Vietnam Journal of Science, Technology and Engineering

8-17

Authors: Thi Nhu Ngoc Nguyen*, Thi Thanh Hang Huynh, Thi Hien To

In this study, batch and continuous-flow sorption experiments were conducted to evaluate the removal of methylene blue (MB) from aqueous solutions by Carica papaya wood (CPW) biosorbents. The effects of critical factors such as initial pH, particle size of the biosorbent, biosorbent dosage, initial dye concentration, contact time, and salt ionic strength were studied in batch experiments. The equilibrium data fit well to the Langmuir isotherm model with the highest monolayer adsorption capacity of 63.29 mg/gat an initial dye concentration of 50 mg/l, pH of 10,and contact time of 60 min. Batch desorption and regeneration studies using 0.1 M HCl as the desorbing agent indicated that the removal efficiency of MB lasted up to 5 cycles. Continuous-flow biosorption experiments were investigated to determine the practical applicability of the biosorbent. The dye removal efficiency increased with an increase in absorbent dosage and decreased with an increase in flow rate. The Thomas model was found to be in good agreement with all the experimental data collected from continuous flow sorption. It was concluded that this study presented CPW as a promising biosorbent material for the removal MB from aqueous solutions.

23-29

Authors: Van-Tai Nguyen, Manh-Ha Bui, Emilie Strady, Thuy-Chung Kieu-Le, Ba-Trung Bui, Thanh-Son Dao

Plastics, plastic additives, and their emission have attracted significant attention and concern both socially and scientifically. Di-2-ethylhexyl phthalate (DEHP) and bisphenol A (BPA) are two of the many plastic additives widely found in aquatic environments, which can have severe impacts on aquatic animals like micro-crustaceans. Therefore, this study assessed the chronic effects of DEHP and BPA, both individually and jointly, at environmental concentrations (e.g. 50 and 500 μg/l) on the survival rate, reproduction, and growth of the tropical micro-crustacean Ceriodaphnia cornuta. We found that each of the two plastic additives, and a mixture of the two, had some influence on the survivorship of C. cornuta. While DEHP marginally enhanced the reproduction of the animals, BPA strongly inhibited it. Additionally, the mixture of DEHP and BPA caused a synergistic effect on reproduction but an antagonistic effect on the growth of C. cornuta. Both DEHP and BPA induced a significantly longer body of C. cornuta when exposed to these plastic additives. Our results showed that the tropical micro-crustacean C. cornuta is more sensitive to DEHP and BPA than the temperate micro-crustacean D. magna in relation to body length development and reproductive characteristics. Our findings enrich the knowledge of DEHP and BPA toxicity to tropical micro-crustaceans. Besides, our results are also of significant value to freshwater monitoring and environmental risk assessments of plastic additives.

36-42

Authors: Thi Hong Diep Nguyen*, Trong Can Nguyen, Thi Ngoc Tran Nguyen, Thien Nhi Doan

An Giang is one of the provinces in the Mekong delta that is greatly affected by flood events, which brings damage and devastation to life and property. This study practices the application of Sentinel-1A images to monitor the distribution of flood depths in the An Giang province in 2019 as well as applies regression correlation and thresholding to scattering value analysis. The research results indicated the exponential regression model on the VV polarization images had correlation coefficients (r) in August, September, and October ranging from 0.8398 to 0.9764 and determination coefficients (R2) ranging from 0.7896 to 0.9533. Results from the map of current flood depth showed that the flood depth ranged from 0-250 cm, which corresponded to four flood levels. The flood area increased from August to October with the largest flooded area being 89,606.82 ha (accounting for 26.15%) mainly on rice lands and in eight urban districts including An Phu, Tinh Bien, Chau Thanh, Chau Phu, Phu Tan, Tri Ton, Chau Doc, and Long Xuyen city. The limit of flood depth determined by using the Sentinel-1A images was below 145 cm. Above this value, the scattering in the image is not significantly different from the actual submerged depth.

49-59

Authors: Kim Tran Thi, Huy Nguyen Dam Quoc, Phung Nguyen Ky, Bay Nguyen Thi*

Numerical models that calculate bed change are becoming increasingly popular because of their long-term forecast projections and their ability to identify causes of bed change. However, the reliability of the simulation results depends on the length of the data series and the algorithms in the model, in which the boundary condition method plays a critical role. The aim of this study is to assess the effectiveness of the HYDIST model to update wet and dry fronts as well as recalculate the wet boundaries of the hydraulic model before its input into the sediment transport model. The moving boundary theories (wet and dry fronts) of Zhao (1994) and Sleigh (1998) were applied. The velocity distribution of the wet boundaries was recalculated after every time step, then the outcomes of the hydraulic model were used as input for the sediment transport model. The results showed good agreement between the simulated and measured data in term of discharge, water level, and sediment concentration. At the same time, the HYDIST model can be successfully used to simulate sediment deposition and riverbank movement.

65-70

Authors: Diep Anh Tuan Dinh*, Thanh Loc Nguyen, Thi Ngoc Phuong Nguyen, Hieu Trung Nguyen

In the recent past, the quality of surface water for domestic use in the Vietnamese Mekong delta (VMD) has been seriously affected by severe water pollution and intense saltwater intrusion.This study aims to assess existing surface water sources in the provinces of Can Tho, Hau Giang, and Soc Trang. By assessing the existing salinity status to point out areas of low salinity frequency hazards, this work identifies suitable areas through water quality assessments. The results indicated that the Hau river and its tributaries from Ke Sach (in Soc Trang) toward inland has a lower risk of salinity. This indicated that water sources in Ke Sach could be a possible raw water source for water supply treatment plants in Soc Trang. Specifically, water sources including the Hau river’s mainstream, Cai Khe canal, Khai Luong canal, and Thom Rom canal in Can Tho city, the Hau river’s mainstream, the Mai Dam river in the Hau Giang province, and the Cai Con river, the Hau river’s mainstream in Ke Sach, and the Cai Vop and Cai Tram canals in the Soc Trang province, could be exploited for water supply. However, a treatment for pollutants such as BOD5, COD, TSS, and total coliform in these water sources musts be taken into consideration.

77-86

Authors: Nguyen Thi Thuy Trang*, Sangam Shrestha, Hiroshi Ishidaira, Pham Thi Thao Nhi

The goal of this study is to examine the responses of hydrology and water resource availability to future climate change in the 3S (Sekong, Sesan, and Srepok) river basin located in the tropical countries of Laos, Vietnam, and Cambodia. The calibrated the Soil and Water Assessment Tool (SWAT) model was used to investigate changes to the hydrological regime and water resources under various climate change scenarios. The climate change scenarios were designed based on an ensemble of 5 GCM simulations (HadGEM2-AO, CanESM2, ISPL-CM5A-LR, CNRM-CM5, and MPI-ESM-MR) for medium emission (RCP4.5) and high emission (RCP8.5) scenarios. The climate of the basin was prognosticated to be warmer and wetter with increased temperature and precipitation in the future. Future climate change causes an increase in stream flow from 29.0 to 45.0%, 2.0 to 8.3%, and 1.2 to 10.6% for the Srepok, Sekong, and Sesan rivers, respectively. Although the discharge is projected to increase in the future, the per capita water availability is projected to decrease to 48.5, 55.1, and 80.2% in the 2090s compared to 2010 for the Srepok, Sekong, and Sesan rivers, respectively, due to population growth. The Sekong and Srepok basins will experience the most serious decline in trend and absolute value of water availability, respectively. The results of this study will be helpful to water resource development, planning, and management under climate change scenarios in the 3S river basin (3SRB).