Comprehensive analyses of functional bacteria and genes in a denitrifying EGSB reactor under Cd(II) stress.

A bench-scale expanded granular sludge bioreactor (EGSB) was continuously operated to treat synthesized high-nitrate industrial wastewater with increasing bivalent cadmium (Cd(II)) stress. The bioreactor showed nearly complete nitrate removal regardless of Cd(II) loadings, while nitrite accumulated in the effluent when influent Cd(II) loading was over 64 mg/L. Mi-seq sequencing of 16S rRNA gene amplicons elucidated that denitrifiers had decreasing abundances while biodiversity showed increasing trend as the Cd(II) loading increased. In the bioreactor, genera Halomonas, Thauera, Pseudomonas, and Zoogloea played major roles in the denitrification under lower Cd(II) loadings (< 32 mg/L), while Halomonas sp. KM-1 and Halomonas sp. BC04 acted as the crucial Cd-resistant denitrifiers under 128 mg/L Cd(II) loading. Metagenomic analyses and real-time quantitative PCR consistently indicated that napA encoding nitrate reductase was the predominant denitrifying gene, that could be mainly functioning on the efficient nitrate removal. Statistical analyses revealed the significantly positive correlation between Halomonas and nirS gene, both of which were functionally responsible for nitrite reduction. The obtained results may be practically useful for regulation and optimization of the biological processes to treat industrial wastewater containing high levels of nitrate and Cd(II).

Performance and microbial diversity of an expanded granular sludge bed reactor for high sulfate and nitrate waste brine treatment.

The disposal of waste brines has become a major challenge that hinders the wide application of ion-exchange resins in the water industry in recent decades. In this study, high sulfate removal efficiency (80%-90%) was achieved at the influent sulfate concentration of 3600 mg/L and 3% NaCl after 145 days in an expanded granular sludge bed (EGSB) reactor. Furthermore, the feasibility of treating synthetic waste brine containing high levels of sulfate and nitrate was investigated in a single EGSB reactor during an operation period of 261 days. The highest nitrate and sulfate loading rate reached 6.38 and 5.78 kg/(m(3)·day) at SO(2-)4-S/NO(-)3-N mass ratio of 4/3, and the corresponding removal efficiency was 99.97% and 82.26% at 3% NaCl, respectively. Meanwhile, 454-pyrosequencing technology was used to analyze the bacterial diversity of the sludge on the 240th day for stable operation of phase X. Results showed that a total of 9194 sequences were obtained, which could be affiliated to 14 phyla, including Proteobacteria, Firmicutes, Chlorobi, Bacteroidetes, Synergistetes and so on. Proteobacteria (77.66%) was the dominant microbial population, followed by Firmicutes (12.23%) and Chlorobi (2.71%).

C3N5-based nanomaterials and their applications in heterogeneous catalysts, energy harvesting, and environmental remediation.

Over the past few decades, the global reliance on fossil fuels and the exponential growth of human population have escalated global energy consumption and environmental issues. To tackle these dual challenges, metal catalysts, in particular precious metal ones, have emerged as pivotal players in the fields of environment and energy. Among the numerous metal-free and organic catalyst materials, C3N5-based materials have a major advantage over their carbon nitride (CxNy) counterparts owing to the abundant availability of raw materials, non-toxicity, non-hazardous nature, and exceptional performance. Although significant efforts have been dedicated to synthesising and optimising the applicable properties of C3N5-based materials in recent years, a comprehensive summary of the immediate parameters of this promising material is still lacking. Given the rapid development of C3N5-based materials, a timely review is essential for staying updated on their strengths and weaknesses across various applications, as well as providing guidance for designing efficient catalysts. In this study, we present an extensive overview of recent advancements in C3N5-based materials, encompassing their physicochemical properties, major synthetic methods, and applications in photocatalysis, electrocatalysis, and adsorption, among others. This systematic review effectively summarises both the advantages and shortcomings associated with C3N5-based materials for energy and environmental applications, thus offering researchers focussed on CxNy-materials an in-depth understanding of those based on C3N5. Finally, considering the limitations and deficiencies of C3N5-based materials, we have proposed enhancement schemes and strategies, while presenting personal perspectives on the challenges and future directions for C3N5. Our ultimate aim is to provide valuable insights for the research community in this field.

Facile solvothermal synthesis of nitrogen-doped SnO2 nanorods towards enhanced photocatalysis.

Heteroatom doping has proved to be one of the most effective approaches to further improve the photocatalytic activities of semiconducting oxides originating from the modulation of their electronic structures. Herein, nitrogen-doped SnO2 nanorods were synthesized via facile solvothermal processes using polyvinylpyrrolidone (PVP) as a dispersing agent and ammonium water as the N source, respectively. Compared with pure SnO2 sample, the as-synthesized nitrogen-doped SnO2 nanorods demonstrated enhanced photocatalytic performances, evaluated by the degradation of rhodamine B (RhB), revealing the effectiveness of nitrogen doping towards photocatalysis. In particular, the optimal photocatalyst (using 0.6 g PVP and 1 mL ammonia water) could achieve up to 86.23% pollutant removal efficiency under ultraviolet (UV) light irradiation within 150 min, showing 17.78% higher efficiency than pure SnO2. Detailed structural and spectroscopic characterization reveals the origin of activity enhancement of nitrogen-doping SnO2 in contrast with pure SnO2. Specifically, the bandgap and the morphologies of nitrogen-doped SnO2 have changed with more chemisorbed sites, which is supposed to result in the enhancement of photocatalytic efficiency. Moreover, the possible formation mechanism of nitrogen-doped SnO2 nanorods was discussed, in which PVP played a crucial role as the structure orientator.

Temperature dependence of denitrification microbial communities and functional genes in an expanded granular sludge bed reactor treating nitrate-rich wastewater.

The temperature dependence of denitrification was investigated for high nitrate nitrogen denitrification in an expanded granular sludge bed (EGSB) reactor. The optimal reaction temperatures were 15-35 °C in which nearly complete denitrification was achieved with the removal of COD maintained over 80%. Nitrite accumulation was observed at 10 °C indicating the incomplete denitrification at low temperature. However, almost complete denitrification was even accomplished as high as 52 °C. High-throughput sequencing detected a total of 84 bacterial genera and 7 phyla, and temperature variation resulted in the shift of microbial community structure and diversity. Proteobacteria thrived while Firmicutes and Bacteroidetes were inhibited by temperature stress. The predominance of Halomonas and the significant decrease of Azoarcus at low temperature indicated a more important role of these two genera in denitrification in an EGSB reactor. The results of qPCR indicated that temperature exerted effects on the abundance of denitrification function genes, nirK, nirS, narG, and nosZ, due to the shift of the bacterial community. This study provided a comprehensive understanding of temperature effects on the denitrification process in an EGSB reactor treating high concentration nitrate wastewater.

Metagenomic insights into Cr(VI) effect on microbial communities and functional genes of an expanded granular sludge bed reactor treating high-nitrate wastewater.

In this study, a lab-scale expanded granular sludge bed reactor was continuously operated to treat high-nitrate wastewater containing different concentrations of hexavalent chromium (Cr(VI)). Nearly complete nitrate removal was achieved even at 120 mg/L influent Cr(VI). Pyrosequencing of 16S rRNA gene showed that Cr(VI) decreased the biodiversity of the bacterial community and potential denitrifiers. Proteobacteria dominated in the bioreactor, and Betaproteobacteria had increased abundance after Cr(VI) feeding. Thauera and Halomonas were the two predominant genera in the bioreactor fed with Cr(VI), demonstrating opposite responses to the Cr(VI) stress. Metagenomic analysis indicated that Cr(VI) feeding posed no obvious effect on the overall function of the bacterial community, but altered the abundance of specific denitrifying genes, which was evidenced by quantitative real time PCR. This study revealed that Halomonas mainly contributed to the denitrification under no or low Cr(VI) stress, while Thauera played a more important role under high Cr(VI) stress.

High-nitrate wastewater treatment in an expanded granular sludge bed reactor and microbial diversity using 454 pyrosequencing analysis.

Denitrification of high concentration of nitrate wastewater was investigated in expanded granular sludge bed (EGSB) reactor with sodium acetate as the carbon source. The optimal parameters were achieved with C/N mole ratio of 2.0, liquid up-flow velocity (Vup) of 3.0 m/h and pH of 6.2-8.2. Complete denitrification can be achieved even with nitrate nitrogen concentration as high as 14000 mg/L. Furthermore, 454-pyrosequencing technology was used to analyze bacterial diversity. Results showed that a total of 5573 sequences were obtained which could be affiliated to 6 phylogenetic groups, including Proteobacteria, Firmicutes, Actinobacteria, Bacteroidetes, Chloroflexi and unclassified phylum. Proteobacteria (84.53%) was the dominant microbial population, followed by Firmicutes (13.24%) and Actinobacteria (0.38%). The dominate phylum was different from that in other anaerobic system.