Search

Due to its rising accumulation in the food chain and ongoing presence in ecosystems, metal contamination has piqued the curiosity of experts from all over the world. Environmentally hazardous heavy metal removal is being pursued utilizing a variety of techniques, such as ion exchange and precipitation, as well as chemical oxidation or reduction, electrochemistry, and filtration. However, these methods require high investment and operating costs, and generate toxic sludge. Spirulina platensis, a filamentous cyanobacteria species, has been reported as a potential bioadsorbent for the removal of some heavy metals from industrial wastewater. In this study, the bioadsorption of Zn2+ ions in an assumed aqueous solution by the dry biomass of S. platensis TH was investigated. The Zn2+ ion adsorption of biomaterials was evaluated under different conditions, including pH, contact time, temperature, and adsorbent mass. The optimal Zn2+ ion removal efficiency reached 90.32 ± 0.29% at Zn2+ ion concentration of 100 mg/L, pH 5.0, a temperature of 26oC, and a dry biomass dose of 1.5 g/L for 90 min. Langmuir and Freundlich's isothermal models were used to describe the adsorption isotherm of Zn2+ ions on S. platensis TH. Equilibrium data fitted well with the Langmuir model as well as the Freundlich model, with a maximum adsorption capacity of 34.56 mg Zn2+/g S. platensis TH under the reaction conditions of 1.5 g/L biomass dosage, the contact time of 90 min, pH 5.0, at 26oC. Research results have shown that S. platensis TH biomass is an easy, readily available, low-cost adsorbent and has a high bioadsorption capacity. Therefore, it can be treated as a bioadsorbent in the treatment of wastewater containing Zn2+ ions. This process is not only environmentally friendly but also versatile as an alternative to conventional heavy metal treatment methods.

Microplastics with particle size less than 5 mm are becoming a raising global environmental crisis. These pollutants were found from the poles to the equator, in continental shelves, coasts and in the oceans, moreover, they have also been identified in the water columns, sediments and even in a variety of organisms. The majority of microplastics that ended up in the oceans originate from the land. Due to their small size, they are easily accumulated in the food chain, causing harmful effects on organisms and human health. The bivalves especially caught the interest of scientific researchers because of their direct contact with microplastics through the filter-feeding habit. Therefore, it is essential to develop methods to determine the presence of microplastics in these organisms and identify their source. This study evaluated the efficiency of extracting microplastics from the tissues of green mussels (Perna viridis) using KOH 10% solution to digest and KI 50% as the separating solution. Mussel soft tissue samples were spiked five different types of microplastics: polystyrene (PS), polyvinyl chloride (PVC), polyethylene terephthalate (PET), polypropylene (PP), high-density polyethylene (HDPE) and treated with KOH 10% solution and KI 50% solution. The presence of microplastics in some green mussel species was also investigated in some mussel farming areas in Giao Thuy, Nam Dinh province, Thi Nai, Quy Nhon, Binh Dinh province and Hue city, Thua Thien Hue province. The research results showed high efficiency of microplastic extraction and recovery with the range from 76% to 97%. Microplastic concentration obtained in all mussel samples variates from 1.0 ± 0.1 particles/g to 1.7 ± 0.6 particles/g, in which fiber microplastics predominated. Microplastics in mussel samples have small sizes of < 1,000 µm and 1,000–2,000 µm, make up 74.15–82.32% and 9.76–14.71%, respectively. Purple was dominant among all mussel samples. This study proved that using KOH 10% solution and KI 50% solution to isolate microplastics is a suitable approach and can be used in monitoring studies of microplastic pollution in bivalves.

Cyanobacteria are photosynthetic microorganisms that have their biosynthesis capacities for secondary compounds with the high application value. They can produce a variety of bioactive compounds such as lipopeptides, fatty acids, toxins, carotenoids, vitamins and plant growth regulators which could be released into the culture medium. The present study aimed to isolate and screen cyanobacteria strains that could synthesize phytohormone, indole-3-acetic acid (IAA) from paddy soild and fresh water ecosystems (canals, river). Soil and water samples were collected from diferent provinces (Bac Giang, Thanh Hoa and Hue). Indole-3-acetic acid was extracted from the culture of isolated cyanobacteria strains and identified using the Salkowski method. As a result, total 10 strains belonging to 4 genera including Nostoc, Anabena, Geitlerinema and Planktothricoides were susscessful isolated from river, canal and rice field. The morphology of isolated taxa was characterized and monoalgal cultures were grown in BG 11 medium. In L-tryptophan-enriched growth media, all cyanobacteria strains in this research were able to biosynthesize growth regulators with IAA concentrations ranging from 9.1 to 95 µg/mL. Among the isolated cyanobacteria strains, the Planktothricoides raciborskii showed potential for the production of IAA even in the absence of tryptophan in the culture medium. Research results of the L-tryptophan concentration effect on the ability of IAA biosynthesis of this cyanobacteria strain showed that IAA concentration increased gradually and reached the highest value (118,28 ± 2,00 µg/mL) when supplementing L- tryptophan in culture medium at 900 µg/mL. The capacity of producing IAA makes these isolated cyanobacteria an appopriate cadidate for agricultural biotechnology.

International audience; Absorptivity control is a very desired feature in many RF applications as it allows enhancing electromagnetic performances such as antenna radiation patterns and reducing radar cross section. In this paper, two Salisbury-inspired structures with absorption level of 20% and 50% in X-band frequencies (8–12 GHz) are presented. Both structures are fabricated by electron beam evaporation technique with Nickel Chrome as material for the resistive coating on PEKK dielectric substrates, which are manufactured by thermal compressing. The RF characterization in non-anechoic environment confirms the results obtained by numerical computations. For both vertical and horizontal polarizations, quasi-perfect agreement over the frequency band of interest is found with a maximal variation of the absorptivity less than 5% between the center frequency at 10 GHz and the edges frequencies at 8 GHz and 12 GHz. The absorption behavior of the two structures was also evaluated under oblique incidence.

Being the second largest coffee producing country worldwide, Vietnam is estimated to annually generate approximately 1 million m3 of coffee pulp. Instead of being effectively utilized in the form of recycling resources, most of the waste is discarded, causing serious environmental pollution even though it contains essential macronutrients in high concentrations. In this study, we performed on-farm composting trials of coffee pulp with simple aeration using wood chips and air flow. After 2 months of composting, samples were collected for analysis and a cultivation experiment was conducted to clarify the effectiveness of the composts. Coffee pulp compost was a nutrient-rich organic material with the total C, total N and total K in the range of 340.35–386.02 g kg–1, 23.80–36.70 g kg –1, and 18.86–25.13 g kg–1, respectively. The C:N ratio was in the range of 10–15 and the NH4–N:NO3–N ratio was in the range of 1–2, indicating compost was mature. In the compost where wood chips were used as the bulking agent under air flow, exhibited a concentration of inorganic N that was significantly higher than that of the other composts. The plant biomass corresponding to the compost showed similarity with chemical fertilizer. Furthermore, the P content and the plant biomass produced by the compost in which chicken manure was added, were investigated. The results indicate that the addition of P-source in the manufacturing process enhanced the fertilizing efficiency of the compost.

Microplastics (particles with a size of less than 5 mm) are a rising environmental problem. Microplastics can disseminate in the air and accumulate in sediments as well as in microorganisms and humans, due to their small size. Sediment is considered to be the major repository of microplastics, particularly those of the PE type. Microplastics in massive amounts accumulated in sediments, perhaps as a result of point sources or diffuse contamination. Microplastic contamination can spread from industrial production facilities, urban areas, agricultural areas, or the air. The current study was carried out to explore the occurrence of MPs in sediments at discharge sources by evaluating 27 sediment samples taken from 9 distinct waste sources from industrial activity locations to determine the amount of microplastic contamination in sediments at discharge sources. Microplastics with relatively high density were found in all sediment samples in this research, ranging from 2,900 to 238,200 particles/kg dw. The most prevalent microplastics detected in sediment samples at these sites were fibers and fragments, accounting for 59-94% and 6-41%, respectively. Fiber microplastics ranged in size from 1000 to 9,000 µm, whereas fragment microplastics ranged from 200,000 to 2,100,000 µm2. Microplastics with < 1000 µm and 1000-2000 µm sizes accounted for a significant portion of the total, reaching 21.05-37.84% and 39.74-61.17%, respectively. The hue of microplastic particles in sediment samples obtained was highly varied.

Flash Interactive Presentation; International audience

Organic fertilizers have recently been gaining popularity, however, their governance is not completely assessed in developing countries. This study investigated the nutrient composition of so-called organic fertilizers in Vietnam&rsquo, s markets and issues related to their production, and evaluated their potential to contaminate the groundwater. We analyzed the physicochemical properties of 12 domestic and four imported products of the fertilizers, and conducted a cultivation experiment in sandy soil with the fertilizer applied at a rate of 200 mg N kg&minus, 1 soil using an automatic watering apparatus in a greenhouse. We further studied the production of an &ldquo, organic fertilizer&rdquo, from coffee by-products. The nutrient content greatly varied among domestic products, whereas they were quite similar among imported products. The product packaging of the collected samples lacked information regarding raw materials. Two thirds of the domestic products contained over 30% of the total N in the inorganic form, implying that the N content dramatically increased in the fertilizers rather than in their supposed raw materials. The stages involved in the production were composting, the addition of extra soil as a bulking agent, and the mixing-in of chemical substances to increase the nutrient content before packing. The remarkably high ratio of inorganic N to total N was attributed to excessive N leaching from soil by the application of domestic fertilizers. These results suggested the need for quality criteria guidelines for organic fertilizers in Vietnam that underline not only nutrient levels, but also the control of raw materials and production process of compost, because they are closely related to nutrient uptake and the leaching loss of nutrients.

Combining compost with sufficient chemical N fertilizer (CF) in agricultural lands is a popular practice to reduce the amount of inorganic nitrogen and accumulation of non-nutrient constituents in soils. A pot culture experiment was conducted to study the effects of 130 mg N of either solids waste compost (Scomp) or biosolids waste compost (Bcomp) complemented with 130 mg (CF, 1N) and 260 mg·N·pot-1 (CF, 2N) as 15N labeled (NH4)2SO4 (13.172 atom %) on growth and N uptake by Italian ryegrass. A separate soil incubation without plants was set up by only blends of Scomp and CF. The results from pot culture experiment show that total plant biomass and N uptake from Bcomp were significantly higher than Scomp alone. Scomp combined with CF improved yield and N uptake over those of Scomp alone. For Scomp + 1N treatment, plant nitrogen uptake derived from compost and CF accounted for 29% and 56% of added N from Scomp and CF, respectively. The incubation study indicates that 16.08 - 29.62 mg·N·kg-1·soil·day-1 from inorganic-N were immobilized into organic pools, while only 0.40 - 0.66 mg·N·kg-1·soil·day-1 from organic-N were mineralized to inorganic pools. Because a part of additional N could be tied up in organic form, combining solids compost with chemical N fertilizer therefore need to consider the effective use of compost-N.

The concentrations of seven toxic metals (cadmium (Cd), nickel (Ni), chromium (Cr), arsenic (As), lead (Pb), copper (Cu), and zinc (Zn)) were determined in sediments and the soft tissues of a bivalve species (Meretrix lyrata) collected from the Tien Estuary in Tien Giang Province, South Vietnam. The total metal concentrations in sediments (mg/kg dry weight) increased as Cd (0.06) Cu (5.0) Pb (13.9) As (16.3) Ni (24) Cr (50) Zn (62). Speciation analysis revealed that these metals existed mainly in the residual fraction (43-94%), followed by the Fe-Mn oxide-bound (5-35%) and organic/sulfide-bound (0.6-9.2%) fractions. The metal concentrations in M. lyrata (mg/kg dry weight) were in the ranges of 1.3-1.9 (Cd), 1.5-2.8 (Ni), 1.8-3.4 (Cr), 11-16 (As), 0.3-0.6 (Pb), 6.9-8.7 (Cu), and 95-128 (Zn), which are safe for human consumption. The order of the mean biota-sediment accumulation factor (BSAF) of the metals in the non-residual fractions of the sediment for M. lyrata was Cd Cu As Zn Cr Ni Pb. The Risk Assessment Codes (RACs) suggest that the highest mobility of Cd (with RAC = 37%) poses greater environmental risk to aquatic biota. Correlation analysis results show that M. lyrata can be used as a biomonitor of Cd and Cu pollution in the exchangeable, acid-soluble, and non-residual sediment fractions.

In this paper, an advanced fast-charging strategy for lithium polymer (Li-Po) battery is proposed, in which a two-stage charging current profile is employed. First, the constant charging current is used and when the battery voltage reaches a specified value, the charging current is reduced according to the root square of time. With this strategy, the charging time is shortened and the discharging energy is increased. The experimental results show that it is capable of charging the battery up to 84% capacity in 28 minutes compared with the constant current and constant voltage charging and pulse current charging methods.

International audience; In EMC behavior of power electronic converters, it is important to predict near-field coupling between the complex components (e.g. in EMC filter). By using the components of near-field multipolar expansion of electromagnetic sources, the close magnetic coupling between two radiating elements is determined from their equivalent model. It is shown that the increase in degree up to the fourth degree together with the complete identification of all components of multipolar expansion provide a more precise representation of the radiating elements and thus a better accuracy of the near-field coupling prediction.

National audience

National audience

National audience

The work presented in this thesis is divided into two parts. The first part is devoted to the development of a computational electromagnetic code based on the TLM method (Transmission Line Matrix) to simulate structures with multi-scale aspects, requiring multigrids-subgrids locally refined. This leads to solve a simultaneous spatial and time domain coupling problem. As it was proved to be very effective for spatial domain coupling, the technique using transformers introduced by Wlodarczyk is implemented. Actual work is focussed on the time domain coupling to allow using the maximum time step in each sub grid. Interpolation techniques such as Taylor second order and cubic Spline and also a prediction technique inspired from the Prony-Pisarenko method for power spectral density estimation were implemented and evaluated. The second part is devoted to the design of rectennas. Such non-linear and multi-scale structures, integrating Schottky diodes, are key elements of wireless power transmission or energy harvesting systems. It is demonstrated that modelling rectennas with a global circuit-electromagnetic simulation tool in time domain as with TLM provides a substantial advantage compared to commercial simulation softwares that requires various experimental adjustments, rendering complex the design process. It becomes then possible to accurately predict the conversion efficiency of an entire rectenna. The design and complete experimental characterization of two compact rectennas operating at 2.45GHz are finally presented.; Les travaux présentés dans cette thèse sont divisés en deux parties. La première partie est consacrée au développement d'un code de calcul électromagnétique basé sur la méthode TLM (Transmission Line Matrix) pour la modélisation des géométries très hétérogènes, nécessitant la prise en compte de maillages non-conformes localement raffinés. Cet aspect multi-échelle consiste à résoudre un problème de couplage spatio-temporel. Le couplage spatial est mis en œuvre en utilisant la technique des transformateurs introduite par Wlodarczyk. Notre effort s'est porté plus particulièrement sur le couplage temporel afin de pouvoir utiliser le pas temporel maximum dans chaque sous-maillage. Des techniques d'interpolation temporelle de type Taylor de second ordre et cubique Spline ainsi qu'une méthode de prédiction temporelle inspirée de la méthode de Prony-Pisarenko pour l'analyse spectrale ont été mises en œuvre et évaluées. La deuxième partie est consacrée à la conception de rectennas. Ces structures non linéaires, à la géométrie complexe et hétérogène, intégrant des diodes Schottky, sont les éléments clés des systèmes de transmission ou de récupération d'énergie sans fil. Leur simulation globale (circuit-électromagnétique) dans le domaine temporel par la TLM constitue un avantage par rapport aux logiciels commerciaux qui nécessitent des ajustements de certains paramètres SPICE par des réalisations et caractérisations expérimentales à priori, compliquant ainsi le processus de conception. Cela a permis de prédire avec précision le rendement de conversion d'une rectenna globale et de développer puis caractériser expérimentalement deux rectennas compactes fonctionnant à 2.45GHz.

Leachate from municipal landfills of the city is often contaminated heavily, especially for parameters such as organic components, heavy metals, microorganisms. However, leachate also contains amounts of valuable nutrients (e.g. N, P, K) which can be used for agriculture as fertilizers. Precipitated of N and P in the form of struvite (MgNH4PO4.6H2O) might be applied as a technique for removal a huge amount of N as well as P in wastewater. This study investigated the recovery ability of N, P in leachate from Nam Son municipal landfill of Hanoi city. Different pH values, anaerobic time and stoichiometric Mg 2+ : NH4 + : PO4 3- was tested to determine the optimal conditions for precipitating struvite. The effect of pH on the forming of struvite was between pH 9 to 11. The results showed that nutrients in landfill leachate could be recovered with the optimum pH around 9.5 and the optimum Mg 2+ : NH4 + : PO4 3- molar ratio as 1.15: 1: 1. With the anaerobic interval of 21 days, COD value in landfill leachate was decreased to 60%, the retrieval reached 80.6% for nitrogen and 82.7% for phosphorus. According to estimates, with the application of struvite precipitation technique, the average annual retrieval amount of NH4 + and PO4 3- can reach 263 tons and 25 tons, respectively.

Not available