| Abstract: | With the recent development of nuclear power and increasing demand for uranium resources, groundwater contamination has become a global concern from uranium production. Uranium is highly radioactive and toxic, posing a long-term potential threat to human health and the environment. Compared with other types of uranium contamination, groundwater uranium contamination has a wider spatial extent and generates higher environmental exposure and health risks. The treatment and remediation of groundwater pollution in uranium mines has become an urgent environmental problem. A comprehensive review is conducted of the basic theories, practical examples, and future development prospects of physicochemical, bioremediation and permeable reactive barrier remediation technologies based on a summary of the recent progress and achievements of groundwater pollution treatment and remediation technologies in uranium mining areas at home and abroad. Review results indicate that the physicochemical remediation technology mainly includes chemical remediation technology, electrochemical remediation technology and natural attenuation of aquifers. The application of this technology is very limited, and its treatment products are expensive. In addition to being influenced by the regional groundwater flow field, improper treatment may easily damage the site structure and its physicochemical properties, causing secondary pollution to groundwater. Microbial remediation of uranium-contaminated groundwater can be achieved through different mechanisms of action such as microbial reduction, microbial mineralization, microbial adsorption and microbial enrichment. This remediation technology has its unique advantages in the real-time, field treatment of large contaminated water bodies and is an effective way to address uranium contamination management and sustainable development. Phytoremediation technology is economically viable, technically effective, free of secondary pollution, and less environmentally disturbing for large areas of low concentration uranium contamination, and has been more widely used. Although the permeable reactive barrier technology has been widely used in the remediation of groundwater pollution in uranium mining areas and has achieved certain remediation results. There are still some problems that affect the long-term effectiveness of permeable reactive barrier operation, such as the selection of media materials, clogging of reaction media materials and complex groundwater quality. The current in situ treatment and remediation technologies for groundwater pollution in uranium mining areas are mainly studied in the laboratory, and there is a lack of engineering practice for the treatment and remediation of groundwater pollution in actual uranium mining areas. How to develop green, efficient, and low-carbon treatment and remediation technologies in combination with the hydrogeological conditions and pollution characteristics of actual uranium mining areas is an important development direction for the treatment and remediation of groundwater pollution in uranium mining areas in the future.
The 101 species of phytoplankton were detected belonging to 76 genera of 8 phyla, 20 species belonging to 17 genera of diatoms, 26 species belonging to 17 genera of cyanophyta, 45 species belonging to 32 genera of chlorophyta, and 10 species belonging to 10 genera of dinoflagellates, chrysophyta, Cryptophyta, xanthophyta and Euphyta. There were 9 dominant phytoplankton species in Danjiangkou Reservoir, which were Melosira granulosus, Melosira granulata var.angustissima, Microcystis aeruginosa, Pseudanabaena sp, Glenodinium, Oscillatoria sp, Chlamydomonas sp, Cyclotella sp, Chlamydomonas globosa Snow . The average biomass of phytoplankton in Danjiangkou Reservoir in winter, spring, summer and autumn were (0.003±0.001) mg/L, (0.006±0.002) mg/L, (0.129±0.018) mg/L and (0.481±0.029) mg/L, respectively. In Danjiangkou Reservoir, the biomass of phytoplankton at Langhekou site S1 and Nancaojiayuan site S2 was relatively high, while that at Xiaogsanxia site S6 was relatively low. The Shannon-Wiener diversity index (
H ''), Pielou evenness index (
J
'') and Margalef richness index (
Dm ) of phytoplankton in Danjiangkou Reservoir ranged from 1.76 to 2.53, 0.48 to 0.75 and 1.89 to 3.44. The dominant species of phytoplankton in Danjiangkou Reservoir varied significantly with the season. Diatoms dominated in winter, followed by green algae-dinoalgae-diatoms in spring, and gradually developed into blue algae-green algae-diatoms in summer and autumn, indicating that the eutrophication degree of water in Danjiangkou Reservoir deepened from winter to autumn. The spatial distribution of phytoplankton in Danjiangkou Reservoir was obvious, and the phytoplankton biomass in Hanjiang Reservoir was higher than that in Danjiang Reservoir. The evaluation of diversity index showed that the water in the reservoir area was mild to moderately polluted, and the trophic status of water was higher in summer and autumn, with a certain eutrophication trend, and the risk of bloom was greater. The phytoplankton community structure in Danjiangkou Reservoir was mainly affected by environmental factors such as water temperature, transparency, total nitrogen and total phosphorus, summer, autumn season cyanobacteria, and green algae overgrowth may cause deterioration of water quality of Danjiangkou Reservoir. |
