Effects of silver nanoparticles and various forms of silver on nitrogen removal by the denitrifier Pseudomonas stutzeri and their toxicity mechanisms.

Silver nanoparticles (AgNPs) are widely used in daily life and industry because of their excellent antibacterial properties. AgNPs can exist in wastewater in various forms, such as Ag+, Ag2SO4, Ag2CO3, Ag2S, Ag2O, and AgCl. To assess the potential environmental risk of AgNPs and various forms of Ag, their toxic effects were investigated using the common denitrifier species Pseudomonas stutzeri (P. stutzeri). The inhibitory effect of AgNPs and various forms of Ag on P. stutzeri growth and its denitrification performance occurred in a concentration-dependent manner. The denitrification efficiency of P. stutzeri decreased from 95%∼97% to 89∼95%, 74∼95%, and 56∼85% under low, medium, and high exposure doses, respectively, of AgNPs and various forms of Ag. The changes in cell membrane morphology and increases in lactate dehydrogenase (LDH) release indicated that AgNPs and various forms of Ag damaged the cell membrane of P. stutzeri. Oxidative stress caused by excessive accumulation of reactive oxygen species (ROS) increased superoxide dismutase (SOD) and catalase (CAT) activities and decreased glutathione (GSH) levels. Overall, this study will help elucidate the impact of AgNPs and their transformation products on nitrogen removal efficiency in wastewater biological treatment systems.

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Livestock wastewater is an important reservoir of antibiotic resistance genes (ARGs), with high environmental risks. We investigated the seasonal variations of distribution and removal of swine wastewater originated high-risk tetracycline resistance genes (TRGs) in horizontal subsurface flow constructed wetlands. The effects of exogenous addition of tetracycline (TC) and copper ion (Cu2+) on the abundance of TRGs in effluent with single and combined pollution of antibiotic and heavy metal were studied. The results showed that all the three high-risk TRGs (tetM, tetO and tetW) were detected in swine wastewater. Wetlands could effectively reduce the ARGs, with the absolute abundance of TRGs in effluent being decreased by 1.1-2.4 and 1.7-2.9 orders of magnitude in summer and winter compared with the influent, respectively. The abundance of TRGs in wetland soils showed the characte-ristics that the outflow side was lower than the inflow side, the non-rhizosphere area was lower than the rhizosphere area, and lower in winter than in summer. In summer and winter, single and combined pollution of TC and Cu2+ in swine wastewater would increase the abundance of TRGs in effluent compared with that in the control. The constructed wetland is suitable for controlling the environmental diffusion of ARGs in livestock wastewater.

Effects of different oxygen conditions on pollutants removal and the abundances of tetracycline resistance genes in activated sludge systems.

The individual and combined effects of tetracycline (TC) and divalent copper (Cu2+) on the performance of activated sludge systems and the abundances of tetracycline resistance genes (TRGs) in activated sludge, under both aerobic and anaerobic conditions, were studied. Activated sludge systems received TC (0.2 mg L-1) and Cu2+ (5 mg L-1) separately or jointly under either aerobic or anaerobic conditions. The addition of TC did not affect the performance of activated sludge systems and the addition of Cu2+ and mixed TC/Cu2+ inhibited biological phosphorus removal. The TC removal efficiencies in systems under aerobic and anaerobic conditions were 98.4%-99.7% and 96.8%-99.9%, respectively, and Cu2+ promoted TC removal in activated sludge systems. The TC degradation product was 4-epitetracycline (ETC) in activated sludge systems under both aerobic and anaerobic conditions. The total relative abundances of TRGs (tetA, tetC, tetE, tetM, tetO, tetW, tetX and tetB(P)) in activated sludge showed opposite development trends under the two oxygen conditions and aerobic condition was beneficial to the attenuation of high-risk TRGs. The results of this study might improve evaluation of the combined effects of antibiotics and heavy metals on wastewater biological treatment systems.

Ecological Livability Assessment of Urban Agglomerations in Guangdong-Hong Kong-Macao Greater Bay Area.

This paper proposes the "citizen-ecology-city" evaluation framework for urban ecological livability theoretically and studies the ecological livability of the Guangdong-Hong Kong-Macao Greater Bay Area (GBA) empirically. In addition, we analyze the factors of urban ecological livability in a spatial dynamic panel model. The results are as follows. (1) Ecological livability levels of Macao and Hong Kong are significantly higher than the nine cities in the PRD; (2) Shenzhen and Guangzhou lead the nine cities in the PRD, while Jiangmen and Zhaoqing perform poorly; (3) GBA cities can be divided into three categories: Macao, Hong Kong, Shenzhen, and Guangzhou in the first tier; Zhuhai, Foshan, and Dongguan in the second tier; Huizhou, Zhongshan, Jiangmen, and Zhaoqing in the third tier; and (4) The ecological livability of the GBA cities has a characteristic of spatial correlation. In terms of the international value, the three-dimensional evaluation framework can apply to other bay areas in the world.

Environmental regulation, environmental responsibility, and green technology innovation: Empirical research from China.

Innovation and green are the directions to promote the circular economy and environmental sustainability at the corporate level. This paper examines the impact of environmental regulation (pollution charge) on green technology innovation and the mediating role of corporate environmental responsibility. Our results indicate that: (1) Environmental regulations stimulate manufacturing enterprises' environmental responsibility and green technology innovation. It is worth noting that corporate environmental responsibility strengthens the relationship between environmental regulation and green technology innovation. (2) Further investigation reveals that R&D expenditure and environmental investment have greatly strengthened the positive effect of environmental regulation on green technology innovation. (3) With more detailed disclosure about enterprises' environment-related information, the more outstanding stimulation effects of environmental regulation. Discussions on the features of enterprise location have revealed that, if the goal of environmental protection is set too high or if the fiscal decentralization is too strong, implementation of environmental regulation would not achieve desirable results. Accordingly, we need to optimize the collection of environmental taxes, strengthen the enterprises' environmental responsibility, and increase investment in R&D and environment protection. Meanwhile, the execution of environmental regulation should also take into account the institutional environment and governance features of the enterprise locations.

Single-shot imaging through scattering media under strong ambient light interference.

Speckle correlation imaging (SCI) has found tremendous versatility compared with other scattering imaging approaches due to its single-shot data acquisition strategy, relatively simple optical setup, and high-fidelity reconstruction performance. However, this simplicity requires SCI experiments to be performed strictly in a darkroom condition. As background noise increases, the speckle contrast rapidly decreases, making precise interpretation of the data extremely difficult. Here, we demonstrate a method by refining the speckle in the autocorrelation domain to achieve high-performance single-shot imaging. Experiment results prove that our method is adapted to estimate objects in a low signal-to-background ratio (SBR) circumstance even if the SBR is about -23dB. Laboratory and outdoor SCI experiments are performed.