Creating nano composite TiO2.Fe2O3/laterite material applying to treat arsenic compound in groundwater: Research article

This article presents nano composite TiO2.Fe2O3/laterite materials, which were successfully prepared by hydrometallurgical method. The materials were modified using urea as the nitrogen source. The particles size of the materials is from 20-30 nanometers. The obtained materials can not only absorb arsenic compounds but also enhance the ability of converting As (III) or As (V) into Aso, which is removed from solution. Arsenic removal efficiency of these materials is high. Using sunlight in a hydraulic retention time, about 180 minutes, the arsenic value at the inflow was about 10 mg/L but the outflow was negligible. Covering TiO2.Fe2O3 nano on laterite have brought high economical efficiency, on one hand, it saved material and on the other hand, it can be continuously operated without the centrifugal separation of the nano material.Bài báo này giới thiệu về phương pháp điều chế vật liệu nano TiO2.Fe2O3 biến tính nitơ được phủtrên đá ong bằng phương pháp thủy luyện. Vật liệu nano thu được có kích thước 20-30 nm. Vật liệu thu được không những có khả năng hấp phụ các hợp chất của asen mà còn có khả năng khử As (III) hoặc As (V) thành Asokhi được chiếu sáng. Sử dụng ánh sáng mặt trời chiếu vào hệ thống xử lý trong thời gian 180 phút có thể loại bỏ được gần như hoàn toàn asen ra khỏi nước mặc dù hàm lượng đầu vào là 10 mg/l. Việc phủ vật liệu TiO2.Fe2O3 nano lên đá ong đã mang lại hiệu quả kinh tế cao, một mặt nó tiết kiệm được vật liệu, mặt khác, vật liệu có thể sử dụng một cách liên tục mà không cần phải tách bằng phương pháp ly tâm

An inquiry into the determinants of Vietnamese product export

Export led growth is the model of economic development that Vietnam has been following. While there are a great number of studies on the determinants of aggregate export of Vietnam, there are few that analyze the impacts of different factors on the export of different product groups. This paper aims at filling this gap in research on international trade of Vietnam. The results show that the fast GDP growth of Vietnam, the large population of importing countries, the wide economic gap between Vietnam and the importing countries, the depreciation of domestic currency, the free trade agreements that Vietnam signed and the shared border with the importing countries contribute to the increase of Vietnam’s export of all product groups. In contrast, the GDP of importing countries and population of Vietnam have no clear impacts on the export of any product groups.

A Unified Approach to Convex and Convexified Generalized Differentiation of Nonsmooth Functions and Set-Valued Mappings

In the early 1960's, Moreau and Rockafellar introduced a concept of called \emph{subgradient} for convex functions, initiating the developments of theoretical and applied convex analysis. The needs of going beyond convexity motivated the pioneer works by Clarke considering generalized differentiation theory of Lipschitz continuous functions. Although Clarke generalized differentiation theory is applicable for nonconvex functions, convexity still plays a crucial role in Clarke subdifferential calculus. In the mid 1970's, Mordukhovich developed another generalized differentiation theory for nonconvex functions and set-valued mappings in which the "umbilical cord with convexity" no longer exists. The primary goal of this paper is to present a unified approach and shed new light on convex and Clarke generalized differentiation theories using the concepts and techniques from Mordukhovich's developments

THE IMPACT OF DATA SECURITY ON THE INTENTION OF VIETNAMESE CONSUMERS TO USE E-WALLETS

E-wallets are used as a form of payment that brings many benefits to users. This article studies the impact of data security on consumer intentions to use e-wallets in the rapidly growing economy of Vietnam. The data consist of 236 observations from a survey of consumers in Vietnam. Covariance-based structural equation modeling (CB-SEM) was employed to test the proposed hypotheses. Research results show that security trust has the greatest impact on the intention to use e-wallets, followed by perceived privacy risk, social influence, and information sensitivity. The study also reveals the role of privacy policies and security concerns in consumer intentions to use e-wallets. Based on the research results, the study provides recommendations for consumers, e-wallet providers, and governmental agencies to increase awareness of and responsibility for information security among the consumers who use e-wallets

Untersuchungen zur Behandlung saurer Grubenwässer in Pflanzenklärsystemen

Der Einsatz von Pflanzenkläranlagen zur Behandlung von Abwässern, insbesondere von sauren Grubenwässern (acid mine drainage, AMD) bzw. die Verwendung von Wasserstoff als Elektronendonatorquelle zur mikrobiellen dissimilatorischen Sulfatreduktion findet in den letzten Jahren zunehmendes Interesse. Der ausgeprägte Vorteil der Pflanzenkläranlagen liegt in der Regel im geringen Aufwand für den Bau und den Betrieb; nachteilig sind die niedrigen flächenspezifischen Umsatzraten. Im Rahmen dieser Arbeit wurde im Labormaßstab bei drei verschiedenen Pflanzenklärsystemen (Wetlandsystemen) wie subsurface-flow Wetland (SSF), schwimmende Pflanzenmatte (HP) und surface-flow Wetland (SF) der Einfluss des Designs, Fließstrecke, Probenahmetiefe, Jahreszeit etc. auf die Reinigung eines Modellwassers für saure Grubenwässer (AMD) charakterisiert. Die Behandlung des künstlichen AMDs in den drei Wetlandsystemen ohne Wasserstoffzudosierung ergab nur eine unwesentliche Veränderung des pH-Wertes. Der Einfluss der Wurzelraumpassage auf die Abnahme der Basenkapazität und Schwermetallentfernung (wie z.B. Eisen, Zink) bzw. Sulfatentfernung war ausgeprägter. Bei der Einschätzung der Leistungsfähigkeit der verschiedenen Wetlandsysteme für die Behandlung saurer Grubenwässer war im Allgemeinen die Behandlungseffektivität des SSF am besten, gefolgt vom SF und HP. Die mikrobiologische dissimilatorische Sulfatreduktion leistete in diesen Systemen keinen entscheidenden Beitrag zu Reinigung des AMD. Aufgrund der sehr begrenzten Reinigungsleistung der Wetlandsysteme wurde die Effizienz des Einsatzes von Wasserstoff als im Vergleich zu anderen Industriechemikalien relativ preiswerte zusätzliche Elektronendonatorquelle für die mikrobielle autotrophe dissimilatorische Sulfatreduktion in der Kombination mit verschiedenen organischen Verbindungen (Methanol bzw. Propionat) in Bioreaktoren getestet. Es zeigte sich, dass auch bei Vorhandensein von Wasserstoff die organischen Kohlenstoffquellen für die mikrobielle Assimilation nutzbar waren. Dies war die Voraussetzung für die strategische Grundkonzeption der Wasserstoffzudosierung in ein Hydroponiksystem zur Stimulation der mikrobiellen autotrophen Sulfatreduktion im Labormaßstab unter verschiedenen Bedingungen zu testen. Nach der Verfahrenskonzeption der aktiven Stimulation von autotrophen sulfatreduzierenden Bakterien wurde unter ausgewählten Bedingungen (verschiedene Zusammensetzungen des AMD, verschiedene Frachten etc.) der Einfluss einer Kombination von HP mit einer Wasserstoffzudosierung auf die Wasserparameter untersucht. Unter diesen Bedingungen spielten die Rhizodepositionsprodukte dieser Pflanzenkläranlage als leicht bioverfügbare organische Verbindungen für das Bakterienbiomassewachstum und für dissimilatorische Sulfatreduktionsprozesse eine essentielle Rolle. Die Wasserstoffzudosierung spielte als Elektronendonator zur Stimulation der autotrophen mikrobiellen dissimilatorischen Sulfatreduktion ebenfalls eine wichtige Rolle. Die Wasserstoffzudosierung in das HP lieferte genügend Reduktionsäquivalente für die mikrobielle Sulfatreduktion. Durch die Sulfidbildung wurden Protonen und Metallionen entfernt. Die durchschnittlichen pH-Werte stiegen an. Unter diesen Bedingungen wurde im Wetlandsystem die Abnahme der Metallfracht im Wesentlichen durch die Bildung von Metallsulfid bzw. Metallhydroxiden (wie z.B. Al(OH)3) bewirkt. Damit ergab sich das Potenzial für die Adsorption weiterer Schwermetalle bzw. Sulfat an die Oberfläche der sedimentierenden Metallminerale. Die Abnahme der Sulfatfracht fand im Wesentlichen durch die mikrobiellen Sulfatreduktionsprozesse statt. Außerdem trugen vermutlich auch die Sorptionsprozesse an der Oberfläche des Sediments und Mitfällungsprozesse zur Sulfatentfernung bei. Unabhängig von der Jahreszeit war die Metallentfernung im Ablauf für Eisen fast vollständig. Es ist zu schließen, dass die Verwendung von Wasserstoff als zusätzliche Elektronendonatorquelle die geforderten Kriterien zur Behandlung von AMD im HPWetlandsystem erfüllte. Wichtige Faktoren waren hierbei die Bereitstellung von genügend Reduktionsäquivalenten für die mikrobielle Sulfatreduktion, die Erzielung hoher Sulfatreduktionsraten sowie fast vollständige Schwermetallentfernung, die Anhebung des pH-Wertes im System sowie niedrige Bereitstellungskosten des Elektronendonators.The use of constructed wetlands (CWs) for wastewater treatment, especially of acid mine waters (acid mine drainage, AMD) and the use of hydrogen as an electron donor for dissimilatory microbial sulphate reduction are of increasing interest in recent years. The distinct advantages of CWs are generally the low costs for construction and operation; the main disadvantage is the low area-specific conversion rate. As part of this study, three different types of laboratory-scale CWs, namely horizontal subsurface-flow CW (HSSF-CW), floating plant mat (HP) and horizontal surface-flow CW (HSF-CW) were characterized concerning the influence of design and season on the purification of an artificial acid mine drainage (AMD). The treatment of AMD in the three CWs without hydrogen gas dosage resulted only in a negligible change in pH. The influence of root zone passage on the reduction in base capacity, heavy metal (such as iron, zinc) and sulphate concentrations was more pronounced. Assessment of the general performance of the various wetland systems for the treatment of AMD showed that the efficiency of the HSSF-CW was best, followed by HSF-CW and HP. Microbial dissimilatory sulphate reduction did not contribute considerably to the treatment of the AMD in these systems. Because of the very limited treatment capacity of the wetland systems, the efficiency of hydrogen addition, as an inexpensive additional electron donor for autotrophic microbial dissimilatory sulphate reduction, was tested in bioreactors in combination with various organic substrates (methanol and propionate). It was found that the organic carbon sources were used for microbial assimilation even in the presence of hydrogen. This was the prerequisite for the strategic design of hydrogen dosage into a hydroponic laboratory-scale test system for the stimulation of microbial autotrophic sulphate reduction under various experimental conditions. For the process design of stimulation of autotrophic sulphate reducing bacteria in the HP system selected conditions (different compositions of AMD, different loads, etc.) were examined. Under these conditions, rhizodeposition products played an essential role as readily bioavailable organic substrates for bacterial biomass growth and for dissimilatory sulphate reduction. Hydrogen played an important role as an electron donor for the stimulation of autotrophic dissimilatory microbial sulphate reduction, providing sufficient reduction equivalents. Through the formation of sulphide, protons and metal ions were removed and average pH values increased. Under these conditions, the decrease of the metal load in the wetland system was mainly caused by the formation of metal sulphides or metal hydroxides (e.g. Al (OH)3). This resulted in the adsorption of other heavy metals and sulphate onto the surface of the precipitated minerals. The decrease of the sulphate load was mainly caused by microbial sulphate reduction. Probably also sorption onto the surface of the sediment and co-precipitation processes contributed to sulphate removal. The metal removal, e.g. of iron, was almost complete throughout the year. It can be concluded that the use of hydrogen as an additional electron donor was required for sufficient treatment of artificial AMD in the laboratory-scale HP system. Important factors here were the provision of sufficient reduction equivalents for microbial sulphate reduction, the achievement of high sulphate reduction, the increase of the pH of the system and the supply of the relatively low cost electron donor hydrogen gas