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Concentrations of seven polybrominated diphenyl ethers (PBDEs) congeners were determined in surface sediments collected from several rivers and lakes in Hanoi, the capital city of Vietnam, to understand the status of background contamination, accumulation pattern, sources, and toxic implications for benthic organisms. Total PBDE concentrations in all sediment samples ranged from 0.03 to 17.5 ng/g dry weight (mean 1.33 ng/g dry wt). The most predominant congeners were BDE-47 and BDE-99, which comprised 30 and 25 % of total PBDE concentrations, respectively. Results from statistical analysis indicated that the potential sources of PBDEs of sediments in Hanoi may come from penta-BDE and octa-BDE mixtures. Risk quotients of PBDEs in sediments were also calculated for a benthic species, ranged from 2.12 × 10 - 1.60 × 10, and were markedly lower than threshold value for occurrence of any ecotoxicological risk. This study provides some of the most comprehensive data on the occurrence of PBDEs in sediments from lake and river systems in Vietnam.

Ammonium NH 4 + is a pollutant that can be harmful to the water environment. The purpose of this study is to access NH 4 + removal capacity from water by coffee husk-derived biochar. The properties of biochar prepared at different temperatures (300, 450, and 600°C) were determined including TOC, and pH , pH pzc , functional groups of H+/OH−, cation-exchange capacity (CEC), and the characteristics of groups of organic matter (FT-IR spectrum) were identified and evaluated. The trend of NH 4 + adsorption equilibrium and kinetics of biochar have been studied. The experimental design of adsorption equilibrium was carried out by exposing biochar to a NH 4 + solution at different concentrations, ranging from 0 to 50 mg NH 4 + / L for 12 hours. Kinetic surveys were carried out when biochar was exposed to a solution containing 8.3 mg NH 4 + / L for a varying length of time. The results showed that Langmuir and Freundlich models and the pseudo-second-order kinetic model are suitable to explain the NH 4 + adsorption equilibrium and kinetics on the biochar forms derived from coffee husk. Biochar derived from coffee husk prepared at lower pyrolysis temperature has a higher adsorption capacity. The results suggest that the biochar could be used as an adsorbent ammonium from water.

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<p>The acidification of agricultural soils should be avoided, and low pH soils should be corrected for better productivity. Soil improvement by applying biochar from agricultural byproducts combined with bentonite, a rich source in Vietnam, is a trend in green agriculture in the country. The current study is important in assessing the potential influences of biochar and bentonite on the pH and pH buffering capacity (pHBC) of low pH soil collected in Cu Chi, Ho Chi Minh City, Vietnam. Experimental methods, including biochar preparation (pyrolysis at 300°C, retention time: 2 h), soil incubation (time: 30 days, temperature: 27°C), and pH and pHBC determination, were performed. Research results have shown that biochar and bentonite have contributed to improving the pH and pHBC of gray soil samples. Using 1% bentonite and 1% biochar raised the pH to 6.21 and improved the pHBC of Cu Chi gray soil to 24.1 mmolH⁺/OH^- kg^-1. This dose is currently suitable for agricultural production in Vietnam. The study confirmed the applicability of biochar derived from cow manure prepared at a low pyrolysis temperature in combination with bentonite to improve soil parameters such as pH and pHBC in Cu Chi gray soil.</p>