Heated laterite as a low-cost adsorbent for arsenic removal from aqueous solution

Existing works reported that the laterite prepared using chemical treatment improved its removal performance compared to the raw laterite. However, this treatment has several drawbacks such as costly and potentially produces pollutant. To overcome this issue, the present work proposed heated laterite (HL) for removal of Arsenic (III) (As(III)) from aqueous solution as a low-cost adsorbent without any chemical use. HL was firstly obtained via the heat treatment a temperature of 550 oC for raw material with geometric sizes of 0.6 to 1.0 mm. Properties of HL in terms of surface morphology, energy dispersive X-ray, porosity, surface area, and Fourier transform infrared spectroscopy were then characterized. Effects of physicochemical parameters such as pH, agitation speed, adsorbent dosage, and initial concentration for optimal adsorption performance of As(III) were investigated. Gibbs free energy, enthalpy, and entropy of the adsorption were also determined, from which the sorption capacity and isotherm were estimated using Langmuir and Freundlich isotherm models. Langmuir model was found to be more reliable than Freundlich in describing the process behavior. This study found that the removal performance of HL was strongly affected by the physicochemical parameters. As the main finding, the optimal conditions for a low-cost and green adsorbent were adsorbent dose of 6 g L-1, with an initial As(III) concentration of 0.5 mg L-1, pH 7, and agitation speed of 250 rpm, which successfully removed 98.8% of As(III)

Kanchan arsenic filter: evaluation and applicability to Cambodia

Arsenic contamination of drinking water in rural Cambodia has driven the search for mitigation options. The Kanchan Arsenic Filter for household water treatment is being evaluated for its applicability as one potential solution to this crisis. In 2008, ten Kanchan filters, in 5 configurations, were tested over a 30 week period. Each filter treated 40 L/day. The ground water had arsenic and phosphate concentrations averaging 637 μg/L and 5.09 mg/L respectively, representing challenging source water. Arsenic removal averaged 9597% for all configurations. After the first week of start up, all but 1 in 224 samples achieved the Cambodian standard of 50 μg/L. Arsenic removal was not significantly affected by the flow rate or the cleaning of the filter. There was no apparent depletion of arsenic adsorption capacity over the 30 weeks (8400 L filtered). Iron and turbidity removals were also very high, improving the user acceptability of this technology

Étude cinétique et métabolique de Corynebacterium glutamicum 2262 au cours de la fermentation glutamique : instabilité de la production de glutamate en procédé continu thermo-induit

Non disponible - Not availableL'objectif général de ce travail est l'étude de la cinétique et du métabolisme de Corynebacterium glutamicum 2262 lors de la fermentation glutamique. L'excrétion de glutamate est induite par une élévation de la température de culture de 33 à 39°C qui permet d'orienter du métabolisme vers la synthèse et l'excrétion de glutamate au détriment de la croissance. En procédé continu à 39°C, D = 0,05 h-1, une production de glutamate sur une période de 150 h a été réalisée ; après cette période, les cellules ne sont plus capables de produire du glutamate mais capables de croître rapidement. Lorsque les cellules produisent du glutamate, les activités pyruvate déshydrogénase et alpha-cétoglutarate déshydrogénase sont respectivement réduite et absente. Les effets du choc de température à 39°C sur le métabolisme de l'oléate et du palmitate ainsi que sur la fluidité de la paroi cellulaire de cette bactérie ont également été étudiés pendant la fermentation glutamique

Étude cinétique et métabolique de Corynebacterium glutamicum 2262 au cours de la fermentation glutamique (instabilité de la production de glutamate en procédé continu thermo-induit)

NANCY-INPL-Bib. électronique (545479901) / SudocSudocFranceF

Characterization of a Corynebacterium glutamicum Lactate Utilization Operon Induced during Temperature-Triggered Glutamate Production

Gene expression changes of glutamate-producing Corynebacterium glutamicum were identified in transcriptome comparisons by DNA microarray analysis. During glutamate production induced by a temperature shift, C. glutamicum strain 2262 showed significantly higher mRNA levels of the NCgl2816 and NCgl2817 genes than its non-glutamate-producing derivative 2262NP. Reverse transcription-PCR analysis showed that the two genes together constitute an operon. NCgl2816 putatively codes for a lactate permease, while NCgl2817 was demonstrated to encode quinone-dependent l-lactate dehydrogenase, which was named LldD. C. glutamicum LldD displayed Michaelis-Menten kinetics for the substrate l-lactate with a K(m) of about 0.51 mM. The specific activity of LldD was about 10-fold higher during growth on l-lactate or on an l-lactate-glucose mixture than during growth on glucose, d-lactate, or pyruvate, while the specific activity of quinone-dependent d-lactate dehydrogenase differed little with the carbon source. RNA levels of NCgl2816 and lldD were about 18-fold higher during growth on l-lactate than on pyruvate. Disruption of the NCgl2816-lldD operon resulted in loss of the ability to utilize l-lactate as the sole carbon source. Expression of lldD restored l-lactate utilization, indicating that the function of the permease gene NCgl2816 is dispensable, while LldD is essential, for growth of C. glutamicum on l-lactate

Development of household arsenic removal system using local adsorbent

The arsenic contamination in the groundwater in Cambodia is a problem for rural people since they are st ill drinking the arsenic contaminated water from their tube well s during the dry season when the rainwater is used up. The village scale arsenic water treatment systems in Cambodia were sustainable in schools but not applicable in villages due to the lack of system of distribution of treated water to each household. Thus, we developed the household arsenic water treatment system by combining the bio- sand filter with the local arsenic adsorbent. Nine filters were tested in three location s using 1 Kg of adsorbent for each filter, where the concentrations of arsenic in the groundwater sources are ranging between 600 - 800 ppb. The kinetics of bio-sand filters and combined bio-sand and adsorbent filters were studied for six months. The filters removed the arsenic from 95 to 99% which provided the treated water with the arsenic concentration conformed to the Cambodian standard for drinking water « 50 ppb) for the period of six months corresponding to a volume of treated water of 7,000 L. The filters removed also iron, manganese, phosphate and turbidity 99.5, 60, 85 and 99% respectively. The filters also removed total plate count, coliforms and . E. coli with efficiency of 98, 100 and 100% respectively. For a long term arsenic treatment, the system should consist of a combined bio-sand and 10 Kg of adsorbent for the material cost of USD 18.With this set-up, the filter could provide treated water of about 70,000 L for the period of several years

Heat-treated laterite as an efficient and low-cost adsorbent for the removal of arsenic

Arsenic removal capacity of heat-treated lat erite, collected from Kampong Thom province, Cambodia, has been investigated. Laterite is a local material and readily available in many parts of Cambodia. It is easily prepared as an absorbent and the cost of preparation is low compared to commercial adsorbent. Characterization study by BET showed that the heating treatment increases the surface area of the laterites. This was confirmed by FESEM study which showed that heating treatment creates tiny cracks on the surface of the laterite particles. EDX study showed t hat the late rite contained iron (37.33%), aluminum (1.25%), silicon (2.45%) and manganese (1.1S%). Heating treatment decomposes t he organic compound present in laterite, thus resulted in the decreasing of carbon and oxygen content from 11.59% to 3.52% and 45.71% to 34.94% respectively. For the removal capacity of arsenic, parameters such as the effects of pH, temperature, adsorbent dose, adsorbent particle size, agitation speed and initial concentration were examined. The maximum adsorption capacity of arsenic by heated laterite was found to be 0.21 mg g" based on Langmuir adsorption isotherm. The removal was observed to be particle size independent which represents less than 0.06% difference of arsenic removal between t he smallest (0.07 - 0.10 mm) and the largest (0.60 - 1.00 mm) size of adsorbent particle. Kinetic results of arsenic removal showed that the uptake of arsenic was rapid in the first hour and slower thereafter. Kinetic data of arsenic adsorption followed the pseudo-second order equation (R' = 0.99) . Thermodynamic study estimated t hat the adsorption was spontaneous, favorable and endothermic reaction

The Evolution of Comparative Advantage: Measurement and Implications

We estimate productivities at the sector level for 72 countries and 5 decades, and examine how they evolve over time in both developed and developing countries. In both country groups, comparative advantage has become weaker: productivity grew systematically faster in sectors that were initially at greater comparative disadvantage. These changes have had a significant impact on trade volumes and patterns, and a non-negligible welfare impact. In the counterfactual scenario in which each country's comparative advantage remained the same as in the 1960s, and technology in all sectors grew at the same country-specific average rate, trade volumes would be higher, cross-country export patterns more dissimilar, and intra-industry trade lower than in the data. In this counterfactual scenario, welfare is also 1.6% higher for the median country compared to the baseline. The welfare impact varies greatly across countries, ranging from ..1.1% to +4.3% among OECD countries, and from ..4.6% to +41.9% among non-OECD countries