Phosphorus retention capacity in red ferralitic soil

In this study the main physical-chemical characteristics of red ferralitic soil to use as substrate in subsurface wetlands was determined. The P-removal was evaluated in a short-term isotherm batch experiment and in a column percolation experiment. The acid characteristic and high content of iron minerals in the red ferralitic soil facilitated the phosphorus removal. Also the sorption isotherms at two different temperatures were obtained. The results showed that the sorption capacity increases with an increase in solution temperature from 25 to 35 degrees C. The experimental data were fitted to Langmuir and Freundlich models, having a better fit to the Freundlich isotherms. The maximum P-sorption capacities estimated using the Langmuir isotherm were 0.96 and 1.13 g/kg at 25 and 35 degrees C respectively. Moreover a column experiment was carried out at two different flows. Sequential extractions of the phosphorus-saturated soil indicated that phosphorus is mainly bound with iron or aluminum minerals. The results have demonstrated a good potential for red ferralitic soil for phosphorus removal from urban wastewater

Total cost of ownership purchasing of a service : the case of airline slection at Alcatel Bell.

The multiple objective problem of purchasing for business falls into two broad categories: the purchasing of components for manufacturing and the purchasing of services. Several supplier selection models have been suggested in the literature for the purchasing of production-related components. To our knowledge, no supplier selection model for the purchasing of services has been published. In this paper we elaborate on a mathematical programming model that selects suppliers of a multiple item service and simultaneously determines market shares of the suppliers selected. The methodology is based on the collection of Total Cost of Ownership (TCO) information, quantifying all the costs associated with the purchasing process throughout the entire value chain of the firm. We apply this methodology to the real life case study of selecting airlines for 56 destinations at Alcatel Bell and have obtained TCO savings of 19.5%.Purchasing; Selection; Manufacturing; Models; Mathematical programming; Suppliers;

An evaluation of vendor selection models from a Total Cost of Ownership perspective.

Many different vendor selection models have been published in the purchasing literature. However there has been no systematic approach to compare the relative efficiency of the systems. In this paper we propose to use the concept of Total Cost of Ownership as a basis for comparing vendor selection models. We illustrate the comparison with real life data set of the purchasing problem of ball bearings at Cockerill Sambre, a Belgian multinational company in the steel industry. Mathematical programming models outperform rating models and multiple item models generate better results than single item models from a Total Cost of Ownership perspective for this specific case study.Evaluation; Models; Selection;

GW quasiparticle band structures of stibnite, antimonselite, bismuthinite, and guanajuatite

We present first-principles calculations of the quasiparticle band structures of four isostructural semiconducting metal chalcogenides A$_2$B$_3$ (with A = Sb, Bi and B = S, Se) of the stibnite family within the G$_0$W$_0$ approach. We perform extensive convergence tests and identify a sensitivity of the quasiparticle corrections to the structural parameters and to the semicore $d$ electrons. Our calculations indicate that all four chalcogenides exhibit direct band gaps, if we exclude some indirect transitions marginally below the direct gap. Relativistic spin-orbit effects are evaluated for the Kohn-Sham band structures, and included as scissor corrections in the quasiparticle band gaps. Our calculated band gaps are 1.5 eV (Sb$_2$S$_3$), 1.3 eV (Sb$_2$Se$_3$), 1.4 eV (Bi$_2$S$_3$) and 0.9 eV (Bi$_2$Se$_3$). By comparing our calculated gaps with the ideal Shockley-Queisser value we find that all four chalcogenides are promising as light sensitizers for nanostructured photovoltaics.Comment: 11 pages, 5 figures. Revised manuscript - includes spin-orbit interactio

Steric engineering of metal-halide perovskites with tunable optical band gaps

Owing to their high energy-conversion efficiency and inexpensive fabrication routes, solar cells based on metal-organic halide perovskites have rapidly gained prominence as a disruptive technology. An attractive feature of perovskite absorbers is the possibility of tailoring their properties by changing the elemental composition through the chemical precursors. In this context, rational in silico design represents a powerful tool for mapping the vast materials landscape and accelerating discovery. Here we show that the optical band gap of metal-halide perovskites, a key design parameter for solar cells, strongly correlates with a simple structural feature, the largest metal-halide-metal bond angle. Using this descriptor we suggest continuous tunability of the optical gap from the mid-infrared to the visible. Precise band gap engineering is achieved by controlling the bond angles through the steric size of the molecular cation. Based on these design principles we predict novel low-gap perovskites for optimum photovoltaic efficiency, and we demonstrate the concept of band gap modulation by synthesising and characterising novel mixed-cation perovskites.Comment: This manuscript was submitted for publication on March 6th, 2014. Many of the results presented in this manuscript were presented at the International Conference on Solution processed Semiconductor Solar Cells, held in Oxford, UK, on 10-12 September 2014. The manuscript is 37 pages long and contains 8 figure

Arsenic in drinking water wells on the Bolivian high plain: field monitoring and effect of salinity on removal efficiency of iron-oxides-containing filters

In the rural areas around Oruro (Bolivia), untreated groundwater is used directly as drinking water. This research aimed to evaluate the general drinking water quality, with focus on arsenic (As) concentrations, based on analysis of 67 samples from about 16 communities of the Oruro district. Subsequently a filter using Iron Oxide Coated Sand (IOCS) and a filter using a Composite Iron Matrix (CIM) were tested for their arsenic removal capacity using synthetic water mimicking real groundwater. Heavy metal concentrations in the sampled drinking water barely exceeded WHO guidelines. Arsenic concentrations reached values up to 964 mu g L-1 and exceeded the current WHO provisional guideline value of 10 mu g L-1 in more than 50% of the sampled wells. The WHO guideline of 250 mg L-1 for chloride and sulphate was also exceeded in more than a third of the samples, indicating high salinity in the drinking waters. Synthetic drinking water could be treated effectively by the IOCS- and CIM-based filters reducing As to concentrations lower than 10 mu g L-1. High levels of chloride and sulphate did not influence As removal efficiency. However, phosphate concentrations in the range from 4 to 24 mg L-1 drastically decreased removal efficiency of the IOCS-based filter but had no effects on removal efficiency of the CIM-based filter. Results of this study can be used as a base for further testing and practical implementation of drinking water purification in the Oruro region