Unraveling the active microbial populations involved in nitrogen utilization in a vertical subsurface flow constructed wetland treating urban wastewater

Metagenomics analysis of microbial community distribution in large-scale and step-by-step purification system of swine wastewater

Biological treatment is one of the most widely used methods to treat swine wastewater in wastewater treatment plants. The microbial community plays an important role in the swine slurry treatment system. However, limited information is available regarding the correlation between pollutant concentration and dominant microbial community in swine wastewater. This work aimed to study the profiling of microbial communities and their abundance in the 40 M³/day large-scale and step-by-step treatment pools of swine wastewater. Metagenome sequencing was applied to study the changes of microbial community structure in biochemical reaction pools. The results showed that in the heavily polluted pools, it was mainly Proteobacteria, Cyanobacteria, Chlorella and other strains that could tolerate high concentration of ammonia nitrogen to remove nitrogen and absorb chemical oxygen demand (COD). In the moderately polluted pools, Nitrospirae, Actinobacteria and other strains further cooperated to purify swine wastewater. In the later stage, the emergence of Brachionus indicated the reduction of water pollution. The dominant microbes and their abundance changed with the purification of swine wastewater in different stages. Moreover, the dominant microflora of swine wastewater treatment pools at all levels reflected little difference in phylum classification level, while in genus classification level, the dominant microflora manifested great difference. Findings demonstrated that the microorganisms maintained ecological balance and absorbed the nutrients in the swine wastewater treatment pools, so as to play the role of purifying sewage. Therefore, the stepwise purification of swine wastewater can be realized by adding bacteria and microalgae of different genera.

Partial Nitrification and Enhanced Biological Phosphorus Removal in a Sequencing Batch Reactor Treating High-Strength Wastewater

Complex and high levels of various pollutants in high-strength wastewaters hinder efficient and stable biological nutrient removal. In this study, the changes in pollutant removal performance and microbial community structure in a laboratory-scale anaerobic/aerobic sequencing batch reactor (SBR) treating simulated pre-fermented high-strength wastewater were investigated under different influent loading conditions. The results showed that when the influent chemical oxygen demand (COD), total nitrogen (TN), and orthophosphate (PO₄³⁻-P) concentrations in the SBR increased to 983, 56, and 20 mg/L, respectively, the COD removal efficiency was maintained above 85%, the TN removal efficiency was 64.5%, and the PO₄³⁻-P removal efficiency increased from 78.3% to 97.5%. Partial nitrification with simultaneous accumulation of ammonia (NH₄⁺-N) and nitrite (NO₂⁻-N) was observed, which may be related to the effect of high influent load on ammonia- and nitrite-oxidising bacteria. The biological phosphorus removal activity was higher when propionate was used as the carbon source instead of acetate. The relative abundance of glycogen accumulating organisms (GAOs) increased significantly with the increase in organic load, while Tetrasphaera was the consistently dominant polyphosphate accumulating organism (PAO) in the reactor. Under high organic loading conditions, there was no significant PAO–GAO competition in the reactor, thus the phosphorus removal performance was not affected.

Response of rotating biological contactor started up by heterotrophic nitrification-aerobic denitrification bacteria to various C/N ratios

To improve the low pollutant removal efficiency of traditional biological methods for treating livestock and poultry breeding wastewater under a relatively low temperature, a rotating biological contactor (RBC) inoculated with heterotrophic nitrification-aerobic denitrification (HN-AD) bacteria was designed. A quick start-up process and a well removal performance had been achieved in the novel RBC. To elucidate the anti-load shock ability of the novel RBC, the effects of C/N ratio on nitrogen removal and microbial assemblage were focused under a low temperature (12 ± 2 °C). Results showed that the highest NH₄⁺-N and TN removal efficiency were 99.57 ± 0.31% and 68.41 ± 0.52%. Microbial diversity analysis based on high throughput sequencing technique showed that Arcobacter and Flavobacterium with an increasing relative abundance were the key to ensure high nitrogen removal efficiently at a low C/N ratio and temperature. Moreover, nitrogen transferring pathways of the novel RBC was revealed and dissimilatory nitrate reduction and denitrification were the main pathways. The excellent pollutant removal performance demonstrates that the novel RBC is a promising process to effectively treat wastewater with low C/N ratio and low temperature.

The ecological clusters of soil organisms drive the ecosystem multifunctionality under long-term fertilization

Long-term fertilization is known to impact the biodiversity and community structures of soil organisms, which are responsible for multiple soil ecosystem functions (multifunctionality). However the relationship between the alterations of soil organisms and ecosystem multifunctionality remains unclear, especially in the case of long-term fertilization. To explore the contribution of soil organismal biodiversity and community structures to ecosystem multifunctionality, we took soil samples from a nearly 25-year field fertilization experiment. Organic matter significantly improved the soil ecosystem multifunctionality. Ecosystem multifunctionality was found to be closely linked to the biodiversity and communities of soil organisms within the major ecological clustering of soil organisms (Module 1) according to the trophic co-occurrence network, rather than the entire community of soil organisms. This indicated that ecological clusters of soil organisms within the network were critical in maintaining soil ecosystem multifunctionality. The application of organic fertilization could enrich specialized soil organisms and increase interactions of soil organisms in the ecological cluster. As a result, our findings emphasize the role of ecological clusters in the soil organismal co-occurrence network in controlling soil multifunctionality after long-term fertilization, presenting a novel perspective on the link between soil biodiversity and ecosystem multifunctionality.

Keystone Species and Niche Differentiation Promote Microbial N, P, and COD Removal in Pilot Scale Constructed Wetlands Treating Domestic Sewage

The microbial characteristics related to nitrogen (N), phosphorus (P), and chemical oxygen demand (COD) removal were investigated in three pilot scale constructed wetlands (CWs). Compared to horizontal subsurface flow (HSSF) and surface flow (SF) CWs, the aerobic vertical flow (VF) CW enriched more functional bacteria carrying genes for nitrification (nxrA, amoA), denitrification (nosZ), dephosphorization (phoD), and methane oxidation (mmoX), while the removal of COD, total P, and total N increased by 33.28%, 255.28%, and 299.06%, respectively. The co-occurrence network of functional bacteria in the HSSF CW was complex, with equivalent bacterial cooperation and competition. Both the VF and SF CWs exhibited a simple functional topological structure. The VF CW reduced functional redundancy by forming niche differentiation, which filtered out keystone species that were closely related to each other, thus achieving effective sewage purification. Alternatively, bacterial niche overlap protected a single function in the SF CW. Compared with the construction type, temperature, and plants had less effect on nutrient removal in the CWs from this subtropical region. Partial least-squares path modeling (PLS-PM) suggests that high dissolved oxygen and oxidation-reduction potential promoted a diverse bacterial community and that the nonkeystone bacteria reduced external stress for functional bacteria, thereby indirectly promoting nutrient removal.

Evaluation of nitrogen removal and the microbial community in a submerged aerated biological filter (SABF), secondary decanters (SD), and horizontal subsurface flow constructed wetlands (HSSF-CW) for the treatment of kennel effluent

To ensure microbial activity and a reaction equilibrium with efficiency and energy saving, it is important to know the factors that influence microbiological nitrogen removal in wastewater. Thus, it was investigated the microorganisms and their products involved in the treatment of kennel effluents operated with different aeration times, phase 1 (7 h of continuous daily aeration), phase 2 (5 h of continuous daily aeration), and phase 3 (intermittent aeration every 2 h), monitoring chemical and physical parameters weekly, monthly microbiological, and qualitative and quantitative microbiological analyzes at the end of each applied aeration phase. The results showed a higher mean growth of nitrifying bacteria (NB) (10⁶) and denitrifying bacteria (DB) (10²²) in phase with intermittent aeration, in which better total nitrogen (TN) removal performance, with 33%, was achieved, against 21% in phase 1 and 17% in phase 2, due to the longer aeration time and lower carbon/nitrogen ratio (15.7), compared with the other phases. The presence of ammonia-oxidizing bacteria (AOB), the genus Nitrobacter nitrite-oxidizing bacteria (NOB), and DB were detected by PCR with specific primers at all phases. The analysis performed by 16S-rRNA DGGE revealed the genres Thauera at all phases; Betaproteobacteria and Acidovorax in phase 3; Azoarcus in phases 2 and 3; Clostridium, Bacillus, Lactobacillus, Turicibacter, Rhodopseudomonas, and Saccharibacteria in phase 1, which are related to the nitrogen removal, most of them by denitrifying. It is concluded that, with the characterization of the microbial community and the analysis of nitrogen compounds, it was determined, consistently, that the studied treatment system has microbiological capacity to remove TN, with the phase 3 aeration strategy, by simultaneous nitrification and denitrification (SND). Due to the high density of DB, most of the nitrification occurred by heterotrophic nitrification-aerobic. And denitrification occurred by heterotrophic and autotrophic forms, since the higher rate of oxygen application did not harm the DB. Therefore, the aeration and carbon conditions in phase 3 favored the activity of the microorganisms involved in these different routes. It is considered that, in order to increase autotrophic nitrification-aerobic, it is necessary to exhaust the volume of sludge in the secondary settlers (SD), further reducing the carbon/nitrogen ratio, through more frequent cleaning, whose periodicity should be the object of further studies. Graphical abstract.

Differences in bacterial N, P, and COD removal in pilot-scale constructed wetlands with varying flow types

The mechanisms of bacterial nitrogen (N), phosphorus (P), and chemical oxygen demand (COD) removal in pilot-scale constructed wetlands (CWs) were investigated in the present work. Three types of CWs were assessed: vertical flow (VF), horizontal flow (HF), and surface flow (SF), each with three planting conditions, with either Thalia, Canna or without plants. The results show that construction types affected microbes more than planting conditions. VF CWs promoted the aerobic processing of total N, total P, COD, and NH₃-N, increasing the respective removal efficiencies by 4-19%, 13-32%, 19-29%, and 75-80%, respectively, compared with SF CWs. The relative abundance of nitrifying, denitrifying, methanotrophic and dephosphorized bacteria, and functional genes such as nxrA, nirK, nosZ, mmoX, and phoD were higher in VF CWs. Positive and simple gene networks in VF CWs can effectively reduce the redundancy in functional genes, enhance bacterial function and gene interactions, thus promoting nutrient removal.

Performance and bacterial communities in unsaturated and saturated zones of a vertical-flow constructed wetland with continuous-feed

In this study, a partially-saturated vertical-flow constructed wetland (VFCW) with continuous-feed was operated to investigate nutrients transformation and possible pathways in unsaturated and saturated zones. Effect of temperature on nutrients removal and microbial community was also evaluated. The variation of temperature barely affected removal of NH₄⁺-N and COD, achieving removal efficiencies of 99.5-100.0% and 96.8-100.0% at effluent temperature of 14.9-27.7 °C. The removal of COD, NH₄⁺-N, total inorganic nitrogen (TIN) and total phosphorus mainly occurred in unsaturated zone, achieving much higher removal rates than saturated zone. Nitrification process in the VFCW was associated with autotrophic/heterotrophic ammonia oxidizing bacteria and nitrite oxidizing bacteria. Denitrification process relied on both autotrophic and heterotrophic denitrifiers. Anaerobic ammonium oxidizing bacteria was also detected, contributing to TIN removal. All of the groups for nutrients removal exhibited higher abundance in unsaturated zone. Diverse pathways co-existed for nitrogen removal, while the main metabolic pathways were different along the depth.

Microbial coupling mechanisms of nitrogen removal in constructed wetlands: A review

Nitrogen removal through microorganisms is the most important pathway in constructed wetlands (CWs). In this review, we summarize the microbial coupling mechanisms of nitrogen removal, which are the common methods of nitrogen transformation. The electron pathways are shortened and consumption of oxygen and energy is reduced during the coupling of nitrogen transformation functional microorganisms. The highly efficient nitrogen removal mechanisms are cultivated from the design conditions in CWs, such as intermittent aeration and tidal flow. The coupling of microorganisms and substrates enhances nitrogen removal mainly by supplying electrons, and plants affect nitrogen transformation functional microorganisms by the release of oxygen and exudates from root systems as well as providing carriers for microbial attachment. In addition, inorganic elements such as Fe, S and H act as electron donors to drive the autotrophic denitrification process in CWs.

Enhanced nitrogen removal in filled-and-drained vertical flow constructed wetlands: microbial responses to aeration mode and carbon source

For the purpose of enhancing the removal rate of nitrogen (N) and organic matters, intermittent aeration and carbon source were used in filled-and-drained vertical flow constructed wetlands (VFCWs). The results showed that the best removal of COD (74.16%), NH₄⁺-N (93.56%), TN (86.88%), and NO₃^--N (79.65%) was achieved in VFCW1 (aerated with carbon source system). Illumina MiSeq300 high-throughput sequencing showed that carbon source aerated system increases the diversity and richness of the microbial community. The copy numbers of nitrification functional genes (nxrA, amoA), denitrification functional genes (nirS, nirK, nosZ), and anammox functional gene (anammox 16S rRNA) displayed various changes when applied different aeration modes and additional carbon source to each system. An increase of the DO concentration and carbon source facilitated the absolute abundance of microbial nitrification and denitrification functional genes, respectively. All in all, these results demonstrate that carbon source combined with intermittent aeration is valid to improve the pollutant treatment performance in these systems.

The effect of re-startup strategies on the recovery of constructed wetlands after long-term resting operation

The objective of this study was to identify the proper re-startup strategies (RSSs) for constructed wetlands (CWs) after long-term resting operation in terms of the recovery of pollutant removal efficiency (RE) and N-cycle gene abundance. The results suggested that backwashing increased the gene abundance without shortening the recovery time of gene abundance. The RSS involving excavation and washing performed better in terms of chemical oxygen demand (COD) RE, especially at the beginning, and performed slightly better or similarly in terms of N-cycle gene abundance and the REs of ammonia nitrogen (NH₄⁺-N) and total nitrogen (TN). The abundance of the Amox gene was 66.1-92.8, 76.3-161.8 and 1550-2492 times larger than that of the napA, narG and amoA genes, respectively, and the anammox process was the dominant N removal pathway. Therefore, excavation and washing is recommended as the RSS for CWs with a long-term rest period.

Reverse transcriptase enzyme and priming strategy affect quantification and diversity of environmental transcripts

Reverse-transcriptase-quantitative PCR (RT-Q-PCR) and RT-PCR amplicon sequencing, provide a convenient, target-specific, high-sensitivity approach for gene expression studies and are widely used in environmental microbiology. Yet, the effectiveness and reproducibility of the reverse transcription step has not been evaluated. Therefore, we tested a combination of four commercial reverse transcriptases with two priming techniques to faithfully transcribe 16S rRNA and amoA transcripts from marine sediments. Both enzyme and priming strategy greatly affected quantification of the exact same target with differences of up to 600-fold. Furthermore, the choice of RT system significantly changed the communities recovered. For 16S rRNA, both enzyme and priming had a significant effect with enzyme having a stronger impact than priming. Inversely, for amoA only the change in priming strategy resulted in significant differences between the same samples. Specifically, more OTUs and better coverage of amoA transcripts diversity were obtained with GS priming indicating this approach was better at recovering the diversity of amoA transcripts. Moreover, sequencing of RNA mock communities revealed that, even though transcript α diversities (i.e., OTU counts within a sample) can be biased by the RT, the comparison of β diversities (i.e., differences in OTU counts between samples) is reliable as those biases are reproducible between environments.

Role of in Situ Natural Organic Matter in Mobilizing As during Microbial Reduction of FeIII-Mineral-Bearing Aquifer Sediments from Hanoi (Vietnam)

Natural organic matter (NOM) can contribute to arsenic (As) mobilization as an electron donor for microbially-mediated reductive dissolution of As-bearing Fe(III) (oxyhydr)oxides. However, to investigate this process, instead of using NOM, most laboratory studies used simple fatty acids or sugars, often at relatively high concentrations. To investigate the role of relevant C sources, we therefore extracted in situ NOM from the upper aquitard (clayey silt) and lower sandy aquifer sediments in Van Phuc (Hanoi area, Vietnam), characterized its composition, and used 100-day microcosm experiments to determine the effect of in situ OM on Fe(III) mineral reduction, As mobilization, and microbial community composition. We found that OM extracted from the clayey silt (OMC) aquitard resembles young, not fully degraded plant-related material, while OM from the sandy sediments (OMS) is more bioavailable and related to microbial biomass. Although all microcosms were amended with the same amount of C (12 mg C/L), the extent of Fe(III) reduction after 100 days was the highest with acetate/lactate (43 ± 3.5% of total Fe present in the sediments) followed by OMS (28 ± 0.3%) and OMC (19 ± 0.8%). Initial Fe(III) reduction rates were also higher with acetate/lactate (0.53 mg Fe(II) in 6 days) than with OMS and OMC (0.18 and 0.08 mg Fe(II) in 6 days, respectively). Although initially more dissolved As was detected in the acetate/lactate setups, after 100 days, higher concentrations of As (8.3 ± 0.3 and 8.8 ± 0.8 μg As/L) were reached in OMC and OMS, respectively, compared to acetate/lactate-amended setups (6.3 ± 0.7 μg As/L). 16S rRNA amplicon sequence analyses revealed that acetate/lactate mainly enriched Geobacter, while in situ OM supported growth and activity of a more diverse microbial community. Our results suggest that although the in situ NOM is less efficient in stimulating microbial Fe(III) reduction than highly bioavailable acetate/lactate, it ultimately has the potential to mobilize the same amount or even more As.

Enhanced optimal removal of nitrogen and organics from intermittently aerated vertical flow constructed wetlands: Relative COD/N ratios and microbial responses

Carbon source and dissolved oxygen are the critical factors which sustain the stable redox environment for the microbes to implement the removal of nitrogen and organics in vertical flow constructed wetlands (VFCWs). The effect mechanisms of the COD/N ratios in intermittently aerated VFCWs are needed to be investigated in order to increase the synchronous removal efficiency of pollutants. In this study, the combined effects of COD/N ratios (3, 6, 12) and intermittent aeration in VFCWs on pollutant removal, microbial communities and related function genes were studied. The results showed the increase of COD/N ratios from 3 to 12 enhanced the removal efficiency of TN, NO₃^--N and COD. The removals of NH₄⁺-N decreased as the COD/N ratio increased. The optimal removals of TN (87.65%), NH₄⁺-N (93.20%), NO₃^--N (80.80%) and COD (73.93%) were obtained in VFCW2 (COD/N ratios was 6). Illumina Miseq High-throughput sequencing analysis showed that high COD/N ratios increased the richness and diversity of microbial communities. The absolute abundance of nirK, nosZ, nirS, amoA, nxrA, and anammox bacterial 16S rRNA presented various changes under the different ratios of COD/N. The increase of COD/N ratios enhanced the copy numbers of nirS, nirK and nosZ, which participate in denitrification process. High COD/N ratios (6 and 12) were in favor of Actinobacteria, Firmicutes and Chloroflexi, which mainly play important roles in the process of denitrification. This paper implies that the combination of carbon source and aeration is necessary to sustain high microbial activities during pollutant removal in VFCWs.

Application of γ-PGA as the primary carbon source to bioremediate a TCE-polluted aquifer: A pilot-scale study

The effectiveness of using gamma poly-glutamic acid (γ-PGA) as the primary carbon and nitrogen sources to bioremediate trichloroethene (TCE)-contaminated groundwater was studied in this pilot-scale study. γ-PGA (40 L) solution was injected into the aquifer via the injection well (IW) for substrate supplement. Groundwater samples were collected from monitor wells and IW and analyzed for TCE and its byproducts, geochemical indicators, dechlorinating bacteria, and microbial diversity periodically. Injected γ-PGA resulted in an increase in total organic carbon (TOC) (up to 9820 mg/L in IW), and the TOC biodegradation caused the formation of anaerobic conditions. Increased ammonia concentration (because of amine release from γ-PGA) resulted in the neutral condition in groundwater, which benefited the growth of Dehalococcoides. The negative zeta potential and micro-scale diameter of γ-PGA allowed its globule to distribute evenly within soil pores. Up to 93% of TCE removal was observed (TCE dropped from 0.14 to 0.01 mg/L) after 59 days of γ-PGA injection, and TCE dechlorination byproducts were also biodegraded subsequently. Next generation sequence (NGS) analyses were applied to determine the dominant bacterial communities. γ-PGA supplement developed reductive dechlorinating conditions and caused variations in microbial diversity and dominant bacterial species. The dominant four groups of bacterial communities including dechlorinating bacteria, vinyl chloride degrading bacteria, hydrogen producing bacteria, and carbon biodegrading bacteria.

RNA Stable Isotope Probing of Potential Feammox Population in Paddy Soil

Anaerobic ammonium oxidation coupled to iron reduction (Feammox) is a recently discovered pathway contributing to nitrogen loss in various ecosystems such as paddy soils and sediments. However, little is known about the microbes driving Feammox in an agricultural ecosystem. Here, we demonstrated the occurrence of Feammox in paddy soils of Southern China using a ¹⁵N isotopic tracing technique, and examined the microbial communities associated with Feammox using RNA based stable isotope probing (RNA-SIP) combined with Illumina sequencing. Feammox was detected in all collected soils with direct N₂ production as the dominant Feammox pathway. It was estimated that approximately 6.91% of the applied nitrogen fertilizers were lost through Feammox in the paddy soils. RNA-SIP results showed that the composition of enriched active microbial communities were dependent on soil properties, especially the soil pH and grain size. Geobacter were enriched in most soils across various properties. The abundance of enriched GOUTA19 were significantly higher in soils with low pH than those in soils with medium pH and high pH, and the relative abundance of active Nitrososphaeraceae and Pseudomonas only increased in soils with medium and high pH during 4-day of incubation. These results suggested Feammox is a ubiquitous and important process for N loss. Geobacter, GOUTA19, Nitrososphaeraceae and Pseudomonas were active during the incubation that favored Feammox and the growth of Feammox microbes, suggesting these microbes were potentially associated with Feammox in natural agricultural soils.

C:N ratio shaped both taxonomic and functional structure of microbial communities in livestock and poultry breeding wastewater treatment reactor

C:N ratios play critical roles in determining the stability and performance of the wastewater treatment reactor. Here, we investigated bacterial and archaeal community composition, diversity, association networks, and functional profiles in livestock and poultry breeding wastewater (LPBW) with C:N gradients from 7.8 to 18.9 using 16S rRNA gene amplicon sequencing. Highest total nitrogen (TN) and total phosphorous (TP) removal rates were detected in the wastewater with high C:N ratios, while bacterial and archaeal communities in the wastewater varied across the four C:N ratios. Proteobacteria, Acidobacteria, and Bacteroides were generally the dominant phyla in the wastewater across treatments, with Candidatus Saccharibacteria being more enriched in the wastewater with high C:N ratios. Association network analysis showed that specific bacterial and archaeal taxa likely have similar metabolic activities allowing them to respond similarly to different C:N ratios. Bacteroidetes, Actinobacteria, Verrucomicrobia, Candidatus Saccharibacteria, and Proteobacteria were the keystone species found in the networks. Most dominant bacterial functions in the wastewater were chemoheterotrophy and aerobic chemoheterotrophy. Nitrite respiration, nitrous oxide denitrification, nitrate denitrification and nitrite denitrification were up-regulated with increased C:N ratios. Our findings provide new insights into our understanding of the compositions, potential associations, and predicted functional profiles of the microbial community in LPBW treated with different C:N ratios.

Functional biodiversity and plasticity of methanogenic biomass from a full-scale mesophilic anaerobic digester treating nitrogen-rich agricultural wastes

The effect of ammonia on methanogenic biomass from a full-scale agricultural digester treating nitrogen-rich materials was characterized in batch activity assays subjected to increasing concentrations of total ammonia N. Acetotrophic and methanogenic profiles displayed prolonged lag phases and reduced specific activity rates at 6.0 gN-TAN L^-1, though identical methane yields were ultimately reached. These results agreed with the expression levels of selected genes from bacteria and methanogenic archaea (qPCR of 16S rRNA and mrcA cDNA transcripts). Compound-specific isotope analysis of biogas indicated that ammonia exposure was associated to a transition in methanogenic activity from acetotrophy at 1.0 gN-TAN L^-1 to intermediate and complete hydrogenotrophy at 3.5 and 6.0 gN-TAN L^-1. Such pattern matched the results of 16S-Illumina sequencing of genes and transcripts in that predominant methanogens shifted, along with increasing ammonia, from the obligate acetotroph Methanosaeta to the hydrogenotrophic Methanoculleus and the poorly understood methylotrophic Methanomassiliicoccus. The underlying bacterial community structure remained rather stable but, at 6.0 gN-TAN L^-1, the expression level increased considerably for a number of ribotypes that are related to potentially syntrophic genera (e.g. Clostridium, Bellilinea, Longilinea, and Bacteroides). The predominance of hydrogenotrophy at high ammonia levels clearly points to the occurrence of the syntrophic acetate oxidation (SAO), but known SAO bacteria were only found in very low numbers. The potential role of the identified bacterial and archaeal taxa with a view on SAO and on stability of the anaerobic digestion process under ammonia stress has been discussed.

Bacterial community activity and dynamics in the biofilm of an experimental hybrid wetland system treating greywater

The objectives of this study were to determine the biofilm microbial activity and bacterial community structure and successions in greywater treatment filters and to relate the treatment efficiency to the bacterial community parameters. This 10-month study was performed in a newly established experimental system for domestic greywater treatment that consisted of three parallel vertical flow filters (VFs) followed by a horizontal flow filter (HF). A rapid increase in the bacterial community abundance occurred during the first 85 days of filter operations, followed by a short-term decrease and the stabilization of the 16S rRNA gene copy numbers at average levels of 1.2 × 10⁹ and 3.2 × 10⁸ copies/g dw in VFs and HF, respectively, until the end of the experiment. The dominant bacterial phyla and genera differed between the VFs and HF. The temporal variation in the bacterial community structure was primarily related to the species replacement, and it was significantly affected by the influent organic carbon and nitrogen compounds in the VFs and the ammonia and organic carbon in the HF filters. Despite the differences in the community structure and assembly mechanisms, the temporal dynamics of the bacterial community showed high congruence between the filter types. The treatment efficiency was related to the biofilm bacterial community diversity and abundance and the abundance of certain bacterial genera in the VF filters. The results suggest that the dominant pathway of nitrogen removal by greywater treatment VFs occurs via coupled heterotrophic nitrification and denitrification, while the contribution of aerobic denitrification is temporally variable in these filters.

Effects of partially saturated conditions on the metabolically active microbiome and on nitrogen removal in vertical subsurface flow constructed wetlands

Nitrogen dynamics and its association to metabolically active microbial populations were assessed in two vertical subsurface vertical flow (VF) wetlands treating urban wastewater. These VF wetlands were operated in parallel with unsaturated (UVF) and partially saturated (SVF) configurations. The SVF wetland exhibited almost 2-fold higher total nitrogen removal rate (5 g TN m^-2 d^-1) in relation to the UVF wetland (3 g TN m^-2 d^-1), as well as a low NO_x-N accumulation (1 mg L^-1 vs. 26 mg L^-1 in SVF and UVF wetland effluents, respectively). After 6 months of operation, ammonia oxidizing prokaryotes (AOP) and nitrite oxidizing bacteria (NOB) displayed an important role in both wetlands. Oxygen availability and ammonia limiting conditions promoted shifts on the metabolically active nitrifying community within 'nitrification aggregates' of wetland biofilms. Ammonia oxidizing archaea (AOA) and Nitrospira spp. overcame ammonia oxidizing bacteria (AOB) in the oxic layers of both wetlands. Microbial quantitative and diversity assessments revealed a positive correlation between Nitrobacter and AOA, whereas Nitrospira resulted negatively correlated with Nitrobacter and AOB populations. The denitrifying gene expression was enhanced mainly in the bottom layer of the SVF wetland, in concomitance with the depletion of NO_x-N from wastewater. Functional gene expression of nitrifying and denitrifying populations combined with the active microbiome diversity brought new insights on the microbial nitrogen-cycling occurring within VF wetland biofilms under different operational conditions.

Nitrifying activity and ammonia-oxidizing microorganisms in a constructed wetland treating polluted surface water

Ammonia oxidation, performed by both ammonia oxidizing bacteria (AOB) and archaea (AOA), is an important step for nitrogen removal in constructed wetlands (CWs). However, little is known about the distribution of these ammonia oxidizing organisms in CWs and the associated wetland environmental variables. Their relative importance to nitrification in CWs remains still controversial. The present study investigated the seasonal dynamics of AOA and AOB communities in a free water surface flow CW (FWSF-CW) used to ameliorate the quality of polluted river water. Strong seasonality effects on potential nitrification rate (PNR) and the abundance, richness, diversity and structure of AOA and AOB communities were observed in the river water treatment FWSF-CW. PNR was positively correlated to AOB abundance. AOB (6.76×10⁵-6.01×10⁷ bacterial amoA gene copies per gram dry sediment/soil) tended to be much more abundant than AOA (from below quantitative PCR detection limit to 9.62×10⁶ archaeal amoA gene copies per gram dry sediment/soil). Both AOA and AOB abundance were regulated by the levels of nitrogen, phosphorus and organic carbon. Different wetland environmental variables determined the diversity and structure of AOA and AOB communities. Wetland AOA communities were mainly composed of unknown species and Nitrosopumilus-like organisms, while AOB communities were mainly represented by both Nitrosospira and Nitrosomonas.

Vitamin B12 effects on chlorinated methanes-degrading microcosms: Dual isotope and metabolically active microbial populations assessment

Field-derived anoxic microcosms were used to characterize chloroform (CF) and carbon tetrachloride (CT) natural attenuation to compare it with biostimulation scenarios in which vitamin B₁₂ was added (B₁₂/pollutant ratio of 0.01 and 0.1) by means of by-products, carbon and chlorine compound-specific stable-isotope analysis, and the active microbial community through 16S rRNA MiSeq high-throughput sequencing. Autoclaved slurry controls discarded abiotic degradation processes. B₁₂ catalyzed CF and CT biodegradation without the accumulation of dichloromethane, carbon disulphide, or CF. The carbon isotopic fractionation value of CF (ƐC_CF) with B₁₂ was -14±4‰, and the value for chlorine (ƐCl_CF) was -2.4±0.4‰. The carbon isotopic fractionation values of CT (ƐC_CT) were -16±6 with B₁₂, and -13±2‰ without B₁₂; and the chlorine isotopic fractionation values of CT (ƐCl_CT) were -6±3 and -4±2‰, respectively. Acidovorax, Ancylobacter, and Pseudomonas were the most metabolically active genera, whereas Dehalobacter and Desulfitobacterium were below 0.1% of relative abundance. The dual C-Cl element isotope slope (Λ=Δδ¹³C/Δδ³⁷Cl) for CF biodegradation (only detected with B₁₂, 7±1) was similar to that reported for CF reduction by Fe(0) (8±2). Several reductive pathways might be competing in the tested CT scenarios, as evidenced by the lack of CF accumulation when B₁₂ was added, which might be linked to a major activity of Pseudomonas stutzeri; by different chlorine apparent kinetic isotope effect values and Λ which was statistically different with and without B₁₂ (5±1 vs 6.1±0.5), respectively. Thus, positive B₁₂ effects such as CT and CF degradation catalyst were quantified for the first time in isotopic terms, and confirmed with the major activity of species potentially capable of their degradation. Moreover, the indirect benefits of B₁₂ on the degradation of chlorinated ethenes were proved, creating a basis for remediation strategies in multi-contaminant polluted sites.

Effect of ammonia on the active microbiome and metagenome from stable full-scale digesters

Four full-scale anaerobic digesters with a long history of stable operation were characterized in terms of active microbiome and metagenome. Isotopic fractionation of biogas demonstrated that acetotrophy was rather prevalent in reactors operated at <3 gTAN L^-1 while hydrogenotrophy was predominant at >6 gTAN L^-1, suggesting that syntrophic acetate oxidizing bacteria (SAOB) played a significant role in the latter. These results were generally coherent with the observed active bacterial and archaeal communities but no known SAOB were observed. Metagenome descriptions yielded 73 assembled population genomes, of which only 7 could be assigned at the species level. Gene annotation and association to relevant metabolic pathways indicated that the phyla Chloroflexi and Bacteroidales might encompass new, currently undescribed, SAOB/formate producing species that would metabolize acetate via the glycine cleavage system. The predominant hydrogenotrophic counterpart at a high ammonia content belonged to the genus Methanoculleus, which could also grow on acetate to a certain extent.

Constructed wetlands and solar-driven disinfection technologies for sustainable wastewater treatment and reclamation in rural India: SWINGS project

SWINGS was a cooperation project between the European Union and India, aiming at implementing state of the art low-cost technologies for the treatment and reuse of domestic wastewater in rural areas of India. The largest wastewater treatment plant consists of a high-rate anaerobic system, followed by vertical and horizontal subsurface flow constructed wetlands with a treatment area of around 1,900 m² and a final step consisting of solar-driven anodic oxidation (AO) and ultraviolet (UV) disinfection units allowing direct reuse of the treated water. The implementation and operation of two pilot plants in north (Aligarh Muslim University, AMU) and central India (Indira Gandhi National Tribal University, IGNTU) are shown in this study. The overall performance of AMU pilot plant during the first 7 months of operation showed organic matter removal efficiencies of 87% total suspended solids, 95% 5-day biological oxygen demand (BOD₅) and 90% chemical oxygen demand, while Kjeldahl nitrogen removal reached 89%. The UV disinfection unit produces water for irrigation and toilet flushing with pathogenic indicator bacteria well below WHO guidelines. On the other hand, the AO disinfection unit implemented at IGNTU and operated for almost a year has been shown to produce an effluent of sufficient quality to be reused by the local population for agriculture and irrigation.