Development of a BR-UASB-DHS system for natural rubber processing wastewater treatment.

Natural rubber processing wastewater contains high concentrations of organic compounds, nitrogen, and other contaminants. In this study, a treatment system composed of a baffled reactor (BR), an upflow anaerobic sludge blanket (UASB) reactor, and a downflow hanging sponge (DHS) reactor was used to treat natural rubber processing wastewater in Vietnam. The BR showed good total suspended solids (TSS) removal of 47.6%, as well as acidification of wastewater. The UASB reactor achieved a high chemical oxygen demand (COD) removal efficiency of 92.7 ± 2.3% and energy recovery in the form of methane with an organic loading rate of 12.2 ± 6.6 kg-COD m-3 day-1. The DHS reactor showed high performance in residual organic matter removal from UASB effluent. In total, the system achieved high-level total COD removal of 98.6% ± 1.2% and TSS removal of 98.0% ± 1.4%. Massive parallel 16S rRNA gene sequencing of the retained sludge in the UASB reactor showed the predominant microbial phyla to be Bacteroidetes, Firmicutes, Proteobacteria, WWE1, and Euryarchaeota. Uncultured bacteria belonging to the phylum Bacteroidetes and Phylum WWE1 were predominant in the UASB reactor. This microbial assemblage utilizes the organic compounds contained in natural rubber processing wastewater. In addition, the methane-producing archaea Methanosaeta sp. and Methanolinea sp. were detected.

Thiosulfate leaching of gold from waste mobile phones.

The present communication deals with the leaching of gold from the printed circuit boards (PCBs) of waste mobile phones using an effective and less hazardous system, i.e., a copper-ammonia-thiosulfate solution, as an alternative to the conventional and toxic cyanide leaching of gold. The influence of thiosulfate, ammonia and copper sulfate concentrations on the leaching of gold from PCBs of waste mobile phones was investigated. Gold extraction was found to be enhanced with solutions containing 15-20 mM cupric, 0.1-0.14 M thiosulfate, and 0.2-0.3 M ammonia. Similar trends were obtained for the leaching of gold from two different types of scraps and PCBs of waste mobile phones. From the scrap samples, 98% of the gold was leached out using a solution containing 20 mM copper, 0.12 M thiosulfate and 0.2 M ammonia. Similarly, the leaching of gold from the PCBs samples was also found to be good, but it was lower than that of scrap samples in similar experimental conditions. In this case, only 90% of the gold was leached, even with a contact time of 10h. The obtained data will be useful for the development of processes for the recycling of gold from waste mobile phones.

Assessment of heavy metal pollution in river water of Hanoi, Vietnam using multivariate analyses.

Concentrations of heavy metals in water of the Nhue River (a suburban/rural river) and one of its tributaries, the To Lich River (an urban river), in Hanoi, Vietnam had been monitored, and spatial and seasonal variations in their composition were evaluated by means of principal component analysis and cluster analysis. Heavy metal concentrations in water of the two rivers were generally lower than the surface water quality standard in Vietnam, except for manganese in several sites, although they were higher than the median values in freshwater of the world by 0.42-43 times in Nhue and 0.13-32 times in To Lich. The two multivariate analyses represented that the composition of heavy metals in river water of To Lich was distinctly different from that of Nhue. It was also suggested that metal concentrations and their composition in Nhue river water would be affected by inflowing water of To Lich and wastewater discharged from the up- and middle-stream basin, and that they gradually recovered along the direction of water flow in the downstream area in rainy season.