As the smallest entities in catalysts, single-atom catalysts (SACs) exhibit superior atomic efficiency, advanced activity, and high selectivity. However, their practical applications are inhibited due to their high preparation costs. Here, we developed a novel cobalt− carbon-based SAC derived from the mild pyrolysis of spent coffee grounds soaked in Co (Co-CGBC), in which cobalt atoms atomically disperse and coordinate with the N and S atoms in the carbon substance, as identified by X-ray absorption fine structure (XAFS) spectroscopy combined with high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM). Co-CGBC is inexpensive and exhibits high efficiency in the activation of peroxymonosulfate (PMS) to degrade a wide range of organic pollutants with a degradation efficiency of 90−100%. Density functional theory (DFT) calculations confirm that the sulfur in the Co−N 3 S 1 active site plays a crucial role in reducing the adsorption energy of PMS and facilitating electron transfer. This work supplies new opportunities to synthesize cost-effective SACs for application in environmental remediation.

An incubation experiment was performed on Potamogeton crispus (P. crispus) using sediment collected from Lake Tangxunhu in the center of China, in order to determine the effects of plant growth on Fe, Si, Cu, Zn, Mn, Mg, P, and Ca concentrations in the sediments and overlying waters. After 3 months of incubation, Ca, Mg, and Si concentrations in the water column were significantly lower, and P and Cu concentrations were significantly higher than in unplanted controls. The effect of P. crispus growth on sediment pore waters and water-extractable elements varied. Concentrations of Ca, Mg, Si, Fe, Cu, and Zn were significantly higher, and P was significantly lower, than in pore waters of the control. Waterextracted concentrations of Fe, Mg, and Si in the sediments were lower, and P was higher, than in the control. Presence of P. crispus generally enhanced concentration gradients of elements between pore waters and overlying waters but not for P. The growth of P. crispus was associated with an increase in water pH and formation of root plaques, resulting in complex effects on the sediment nutritional status.

A 1-D-2-D coupled numerical model embedded with the impact of hydrodynamic conditions on algae growth was developed to simulate the algae concentration for a river-lake system. Based on the laboratory experiment and field investigation, the 'flowdisturbance parameter α' was presented to improve the algae growth formula. By numerical simulation, the algae growth processes in a river-lake system were simulated, and the temporal and spatial distributions of Chl-a concentration in the area were analysed. Our results show the following: (1) Hydrodynamic conditions play an apparent effect on algae growth. A suitable turbulence is more beneficial for algal proliferation than the static or intense mixing. (2) In the studied area, the flow disturbances in the east-west rivers are generally stronger than that in the north-south rivers, while the Chl-a concentration is oppositely distributed in the river networks. (3) As a result of the different flow disturbance intensities during periods, the algae cell density in all investigated sections also alters evidently along with the seasons. The average Chl-a concentration in the dry seasons (November-April) increased by 9.22% than that in the flood seasons (May-October). (4) From the point of the whole river-lake system, the dynamic conditions in the lake inlet areas are more suitable for algae growth than that in the river networks. The Chl-a concentrations of S2 and S4 are averagely increased by 18.5% than that in the river networks.

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Advanced oxidation processes (AOPs) have revealed wide prospects in the application of the degradation of organic contaminants in ground water and soil. High-performance, environmentally friendly, and low-cost single-atom catalysts (SACs) are promising approaches to active persulfate in AOPs. However, the practical application of SACs is restricted by high preparation costs and tedious procedures. Herein, a manganese (Mn) hyperaccumulator, Phytolacca americana, was successfully exploited as a precursor to synthesize a novel Mn SAC (SPBC-700N) via a one-step pyrolysis method. In SPBC-700N, Mn atoms are dispersed atomically upon the carbon matrix and coordinate with four N atoms to form Mn–N4 active sites, which exhibits an extraordinary catalytic activity for peroxymonosulfate (PMS) activation. A large number of reactive oxygen species are formed during the reaction, and over 90% of the antibiotic (chloroquine phosphate/CQP) could be removed within 30 min. The superior catalytic performance of the Mn SAC/PMS system for CQP degradation is ascribed to the synergistic effect of the maximized utilization of Mn atoms and the neighboring pyrrolic N sites, as identified by X-ray absorption fine structure spectroscopy and density function theory calculations. This work not only provides a green and low-cost strategy for synthesizing SACs but also gives an atomic-level insight into the catalytic activity of the Mn–N4 sites for PMS activation.

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A new method, with the non-fully mixed coefficient (NFMC) considered, was put forward to calculate the water environmental carrying capacity (WECC) for huge river-connected lakes, of which the hydrological conditions always vary widely during a year. Poyang Lake, the most typical river-connected lake and the largest freshwater lake in China, was selected as the research area. Based on field investigations and numerical simulation, the monthly pollutant degradation coefficients and non-fully mixed coefficients of different lake regions were determined to explore the WECCs of COD, TN and TP of Poyang Lake in a common water year. It was found that under the hydrological conditions of a common water year the total WECCs of COD, TN and TP in the lake were respectively 181.9 × 104 t, 33.3 × 104 t and 1.86 × 104 t. Due to the varied lake water volume and self-purification ability, an evident temporal fluctuation of WECCs in Poyang Lake was observed. The dry seasons were characterized by a higher NFMCs but lower WECCs owing to the lower water level and degradation ability. Variation coefficients of COD and TN WECC were close to each other, of which the average level was about 58.5%, a little higher than that of TP.

We evaluated the influence of sediment dredging on sedimentary As release for the Inner Lake, a typical tide-influenced waterfront body in the middle to lower reaches of the Yangtze River in Zhengjiang, China. By field investigation and laboratory experiment, the As content in the deposited sediment before dredging was analyzed and the relationship between dynamic disturbance and sedimentary As release intensity was established. Using a numerical model in which the factors of water current, suspended sediment, and As were coupled, the processes of As migration were simulated for typical years and tidal cycles before and after dredging. The results show that: (i) the amounts of sedimentary As release during the tidal cycles in the flood season and the dry season after dredging were reduced by 14.6 and 28.1%, respectively, compared with before dredging; (ii) after removal of the surface polluted sediment, the annual volumes of internal released As in the high-water year, common-water year, and low-water year were decreased to 11.89, 4.94, and 4.89 Mg, respectively; and (iii) the highest reduction rate could reach 27.5% in the common-water year, while the lowest was 10.92% in the high-water year because the massive water exchange with the Yangtze River in the high-water year resulted in an enhanced dynamic disturbance that played a more dominating role in the internal As release than the surface sediment removal. The results of this study may be useful for other researchers of water environment protection for waterfront bodies.