Bibliometric insights into the evolution of uranium contamination reduction research topics: Focus on microbial reduction of uranium.

Confronting the threat of environment uranium pollution, decades of research have yielded advanced and significant findings in uranium bioremediation, resulting in the accumulation of tremendous amount of high-quality literature. In this study, we analyzed over 10,000 uranium reduction-related papers published from 1990 to the present in the Web of Science based on bibliometrics, and revealed some critical information on knowledge structure, thematic evolution and additional attention. Methods including contribution comparison, co-occurrence and temporal evolution analysis are applied. The results of the distribution and impact analysis of authors, sources, and journals indicated that the United States is a leader in this field of research and China is on the rise. The top keywords remained stable, primarily focused on chemicals (uranium, iron, plutonium, nitrat, carbon), characters (divers, surfac, speciat), and microbiology (microbial commun, cytochrome, extracellular polymeric subst). Keywords related to new strains, reduction mechanisms and product characteristics demonstrated the strongest uptrend, while some keywords related to mechanism and performance were clearly emerging in the past 5 years. Furthermore, the evolution of the thematic progression can be categorized into three stages, commencing with the discovery of the enzymatic reduction of hexavalent uranium to tetravalent uranium, developing in the groundwater remediation process at uranium-contaminated sites, and delving into the research on microbial reduction mechanisms of uranium. For future research, enhancing the understanding of mechanisms, improving uranium removal performance, and exploring practical applications can be considered. This study provides unique insights into microbial uranium reduction research, providing valuable references for related studies in this field.

Spatiotemporal dynamics and anthropologically dominated drivers of chlorophyll-a, TN and TP concentrations in the Pearl River Estuary based on retrieval algorithm and random forest regression.

Estimation of large-scale and high-precision water quality parameters is critical in explaining the spatiotemporal dynamics and the driving factors of water quality variability, especially in areas with environmental complexity (e.g., crisscrossing waterways, high flood risk in rainy season and seawater invasion). Thus, in this study, a retrieval algorithm was developed to predict chlorophyll-a (Chl-a), total nitrogen (TN) and total phosphorus (TP) concentrations in the Pearl River Estuary (PRE) based on a large amount of in situ measurements and Landsat 8 remote sensing images. Random Forest (RF) machine learning was conducted to identify the relationship between environmental indicators (pH, turbidity, conductivity, total dissolved solids and water temperature), Chl-a, TN and TP. The results showed that the NIR/R Binomial algorithm for Chl-a estimation presented appreciable reliability with R2 of 0.7429, root mean square error (RMSE) of 1.2089 and mean absolute percent error (MAPE) of 15.33%. The water quality variation in the PRE showed a characteristic of overall improvement and regional deterioration with average concentrations of 7.28 µg/L, 1.15 mg/L and 0.12 mg/L for Chl-a, TN, and TP respectively. Turbidity and pH were identified as the most important indicators to explain Chl-a (52.86%, 39.91%), TN (52.38%, 40.57%) and TP (55.23%, 40.03%) variation. Agricultural pollution was the main pollution source due to the intensive application of fertilizer and increased field size. Besides, land use patterns (e.g., increasing farmland but decreasing forest) greatly influenced water quality from 2010 to 2020. Moreover, light limitation caused by high turbidity reduced the algae productivity and further lowered the Chl-a concentration. The driving factors for regional water quality variations were anthropologically dominated and supplemented by climate change. This study improved the monitoring accuracy of regional water environment and provided quantitative early warning of water pollution events for environmental practitioners, so as to achieve long-term monitoring, precise pollution management and efficient water resources management.

Overlooked Ecological Roles of Influent Wastewater Microflora in Improving Biological Phosphorus Removal in an Anoxic/Aerobic MBR Process.

The ecological roles of influent microflora in activated sludge communities have not been well investigated. Herein, parallel lab-scale anoxic/aerobic (A/O) membrane bioreactors (MBRs), which were fed with raw (MBR-C) and sterilized (MBR-T) municipal wastewater, were operated. The MBRs showed comparable nitrogen removal but superior phosphorus removal in MBR-C than MBR-T over the long-term operation. The MBR-C sludge community had higher diversity and deterministic assembly than the MBR-T sludge community as revealed by 16S rRNA gene sequencing and null model analysis. Moreover, the MBR-C sludge community had higher abundance of polyphosphate accumulating organisms (PAOs) and hydrolytic/fermentative bacteria (HFB) but lower abundance of glycogen-accumulating organisms (GAOs), in comparison with MBR-T sludge. Intriguingly, the results of both the net growth rate and Sloan's neutral model demonstrated that HFB in the sludge community were generally slow-growing or nongrowing and their consistent presence in activated sludge was primarily attributed to the HFB immigration from influent microflora. Positive correlations between PAOs and HFB and potential competitions between HFB and GAOs were observed, as revealed by the putative species-species associations in the ecological networks. Taken together, this work deciphers the positive ecological roles of influent microflora, particularly HFB, in system functioning and highlights the necessity of incorporating influent microbiota for the design and modeling of A/O MBR plants.

A novel pilot-scale IFAS-MBR system with low aeration for municipal wastewater treatment: Linkages between nutrient removal and core functional microbiota.

In this study, we proposed a novel IFAS-MBR with low aeration for the treatment of real municipal wastewater. With biocarriers packed in the anoxic tank, the pilot-scale IFAS-MBR operated with average dissolved oxygen concentrations of 0.56 mg/L in the oxic tank. Over 110 days of operation, highly efficient nutrient removal was achieved with the total nitrogen (TN) and phosphorus (TP) removal efficiencies of 78.1 ± 7.2% and 93.7 ± 5.8%, respectively. The average effluent concentrations of TN and TP reached 5.4 and 0.26 mg/L, respectively. Meanwhile, the removal efficiency of COD reached 95.3 ± 1.3% in the system, and the concentrations of COD decreased from 31.9 ± 3.7 (sludge supernatant) to 12.7 ± 1.6 mg/L (permeate) after membrane filtration. Microbial community analysis showed that Nitrosomonas (0.32%) and Nitrospira (1.85%) in activated sludge were the main drivers of the nitrification process, while various denitrifying bacteria in activated sludge and biofilms were responsible for nitrate reduction in the anoxic tank. Candidatus Accumulibacter (0.34%) and Dechloromonas (1.31%) primarily contributed to denitrifying phosphorus uptake in the anoxic tank. Furthermore, these organisms (i.e., core functional microbiota) exhibited stable levels over the entire operation. The highly enriched hydrolytic fermentation bacteria drove community succession, and the remarkable functional robustness of microbial communities in activated sludge and biofilms favored nutrient removal. Overall, the novel IFAS-MBR system provides an energy-efficient MBR alternative owing to its highly efficient performance and low operating costs enabled by low aeration rates and the absence of an external carbon source.

Microbial degradation of four crude oil by biosurfactant producing strain Rhodococcus sp.

Rhodococcus erythropolis M-25, one of the representative biosurfactant producers, performed effectively during the biodegradation of four crude oil. The microbial degradation efficiency is positively relevant to the API of the crude oil. The chemical dispersant Corexit 9500A did not enhance the biodegradation of the petroleum hydrocarbons during the experimental period. 70.7% of the N-4 oil was degraded after 30days, while in the Corexit 9500A plus sample the biodegradation removal was 42.8%. The Corexit-derived compounds were metabolized by M-25 at the same time of the petroleum hydrocarbons biodegrading. Neither biodegradation nor chemical dispersion process has almost no effect on the biomarker (m/z=231). The saturated methyl-branched fatty acids increased from 37.3%, to 49.4%, when M-25 was exposed with the N-4 crude oil. Similarly, the saturated methyl-branched fatty acids in the membrane of N3-2P increased from 20.25% to 44.1%, when exposed it with the N-4 crude oil.