Identification of active denitrifiers in full-scale nutrient removal wastewater treatment systems

Zeolite mediated processing of nitrogenous waste in the rearing environment influences gut and sediment microbial community in freshwater crayfish (Cherax cainii) culture

Zeolite is known to uptake toxic metals and filter nitrogenous waste from aquaculture effluents. The present study aimed to investigate the impacts of zeolite in three different applications namely, dietary zeolite (DZ), suspended zeolite (SZ) in the water column, and a combination of both (DZSZ) relative to unexposed freshwater crayfish, marron (control). At the end of the 56-days trial, the impact was assessed in terms of characterization of microbial communities in the culture environment and the intestine of marron. Alongside the microbial communities, the innate immune response of marron was also evaluated. The 16S rRNA data showed that marrons exposed to the suspended zeolite had a significant increase of bacterial diversity in the gut, including the restoration of marron core operational taxonomic units (OTUs), relative to other forms of exposures (DZ, DZSZ) and the control. Suspended zeolite alone also increased the number of unshared OTUs and genera, and improved predicted metabolic functions for the biosynthesis and digestion of proteins, amino acids, fatty acids, and hormones. In the tank sediment, the shift of microbial communities was connected more strongly with the time of experiment than the type of zeolite exposure. In the second case, only control marron had a different microbial ordination in terms of rare taxa present in the community. Nevertheless, the modulation in the gut environment was found more prominent in DZ, relative to modulation in the tank sediments. The taxa-environment correlation identified Rhodoferax as the most potential bacteria in removing nitrogenous waste from the rearing environment. Further analysis showed that SZ resulted in the upregulation of genes associated with the innate immune response of marron. Overall results suggest that SZ can be used to enrich microbial communities in the gut and tank sediments and better immune performance of marron.

Unveiling changes of microbial community involved in N and P removal in constructed wetlands with exposing to silver nanoparticles

Constructed wetlands (CWs) are environmentally friendly engineered systems to purify wastewater, with low-cost and easy maintenance. However, it is not clear on responses of functional microbes for nitrogen (N) and phosphorus (P) biotransformation in CWs to silver nanoparticles (Ag NPs). The high throughput sequencings were employed to reveal microbial communities in vertical flow subsurface CWs with stable operation for 120 days. The results indicated that NH₄⁺-N, TN and TP removal of soil layer decreased by 43.56%, 15.7% and 22.7% under stress of Ag NPs. Microbial richness index and compositions were affected, and control wetland enriched Sulfurospirillum, Desulfarculaceae and Flavobacterium whereas CWs exposed to Ag NPs enriched Desulfosporosinus and Desulfurispora from LEfSe analysis. Moreover, after dosing Ag NPs, relative abundances of functional genes amoA and hao for nitrification, nirK and norB for denitrification and ppx and phoA/phoD for phosphorus conversions in upper soil were significantly downregulated. Inhibition on functional bacteria and genes of Ag NPs explained poor removal efficiencies of nitrogen and phosphorus pollutants in CWs. Our findings give an insight into ecological toxicity of Ag NPs on CWs with N and P bioconversions and provide the understanding of response of nitrifiers, denitrifies and PAOs.

Enhanced Nitrogen Removal in a Pilot-Scale Anoxic/Aerobic (A/O) Process Coupling PE Carrier and Nitrifying Bacteria PE Carrier: Performance and Microbial Shift

Integrated fixed-film activated sludge technology (IFAS) has a great advantage in improving nitrogen removal performance and increasing treatment capacity of municipal wastewater treatment plants with limited land for upgrading and reconstruction. This research aims at investigating the enhancing effects of polyethylene (PE) carrier and nitrifying bacteria PE (NBPE) carrier on nitrogen removal efficiency of an anoxic/aerobic (A/O) system from municipal wastewater and revealing temporal changes in microbial community evolution. A pilot-scale A/O system and a pilot-scale IFAS system were operated for nearly 200 days, respectively. Traditional PE and NBPE carriers were added to the IFAS system at different operating phases. Results showed that the treatment capacity of the IFAS system was enhanced by almost 50% and 100% by coupling the PE carrier and NBPE carrier, respectively. For the PE carrier, nitrifying bacteria abundance was maintained at 7.05%. In contrast, the nitrifying bacteria on the NBPE carrier was enriched from 6.66% to 23.17%, which could improve the nitrogen removal and treating capacity of the IFAS system. Finally, the ammonia efficiency of the IFAS system with NBPE carrier reached 73.0 ± 7.9% under 400% influent shock load and hydraulic retention time of 1.8 h. The study supplies a suitable nitrifying bacteria enrichment method that can be used to help enhance the nitrogen removal performance of municipal wastewater treatment plants. The study’s results advance the understanding of this enrichment method that effectively improves nitrogen removal and anti-resistance shock-load capacity.

Elucidating nitrifying performance, nitrite accumulation and microbial community in a three-stage plug flow moving bed biofilm reactor (PF - MBBR)

A three-stage plug flow moving bed biofilm reactor (PF - MBBR, consisting of three identical chambers of N1, N2 and N3) was proposed for nitrifier enrichment using synthetic wastewater. During the stable operation, the average NH₄⁺-N effluent was 0.67 mg/L and NH₄⁺-N removal was as high as 97.19% with the nitrite accumulation ratio (NAR) of 54.23%, although the biofilm thickness and biomass both presented downward trends from N1 (296 μm, 2280 mg/L), N2 (248 μm, 1850 mg/L) to N3 (198 μm, 1545 mg/L). Particularly, the comparative results of three stages revealed that N2 showed the optimum NH₄⁺-N removal (77.27%) and NAR (75.21%) in the continuous-flow, while NAR of N3 unexpectedly maintained a high level of 65.83% in the batch test, suggesting that ammonia oxidizing bacteria (AOB) accounted for absolute advantage over nitrite oxidizing bacteria (NOB). High-throughput sequencing initially verified different distribution of bacterial community structure, where N2 was far away from N1 and N3 with the lowest community richness and community diversity (operational taxonomic units (OTUs): 454(N2)<527(N3)<621(N1)). Proteobacteria (77.60%-83.09%), Bacteroidetes (1.66%-3.66%), Acidobacteria (2.28%-4.67%), and Planctomycetes (1.19%-6.63%) were the major phyla. At the genus level, AOB (mainly Nitrosomonas) accounted for 5.08% (N1), 20.74% (N2) and 14.24% (N3) while NOB (mainly Nitrospira) increased from 0.14% (N1), 7.06% (N2) to 4.91% (N3) with the total percentages of 5.22%, 27.80% and 19.15%. Finally, the application feasibility of MBBR optimization linked with nitrite (NO₂^--N) accumulation for deep-level nutrient removal was discussed.

Regional discrepancy of microbial community structure in activated sludge system from Chinese WWTPs based on high-throughput 16S rDNA sequencing

Overall understanding of microbial community structure in activated sludge (AS) system at regional level is of great significance for operation regulation of wastewater treatment plants (WWTPs). In this study, 110 AS samples from 21 cities in different Chinese regions were analyzed based on high-throughput 16S ribosomal DNA (rDNA) sequencing to explore effects of different regions on microbial community structure. Results showed that the regions with different characteristics (south and north, coastal and inland, high GDP and low GDP) had great impact on AS bacterial community in China. Core bacterial communities (101 OTUs) in south China were more abundant than those in north China (49 OTUs), and many core species in south China were associated with nutrient removal. Coastal WWTPs possessed unique bacterial communities due to the influence of marine bacteria. Phyla Chloroflexi and Acidobacteria were observed to be main biomarkers in coastal WWTPs. Compared with low GDP regions, more diverse microbial community and effective wastewater treatment were discovered in high GDP regions, and environmental factor analysis suggested that they were mainly correlated with high capacity and influent TP in the WWTPs. β nearest taxon index (βNTI) analysis showed that microbial community assembly in the analyzed AS samples was dominated by deterministic factors (70.67%) and influent quality was observed to be main factor.

Quantification of Biologically and Chemically Bound Phosphorus in Activated Sludge from Full-Scale Plants with Biological P-Removal

Phosphorus (P) is present in activated sludge from wastewater treatment plants in the form of metal salt precipitates, extracellular polymeric substances, or bound into the biomass, for example, as intracellular polyphosphate (poly-P). Several methods for a reliable quantification of the different P-fractions have recently been developed, and this study combines them to obtain a comprehensive P mass-balance of activated sludge from four enhanced biological phosphate removal (EBPR) plants. Chemical characterization by ICP-OES and sequential P fractionation showed that chemically bound P constituted 38-69% of total P, most likely in the form of Fe, Mg, or Al minerals. Raman microspectroscopy, solution state ³¹P NMR, and ³¹P MAS NMR spectroscopy applied before and after anaerobic P-release experiments, were used to quantify poly-P, which constituted 22-54% of total P and was found in approximately 25% of all bacterial cells. Raman microspectroscopy in combination with fluorescence in situ hybridization was used to quantify poly-P in known polyphosphate-accumulating organisms (PAO) (Tetrasphaera, Candidatus Accumulibacter, and Dechloromonas) and other microorganisms known to possess high level of poly-P, such as the filamentous Ca. Microthrix. Interestingly, only 1-13% of total P was stored by unidentified PAO, highlighting that most PAOs in the full-scale EBPR plants investigated are known.

Rapid granulation of aerobic granular sludge and maintaining its stability by combining the effects of multi-ionic matrix and bio-carrier in a continuous-flow membrane bioreactor

The present investigation aimed at providing a novel approach to promote the rapid granulation and stability of aerobic granular sludge (AGS) in a continuous-flow membrane bioreactor (MBR). By operating two identical MBRs with or with no bio-carrier for 125 days, it was found that the combination of multi-ionic matrix and bio-carrier could promote the rapid formation and maintain the long-term stability of AGS. The primary AGS was first observed inside the reactor on day 14, and the mature AGS appeared soon and kept stable for more than 4 months (its average size still was about 800 μm on day 125). Suitable filling ratio of bio-carrier was beneficial to form a stable and regular circulating water flow inside, and adding divalent metal ions quickly reduced the negative charges of tiny sludge particles, which were two essential factors leading to the rapid granulation of AGS and maintaining its stability. The multi-ionic matrix not only enhanced the biological aggregation process, but also facilitated the expansion of the cultivated AGS into a new multi-habitat system of Mn-AGS, in which, complex microbial communities with rich bio-diversity robustly promoted the efficient removal of organic pollutants and nutrients.

Enhanced mainstream nitrogen removal from synthetic wastewater using gel-immobilized anammox in fluidized bed bioreactors: Process performance and disintegration mechanisms

Anammox retention, which is crucial for successful nitrogen removal because of slow growth, is still a major challenge. Fixed film processes or gel-immobilization techniques can minimize biomass washout. However, the detachment mechanisms from gel-immobilized beads are still unclear. Despite the widely known advantages of fluidized bed reactor (FBR) with respect to biomass retention, the technology has not been investigated for anammox processes, and thus, the current study evaluated the feasibility of using immobilized anammox gel beads as a carrier media in anammox fluidized bed reactor (AFBR), with a particular focus on understanding detachment mechanisms. The study optimized the packing ratio in AFBR and compared holed and non-holed beads. The optimum packing ratio (on a volumetric basis) was 30% (v/v) with a nitrogen removal rate (NRR) of 0.40 kg N/m³-d at a volumetric nitrogen loading rate (NLR) of 0.51 kg N/m³-d. Biomass detachment rates increased linearly with specific anammox activity (SAA). The fluidized bed reactor employing holed (more porous) anammox gel beads (HFBR) exhibited 20% lower biomass detachment rates than the non-holed fluidized bed reactor (NHFBR). Moreover, the HFBR achieved a maximum NRR of 0.81 kg N/m³-d at NLR of 1.01 kg N/m³-d after 35 days without operational problems, whereas the NHFBR with non-holed anammox gel beads failed after 30 days. The hindrance to diffusion of the generated nitrogen gas was the main mechanism of beads breakup and biomass washout, and thus, the sustainability of the beads hinges on increased external porosity. Therefore, developing microporous gel beads is critical for achieving a high rate stable anammox process that overcomes the limitations of the current technologies.

The structure of microbial communities of activated sludge of large-scale wastewater treatment plants in the city of Moscow

Microbial communities in wastewater treatment plants (WWTPs) play a key role in water purification. Microbial communities of activated sludge (AS) vary extensively based on plant operating technology, influent characteristics and WWTP capacity. In this study we performed 16S rRNA gene profiling of AS at nine large-scale WWTPs responsible for the treatment of municipal sewage from the city of Moscow, Russia. Two plants employed conventional aerobic process, one plant-nitrification/denitrification technology, and six plants were operated with the University of Cape Town (UCT) anaerobic/anoxic/oxic process. Microbial communities were impacted by the technology and dominated by the Proteobacteria, Bacteroidota and Actinobacteriota. WWTPs employing the UCT process enabled efficient removal of not only organic matter, but also nitrogen and phosphorus, consistently with the high content of ammonia-oxidizing Nitrosomonas sp. and phosphate-accumulating bacteria. The latter group was represented by Candidatus Accumulibacter, Tetrasphaera sp. and denitrifiers. Co-occurrence network analysis provided information on key hub microorganisms in AS, which may be targeted for manipulating the AS stability and performance. Comparison of AS communities from WWTPs in Moscow and worldwide revealed that Moscow samples clustered together indicating that influent characteristics, related to social, cultural and environmental factors, could be more important than a plant operating technology.

Efficacies of Nitrogen Removal and Comparisons of Microbial Communities in Full-Scale (Pre-Anoxic Systems) Municipal Water Resource Recovery Facilities at Low and High COD:TN Ratios

At a low COD:TN ratio (≤5) in influent, maintaining a longer HRT (≥9 h) and longer SRT (≥30 d) are suggested to improve higher N removal efficiency in case of operation at low DO (Dissolved oxygen) level (0.9 ± 0.2 mg-O2/L). However, in case of operation at high DO level (4.0 ± 0.5 mg-O2/L), short HRT (1 h) and typical SRT (17 d) make it possible to achieve nitrogen removal. On the other hand, at a high COD:TN ratio (≥8.4), a typical HRT (9–15 h), SRT (12–19 d), and DO level (1.3–2.6 mg-O2/L) would be applied. Microbial distribution analysis showed an abundance of AOA (Ammonia-oxidizing archaea) under conditions of low DO (≤0.9 mg-O2/L). Nitrosomonas sp. are mostly found in the all investigated water resource recovery facilities (WRRFs). Nitrosospira sp. are only found under operating conditions of longer SRT for WRRFs with a low COD:TN ratio. In comparison between abundances of Nitrobacter sp. and Nitrospira sp., abundances of Nitrobacter sp. are proportional to low DO concentration rather than abundance of Nitrospira sp. A predominance of nosZ-type denitrifiers were found at low DO level. Abundance of denitrifiers by using nirS genes showed an over-abundance of denitrifiers by using nirK genes at low and high COD:TN ratios.

Mainstream partial denitrification-anammox (PD/A) for municipal sewage treatment from moderate to low temperature: Reactor performance and bacterial structure

Anammox is sensitive to temperature, which can limit its practical application in wastewater treatment. In this study, a step-feed anoxic-oxic (A/O) process coupled with PD/A was operated steadily from 26.8 °C to 13.1 °C for wastewater treatment for 200 days. The effluent total inorganic nitrogen (TIN) and phosphorus concentrations were 10.2 mg/L and 0.29 mg/L at C/N ratio of 4.6 and 15.0 °C even with increasing nitrogen loading rate (NLR). The anammox activity was 5.60 mg NH₄⁺-N/gMLSS/d even at 14 °C, moreover, anammox abundance on the biocarriers increased with decreasing temperature. It was observed that the effect of partial denitrification (PD) was enhanced under low temperature, thus the contribution of anammox for nitrogen removal was improved. The pathway of anammox for nitrogen removal accounted for 48% and the effect of effluent did not deteriorate under low temperature. This study states that PD/A has advantages under low temperature operation, which is suitable for treatment of wastewater with low C/N ratio.

When FLOW-FISH met FACS: Combining multiparametric, dynamic approaches for microbial single-cell research in the total environment

In environmental microbiology, the ability to assess, in a high-throughput way, single-cells within microbial communities is key to understand their heterogeneity. Fluorescence in situ hybridization (FISH) uses fluorescently labeled oligonucleotide probes to detect, identify, and quantify single cells of specific taxonomic groups. The combination of Flow Cytometry (FLOW) with FISH (FLOW-FISH) enables high-throughput quantification of complex whole cell populations, which when associated with fluorescence-activated cell sorting (FACS) enables sorting of target microorganisms. These sorted cells may be investigated in many ways, for instance opening new avenues for cytomics at a single-cell scale. In this review, an overview of FISH and FLOW methodologies is provided, addressing conventional methods, signal amplification approaches, common fluorophores for cell physiology parameters evaluation, and model variation techniques as well. The coupling of FLOW-FISH-FACS is explored in the context of different downstream applications of sorted cells. Current and emerging applications in environmental microbiology to outline the interactions and processes of complex microbial communities within soil, water, animal microbiota, polymicrobial biofilms, and food samples, are described.

Achieving rapid mainstream deammonification through inoculating long-term refrigerated sidestream sludge in plug-flow fixed-bed biofilm reactor

The start-up of a stable mainstream deammonification requires sufficient anaerobic ammonia-oxidizing bacteria (AnAOB). This study used a plug-flow fixed-bed reactor (PFBR) to verify the feasibility of establishing the mainstream deammonification system by inoculating the sidestream sludge after long-term refrigeration. A rapid resuscitation of the mainstream deammonification system was accomplished by controlling the front-end aeration rate of the PFBR. Results showed that the system was rapidly resuscitated in 44 days eventually with the nitrogen removal rate and nitrogen removal efficiency of 0.1 kg N·(m³·d)^-1 and 79.1%, respectively. Also, the efficient performance was secured by the proportionate approaching equilibrium of AnAOB and ammonia-oxidizing bacteria (AOB) activity of 2.35 ± 0.40 and 2.60 ± 0.29 mg N·(g VSS·h)^-1, respectively. In addition, Pearson correlation analysis revealed that AnAOB abundance (detected Candidatus Kuenenia) negatively correlated with the AOB (mainly Nitrosomonas)/AnAOB abundance ratio, while correlated positively with the residual ammonium concentration of a region. Furthermore, long-term refrigeration probably reduced the cross-feed relationship between AnAOB and other symbiotic organisms (Armatimonadetes and Chloroflexi) to maintain the basic metabolism. Meanwhile, extracellular polymeric substances produced by other genera (order Xanthomonadales and Pseudomonadales) decreased the mass transfer, protecting AnAOB from unfavorable conditions, thereby facilitating high AnAOB abundance during refrigeration. Thus, this study provides a promising perspective towards the practical applications of mainstream process.

Contrasting Patterns of the Resident and Active Rhizosphere Bacterial Communities of Phragmites Australis

Rhizosphere microbes play a key role in maintaining plant health and regulating biogeochemical cycles. The active bacterial community (ABC) in rhizosphere, as a small fraction of the rhizosphere resident bacterial community (RBC), has the potential to actively participate in nutrient cycling processes at the root-sediment interface. Here, we investigated the ABC and RBC within the rhizosphere of Phragmites australis (P. australis) subjected to different environmental conditions (i.e., seasons and flooding conditions) in Lake Taihu, China. Our results indicated that RBC exhibited significantly higher alpha diversity as well as lower beta diversity than ABC. The active ratios of 16S rRNA to 16S rDNA (also RNA/DNA) of the bacterial communities in summer and winter suggested a lower proportion of potential active taxa in the rhizosphere bacterial community during summer. Network analysis showed that negative correlations in each network were observed to dominate the species correlations between the rhizosphere and bulk sediment bacterial communities. Our results revealed that niche differentiation and seasonal variation played crucial roles in driving the assembly of ABC and RBC associated with the rhizospheres of P. australis. These findings broaden our knowledge about how rhizosphere bacterial communities respond to environmental variations through changing their diversity and composition.

Effect of dredging and capping with clean soil on the mitigation of algae-induced black blooms in Lake Taihu, China: A simulation study

Sediment is an important source of matter that causes blackening and odor formation in a water body. The restoration of polluted sediment can suppress algae-induced black blooms to a certain degree. In this study, we compared the control effects of sediment dredging and capping with clean soil on algae-induced black blooms in Lake Taihu using indoor simulation experiments. In addition, we explored the driving effect of temperature on algae-induced black blooms using the method of gradual warming (18, 23, and 28 °C) during the experiment. No blackening of the water body was observed in the simulation stages I (18 °C) and II (23 °C), and the blackening and odor formation occurred within 3 d when the temperature increased to 28 °C in stage III, implying that high temperature was an important driving factor for algae-induced black blooms. Dredging and capping inhibited the blackening and odor formation to some extent, and the colorimetric values in the water columns were lower in the treatment groups than in the control group. At the end of the experiment, the colorimetric values of dredging and capping treatments were 56.5% and 96.7% of the colorimetric value of the control group, respectively. The control effect of dredging on the blackening elements, i.e., Fe²⁺ and S^2- and the main odor forming compounds, i.e., dimethyl disulfide (DMDS) and dimethyl trisulfide (DMTS) was observed in stage II (11-20 d) and stage III (21-27 d), respectively, and the inhibition ability of dredging to suppress algal-induced black blooms was superior than that of capping with clean soil.

Machine-learning insights into nitrate-reducing communities in a full-scale municipal wastewater treatment plant

This study carried out machine-learning (ML) modeling using activated sludge microbiome data to predict the operational characteristics of biological unit processes (i.e., anaerobic, anoxic, and aerobic) in a full-scale municipal wastewater treatment plant. An ML application pipeline with optimization strategies (e.g., model selection, input data preprocessing, and hyperparameter tuning) could significantly improve prediction performance. Comparative analysis of the ML prediction performance suggested that linear models (support vector machine and logistic regression) had a high prediction performance (93% accuracy), comparable to that of non-linear models such as random forest. Feature importance analysis using the linear ML models identified the microbial taxa that were specifically associated with anoxic processes, many of which (e.g., Ferruginibacter) were found to have ecologically important genomic and phenotypic characteristics (e.g., for nitrate reduction). Time-series microbial community dynamics demonstrated that the taxa identified using ML were frequently occurring and dominating in the anoxic process over time, thus representing the core nitrate-reducing community. Despite the general dominance of the core community over time, the analysis further revealed successional seasonal patterns of distinct sub-groups, indicating differences in the functional contribution of sub-groups by season to the overall nitrate-reducing potential of the system. Overall, the results of this study suggest that ML modeling holds great promise for the predictive identification and understanding of key microbial players governing the functioning and stability of biological wastewater systems.

Nutrients removal from low C/N actual municipal wastewater by partial nitritation/anammox (PN/A) coupling with a step-feed anaerobic-anoxic-oxic (A/A/O) system

In this study, a novel combined strategy was successfully established by partial nitritation/anammox (PN/A) within a step-feed A/A/O process integrated with fixed-biocarriers to treat municipal sewage for 200 days. The excellent nutrients removal performance of this system compared with national level of discharging standard were achieved: low total inorganic nitrogen (7.1 mg/L) and phosphorus (0.3 mg/L) in the effluent with the influent (51.1 and 4.2 mg/L) at C/N ratios of 3.4 ± 0.5, mainly attributed to the stable PN (oxic zone) and subsequently anammox effect (anoxic zone). Nitrogen mass balance indicated that anammox contribution in anoxic zones to nitrogen loss could be up to 42% at stable phase. Therefore, aeration and carbon cost could be greatly reduced under low DO, low C/N and aerobic hydraulic retention time (HRT) of 7.4 h condition. The low DO and anammox bacteria retention in anoxic chambers promoted the washout of NOB and combination of anammox and partial nitritation process. During long-term operation, the activity of AOB effectively maintained while that of NOB drastically reduced to 0.1 mg N / g MLSS / h resulting in high and stable nitrite accumulation ratios (about 90%). The achievement of partial nitritation was mainly due to low DO (0.4-0.5 mg/L) and effective retention of anammox bacteria even with a low temperature (14.5 °C). Notedly, anammox activity gradually increased both on the biocarriers and in the flocs while a higher anammox abundance was observed on the biocarriers (2.48%) than that in suspend flocs (0.03%). As above, this study indicated that the novel combined strategies could be applicable to mainstream anammox, and a pilot-scale reactor will be established to verify and promote the industrial application of mainstream anammox.

The metabolic patterns of the complete nitrates removal in the biofilm denitrification systems supported by polymer and water-soluble carbon sources as the electron donors

In this study, two denitrification bio-filters adopted polycaprolactone (PCL) and sodium acetate (NaAc) as polymer and water-soluble carbon sources respectively. With the increasing influent nitrate concentrations, NaAc bio-filter always had shorter HRT to achieve complete nitrate removal. Furthermore, the optimal volumetric denitrification rate in NaAc bio-filter was 0.728 g N/(L·d), which was higher than 0.561 g N/(L·d) in PCL bio-filter. For nitrates removal, the costs of bio-filters supported by NaAc and PCL were 24.93 and 120.25 CNY/kg N respectively. Although Proteobacteria in PCL bio-filter was abundant with 83.98%, NaAc bio-filter had better denitrification performance, due to the appropriate ratio of nitrate removal microorganisms and organic matters degradation organisms. The total abundance value of the denitrification genera is NaAc (16.06%) < PCL (41.19%). However, PCL bio-filter had poor denitrification performance, due to the lower adequacy of PCL depolymerization enzymes and the low expression of the key genes for denitrification.

"Candidatus Dechloromonas phosphoritropha" and "Ca. D. phosphorivorans", novel polyphosphate accumulating organisms abundant in wastewater treatment systems

Members of the genus Dechloromonas are often abundant in enhanced biological phosphorus removal (EBPR) systems and are recognized putative polyphosphate accumulating organisms (PAOs), but their role in phosphate removal is still unclear. Here, we used 16S rRNA gene sequencing and fluorescence in situ hybridization (FISH) to investigate the abundance and distribution of Dechloromonas spp. in Danish and global wastewater treatment plants. The two most abundant species worldwide revealed in situ dynamics of important intracellular storage polymers, measured by FISH-Raman in activated sludge from four full-scale EBPR plants and from a lab-scale reactor fed with different substrates. Moreover, seven distinct Dechloromonas species were determined from a set of ten high-quality metagenome-assembled genomes (MAGs) from Danish EBPR plants, each encoding the potential for polyphosphate (poly-P), glycogen, and polyhydroxyalkanoates (PHA) accumulation. The two species exhibited an in situ phenotype in complete accordance with the metabolic information retrieved by the MAGs, with dynamic levels of poly-P, glycogen, and PHA during feast-famine anaerobic-aerobic cycling, legitimately placing these microorganisms among the important PAOs. They are potentially involved in denitrification showing niche partitioning within the genus and with other important PAOs. As no isolates are available for the two species, we propose the names Candidatus Dechloromonas phosphoritropha and Candidatus Dechloromonas phosphorivorans.

Response of microbial nitrogen transformation processes to antibiotic stress in a drinking water reservoir

Effects of antibiotics on microbial nitrogen transformation processes in natural aquatic ecosystems are largely unknown. In this study, we utilized the ¹⁵N stable isotope tracers and metagenomic sequencing to identify how antibiotics drive nitrogen transformation processes in Danjiangkou Reservoir, which is the largest artificial drinking water reservoir in China. We retrieved 51 nitrogen functional genes, and found that the highest abundances of nitrate reduction and denitrification-related genes occurred in dissimilatory nitrogen transformation pathways. ¹⁵N-labelling analysis substantiated that denitrification was the main pathway for nitrogen removal, accounting for 57.1% of nitrogen loss. Nitrogen functional genes and antibiotic resistance genes co-occurred in Danjiangkou Reservoir, and they were mainly carried by the denitrifying bacteria such as Rhodoferax, Polaromonas, Limnohabitans, Pararheinheimera, Desulfobulbus, and Pseudopelobacter. Genome annotation revealed that antibiotic deactivation, Resistance-Nodulation-Division and facilitator superfamily efflux pumps were responsible for the multiple-resistance to antibiotics in these bacteria. Moreover, antibiotics showed non-significant effects on nitrogen transformation processes. It is speculated that denitrifying bacteria harboring ARGs played crucial roles in protecting nitrogen transformation from low-level antibiotics stress in the reservoir. Our results highlight that denitrifying bacteria are important hosts of ARGs, which provides a novel perspective for evaluating the effects of antibiotics on nitrogen cycle in natural aquatic ecosystems.

Spatial Variation of Cladophora Epiphytes in the Nan River, Thailand

Cladophora is an algal genus known to be ecologically important. It provides habitats for microorganisms known to provide ecological services such as biosynthesis of cobalamin (vitamin B12) and nutrient cycling. Most knowledge of microbiomes was obtained from studies of lacustrine Cladophora species. However, whether lotic freshwater Cladophora microbiomes are as complex as the lentic ones or provide similar ecological services is not known. To illuminate these issues, we used amplicons of 16S rDNA, 18S rDNA, and ITS to investigate the taxonomy and diversity of the microorganisms associated with replicate Cladophora samples from three sites along the Nan River, Thailand. Results showed that the diversity of prokaryotic and eukaryotic members of Cladophora microbiomes collected from different sampling sites was statistically different. Fifty percent of the identifiable taxa were shared across sampling sites: these included organisms belonging to different trophic levels, decomposers, and heterotrophic bacteria. These heterogeneous assemblages of bacteria, by functional inference, have the potential to perform various ecological functions, i.e., cellulose degradation, cobalamin biosynthesis, fermentative hydrogen production, ammonium oxidation, amino acid fermentation, dissimilatory reduction of nitrate to ammonium, nitrite reduction, nitrate reduction, sulfur reduction, polyphosphate accumulation, denitrifying phosphorus-accumulation, and degradation of aromatic compounds. Results suggested that river populations of Cladophora provide ecologically important habitat for microorganisms that are key to nutrient cycling in lotic ecosystems.

Tracking de novo protein synthesis in the activated sludge microbiome using BONCAT-FACS

In order to ensure stable performance of engineered biotechnologies that rely on mixed microbial community systems, it is important to identify process-specific microbial traits and study their in-situ activity and responses to changing environmental conditions and system operational parameters. We used BioOrthogonal Non-Canonical Amino acid Tagging (BONCAT) in combination with Fluorescence-Activated Cell Sorting (FACS) and 16S rRNA gene amplicon sequencing to identify translationally active cells in activated sludge. We found that only a subset of the activated sludge microbiome is translationally active during the aerobic treatment phase of a full-scale sequencing batch reactor designed to enhance biological phosphorus removal from municipal wastewater. Relative abundance of amplicon sequence variants was not a reliable predictor of species activity. BONCAT-positive and -negative cells revealed a broad range of population-wide and taxa-specific translational heterogeneity. BONCAT-FACS in combination with amplicon sequencing can provide new insights into the ecophysiology of highly dynamic microbiomes in activated sludge systems.

Effects of cloransulam-methyl and diclosulam on soil nitrogen and carbon cycle-related microorganisms

Cloransulam-methyl and diclosulam are applied to soybean fields to control broad-leaved weeds. These herbicides have become a focus of attention because of their low application dose and high-efficiency advantages. However, the effects of these two herbicides on soil microorganisms are unknown. The present study investigated the effects of 0.05, 0.5, and 2.5 mg kg^-1 of cloransulam-methyl or diclosulam on soil microbes after 7, 14, 28, 42, and 56 days of exposure. The results showed that the two herbicides increased the abundances of functional bacteria related to pesticide degradation. Based on the genetic expression results, we speculated that 0.05 mg kg^-1 of these two herbicides inhibited the nitrification reaction but promoted the denitrification reaction. Diclosulam at a concentration of 0.5 mg kg^-1 may enhance the ability of microbes to fix carbon. β-glucosidase activity was activated by the two herbicides at a concentration of 2.5 mg kg^-1. Diclosulam had a positive effect on urease, but cloransulam-methyl activated urease activity only at concentrations of 0.05 and 0.5 mg kg^-1. The results of the integrated biomarker response showed that the toxicity of diclosulam was greater than that of cloransulam-methyl. Our research provides data for evaluating the environmental risks of cloransulam-methyl and diclosulam.

Partitioning of nutrient removal contribution between granules and flocs in a hybrid granular activated sludge system

Sludge granulation in continuous-flow systems is an emerging technology to intensify existing activated sludge infrastructure for nutrient removal. In these systems, the nutrient removal contributions and partitioning of microbial functions between granules and flocs can offer insights into process implementations. To this end, a reactor system that simulates the continuous-flow environment using an equal amount of initial granule and floc biomass was investigated. The two operational strategies for maintaining granule growth in the continuous-flow system were (a) the higher solids retention time (SRT) for the granules versus flocs, as well as (b) selective feeding of carbon to the granules. The SRT of the large granule fractions (>425 µm, LG) and floc/small granule fractions (<425 µm, FSG) were controlled at 20 and 2.7-6.0 days, respectively. Long term operation of the hybrid granule/floc system achieved high PO₄^3- and NH₄⁺ removal efficiencies. Higher polyphosphate-accumulating organisms (PAO) activity was observed in the FSG than LG, while ammonia-oxidizing bacteria (AOB) activities were similar in the two biomass fractions. Nitrite shunt was observed in the FSG, possibly due to out-competition by the high NOB activity in LG. More importantly, washing out the FSG caused a reduction in LG's AOB and PAO activity, indicating a possible dependency of LG on FSG for maintaining its nutrient removal capacity. Our findings highlighted the partitioning and potential competition/cooperation of key microbial functional groups between LG and FSG, facilitating nutrient removal in a hybrid granular activated sludge system, as well as implications for practical application of the treatment platform.

Micropollutant transformation and taxonomic composition in hybrid MBBR - A comparison of carrier-attached biofilm and suspended sludge

The suspended sludge and carrier-attached biofilms of three different hybrid moving bed biofilm reactor (MBBR) systems were investigated with respect to their transformation potential for a broad range of micropollutants (MPs) as well as their microbial community composition. For this purpose, laboratory-scale batch experiments were conducted with the separated suspended sludge and the carrier-attached biofilm of every system in triplicate. For all batches the removal of 31 MPs as well as the composition of the microbial community were analyzed. The carrier-attached biofilms from two hybrid MBBR systems showed a significant higher overall transformation potential in comparison to the respective suspended sludge. Especially for the MPs trimethoprim, diclofenac, mecoprop, climbazole and the human metabolite 10,11-dihydro-10-hydroxycarbamazepine consistently higher pseudo-first-order transformation rates could be observed in all three systems. The analysis of the taxonomic composition revealed taxa showing higher relative abundances in the carrier-attached biofilms (e. g. Nitrospirae and Chloroflexi) and in the suspended biomasses (e. g. Bacteroidetes and Betaproteobacteria). Correlations of the biodiversity indices and the MP biotransformation rates resulted in significant positive associations for 11 compounds in suspended sludge, but mostly negative associations for the carrier-attached biofilms. The distinct differences in MP removal between suspended sludge and carrier-attached biofilm of the three different MBBR systems were also reflected by a statistically significant link between the occurrence of specific bacterial taxa (Acidibacter, Nitrospira and Rhizomicrobium) and MP transformation rates of certain MPs. Even though the identified correlations might not necessarily be of causal nature, some of the identified taxa might serve as suitable indicators for the transformation potential of suspended sludge or carrier-attached biofilms.

Intercropping improves heavy metal phytoremediation efficiency through changing properties of rhizosphere soil in bamboo plantation

Moso bamboo is considered a potential species for heavy metal (HM) phytoremediation; however, the effect of intercropping on rhizosphere and phytoextraction remains to be elucidated. We comparatively investigated rhizobacteria, soil properties, and phytoextraction efficiency of monoculture and intercropping of Moso bamboo and Sedum plumbizincicola in Cu/Zn/Cd-contaminated soil. Compared with monocultures, intercropping increased the bacterial α-diversity indices (Shannon, Chao1) and the number of biomarkers. Intercropping reduced the contents of soil organic matter (SOM), available nutrients, and Cd and Cu in rhizosphere soils, and reduced the Cd and Zn contents in tissues of sedum. By contrast, Cd and Zn contents in tissues of bamboo increased, and the increase of organic acid in root exudates from intercropping could facilitate the HM absorption. The total amount of Cu, Zn, and Cd removed from the soil in intercropping system was 1.2, 1.9, and 1.8 times than those in monoculture bamboo, respectively. The abundances of Proteobacteria, Acidobacteria, Verrucomicrobia and Actinobacteria were higher in intercropping, playing an important role in soil nutrient cycles and HM remediation. These bacterial communities were closely correlated (P < 0.01) with SOM, available nitrogen, available phosphorus, and HMs. The results suggested this intercropping pattern can increase HM removal efficiency from polluted soils.

Nitrate Removal by a Novel Lithoautotrophic Nitrate-Reducing, Iron(II)-Oxidizing Culture Enriched from a Pyrite-Rich Limestone Aquifer

Nitrate removal in oligotrophic environments is often limited by the availability of suitable organic electron donors. Chemolithoautotrophic bacteria may play a key role in denitrification in aquifers depleted in organic carbon. Under anoxic and circumneutral pH conditions, iron(II) was hypothesized to serve as an electron donor for microbially mediated nitrate reduction by Fe(II)-oxidizing (NRFeOx) microorganisms. However, lithoautotrophic NRFeOx cultures have never been enriched from any aquifer, and as such, there are no model cultures available to study the physiology and geochemistry of this potentially environmentally relevant process. Using iron(II) as an electron donor, we enriched a lithoautotrophic NRFeOx culture from nitrate-containing groundwater of a pyrite-rich limestone aquifer. In the enriched NRFeOx culture that does not require additional organic cosubstrates for growth, within 7 to 11 days, 0.3 to 0.5 mM nitrate was reduced and 1.3 to 2 mM iron(II) was oxidized, leading to a stoichiometric NO₃^-/Fe(II) ratio of 0.2, with N₂ and N₂O identified as the main nitrate reduction products. Short-range ordered Fe(III) (oxyhydr)oxides were the product of iron(II) oxidation. Microorganisms were observed to be closely associated with formed minerals, but only few cells were encrusted, suggesting that most of the bacteria were able to avoid mineral precipitation at their surface. Analysis of the microbial community by long-read 16S rRNA gene sequencing revealed that the culture is dominated by members of the Gallionellaceae family that are known as autotrophic, neutrophilic, and microaerophilic iron(II) oxidizers. In summary, our study suggests that NRFeOx mediated by lithoautotrophic bacteria can lead to nitrate removal in anthropogenically affected aquifers. IMPORTANCE Removal of nitrate by microbial denitrification in groundwater is often limited by low concentrations of organic carbon. In these carbon-poor ecosystems, nitrate-reducing bacteria that can use inorganic compounds such as Fe(II) (NRFeOx) as electron donors could play a major role in nitrate removal. However, no lithoautotrophic NRFeOx culture has been successfully isolated or enriched from this type of environment, and as such, there are no model cultures available to study the rate-limiting factors of this potentially important process. Here, we present the physiology and microbial community composition of a novel lithoautotrophic NRFeOx culture enriched from a fractured aquifer in southern Germany. The culture is dominated by a putative Fe(II) oxidizer affiliated with the Gallionellaceae family and performs nitrate reduction coupled to Fe(II) oxidation leading to N₂O and N₂ formation without the addition of organic substrates. Our analyses demonstrate that lithoautotrophic NRFeOx can potentially lead to nitrate removal in nitrate-contaminated aquifers.

Anammox enrichment: impact of sludge retention time on nitrogen removal

Enrichment of anammox bacteria has long been considered to be time-consuming because of the slow growth rate. This study evaluated the impact of sludge retention time (SRT) on the enrichment of anammox bacteria with a focus on nitrogen removal and specific anammox activity (SAA) in sequencing batch reactors (SBR). A total of eight different SRTs in the range of 30-1280 days at nitrogen loading rates (NLR) range from 12.1 to 122.1 mg/L-d were used to evaluate the anammox activity. SAA was negligible during the first 105 days due to denitrification and continued to increase thereafter to peak at 0.22 g N/g VSS-d on day 530 as the solids and hydraulic retention times (SRT and HRT) decreased from 120 to 80 days and 10 to 2 days, respectively. The stability of SAA (0.21 ± 0.02 g N/g VSS-d) from day 503 to day 670 indicates that anammox bacteria should be enriched at SRTs ranging from 30 to 80 days and NLR of 122.1 mg N/L-d. Moreover, the SBR achieved a maximum nitrogen removal efficiency of 86.6% at an SRT of 30 days and an NLR of 122 mg/L-d. Microbial analysis indicated that the two most abundant microorganisms accounting for 48% of the bacterial population are Anammoxoglobus followed by the heterotrophic denitrifier Rhizobiales. The maximum specific growth rate (was estimated as 0.062 d-1, consistent with typical of 0.057 d-1. The average first-order decay rate was estimated as 0.008 d-1, and the half-saturation constants (ks) averaged 16.2 mg NH4-N/L.

Seasonal dynamics of the microbial community in two full-scale wastewater treatment plants: Diversity, composition, phylogenetic group based assembly and co-occurrence pattern

The optimal operation and functional stability of a wastewater treatment plant (WWTP) strongly depend on the properties of its microbial community. However, a knowledge gap remains regarding the seasonal dynamics of microbial community properties, especially phylogenetic group based assembly and co-occurrence patterns. Accordingly, in this study, influent and activated sludge (AS) samples were weekly collected from 2 full-scale WWTPs for one year (89 influent and 103 AS samples in total) and examined by high-throughput Illumina-MiSeq sequencing. The results suggested that the microbial community diversity and composition in the influent fluctuated substantially with season, while those in the AS had a relatively more stable pattern throughout the year. The phylogenetic group based assembly mechanisms of AS community were identified by using "Infer Community Assembly Mechanisms by Phylogenetic-bin-based null model (iCAMP)". The results showed that drift accounted for the largest proportion (52.8%), while homogeneous selection (18.2%) was the most important deterministic process. Deterministic processes dominated in 47 microbial groups (bins), which were also found (~40%) in the AS core taxa dataset. Moreover, the results suggested that Nitrospira were more susceptible to stochastic processes in winter, which may provide a possible explanation for nitrification failure in winter. Network analysis results suggested that the network structure of the AS community could be more stable in summer and autumn. In addition, there were no identical keystone taxa found in different networks (constructed from different plants, sources, and seasons), which supported the context dependency theory. The results of this study deepened our understanding of the microbial ecology in AS systems and provided a foundation for further studies on the community regulation strategy of WWTPs.

Impacts of Ag and Ag2S nanoparticles on the nitrogen removal within vertical flow constructed wetlands treating secondary effluent

In this study, the effects of silver (Ag NPs) and sliver sulfide nanoparticles (Ag₂S NPs) on nitrogen removal and nitrogen functional microbes in constructed wetlands were investigated. The obtained results demonstrated that inhibition extent on nitrogen removal relied on NPs types and high concentrations NPs showed higher negative effects. 0.5 mg/L Ag NPs had no influence on NH₄⁺-N removal, amoA and nxrA gene copies, whereas Ag₂S NPs and Ag⁺ decreased NH₄⁺-N removal by reducing abundances of nitrifying genes. The concentrations of NO₃^--N and TN in all 0.5 mg/L obviously increased compared with control, resulting from decreasing functional genes and denitrifying bacteria. And 0.5 mg/L Ag NPs exhibited largest inhibitory effects, with the highest NO₃^--N effluent concentrations. 2 mg/L Ag NPs decreased NH₄⁺-N removal, but adverse effects gradually vanished with extension of time, whereas both Ag₂S NPs and Ag⁺ at 2 mg/L influenced NH₄⁺-N transformation and decreased the abundance of amoA and nxrA genes and the AOB Nitrosomonas in CWs. Moreover, 2 mg/L of Ag NPs reduced NO₃^--N removal by decreasing abundance of nirS and key denitrifying bacteria. To sum up, the inhibition mechanisms concluded from current results were possibly in that Ag NPs exhibited nanotoxicity rather than ionic toxicity.

Microbial community response to ciprofloxacin toxicity in sponge membrane bioreactor

This study aims to offer insights into how ciprofloxacin (CIP) impact bacterial community structures in the Sponge-MBR process when CIP is spiked into hospital wastewater. We found that the CIP toxicity decreased richness critical phylotypes such as phylum class ẟ-, β-, ɣ-proteobacteria, and Flavobacteria that co-respond to suppress denitrification and cake fouling to 37% and 28% respectively. Cluster analysis shows that the different community structures were formed under the influence of CIP toxicity. CIP decreased attached growth biomass by 2.3 times while increasing the concentration of permeate nitrate by 3.8 times, greatly affecting TN removal by up to 26%. Ammonia removal was kept stable by inflating the ammonia removal rate (p < 0.003), with the wealthy Nitrospira genus guaranteeing the nitrification activity. In addition, we observed an increasing richness of Chloroflexi and Planctomycetes, which may play a role in fouling reduction in the Sponge-MBR. Therefore, if the amount of antibiotics in hospital wastewater continues to increase, it is so important to extend biomass retention for denitrification recovery.

Connecting structure to function with the recovery of over 1000 high-quality metagenome-assembled genomes from activated sludge using long-read sequencing

Microorganisms play crucial roles in water recycling, pollution removal and resource recovery in the wastewater industry. The structure of these microbial communities is increasingly understood based on 16S rRNA amplicon sequencing data. However, such data cannot be linked to functional potential in the absence of high-quality metagenome-assembled genomes (MAGs) for nearly all species. Here, we use long-read and short-read sequencing to recover 1083 high-quality MAGs, including 57 closed circular genomes, from 23 Danish full-scale wastewater treatment plants. The MAGs account for ~30% of the community based on relative abundance, and meet the stringent MIMAG high-quality draft requirements including full-length rRNA genes. We use the information provided by these MAGs in combination with >13 years of 16S rRNA amplicon sequencing data, as well as Raman microspectroscopy and fluorescence in situ hybridisation, to uncover abundant undescribed lineages belonging to important functional groups.

Rapid start-up of an aerobic granular sludge system for nitrogen and phosphorus removal through seeding chitosan-based sludge aggregates

This study presents a novel strategy to accelerate the start-up of aerobic granular sludge (AGS) system and ensure the nutrient removal during cultivation. This new method consists of preparing the chitosan-based sludge aggregates outside the reactor and then seeding the reactor with such sludge aggregates. To prepare chitosan-based sludge aggregates, chitosan was dissolved in acetic acid solution acting as a cationic flocculant to bind negatively charged sludge together, and then the dissolved chitosan was in situ precipitated by readjusting pH to form stable sludge aggregates. The chitosan-induced charge neutralization and water-insolubility of chitosan were the two main reasons for the super-rapid formation of chitosan-based sludge aggregates. The as-prepared chitosan-based sludge aggregates had a much lower sludge volume index at 30 min (SVI₃₀) (90.1 mL/g) than the original sludge (SVI₃₀ = 328.0 mL/g). They also had some AGS-like characteristics such as large particle size (1300 μm) and fast settling velocity (23.8 m/h). Consequently, short settling time can be achieved and excessive biomass wash-out can be avoided in the rapid start-up of AGS system with chitosan-based sludge aggregates as inoculant, which was beneficial to accelerating sludge granulation while maintaining nutrient removal. Additionally, the abundances of filamentous bacteria and Candidatus Accumulibacter and the content of extracellular polymeric substances increased during cultivation, which could also contribute to the AGS formation. By seeding chitosan-based sludge aggregates in the anaerobic/oxic sequencing batch reactor, complete granulation was rapidly achieved in 10 days, and good removals of nitrogen and phosphorus was obtained after 14-18 days of cultivation.

Monitoring Microbial Populations and Antibiotic Resistance Gene Enrichment Associated with Arctic Waste Stabilization Ponds

Given that the microbial communities of Arctic waste stabilization ponds (WSPs) are poorly studied to date, our characterization of multiple WSP systems and time points provides important baseline data that will assist with ongoing monitoring of effluent impacts on downstream aquatic ecosystems in the Arctic. This research also identifies indicator amplicon sequence variants (ASVs) of WSPs that will be helpful for future monitoring for WSP effluent attenuation and demonstrates that WSP microbial communities are enriched in antibiotic resistance genes.

Wastewater management in the Canadian Arctic is challenging due to climate extremes, small population sizes, and lack of conventional infrastructure for wastewater treatment. Although many northern communities use waste stabilization ponds (WSPs) as their primary form of wastewater treatment, few studies have explored WSP microbial communities and assessed effluent impacts on receiving waters from a microbiological perspective. Here, we used 16S rRNA gene and metagenome sequencing to characterize WSP and receiving water microbial communities for two time points bracketing the spring WSP thaw in Baker Lake (Nunavut) and compared these results to other Nunavut WSPs in Cambridge Bay and Kugluktuk. Most amplicon sequence variants (ASVs) recovered from these WSP samples belonged to the phylum Proteobacteria, with considerable variation between the three locations and only six ASVs shared among the WSPs at >0.2% relative abundance. Wastewater indicator ASVs for the Baker Lake WSP were identified, and few indicator ASVs were detected in samples originating from other upstream or downstream sites. The metagenomic data revealed a strong enrichment of antibiotic resistance genes for WSP samples relative to downstream and reference samples, especially for genes associated with macrolide resistance. Together, our results provide a baseline characterization for WSP microbial communities, demonstrate how indicator ASVs can be used to monitor attenuation and dilution of effluent microorganisms, and reveal that WSPs can serve as hot spots for antibiotic resistance genes.

IMPORTANCE Given that the microbial communities of Arctic waste stabilization ponds (WSPs) are poorly studied to date, our characterization of multiple WSP systems and time points provides important baseline data that will assist with ongoing monitoring of effluent impacts on downstream aquatic ecosystems in the Arctic. This research also identifies indicator amplicon sequence variants (ASVs) of WSPs that will be helpful for future monitoring for WSP effluent attenuation and demonstrates that WSP microbial communities are enriched in antibiotic resistance genes. Given operational and infrastructure changes anticipated for wastewater treatment systems in the Arctic, baseline data such as these are essential for further development of safe and effective wastewater treatment systems.

Degradation of Nitrogen, Phosphorus, and Organic Matter in Urban River Sediments by Adding Microorganisms

Reducing and remediating endogenous sediment pollution in urban rivers using appropriate microbiological remediation technology is regarded as a safe, effective, and environmentally sustainable mechanism. In this study, the pollutant removal efficiency of three microorganism types at different dosages was studied in the laboratory. To optimize the microbial restoration scheme, a comprehensive analysis of their effectiveness in removing total nitrogen (TN), total phosphorus (TP), total organic matter (OM), and polycyclic aromatic hydrocarbons (PAHs) was conducted, and associated structural changes in the sediment bacteria were analyzed. The results showed that using nitrifying bacteria and Bacillus as microbial agents resulted in superior removal efficiencies of TN and TP in sediments, whereas yeast was not as effective. The removal rates of TN reached 27.65% and 20.88% when 5 mg nitrifying bacteria and 10 mg Bacillus respectively, were used. A comparative analysis showed that nitrifying bacteria exhibited a better TN removal effect; however, Bacillus exhibited a better TP removal effect. The results of high-throughput sequencing revealed no significant changes to the microbial community structures when optimal microorganisms or beneficial microorganisms that thrive using OM as a source of C and energy were added. This study provides insights into the processes and mechanisms involved in the microorganism degradation of black and odorous sediment, and the results can be used as a basis for developing endogenous pollution control policies and methods for urban rivers.

Recent advances in understanding the ecophysiology of enhanced biological phosphorus removal

Enhanced biological phosphorus removal (EBPR) is an efficient, cost-effective, and sustainable method for removing excess phosphorus from wastewater. Polyphosphate accumulating organisms (PAOs) exhibit a unique physiology alternating between anaerobic conditions for uptake of carbon substrates and aerobic or anoxic conditions for phosphorus uptake. The implementation of high-throughput sequencing technologies and advanced molecular tools along with biochemical characterization has provided many new perspectives on the EBPR process. These approaches have helped identify a wide range of carbon substrates and electron acceptors utilized by PAOs that in turn influence interactions with microbial community members and determine overall phosphorus removal efficiency. In this review, we systematically discuss the microbial diversity and metabolic response to a range of environmental conditions and process control strategies in EBPR.

Conditions that promote the formation of black bloom in aquatic microcosms and its effects on sediment bacteria related to iron and sulfur cycling

Black bloom occurs frequently in eutrophic waters. We investigated the conditions promoted the formation of black bloom via in-situ measurement in two aquatic microcosms and the effects of black bloom on the bacterial community composition. Although larger changes in dissolved oxygen (DO) were detected in the Hydrilla verticillata-dominated microcosm over the 90-day simulation, black bloom occurred more readily in the phytoplankton-dominated than macrophyte-dominated microcosm under conditions of O₂ depletion and temperature above 30 °C. The sediment bacterial community composition shifted after black bloom; the relative abundance of Thiobacillus and Sideroxydans, which oxidize iron (Fe) and sulfur (S), decreased by 47% and 48%, respectively, in the phytoplankton-dominated microcosm and by 18% and 20% in the macrophyte-dominated microcosm. By contrast, Desulfatiglans increased by 13% and 19%, respectively, after black bloom. Furthermore, inter-taxa correlations remarkably changed according to co-occurrence network analysis. Thirty-six different taxa from the phylum to the genus level were identified as biomarkers of sediments collected before and after the black bloom event. Most of these biomarkers are related to Fe/S cycling in aquatic ecosystems.

Pilot study on urban sewage treatment with micro pressure swirl reactor

This study aimed to propose a new type of micro-pressure swirl reactor (MPSR) to treat urban sewage. The MPSR could form a stable swirl in the reactor, and realized the coexistence of anaerobic, anoxic, and aerobic zones in a single aeration tank. The pilot study showed that MPSR achieved high removal efficient of SS, COD, NH₄⁺-N, TN, TP under the conditions of drastic fluctuation in influent quality and temperature, and the average removal rate were 88.58%, 93.32%, 94.47%, 73.19%, 96.16%. The relative high abundance of Thermomonas, Thaurea, and Dechloromonas, etc, guaranteed the denitrification efficiency of the MPSR, and Dechloromonas was the main phosphorus removal bacteria in the system. The study confirmed the rationality of the structural design of the MPSR, and it was excellent in sewage treatment and stability.

The synergy of porous substrates and functional genera for efficient nutrients removal at low temperature in a pilot-scale two-stage tidal flow constructed wetland

A pilot-scale two-stage tidal flow constructed wetland (TFCW) with working volume of 0.46 m³/d packing with shale ceramsite (SC) and activated alumina (AA) was constructed (named as SC-AA-TFCW) for nutrients removal at low temperature (<15 °C). SC-AA-TFCW achieved stable removals of 78.1% nitrogen and 98.3% phosphorous. SC-TFCW contributed to 55.2% of organics and 85.6% of particulate phosphorous removal. Among 17 denitrifiers, the absolute abundance of aerobic denitrification bacteria (ADNB) was highest, followed by facultative anaerobic denitrification bacteria (FADNB) and autotrophic denitrification bacteria (AUDNB). Nitrogen assimilating into organic nitrogen, dissimilatory and assimilatory nitrate reduction and complete denitrification may be main nitrogen metabolic pathways. Some ADNB (e. g. Zoogloea, Pseudomonas and Acidovorax) showed positive interactions with various key functional genes related to nutrients removal. Dissolved oxygen and reducing elements were main environmental factors in changing ADNB compositions. This study highlights the importance of ADNB and their synergy to porous substrates in SC-AA-TFCW.

Characteristics and metabolic pathway of the bacteria for heterotrophic nitrification and aerobic denitrification in aquatic ecosystems

The present study investigated the nitrogen removal characteristics and metabolic pathway of bacteria in aquatic ecosystem, with a focus on heterotrophic nitrification and aerobic denitrification. The bacteria demonstrated significant heterotrophic nitrification and aerobic denitrification capacity. The highest ammonium-N, nitrate-N, and nitrite-N removal efficiencies were 95.31 ± 0.11%, 98.91 ± 0.05%, and 98.79 ± 0.09%, respectively. The Monod model was used to estimate the maximum rate of substrate utilization (R_mo) and the half-saturation concentration (K_s) for the two substrates, i.e., ammonium and nitrate. The kinetic coefficients were 3.34 mg/L/d (R_mo) and 30.59 mg/L (K_s) for ammonium-N, respectively, and 14.23 mg/L/d (R_mo) and 215.24 mg/L (K_s) for nitrate-N, respectively. The effects of initial nitrogen (ammonium-N or nitrate-N) concentration, temperature, and dissolved oxygen (DO) on nitrogen removal rate were investigated using response surface methodology (RSM), and the optimal conditions for nitrogen removal were determined. The principal nitrogen removal pathway of the bacteria was proposed as complete heterotrophic nitrification and aerobic denitrification, which was performed by six key genera: Arthrobacter, Pseudomonas, Rhodococcus, Bacillus, Massilia, and Rhizobium. Chryseobacterium and other denitrifying species may also reduce nitrification products (NO_X^-) via aerobic denitrification.

A bioelectrochemical-system-based trickling filter reactor for wastewater treatment

A bioelectrochemical system (BES)-based trickling filter (TF) reactor was utilized for wastewater treatment. At a COD load of 1.0 g-COD/L/day, effluent chemical oxygen demand (COD) and total nitrogen (TN) were 115 and 108 mg/L, respectively, which were allowed for discharge. Superior performance was achieved at 0.5 g-COD/L/day with a circulation rate of 8 L/h, and both COD and TN removal were >98%. Coulombic efficiency was 11% at 1.0 g-COD/L/day and at most 16% at 0.5 g-COD/L/day. COD removal decreased when the BES was removed, demonstrating that BES improved COD removal capability. In anodic biofilms, exoelectrogenic, facultative, nitrifying, and sulfate-reducing bacteria could coexist. Geobacter for current generation grew inside the biofilm, and bacteria in the middle and outer layers consumed oxygen and degraded organic matter and nitrogen. This BES-based TF reactor may be used for efficient and cost-effective COD and TN removal at high loads without excess sludge removal.

The impact of temperature and dissolved oxygen (DO) on the partial nitrification of immobilized fillers, and application in municipal wastewater

To achieve the stable partial nitrification of municipal wastewater, activated sludge with high ammonia-oxidizing bacteria (AOB) content and low nitrite-oxidizing bacteria (NOB) content were immobilized in a polyvinyl alcohol filler. The effects of different levels of dissolved oxygen (DO) on the activity of AOB and NOB in the filler with temperature changes at the initial ammonia concentration of approximately 100 mg L-1 were investigated. At 25 °C, when the DO concentration was greater than 5 mg L-1, the O2-limiting condition inside the filler was destroyed as the demand for oxygen in AOB was certain, and resulted in enhanced NOB activity. At 15 °C, the DO concentration was not a key factor in determining the NOB activity due to the negative effect of temperature on NOB activity. The immobilized filler reactor of municipal wastewater achieved a nitrite accumulation rate (NAR) of >86.7 and >82% at 24-26 °C and 14-16 °C, respectively. Low temperatures did not deteriorate the stable partial nitrification performance. The total nitrogen (TN) removal efficiency of the immobilized filler reactor was 21.7-26.1% and 10.3-15.3% at 24-26 °C and 14-16 °C, respectively. The TN removal efficiency and NAR in municipal wastewater were higher as compared to simulated wastewater, indicating that the organic carbon in municipal wastewater enhanced nitrate reduction by denitrification. High-throughput sequencing analysis showed that denitrifying bacteria and nitrifying bacteria were identified as the predominant bacteria genera, while the dominant species of NOB was Nitrobacter. This study is a viable approach to promoting partial nitrification in municipal WWTPs.

Seasonal Dynamics of the Activated Sludge Microbiome in Sequencing Batch Reactors, Assessed Using 16S rRNA Transcript Amplicon Sequencing

Activated sludge is comprised of diverse microorganisms which remediate wastewater. Previous research has characterized activated sludge using 16S rRNA gene amplicon sequencing, which can help to address questions on the relative abundance of microorganisms. In this study, we used 16S rRNA transcript sequencing in order to characterize "active" populations (via protein synthesis potential) and gain a deeper understanding of microbial activity patterns within activated sludge. Seasonal abundances of individual populations in activated sludge change over time, yet a persistent group of core microorganisms remains throughout the year which are traditionally classified on presence or absence without monitoring of their activity or growth. The goal of this study was to further our understanding of how the activated sludge microbiome changes between seasons with respect to population abundance, activity, and growth. Triplicate sequencing batch reactors were sampled at 10-min intervals throughout reaction cycles during all four seasons. We quantified the gene and transcript copy numbers of 16S rRNA amplicons using real-time PCR and sequenced the products to reveal community abundance and activity changes. We identified 108 operational taxonomic units (OTUs) with stable abundance, activity, and growth throughout the year. Nonproliferating OTUs were commonly human health related, while OTUs that showed seasonal abundance changes have previously been identified as being associated with floc formation and bulking. We observed significant differences in 16S rRNA transcript copy numbers, particularly at lower temperatures in winter and spring. The study provides an analysis of the seasonal dynamics of microbial activity variations in activated sludge based on quantifying and sequencing 16S rRNA transcripts.IMPORTANCE Sequencing batch reactors are a common design for wastewater treatment plants, particularly in smaller municipalities, due to their low footprint and ease of operations. However, like for most treatment plants in temperate/continental climates, the microbial community involved in water treatment is highly seasonal and its biological processes can be sensitive to cold temperatures. The seasonality of these microbial communities has been explored primarily in conventional treatment plants and not in sequencing batch reactors. Furthermore, most studies often only address which organisms are present. However, the activated sludge microbial community is very diverse, and it is often hard to discern which organisms are active and which organisms are simply present. In this study, we applied additional sequencing techniques to also address the issues of which organisms are active and which organisms are growing. By addressing these issues, we gained new insights into seasonal microbial populations dynamics and activity patterns affecting wastewater treatment.

Flocs in disguise? High granule abundance found in continuous-flow activated sludge treatment plants

To date, high performance of full-scale aerobic granular sludge (AGS) technology has been demonstrated on a global scale. Its further integration with existing continuous flow activated sludge (CFAS) treatment plants is the next logical step. All granular sludge reactors operated in sequencing batch reactors (SBR) mode with anaerobic feeding conditions select for growth of phosphorus and glycogen accumulating organisms (PAO and GAO, respectively), which are known to enhance sludge settling characteristics. Therefore, we hypothesized that AGS are commonly present at full-scale CFAS processes with enhanced biological phosphorus removal (EBPR) and low sludge volume index (SVI). This hypothesis was confirmed at 13 EBPR plants, where granules were found present (at plants where SVI was lower than 100 ml/g) with a strong correlation between high granule abundance and low SVI. A wide range of granule abundance was found among the plants, ranging from 0.5% to as high as 80%. Evaluations of the EBPR plant process configurations showed that high granule abundances may be related to selector design features such as high anaerobic food to mass (F/M) ratios, unmixed in-line fermentation, and high influent soluble COD fraction. Granules were also observed at a non-EBPR plant with an aerobic selector receiving high F/M feeds. Quantitative PCR and 16S rRNA gene sequencing analyses revealed higher relative gene abundance of Accumulibacter PAO and Competibacter GAO in the granules over flocs, as well as a correlation between granule abundance and some possible EPS producers such as Flavobacterium and Competibacter. Our results indicated that process configurations that select for slow-growing or EPS-producing heterotrophs play an important role for granule formation in full-scale CFAS systems as previously shown in SBR configurations.

Intensified simultaneous nitrification and denitrification performance in integrated packed bed bioreactors using PHBV with different dosing methods

To explore an effective approach of simultaneous nitrification and denitrification in wastewater with low C/N ratios, integrated packed bed bioreactors based on poly(3-hydroxybutyrate-hydroxyvalerate) (PHBV) with different dosing methods were designed. The removal efficiency of NH₄⁺-N in bioreactor with aeration was 88.62%, and higher NO₃^--N removal efficiency was observed in bioreactor filled with grainy PHBV (95.21%) than bioreactor filled with strip PHBV (93.34%). Microbial study indicated that microbes harboring amoA and nirS genes preferred to attach on the surface of ceramsite, and significant differences in microbial community compositions at phylum and genus levels were observed. To summarize, it is feasible to utilize grainy PHBV for simultaneous and efficient removal of NH₄⁺-N and NO₃^--N from wastewater with low C/N ratios.

Performance and bacterial community structure of a novel inverse fluidized bed bioreactor (IFBBR) treating synthetic municipal wastewater

The performance of a lab-scale integrated anoxic and aerobic inverse fluidized bed bioreactors (IFBBR) for biological nutrient removal from synthetic municipal wastewater was studied at chemical oxygen demand (COD) loading rates of 0.34-2.10 kg COD/(m³-d) and nitrogen loading rates of 0.035-0.213 kg N/(m³-d). Total COD removal efficiencies of >84% were achieved, concomitantly with complete nitrification. The overall nitrogen removal efficiencies were >75%. Low biomass yields of 0.030-0.101 g VSS/g COD were achieved. Compared with other FBBR systems, the energy consumption for this IFBBR system was an average 59% less at organic loading rates (OLRs) of 1.02 and 2.10 kg COD/(m³-d). Bacterial community structures of attached and suspended biomass revealed that the dominant phyla were Proteobacteria, Bacteroidetes, and Epsilonbacteraeota, etc. The relative abundance of ammonia-oxidizing bacteria (AOBs) and nitrite-oxidizing bacteria (NOBs) in the aerobic attached biomass were 0.451% and 0.110%, respectively. COD mass balance in the anoxic zone was closed by consideration of sulfate reduction, which was confirmed by the presence of genus Chlorobium (sulfate-reducing bacteria) in the anoxic attached biofilm with a relative abundance of 0.32%.

Aggregate size-dependence of bacterial community separation in a full-scale membrane bioreactor plant

The size of bacterial aggregates can determine both nutrient removal and sludge/water separation in activated sludge processes. In this study, the bacterial community structures and network associations of different sized aggregates obtained from a full-scale membrane bioreactor plant over a one-year period were investigated. Our results showed that biodiversity of larger sized aggregates was significantly higher than that of smaller ones and that the bacterial compositions of different sized aggregates differed significantly from each other. Bacteria related to nutrient removal (e.g. denitrification, hydrolysis and fermentation) were found to be significantly more abundant in larger aggregates than smaller ones. Network analysis revealed significant difference in species-species interactions, topological roles of individual OTU and keystone populations among different sized aggregates. Moreover, the occurrence of keystone OTUs affiliated with denitrifiers (Thermomonas) in networks of large and medium aggregates may suggest that denitrification influences bacterial interactions in large and medium aggregates. Overall, our results indicate the aggregates size-dependence of bacterial community separation in activated sludge. The current findings not only can provide guidance for process design and operation optimization, but also highlight the necessity for paying more attentions to the aggregate-based community, metabolic function and gene expression of activated sludge in future studies.