Anaerobic digestion of mixed urban biowaste: The microbial community shift towards stability

Anaerobic digestion is applied worldwide to treat food waste (FW) with the aim of obtaining renewable bioenergy by exploiting the methane gas produced. However, there are several problems in practical applications, primarily due to system instability. Although exhaustive knowledge regarding anaerobic microbial community composition has been established, few studies have investigated long-term correlations between microbial consortia, operative conditions and feedstock characteristics. Here, microbial community shifts as a response to feedstock variations were investigated in long-term semi-continuous systems, which were evaluated by an in situ cell detection method and 16S rRNA gene amplicon sequencing. FW digestion showed progressive system instability caused by the inhibition of methanogens, which resulted in volatile fatty acid accumulation and process failure at the low organic loading rate (OLR). Conversely, by co-digesting FW with waste-activated sludge (WAS), a stable process with methane yields of up to 0.27 Nm³  kg^-1VS_fed for OLR = 1.7 gVS L^-1d^-1 was achieved. This stabilizing effect was not related to the buffering capacity of WAS, but to its capacity to avoid volatile fatty acid accumulation and falls in pH by overcoming methanogenic activity inhibition. WAS addition promoted the establishment of a stable and active archaeal population in anaerobic co-digestion (AcoD) reactors. The continuous supply of trace elements together with the seeding of microbial functional groups were the main drivers that positively affected process stability.

Abundance of total and metabolically active Candidatus Microthrix and fungal populations in three full-scale wastewater treatment plants

The abundances of total and metabolically active populations of Candidatus Microthrix and Fungi were evaluated by quantitative PCR (qPCR) and retrotranscribed qPCR of ribosomal molecular markers in three different full-scale wastewater treatment plants (WWTPs), in absence of bulking/foaming episodes. Significant differences of the abundance of rDNAs and rRNAs of Candidatus Microthrix and Fungi were observed among the three WWTPs. The average relative abundances of 16S rDNA copies of Candidatus Microthrix to those of Bacteria ranged 3.4-8.9%. Biota-environment analysis (BIO-ENV) demonstrated that the number of copies of both 16S rDNA and rRNA of Candidatus Microthrix increased at longer hydraulic and solids' retention times and with higher nitrate concentrations in the activated sludge. The abundance of Candidatus Microthrix correlated strongly and positively with the removal efficiencies of organic matter and total nitrogen in the tested WWTPs, highlighting the role of these particular microbial group in the performance of these engineered systems.

The microbial community in filamentous bulking sludge with the ultra-low sludge loading and long sludge retention time in oxidation ditch

Sludge bulking is a major problem that restricts the development of the activated sludge process. The microbial community responsible for sludge bulking varies depending on water quality and operational conditions. This study analysed the microbial community of bulking sludge in oxidation ditch with ultra-low sludge loading and long sludge retention time using high-throughput sequencing. The study found that the relative abundance of bacterial genus Saprospiraceae_norank was the highest in bulking sludge, reaching 13.39-28.83%, followed by Comamonadaceae_unclassified, Ardenticatenia_norank and Tetrasphaera, with the relative abundance of 4.59-11.08%, 0.52-16.60% and 0.17-8.92% respectively. In contrast, the relative abundance of bacteria that easily caused sludge bulking including Microthrix (0.54-2.47%), Trichococcus (0.32-1.71%), Gordonia (0.14-1.28%), and Thiothrix (0.01-0.06%) were relatively low. Saprospiraceae_norank was predominant and induced sludge bulking in oxidation ditch. The relative abundance of fungal genus Trichosporon was the highest in bulking sludge, reaching 16.95-24.98%, while other fungal genera were Saccharomycetales_unclassified (5.59-14.55%), Ascomycota_norank (1.45-13.51%), Galactomyces (5.23-11.23%), and Debaryomyces (7.69-9.42%), whereas Trichosporon was the dominant fungal genus in bulking sludge. This study reported that excessive Saprospiraceae_norank can induce sludge bulking for the first time, which provides important knowledge to control sludge bulking.

The Phylogeny, Biodiversity, and Ecology of the Chloroflexi in Activated Sludge

It is now clear that several of the filamentous bacteria in activated sludge wastewater treatment plants globally, are members of the phylum Chloroflexi. They appear to be more commonly found in treatment plants designed to remove nitrogen (N) and phosphorus (P), most of which operate at long sludge ages and expose the biomass to anaerobic conditions. The Chloroflexi seem to play an important beneficial role in providing the filamentous scaffolding around which flocs are formed, to feed on the debris from lysed bacterial cells, to ferment carbohydrates and to degrade other complex polymeric organic compounds to low molecular weight substrates to support their growth and that of other bacterial populations. A few commonly extend beyond the floc surface, while others can align in bundles, which may facilitate interfloc bridging and hence generate a bulking sludge. Although several recent papers have examined the phylogeny and in situ physiology of Chloroflexi in activated sludge plants in Denmark, this review takes a wider look at what we now know about these filaments, especially their global distribution in activated sludge plants, and what their functional roles there might be. It also attempts to outline why such information might provide us with clues as to how their population levels may be manipulated, and the main research questions that need addressing to achieve these outcomes.

Acute effects of hexavalent chromium on the performance and microbial community of activated sludge in aerobiotic reactors

This study investigated the acute effects of hexavalent chromium (Cr(VI)) shock load at 2.5, 6 and 25 mg/L on the performance and bacterial community structures in aerobiotic activated sludge reactors. The results showed that eight-day Cr(VI) toxicity made the removal rates of COD and NH₃-N to obviously decrease in all reactors. Furthermore, the higher the Cr(VI) concentration was, the more severe the influence on the whole system would be. The effect of Cr(VI) on NH₃-N removal was more serious than that on COD and the function of nitrification was harder to recover. The specific oxygen uptake rate (SOUR) values dropped by 73%, 68% and 31% at 2.5, 6 and 25 mg Cr(VI)/L, respectively. The data of SOUR showed that though the concentration of Cr(VI) was low, the whole respiratory activity of bacteria was much affected. The relative abundance change of genus between the initial stage and the last showed that the bacterial community structure changed significantly. Comparing with the initial stage, the phyla of Proteobacteria, Acidobacteria and Planctomycetes were markedly reduced at the end stage. The genera of Ferruginibacter, Coxiella and Rhodanobacter were also markedly reduced. Although the performance of activated sludge can be restored at the end, the whole respiratory activity of bacteria was still at a low level according to the data of SOUR.

Agricultural Risk Factors Influence Microbial Ecology in Honghu Lake

Agricultural activities, including stock-farming, planting industry, and fish aquaculture, can affect the physicochemical and biological characters of freshwater lakes. However, the effects of pollution producing by agricultural activities on microbial ecosystem of lakes remain unclear. Hence, in this work, we selected Honghu Lake as a typical lake that is influenced by agriculture activities. We collected water and sediment samples from 18 sites, which span a wide range of areas from impacted and less-impacted areas. We performed a geospatial analysis on the composition of microbial communities associated with physicochemical properties and antibiotic pollution of samples. The co-occurrence networks of water and sediment were also built and analyzed. Our results showed that the microbial communities of impacted and less-impacted samples of water were largely driven by the concentrations of TN, TP, NO₃⁻-N, and NO₂⁻-N, while those of sediment were affected by the concentrations of Sed-OM and Sed-TN. Antibiotics have also played important roles in shaping these microbial communities: the concentrations of oxytetracycline and tetracycline clearly reflected the variance in taxonomic diversity and predicted functional diversity between impacted and less-impacted sites in water and sediment samples, respectively. Furthermore, for samples from both water and sediment, large differences of network topology structures between impacted and less-impacted were also observed. Our results provide compelling evidence that the microbial community can be used as a sentinel of eutrophication and antibiotics pollution risk associated with agricultural activity; and that proper monitoring of this environment is vital to maintain a sustainable environment in Honghu Lake.

Deciphering the Assembly Processes of the Key Ecological Assemblages of Microbial Communities in Thirteen Full-Scale Wastewater Treatment Plants

Limited information is currently available on the assembly processes (deterministic vs. stochastic) shaping the compositions of key microbial communities in activated sludge (AS). The relative importance of deterministic and stochastic processes for key bacterial and archaeal assemblages (i.e., core-satellite and habitat generalist-specialist) in AS from 13 wastewater treatment plants in China was investigated using 16S rDNA amplicon sequencing. The results obtained indicated 1,388 and 369 core operational taxonomic units (OTUs), 1,038 and 1,683 satellite OTUs, 255 and 48 habitat generalist OTUs, and 192 and 111 habitat specialist OTUs for Bacteria and Archaea, respectively. The proportions of shared OTUs between core and habitat specialist communities were similar to or higher than those between core and habitat generalist communities, suggesting a stronger inter-linkage between the former two groups. Deterministic processes, indicated by abundance-based β-null models, were responsible for shaping core communities, in which NH₄-N, OrgC/OrgN, Cr, and Ni were the main controlling factors. In contrast, satellite communities were predominantly influenced by stochastic processes. Moreover, we found that deterministic and stochastic processes were mainly responsible for shaping the assembly of habitat specialists and generalists, respectively. However, the influence of deterministic factors on habitat specialists remains unclear. The present study provides novel insights into the assembly mechanisms of AS microbial communities.

Monitoring, isolation and characterization of Microthrix parvicella strains from a Chinese wastewater treatment plant

Microthrix parvicella is a filamentous bacterium that frequently causes severe bulking events in wastewater treatment plants (WWTPs) worldwide. In this study, sludge properties and dynamics of filamentous bacteria in a Beijing WWTP seasonally suffering from M. parvicella bulking were continuously monitored over a duration of 15 months, and the correlations between M. parvicella and operating parameters were evaluated. The predominance of M. parvicella was observed at low temperatures (14-18.8 °C) with the relative abundance of around 30% (estimated by both qPCR and FISH analysis). Using micromanipulation technology, 545 filaments of M. parvicella were micromanipulated from bulking sludge (SVI > 180 mL g^-1) on six different media. After 3-month purification and enrichment, six strains, phylogenetically closely related to Candidatus Microthrix parvicella, were successfully acquired on R₂A medium (20 °C) in pure cultures. Considering the limitation and extremely slow growth rate of M. parvicella filaments, newly isolated strains represent valuable sources for further investigations on the physiology and behavior of this filamentous bacterium, with the focus on the establishment of bulking control strategy.

Thiothrix eikelboomii interferes oxygen transfer in activated sludge

This study revealed that, Thiothrix eikelboomii, a well-known filamentous bacterium that causes sludge bulking, could also interfere oxygen transfer during wastewater treatment. The volumetric oxygen transfer coefficient (K_La) in filamentous-bulking sludge (FBS) was found to be 43% lower than that in floc-forming sludge (FFS) at similar biomass concentrations, partially because the filamentous bacteria had increased the sludge apparent viscosity. The K_La value for FBS, however, was still significantly lower than that for FFS even if both sludges had similar apparent viscosity. Numerous tiny and free-swimming filaments were observed to attach on the air bubble surface, presumably reducing the liquid film renewal and increasing the liquid film thickness. Moreover, the filaments were co-coated with extracellular polymeric substances of protein and polysaccharide, which could make them performing like "amphiphilic molecules" of surfactants to hinder oxygen transfer. Therefore, the particular surface property of filaments and their interaction with air bubbles could also impact oxygen transfer. Thiothrix eikelboomii was identified to be the responsible filamentous bacterium that lowered the K_La value, while other filamentous bacteria with short filaments did not interfere oxygen transfer. This study implies that controlling sludge bulking benefits not only sludge settling but also oxygen transfer.

Geographical Patterns of nirS Gene Abundance and nirS-Type Denitrifying Bacterial Community Associated with Activated Sludge from Different Wastewater Treatment Plants

Denitrifying bacteria is a driver of nitrogen removal process in wastewater treatment ecosystem. However, the geographical characteristics of denitrifying bacterial communities associated with activated sludge from diverse wastewater treatment plants (WWTPs) are still unclear. Here, quantitative PCR and next-generation sequencing of the nirS gene were applied to characterize the abundance and denitrifying bacterial communities from 18 geographically distributed WWTPs. The results showed that the nirS abundance ranged from 4.6 × 10² to 2.4 × 10³ copies per ng DNA, while nirS-type denitrifying bacterial populations were diverse and distinct from activated sludge communities. Among WWTPs, total nitrogen removal efficiencies varied from 25.8 to 84%, which was positively correlated with diversity indices, whereas abundance-based coverage estimator index decreased with an increase in latitude. The dominant phyla across all samples were proteobacteria, accounting for 46.23% (ranging from 17.98 to 87.07%) of the sequences. Eight of the 22 genera detected were dominant: Thauera sp., Alicycliphilus sp., and Pseudomonas sp., etc. Based on network analysis, the coexistence and interaction between dominant genera may be vital for regulating the nitrogen and carbon removal behaviors. Multivariate statistical analysis revealed that both geographic location and wastewater factors concurrently govern the distribution patterns of nirS-type denitrifying bacterial community harbored in WWTPs. Taking together, these results from the present study provide novel insights into the nirS gene abundance and nirS-type denitrifying bacterial community composition in geographically distributed WWTPs. Moreover, the knowledge gained will improve the operation and management of WWTPs for nitrogen removal.

Practical approach to the evaluation of industrial wastewater treatment by the application of advanced microbiological techniques

In cork industry, the operation of boiling raw cork generates large volumes of wastewater named Cork Boiling Wastewater (CBW). The main characteristics are the low biodegradability and medium to low acute toxicity, resulting in the necessity of designing advanced biological treatments by possible conventional activated sludge adaptation. In order to evaluate the variation of bacterial population along that process, a study based on optical microscopy, plate count, DNA extraction, qPCR and massive sequencing techniques was performed. Results showed a diminution of the total and volatile solids (TSS and VSS), jointly with a decrease in DNA concentration, general bacteria (16 S) and ammonia-oxidizing bacteria (AOB). After a few hours of testing, diverse microbiological species died while others showed a possible adaptation of the biological system, accompained by a dissolved organic carbon (DOC) reduction. In addition, toxicity tests based on activated sludge showed the development of chronic toxicity through the contact time. Combination of classical and advanced microbiological techniques, such as quantitative real time Polymerase Chain Reaction (qPCR) and metagenomics, was essential to predict the variation of species during the experiment and to conclude if effective biological adaptation could be finally attained for the target complex wastewater.

Removal of anti-inflammatory/analgesic pharmaceuticals from urban wastewater in a pilot-scale A2O system: Linking performance and microbial population dynamics to operating variables

In this study, the removal rates of eight anti-inflammatory and/or analgesic pharmaceuticals, AIAPs (acetaminophen, ibuprofen, naproxen, ketoprofen, diclofenac, codeine, indomethacin and propyphenazone) were assessed in a pilot-scale A²O system (including anaerobic/anoxic/aerobic zones), long term operated during two experimental phases using different sets of environmental conditions and operating parameters. qPCR was used to quantify the absolute abundances of total Bacteria, total Archaea, mycolic-acid containing filamentous Actinobacteria (Mycolata) and Fungi within the activated sludge microbial community developed in the system. Multivariate analyses and Spearman correlation coefficients were used in search of significant links among the removal rates of the AIAPs, the abundances of the targeted microbial groups in the activated sludge, and the changes of environmental/operating variables in the A²O system. Improved removal efficiencies of several of the AIAPs analyzed (acetaminophen, ibuprofen, naproxen, ketoprofen) were correlated to higher organic load in the influent water, higher concentration of mixed liquor suspended solids (MLSS), lower temperature and lower food-to-microorganisms ratio (F/M). Removal efficiencies of several pharmaceuticals correlated with increased abundances of Mycolata in the A²O system, pointing at this group of bacteria as candidate key players for AIAPs removal in activated sludge.

Control strategy for filamentous sludge bulking: Bench-scale test and full-scale application

Sludge bulking caused by the overgrowth of filamentous bacteria, especially Microthrix parvicella, has been observed in WWTPs worldwide during low-temperature periods. In this study, the impacts of sludge load on the in situ growth of M. parvicella and sludge settleability were first evaluated at 15 °C over a period of 500 d using a bench-scale anaerobic-anoxic-aerobic reactor fed with raw sewage from a full-scale WWTP. When the reactor was operated at a sludge load of 0.07 ± 0.015 kg Chemical Oxygen Demand (COD) (kg MLSS·d)^-1 for 120 d, the sludge volume index (SVI) increased gradually from 85 mL g^-1 to 157 mL g^-1, and the abundance of M. parvicella quantified by qPCR and FISH methods also increased from 0.42% to 4.63% and 1.56%-13.59%, respectively. When the sludge load was further reduced to 0.04 ± 0.004 kg COD (kg MLSS·d)^-1, the SVI value varied in a narrow range of 135-164 mL g^-1 over a duration of 280 d, while the M. parvicella abundance increased to the maximum values of 10.13% (qPCR) and 18.53% (FISH), respectively. When the sludge load was increased to 0.12 ± 0.016 kg COD (kg MLSS·d)^-1, filamentous abundance and SVI were reduced to 1.06% (qPCR) and 105 mL g^-1 within 100 d, suggesting that it might be possible to control the growth of M. parvicella by keeping the sludge load above 0.1 kg COD (kg MLSS·d)^-1. The feasibility of the strategy was further validated in the same WWTP. It was found that the SVI and filamentous abundance in winter were successfully controlled for two successive years at below 120 mL g^-1 and 7% (FISH), respectively, when the sludge load was maintained at 0.14 ± 0.04 kg COD (kg MLSS·d)^-1 by adjusting sludge discharge, proving that this sludge-load-based strategy could be an efficient approach to control filamentous bulking.

Genomic insights into Candidatus Amarolinea aalborgensis gen. nov., sp. nov., associated with settleability problems in wastewater treatment plants

Settleability of particles in activated sludge systems can be impaired by an overgrowth of filamentous bacteria, a problem known as bulking. These filaments are often members of the phylum Chloroflexi, sometimes reaching abundances in excess of 30% of the biovolume. The uncultured Chloroflexi phylotype, Candidatus Amarolinea, has been observed in high abundances in Danish full-scale activated sludge systems by 16S rRNA gene amplicon surveys, where it has been associated with bulking. In this study, fluorescence in situ hybridization was applied to confirm their high abundance, filamentous morphology, and contribution to the interfloc bridging that characterizes filamentous bulking. Furthermore, genome-centric metagenomics using both Illumina and Oxford Nanopore sequencing was used to obtain a near complete population genome (5.7Mbp) of the Ca. Amarolinea phylotype, which belongs to the proposed novel family Amarolineaceae within the order Caldilineales of Chloroflexi. Annotation of the genome indicated that the phylotype is capable of aerobic respiration, fermentation, and dissimilatory nitrate reduction to ammonia. The genome sequence also gives a better insight into the phylogenetic and evolutionary relationships of the organism. The name Candidatus Amarolinea aalborgensis is proposed for the species.

Filamentous bacteria in the nitrifying activated sludge

Filamentous bacteria in addition to wastewater treatment are responsible for the shape of flocs and sedimentation properties of activated sludge. Their dynamics in activated sludge influences the performance of the whole sewage treatment plant. Therefore the composition of activated sludge biocenosis and its dynamics in the nitrification process were investigated. Four laboratory-scale activated sludge membrane bioreactors fed with wastewater highly concentrated with ammonium (synthetic wastewater imitating landfill leachate) were operated to obtain a high rate of nitrification. The sludge age was 8, 12, 24 and 32 days. An additional fifth reactor was conventionally ammonium loaded at 12-day sludge age and served as the reference. A shift in filamentous bacteria population was observed in all operated reactors. There was no influence of sludge age on composition or abundance of filamentous biocenosis. In high ammonium loaded activated sludge Nostocoida limicola, Haliscomenobacter hydrossis and also Type 021N were the most abundant filamentous bacteria. In the reference reactor Type 021N and Sphaerotilus natans dominated the activated sludge.

Combined polyhydroxyalkanoates (PHA) and 1,3-propanediol production from crude glycerol: Selective conversion of volatile fatty acids into PHA by mixed microbial consortia

Crude glycerol is an important by-product of the biodiesel industry, which can be converted into volatile fatty acids (VFA) and/or 1,3-propanediol (1,3-PDO) by fermentation. In this study, a selective conversion of VFA to polyhydroxyalkanoates (PHA) was attained while leaving 1,3-PDO in the supernatant by means of mixed microbial consortia selection strategies. The process showed highly reproducible results in terms of PHA yield, 0.99 ± 0.07 C_mol PHA/C_mol S (0.84 g COD PHA/g COD S), PHA content (76 ± 3.1 g PHA/100 g TSS) and 1,3-PDO recovery (99 ± 2.1%). The combined process had an ultimate yield from crude glycerol of 0.19 g COD PHA and 0.42 g COD 1,3-PDO per g of input COD. The novel enrichment strategy applied for selectively transforming fermentation by-products into a high value product (PHA) demonstrates the significance of the enrichment process for targeting specific bio-transformations and could potentially prove valuable for other biotechnological applications as well.

Activated sludge foaming: can phage therapy provide a control strategy?

Foaming in activated sludge systems is a global problem leading to environmental, cosmetic and operational problems. Proliferation of filamentous hydrophobic bacteria (including the Mycolata) are responsible for the stabilisation of foams. Currently no reliable methods exist to control these. Reducing the levels of the filamentous bacteria with bacteriophages below the threshold supporting foaming is an attractive approach to control their impact. We have isolated 88 bacteriophages that target members of the foaming Mycolata. These double stranded DNA phages have been characterised and are currently being assessed for their performance as antifoam agents.

Factors affecting the growth of Microthrix parvicella: Batch tests using bulking sludge as seed sludge

Sludge bulking caused by the overgrowth of filamentous bacteria, particularly Microthrix parvicella, is one of the challenges for the stable operation of municipal wastewater treatment plants (WWTPs). The driving forces for the development of sludge bulking, however, have not been well understood because of the extremely low growth rate of M. parvicella. In this study, batch experiments were performed using bulking sludge (sludge volume index (SVI), around 185mLg^-1) from a full-scale WWTP as the seed sludge to investigate the influences of carbon source, anaerobic/aerobic alternation condition and temperature on the growth of M. parvicella. The qPCR results showed that the use of oleic acid as carbon source, anaerobic/aerobic alternation treatment and low temperature (13°C) were favorable conditions for maintaining the dominance of M. parvicella in the tested activated sludge. Under these conditions, the SVI values remained at comparatively high values of 170.5mLg^-1, 162.5mLg^-1 and 129.5mLg^-1 after operation for approximately two months, and the relative abundances of M. parvicella were 36.7%, 9.74% and 34.07%, respectively, in comparison with the initial values of 33.04%, 29.29% and 54.66%. However, the relative abundances of M. parvicella decreased to 0.86-4.44%, 0.7% and 4.94%, respectively, under the conditions of other carbon sources, aerobic-only treatment and a temperature of 20°C. The FISH analysis gave a similar result. This study was performed with mixed sludge under controlled operating conditions, which provided a valuable information for the pure culture of M. parvicella and further investigations on its physiology and metabolism.

Epibiont growth on filamentous bacteria found in activated sludge: a morphological approach

Occurrence of epibiont attachment on filamentous bacteria is a common phenomenon in activated sludge. In this study, an attempt has been made to elucidate the intrinsic nature of the attachment between the epibionts and filamentous bacteria based on microscopic observations. Characterization of the epiflora based on fluorescence in situ hybridization using group level probes revealed that the epibionts colonizing these filamentous bacteria largely belongs to the class Alphaproteobacteria, followed by Beta and Gammaproteobacteria. The ultrastructural examination using transmission electron microscopy pointed to the existence of a possible cell-to-cell interaction between epibionts and the selected filaments. Common bacterial appendages such as pili and fimbria were absent at the interface and further noted was the presence of cell membrane extensions on epibiont bacteria protruding towards the targeted filamentous cell. Fibrillar structures resembling amyloid-like proteins were observed within the filament cells targeted by the epibionts. An interaction was apparent between amyloid such as proteins and epibionts with regards to the direction of fibrillar structures and the distance of approaching epibiont bacteria. Due to the lack of visual evidence in support of penetration, the role of these amyloid-like fibrils as potential attachment sites for the epibionts was taken into consideration, and required further validation using conformational antibodies.

Microbial biotechnology and circular economy in wastewater treatment

Microbial biotechnology is essential for the development of circular economy in wastewater treatment by integrating energy production and resource recovery into the production of clean water. A comprehensive knowledge about identity, physiology, ecology, and population dynamics of process‐critical microorganisms will improve process stability, reduce CO2 footprints, optimize recovery and bioenergy production, and help finding new approaches and solutions. Examples of research needs and perspectives are provided, demonstrating the great importance of microbial biotechnology.

Effect of intermittent aeration on microbial diversity in an intermittently aerated IFAS reactor treating municipal wastewater: A field study

In the present study, the effect of three intermittent aeration (IA) cycles on treatment performance and microbial diversity was investigated in an integrated fixed film activated sludge (IFAS) reactor treating municipal wastewater. The results showed that IA strategies were able to achieve efficient removal of organics and nitrogen ranging between 90 and 95% and 70 and 80%, respectively, however the phosphorus removal was found to be inversely proportional to the duration of aeration off time in each IA cycle. The microscopic analysis revealed that the suspended and attached biomass had compact morphology and open floc structure, respectively. For each gram of volatile suspended solids, 165 and 148 mg of extracellular polymeric substances (EPS) were extracted from attached and suspended biomass, respectively, constituting carbohydrates (∼24%), proteins (∼31%), humic acids (∼28%), DNA (∼2%) and unknown substances (∼12%). The microbial diversities of suspended biomass in IFAS reactor were investigated using culture-dependent approach, which confirmed the presence of Clostridium spp., Pseudomonas spp., Bacillus spp., Escherichia coli spp., Nitrosococcus spp., Streptococcus spp., Acinetobacter spp., Betaproteobacteria outliers, Klebsiella pneumoniae, Klebsiella aerogenes, Serratia marcescens, Micrococcus, Proteus vulgaris spp., Actinomycetes spp., and Actinobacteria including Micromonospora spp. and Streptomyces spp. Molecular tools for diversity analyses were used for ammonia and nitrite oxidizer identification, such as Nitrospira and Nitrosococcus species. Denitrifiers include the species of Pseudomonas, Betaproteobacteria and Flavobacterium. Acinetobacter, Betaproteobacteria and Gammaproteobacteria were responsible for the phosphorus removal in the present system. Overall, the system performed efficiently showing Proteobacteria (59%), Acinetobacter (12%) and Bacteroidetes (11%) as the dominant bacterial groups. However, the dominance of the bacterial diversity varied with the IA cycle time numerating the maximum percentage of bacterial species during IA1 phase i.e. 2.5 h aeration/0.5 h non-aeration.

Non-denitrifying polyphosphate accumulating organisms obviate requirement for anaerobic condition

Enhanced biological phosphorus removal (EBPR) is a widely used process in wastewater treatment that requires anaerobic/aerobic or anaerobic/anoxic cycling. Surprisingly, phosphorus (P) release was observed in the presence of nitrate in the anoxic compartment of the activated sludge tank in a full-scale treatment plant with the Modified Ludzack Ettinger configuration. We therefore studied the potential of this full-scale activated sludge community to perform EBPR under anoxic/aerobic cycling. The polyphosphate accumulating organism (PAO) Candidatus Accumulibacter represented 3.3% of total bacteria based on 16S rRNA gene amplicon sequencing, and metagenome analysis suggested it was likely to be dominated by Clade IIC. Using acetate as the carbon source in batch experiments, active denitrifying organisms (DPAOs) were estimated to comprise 39-44% of the total PAO population in the sludge, with the remaining 56-61% unable to utilize nitrate. When propionate was provided as the organic carbon source, 95% of the PAO population was unable to denitrify. EBPR occurred under defined anoxic/aerobic conditions, despite the presence of DPAOs, when synthetic wastewater was supplemented with either acetate or propionate or when primary effluent was supplied. In addition, the P release and subsequent uptake rates under anoxic/aerobic conditions were comparable to those observed under anaerobic/aerobic conditions. In contrast, a significant reduction in P release rate was observed when acetate was provided under oxic conditions. We postulate that non-DPAOs that recognize the anoxic condition as pseudo-anaerobic were the key players in anoxic/aerobic EBPR.

Temporal dynamics of bacterial communities and predicted nitrogen metabolism genes in a full-scale wastewater treatment plant

Dynamics of bacterial communities and nitrogen metabolism genes in a full-scale WWTP as revealed by Illumina sequencing and PICRUSt.

Effect of humic acid on anaerobic digestion of cellulose and xylan in completely stirred tank reactors: inhibitory effect, mitigation of the inhibition and the dynamics of the microbial communities

Inhibition effect of humic acid (HA) on anaerobic digestion of cellulose and xylan and the mitigation potential of the inhibition were evaluated in controlled fed batch reactors at 30 °C and a hydraulic retention time (HRT) of 20 days. Reactor performances were evaluated by biogas production and metabolite measurements for 220 days. Microbial population dynamics of the reactors were monitored with next-generation 16S rRNA gene sequencing at nine different sampling times. Our results showed that increasing levels of HA inhibited the hydrolysis efficiency of the digestion by 40% and concomitantly reduced the methane yield. Addition of hydrolytic enzymes helped to reverse the negative effects of HA, whereas calcium addition did not reverse HA inhibition. Microbiological analyses showed that the relative abundance of hydrolytic/fermentative bacterial groups such as Clostridiales, Bacteroidales and Anaerolineales was significantly lowered by the presence of HA. HA also affected the archaeal populations. Mostly hydrogenotrophic methanogens were negatively affected by HA. The relative abundance of Methanobacteriaceae, Methanomicrobiales-WCHA208 and Unassigned Thermoplasmata WCHA1-57 were negatively affected by the presence of HA, whereas Methanosaetacea was not affected.

Acetate-triggered granular sludge floatation in methanogenic bioreactors

Methanogenic granular sludge from anaerobic bioreactors plays a primary role in treatment of various high-strength industrial wastewaters. The common problem of sludge floatation can lead to washout of granules from the reactor and severely affect reactor performance. However, an understanding of the specific key trigger-factors and appropriate control strategies for granular sludge floatation remains elusive. In this study, the concentration of acetate, rather than that of other volatile fatty acids (VFAs, i.e. propionate and butyrate) and granular sludge properties, was identified to be positively, linearly correlated with the amount of floating granules. The number of floating granules on propionate (18 ± 6) or butyrate-containing (34 ± 13) wastewater was comparable with that of non-VFA control wastewater (30.5 ± 7.5), and much lower than that of acetate-containing wastewater (80.5 ± 10.5). A scenario of excessive acetate-triggered granular sludge floatation is proposed based on these results as well as on the microbial community profile and spatial distribution, porous structure of granules, and impacts of operational parameters. Two new strategies, acetate-depletion and co-substrate addition, effectively reduced the number of floating granules by 28.5% and 51.6%, respectively. These results deepen our understanding of granular sludge floatation in methanogenic bioreactors and provide effective strategies to control sludge floatation.

Detailed comparison of bacterial communities during seasonal sludge bulking in a municipal wastewater treatment plant

In this study, pyrosequencing combined with clone library analysis, qPCR, and fluorescent in situ hybridization (FISH) were performed to identify detailed changes of bacterial and filamentous bacterial communities in activated sludge (AS) in 3 types of typical AS samples: sludge bulking (B-AS), excessive bulking (EB-AS), and non-bulking (N-AS). Sludge bulking resulted in a decrease in total bacterial numbers from (6.4 ± 0.18) × 10⁸ gene copies/mL in N-AS to (2.4 ± 0.22) × 10⁸ in EB-AS and a decrease in bacterial diversity from 2757 OTUs in N-AS to 2217 OTUs in EB-AS. With the occurrence of sludge bulking, Actinobacteria and Firmicutes increased sharply, whereas Proteobacteria, which was the predominant phylum in N-AS, decreased markedly. In addition, Nitrospirae, a major lineage of the nitrite-oxidizing bacteria, had quite a low abundance in EB-AS (0.15%), while it was relatively high in N-AS (1.17%). On the other hand, filamentous bacteria accounted for 28.77% and 5.72% of total sequences in EB-AS and N-AS, respectively. More interestingly, 11 types of filamentous bacteria were always present in 3 types of typical AS samples from different stages of sludge bulking, and most of them enriched in EB-AS compared to N-AS. It is noteworthy that, in addition to the frequently reported filamentous bacteria such as Candidatus M. parvicella and Tetrasphaera, novel filamentous species of Trichococcus might exist in this bulking WWTP. Our results reveal that sludge bulking are derived from diverse taxa, which expands previous understanding and provides new insight into the underlying complications of the bulking phenomenon in AS.

Short-sludge age EBPR process - Microbial and biochemical process characterisation during reactor start-up and operation

The new paradigm for used water treatment suggests the use of short solid retention times (SRT) to minimize organic substrate mineralization and to maximize resource recovery. However, little is known about the microbes and the underlying biogeochemical mechanisms driving these short-SRT systems. In this paper, we report the start-up and operation of a short-SRT enhanced biological phosphorus removal (EBPR) system operated as a sequencing batch reactor (SBR) fed with preclarified municipal wastewater, which is supplemented with propionate. The microbial community was analysed via 16S rRNA amplicon sequencing. During start-up (SRT = 8 d), the EBPR was removing up to 99% of the influent phosphate and completely oxidized the incoming ammonia. Furthermore, the sludge showed excellent settling properties. However, once the SRT was shifted to 3.5 days nitrification was inhibited and bacteria of the Thiothrix taxon proliferated in the reactor, thereby leading to filamentous bulking (sludge volume index up to SVI = 1100 mL/g). Phosphorus removal deteriorated during this period, likely due to the out-competition of polyphosphate accumulating organisms (PAO) by sulphate reducing bacteria (SRB). Subsequently, SRB activity was suppressed by reducing the anaerobic SRT from 1.2 day to 0.68 day, with a consequent rapid SVI decrease to ∼200 ml/g. The short-SRT EBPR effectively removed phosphate and nitrification was mitigated at SRT = 3 days and oxygen levels ranging from 2 to 3 mg/L.

Assessing the composition of microbial communities in textile wastewater treatment plants in comparison with municipal wastewater treatment plants

It is assumed that microbial communities involved in the biological treatment of different wastewaters having a different chemical composition harbor different microbial populations which are specifically adapted to the environmental stresses encountered in these systems. Yet, little is known about the composition of these microbial communities. Therefore, the aim of this study was to assess the microbial community composition over two seasons (winter and summer) in activated sludge from well‐operating textile wastewater treatment plants (WWTPs) in comparison with municipal WWTPs, and to explain observed differences by environmental variables. 454‐pyrosequencing generated 160 archaeal and 1645 bacterial species‐level Operational Taxonomic Units (OTUs), with lower observed richness in activated sludge from textile WWTPs compared to municipal WWTPs. The bacterial phyla Planctomycetes, Chloroflexi, Chlorobi, and Acidobacteria were more abundant in activated sludge samples from textile WWTPs, together with archaeal members of Thaumarchaeota. Nonmetric multidimensional scaling analysis of the microbial communities showed that microbial communities from textile and municipal WWTPs were significantly different, with a seasonal effect on archaea. Nitrifying and denitrifying bacteria as well as phosphate‐accumulation bacteria were more abundant in municipal WWTPs, while sulfate‐reducing bacteria were almost only detected in textile WWTPs. Additionally, microbial communities from textile WWTPs were more dissimilar than those of municipal WWTPs, possibly due to a wider diversity in environmental stresses to which microbial communities in textile WWTPs are subjected to. High salinity, high organic loads, and a higher water temperature were important potential variables driving the microbial community composition in textile WWTPs. This study provides a general view on the composition of microbial communities in activated sludge of textile WWTPs, and may provide novel insights for identifying key players performing important functions in the purification of textile wastewaters.

Characterization and Adaptation of Anaerobic Sludge Microbial Communities Exposed to Tetrabromobisphenol A

The increasing occurrence of tetrabromobisphenol A (TBBPA) in the environment is raising questions about its potential ecological and human health impacts. TBBPA is microbially transformed under anaerobic conditions to bisphenol A (BPA). However, little is known about which taxa degrade TBBPA and the adaptation of microbial communities exposed to TBBPA. The objectives of this study were to characterize the effect of TBBPA on microbial community structure during the start-up phase of a bench-scale anaerobic sludge reactor, and identify taxa that may be associated with TBBPA degradation. TBBPA degradation was monitored using LC/MS-MS, and the microbial community was characterized using Ion Torrent sequencing and qPCR. TBBPA was nearly completely transformed to BPA via reductive debromination in 55 days. Anaerobic reactor performance was not negatively affected by the presence of TBBPA and the bulk of the microbial community did not experience significant shifts. Several taxa showed a positive response to TBBPA, suggesting they may be associated with TBBPA degradation. Some of these taxa had been previously identified as dehalogenating bacteria including Dehalococcoides, Desulfovibrio, Propionibacterium, and Methylosinus species, but most had not previously been identified as having dehalogenating capacities. This study is the first to provide in-depth information on the microbial dynamics of anaerobic microbial communities exposed to TBBPA.

Seasonal Changes in Bacterial Communities Cause Foaming in a Wastewater Treatment Plant

Bio-foaming is a major problem in solid separation in activated sludge (AS) wastewater treatment systems. Understanding the changes in bacterial communities during sludge foaming is vital for explaining foam formation. Changes in bacterial communities in the foam, corresponding foaming AS, and non-foaming AS in a seasonal foaming wastewater treatment plant (WWTP) in Northern China were investigated by high-throughput pyrosequencing and molecular quantification-based approaches. We found that bacterial communities of the foam and the corresponding foaming AS were similar but markedly different from those of the non-foaming AS. Actinobacteria was the predominant phylum in the foam and the corresponding foaming AS, whereas Proteobacteria was predominant in the non-foaming AS. Similar to the results of most previous studies, our results showed that Candidatus "Microthrix parvicella" was the predominant filamentous bacteria in the foam and the corresponding foaming AS and was significantly enriched in the foam compared to the corresponding foaming AS. Its abundance decreased gradually with a slow disappearance of sludge foaming, indicating that its overgrowth had a direct relationship with sludge foaming. In addition to Candidatus M. parvicella, Tetrasphaera and Trichococcus might play a role in sludge foaming, because they supported the changes in AS microbial ecology for foam formation. The effluent water quality of the surveyed plant remained stable during the period of sludge foaming, but the microbial consortia responsible for nitrogen and phosphorus transformation and removal markedly changed compared to that in the non-foaming AS. This study adds to the previous understanding of bacterial communities causing foaming in WWTPs.

The ratio of metabolically active versus total Mycolata populations triggers foaming in a membrane bioreactor

The abundance of total and metabolically active populations of Mycolata was evaluated in a full-scale membrane bioreactor (MBR) experiencing seasonal foaming, using quantitative PCR (qPCR) and retrotranscribed qPCR (RT-qPCR) targeting the 16S rRNA gene sequence. While the abundance of total Mycolata remained stable (10(10) copies of 16S rRNA genes/L activated sludge) throughout four different experimental phases, significant variations (up to one order of magnitude) were observed when the 16S rRNA was targeted. The highest ratios of metabolically active versus total Mycolata populations were observed in samples of two experimental phases when foaming was experienced in the MBR. Non-metric multidimensional scaling and BIO-ENV analyses demonstrated that this ratio was positively correlated to the concentrations of substrates in the influent water, F/M ratio, and pH, and negatively correlated to temperature and solids retention time. It the first time that the ratio of metabolically active versus total Mycolata is found to be a key parameter triggering foaming in the MBR; thus, we propose it as a candidate predictive tool.

Genomic and in situ investigations of the novel uncultured Chloroflexi associated with 0092 morphotype filamentous bulking in activated sludge

Overgrowth of filamentous bacteria in activated sludge wastewater treatment plants (WWTPs) leads to impaired sludge settleability, a condition known as bulking, which is a common operational problem worldwide. Filaments with the Eikelboom 0092 morphotype are commonly associated with such bulking episodes. Members of the uncultured B45 phylotype, which is embraced within the phylum Chloroflexi, were recently shown to exhibit this morphology. Although these organisms are among the most abundant populations recorded in activated sludge processes, nothing is known about their metabolic characteristics. In this study, a genome sequence, representing the B45 phylotype, was retrieved from a metagenome generated from an activated sludge WWTP. The genome consisted of two chromosomes and one plasmid, which were 4.0, 1.0 and 0.04 Mbps in size, respectively. A metabolic model was constructed for this organism, based on annotation of its genome, showing its ability to generate energy by respiration, utilizing oxygen, nitrite or nitrous oxide as electron acceptors, or by fermentation of sugars. The ability of B45 members to ferment sugars under anaerobic conditions was validated in situ with microautoradiography-fluorescence in situ hybridization. The provisional name of 'Candidatus Promineofilum breve' is proposed for this species. This study represents the first detailed information on an uncultured genus of filamentous organisms from activated sludge.

Integrated multi-omics analyses reveal the biochemical mechanisms and phylogenetic relevance of anaerobic androgen biodegradation in the environment

Steroid hormones, such as androgens, are common surface-water contaminants. However, literature on the ecophysiological relevance of steroid-degrading organisms in the environment, particularly in anoxic ecosystems, is extremely limited. We previously reported that Steroidobacter denitrificans anaerobically degrades androgens through the 2,3-seco pathway. In this study, the genome of Sdo. denitrificans was completely sequenced. Transcriptomic data revealed gene clusters that were distinctly expressed during anaerobic growth on testosterone. We isolated and characterized the bifunctional 1-testosterone hydratase/dehydrogenase, which is essential for anaerobic degradation of steroid A-ring. Because of apparent substrate preference of this molybdoenzyme, corresponding genes, along with the signature metabolites of the 2,3-seco pathway, were used as biomarkers to investigate androgen biodegradation in the largest sewage treatment plant in Taipei, Taiwan. Androgen metabolite analysis indicated that denitrifying bacteria in anoxic sewage use the 2,3-seco pathway to degrade androgens. Metagenomic analysis and PCR-based functional assays showed androgen degradation in anoxic sewage by Thauera spp. through the action of 1-testosterone hydratase/dehydrogenase. Our integrative 'omics' approach can be used for culture-independent investigations of the microbial degradation of structurally complex compounds where isotope-labeled substrates are not easily available.

Factors affecting population of filamentous bacteria in wastewater treatment plants with nutrients removal

Filamentous population in activated sludge and key operational parameters of full-scale municipal wastewater treatment plants (WWTPs) with bulking problems representative for Poland were investigated with quantitative fluorescence in situ hybridization. Statistical analyses revealed few relationships between operational parameters and biovolume of filamentous bacteria. Sludge age was not only positively correlated with abundance of Chloroflexi (parametric correlation and principal component analysis (PCA)), but also differentiated Microthrix population (analysis of variance (ANOVA)). Phylum Chloroflexi and pH presented a negative relation during the study (PCA). ANOVA showed that pH of influent and sludge volume index (SVI) differentiated abundance of types 0803 and 1851 of Chloroflexi and candidate division TM7. SVI increased along with higher abundance of Microthrix (positive parametric and non-parametric correlations and positive relation in PCA). Biovolumes of morphotypes 0803 and 1851 of Chloroflexi were differentiated by organic matter in influent, also by nutrients in the case of Chloroflexi type 1851. Chemical and biological oxygen demands (COD and BOD5, respectively) were negatively correlated with Microthrix. COD also differentiated the abundance of Haliscomenobacter hydrossis. Results of the study can be used to prevent WWTPs from excessive proliferation of filamentous bacteria and operational problems caused by them--bulking and foaming of activated sludge.

Interlinkages between bacterial populations dynamics and the operational parameters in a moving bed membrane bioreactor treating urban sewage

Bacteria are key players in biological wastewater treatments (WWTs), thus a firm knowledge of the bacterial population dynamics is crucial to understand environmental/operational factors affecting the efficiency and stability of the biological depuration process. Unfortunately, little is known about the microbial ecology of the advanced biological WWTs combining suspended biomass (SB) and attached biofilms (AB). This study explored in depth the bacterial community structure and population dynamics in each biomass fraction from a pilot-scale moving bed membrane bioreactor (MBMBR) treating municipal sewage, by means of temperature-gradient gel electrophoresis (TGGE) and 454-pyrosequencing. Eight experimental phases were conducted, combining different carrier filling ratios, hydraulic retention times and concentrations of mixed liquor total suspended solids. The bacterial community, dominated by Proteobacteria (20.9-53.8%) and Actinobacteria (20.6-57.6%), was very similar in both biomass fractions and able to maintain its functional stability under all the operating conditions, ensuring a successful and steady depuration process. Multivariate statistical analysis demonstrated that solids concentration, carrier filling ratio, temperature and organic matter concentration in the influent were the significant factors explaining population dynamics. Bacterial diversity increased as carrier filling ratio increased (from 20% to 35%, v/v), and solids concentration was the main factor triggering the shifts of the community structure. These findings provide new insights on the influence of operational parameters on the biology of the innovative MBMBRs.

Long term effect of alkali types on waste activated sludge hydrolytic acidification and microbial community at low temperature

The effect of four alkali reagents (NaOH, KOH, Ca(OH)2, mixed alkali) on waste activated sludge (WAS) hydrolytic acidification and microbial community was studied in semi-continuous fermentation systems at low temperature (15°C) over long term operational time (65day). The results showed that protein and polysaccharide of NaOH (124.26, 11.92) was similar to that of KOH (109.53, 11.30), both were higher than Ca(OH)2 (70.66, 3.74) and mixed alkali (90.66, 8.71). The short chain fatty acids (SCFAs) of NaOH (231.62) was higher than KOH (220.62mg chemical oxygen demand (COD)/g VSS). Although Ca(OH)2 system had strong acidification capacity, the shortage of SCFAs occurred due to the low activity of hydrolase. Illumina MiSeq sequencing revealed that Tissierella and Erysipelothrix were enriched in the NaOH and Ca(OH)2 systems, where Peptostreptococcaceae incertae_sedis was enriched in the NaOH and KOH systems, less Anaerolinea was involved in Ca(OH)2 condition.

An integrated insight into the response of sedimentary microbial communities to heavy metal contamination

Response of biological communities to environmental stresses is a critical issue in ecology, but how microbial communities shift across heavy metal gradients remain unclear. To explore the microbial response to heavy metal contamination (e.g., Cr, Mn, Zn), the composition, structure and functional potential of sedimentary microbial community were investigated by sequencing of 16S rRNA gene amplicons and a functional gene microarray. Analysis of 16S rRNA sequences revealed that the composition and structure of sedimentary microbial communities changed significantly across a gradient of heavy metal contamination, and the relative abundances were higher for Firmicutes, Chloroflexi and Crenarchaeota, but lower for Proteobacteria and Actinobacteria in highly contaminated samples. Also, molecular ecological network analysis of sequencing data indicated that their possible interactions might be enhanced in highly contaminated communities. Correspondently, key functional genes involved in metal homeostasis (e.g., chrR, metC, merB), carbon metabolism, and organic remediation showed a higher abundance in highly contaminated samples, indicating that bacterial communities in contaminated areas may modulate their energy consumption and organic remediation ability. This study indicated that the sedimentary indigenous microbial community may shift the composition and structure as well as function priority and interaction network to increase their adaptability and/or resistance to environmental contamination.

Bacteriophages of wastewater foaming-associated filamentous Gordonia reduce host levels in raw activated sludge

Filamentous bacteria are a normal and necessary component of the activated sludge wastewater treatment process, but the overgrowth of filamentous bacteria results in foaming and bulking associated disruptions. Bacteriophages, or phages, were investigated for their potential to reduce the titer of foaming bacteria in a mixed-microbial activated sludge matrix. Foaming-associated filamentous bacteria were isolated from activated sludge of a commercial wastewater treatment plan and identified as Gordonia species by 16S rDNA sequencing. Four representative phages were isolated that target G. malaquae and two un-named Gordonia species isolates. Electron microscopy revealed the phages to be siphophages with long tails. Three of the phages - GordTnk2, Gmala1, and GordDuk1 - had very similar ~76 kb genomes, with >93% DNA identity. These genomes shared limited synteny with Rhodococcus equi phage ReqiDocB7 and Gordonia phage GTE7. In contrast, the genome of phage Gsput1 was smaller (43 kb) and was not similar enough to any known phage to be placed within an established phage type. Application of these four phages at MOIs of 5–15 significantly reduced Gordonia host levels in a wastewater sludge model by approximately 10-fold as compared to non-phage treated reactors. Phage control was observed for nine days after treatment.

The activated sludge bulking filament Eikelboom morphotype 0803 embraces more than one member of the Chloroflexi

The Eikelboom filamentous morphotype 0803 is commonly found in activated sludge systems globally, where it contributes to sludge bulking events. Earlier reports have suggested that it is a member of both the Proteobacteria and Chloroflexi. This study shows that this filament contributing to a period of poor sludge settleability in an Australian activated sludge plant is a member of the Chloroflexi, but not within the Caldilinea, as reported for this morphotype in Danish plants. Instead, it is a member of the Anaerolineae. The fluorescent signals generated in these filaments using the FISH probes designed here were unevenly distributed, a situation similar to that seen earlier in the Anaerolineae morphotype 0092 to which it is more closely related phylogenetically than it is to the Caldilinea morphotype 0803. FISH-based surveys showed that this 0803 phylotype is uncommon in Australian activated sludge systems, and where seen is present usually at low abundances. The FISH probes described here will facilitate attempts to map the distribution and impact of this Australian filament morphotype 0803 in activated sludge systems of different configurations in plants around the world.

The activated sludge ecosystem contains a core community of abundant organisms

Understanding the microbial ecology of a system requires that the observed population dynamics can be linked to their metabolic functions. However, functional characterization is laborious and the choice of organisms should be prioritized to those that are frequently abundant (core) or transiently abundant, which are therefore putatively make the greatest contribution to carbon turnover in the system. We analyzed the microbial communities in 13 Danish wastewater treatment plants with nutrient removal in consecutive years and a single plant periodically over 6 years, using Illumina sequencing of 16S ribosomal RNA amplicons of the V4 region. The plants contained a core community of 63 abundant genus-level operational taxonomic units (OTUs) that made up 68% of the total reads. A core community consisting of abundant OTUs was also observed within the incoming wastewater to three plants. The net growth rate for individual OTUs was quantified using mass balance, and it was found that 10% of the total reads in the activated sludge were from slow or non-growing OTUs, and that their measured abundance was primarily because of immigration with the wastewater. Transiently abundant organisms were also identified. Among them the genus Nitrotoga (class Betaproteobacteria) was the most abundant putative nitrite oxidizer in a number of activated sludge plants, which challenges previous assumptions that Nitrospira (phylum Nitrospirae) are the primary nitrite-oxidizers in activated sludge systems with nutrient removal.

Combined organic matter and nitrogen removal from a chemical industry wastewater in a two-stage MBBR system

Pesticide-producing factories generate highly polluting wastewaters containing toxic and hazardous compounds which should be reduced to acceptable levels before discharge. In this study, a chemical industry wastewater was treated in a pre-denitrification moving-bed biofilm reactor system subjected to an increasing internal mixed liquor recycle ratio from 2 to 4. Although the influent wastewater characteristics substantially varied over time, the removal of chemical oxygen demand (COD) and dissolved organic carbon was quite stable and mostly higher than 90%. The highest fraction of the incoming organic matter was removed anoxically, favouring a low COD/N environment in the subsequent aerobic nitrifying tank and thus ensuring stable ammonium removal (90-95%). However, during pH and salt shock periods, nitrifiers were severely inhibited but gradually restored their full nitrifying capability as non-stressing conditions were reestablished. Besides promoting an increase in the maximum nitrification potential of the aerobic attached biomass from 0.34 to 0.63 mg [Formula: see text], the increase in the internal recycle ratio was accompanied by an increase in nitrogen removal (60-78%) and maximum specific denitrification rate (2.7-3.3 mg NOx(-)--N). Total polysaccharides (PS) and protein (PT) concentrations of attached biomass were observed to be directly influenced by the influent organic loading rate, while the PS/PT ratio mainly ranged from 0.3 to 0.5. Results of Microtox tests showed that no toxicity was found in the effluent of both the anoxic and aerobic reactors, indicating that the biological process was effective in removing residual substances which might adversely affect the receiving waters' ecosystem.

MiDAS: the field guide to the microbes of activated sludge

The Microbial Database for Activated Sludge (MiDAS) field guide is a freely available online resource linking the identity of abundant and process critical microorganisms in activated sludge wastewater treatment systems to available data related to their functional importance. Phenotypic properties of some of these genera are described, but most are known only from sequence data. The MiDAS taxonomy is a manual curation of the SILVA taxonomy that proposes a name for all genus-level taxa observed to be abundant by large-scale 16 S rRNA gene amplicon sequencing of full-scale activated sludge communities. The taxonomy can be used to classify unknown sequences, and the online MiDAS field guide links the identity to the available information about their morphology, diversity, physiology and distribution. The use of a common taxonomy across the field will provide a solid foundation for the study of microbial ecology of the activated sludge process and related treatment processes. The online MiDAS field guide is a collaborative workspace intended to facilitate a better understanding of the ecology of activated sludge and related treatment processes—knowledge that will be an invaluable resource for the optimal design and operation of these systems.

Database URL:http://www.midasfieldguide.org

Linking operation parameters and environmental variables to population dynamics of Mycolata in a membrane bioreactor

The community structure and population dynamics of Mycolata were monitored in a full-scale membrane bioreactor during four experimental phases under changing operating and environmental conditions, by means of temperature-gradient gel electrophoresis of partial 16S-rRNA genes amplified from community DNA and RNA templates (total and active populations). Non-metric multidimensional scaling and BIO-ENV analyses demonstrated that population dynamics were mostly explained (30-32%) by changes in the input of nutrients in the influent water and the accumulation of biomass in the bioreactors, while the influence of hydraulic and solid retention times, temperature and F/M ratio was minor. Significant correlations were observed between particular Mycolata phylotypes and one or more variables, contributing information for the prediction of their abundance and activity under changing conditions. Fingerprinting and multivariate analyses demonstrated that two foaming episodes, recorded at temperatures <20°C, were connected to the increase of the relative abundance of Mycolata unrelated to Gordonia amarae.