Vietnam Journal of Science, Technology and Engineering

9-13

Authors: Anh D. Nguyen*, Phuong T. Pham, An T. Dam, Phong D. Tran

Amorphous molybdenum sulfide (MoSx) is an attractive Pt-free catalyst for the hydrogen evolution reaction (HER) in both neutral and acidic pH electrolytes. Among the available approaches for the preparation of MoSx, the electrochemical oxidation and reduction of a tetrathiomolybdate salt ([MoS4]2-) represents the most convenient. Herein we describe new insightsontothe electrochemical oxidation of [MoS4]2- to grow MoSx thin films by employing an advanced technique called electrochemical quartz crystal microbalance (EQCM). These new findings enrich the current understanding of the structure, growth mechanism, redox property and catalytic operation of the MoSx material.One sentence summary: a new mechanism for growth of amorphous molybdenum sulfide thin films via the electrochemical polymerization of [MoS4]2- is discussed.

29-34

Authors: Hung Dang Thien, Dan Nguyen Phuoc*, Thanh Bui Xuan, Joon Yong Soo

A lab-scale flat sheet membrane bioreactor (MBR) system was used for the treatment of piggery wastewater to produce an effluent with the appropriate ratio of nitrite:ammonia (1:1 to 1:1.3) as a pre-treatment for the anammox process. The feed wastewater, which was the effluent of a biogas digester, contained 253±49 (n=60) mg.l-1as COD, 231±18 mg.l-1 as N-ammonia, 223±19 mg.l-1 as total Kjeldalh nitrogen (TKN), alkalinity of 1433±153 mg.l-1as CaCO3, and pH=7.5±0.3. This study aimed to determine the suitable hydraulic retention time (HRT) and alkalinity to yield the appropriate influent for the annamox process. The results showed that the suitable effluent of the partial nitrification with ratio of nitrite:ammonia 1.0:1.1 at HRT of 7h30, equivalent to total nitrogen loading of 0.77 kgNm-3d-1. The nitrite accumulation rate (NAR) was 82% at HRT of 7h30, whereas NAR were 11 and 63% at HRT of 12h30 and 8h45, respectively, due to the high growth of nitrite oxidation bacteria (NOB) at long HRTs. As increasing alkalinity of up to 1600 mg.l-1 and pH of 8.0 at HRT of 8h45, NAR was increased from 63 to 73%, ratio of ammonia:nitrite reduced from 1.0:1.8 to 1.0:1.6 and free ammonia concentration reached to 20.2 mg.l-1 nitrogen. This shows that the increase of alkalinity inhibited strongly NOB.

40-47

Authors: nthavongkham Phanutda, Ngo Anh Dao Ho*

The reaction between natural organic matter (NOM) and chlorine during disinfection of water potentially forms trihalomethanes (THMs), which are classified as dangerous, carcinogenic disinfection by-products. Thus, this study aimed to investigate the removal of NOM by using coagulation and flocculation via jar tests of the raw water collected from the Chinaimo water treatment plant in Laos. Several different coagulants, such as Al2(SO4)3 (alum), polyaluminium chloride (PAC), and iron chloride (FeCl3), and the flocculant polyacrylamide (PAM) were examined to determine the optimal operational conditions (i.e. coagulant dosage, flocculant dosage, and initial pH). The removal efficiency was evaluated by turbidity, NOM measured as total and dissolved organic carbon (TOC and DOC), ultraviolet absorbance at 254 nm (UV-254), and trihalomethane formation potential (THMFP). Results showed that 60 mg/l of alum, 40 mg/l of PAC, and 80 mg/l of FeCl3 were the optimal dosages for coagulation, while a 0.2-0.3 mg/l of PAM was effective for flocculation. Optimal initial pH values of 7.0, 6.0, and 8.0 were found for the alum, PAC, and FeCl3 coagulants, respectively. At the optimal conditions, the removal efficiency of turbidity was over 90% in all cases, which was higher than that of NOM (i.e. DOC of 31-42%, TOC of 19-52%, UV-254 of 17-39%, THMFP of 44-48%).One sentence summary: NOM can be removed from water by coagulation-flocculation with Al2(SO4)3 (alum) at a dosage of 60 mg/l, PAM dosage of 0.2 mg/l, and adjusted pH of 7.0

53-57

Authors: T.M. Quynh*, N.T.T. Thuy, T.X. An, N.T. Thom, N.V. Binh, H.D. Sang, T.B. Diep, N.T. Ha, L.T.M. Luong

The aim of this study was to study the use of a beads-based biofertilizer in crop production. The study focuses on the production of a beads-based biofertilizer containing spores and vegetative cells of Bacillus megaterium(B. megaterium) VACC 118. It also evaluated the quality of the biofertilizer and its effects on the growth and yield of cabbage. The results show that the density of B. megaterium in the beads-based biofertilizer reached 4.34×1010 CFU/g and did not change after 6 months of storage. The degree of swelling of the beads was 1.57 times after 24 hours of immersion in an alkaline solution. The number of released cells of B. megaterium reached 4.2×108 CFU/ml after 1 week of soaking in the alkaline solution. The application of the beads-based biofertilizer with NPK fertilizer increased the rate of folded plant, the fresh weight of head and the yield of cabbages grown in alluvial soil. When the beads-based biofertilizer was used along with a 20% reduction of the recommended NPK dosage, the yield of cabbage still increased by 12.36% compared to the control. This indicates that the beads-based biofertilizer can partially replace for chemical fertilizers

64-69

Authors: Thi-Phuong-Dung Le*, Van-Tai Nguyen, Thi-My-Chi Vo, Nghia-Hiep Bui, Thanh-Son Dao

In this study, we conducted a chronic toxicity assessment of di-2-ethylhexyl phthalate (DEHP) on the life history traits of Daphnia magna across three generations. In the first generation, the neonates (called F0 Daphnia) were raised in a control environment (C, toxin-free medium) or in a medium containing DEHP at three concentrations 5, 50, and 500 μgl-1, abbreviated as P5, P50, and P500, respectively. The offspring from the F0 control (called F1 Daphnia) were raised in toxin-free medium (denoted as C-C). However, the offspring from the P500 exposure were split into two groups: (i) the first group was raised in a toxin-free, control medium (denoted as P-C) and (ii) the second group was raised again in a medium containing 500 μgl-1 DEHP (denoted as P-P). The offspring from the F1 (called F2 Daphnia) were split again and treated in the same manner as F1, resulting in C-C-C, P-P-C, and P-P-P. The exposure time for each generation (F0, F1, F2) was 21 days. The survival and reproduction of D. magnaover the three generations (F0, F1 and F2) were recorded daily during the 21 days of incubation. The body length of the animals in the F0 was measured by the end of incubation. The results showed that the survival rate of D. magna in the control and DEHP treatments was similar, while the DEHP strongly enhanced the reproduction of D. magna in the F0 and F1 generations. However, in the F2 generation, the survival rate for P-P-C and P-P-P was only 45-50% compared to the control. Consequently a much lower accumulative neonate proportion in DEHP treatment was found, around 50% compared to the control. The reduction in survivorship and reproduction of D. magna in the F2 generation and the smaller body length of the P500 treatment is a consequence of energy cost and trade-off under the chronic effects of DHEP. The results revealed that the population development of the micro-crustacean may lead to an extinction upon continuous exposure to high phthalate concentrations in natural water bodies. In situ monitoring on phthalates and zooplankton in aquatic ecosystems is suggested.

76-81

Authors: Phu Cuong Tran*, Thi Van Tran

Recently, climate change and its effects have been significantly influenced by human life. Human activities, mostly from urbanization, are the main contributors to the pollution of soil, water, and air, which has been proven by several observations and studies. However, it is necessary to raise awareness, by including support from society as a whole, in order to maximize the efficiency of environmental campaigns. In this work, the geodatabase model of geographic information system (GIS) combined with the WebGIS system based on ArcGIS server technology was employed to build environmental database for Ho Chi Minh city, which will be used by the HCM-SSED system (Ho Chi Minh city - system for sharing environmental database). This system supports the environmental administration with the management, updating, and sharing of environmental databases, as well as providing environmental information to the community quickly and efficiently.

88-94

Authors: Nguyen Hoang Tan Truong, Thi Cam Huong Le, Duong Xuan Bao Ha, Thi Van Tran*

Due to the strong development of agricultural and industrial activities in this day and age, the widespread use of fossil fuels has caused the concentration of greenhouse gases in the atmosphere to significantly increase. With a high concentration of greenhouse gases comes an increase in the temperature of the Earth, which contributes to the acceleration of climate change. This paper presents a remote sensing technique capable of determining atmospheric CO2concentrations from spectral radiation values obtained by satellite images, thereby simulating the distribution of CO2 concentrations over the entire city of Ho Chi Minh. This study uses two data sources: Greenhouse Gases Observing Satellite (GOSAT) and Moderate Resolution Imaging Spectroradiometer (MODIS) images. Calculation results show that throughout the city the average CO2 concentration in the first 6 months of 2019 has a minimum value of 360 ppm and maximum value of 410 ppm; these values change monthly and depend on the type of surface land cover. The highest concentration of CO2 is found over areas of water, bare land, and urban land. On the contrary, over green areas and forests, the CO2 concentration values are about 360-370 ppm. These results are a suitable reference available to support strategic planners focused on CO2 emission management, and suggest that expanding urban vegetation to increase the absorption capacity of carbon will contribute to the reduction of the greenhouse effect