Metabolic Profiles and Microbial Synergy Mechanism of Anammox Biomass Enrichment and Membrane Fouling Alleviation in the Anammox Dynamic Membrane Bioreactor.

The anammox dynamic membrane bioreactor (DMBR) is promising in applications with enhanced anammox biomass enrichment and fouling alleviation. However, the metabolic mechanism underlying the functional features of anammox sludge and the biofilm membrane is still obscure. We investigated the metabolic networks of anammox sludge and membrane biofilm in the DMBR. The cooperation between anammox and dissimilatory nitrate reduction to ammonium processes favored the robust anammox process in the DMBR. The rapid bacterial growth occurred in the DMBR sludge with 1.33 times higher biomass yield compared to the MBR sludge, linked to the higher activities of lipid metabolism, nucleotide metabolism, and B vitamin-related metabolism of the DMBR sludge. The metabolism of the DMBR biofilm microbial community benefited the fouling alleviation that the abundant fermentative bacteria and their cooperation with the anammox sludge microbial community promoted organics degradation. The intensified degradation of foulants by the DMBR biofilm community was further evidenced by the active carbohydrate metabolism and the upregulated vitamin B intermediates in the biofilms of the DMBR. Our findings provide insights into key metabolic mechanisms for enhanced biomass enrichment and fouling control of the anammox DMBR, guiding manipulations and applications for overcoming anammox biomass loss in the treatment of wastewater under detrimental environmental conditions.

Mechanisms and Strategies of Advanced Oxidation Processes for Membrane Fouling Control in MBRs: Membrane-Foulant Removal versus Mixed-Liquor Improvement.

Membrane bioreactors (MBRs) are well-established and widely utilized technologies with substantial large-scale plants around the world for municipal and industrial wastewater treatment. Despite their widespread adoption, membrane fouling presents a significant impediment to the broader application of MBRs, necessitating ongoing research and development of effective antifouling strategies. As highly promising, efficient, and environmentally friendly chemical methods for water and wastewater treatment, advanced oxidation processes (AOPs) have demonstrated exceptional competence in the degradation of pollutants and inactivation of bacteria in aqueous environments, exhibiting considerable potential in controlling membrane fouling in MBRs through direct membrane foulant removal (MFR) and indirect mixed-liquor improvement (MLI). Recent proliferation of research on AOPs-based antifouling technologies has catalyzed revolutionary advancements in traditional antifouling methods in MBRs, shedding new light on antifouling mechanisms. To keep pace with the rapid evolution of MBRs, there is an urgent need for a comprehensive summary and discussion of the antifouling advances of AOPs in MBRs, particularly with a focus on understanding the realizing pathways of MFR and MLI. In this critical review, we emphasize the superiority and feasibility of implementing AOPs-based antifouling technologies in MBRs. Moreover, we systematically overview antifouling mechanisms and strategies, such as membrane modification and cleaning for MFR, as well as pretreatment and in-situ treatment for MLI, based on specific AOPs including electrochemical oxidation, photocatalysis, Fenton, and ozonation. Furthermore, we provide recommendations for selecting antifouling strategies (MFR or MLI) in MBRs, along with proposed regulatory measures for specific AOPs-based technologies according to the operational conditions and energy consumption of MBRs. Finally, we highlight future research prospects rooted in the existing application challenges of AOPs in MBRs, including low antifouling efficiency, elevated additional costs, production of metal sludge, and potential damage to polymeric membranes. The fundamental insights presented in this review aim to elevate research interest and ignite innovative thinking regarding the design, improvement, and deployment of AOPs-based antifouling approaches in MBRs, thereby advancing the extensive utilization of membrane-separation technology in the field of wastewater treatment.

Impact of waste separation on the biological nitrogen removal in a MSW incineration leachate treatment plant: Performance and microbial community shift.

After waste separation program was launched in China in 2019, incineration leachate treatment plants are facing a challenge of effective removal of nitrogen from leachate due to lack of sufficient carbon source. In this study, the performance of a biological incineration leachate treatment process (anaerobic digestion (AD) - two-stage anoxic/aerobic (A/O) process) was evaluated after adopting the waste separation program, and the changes in the microbial community and function was analyzed using 16S rRNA amplicon sequencing technology. Results showed that after the waste separation, the influent chemical oxygen demand (COD) concentration reduced by 90% (from 19,300 to 1780 mg L-1) with the COD/N ratio decreased from 12.3 to 1.4, which led to a decreased nitrogen removal efficiency (NRE) of <65% and a high effluent NO3- accumulation (445.8-986.5 mg N·L-1). By bypassing approximately 60% of the influent to the two-stage A/O process and adding external carbon source (glucose), the mean NRE increased to 86.3 ± 7.4%. Spearman's analysis revealed that refractory compounds in the bypassed leachate were closely related to the variations in bacterial community composition and nitrogen removal function in the two-stage A/O, leading to a weakened correlation of microbial network. KEGG functional pathway predictions based on Tax4Fun also confirmed that the bypassed leachate induced xenobiotic compounds to the two-stage A/O process, the relative abundance of nitrogen metabolism was reduced by 32%, and more external carbon source was required to ensure the satisfactory nitrogen removal of >80%. The findings provide a good guide for regulation of incineration leachate treatment processes after the waste separation.

How to Provide Nitrite Robustly for Anaerobic Ammonium Oxidation in Mainstream Nitrogen Removal.

Innovation in decarbonizing wastewater treatment is urgent in response to global climate change. The practical implementation of anaerobic ammonium oxidation (anammox) treating domestic wastewater is the key to reconciling carbon-neutral management of wastewater treatment with sustainable development. Nitrite availability is the prerequisite of the anammox reaction, but how to achieve robust nitrite supply and accumulation for mainstream systems remains elusive. This work presents a state-of-the-art review on the recent advances in nitrite supply for mainstream anammox, paying special attention to available pathways (forward-going (from ammonium to nitrite) and backward-going (from nitrate to nitrite)), key controlling strategies, and physiological and ecological characteristics of functional microorganisms involved in nitrite supply. First, we comprehensively assessed the mainstream nitrite-oxidizing bacteria control methods, outlining that these technologies are transitioning to technologies possessing multiple selective pressures (such as intermittent aeration and membrane-aerated biological reactor), integrating side stream treatment (such as free ammonia/free nitrous acid suppression in recirculated sludge treatment), and maintaining high activity of ammonia-oxidizing bacteria and anammox bacteria for competing oxygen and nitrite with nitrite-oxidizing bacteria. We then highlight emerging strategies of nitrite supply, including the nitrite production driven by novel ammonia-oxidizing microbes (ammonia-oxidizing archaea and complete ammonia oxidation bacteria) and nitrate reduction pathways (partial denitrification and nitrate-dependent anaerobic methane oxidation). The resources requirement of different mainstream nitrite supply pathways is analyzed, and a hybrid nitrite supply pathway by combining partial nitrification and nitrate reduction is encouraged. Moreover, data-driven modeling of a mainstream nitrite supply process as well as proactive microbiome management is proposed in the hope of achieving mainstream nitrite supply in practical application. Finally, the existing challenges and further perspectives are highlighted, i.e., investigation of nitrite-supplying bacteria, the scaling-up of hybrid nitrite supply technologies from laboratory to practical implementation under real conditions, and the data-driven management for the stable performance of mainstream nitrite supply. The fundamental insights in this review aim to inspire and advance our understanding about how to provide nitrite robustly for mainstream anammox and shed light on important obstacles warranting further settlement.

Metagenomics insight into the long-term effect of ferrous ions on the mainstream anammox system.

Anaerobic ammonium oxidation (anammox) bacteria have a high requirement for iron for their growth and metabolism. However, it remains unclear whether iron supplementation can sustain the stability of mainstream anammox systems at varying temperatures. Here, we investigated the long-term effects of Fe2+ on the mainstream anammox systems. Our findings revealed that the nitrogen removal efficiency (NRE) of the anammox system supplemented with 5 mg/L Fe2+ decreased from 76.5 ± 0.76% at 35 °C to 39.0 ± 9.9% at 25 °C. Notably, higher dosages of Fe2+ (15 mg/L and 30 mg/L) inhibited the anammox system, resulting in NREs of 15.9 ± 8.1% and 2.5 ± 1.1% at 25 °C, respectively. The results of microbial communities and function profiles suggested that the high Fe2+ dosage seriously affected the iron assimilation and utilization in the mainstream anammox system. This was evident from the decreased abundance of genes associated with Fe(II) transport and uptake, which in turn hindered the biosynthesis of intracellular iron-cofactors, resulting in decrease in the absolute abundance of Candidatus Brocadia, a key anammox bacterium, as well as a decline in NRE. Furthermore, our results showed that the anammox process was more susceptible to iron supplementation at 25 °C compared to 35 °C, which may be due to the oxidative stress reactions induced by combined lowered temperature and a high Fe2+ dosage. Overall, these findings offer a deeper understanding of the effect of iron in mainstream anammox systems, which can contribute to improved stability maintenance and effectiveness of anammox processes.

Antibiofouling Characteristics and Mechanisms in an Anammox Membrane Bioreactor Based on an Optimized Photocatalytic Technology─Photocatalytic Optical Fibers.

As an ecofriendly photocatalytic antifouling technology for membrane bioreactors (MBRs), photocatalytic optical fibers (POFs) can decrease the replacement cost of modified membranes and prevent the proliferation of photosynthetic bacteria caused by direct light illumination. Here, POFs were applied in situ in an anaerobic ammonium oxidation (anammox) MBR for membrane biofouling control. Compared with the control MBR without POFs treatment, the average fouling cycle of the POFs-loaded MBR was extended by 137%, and the energy consumption caused by membrane fouling was saved by 18%. In the antibiofouling process, •OH was the key photocatalytic reactive species. On the fouled POFs-loaded membranes, the membrane-adhered foulant was significantly decreased by photocatalytic degradation of the proteins, polysaccharides and humic substances in the microbial metabolites. The membrane-attached bacteria were inactivated by the POFs by the mechanisms of cell-membrane destruction and cell-membrane permeabilization, which caused bacterial necrosis and apoptosis, respectively. Moreover, the total nitrogen-removal efficiencies of the two MBRs were maintained at 85.3-90.4%, and the abundance of anammox bacteria increased from 21.3% to 46.2% during the 202 days of operation, indicating an efficient anammox process with excellent nitrogen-removal performance, biomass retention, and anammox bacteria enrichment. The systematic insights into the antibiofouling performance and mechanisms of POFs in anammox MBRs will promote application and development of membrane-filtration technology in wastewater treatment using environmentally friendly and energy-efficient antifouling strategies.

Novel Control Strategy for Membrane Biofouling by Surface Loading of Aerobically and Anaerobically Applicable Photocatalytic Optical Fibers Based on a Z-Scheme Heterostructure Zr-MOFs/rGO/Ag3PO4 Photocatalyst.

The high replacement cost of modified membranes in antibiofouling application is inevitable. Here, surface-loaded photocatalytic optical fibers (POFs) were developed as antibiofouling strategies to replace membrane modification. To prepare aerobically and anaerobically applicable POFs, novel visible light-driven zirconium-based metal-organic framework/reduced graphene oxide/Ag3PO4 (Zr-MOFs/rGO/Ag3PO4) Z-scheme heterojunctions were constructed and coated on optical fibers. After loading the POFs on the membrane surface, the antibiofouling capability of the POFs was demonstrated during membrane filtration of bacteria and foulants under visible light irradiation. The disinfection efficiencies of the POFs against Escherichia coli and Staphylococcus aureus reached 95.7 and 92.4%, respectively, by aerobic treatment and 90.3 and 85.5%, respectively, by anaerobic treatment. For the inactivated bacteria, cell membrane and membrane-associated functions were destroyed, accompanied by antioxidant enzyme decomposition, loss of cell respiration and adenosine triphosphate (ATP) synthesis capacity, and leakage and oxidation of protein, lipid, potassium, DNA, and RNA. During membrane filtration of model foulants and membrane bioreactor sludge, the POFs significantly alleviated the membrane flux decline by foulant disintegration. By qualitative and quantitative detection and quenching tests of reactive species, aerobically generated •O2- and •OH and anaerobically generated •OH from POFs played dominant roles in the antibiofouling process. This work provides unique insights into membrane fouling control based on environmentally friendly and efficient photocatalytic technology.

Intensified nitrogen removal by endogenous denitrification in a full-scale municipal wastewater treatment plant.

In this study, for the first time, endogenous denitrification (ED) was enhanced in a practical anaerobic-anoxic-oxic-[post-anoxic]-[post-oxic] (AAO-AO) process, contributing to a remarkable increase in the nitrogen removal efficiency (NRE). The long-term operation (203 days) result showed that the NRE was improved by 7% compared to the theoretical maximum NRE (68-70%) of AAO processes, with the effluent total nitrogen (TN) decreasing from 13.7 (1 d) to 6.1 mg/L (203 d). Approximately 99.4% of the influent COD was transformed to poly-ß-hydroxyalkanoates (PHAs) in the anaerobic zone. The synthesized PHAs were consumed in the following zones and the secondary sedimentation tank accompanied by over 32.5% N-loss, indicating that the ED process could be responsible for the enhanced NRE. 16S rRNA amplicon sequencing results further confirmed that denitrifying glycogen-accumulating organisms, which are capable of ED, were enriched with the relative abundance of 2.10%. Our findings provide a novel cost- and energy-efficient strategy to improve nitrogen removal without external carbon additions but by enhancing ED performance.

High adhesion ability of anammox granular microbes directly revealed by QCM-D technique.

Anammox bacteria are widely found to grow in bioaggregates form, but the reason for their high aggregation ability remains elusive. In this study, four kinds of sludge, i.e., anammox granules, anaerobic granules, aerobic granules, and partial nitrification flocs, were studied and compared to investigate their differences in adherence properties. We directly explored the adherence properties of sludge samples before and after extracellular polymeric substances (EPS) extraction, using quartz-crystal microbalance technique with dissipation monitoring technique. Results showed that EPS indeed stimulated the adherence properties of all sludge samples. The most striking feature here is that anammox consortia had the highest adhesion rate and mass, and formed the most compact layer on the gold-coated sensor surfaces both before and after EPS extraction among the four sludge samples, indicating their inherent high adhesion ability. The composition and spectral characteristics of EPS samples were also investigated, and it reveals that the relatively high extracellular proteins/polysaccharides ratio of anammox granules (3.2 ± 0.4) rather than total EPS concentration had contributed to their high adhesion ability. The findings are helpful for understanding the adherence properties of anammox bacteria, and will serve as a guide for further researches to exploring the aggregation process of anammox bacteria.

Transcriptomics Uncovers the Response of Anammox Bacteria to Dissolved Oxygen Inhibition and the Subsequent Recovery Mechanism.

Understanding the recovery of anaerobic ammonium-oxidizing (anammox) bacteria after inhibition by dissolved oxygen (DO) is critical for the successful applications of anammox-based processes. Therefore, the effects of oxygen exposure (2 mg L-1 DO for 90 min) and subsequent recovery treatments [N2 purging or nano zero-valent iron (nZVI) addition] on the activity and gene expression in a Kuenenia stuttgartiensis enrichment culture were examined. Combining the self-organizing map clustering and enrichment analysis, we proposed the oxidative stress response of anammox bacteria based on the existing concepts of oxidative stress in microbes: the DO exposure triggered a stringent response in K. stuttgartiensis, which downregulated the transcription levels of genes involved in the central metabolism and diverted energy to a flagellar assembly and metal transport modules; these changes possibly promoted survival during the inhibition of anammox activity. According to the cotranscription with central catabolism genes, putative reactive oxygen species (ROS) scavenger genes (kat and sod) were presumed to detoxify the anammox intermediates rather than ROS. In addition, both activity and mRNA profiles with appropriate amount of nZVI addition (5 and 25 mg L-1) were close to that of control, which proved the effectiveness of nZVI addition in anammox recovery. These results would be relevant to the physio-biochemistry development of anammox bacteria and further enhancement of nitrogen removal in wastewater treatment.

Olefin Amine (OLA) Reagents for the Synthesis of Bridged Bicyclic and Spirocyclic Saturated N-Heterocycles by Catalytic Hydrogen Atom Transfer (HAT) Reactions.

Spiro- and bridged bicyclic structures are in demand for their sp3-rich frameworks that offer unique physiochemical properties and precisely positioned substituent groups. In order to rapidly access such molecules in a cross-coupling fashion we describe olefin amine (OLA) reagents for the transformation of aldehydes and ketones into all three topological types of bicyclic N-heterocycles: bridged, spiro-, and fused rings. The OLA reagents are easily prepared and allow the synthesis of complex molecular frameworks under operationally simple conditions that tolerate a wide array of functional groups. Investigations into the Mn or Fe promoted reaction pathway support a metal hydride hydrogen atom transfer (MH-HAT) to generate a C-centered radical that undergoes addition to an unactivated imine, leading to an N-centered radical. A catalytic cycle featuring regeneration of the metal catalyst by O2 and a second HAT to form the unprotected saturated N-heterocycle appears to be operative.

Characteristics of a Self-Forming Dynamic Membrane Coupled with a Bioreactor in Application of Anammox Processes.

A novel anammox self-forming dynamic membrane bioreactor (SFDMBR) was proposed to achieve an efficient anammox process with high biomass retention and cost-effective operation. The cake layer formed on nylon mesh (pore size, 20-25 µm) was referred to as a dynamic membrane (DM). The high permeability of the DM layer contributed to low transmembrane pressure (TMP), which kept below 10 kPa for 50 days in one filtration cycle of 82 days. Compared to the high TMP (mainly > 20 kPa) in the MBR using polyvinylidene fluoride (PVDF) microfiltration membrane, energy can be significantly conserved in the SFDMBR. Besides, the mature DM layer achieved efficient biomass retention comparable to that of PVDF membrane, which favored anammox bacteria enrichment. Concomitantly, an appropriate microenvironment for autotrophic anammox bacterial growth with well-controlled extracellular polymeric substances (EPS) concentration (33.22 mg·g-1 VSS) was achieved in SFDMBR. According to specific filtration resistance (SFR) analysis, reducing the EPS concentration in the bulk sludge improves sludge filterability and alleviate fouling, which was achieved in the SFDMBR system with a low SFR of 1.47 × 1012 m-1·kg-1. Our results show that the cost-effective operations and technical merits make anammox SFDMBRs promising for practical applications.

Rapid and Sensitive Quantification of Anammox Bacteria by Flow Cytometric Analysis Based on Catalyzed Reporter Deposition Fluorescence In Situ Hybridization.

The quantification of anammox bacteria is crucial to manipulation and management of anammox biosystems. In this study, we proposed a protocol specifically optimized for quantification of anammox bacteria abundance in anammox sludge samples using catalyzed reporter deposition-fluorescence in situ hybridization (CARD-FISH) and flow cytometry (FCM) in combination (Flow-CARD-FISH). We optimized the pretreatment procedures for FCM-compatibility, as well as the permeabilization, hybridization and staining protocols of the CARD-FISH. The developed method was compared with other methods for specific bacteria quantification (standard FISH, 16S rRNA sequencing and quantitative polymerase chain reaction). Anammox sludge samples could be disaggregated effectively by sonication (specific energy of 90 kJ·L-1 with MLVSS of 3-5 g·L-1) with the mixed ionic and nonionic dispersants Triton X-100 (5%) and sodium pyrophosphate (10 mM). Lysozyme treatment for permeabilizing bacterial cell walls and H2O2 incubation for completely quenching endogenous peroxidase of anammox sludges were essential to fluorescence enhancement and false positive signals control, respectively. Horseradish peroxidase molecules labeling at 20 °C for 12 h and the fluorescent tyramide labeling at 25 °C for 30 min with a fluorescent substrate concentration of 1:50 maintained the balance between increasing the signal and preventing nonspecific binding. Flow-CARD-FISH results showed that anammox bacteria absolute abundance in two different sludge samples were (2.31 ± 0.01) × 107 and (1.20 ± 0.06) × 107 cells·mL-1, respectively, with the relative abundances of 36.7 ± 4.1% and 26.5 ± 3.7%, respectively, comparable with those of qPCR and 16S rRNA sequencing analysis. The enhanced fluorescence signals induced by CARD-FISH combined with the high quantitative fluorescence sensitivity of FCM provide a rapid and sensitive method that yields accurate quantification results that will be valuable in future studies of microbial community determination.

Evidence of differential adaptation to decreased temperature by anammox bacteria.

Low temperature is recognized as one of the major barriers for the application of the anaerobic ammonium oxidation (anammox) process to treat mainstream wastewater. Studies are yet to reveal the underlying biological limitations and molecular mechanisms associated with the inhibition of low temperature on the anammox process. In this study, metaproteomics was used to examine proteome modulation patterns of the anammox community occurring at different temperatures. The anammox community remarkably altered their proteomes when the temperature decreased from 35 °C to 20 °C. This was especially for proteins involved in energy conversion, transcription and translation and inorganic ion transport. However, at 15 °C the anammox activities became distinctly inhibited, and there was evidence of energy limitations and severe stress in Candidatus Kuenenia and to a lesser degree in Candidatus Brocadia. Candidatus Jettenia exhibited more changes in its proteome at 15 °C. From the proteomes, at the lower temperatures there was evidence of stress caused by toxic nitrogen compounds or reactive oxygen species in the anammox bacteria. Hydroxylamine oxidoreductase (HAO)-like proteins and an oxidative stress response protein (a catalase) were in high abundance to potentially ameliorate these inhibitory effects. This study offers metaproteomic insight into the anammox community-based physiological response to decreasing temperatures.

CRISPR-Cas9 mediated gene knockout in human coronary artery endothelial cells reveals a pro-inflammatory role of TLR2.

Endothelial inflammatory responses promote the development and progression of atherosclerosis. It was reported that Toll-like receptors 2 (TLR2) is associated with endothelial inflammation. However, the effect of TLR2 on inflammatory responses in human coronary artery endothelial cells (HCAECs) remains largely unknown. Here, we tested the hypothesis that TLR2 can enhance inflammatory reactions in HCAECs after stimulated by TLR2 agonist. First, we used CRISPR-Cas9 technology to knockout TLR2 gene in HCAECs. Then, TLR2-KO and wild type HCAECs were treated with TLR2 agonist peptidoglycan (PGN). The expression levels of intercellular cell adhesion molecule-1 (ICAM-1), interleukin-6 (IL-6), and interleukin-8 (IL-8) were analyzed by real-time PCR, Western blot, and ELISA. The expression status of myeloid differentiation primary response gene 88 (MyD88), phosphorylated IRAK-1 (pIRAK-1) and phosphorylated NF-κB (pNF-κB) were detected by Western blot. Our results show that after treated with TLR2 agonist, the expression levels of ICAM-1, IL-6, and IL-8 were downregulated in TLR2-KO cells compared to those of wild type cells. Further, Western blots of MyD88, pIRAK-1, and pNF-κB show that the expression levels of these pro-inflammatory molecules were much lower in TLR2-KO cells compared to that of wild type cells by stimulating with TLR2 agonist. We suggest that TLR2 may affect inflammatory reaction in HCAECs by introducing pro-inflammatory molecules like MyD88, pIRAK-1, and pNF-κB.

Expression of the nirS, hzsA, and hdh Genes in Response to Nitrite Shock and Recovery in Candidatus Kuenenia stuttgartiensis.

In this study, Candidatus Kuenenia stuttgartiensis were subjected to distinct nitrite shocks (66 (control), 200, 300, 400, and 500 mg N/L), and the responses of mRNA levels of cytochrome cd1 nitrite/nitric oxide oxidoreductase (nirS), hydrazine synthase (hzsA), and hydrazine dehydrogenase (hdh) were assessed. Changes in the hydrazine dehydrogenase (HDH) protein level were monitored. At 200 mg NO2(-)-N/L, the normalized specific anaerobic ammonium-oxidizing activity (nSAA) slightly increased relative to the control despite a significant decrease in nirS, hzsA, and hdh mRNA levels. When nitrite increased to 300 and 400 mg N/L, increased nirS, hzsA, and hdh mRNA levels were observed, but the nSAA decreased, relative to the 200 mg NO2(-)-N/L exposure. HDH protein detection revealed that Candidatus Kuenenia stuttgartiensis attempted to yield high enzyme levels by stimulating mRNA synthesis to resist the nitrite-induced stress. On 500 mg NO2(-)-N/L shock, the nirS, hzsA, and hdh mRNA levels decreased, alongside decreased nSAA and HDH levels. Although the mRNA levels did not always coincide with activities, our findings advance understanding of the mechanisms that anammox bacteria use to cope with nitrite inhibition at the transcriptional and translational levels, which will improve the diagnostic accuracy of bioreactor failures when nitrite accumulation occurs.

Enantioselective Aza Michael-Type Addition to Alkenyl Benzimidazoles Catalyzed by a Chiral Phosphoric Acid.

Highly enantioselective Michael-type addition (MTA) reactions between N-protected alkenyl benzimidazoles and either pyrazoles or indazoles as nitrogen nucleophiles are accomplished for the first time using chiral phosphoric acid catalyst. Theoretical studies elucidated the reaction pathway and the origin of the stereochemical outcomes, where the catalyst substituent and the N-protecting group of benzimidazole contributed to the resulting high enantioselectivity.

The Thr241Met polymorphism in the XRCC3 gene is associated with increased risk of cancer in Chinese mainland populations.

The Thr241Met polymorphism in XRCC3 gene may affect the DNA repair pathways and be associated with the risk of cancer. However, the results of previous studies are inconsistent in Chinese mainland populations. The objective of this study is to investigate the association between the Thr241Met polymorphism in XRCC3 gene and risk of cancer for the Chinese Mainland populations by meta-analysis. We searched PubMed database, Embase database, CNKI database, and Wanfang database, and the last search was updated on July 24, 2013. Statistical analysis was performed using RevMan4.2 and Stata10.0 software. Finally, a total of 23 case-control studies in 23 articles were included. The results suggested a significant association between the Thr241Met polymorphism in XRCC3 gene and cancer risk in Chinese mainland populations (Met/Met + Thr/Met vs. Thr/Thr: OR = 1.25, 95 % CI = 1.02-1.54, P = 0.04). In the subgroup analyses by cancer types, significant associations were found in cervical cancer and nasopharyngeal cancer. The current meta-analysis suggested that the Thr241Met polymorphism in the XRCC3 gene may be a risk factor for cancer in Chinese mainland populations. In the future, more case-control studies are needed to validate these results.

Salt stimulates sulfide-driven autotrophic denitrification: Microbial network and metagenomics analyses.

Sulfur autotrophic denitrification (SADN) is a promising biological wastewater treatment technology for nitrogen removal, and its performance highly relies on the collective activities of the microbial community. However, the effect of salt (a prevailing characteristic of some nitrogen-containing industrial wastewaters) on the microbial community of SADN is still unclear. In this study, the response of the sulfide-SADN process to different salinities (i.e., 1.5 % salinity, 0.5 % salinity, and without salinity) as well as the involved microbial mechanisms were investigated by molecular ecological network and metagenomics analyses. Results showed that the satisfactory nitrogen removal efficiency (>97 %) was achieved in the sulfide-SADN process (S/N molar ratio of 0.88) with 1.5 % salinity. In salinity scenarios, the genus Thiobacillus significantly proliferated and was detected as the dominant sulfur-oxidizing bacteria in the sulfide-SADN system, occupying a relative abundance of 29.4 %. Network analysis further elucidated that 1.5 % salinity had enabled the microbial community to form a more densely clustered network, which intensified the interactions between microorganisms and effectively improved the nitrogen removal performance of the sulfide-SADN. Metagenomics sequencing revealed that the abundance of functional genes encoding for key enzymes involved in SADN, dissimilatory nitrate reduction to ammonium, and nitrification was up-regulated in the 1.5 % salinity scenario compared to that without salinity, stimulating the occurrence of multiple nitrogen transformation pathways. These multi-paths contributed to a robust SADN process (i.e., nitrogen removal efficiency >97 %, effluent nitrogen <2.5 mg N/L). This study deepens our understanding of the effect of salt on the SADN system at the community and functional level, and favors to advance the application of this sustainable bioprocess in saline wastewater treatment.

Innovative determination of the specific anammox activity for anammox sludge from continuous flow reactors: A comparison between continuous flow test and batch test.

A novel method for measuring specific anammox activity (SAA) was proposed based on continuous flow tests to accurately determine the SAA of anammox sludge from continuous flow reactors, resolving the challenges of inaccurate SAA assessment caused by substrate shock to anammox bacteria. Results showed SAA of expanded granular sludge bed sludge via batch tests (0.101 ± 0.018 g-N·g-VSS-1·d-1) was lower than continuous flow tests (0.206 ± 0.010 g-N·g-VSS-1·d-1) (p < 0.05), highlighting the impact of substrate shock. Conversely, SAA of sequencing batch reactor sludge assessed via batch tests (0.878 ± 0.008 g-N·g-VSS-1·d-1) was higher than continuous flow tests (0.809 ± 0.005 g-N·g-VSS-1·d-1) (p < 0.01), attributed to endogenous denitrification. The advantages of continuous flow tests over batch tests included milder feeding way, stricter anaerobic conditions, and minimal sampling impact on system. Our study contributes to more accurate measurements of SAA of anammox sludge from continuous flow reactors, favoring long-term robust operation of anammox reactors.