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This paper reviews the current quality of groundwater in Vietnam. In Vietnam, groundwater is obtained primarily from tubewells, which have high concentrations of pollutants such as As, Fe, Mn, and NH 4 + . In the areas where groundwater tests were conducted, arsenic levels ranged from 0.1-3050 μg/L, which substantially exceed the standard of 10 μg/L which has been established by the WHO. Contamination sources are distributed over a large area from the Red River Delta in the north to the Mekong River Delta in the south, putting as many as ten million people at risk of adverse health effects. Levels of arsenic and iron in sediment are strongly correlated, which indicate that the presence of arsenic in groundwater results from the reduction of arsenic bound to iron oxyhydroxides. It is important to raise awareness of these issues among the Vietnamese public by disseminating information about the negative effects of contaminated drinking water, as well as carrying out long-term research projects to identify other sources of contamination and improving water treatment technology and water management capabilities.

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Tannery wastewater is known to contain high concentrations of organic compounds, pathogens, and other toxic inorganic elements such as heavy metals, nitrogen, sulfur, etc. Biological methods such as aerobic and anaerobic processes are unsuitable for tannery wastewater treatment due to its high salinity, and electrochemical oxidation offers a promising method to solve this problem. In this study, raw tannery wastewater treatment using DSA® Ti/RuO 2 , Ti/IrO 2 and Ti/BDD electrodes with continuous flow systems was examined. Effects of current densities and electrolysis times were investigated, to evaluate the process performance and energy consumption. The results showed that a Ti/BDD electrode is able to reach a higher treatment efficiency than Ti/IrO 2 , and Ti/RuO 2 electrodes across all parameters, excluding Total Nitrogen. The main mechanism of tannery wastewater oxidation at a Ti/BDD electrode is based on direct oxidation on the electrode surface combined with the generation of oxidants such as o OH and Cl 2 , while at DSA® Ti/RuO 2 and Ti/IrO 2 electrodes, the oxidation mechanisms are based on the generation of chlorine. After treatment, the effluents can be discharged to the environment after 6-12 h of electrolysis. Electrooxidation thus offers a promising method for removing the nutrients and non-biodegradable organic compounds in tannery wastewater.

This study investigated if biochar, a low-cost carbon-rich material, can be modified with reactive materials for decolorization of dyeing wastewater. Two types of rice husk biochars were produced by using different processes of gasification and pyrolysis in limited air condition. The biochars were first magnetized and then modified with nano-scale zero-valent iron (nZVI) to achieve the final products of magnetic-nZVI biochars. Batch experiments were conducted to investigate the efficiency of the modified biochars for reducing color of the reactive dyes yellow (RY145), red (RR195), and blue (RB19) from dyeing solutions. Results showed that color removal efficiency of the modified biochars was significantly enhanced, achieving the values of 100% for RY145 and RR195 and ≥65% for RB19, while the effectiveness of the original biochar was significantly lower. In addition, with increasing dose of the modified biochars, the color removal efficiency increased accordingly. In contrast, when the dose of nZVI was increased beyond a certain value then its color removal efficiency decreased accordingly. It is reported that the magnetic-nZVI rice husk biochars effectively removed the reactive dyes. The impregnation of nZVI particles on the biochar surface spatially separates the nZVI particles, prevents its aggregation and therefore enhances the decolorization efficiency.