Yumei Hua

The use of red mud as an immobiliser for metal/metalloid-contaminated soil: A review

This review focuses on the applicability of red mud as an amendment for metal/metalloid-contaminated soil. The varying properties of red muds from different sources are presented as they influence the potentially toxic element (PTE) concentration in amended soil. Experiments conducted worldwide from the laboratory to the field scale are screened and the influencing parameters and processes in soils are highlighted. Overall red mud amendment is likely to contribute to lowering the PTE availability in contaminated soil. This is attributed to the high pH, Fe and Al oxide/oxyhydroxide content of red mud, especially hematite, boehmite, gibbsite and cancrinite phases involved in immobilising metals/metalloids. In most cases red mud amendment resulted in a lowering of metal concentrations in plants. Bacterial activity was intensified in red mud-amended contaminated soil, suggesting the toxicity from PTEs was reduced by red mud, as well as indirect effects due to changes in soil properties. Besides positive effects of red mud amendment, negative effects may also appear (e.g. increased mobility of As, Cu) which require site-specific risk assessments. Red mud remediation of metal/metalloid contaminated sites has the potential benefit of reducing red mud storage and associated problems.

Analysis of utilization technologies for Eichhornia crassipes biomass harvested after restoration of wastewater

Eichhornia crassipes (EC, water hyacinth) has gained attention due to its alarming reproductive capacity, which subsequently leads to serious ecological damage of water in many eutrophic lakes in the world. The traditional mechanical removal methods have disadvantages. They squander this valuable lignocellulosic resource. Meanwhile, there is a bottleneck for the subsequently reasonable and efficient utilization of EC biomass on a large scale after phytoremediation of polluted water using EC. As a result, the exploration of effective EC utilization technologies has become a popular research field. After years of exploration and amelioration, there have been significant breakthroughs in this research area, including the synthesis of excellent EC cellulose-derived materials, innovative bioenergy production, etc. This review organizes the research of the utilization of the EC biomass among several important fields and then analyses the advantages and disadvantages for each pathway. Finally, comprehensive EC utilization technologies are proposed as a reference.

Metal adsorption by quasi cellulose xanthogenates derived from aquatic and terrestrial plant materials

The FTIR spectra, SEM-EDXA and copper adsorption capacities of the raw plant materials, alkali-treated straws and cellulose xanthogenate derivatives of Eichhornia crassipes shoot, rape straw and corn stalk were investigated. FTIR spectra indicated that of the three plant materials, the aquatic biomass of E. crassipes shoot contained more OH and CO groups which accounted for the higher Cu(2+) adsorption capacities of the raw and alkali treated plant material. SEM-EDXA indicated the incorporation of sulphur and magnesium in the cellulose xanthogenate. The Cu(2+) adsorption capacities of the xanthogenates increased with their magnesium and sulphur contents. However more copper was adsorbed than that can be explained by exchange of copper with magnesium. Precipitation may contribute to the enhanced uptake of copper by the cellulose xanthogenate.

Synthesis and Characterization of Mn–C–Codoped Nanoparticles and Photocatalytic Degradation of Methyl Orange Dye under Sunlight Irradiation

Novel visible-light-active Mn–C–TiO2 nanoparticles were synthesized by modified sol-gel method based on the self-assembly technique using polyoxyethylenes orbitan monooleate (Tween 80) as template and carbon precursor and manganese acetate as manganese precursor. The samples were characterized by XRD, FTIR, UV-vis diffuse reflectance, XPS, and laser particle size analysis. The XRD results showed that Mn–C–TiO2 sample exhibited anatase phase and no other crystal phase was identified. High specific surface area, small crystallite size, and small particle size distribution could be obtained by manganese and carbon codoped and Mn–C–TiO2 exhibited greater red shift in absorption edge of samples in visible region than that of C–TiO2 and pure TiO2. The photocatalytic activity of synthesized catalyst was evaluated by photocatalytic oxidation of methyl orange (MO) solution under the sunlight irradiation. The results showed that Mn–C–TiO2 nanoparticles have higher activity than other samples under sunlight, which could be attributed to the high specific surface area, smaller particle size, and lower band gap energy.

Distinguishable root plaque on root surface of Potamogeton crispus grown in two sediments with different nutrient status

The properties of plaques were different on the root surface of Potamogeton crispus planted in sediments from two different shallow lakes. Lake Tangxunhu sediment, with low pH, contained low organic matter, whereas Lake Yuehu sediment, with high pH, had high calcium deposits mixed with high organic matter. The contents of mineral elements in sediment of Lake Tangxunhu was lower than that of Lake Yuehu, except for iron (Fe) content, but the contents of mineral elements extracted by sodium dithionite–sodium citrate–sodium bicarbonate (DCB) from root plaques were higher in Lake Tangxunhu than those in Lake Yuehu, except for Fe. These element distributions on P. crispus root plaques were characterized by scanning electron microscope combined with energy-dispersive X-ray spectrometer and were consistent with the contents of mineral elements in sediment. The root plaque of P. crispus planted in Lake Tangxunhu sediment mainly contained silicon (Si) and Fe, and the content of Si was greater than Fe, which may be contributed to the formation of poly-silicic-ferric in the natural conditions. However, the root plaque of P. crispus planted in the sediment with higher calcium content of Lake Yuehu was rich in Fe, Si, phosphorus (P), and calcium (Ca). Due to oxygen secretion by plant roots, the root plaque has more Fe3(PO4)2 and a certain amount of Ca3(PO4)2. The ratio of magnesium (Mn) to Fe extracted by DCB from root plaque in Lake Tangxunhu sediment was 0.031 and 0.010 in Lake Yuehu sediment. In Lake Tangxunhu sediment, lower content of organic matter results in weak reducibility. Enhanced oxidation ability by oxygen secretion of P. crispus root could oxidize low-valent Fe and Mn into iron–manganese oxide, which leads to formation of iron–manganese plaque on the root surface. However, this case is different in Lake Yuehu sediment, where Fe and Mn can be reduced in high organic sediment and low-valent Mn can precipitate in the sediment in which pH is >8. Thus, low-valent Fe in Lake Yuehu sediment moves to the root surface of P. crispus, where it oxidizes into Fe oxide, i.e., Fe plaque.

Transformation of external sulphate and its effect on phosphorus mobilization in Lake Moshui, Wuhan, China

Average concentrations of sulphate in lakes continue to increase sharply. The response of phosphorus to sulphate input is of great importance due to the relationship between eutrophication and ecological health. A four-week experiment was conducted under simulated conditions using samples from a heavily polluted lake, Lake Moshui, in Wuhan, China, to examine the influence of external sulphate on phosphorus release and the transformation of sulphate. The results showed that the diffusion of sulphate into the sediments promoted the proliferation of sulphate-reducing bacteria (SRB) and the reduction of sulphate. Acetic acid was consumed due to sulphate reduction. The soluble reactive phosphorus (SRP) and soluble Fe measured with diffusive equilibration in thin-films (DET) probes increased significantly after the input of sulphate. The content of SRP was consistent with the variation in both the SRB number and the S(0) content in the sediments. The maximum SRP concentration of 100.43 mg L(-1) was recorded 3 cm below the sediment-water interface on the 29th d, which was more than twice the value of the control. There was a positive correlation between concentrations of Fe and SRP in the overlying water and the pore water of the sediments.

Microbial community of nitrogen cycle-related genes in aquatic plant rhizospheres of Lake Liangzi in winter

This study investigated the community structure of ammonia‐oxidizing bacteria /archaea (AOB and AOA), as well as the effects of four aquatic plants (namely Ceratophyllum demersum, Hydrilla verticillata, Potamogeton crispus, and Nymphaea tetragona) rhizospheres on the abundance of AOB amoA, AOA amoA, anammox 16S rRNA, nirK, and nirS in Lake Liangzi, China. Phylogenetic analysis revealed that most AOB groups were Nitrosospira and Nitrosomonas, in which Nitrosospira was dominant. The AOA amoA were affiliated with two branches of classical sequences which belonging to Thaumarchaeota: water/sediments branch and soil/sediments branch. The abundance of AOA amoA in the rhizospheres of aquatic plants were higher than in the non‐rhizosphere (p < 0.05), indicating that aquatic plants may promote the growth of AOA. However, the anammox 16S rRNA showed the opposite trend relative to AOA amoA (p < 0.05). Redundancy analysis (RDA) showed that the differences in abundance of AOB, AOA, anammox bacteria, and denitrifying bacteria are very likely related to the different contents of ammonia nitrogen (NH4+‐N), pH and dissolved oxygen (DO) and thus to the rhizosphere states of aquatic plants.