Tạp chí Khoa học Trái Đất và Môi trường Đại học Quốc gia Thành phố Hồ Chí Minh

The purpose of this study is to evaluate and analyze the possibility of nitrogen recirculation when applying a closed eco-system for intensive catfish ponds in the Mekong Delta in accordance with the existing available natural conditions in the local area. A closed ecosystem is proposed for optimizing N emissions from intensive pangasius farming on the basis of closed flows of materials, waste, and energy. The entire system is applied to Tran Trung Nhan household in An Binh B ward, Hong Ngu city, Dong Thap province consisting of 6 sub-systems (catfish ponds, composting, rice cultivation, livestock, liquid fertilizer, aquatic ditches) which are designed to be interacted, and Nitrogen in the catfish ponds are used as the main nutrient sources throughout the integrated system. The material flow analysis (MFA) method, which is based on the principle of material flow balance, is applied in the integrated system to analyze the potential of Nitrogen circulation in the whole system. The results show that the input N source is mainly from feed (43.35 kgN), and there are 3 main sources of N emissions from the system: sewage sludge (20.55 KgN), wastewater (3.4 KgN), and hydrolyzed nitrogen from dead fish (3 KgN). The source of N generated from sewage sludge is mixed with other wastes (biomass from rice straw and water hyacinth) in the system to produce compost (26 KgN), and wastewater generated from catfish ponds after aquatic treatment is supplied to agricultural activities (4.9 KgN).

The port system of Ho Chi Minh City including 34 ports, serves as the gateway to the South (including the South East and the Mekong Delta) in export and import activities. In which contribute a huge amount of pollutants to the atmosphere in Ho Chi Minh City. The objective of this study is to: (i) Calculating air emissions from ports system in Ho Chi Minh city using the SPDGIZ model which emits a large amount of air pollutants such as sulfur oxide (SOX), nitrogen oxide (NOX), fine dust (PM2.5, PM10), volatile organic compounds (VOC), carbon monoxide (CO) from large ships (Ocean going vessels - OGVs), towing ships (Harbor Crafts - HCs), cargo handling equipment (Cargo handling equipment - CHE) and other vehicles (Heavy trucks – HVs); (ii) Using dispersion model TAPM-AERMOD to assess the impact of port operations to air quality in surouding port area; (iii) Proposing abatement measures based on the results of simulation to reduce emissions/ air pollution levels. The results of emission inventory show that the total port emissions are largely NOX and SOX mainly from large ships (OGVs) and cargo handling equipment (CHE) due to the use of heavy oil and diesel which have high sulfur content. The results show that the time at which a mooring boat is the most time consuming (accounting for over 90% of total emissions from OGVs).

Permanent Scatterer InSAR (PSInSAR) technique is used commonly to evaluate land subsidence for some cities in the world and the pilot project in Ho Chi Minh City has shown the capability of this technique for mapping land subsidence in the period from 2006 to 2010. The result shows that PSInSAR can be applied to study the land subsidence phenomenon more efficiently than any traditional methods. However, SAR data often are commercial images such as ERS, ALOS, COSMO SkyMed… that a large number of SAR scenes must be collected to ensure the best results. This paper introduces results of the average subsidence velocities in Ho Chi Minh City that PSInSAR technique is applied to process SAR data from Sentinel-1 and COSMO SkyMed satellite. Evaluating the preliminary result showed that the capacity of using free Sentinel-1 images to replace commercial images for monitoring land subsidence.

Numerical model is a useful tool in studying the flow and sediment transport, change in river bed and is built on solving governing differential equations. Numerical model has many different levels and three-dimensional model is the highest level, allowing detailed simulation of flow and sediment transport process in 3D space. The paper presents a method calculating three - dimensional flow and sediment transport in the open channel. Water level and flow velocity are solved from three-dimensional equations with hydrostatic hypothesis. Concentration of suspended sediment, bottom sediment and bottom evolution is solved from transport equations. The governing differential equations in the "sigma" transform coordinate system are solved by finite volume method on unstructured grid of quadrilateral elements. Boundary condition of water level or flow will be imposed on open boundary. For suspended sediment concentrations in the injected phase, suspended sediment concentrations are applied and the outflow phase applies free drainage conditions. This method of calculation was tested with the problem of curved channel sediment transport which was studied experimentally by Odgaard and Bergs. Calculation results are quite consistent with the measured data. In order to test the practical applicability, this method is also tested with the problem of sediment transport in Cu lao Pho islet on Dong Nai river. To solve the matter of hydraulic boundary condition of this problem, the model of Cu lao Pho islet is integrated into the Sai Gon - Dong Nai river system model. Results of the calculation of the river bed evolution of the Cu lao Pho islet on the Dong Nai river also show that this calculation method gives results consistent with the rule and can be used in practical research.  

A backarc basin represented by a mafic/ultramafic magmatic ophiolitic sequence has been discovered first time within Vietnam territory. Backarc basin/forearc basin and other features of a convergent tectonic system are being considered as a location of the two geological blocks that almagamated together and preferred as a geological suture. The middle Triassic suture resulted from the welding of the Indochina and Sibumasu blocks has been studied in details and traced from northen Thailand as Nan-Attaradit suture southward to Cambodia as Sra Kaeo suture. After a gap comparable to the territory of Vietnam it reappears in the northern Malaysia and being recognized as Bentong-Raub suture. With this new discovery of a back arc basin of this suture system located within Vietnam, the complete geographical location of the suture between the Indochina and Sibumasu block has been clearly verified and would be valuable information for geological studies in the area.

The purpose of this study is centered on the removal of atrazine, one of the popular organochlorines in Vietnam, from an aqueous solution, using an electro Fenton process with iron and carbon plated steel electrodes at a batch electro reactor. This study had applied the Taguchi method, one of the most uncomplicated cases of design of experiments involving the minimum number of experiments to be performed within the permissible limit of factors and levels through the Signal to Noise ratio. This study design was conducted with five independent factors: initial pH, current density, Fe2+ concentration, sodium sulfate and reaction time, at a fixed atrazine concentration of 10 mg/L to find the best condition to eliminate atrazine from the solution. The Signal to Noise ratio results illustrates that the initial pH is the most important factor, followed by the reaction time and Fe2+ concentration, while sodium sulfate and current density seem neglectable to the removal of atrazine using electro Fenton process. The optimal Taguchi condition shows that the electro Fenton process reached the best efficiency, approximately 76% atrazine eliminated after 180 min of reaction time at initial pH 3.5, sodium sulfate of 990 mg/L, Fe2+ concentration of 2 mM and current density of 2.22 mA/cm2. Three confirm experiments at optimal test conditions also indicated good agreement with predicted results with small error variation (1.21 - 3.54%). Thus, the relationship between the removal efficiency and operating parameters could be understood. These obtained results highlight the potential of using the electro Fenton process to eradicate or reduce pesticide contaminants. Electron beam also could be one of the pre-treatment techniques to eliminate persistent organic pollutants before biological treatment systems.

Anaerobic/Anoxic/Oxic – Membrane BioReactor (A2O-MBR) system was used to enhance simultaneous removal of nitrogen and phosphorus from brewery wastewater. The A2O unit containing microorganisms with short solids retention time (SRT) was employed mainly for removal of organic matter and phosphorus together with denitrification. The MBR containing microorganisms with long SRT was employed mainly for nitrification of NH4+-N and recirculation of NO3--N. The model of A2O-MBR system made from polyacrylic with the capacity of 49.5 liters was operated with hydraulic retention times decreased from 24, 18 to 12 hours corresponding to organic loading rates increased from 0.50, 0.75 to 1.00 kg COD/m3.day. The results showed that the model not only treated organic matter well but also nearly completely removed both nitrogen and phosphorus. For all three loading rates, chemical oxygen demand (COD) concentration decreased significantly in the anaerobic and anoxic compartments of the A2O unit, indicating that most of organic matter was utilized in the anaerobic and anoxic compartments for phosphorus release and denitrification, respectively. Nitrification in the MBR was almost perfectly completed, with average NH4 +-N removal efficiencies of over 98%. Denitrification in the anoxic compartment happened as much as possible. Demands for the development of PAOs, which were responsible for enhanced biological phosphorus removal (EBPR) processes, could be provided. For loading rate of 0.75 kg COD/m3.day, treatment efficiencies of COD, NH4+-N, total nitrogen (TN) and total phosphorus (TP) of the model were the highest as 95.4, 99.2, 86.7 and 84.6%, respectively. Output values of these parameters were within the limits of Vietnam National Technical Regulation on Industrial Wastewater (QCVN 40:2011/BTNMT), column A. The model of A2O-MBR system was capable of achieving effluents with very low nitrogen and phosphorus concentrations from brewery wastewater.  

Groundwater in Phu My town is exploited essentially in Pleistocene aquifer and, used for many purposes like irrigation, domestic, production and animal husbandry. In this study, Groundwater Quality Index (EWQI) is calculated with Entropy weight method to determine the suitability of groundwater quality in study area. This method demonstrates the objectivity of each parameter calculated based on the degree of variability of each value and depends on the sample data source. The groundwater samples were collected from 17 wells in dry and wet seasons in 2017 with ten water quality parameters (pH, TDS, TH, Cl-, F-, NH4+-N, NO3--N, SO42-, Pb và Fe2+) were selected for analysising. The analysis results indicate groundwater quality is divided into 4 categories in this study area. In particular, over 70% of wells are "very good" water quality in both dry and wet seasons. Only 6% of wells are " water unsuitable for drinking purpose" of the total number of mornitoring wells in the study area.