The high aggregation ability of anammox sludge has been extensively observed, but the cause for their aggregation is challenging. Here the structure and composition of extracellular polymeric ...substance (EPS) excreted from anammox sludge were systematically investigated to interpret the high aggregation ability. We combine results of contact angle, zeta potential and surface thermodynamics analysis as well as the following DLVO theory to address this issue. The results show that hydrophobic interaction is the main force determining the aggregation of anammox sludge. To go insight into inherent mechanism, Fourier transform infrared (FTIR) and x-ray photoelectron (XPS) spectroscopy were conducted and demonstrated there were comparatively few hydrophilic functional groups in the EPS of anammox sludge, compared to that of activated sludge, nitrifying and denitrifying sludge. Further, amino acid composition and secondary structure analyses of protein indicated that large amounts of hydrophobic amino acids and high level of protein loose structure for exposing inner hydrophobic groups of protein in EPS significantly contributed to the hydrophobic interaction and further to the high aggregation ability of anammox sludge, which is the critical finding of this work. This investigation is useful for understanding anammox bacteria and then for accelerating the application of the anammox process in wastewater treatment.
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•Hydrophobic interaction is main force determining high aggregation ability of anammox sludge.•More hydrophobic characteristics were detected in anammox EPS than other tested sludge.•Large amounts of hydrophobic amino acids in anammox EPS contributed to hydrophobic interaction.•High level of protein loose structure in anammox EPS also contributed to hydrophobic interaction.
Microplastic (MP) pollution poses a huge threat to agroecosystems, but the distribution characteristics of MPs in different types of farmland are still largely unknown. In this work, samples from six ...land-use types were collected from Chinese farmlands in five provinces. It was found that MP abundances were in the range of 2783–6366 items/kg in all samples. MP distribution results showed that over 80% of particles were less than 1 mm, and that MP sizes ranging between 0.02 and 0.2 mm represented the greatest proportion. The particle shape classified as fragment (with edges and angular) was the most frequent shape, with an abundance of approximately 54.05%. Polyethylene (PE) and polyamides (PA) were the most abundant polymers in cropped lands; 20.88% and 20.31%, respectively. Statistical analyses showed that lands used for plastic mulching (mulch film and greenhouse crops) had a significantly higher particle abundance, hence identifying plastic mulching as a major contributor to MP pollution in agricultural lands. Furthermore, paddy lands had a significantly higher MP abundance than wheat lands. Variation analyses of MP characteristics revealed that cereal crop farmlands (wheat, paddy land) were more likely to contain fibrous shapes and large MP particles (1–5 mm). Economically important tree lands (orchards, woodlands) were likely to contain fragment shapes and pony-size MPs (0.02–0.2 mm). Discrepancies among farmlands may depend on various reasons, such as mulching plastic application, irrigation, atmospheric fallout, etc. This study provides firsthand evidences about the characteristics of MP pollution in farmlands and explores some predominant MP sources in agroecosystems.
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•MPs pollution of different land-use types of farmland was studied.•The plastic mulching lands exhibited significantly higher particle abundances.•The MP abundances were significantly higher in paddy lands than wheat lands.•Fibers and large particle size (1–5 mm) dominated the MPs in cereal crops farmlands.•Fragment shapes and pony-size MPs (<0.2 mm) were abundant in economical tree lands.
The MP distribution in six land-use types were distinctive, where cereal croplands were more fibers and large MPs, but economical tree lands were fragments and small MPs.
The recent discovery of comammox Nitrospira as complete nitrifiers has fundamentally renewed perceptions of nitrogen cycling in natural and engineered systems, yet little is known about the ...environmental controls on these newly recognized bacteria. Based on improved phylogenetic resolution through successful assembly of ten novel genomes (71-96% completeness), we provided the first biogeographic patterns for planktonic and benthic comammox Nitrospira in the Yangtze River over a 6030 km continuum. Our study revealed the widespread distributions and relative abundance of comammox Nitrospira in this large freshwater system, constituting 30 and 46% of ammonia-oxidizing prokaryotes (AOPs) and displaying 30.4- and 17.9-fold greater abundances than canonical Nitrospira representatives in water and sediments, respectively. Comammox Nitrospira contributed more to nitrifier abundances (34-87% of AOPs) in typical oligotrophic environments with a higher pH and lower temperature, particularly in the plateau (clade B), mountain and foothill (clade A) areas of the upper reach. The dominant position of planktonic comammox Nitrospira was replaced by canonical Nitrospira sublineages I/II and ammonia-oxidizing bacteria from the plateau to downstream plain due to environmental selection, while the dissimilarity of benthic comammox Nitrospira was moderately associated with geographic distance. A substantial decrease (83%) in benthic comammox Nitrospira abundance occurred immediately downstream of the Three Gorges Dam, consistent with a similarly considerable decrease in overall sediment bacterial taxa. Together, this study highlights the previously unrecognized dominance of comammox Nitrospira in major river systems and underlines the importance of revisiting the distributions of and controls on nitrification processes within global freshwater environments.
Increasing attention has been paid to the anammox community for its significant function in high-efficiency wastewater treatment. However, bacterial interaction in terms of bacterial communication is ...still elusive. This study firstly explored the intra- and interspecific communication of bacteria in the anammox community using metagenomic sequence data obtained during bioreactor operation. We verified the existence of multiple bacterial communication gene (BCG) subtypes by alignment with the constructed BCG database containing 11 identified gene subtypes. Bacterial communication was more active at the initial start-up than in the high loading-rate phase, and was correlated with the gradually decreasing bacterial diversity. Hdts, one of the key genes that produced the intraspecific signaling molecule AHL, and RpfF, the key gene that produced the intra- and interspecific signaling molecule DSF, were the primary communication engines in the anammox community because of their high abundance. Anammox bacteria mainly used Hdts genes to communicate with others, while RpfF gene played a core role characterized by their multiple correlations with other BCG subtypes. Interestingly, bacteria with abundant BCGs were more inclined to interact with the bacteria with the same functional traits, indicating the potential communication-related interaction among these bacteria in addition to the frequently reported substrate co-utilization. This highlights the primary importance of AHL and DSF for the anammox community, and thereby hints at a potential strategy for the target regulation of the signals to improve anammox viability and competitive capacity in wastewater treatment.
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•Intra- and interspecific bacterial communication in anammox culture are verified.•HdtS and RpfF genes are important engines for communication during start-up.•Anammox bacteria use HdtS genes to communicate.•RpfF genes plays a core role in intra- and interspecific species communication.•Bacteria are inclined to communicate with other bacteria with the same function.
The ability of anammox bacteria to utilize organic matter has drawn extensive attention. However, the metabolic discrepancies between autotrophic and mixotrophic anammox consortia need to be further ...explored. Here, microbial transcript and metabolomic analysis were conducted for the samples harvested in the reactors and batch assays to investigate the phenotype discrepancies and intrinsic causes in autotrophic and mixotrophic anammox consortia. Results showed that metabolically active community structures did not show significant difference between autotrophic and mixotrophic anammox consortia (C/N = 0.3). Changes in the metabolic state were the main cause for those discrepancies in virtue of the added acetate oxidized via the acetyl-CoA pathway by mixotrophic anammox bacteria. At C/N ratio of 0.3, anammox activity was obviously promoted compared to that in the autotrophic condition, due to higher levels of NADH and NAD+, as well as ATP consumption. Mixotrophic anammox consortia were found to yield more biomass, resulting from enhanced purine, pyrimidine, and putrescine synthetic pathways for regulating bacterial growth. Up-regulated amino sugar and nucleotide sugar metabolism pathways participating in regulating more extracellular polysaccharides secreted by mixotrophic anammox consortia. In adverse environment with higher COD concentration, more extracellular proteins were produced by anammox consortia to protect themselves and amino acids also accumulated in the cell. This study provides useful information to catch the optimal metabolism way of anammox consortia and accelerate anammox bacterial cultivation or reactor startup for wastewater treatment.
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•Changes of metabolic state are in charge of discrepant consortia phenotypes.•Higher levels of NADH(NAD+), ATP consumption led to high mixotrophic anammox consortia activity.•Elevated metabolic polyamine, Pyr and Pur promoted anammox growth rate feeding with acetate.•Up-regulated amino and nucleotide sugar metabolism via UDP-Glc and UDP-Gal resulted in more PS.•Amino acids tended to accumulate to cope with environmental stress in anammox consortia.
•Autotrophs and heterotrophs in anammox systems are versatile in using organics.•Endogenous organics facilitate biofilm formation and cross-feeding interactions.•19 core and 7 keystone taxa are ...identified based on 149 wastewater anammox samples.•Appropriate organics management is key to enhancing nitrogen removal by anammox.
Anaerobic ammonium oxidation (anammox) represents a promising technology for wastewater nitrogen removal. Organics management is critical to achieving efficient and stable performance of anammox or integrated processes, e.g., denitratation-anammox. The aim of this systematic review is to synthesize the state-of-the-art knowledge on the multifaceted impacts of organics on wastewater anammox community structure and function. Both exogenous and endogenous organics are discussed with respect to their effects on the biofilm/granule structure and function, as well as the interactions between anammox bacteria (AnAOB) and a broad range of coexisting functional groups. A global core community consisting of 19 taxa is identified and a co-occurrence network is constructed by meta-analysis on the 16S rDNA sequences of 149 wastewater anammox samples. Correlations between core taxa, keystone taxa, and environmental factors, including COD, nitrogen loading rate (NLR) and C/N ratio are obtained. This review provides a holistic understanding of the microbial responses to different origins and types of organics in wastewater anammox reactors, which will facilitate the design and operation of more efficient anammox-based wastewater nitrogen removal process.
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•Verified the existence of QS communication system among anammox bacteria.•Confirmed the release of C6-HSL, C8-HSL, C12-HSL by anammox culture.•C6-HSL and C8-HSL increased activity ...and growth rate of anammox bacteria.•Additional signals activated bacteria by inducing endogenous signals in bacteria.•Opened a new window to accelerate the start-up period of anammox reactor.
Quorum sensing (QS) is a microorganism communication system. This study verified the potential existence of the QS system among ANaerobic AMMonium OXidation (anammox) bacteria. The release of three Acyl Homoserine Lactones (AHLs; C6-HSL, C8-HSL, C12-HSL) by anammox culture was confirmed. By conducting series of batch test, the introduction of exogenous C6-HSL and C8-HSL could significantly increase activity of anammox bacteria, and meanwhile, C6-HSL significant increased the growth rate, finally resulting in the increased ammonium nitrogen removal performance of 35% and 20%, respectively, whereas the exogenous C12-HSL apparently promoted the growth of heterotrophic bacteria in the community. To further identify how exogenous signal molecular affects anammox culture, analyses of anammox culture supernatant and biomass extraction revealed that these additional signal molecules activated bacteria by inducing the production of endogenous signal molecular by anammox culture. This study might open a new window to overcome the disadvantage of the long-start-up period of anammox reactor restricting the development of current anammox process.
The anaerobic ammonium oxidation (anammox) is becoming a critical technology for energy neutral in mainstream wastewater treatment. However, the presence of chemical oxygen demanding in influent ...would result in a poor nitrogen removal efficiency during the deammonification process. In this study, the simultaneous partial nitrification, anammox and denitrification process (SNAD) for mainstream nitrogen removal was investigated in an integrated fixed film activated sludge (IFAS) reactor. SNAD-IFAS process achieved a total nitrogen (TN) removal efficiency of 72 ± 2% and an average COD removal efficiency was 88%. The optimum COD/N ratio for mainstream wastewater treatment was 1.2 ± 0.2. Illumina sequencing analysis and activity tests showed that anammox and denitrifying bacteria were the dominant nitrogen removal microorganism in the biofilm and the high COD/N ratios (≥2.0) leaded to the proliferation of heterotrophic bacteria (Hydrogenophaga) and nitrite-oxidizing bacteria (Nitrospira) in the suspended sludge. Network analysis confirmed that anammox bacteria (Candidatus Kuenenia) could survive in organic matter environment due to that anammox bacteria displayed significant co-occurrence through positive correlations with some heterotrophic bacteria (Limnobacter) which could protect anammox bacteria from hostile environments. Overall, the results of this study provided more comprehensive information regarding the community composition and assemblies in SNAD-IFAS process for mainstream nitrogen removal.
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•SNAD-IFAS process was feasible for mainstream nitrogen removal.•The optimum COD/N ratio for mainstream nitrogen removal by SNAD-IFAS was 1.2 ± 0.2.•Biodiversity of heterotrophic bacteria and NOB both increased with COD increasing.•Anammox displayed significant co-occurrence with some heterotrophic bacteria.
Acyl-homoserine lactones (AHLs)-mediated quorum sensing in bacterial communities have been extensively observed. However, the metabolic pathways regulated by AHLs in bacteria remain elusive. Here, we ...combined long-term reactor operation with microbiological and metabolomics analyses to explore the regulatory pathways for different AHLs in anammox consortia, which perform promising nitrogen removal for wastewater treatment. The results showed that no obvious shifts induced by exogenous AHLs occurred in the microbial community and, mainly, dosing AHLs induced changes in the metabolites. 3OC6-HSL, C6-HSL, and C8-HSL controlled the electron transport carriers that influence the bacterial activity. In contrast, only 3OC6-HSL regulated LysoPC(20:0) metabolism, which affected bacterial growth. AHLs mainly regulated the synthesis of the amino acids Ala, Val, and Glu and selectively regulated Asp and Leu to affect extracellular proteins. Simultaneously, all the AHLs regulated the ManNAc biosynthetic pathways, while OC6-HSL, OC8-HSL, and C6-HSL particularly enriched the UDP-GlcNAc pathway to promote exopolysaccharides, resulting in different aggregation levels of the anammox consortia. Our results not only provide the first metabolic insights into the means by which AHLs affect anammox consortia but also hint at potential strategies for overcoming the limitations of the long start-up period required for wastewater treatment by anammox processing.
Photocatalysis holds great promise as an efficient and sustainable oxidation technology for application in wastewater treatment. Rapid progress developing novel materials has propelled photocatalysis ...to the forefront of sustainable wastewater treatments. This review presents the latest progress on applications of photocatalytic wastewater treatment. Our focus is on strategies for improving performance. Challenges and outlooks in this promising field are also discussed. We hope this review will help researchers design low-cost and high-efficiency photocatalysts for water treatment.
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