewerage system of Ekaterinburg, Russia was studied within this paper. The total length of centralized sewerage system in Ekaterinburg is over 1500 km of pipes within two main sewerage basins: northern and southern. The methodological framework for the current research consisted of three steps: (i) WWT quality evaluation, (ii) energy efficiency evaluation, and (iii) WWTP Quality/Energy (Q/E) efficiency dependency matrix. For the purpose of research, authors investigated the 2015\u20132018 period. The results showed that the outputs correlate with the technical conditions of WWTPs and the implementation of the best available techniques (BATs): most of the northern WWTP values are referred to the green zone (good rank), while the southern WWTP values are situated generally in the orange zone (unsatisfactory rank). The proposed methodological approach for Q/E dependency of WWT process creates a strong but simple tool for managers to evaluate the current success of the operation of WWTP and progress towards circular economy practices implementation

    Evaluation of green coffee-roasting biogas with modeling valorization of possible solutions

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    According to the European Union Directive 2009/28/EC, the goals of obtaining 20% of all energy requirements from renewable sources and a 20% reduction in primary energy use must be fulfilled by 2020. In this work, an evaluation was performed, from the environmental and energy point of view, of anaerobic digestion as a valid solution for the treatment of the byproducts obtained from the coffee-roasting process. In particular, thermophilic anaerobic digestion tests were carried out. Output values from the laboratory were used as input for the MCBioCH4 model to evaluate the produced flow of biogas and biomethane and two different biogas valorization alternatives, namely, the traditional exploitation of biogas for heat/energy production and biomethane conversion. The results of the preliminary simulation showed that a full-scale implementation of the coffee waste biogas production process is technically feasible and environmentally sustainable. Furthermore, the performed analysis validates a general methodology for energy production compatibility planning

    Evaluation of Ca-Based Sorbents for Gaseous HCl Emissions Adsorption

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    The problem of acid gas exhaust emissions treatment has not been fully resolved at present. Dry adsorption of acid gases with alkaline sorbents is currently being investigated, to improve solid sorbents. In this study, 5 types of hydrated lime were characterised and tested. The sorption capacities were measured by means of a system consisting of a feed line (HCl/N2), a thermostatic reactor and a water absorber. The physical characteristics of sorbent samples were also compared. Analyses conducted with scanning electronic microscopy revealed that sample C1 showed uniform particle distribution. Samples C2 and C3 showed the co-presence of fine and coarse particles. Sample C4 showed very fine particles with agglomeration phenomena. In sample C5, fibrous elements were found. Energy dispersive spectrometry (EDS) analyses showed a similar composition of the samples, with the exception of the presence of Mg in some of them. After 30 min of testing, the following differences in sorption capacities with respect to C1 (3.59 mg g−1) were found: C2, −20%; C3, −13%; C4, −17%; C5, −3%. Higher sorption capacities were associated with more uniform particle size distributions. Conversely, agglomeration of fine particles may have adversely affected the performance of sorbents

    Optimizing Sewage Sludge Digestion in Wastewater Treatment Plants: a Case Study from the Largest WWTP in Italy

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    This study is part of a multi-objective, integrated approach to analyze various possibilities for increasing energy efficiency of the largest Italian wastewater treatment plant (WWTP) at Castiglione Torinese, NW Italy. The final goal of this study was evaluating the optimization interventions on the sludge treatment process in terms of mass, energy and greenhouse gas (GHG) emission balance. An optimization scenario of sludge digestion was simulated and compared the present operating situation. In the optimized scenario, a hybrid thermo-chemical pre-treatment of the waste activated sludge (WAS) entering the digestion process was considered. The biogas produced was upgraded to biomethane with a process working with selective membranes. Full scale simulation of the whole sewage sludge treatment line was performed with the screening model MCBioCH4, developed by the Authors. The results showed that the optimization interventions would provide two important positive impacts. Firstly, a reduction of the sludge volume entering into the digestion process. Secondly, biomethane production would be around 20% higher than the methane fraction contained in the biogas actually produced. The energy saving and the increased specific biomethane production would improve the overall GHG balance of the system

    Characterization of odorous emissions from a civil wastewater treatment plant in Italy

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    The characterization and reduction of odour emissions represents an open debate among the scientific community. Odour nuisances are connected to a large number of substances, mostly detectable at low concentrations. Direct estimation of odour impacts through olfactometry is not always applicable, as this approach requires air sampling and a pool of trained panellists. Measuring the concentration of odorous substances provides support to the characterization of emission sources and the design of odour monitoring systems. Civil wastewater treatment plants (WWTPs) are known sources of odours. The objective of this project is the design and development of an integrated odour emission monitoring system at the Castiglione Torinese WWTP in Italy. In this paper, the preliminary characterization of the emission sources and the odour emitting components are presented. The characterization of the emission sources and tracers was obtained by mean of a number of site inspections and measurement campaigns held between 2017 and 2019. In the last campaign, held in January 2019, chemical odour tracers (H2S, NH3, VOC) and dynamic olfactometry measurements were performed simultaneously. The screening of VOC species through gas chromatograph/mass spectrometer analysis of air samples was also performed. Odour emitting components were ranked in terms of odour activity value (OAV). Results show that VOC is the only group of compounds that is always detectable on the site. NH3 and H2S may, in some cases, be present at considerable concentrations. Results of OAV calculations show that a number of VOCs are detected on the site with a high spatial and temporal frequency. Additional considerations are reported on the site-specific correlation between chemical species and odour measurements. This detailed characterization of the emission sources and tracers results in the design of the final integrated monitoring system, which will be based on continuous measurement of H2S, NH3 and VOC and advanced dispersion modelling
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