Heavy metal-contaminated sediments posed a serious threat to both human beings and environment. A biosurfactant, rhamnolipid, was employed as the washing agent to remove heavy metals in river sediment. Batch experiments were conducted to test the removal capability. The effects of rhamnolipid concentration, washing time, solution pH, and liquid/solid ratio were investigated. The speciation of heavy metals before and after washing in sediment was also analyzed. Heavy metal washing was favored at high concentration, long washing time, and high pH. In addition, the efficiency of washing was closely related to the original speciation of heavy metals in sediment. Rhamnolipid mainly targeted metals in exchangeable, carbonate-bound or Fe-Mn oxide-bound fractions. Overall, rhamnolipid biosurfactant as a washing agent could effectively remove heavy metals from sediment.
The effective concentrations of copper on the inhibition of the growth of Scenedesmus obliquus, Chlorella pyrenoidosa and Closterium lunula at 96 h (96 h EC50) were determined to be 50, 68 and 200 microg/l, respectively. The low initial bioaccumulation of Cu by C. lunula was found to be responsible for its tolerance to Cu. The amount of Cu accumulated by all three microalgae reached the maximum value and decreased quickly after the peak followed by a slow decrease over the next 6 d. Bioaccumulation of Cu by C. lunula was directly proportional to the initial Cu concentration. After reaching the first peak after 1 d, the bioconcentration factor of Cu by microalgae declined to its minimum value during the exponential growth phase but increased in the stationary growth phase again. This indicates that desorption of Cu from microalgae was higher during the exponential growth phase but lower in the stationary growth phase. Smaller microalgae with low 96 h EC50 values are more efficient in removing Cu from wastewater. 相似文献
Used tires were pyrolyzed in a pilot-scale quasi-inert rotary kiln. Influences of variables, such as time, temperature, and agent flow, on the activation of obtained char were subsequently investigated in a laboratory-scale fixed bed. Mesoporous pores are found to be dominant in the pore structures of raw char. Brunauer-Emmett-Teller (BET) surfaces of activated chars increased linearly with carbon burnoff. The carbon burnoff of tire char achieved by carbon dioxide (CO2) under otherwise identical conditions was on average 75% of that achieved by steam, but their BET surfaces are almost the same. The proper activation greatly improved the aqueous adsorption of raw char, especially for small molecular adsorbates, for example, phenol from 6 to 51 mg/g. With increasing burnoff, phenol adsorption exhibited a first-stage linear increase followed by a rapid drop after 30% burnoff. Similarly, iodine adsorption first increased linearly, but it held as the burnoff exceeded 40%, which implied that the reduction of iodine adsorption due to decreasing micropores was partially made up by increasing mesopores. Both raw chars and activated chars showed appreciable adsorption capacity of methylene-blue comparable with that of commercial carbons. Thus, tire-derived activated carbons can be used as an excellent mesoporous adsorbent for larger molecular species. 相似文献
Virus contamination in wastewater is usually accompanied by the existence of various bacteria. Nanoparticles (NPs) have been shown to efficiently remove virus. In this study, bacterial cells, supernatants, and cultures were harvested separately from three strains at the culture ages of 6 and 24 h, corresponding to the log and stationary phases, respectively. The aim is to investigate how their presence affects virus adsorption on the three Fe and Al oxide NPs (α-Fe2O3, γ-Fe2O3-B, and Al2O3) and how these effects change with bacterial growth phase. Bacteriophage phiX174 was used as a virus model. Results showed that bacterial cells, supernatants, and cultures harvested at 6 h generally reduced virus adsorption by an average of 0.75?±?0.84, 7.7?±?9.0, and 10.3?±?8.6 %, respectively, while those harvested at 24 h reduced virus adsorption by an average of 2.1?±?0.93, 21.5?±?6.6, and 24.6?±?6.9 %, respectively. Among the NPs, α-Fe2O3 showed more sensitivity to bacteria than the other two, probably because of its relatively higher value of point of zero charge. It was found that cell-induced and supernatant-induced reductions were combined to achieve added results, in which the supernatants contributed much more than the cells, implying that the bacterial exudates might be more crucial in the reduced virus adsorption than the bacterial cells. These results strongly demonstrated that the bacteria-induced reduction in virus adsorption became more significant with culture age. It is suggested that studies conducted in the absence of bacteria may not accurately evaluate the potential of virus removal efficiency of the NPs in bacteria-containing environments. 相似文献
Panax notoginseng (Burk.) F.H. Chen, a rare traditional Chinese medicinal herb, is a widely used phytomedicine used all over the world. In recent years, the arsenic contamination of the herb and its relative products becomes a serious problem due to elevated soil As concentration. This study aimed to evaluate the effects of different types and dosages of amendments on As stabilization in soil and its uptake by P. notoginseng. Results showed that comparing to control treatment, the As concentrations of P. notoginseng declined by 49–63%, 43–61% and 52–66% in 0.25% zero-valent iron (Fe(0)), 0.5% bauxite residue, and 1% zeolite treatment, respectively; whereas the biomasses were elevated by 62–116%, 45–152% and 114–265%, respectively. The As(III) proportions of P. notoginseng increased by 8%, 9%, and 8%, and the transfer factors of As from root to shoot increased by 37%, 42% and 84% in the optimal treatments of Fe(0), bauxite residue, and zeolite. For soil As, all the three amendments could transform the non-specifically adsorbed As fraction to hydrous oxides Fe/Al fractions (by Fe(0) and red mud) or specifically adsorbed As fraction (by zeolite), therefore reduced the bioavailability of soil As. With a comprehensive consideration of stabilization efficiency, plant growth, environmental influence, and cost, Fe(0) appeared to be the best amendment, and zeolite could also be a good choice. In conclusion, this study was of significance in developing As contamination control in P. notoginseng planting areas, and even other areas for medicinal herb growing. 相似文献