The Saigon River, Southern Vietnam, crosses one of the most dynamic developing Megacity in Southeast Asia: Ho Chi Minh City (HCMC). The increased economic, industrial, and domestic developments may affect the environmental quality of water and halieutic resources. In this study, we evaluated the seasonal (dry and wet seasons) biogeochemical state of the Saigon River during two snapshot campaigns conducted along the river basin upstream from HCMC; the Saigon River was characterized by slightly acidic (pH 5.7-7.7) and oxygen-depleted water (dissolved oxygen (DO), 0.36-5.18 mg l). Nutrients (N-NH = 0.01-2.41, N-NO = 0.14-2.72, and P-PO = ~0-0.42 mg l), DOC (2.2-8.0 mg l), POC, and trace metal(oid) (As, Cd, Cr, Cu, Zn, and Hg) concentrations were low showing a good quality of the upstream river. In the urban center area, DO dropped to 0.03 mg l accompanied with a rise of nutrient concentrations (e.g., N-NH, up to 17.7 mg l) likely originating from wastewater discharges. Trace metal concentrations also rose sharply (e.g., Cr and Hg rose up to 10-fold higher) in both water and sediments but remained under the World Health Organization (WHO) and Vietnamese concentration guidelines. In the downstream estuarine area, the intrusion of marine waters diluted water flowing from HCMC, leading water quality to return close to the state observed upstream from HCMC. In general, levels of nutrient and metal contaminations along the Saigon River during both seasons appear moderate regarding to Vietnamese and WHO guidelines although the urban area is highlighted as the major contributor for metal(oid) emissions. Finally, we showed that apart from wastewater and industrial discharges that affect the river quality, metal(oid) partitioning between solid and solution is controlled by the change in water geochemistry along the continuum during both seasons, such as DO (e.g., for As and Cr) and pH (e.g., for Pb) which drives their sorption/dissolution dynamics.

To establish a sustainable regional biomass use system, clarifying the present condition in the objective area and proposing a proper scenario to improve the present conditions are important. In this study, one suburban village where rice cultivation and livestock industries are popular in Southern Vietnam was selected as the objective area.Literature review, interviews at the site and field surveys were conducted to analyze material flow in agricultural production and excreta treatment of livestock. As a result, it was clarified that surface water quality at some points in the canals, rivers and wells of the village did not meet the national standard, and contributions of discharges of untreated livestock excreta to total nitrogen loads to lower water bodies were large (43% in total). From another aspect, some rice straw was burned without any effective use at the paddy fields. For this situation, two scenarios were proposed and designed as "Plan model 1" and "Plan model 2". The one is to increase biogas digesters in the village for treatment of untreated livestock excreta, decrease washing water rate poured into biogas digesters and use slurry from the biogas digester (hereafter, slurry) at paddy and non-paddy fields as a fertilizer. Another is to use unused rice straw for producing bio-ethanol. By these scenarios, the possibility was shown that approximately 327,000 Nm 3 /year of biogas and more than 240 kL/year ( ≓ 190 t/y) of bio-ethanol can be produced in objective village, 39% of nitrogen load to water bodies and 95% of application rate of chemical fertilizer to agricultural field could be decreased, and greenhouse gas emission rate could be decreased if bio-ethanol is substituted for fossil fuel.

In this study, we successfully crosslinked chitosan using STPP and produced chitosan beads to adsorb copper ions and subsequently phosphate ions from aqueous solutions. The optimal concentrations of chitosan (2% w/v) and STPP (7.5% w/v) during chitosan beads preparation and the optimal pH of 5.0 during adsorption were determined. Several adsorption models, including pseudo-first-order, pseudo-second-order, Langmuir, and Freundlich models, were used to evaluate the static adsorption experimental data. Moreover, the chitosan beads were applied in a dynamic adsorption column and several models including Bohart-Adam, Thomas, Yoon-Nelson, and Clark models were used to describe the system. This study showed that after adsorbing heavy metal ions, chitosan-STPP beads can be used for further adsorption of toxic anions from wastewater.

Depending on different applications or materials that integrate with the substrate as well as the transduction method used in the biosensors, different materials of the substrate are considered. This research focuses on selecting the appropriate substrate in designing biosensors, detecting microorganisms in the environment. In this study, the glass slide (glass), Polyethylen plastic (PE plastic), and the cellulose paper (cellulose acetate (CA) & cellulose nitrate (CN)) are investigated substrates for coating AgNPs/ZIF-8 – material used as an optical signal amplification in further steps, using structural analysis techniques – Scanning Electron Microscopy (SEM) for morphology characterization and the Energy Dispersive Spectrometer (EDS) for optical characterization. A morphology characterization with SEM showed that cellulose paper is a better substrate in comparing with the other substrates (glass, PE), because the sensity of distribution on CN was the highest (85-90%) when it coated with AgNPs/ZIF-8. According to EDS analysis, the ratios of Ag in mixture on CN substrate (15.38±0.39% mass) is slightly higher than CA substrate (13.58±0.39% mass); and about 53 times higher than glass substrate (0.37±0.13% mass) and PE plastic substrate (0.29±0.08%). Therefore, cellulose paper (CA) will be suggested to select for further research as a new material with cost (inexpensive) and effectiveness in coating AgNPs/ZIF-8.