Effects of high organic load on amoA and nirS gene diversity of an intermittently aerated and fed membrane bioreactor treating landfill leachate

Loss of submerged macrophytes in shallow lakes alters bacterial and archaeal community structures, and reduces their co-occurrence networks connectivity and complexity

Introduction

Bacteria and archaea are important components in shallow lake ecosystems and are crucial for biogeochemical cycling. While the submerged macrophyte loss is widespread in shallow lakes, the effect on the bacteria and archaea in the sediment and water is not yet widely understood.

Methods

In this study, 16S rRNA gene sequencing was used to explore the bacteria and archaea in samples taken from the sediment and water in the submerged macrophyte abundant (MA) and submerged macrophyte loss (ML) areas of Caohai Lake, Guizhou, China.

Results

The results showed that the dominant bacterial phyla were Proteobacteria and Chloroflexi in the sediment; the dominant phyla were Proteobacteria, Actinobacteriota, and Bacteroidota in the water. The dominant archaea in sediment and water were the same, in the order of Crenarchaeota, Thermoplasmatota, and Halobacterota. Non-metric multidimensional scaling (NMDS) analyses showed that bacterial and archaeal community structures in the water were significantly affected by the loss of submerged macrophytes, but not by significant changes in the sediment. This suggests that the loss of submerged macrophytes has a stronger effect on the bacterial and archaeal community structures in water than in sediment. Furthermore, plant biomass (PB) was the key factor significantly influencing the bacterial community structure in water, while total nitrogen (TN) was the main factor significantly influencing the archaeal community structure in water. The loss of submerged macrophytes did not significantly affect the alpha diversity of the bacterial and archaeal communities in either the sediment or water. Based on network analyses, we found that the loss of submerged macrophytes reduced the connectivity and complexity of bacterial patterns in sediment and water. For archaea, network associations were stronger for MA network than for ML network in sediment, but network complexity for archaea in water was not significantly different between the two areas.

Discussion

This study assesses the impacts of submerged macrophyte loss on bacteria and archaea in lakes from microbial perspective, which can help to provide further theoretical basis for microbiological research and submerged macrophytes restoration in shallow lakes.

Responses of rhizosphere microbial community structure and metabolic function to heavy metal coinhibition

Metal mineral mining results in releases of large amounts of heavy metals into the environment, and it is necessary to better understand the response of rhizosphere microbial communities to simultaneous stress from multiple heavy metals (HMs), which directly impacts plant growth and human health. In this study, by adding different concentrations of cadmium (Cd) to a soil with high background concentrations of vanadium (V) and chromium (Cr), the growth of maize during the jointing stage was explored under limiting conditions. High-throughput sequencing was used to explore the response and survival strategies of rhizosphere soil microbial communities to complex HM stress. The results showed that complex HMs inhibited the growth of maize at the jointing stage, and the diversity and abundance of maize rhizosphere soil microorganisms were significantly different at different metal enrichment levels. In addition, according to the different stress levels, the maize rhizosphere attracted many tolerant colonizing bacteria, and cooccurrence network analysis showed that these bacteria interacted very closely. The effects of residual heavy metals on beneficial microorganisms (such as Xanthomonas, Sphingomonas, and lysozyme) were significantly stronger than those of bioavailable metals and soil physical and chemical properties. PICRUSt analysis revealed that the different forms of V and Cd had significantly greater effects on microbial metabolic pathways than all forms of Cr. Cr mainly affected the two major metabolic pathways: microbial cell growth and division and environmental information transmission. In addition, significant differences in rhizosphere microbial metabolism under different concentrations were found, and this can serve as a reference for subsequent metagenomic analysis. This study is helpful for exploring the threshold for the growth of crops in toxic HM soils in mining areas and achieving further biological remediation.

Landfill: An eclectic review on structure, reactions and remediation approach

Since the enactment of the Clean Water Act (1972), which was supplemented by increased accountability under Resource Conservation and Recovery Act (RCRA) Subtitle D (1991) and the Clean Air Act Amendments (1996), landfills have indeed been widely used all around the world for treating various wastes. The landfill's biological and biogeochemical processes are believed to be originated about 2 to 4 decades ago. Scopus and web of Science based bibliometric study reveals that there are few papers available in scientific domain. Further, till today not a single paper demonstrated the detailed landfills heterogenicity, chemistry and microbiological processes and their associated dynamics in a combined approach. Accordingly, the paper addresses the recent applications of cutting-edge biogeochemical and biological methods adopted by different countries to sketch an emerging perspective of landfill biological and biogeochemical reactions and dynamics. Additionally, the significance of several regulatory factors controlling the landfill's biogeochemical and biological processes is highlighted. Finally, this article emphasizes the future opportunities for integrating advanced techniques to explain landfill chemistry explicitly. In conclusion, this paper will provide a comprehensive vision of the diverse dimensions of landfill biological and biogeochemical reactions and dynamics to the scientific world and policymakers.

The positive roles of influent species immigration in mitigating membrane fouling in membrane bioreactors treating municipal wastewater

The influence of influent species immigration (ISI) on membrane fouling behaviors of membrane bioreactors (MBRs) treating municipal wastewater remains elusive, leading to an incomprehensive understanding of fouling ecology in MBRs. To address this issue, two anoxic/aerobic MBRs, which were fed with raw (named MBR-C) and sterilized (MBR-E) municipal wastewater, were operated. Compared with the MBR-E, the average fouling rate of the MBR-C was lowered by 30% over the long-term operation. In addition, the MBR-E sludge had significantly higher unified membrane fouling index and biofilm formation potential than the MBR-C sludge. Considerably larger flocs size and lower soluble microbial products (SMP) concentrations were observed in the MBR-C than in the MBR-E. Moreover, the 16S rRNA gene sequencing results showed that highly diverse and abundant populations responsible for floc-forming, hydrolysis/fermentation and SMP degradation readily inhabited the influent, shaping a unique microbial niche. Based on species mass balance-based assessment, most of these populations were nongrowing and their relative abundances were higher in the MBR-C than in the MBR-E. This suggested an important contribution of the ISI on the assemblage of these bacteria, thus supporting the increased flocs size and lowered SMP concentrations in the MBR-C. Moreover, the SMP-degrading related bacteria and functional pathways played a more crucial role in the MBR-C ecosystem as revealed by the bacterial co-occurrence network and Picrust2 analysis. Taken together, this study reveals the positive role of ISI in fouling mitigation and highlights the necessity for incorporating influent wastewater communities for fouling control in MBR plants.

Exploiting refractory organic matter for advanced nitrogen removal from mature landfill leachate via anammox in an expanded granular sludge bed reactor

Anammox is an efficient low-carbon nitrogen removal technology for mature landfill leachate (MLL). However, it produces 11 % nitrate theoretically, which needs further removal. In this study, the mechanisms of exploiting refractory organic matter (ROM) from an MLL as an inner carbon source for advanced nitrogen removal via anammox were systematically analyzed, and the effects of hydraulic retention time on nitrogen and ROM removal/utilization were investigated. Without any external carbon source, a total nitrogen and organic carbon removal efficiency of 94.50 % and 27.12 %, respectively, were achieved, with a nitrogen loading rate of 2.4 kg N/(m³·d). The abundances of norank_f_norank_o_SBR1031, OLB13, and norank_f_A4b, which had the capacity to degrade ROM, increased from 21.63 % to 49.21 %. This study reveals that the ROM in an MLL can be exploited for synchronous advanced nitrogen and organic matter removal.

Bacterial dynamics and functions driven by biomass wastes to promote rural toilet blackwater absorption and recycling in an ectopic fermentation system

Due to high concentration of organic matter and the ease of disease transmission, blackwater pose a serious threat to both the environment and human health, especially in rural areas where wastewater treatment is dispersed. The reuse of biomass waste is also a difficult issue to be addressed urgently. In this study, an ectopic fermentation system (EFS) was used to treat toilet blackwater, and the effects of different biomass waste combinations on bacterial communities and functions during aerobic fermentation of blackwater were compared. The results showed that adding bran powder prolonged the high temperature period of 11 d, improved blackwater absorption capacity by 7.5% and was beneficial to microbial metabolic activities to enhance organic degradation. By contrast, the combination of corn straw and rice husk obtained abundant bacterial OTUs and diversity. Bacillus, Thermobifida and Thermopolyspora were the main microorganisms involved in the degradation of organic matter in EFS, and their abundance varied in different filler combinations. Bacterial communities were directly affected by environmental factors such as temperature, NH₄⁺-N and organic carbon as well as biomass materials during fermentation. This study revealed the role of corn straw, rice husk and bran powder in EFSs, provided new technical support for blackwater treatment and a new direction for the resource utilization of agricultural biomass waste.

Treatment of nanofiltration concentrate of landfill leachate using advanced oxidation processes incorporated with bioaugmentation

Advanced oxidation processes have been broadly applied in wastewater treatment, but few studies have focused on its degradative effect on refractory organic contaminants in membrane concentrates of landfill leachate. In this study, the treatment effects of advanced oxidation processes including electrocoagulation (EC), ozone (OZ), anodic oxidation (AO) and electro-Fenton (EF) incorporated with genetically engineered nitrifying bacteria Rhodococcus erythropolis expressing Nirs and AMO (rRho-NM) on nanofiltration concentrate (NFC) of old landfill leachate were investigated in a lab-scale experiment. The results showed that advanced oxidation processes degraded the refractory organic contaminants including coagulation-resistant substances (CRS), humic acid (HA), fulvic acid (FvA), macro molecular organics (MMOs) and benzene ring compounds (BRCs) and increased the biodegradability in NFC of old landfill leachate. Compared to activated sludge (AS), rRho-NM exhibited an excellent removal performance for total organic carbon (TOC), ammonia nitrogen (NH₄-N), total nitrogen (TN), biochemical oxygen demand (BOD) and chemical oxygen demand (COD) for advanced oxidation processes-treated NFC of old landfill leachate. Advanced oxidation processes incorporated with bioaugmentation demonstrated an outstanding degradation performance for removing refractory organic contaminants, TOC, NH₄-N, TN, BOD, COD and heavy metal in NFC of old landfill leachate. In addition, OZ incorporated with rRho-NM (OZ-rRho-NM) showed the optimal removal efficacy in reduction of refractory organic contaminants, TOC, NH₄-N, TN, BOD and COD, the shortest hydraulic retention time (HRT) and the minimum energy consumption in NFC of landfill leachate. Furthermore, the cheapest treatment cost for NFC could be achieved by EC incorporated with rRho-NM (EC-rRho-NM). More impressively, rRho-NM remained stable in expressing Nirs and AMO genes, increased nitrification and denitrification rate, and improved MBR effluent quality in the treatment of NFC. In conclusion, this work provides new insights into the application of advanced oxidation processes incorporated with bioaugmentation using rRho-NM for the treatment of NFC of old landfill leachate.

Nitrification resistance and functional redundancy maintain the system stability of partial nitrification in high-strength ammonium wastewater system

The sudden change of ammonia loading in high-strength ammonium wastewater treatment can directly affect the system stability by altering microbial community dynamics. To maintain the system stability, the effects of ammonia shock loading on microbial community dynamics must be studied. Two sets of sequencing batch reactors were operated with 6 shock cycles (maximum volumetric loading rate of 1928 mg N/(L·d)). CN system contained both organic carbon and ammonia and N system contained only ammonia. Comparing with N system, CN system operated more stably and had higher nitrite accumulation rate. Free ammonia (FA) was the select stress for the turnover of CN microbial communities, while the N communities didn t shift much. The increase of Nitrosomonas and the appearance of heterotrophic nitrification-aerobic denitrification bacteria in CN system presented its resistance and redundancy against FA impact, while the increase of functional genes exhibited functional genes redundancy which maintained the system stability.

Performance exploration and microbial dynamics of urine diverting composting toilets in rural China

The ongoing "toilet revolution" in China provides new opportunities to improve the rural living environment and sanitation, and the introduction of new sanitation facilities such as urine diverting composting toilets (UDCTs) is conducive to the effective treatment and resource utilization of feces. This study revealed the degradation performance and microbial community dynamics of UDCTs and clarified the influence mechanism of fecal volume in aerobic composting treatment. The results showed that UDCTs could effectively decompose human feces, with an organic matter degradation rate of 25%⁓30%. The temperature, water content, NH₄⁺-N and nutrient accumulation were higher in the high fecal volume treatment than in the low fecal volume treatment. Bacterial community composition and structure in UDCTs varied with composting stage and fecal volume. The diversity and richness of bacterial community in compost were changed with different fecal volumes, but the dominant groups were similar. Redundancy analysis (RDA) showed that nitrogen and organic carbon were the main drivers of bacterial community changes during composting. Highly nutritious and non-phytotoxic compost products were suitable for agronomic uses. Based on these results, UDCTs can be an effective way to solve the problem of fecal pollution in rural areas, and fecal dosage is a potential influencing factor in the operation and maintenance of composting systems.

Key enzymes involved in anammox-based processes for wastewater treatment: An applied overview

The anaerobic ammonium oxidation (anammox) process has attracted significant attention as an economic, robustness, and sustainable method for the treatment of nitrogen (N)-rich wastewater. Anammox bacteria (AnAOB) coexist with other microorganisms, and particularly with ammonia-oxidizing bacteria (AOB) and/or heterotrophic bacteria (HB), in symbiosis in favor of the substrate requirement (ammonium and nitrite) of the AnAOB being supplied by these other organisms. The dynamics of these microbial communities have a significant effect on the N-removal performance, but the corresponding metabolic pathways are still not fully understood. These processes involve many common metabolites that may act as key factors to control the symbiotic interactions between these organisms, to maximize N-removal efficiency from wastewater. Therefore, this work overviews the current state of knowledge about the metabolism of these microorganisms including key enzymes and intermediate metabolites and summarizes already reported experiences based on the employment of certain metabolites for the improvement of N-removal using anammox-based processes. PRACTITIONER POINTS: Approaches knowledge about the biochemistry and metabolic pathways involved in anammox-based processes. Some molecular tools can be used to determine enzymatic activity, serving as an optimization in nitrogen removal processes. Enzymatic evaluation allied to the physical-chemical and biomolecular analysis of the nitrogen removal processes expands the application in different effluents.

Identification of key water parameters and microbiological compositions triggering intensive N2O emissions during landfill leachate treatment process

Landfill leachate treatment processes tend to emit more N₂O compared to domestic wastewater treatment. This discrepancy may be ascribed to leachate water characteristics such as high refractory COD, ammonium (NH₄⁺) content, and salinity. In this work, the leachate influent was varied to examine the N₂O emission scenarios. NH₄⁺-N, COD, and Cl^- concentrations ranged between 1000-2500, 1000-10,000, and 500-3000 mg L^-1, respectively. Simultaneously, we attempted to combine statistical analysis with high-throughput sequencing to understand the microbial mechanism with regards to N₂O emission. Results show that the strong N₂O emissions occur in the nitrifying tank due to the intensive aeration. The system receiving the lowest COD shows the maximum N₂O emission factor of 42.7% of the removed nitrogen. Both redundancy analysis and a structural equation model verify that insufficient degradable organics are the key water parameter triggering intensive N₂O emission within the designed influent limits. Furthermore, two essential but non-abundant functional bacteria, Flavobacterium (acting as a denitrifier) and Nitrosomonas (acting as a nitrifier), are identified as the core functional species that dramatically influence N₂O emissions. An increase in influent COD promotes the proliferation of Flavobacterium and inhibits Nitrosomonas, which in turn reduce N₂O release. Meanwhile, two keystone species of Castellaniella and Saprospiraceae unclassified are recognized. They may supply a suitable niche and integrity of the microbial community for N-cycle functional bacteria. These findings reveal the essential role of non-abundant species in microbial community, and expand the current understanding of microbial interactions underlying N₂O dynamics in leachate treatment systems.

Activated sludge microbial communities and hydrolytic potential in a full-scale SBR system treating landfill leachate

Landfill leachate, due to its recalcitrant nature and toxicity, poses a serious environmental threat, which requires the implementation of effective treatment processes. In this work, a full-scale treatment system consisting of two Sequencing Batch Reactors (SBRs) was used for the processing of landfill leachate of intermediate to mature age (BOD/COD ratio of 0.16). Biosystem operation resulted in BOD₅, COD and TKN removal efficiencies of 81%, 39% and 76%, respectively, whereas the low residual NO₃^--N concentration in the effluent (4.01 ± 0.10 mg/L) was indicative of the efficient denitrification process. Assessment of hydrolytic potential of activated sludge revealed high endocellular and extracellular lipase activities, which reached values up to 206 and 141 U/g protein respectively, possibly as the consequence of plastics degradation during maturation process. Implementation of Illumina sequencing indicated the predominance of Alphaproteobacteria, accompanied by members of Bacteroidetes, Betaproteobacteria and Chloroflexi. Paracoccus was the predominant genus identified, followed by representatives of the genera Bellilinea, Flavobacterium, Thauera and Truepera. Nitrosomonas was the major ammonia-oxidizing bacterium (AOB), while nitrite oxidation was mainly achieved by the uncultured nitrite-oxidizing bacterium (NOB) Candidatus Nitrotoga.

COD/TN ratios shift the microbial community assembly of a pilot-scale shortcut nitrification-denitrification process for biogas slurry treatment

In this study, effects of carbon to nitrogen (COD/TN) ratios of biogas slurry on shortcut nitrification-denitrification in a pilot-scale integrated fixed film activated sludge (IFAS) system were investigated. Lowering the COD/TN ratio from 11.7 to 6.2 exerted a negative impact on shortcut nitrification-denitrification performance. Accordingly, the NH₃-N and TN removal rates decreased from 94.4 to 91.2% and 92.3 to 85.9%, respectively. The dynamics of microbial assembly was analyzed by MiSeq sequencing, and the denitrifying functional genes were quantified by qPCR. The results showed that ammonia oxidizing bacteria and amoA gene were more abundant on the biofilm of oxic tank, indicating they play a key role in NH₃-N removal. Autotrophic, endogenous, and fast heterotrophic kinetics denitrifiers were coexisted and enriched in the IFAS system with a decreasing of COD/TN ratio. TN removal was mainly affected by denitrifiers (including Arenimonas, Acidovorax, and Thaurea) harboring narG and nirS genes. Canonical correspondence analysis proved that COD/TN ratio was the most critical factor driving the succession of microbial community. Dissolved oxygen (DO) and pH were found positively correlated with denitrifiers at low COD/TN ratio conditions. As a result, NH₃-N and TN removal were effectively enhanced when the DO level in the oxic tank of IFAS system was increased to 1.0-3.0 mg/L.

Purposely Development of the Adaptive Potential of Activated Sludge from Municipal Wastewater Treatment Plant Focused on the Treatment of Landfill Leachate

Biological treatment is a key technology in landfill leachate treatment However, often its efficiency is not high enough due to the pollutants in concentrations above the critical ones. The present study aimed to investigate the adaptive responses that occur in activated sludge (AS) during landfill leachate purification. A model process with AS from a municipal wastewater treatment plant and landfill leachate in increasing concentrations was constructed. The data showed that when dilutions 25 and 50 times had been applied the structure of the AS was preserved, but the COD cannot be reduced below 209 mg O2/L. The feed of undiluted leachate destroyed the AS structure as SVI was reduced to 1 mL/g, biotic index to 1, floc size was greatly reduced and COD remained high (2526 mg O2/L). The dominant group of protozoa was changed from attached to free-swimming ciliates. An increase of the bacterial groups responsible for the xenobiotics elimination (aerobic heterotrophs, genera Pseudomonas, Acinetobacter, Azoarcus, Thauera, Alcaligenes) was registered. This was accompanied by a significant increase in free bacteria. The obtained data showed that for optimal treatment of this type of water it is necessary to include a combination of biological treatment with another non-biological method (membrane filtration, reverse osmosis, etc.).

Culturing sludge fermentation liquid-driven partial denitrification in two-stage Anammox process to realize advanced nitrogen removal from mature landfill leachate

The two-stage partial nitrification (PN)-Anammox process, during long term treatment of high-ammonia nitrogen leachate, faces challenges such as the adaptation of nitrite oxidation bacteria (NOB) and failure of real-time control of pH. Resultant instabilities including NH₄⁺-N and NO₃^--N accumulation were overcome by culturing sludge fermentation liquid (SFL)-driven partial denitrification (PD) in situ in the Anammox process. Biodegradation of slowly biodegradable organics (SBO) in SFL created organics restriction condition, which limited the activity of denitrification bacteria and achieved its balance with Anammox bacteria. Produced NO₃^--N is reduced to NO₂^--N through PD, which further improved the removal of NH₄⁺-N through Anammox. NO₂^--N was utilized timely by Anammox bacteria, which avoid further reduction of NO₂^--N to N₂, and result in a high nitrate to nitrite transformation ratio (NTR) of 93.3%. Satisfactory nitrogen removal efficiency (NRE) and nitrogen removal rate (NRR) of 99.6% and 822.0 ± 9.0 g N/(m³∙d) were obtained, respectively. Key genera related to degradation of SBO, PD and Anammox were enriched. The value of narG/(nirK+nirS) increased from 0.05 on day 1-0.15 on day 250. Combining SFL-driven PD with two-stage Anammox process provided a novel insight for applying this process to realize advanced nitrogen removal in practical engineering.

Advances in Biological Nitrogen Removal of Landfill Leachate

With the development of economy and the improvement of people’s living standard, landfill leachate has been increasing year by year with the increase in municipal solid waste output. How to treat landfill leachate with high efficiency and low consumption has become a major problem, because of its high ammonia nitrogen and organic matter content, low carbon to nitrogen ratio and difficult degradation. In order to provide reference for future engineering application of landfill leachate treatment, this paper mainly reviews the biological treatment methods of landfill leachate, which focuses on the comparison of nitrogen removal processes combined with microorganisms, the biological nitrogen removal methods combined with ecology and the technology of direct application of microorganisms. In addition, the mechanism of biological nitrogen removal of landfill leachate and the factors affecting the microbial activity during the nitrogen removal process are also described. It is concluded that the treatment processes combined with microorganisms have higher nitrogen removal efficiency compared with the direct application of microorganisms. For example, the nitrogen removal efficiency of the combined process based on anaerobic ammonium oxidation (ANAMMOX) technology can reach more than 99%. Therefore, the treatment processes combined with microorganisms in the future engineering application of nitrogen removal in landfill leachate should be paid more attention to, and the efficiency of nitrogen removal should be improved from the aspects of microorganisms by considering factors affecting its activity.

Partial-nitritation of low-strength anaerobic effluent: A moderate-high dissolved oxygen concentration facilitates ammonia-oxidizing bacteria disinhibition and nitrite-oxidizing bacteria suppression

Integrating anaerobic treatment with partial nitritation (PN)/anammox is a promising technology to achieve energy-efficient wastewater treatment, while partial nitritation of the mainstream anaerobic effluent (Aneff) was rarely reported. A PN reactor fed with low-strength Aneff was employed in this study to investigate the performance and technology bottleneck of this process. When operated at low dissolved oxygen (DO) concentration (0.30-0.43 mg/L), gene coding hydroxylamine oxidation (hao) was severely suppressed by bio-refractory organics, which results in a decreased ammonia-oxidizing bacteria activity and nitrite accumulation rate. The ammonium conversion and nitrite accumulation were recovered by increasing the DO concentration to a moderate-high level (1.10 ± 0.20 mg/L) and achieved long-term stable operation. At this condition, hao showed a dramatic increase while gene encoding nitrite oxidoreductase was appropriately suppressed; the effluent NO₂^-/NH₄⁺ ratio reached 1.17, and a low NO₃^-/NO_x^- ratio of 0.38 was achieved simultaneously. The findings in this study revealed the adverse effects of Aneff on PN and supported a practical operating strategy for efficient PN of Aneff.

Novel Endosymbionts in Rhizarian Amoebae Imply Universal Infection of Unrelated Free-Living Amoebae by Legionellales

Legionellales-infected water is a frequent cause of local outbreaks of Legionnaires’ disease and Pontiac fever. Decontaminations are difficult because Legionellales reproduce in eukaryotic microorganisms (protists). Most often, Legionellales have been isolated from amoebae; however, the culture-based sampling methods are taxonomically biased. Sequencing studies show that amoebae in the cercozoan class Thecofilosea are dominant in soils and wastewater treatment plants, prompting us to screen their capability to serve as potential hosts of endosymbiotic bacteria. Environmental isolates of Thecofilosea contained a surprising richness of endosymbiotic Legionellales, including Legionella. Considering the widespread dispersal of Legionellales in apparently unrelated amoeboid protist taxa, it appears that the morphotype and not the evolutionary origin of amoebae determines their suitability as hosts for Legionellales. We further provide a protocol for gnotobiotic cultivation of Legionellales and their respective hosts, facilitating future genomic and transcriptomic research of host–symbiont relationships.

Effects of submerged vegetation on sediment nitrogen-cycling bacterial communities in Honghu Lake (China)

Sediment nitrogen (N) cycling is an important biological removal process for N permanently and driven by N-cycling microbial community. There is a growing interest in interactions between submerged vegetation (SV) and sediment N-cycling bacterial community, because of the close link between rooted aquatic plants and the sediment microbes. However, the effects of SV on the sediment N-cycling bacterial community are still controversial. Furthermore, the discrimination of direct and indirect effects of SV on the N-cycling bacterial community remains unclear. Here, we investigated the biomass and species richness of SV and determined the corresponding environment factors (water quality and sediment properties) in Honghu Lake (China). We also used functional genes as markers to unveil the bacterial diversity and community composition and abundance in lake sediments. Our results showed that biomass and species richness of SV affected the composition, diversity and abundance of sediment N-cycling bacterial communities through improving lake water quality and sediment properties. With the increasing richness and abundance of SV, the diversity of most N-cycling bacterial assemblages including nitrifying, denitrifying and DNRA bacteria decreased, while the abundance increased. However, the anammox bacterial assemblage in sediments showed inverse trends. Sediment carbon vs. nitrogen (C:N) ratio negatively affected the abundance of amoA and nirS + nirK + nosZ bacterial assemblages. Additionally, due to the presence of SV, positive interactions among N-cycling bacterial assemblages were found, such as amoA and nrfA bacterial assemblages. Overall, our findings confirmed the significant effects of SV on the N-cycling bacterial community structure and abundance. Moreover, the direct effects of SV on the N-cycling bacterial community and the indirect effects through altering the sediment C were clarified in our study. Our results casted a new light on the negative effects of high C:N ratio. From the study, we made a conclusion that the better SV develops, the greater nitrogen removal occurs in lake sediments.

Whether glycine betaine improves the thermotolerance of mesophilic anammox consortia

While the application of mesophilic anammox process is currently the state of the art, the feasibility of a thermophilic anammox bioprocess is still unclear. In this study, we investigate whether glycine betaine (GB) addition can enhance the thermotolerance of mesophilic anammox biomass in the upflow anaerobic sludge blanket (UASB) reactors fed with synthetic wastewater at a nitrogen loading of approximately 4 kg N m^-3 d^-1. The results showed that during a long-term operation at 45°C with GB (0, 0.1, 1, 2 mM) addition, anammox performance became worse with the final effluent concentrations of NO₂ ^-N of 145 ± 11.6 mg L^-1 and nitrogen removal efficiency decreased from 92.3-6.9%. Specific anammox activity decreased from 392.1 ± 12.1-6.0 ± 0.8 mg N g^-1 VSS d^-1, which were not significantly higher than those in the control reactor. The content of heme c showed a stronger downward trend in T₁ (with GB addition) than in the control reactor T₀. The qPCR results showed that the relative abundance of Candidatus Kuenenia decreased in both the experimental (from 53.5-28.8%) and control reactors (from 54.1-35.1%). Overall, continuous addition of exogenous GB did not improve the thermotolerance of mesophilic anammox consortia at 45°C.

Landfill leachate treatment through the combination of genetically engineered bacteria Rhodococcus erythropolis expressing Nirs and AMO and membrane filtration processes

This study developed a process of genetically engineered bacteria Rhodococcus erythropolis expressing Nirs and AMO combined with membrane bioreactor (MBR), nanofiltration (NF) and reverse osmosis (RO) membrane (pRho-NA-MNR) for advanced treatment of landfill leachate. Results demonstrated that pRho-NA-MNR presented higher removal rate of chemical oxygen demand (COD), biological oxygen demand (BOD), ammonia nitrogen (N-NH₄), total nitrogen (TN) and total organic carbon (TOC) than activated sludge (AS-MNR) system. Administration of pRho-NA increased nitrification by converting N-NH₄ to nitrite (N-NO₂) and Nitrate (N-NO₃), and promoting denitrification by converting N-NO₂ to nitrogen (N₂) in the landfill leachate treatment, promoted the pH control, increased sludge activity and effluent yield, shortened phase length adaptation under alternating aerobic-anoxic conditions. pRho-NA increased the nitration and denitrifying rate in the aerobic and anaerobic stage in the system by increasing Cyt cd1 and Cyt c expression in the activated sludge. Nitrogen removal by nitrification and denitrification was positively correlated to the concentration of Nirs and AMO expression. Treatment with pRho-NA promoted pollutant removal efficiency of membrane bioreactor, nanofiltration and reverse osmosis membrane processes in landfill leachate. In conclusion, data suggest that pRho-NA-MNR facilitates the formation of granular sludge and enhances comparable removal of nitrogen and organic compounds, indicating the practice of this process should be considered in landfill leachate treatment system.

Intensified nutrients removal in a modified sequencing batch reactor at low temperature: Metagenomic approach reveals the microbial community structure and mechanisms

To achieve efficient biological nutrients removal at low temperature, a modified sequencing batch reactor (SBR) was developed at 10 °C by extending sludge retention time (SRT), shortening aerobic stage and compensating anoxic stage. The average removal rates of ammonium (NH₄⁺-N), total nitrogen (TN) and total phosphorus (TP) were 98.82%, 94.12% and 96.04%, respectively. Variation of carbon source in a typical cycle demonstrated the maximum synthesis of poly-β-hydroxybutyrate (PHB) (60 mg/L) occurred after feast period. Furthermore, the TP in sludge reached 50.4 mg/g mixed liquor suspended solids (MLSS) (78.4% was inorganic phosphorus and 21.6% was organic phosphorus) after 120 days of operation, indicating an excellent P-accumulating capacity was achieved in this system. Ammonia oxidizing bacteria (AOB) activity inhibition test verified both AOB and ammonia oxidizing archaea (AOA) were involved in ammonia-oxidizing process and the latter accounted for 17%-19%. Metagenomic-based taxonomy revealed the dominant genera were Candidatus Accumulibacter (12.18%), Dechloromonas (7.54%), Haliangium (6.69%) and Candidatus Contendobacter (3.40%). As described from the denitrifying genes perspective, with the exception of nitrite reduction (performed by denitrifiers), denitrifying phosphorus-accumulating organisms (DPAOs) played a leading role in denitrification pathway, showing that poly-β-hydroxyalkanoates (PHA)-driven nutrients removal was the dominate process.

Identifying the link between MBRs' key operating parameters and bacterial community: A step towards optimized leachate treatment

A MBR treating compost leachate was studied in order to link the operating parameters (solid and hydraulic retention time) to contaminant's specific bacterial catabolic activity. In this context, a lab-scale aerobic membrane bioreactor was operated for 200 days, at solid retention times (SRT) of 30 and 45 days and four different contaminant load rates. Results showed that increasing the food to microorganism ratio (F/M) by increasing the contaminant load rates lessened the selectivity pressure, which allowed the proliferation of subdominant operational taxonomic units (OTU) (relative abundance >3%) that were otherwise inhibited by highly adapted dominant OTUs (relative abundance >10%). Subsequently, increasing the SRT resulted in a lower species richness and the selection of two dominant types of bacteria: 1) genera with low growth rates that feed on non-limiting substrates or substrates with few competitors, and 2) genera with metabolisms that are highly specific to the available substrates and that can outcompete the other genera by using the substrate more efficiently. The bacterial population evolution observed during this study suggests that the mixed liquor population diversity and structure can be modulated with the operating conditions for the bioenhancement of contaminant specific catabolic activity. Identified dominant and subdominant genera were linked to the MBR's NH₄⁺ and COD removal performances. Interestingly, nitrification performances were unaffected by the organic load rate and the Nitrosomonas relative abundance.

Cooperation between partial-nitrification, complete ammonia oxidation (comammox), and anaerobic ammonia oxidation (anammox) in sludge digestion liquid for nitrogen removal

The challenge of sludge digester liquor treatment is its high ammonium nitrogen (NH₄⁺-N) concentration. Early reports found that complete ammonia oxidation (comammox) was not present and anaerobic ammonia oxidation (anammox) was difficult to achieve in most sludge digester liquor treatments. In this study, NH₄⁺-N removal by cooperation between partial-nitrification, comammox, and anammox processes was achieved in a sequencing batch reactor (SBR) for sludge digester liquor treatment. The results showed that 2100-2200 mg/L of NH₄⁺-N was removed in the SBR with 98.82% removal efficiency. In addition, 55.11% of NH₄⁺-N was converted to nitrite nitrogen (NO₂^--N) by partial-nitrification, 25.43% of NH₄⁺-N was converted to nitrate nitrogen (NO₃^--N) by comammox, and 18.28% of NH₄⁺-N was removed by anammox. During the operation, in the SBR, the relative abundance of the dominant ammonia-oxidizing bacteria (Chitinophagaceae) was 18.89%, that of the dominant anammox bacteria (Candidatus Kuenenia) was 0.10%, and that of the dominant comammox bacteria (Nitrospira) was 0.20%. Therefore, the high nitrogen removal efficiency in this system was considered the result of the combination of the three processes. These results showed that comammox and anammox could play very important roles in nitrogen transformation and energy-saving in nitrogen removal systems.

Performance and recovery of a completely separated partial nitritation and anammox process treating phenol-containing wastewater

Anammox process is considered as a promising technology for removing total nitrogen from low-strength ammonium and phenol-containing wastewater. However, it is still a challenge for the anammox process to treat high-strength ammonium and phenol-containing wastewater. A completely separated partial nitritation and anammox (CSPN/A) process was developed to remove total nitrogen from high-strength phenol-containing wastewater. About 92% of COD, 100% of phenol, and 82.4% of total nitrogen were successfully removed at a NH₄⁺-N concentration of 200 mg L^-1 with a phenol/NH₄⁺-N mass ratio of 0.5 in the CSPN/A process. Furthermore, a shock loading of 300 mg phenol L^-1 with a phenol/NH₄⁺-N mass ratio of 1.5 led to a complete failure of partial nitritation, but the performance was rapidly recovered by the increase of NH₄⁺-N concentration. Although the activities of ammonium-oxidizing bacteria and anammox bacteria were severely inhibited at a phenol/NH₄⁺-N mass ratio of 1.5, the enrichment of efficient phenol degraders in the CSPN stage could strengthen the performance robustness of partial nitritation and anammox process. Therefore, this study presented a new insight on the feasibility of the anammox process for treating high-strength ammonium and phenol-containing wastewater.

Effects of earthworms on nitrogen transformation and the correspond genes (amoA and nirS) in vermicomposting of sewage sludge and rice straw

The effects of earthworms on nitrogen transformation and the responsible functional genes during disposal of sewage sludge and rice straw were investigated in this study. Vermicomposting resulted in the lower pH and total organic carbon (TOC) compared to the control treatment without earthworms. Moreover, the presence of earthworms could promote the nitrogen mineralization and nitrification process in vermicomposting. Earthworms increased the activity of ammonia monooxygenase and abundance of amoA-nitrifier and reduced its diversity, whereas they reduced the density of nirS-denitrifying bacteria but enhanced its diversity. Nitrosospira was the dominant amoA-nitrifier and earthworms stimulated its growth in the vermicomposting. The presence of earthworms could also affect the community composition of nirS-denitrifying bacteria despite most of the nirS-denitrifier was not be classified at the genus level. In conclusion, the presence of earthworms had significant influence on the diversity and abundances of amoA and nirS genes and affect the nitrogen bio-transformation in vermicomposting.

Advanced treatment of sewage by membrane bioreactor associate with genetically engineered autotrophic nitrifying bacteria

This study introduced a process of MBR combing with genetically engineered bacteria of expressing nirs and ppk genes (GEB-Nirs/PPK) for advanced treatment of sewage in scenic area. An industrial scale application was staged anaerobic digestion, aerobic digestion. Over more than 150 days of continuous operation, TMP in this system was less than 0.18 bar. With a membrane flux of 6.48 m³/h, TMP remained below 0.2 bar and effluent remained above 70 m³ during continuous operation. Average COD and BOD removals averaged 94.2% and 93.6%, and were obtained with average effluent COD and BOD below 10.4 mg/L and 4.2 mg/L, respectively. The TN and TP removals averaged 98.8% and 94.3%, and never higher than 3.2 mg/L and 0.2 mg/L, respectively, in the processing system. In conclusion, these results indicate that the process of MBR associate with genetically engineered autotrophic nitrifying bacteria is of high-efficiency for advanced treatment of sewage.

Insights into functional microbial succession during nitrogen transformation in an ectopic fermentation system

The ectopic fermentation system (EFS) is an advanced technology for treating farm wastewater, and it reduces ammonia nitrogen emission and nitrogen loss of fermentation products. This study observed the functional bacteria succession related to nitrogen metabolism in EFS by high throughput sequencing, and evaluated their associations with environmental factors. Results revealed that with the changes of temperature, pH, moisture content, and nitrogen content during fermentation, the species richness and diversity of ammonia oxidizing bacteria (AOB) with amoA increased, but those of denitrifying bacteria carrying nirK and nosZ decreased. During the fermentation process, the dominant bacterial populations of AOB and denitrifying bacteria changed significantly, and different bacterial populations showed different positive/negative correlations with the environmental factors. This study revealed the role of functional bacteria in ammonia removal and nitrogen conservation of EFS, and provided a theoretical basis for the improvement of microbial agents and EFS application.

Low energy treatment of landfill leachate using simultaneous partial nitrification and partial denitrification with anaerobic ammonia oxidation

An up-flow anaerobic sludge blanket reactor (UASB), anoxic/oxic (A/O)-anaerobic ammonia oxidation reactor (ANAOR or anammox reactor), and anaerobic sequencing batch reactor (ASBR) were employed in the treatment of landfill leachate with partial nitrification-anammox and half-denitrification-anammox. The Chemical Oxygen Demand (COD) concentration, ammonium nitrogen (NH₄⁺-N) concentration, and total nitrogen (TN) concentration of the basal leachate was 2200-2500 mg/L, 1200-1300 mg/L, and 1300-1400 mg/L, respectively. After a 1:2 dilution using domestic sewage, the COD, NH₄⁺-N, and TN concentrations in the influent were 800-1000 mg/L, 400-430 mg/L, and 420-440 mg/L, respectively. After treatment, the final COD, NH₄⁺-N, and TN were decreased to 90-100 mg/L, 13-14 mg/L, and 35-38 mg/L, respectively. In the ASBR, organic carbon sources in sewage-diluted landfill leachate were introduced for the conversion of nitrate nitrogen (NO₃^--N) into nitrite nitrogen (NO₂^--N). This enabled the continued reaction of NO₂^--N with NH₄⁺-N from the newly introduced sewage-diluted landfill leachate via anammox. As a result, complete TN removal was achieved in the system. Microbial diversity analysis indicated that the relative abundance of ammonia-oxidizing bacteria (AOB) was four to five times greater than nitrite-oxidizing bacteria (NOB) in the A/O reactor, showing that partial nitrification was prevalent. The relative abundance of the anammox bacterium Candidatus Kuenenia gradually increased in each reactor, reaching a maximum of 1.17%-1.39%. Using this set-up, we achieved advanced, efficient, and economical, COD reduction and nitrogen removal. Taken together, the findings provide important insights into the optimal operation of landfill leachate treatments.

Recent advances in nitrogen removal from landfill leachate using biological treatments - A review

Landfill leachate, generated from the wastes in a landfill, is a type of wastewater with high concentrations of ammonia and organics, causing a serious environmental pollution. Because of its complex and changing characteristics, it is difficult to remove nitrogen from landfill leachate economically and effectively. Hence, nitrogen removal is a significant research priority of landfill leachate treatment in recent years. Biological processes are known to be effective in nitrogen removal. In this work, the biological nitrogen removal treatments were divided into the following processes: conventional nitrification-denitrification process, nitritation-denitritation process, endogenous denitritation process, and anaerobic ammonium oxidation (Anammox) process. This manuscript summarized the theories and applications of these approaches in detail, and concluded that appropriate processes should be selected in accordance with different characteristics of landfill leachate, in order to effectively remove nitrogen from all stages of landfill leachate and reduce disposal costs. Finally, perspective on the challenges and opportunities of biological nitrogen removal from landfill leachate was also presented.

Enhanced nitrate reduction in water by a combined bio-electrochemical system of microbial fuel cells and submerged aquatic plant Ceratophyllum demersum

High nitrate (NO₃^-) loading in water bodies is a crucial factor inducing the eutrophication of lakes. We tried to enhance NO₃^- reduction in overlying water by coupling sediment microbial fuel cells (SMFCs) with submerged aquatic plant Ceratophyllum demersum. A comparative study was conducted by setting four treatments: open-circuit SMFC (Control), closed-circuit SMFC (SMFC-c), open-circuit SMFC with C. demersum (Plant), and closed-circuit SMFC with C. demersum (P-SMFC-c). The electrochemical parameters were documented to illustrate the bio-electrochemical characteristics of SMFC-c and P-SMFC-c. Removal pathways of NO₃^- in different treatments were studied by adding quantitative ¹⁵NO₃^- to water column. The results showed that the cathodic reaction in SMFC-c was mainly catalyzed by aerobic organisms attached on the cathode, including algae, Pseudomonas, Bacillus, and Albidiferax. The oxygen secreted by plants significantly improved the power generation of SMFC-c. Both electrogenesis and plants enhanced the complete removal of NO₃^- from the sediment-water system. The complete removal rates of added ¹⁵N increased by 17.6% and 10.2% for SMFC-c and plant, respectively, when compared with control at the end of experiment. The electrochemical/heterotrophic and aerobic denitrification on cathodes mainly drove the higher reduction of NO₃^- in SMFC-c and plant, respectively. The coexistence of electrogenesis and plants further increased the complete removal of NO₃^- with a rate of 23.1%. The heterotrophic and aerobic denitrifications were simultaneously promoted with a highest abundance of Flavobacterium, Bacillus, Geobacter, Pseudomonas, Rhodobacter, and Arenimonas on the cathode.

Effect of nitrogen deficiency on the stability of aerobic granular sludge

To assess the stability of aerobic granular sludge (AGS) under nitrogen deficiency conditions, three sequence batch reactors were operated with chemical oxygen demand (COD) to nitrogen (N) ratios of 100/5, 100/2.5, and 100/2, while COD concentration was kept consistent. AGS variations in its physicochemical characteristics, microbial community, and treatment performance were investigated. The results indicated that good treatment performance and stable AGS were achieved under nitrogen deficiency. Extracellular polymeric substances (EPS) regulating mechanism preserved AGS stability under nitrogen deficiency, especially through increased secretion of polysaccharide. In addition, members of the Anaerolineaceae were the major filamentous bacteria, which are strictly anaerobic organism, providing a possible explanation to the lack of filamentous bacteria outgrowth under N deficient condition. Insights from this study could help lower chemical costs in AGS applications for specific industrial wastewater treatments.

Nitrification/denitrification shaped the mercury-oxidizing microbial community for simultaneous Hg0 and NO removal

A denitrifying/nitrifying membrane biofilm reactor for simultaneous removal of Hg⁰ and NO was investigated. Hg⁰ and NO removal efficiency attained 94.5% and 86%, respectively. The mercury-oxidizing microbial community was significantly shaped by nitrification/denitrification after the supply of gaseous Hg⁰and NO continuously. Dominant genera Rhodanobacter and Nitrosomonas participated in Hg⁰ oxidation, nitrification and denitrification simultaneously. Hg⁰ oxidizing bacteria (Gallionella, Rhodanobacter, Ottowia, Nitrosomonas and etc.), nitrifying bacteria (Nitrosomonas, Rhodanobacter, Diaphorobacte and etc.) and denitrifying bacteria (Nitrosomonas, Rhodanobacter, Castellaniella and etc.) co-existed in the MBfR, as shown by metagenomic sequencing. X-ray photoelectron spectroscopy (XPS) and high performance liquid chromatography-inductively coupled plasma mass spectrometry (HPLC-ICP-MS) confirmed the formation of a mercuric species (Hg²⁺) from mercury bio-oxidation. Mechanism of mercury oxidation can be described as the bacterial oxidation of Hg⁰ in which Hg⁰ serves as electron donor, NO serves as electron donor in nitrification and electron acceptor in denitrification, oxygen serves as electron acceptor.

Dynamic membrane bioreactor (DMBR) for the treatment of landfill leachate; bioreactor's performance and metagenomic insights into microbial community evolution

The use of dynamic membranes as a low-cost alternative for conventional membrane for the treatment of landfill leachate (LFL) was investigated in this study. For this purpose a lab-scale, submerged pre-anoxic and post-aerobic bioreactor configuration was used with nylon mesh as dynamic membrane support. The study was conducted at ambient temperature and LFL was fed to the bioreactor in gradually increasing concentration mixed with tap water (from 20% to 100%). The results of this study demonstrated that lower mesh pore size of 52 μm achieved better results in terms of solid-liquid separation performance (turbidity <10 NTU) of the formed dynamic membrane layer as compared to 200 and 85 μm meshes while treating LFL. Consistently high NH₄⁺-N conversion efficiency of more than 98% was achieved under all nitrogen loading conditions, showing effectiveness of the formed dynamic membrane in retaining slow growing nitrifying species. Total nitrogen removal reached more than 90% however, the denitrification activity showed a fluctuating profile and found to be inhibited by elevated concentrations of free nitrous acid and NO₂^--N at low pH values inside the anoxic bioreactor. A detailed metagenomic analysis allowed a taxonomic investigation over time and revealed the potential biochemical pathways involved in NH₄⁺-N conversion. This study led to the identification of a dynamic system in which nitrite concentration is determined by the contribution of NH₄⁺ oxidizers (Nitrosomonas), and by a competition between nitrite oxidizers (Nitrospira and Nitrobacter) and reducers (Thauera).

Stability of aerobic granular sludge under condition of low influent C/N ratio: Correlation of sludge property and functional microorganism

Aerobic granular sludge process treating domestic wastewater with low C/N ratio is necessary to be studied for rapid urbanization in China and other countries. In this study, two parallel reactors with different influent C/N ratio (15 in R1, 5 in R2) were established. Compared to the disintegrated granule in R1 with high influent C/N ratio, granules with large size (650 μm) and compact structure (integrity coefficient <0.1) were stable in R2 along with influent C/N ratio decreased to 5. High-through sequencing illustrated the functional microbes like Thauera and Paracoccus enriched under low influent C/N ratio, and principal component analysis further showed these microbes were positive correlation with tryptophan and protein-like substances in extracellular polymeric substances (EPS) and granular strength. It was indicated that under low influent C/N ratio, several resistant microbes like Thauera (19.5%) enriched and then secreted tryptophan and protein-like substances, and stable granules with multi-functional microbes could be formed finally.

Start-up performance of anaerobic/aerobic/anoxic-sequencing batch reactor (SBR) augmented with denitrifying polyphosphate-accumulating organism (DPAO) and their gene analysis

This paper was aimed at investigating the bio-augmentation performance of anaerobic/aerobic/anoxic-type sequencing batch reactor (SBR) during its start-up period by introducing a strain of denitrifying polyphosphate-accumulating organism (DPAO). Two SBR reactors were inoculated to study the start-up performance, with one for DPAO introduction and the other as the control specimen. A comparison, of microbial community diversity based on the reactor which obtained a better performance, was made between polymerase chain reaction-denaturing gradient gel electrophoresis (PCR-DGGE) analyses encoded by 16S rRNA and functional genes (nirS, nirK). The results indicated that the introduction of DPAO had a positive effect on the biological system, including a reduction of the start-up period, the improvement of sludge characteristics and the removal efficiency of nutrients, especially for phosphorus. By comparing the phylogenetic relationship of 16S rRNA and functional genes (nirS, nirK) of the reactor augmented with DPAO, it could be found that the phylogenetic relationship of these genes were remarkably inconsistent with each other. Therefore, 16SrRNA should not be used to determine the microbial community diversity of functional bacteria which could accomplish denitrification, and gene nirK should not be neglected when determining functional bacteria.

Optimization aspects of the biological nitrogen removal process in a full-scale twin sequencing batch reactor (SBR) system in series treating landfill leachate

Despite the fact that biological nitrogen removal (BNR) process has been studied in detail in laboratory- and pilot-scale sequencing batch reactor (SBR) systems treating landfill leachate, a limited number of research works have been performed in full-scale SBR plants regarding nitrification and denitrification. In the current study, a full-scale twin SBR system in series of 700 m³ (350 m³ each) treating medium-age landfill leachate was evaluated in terms of its carbon and nitrogen removal efficiency in the absence and presence of external carbon source, i.e., glycerol from biodiesel production. Both biodegradable organic carbon and ammonia were highly oxidized [biochemical oxygen demand (BOD₅) and total Kjehldahl nitrogen (TKN) removal efficiencies above 90%], whereas chemical oxygen demand (COD) removal efficiency was slightly above 40%, which is within the range reported in the literature for pilot-scale SBRs. As the consequence of the high recalcitrant organic fraction of the landfill leachate, dissimilatory nitrate reduction was restricted in the absence of crude glycerol, although denitrification was improved by electron donor addition, resulting in TN removal efficiencies above 70%. Experimental data revealed that the second SBR negligibly contributed to BNR process, since carbon and ammonia oxidation completion was achieved in the first SBR. On the other hand, the low VSS/SS ratio, due to the lack of primary sedimentation, highly improved sludge settleability, resulting in sludge volume indices (SVI) below 30 mL g^-1.

Assessment of dynamic membrane filtration for biological treatment of old landfill leachate

This study investigated the behaviour of dynamic membrane (DM) filtration for the treatment of stabilised landfill leachate in a bench-scale pre-anoxic and aerobic submerged dynamic membrane bioreactor (DMBR). Four meshes with different openings (10, 52, 85 and 200 μm) were tested to support the development of DM. Differences were observed among the meshes in supporting the development of the cake layer constituting the DM. The treatment of landfill leachate had an impact on sludge characteristics resulting in deteriorated filtration performance of the DM. Effluent turbidity was often higher than 100 NTU for larger mesh pore size (85 and 200 μm). Low effluent turbidity was achieved with meshes with 10 and 52 μm (13 ± 2 and 26 ± 4 NTU, respectively) although at membrane fluxes lower than 10 L m^{- 2} h^-1. The bioreactor exhibited a moderate organics removal of 50-60% and an ammonia oxidation between 80 and 90%. Incomplete nitrification was observed due to increased concentrations of free ammonia and free nitrous acid, with nitrite effluent concentrations up to 1062 mgNO₂^--N L^-1. Due to the large presence of refractory organic matter in landfill leachate, denitrification was limited resulting in a total nitrogen removal of approximately 20%.

Continuously Monocropped Jerusalem Artichoke Changed Soil Bacterial Community Composition and Ammonia-Oxidizing and Denitrifying Bacteria Abundances

Soil microbial communities have profound effects on the growth, nutrition and health of plants in agroecosystems. Understanding soil microbial dynamics in cropping systems can assist in determining how agricultural practices influence soil processes mediated by microorganisms. In this study, soil bacterial communities were monitored in a continuously monocropped Jerusalem artichoke (JA) system, in which JA was successively monocropped for 3 years in a wheat field. Soil bacterial community compositions were estimated by amplicon sequencing of the 16S rRNA gene. Abundances of ammonia-oxidizing and denitrifying bacteria were estimated by quantitative PCR analysis of the amoA, nirS, and nirK genes. Results showed that 1-2 years of monocropping of JA did not significantly impact the microbial alpha diversity, and the third cropping of JA decreased the microbial alpha diversity (P < 0.05). Principal coordinates analysis and permutational multivariate analysis of variance analyses revealed that continuous monocropping of JA changed soil bacterial community structure and function profile (P < 0.001). At the phylum level, the wheat field was characterized with higher relative abundances of Latescibacteria, Planctomycetes, and Cyanobacteria, the first cropping of JA with Actinobacteria, the second cropping of JA with Acidobacteria, Armatimonadetes, Gemmatimonadetes, and Proteobacteria. At the genus level, the first cropping of JA was enriched with bacterial species with pathogen-antagonistic and/or plant growth promoting potentials, while members of genera that included potential denitrifiers increased in the second and third cropping of JA. The first cropping of JA had higher relative abundances of KO terms related to lignocellulose degradation and phosphorus cycling, the second cropping of JA had higher relative abundances of KO terms nitrous-oxide reductase and nitric-oxide reductase, and the third cropping of JA had higher relative abundances of KO terms nitrate reductase and nitrite reductase. The abundances of amoA genes decreased while nirK increased in the third cropping of JA, nirS continuously increased in the second and third cropping of JA (P < 0.05). Redundancy analysis and Mantel test found that soil organic carbon and Olsen phosphorus contents played important roles in shaping soil bacterial communities. Overall, our results revealed that continuous monocropping of JA changed soil bacterial community composition and its functional potentials.

Pathway and mechanism of nitrogen transformation during composting: Functional enzymes and genes under different concentrations of PVP-AgNPs

Polyvinylpyrrolidone coated silver nanoparticles (PVP-AgNPs) were applied at different concentrations to reduce total nitrogen (TN) losses and the mechanisms of nitrogen bio-transformation were investigated in terms of the nitrogen functional enzymes and genes. Results showed that mineral N in pile 3 which was treated with AgNPs at a concentration of 10 mg/kg compost was the highest (6.58 g/kg dry weight (DW) compost) and the TN loss (47.07%) was the lowest at the end of composting. Correlation analysis indicated that TN loss was significantly correlated with amoA abundance. High throughput sequencing showed that the dominant family of ammonia-oxidizing bacteria (AOB) was Nitrosomonadaceae, and the number of Operational Taxonomic Units (OTUs) reduced after the beginning of composting when compared with day 1. In summary, treatment with AgNPs at a concentration of 10 mg/kg compost was considerable to reduce TN losses and reserve more mineral N during composting.

Vanillic acid changed cucumber (Cucumis sativus L.) seedling rhizosphere total bacterial, Pseudomonas and Bacillus spp. communities

Soil microorganisms are key drivers of plant productivity in terrestrial ecosystems, yet controls on their diversities and abundances are not fully elucidated. Phenolic acids, released through plant root exudation and residues decomposition, are usually referred as autotoxins of several crops, including cucumber. In this study, effects of vanillic acid (VA) on cucumber rhizosphere microbial communities were investigated by treating cucumber seedlings with VA every two days for five times. Amplicon sequencing, PCR-denaturing gradient gel electrophoresis and quantitative PCR were used to analyzed the 16S rRNA genes of total bacterial, Pseudomonas and Bacillus spp. communities. Results showed that VA at 0.05 μmol g⁻¹ soil changed total bacterial community diversity and composition. In particular, VA inhibited the relative abundances of genera with plant-beneficial potentials, such as Bacillus and Lysobacter spp. Moreover, VA changed Pseudomonas and Bacillus spp. community compositions by altering the number and/or relative abundances of their OTUs; and decreased Bacillus spp. community abundance at 0.02 to 0.2 μmol g⁻¹ soil and Pseudomonas spp. community abundance at 0.2 μmol g⁻¹ soil. Overall, VA changed cucumber seedling rhizosphere total bacterial, Pseudomonas and Bacillus spp. communities, which maybe be associated with the adverse effects of VA on cucumber growth under soil conditions.

Impact of SRT on the performance of MBRs for the treatment of high strength landfill leachate

This study examines the performance and fouling potential of flat sheet (FS) and hollow fiber (HF) membrane bioreactors (MBRs) during the treatment of high strength landfill leachate under varying solid retention times (SRT = 5-20 days). Mixed-liquor bacterial communities were examined over time using 16S rRNA gene sequence analysis in an attempt to define linkages between the system performance and the microbial community composition. Similarly, biofilm samples were collected at the end of each SRT to characterize the microbial communities that evolved on the surface of the FS and HF membranes. In general, both systems exhibited comparable removal efficiencies that dropped significantly as SRT was decreased down to 5 days. Noticeably, ammonia and nitrite oxidizing bacteria were not detected at the tested SRTs. This suggests that the nitrifiers were not enriched, possibly due to the high organic and ammonium content of the leachate that led to low TN and NH₃ removal efficiency. The steady-state fouling rate of both membranes increased linearly with the decrease in SRT at an estimated factor of 1.1 and 1.2 for the FS- and HF-MBR, respectively, when the SRT was reduced from 15 to 10 days and from 10 to 5 days. Similar dominant genera were detected in both MBRs, including Pseudomonas, Aequorivita, Ulvibacter, Taibaiella, and Thermus. Aequorivita, Taibaiella; Thermus were the dominant genera in the biofilms. Hierarchical clustering and non-metric multidimensional scaling revealed that while the mixed liquor communities in the FS-MBR and HF-MBRs were dynamic, they clustered separately. Similarly, biofilm communities on the FS and HF membranes differed in the dynamic bacterial community structure, especially for the FS-MBR; however this was less dynamic than the mixed liquor community.

Influence of fermentation liquid from waste activated sludge on anoxic/oxic- membrane bioreactor performance: Nitrogen removal, membrane fouling and microbial community

In order to investigate effects of waste activated sludge (WAS) fermentation liquid on anoxic/oxic- membrane bioreactor (A/O-MBR), two A/O-MBRs with and without WAS fermentation liquid addition were operated in parallel. Results show that addition of WAS fermentation liquid clearly improved denitrification efficiency without deterioration of nitrification, while severe membrane fouling occurred. WAS fermentation liquid resulted in an elevated production of proteins and humic acids in bound extracellular polymeric substance (EPS) and release of organic matter with high MW fractions in soluble microbial product (SMP) and loosely bound EPS (LB-EPS). Measurement of deposition rate and fluid structure confirmed increased fouling potential of SMP and LB-EPS. γ-Proteobacteria and Ferruginibacter, which can secrete and export EPS, were also found to be abundant in the MBR with WAS fermentation liquid. It is implied that when WAS fermentation liquid was applied, some operational steps to control membrane fouling should be employed.

Effects of single and combined copper/perfluorooctane sulfonate on sequencing batch reactor process and microbial community in activated sludge

Long-term exposure experiments with single and combined pollutants of copper (Cu)/perfluorooctane sulfonate (PFOS) were conducted to explore the influence on activated sludge in SBRs. Compared with the control, the removal of organics, nitrogen and phosphorus in the presence of PFOS exhibited no apparent difference, but reduced in different degrees when Cu and Cu/PFOS existed. PFOS exposure deteriorated the settling performance of activated sludge with SVI value and amount of extracellular polymeric substance (EPS) increasing, but posed little impacts on microbial activity (dehydrogenase, protease) and antioxidant activity (SOD, CAT). Under Cu and Cu/PFOS loading, dehydrogenase and protease activity were observed to decrease as well as SOD and CAT activity. The sequencing results revealed that bacterial richness and community diversity reduced under Cu and Cu/PFOS exposure. Overall, adverse effect of combined pollution was lower than that of single Cu in long-time due to antagonistic effect existed between Cu and PFOS.

Quantitative dynamics of ammonia-oxidizers during biological stabilization of municipal landfill leachate pretreated by Fenton's reagent at neutral pH

The application of multi-stage systems including biological step, for the treatment of leachate from municipal landfills, is economically and technologically justified. When microbial activity is utilized as 2nd stage of treatment, the task of 1st stage is to increase the bioavailability of organic matter. In this work, the effect of advanced oxidation process by Fenton's reagent for treatment efficiency of landfill leachate in the sequencing batch reactor was assessed. The quantitative dynamics of bacteria taking a part in ammonia removal process was evaluated by determination of number of DNA copies of 16S rRNA and amoA. Products of neutral pH chemical oxidation, had a definite positive impact on the quantity of β-proteobacteria 16S rRNA, whereas the same gene specified for Nitrospira sp. as well as amoA did not show a significant increase during the process of biological treatment, regardless of whether the reactor was fed with raw leachate or chemically pre-treated.