Analysis of enhanced nitrogen removal mechanisms in a validation wastewater treatment plant containing anammox bacteria

Substrate-dependent strategies to mitigate sulfate inhibition on microbial reductive dechlorination of polychlorinated biphenyls

Sulfate widely co-exists with polychlorinated biphenyls (PCBs) at various concentrations in the subsurface environment. Previous studies have suggested that sulfate often hampers microbial degradation of aliphatic chlorinated solvents such as chloroethenes. However, the impact of sulfate on microbial reductive dechlorination of aromatic PCBs and the underlying mechanisms have received limited attention. Likewise, strategies to mitigate such inhibition remain scarce. Here we found that the mechanisms and mitigation strategies of sulfate inhibition on PCB dechlorination were substrate-dependent. Under electron donor-limiting conditions, even a low concentration of sulfate (2 mM) resulted in a decreased PCB dechlorination rate by 88.7% in a co-culture comprising Dehalococcoides mccartyi CG1 and the sulfate-reducing bacterium Desulfovibrio desulfuricans F1, an inhibition which was attributed to the competition for electron donor between sulfate reduction and PCB dechlorination. As expected, re-amendment of 5 mM lactate effectively re-initiated PCB dechlorination. However, in the presence of a higher concentration of sulfate (5 mM), the PCB dechlorination rate in the co-culture was 77.7% lower than in the control, even with excessive electron donor supply. This inhibition was linked to high concentration of sulfide (∼5 mM) produced from sulfate reduction, as suggested by high availability of electron donor, recovery of dechlorination activity after removal of sulfide, and negligible influence of sulfate on PCB dechlorination in the axenic culture of D. mccartyi CG1. Indeed, sulfide (>5 mM) was found to directly suppress expression of PCB-dechlorinating reductive dehalogenase gene. The highest transcriptional level of pcbA1 was 2.9 ± 0.3 transcripts·cell-1 in the presence of ∼5 mM sulfide, which was increased to 37.4 ± 5.0 transcripts·cell-1 when sulfide was removed. Under this scenario, introduction of ferrous salts (5 mM) efficiently alleviated sulfide inhibition on PCB dechlorination. Interestingly, the augmentation of methanogens in the co-culture was also effective in mitigating sulfide inhibition on PCB dechlorination, offering a new approach to protect Dehalococcoides under sulfide stress. Collectively, these findings deepen our understanding of the influence of sulfate on microbial reductive dechlorination of PCBs and contribute to developing appropriate strategies based on geochemical conditions to alleviate sulfate inhibition during bioremediation of PCB-contaminated sites.

From hybrid process to pure biofilm anammox process: Suspended sludge biomass management contributing to high-level anammox enrichment in biofilms

The application of mainstream anammox is highly desirable for municipal wastewater treatment. However, enrichment of anammox bacteria (AnAOB) is challenging, particularly given the vicious competition from denitrifying bacteria (DB). Here, suspended sludge biomass management, a novel operational strategy for hybrid process (suspended sludge/biofilm), was investigated for 570 days based on a modified anaerobic-anoxic-oxic system treating municipal wastewater. By successively decreasing the suspended sludge concentration, the traditional hybrid process was successfully upgraded to a pure biofilm anammox process. During this process, both the nitrogen removal efficiency (NRE) and rate (NRR) were significantly improved (P < 0.001), from 62.1 ± 4.5% to 79.2 ± 3.9% and from 48.7 ± 9.7 to 62.3 ± 9.0 g N/(m³·d), respectively. Mainstream anammox was improved in the following: Candidatus Brocadia was enriched from 0.70% to 5.99% in anoxic biofilms [from (9.94 ± 0.99) × 10⁸ to (1.16 ± 0.01) × 10¹⁰ copies/g VSS, P < 0.001]; the in situ anammox reaction rate increased from 8.8 ± 1.9 to 45.5 ± 3.2 g N/(m³·d) (P < 0.001); the anammox contribution to nitrogen removal rose from 9.2 ± 2.8% to 67.1 ± 8.3% (P < 0.001). Core bacterial microbiome analysis, functional gene quantification, and a series of ex situ batch experiments demonstrated that the stepwise decreases in suspended sludge concentration effectively mitigated the vicious competition of DB against AnAOB, enabling high-level AnAOB enrichment. This study presents a straightforward and effective strategy for enriching AnAOB in municipal wastewater, shedding fresh light on the application and upgradation of mainstream anammox.

Mathematical modelling of an intermittent anoxic/aerobic MBBR: Estimation of nitrification rates and energy savings

This study aimed at modelling the performance of a novel MBBR configuration, named A/O-MBBR, comprised of a pre-anoxic reactor, with an HRT of 4.5 h, coupled with an intermittent anoxic/aerobic MBBR (HRT = 6.8 h). The lab-scale system was fed with municipal wastewater with an average influent Total Ammonia Nitrogen (TAN) and total COD (TCOD) concentrations of 46 mg of TAN-N L^-1 and 310 mg TCOD L^-1. During the whole experimental period, TAN removal efficiency was always higher than 96%; denitrification was also very effective, achieving nitrate and nitrite concentrations in the effluent both lower than 5 mg NO_x-N L^-1 on average. Moreover, TCOD average removal efficiency was equal to 85%. Modelling was performed to investigate the nitrification efficacy enhancement; to this aim, a biofilm model was developed, adopting the equations for mixed-culture biofilms and the Activated Model Sludge n°1 (ASM1) for the biological processes rates. The model allowed to determine the maximum uptake rate for autotrophic growth (μ_A was 2.5 d^-1) and the semisaturation constant (K_OA was 0.2 mg O₂ L^-1), suggesting that the nitrification process was 3-fold faster than average and very effective at low oxygen concentrations. The model estimated that about 85% of TAN was removed by the biofilm and only the remaining part by suspended biomass in the bulk liquid. Finally, it was assessed that the A/O-MBBR configuration allowed for a 45-60% savings of the energy requirement compared to a Benchmark WWTP layout.

Successful Application of Anammox Using the Hybrid Autotrophic-Heterotrophic Denitrification Process for Low-Strength Wastewater Treatment

Directly integrating anammox into sewage treatment is attractive, but anammox bacteria (AnAOB) enrichment is complex due to vicious competition from heterotrophic bacteria (HB). A novel strategy of optimal organics management using a preanaerobic stage and subsequent limited-oxygen conditions (0.32 ± 0.15 mg-O₂/L) is applied, and a hybrid autotrophic-heterotrophic denitrification process is developed to treat sewage-like wastewater with a COD/N ratio of 3.1 for 420 days. The stable process was achieved, and a high total nitrogen removal rate of 0.53 kg-N/(m³·d) was obtained compared to conventional nitrification/denitrification. The 16S rRNA high-throughput sequencing analysis suggested that the relative abundance of the nonendogenous HB (Denitratisoma and Thauera) was drastically reduced (P ≤ 0.001), whereas the endogenous denitrifying HB (Candidatus (Ca.) Competibacter) was significantly enriched in the anammox granules (9.98%, P ≤ 0.001). Moreover, Ca. Competibacter as an inner core and Nitrospira and Ca. Brocadia as an outside coating of the anammox granules indicated the cooperation of AnAOB with HB as revealed by laser-scanning confocal microscopy and qPCR. In situ tests further confirmed nitrite from two pathways (partial nitritation and endogenous partial denitritation) that favored AnAOB enrichment. Optimal organics management can mitigate the competition of HB with AnAOB by redirecting the metabolic pathways and microbial community, which is critical to directly integrating anammox into sewage treatment.

Resilience of organohalide-detoxifying microbial community to oxygen stress in sewage sludge

Organohalide pollutants are prevalent in the environment, causing harms to wildlife and human. Organohalide-respiring bacteria (OHRB) could detoxify these pollutants in anaerobic environments, but the most competent OHRB (i.e., Dehalococcoides) is susceptible to oxygen. This study reports exceptional resistance and resilience of sewage sludge microbial communities to oxygen stress for attenuation of structurally distinct organohalide pollutants, including tetrachloroethene, tetrabromobisphenol A, and polybrominated diphenyl ethers. The dehalogenation rate constant of these organohalide pollutants in oxygen-exposed sludge microcosms was maintained as 74-120% as that in the control without oxygen exposure. Subsequent top-down experiments clarified that sludge flocs and non-OHRB contributed to alleviating oxygen stress on OHRB. In the dehalogenating microcosms, multiple OHRB (Dehahlococcoides, Dehalogenimonas, and Sulfurospirillum) harboring distinct reductive dehalogenase genes (pceA, pteA, tceA, vcrA, and bdeA) collaborated to detoxify organohalide pollutants but responded differentially to oxygen stress. Comprehensive microbial community analyses (taxonomy, diversity, and structure) demonstrated certain resilience of the sludge-derived dehalogenating microbial communities to oxygen stress. Additionally, microbial co-occurrence networks were intensified by oxygen stress in most microcosms, as a possible stress mitigation strategy. Altogether the mechanistic and ecological findings in this study contribute to remediation of organohalide-contaminated sites encountering oxygen disturbance.

Sustainable upgrading of biological municipal wastewater treatment based on anammox: From microbial understanding to engineering application

Anaerobic ammonium oxidation (anammox) has drawn increasing attention as a promising option to energy-neutral wastewater treatment. While anammox process still faces challenges in the low-strength and organics-contained municipal wastewater due to its susceptibility and the technical gaps in substrate supply. Effective strategies for extensive implementation of anammox in municipal wastewater treatment plants (WWTPs) remain poorly summarized. In view of the significance and necessity of introducing anammox into mainstream treatment, the growing understanding not only at level of microbial interactions but also on view of upgrading municipal WWTPs with anammox-based processes need to be considered urgently. In this review, the critical view and comprehensive analysis were offered from the perspective of microbial interactions within partial nitrification- and partial denitrification-based anammox processes. To minimize the microbial competition and enhance the cooperation among anammox bacteria and other functional bacteria, targeted control strategies were systematically evaluated. Based on the comprehensive overview of recent advances, the combination of flexible regulation of input organic carbon with anaerobic/oxic/anoxic process and the integration of sludge fermentation with anoxic biofilms in anaerobic/anoxic/oxic process were proposed as promising solutions to upgrade municipal WWTPs with anammox technology. Furthermore, a new perspective of coupling anammox with denitrifying dephosphatation was proposed as a promising method for in-depth nutrients removal from carbon-limit municipal wastewater in this study. This review provides the critical and comprehensive viewpoints on anammox engineering in municipal wastewater and paves the way for the anammox-based upgrading of municipal WWTPs.

Simultaneous shortcut nitrification and denitrification in a hybrid membrane aerated biofilms reactor (H-MBfR) for nitrogen removal from low COD/N wastewater

The residues of nitrogen contaminants due to insufficient organic carbon sources in sewage has always been the main problem faced by wastewater treatment plants in the process of nitrogen removal. In this study, simultaneous shortcut nitrification and denitrification (SND) was achieved in the hybrid membrane aerated biofilm reactor (H-MBfR) for treating low COD/N ratio (∼x223C 4: 1) wastewater. The effects of the aeration pressure and the influent COD/N ratio in H-MBfR were investigated and further optimized by the response surface methodology (RSM). By controlling the dissolved oxygen to achieve SND, the removal efficiencies of NH₄⁺-N, COD and TN of low COD/N ratio wastewater reached maximum values of 95.52%, 96.61% and 72.23%, respectively. Microbial community analysis showed that the influent COD/N ratio had an obvious influence on the microbial community structure. In particular, ammonia oxidizing bacteria (AOB) and denitrifying bacteria had a good commensalism when the COD/N ratio was 4.3. Compared to control reactor, the analysis of membrane bio-fouling showed that H-MBfR has a lower amount of extracellular polymeric substance (EPS) on membrane and a low concentration of MLSS in bulk liquid, which is helpful for the longer-term operation of H-MBfR.

Nitrogen removal from ammonium- and sulfate-rich wastewater in an upflow anaerobic sludge bed reactor: performance and microbial community structure

Autotrophic ammonium removal by sulfate-dependent anaerobic ammonium oxidation (S-Anammox) process was studied in an upflow anaerobic sludge bed reactor inoculated with Anammox sludge. Over an operation period of 371 days, the reactor with a hydraulic retention time of 16 h was fed with influent in which NH₄⁺ concentration was fixed at 70 mg N L^-1, and the molar ratio of NO₂^-:NO₃^-:SO₄^2- was 1:0.2:0.2, 0.5:0.1:0.3 and 0:0:0.5 in stages I, II and III, respectively. As the NO₂^- in influent was entirely replaced by SO₄^2-, the NH₄⁺ removal rate was 31.02 mg N L^-1 d^-1, and the conversion rate of SO₄^2- was 8.18 mg S L^-1 d^-1. On grounds of the high NH₄⁺:SO₄^2- removal ratio (8.67:1), the S^2- accumulation and pH drop in effluent, as well as the analysis results of microbial community structure, the S-Anammox process was speculated to play a dominant role in stage III. The NH₄⁺ over-transformation was presumably as a consequence of the cyclic regeneration of SO₄^2-. Concerning the microbial characteristics in the system, the Anammox bacteria (Candidatus Brocadia), sulfate-reducing bacteria (SRB) (Desulfatiglans and Desulfurivibrio) and sulfur-oxidizing bacteria (SOB) (Thiobacillus) in biomass was enriched in the case of without addition of NO₂^- in influent. Sulfate reduction driven ammonium anaerobic oxidation was probably attributed to the coordinated metabolism of nitrogen- and sulfur-utilizing bacteria consortium, in which Anammox bacteria dominates the nitrogen removal, and the SRB and SOB participates in the sulfur cycle as well as accepts required electrons from Anammox bacteria through a direct inter-species electron transfer (DIET) pathway.

Rapid initiation and stable maintenance of municipal wastewater nitritation during the continuous flow anaerobic/oxic process with an ultra-low sludge retention time

Rapid achievement of nitritation of mainstream municipal wastewater in a continuous-flow process is attractive since it favors the involvement of the anammox process and reduces the operational costs. In this study, a feasible and economical strategy is proposed to rapidly achieve the nitritation of municipal wastewater. By aggressively discharging excess sludge during the seasonal warming period (temperature increasing from 18°C to 22°C), nitritation was established in 15 days with a nitrite accumulation ratio of 85.09% in a continuous-flow anaerobic/oxic (An/O) reactor. Meanwhile, qPCR results revealed that amoA abundance increased from (1.78±0.10) × 10⁸ copies/(g VSS) to (1.05±0.11) × 10¹⁰ copies/(g VSS) while the abundance of nitrite-oxidizing bacteria decreased from (1.1±0.02) × 10¹⁰ copies/(g VSS) to (5.01±0.02) × 10⁸ copies/(g VSS). The temperature gradually stabilized at 26°C during the following operational period and stable nitritation was maintained with a nitrite accumulation ratio above 90%, which was mainly attributed to a short sludge retention time (SRT) of 4.3 days and a low dissolved oxygen of 0.86 ± 0.5 mg/L. Falling temperature negatively impacted the stability of nitritation, but nitritation could be restarted by aggressively discharging excess sludge during another temperature increase period. Overall, this study provides a feasible strategy to start-up nitritation that has great potential applications for municipal wastewater treatment.

Insights into the Occurrence, Fate, and Impacts of Halogenated Flame Retardants in Municipal Wastewater Treatment Plants

Halogenated flame retardants (HFRs) have been extensively used in various consumer products and many are classified as persistent organic pollutants due to their resistance to degradation, bioaccumulation potential and toxicity. HFRs have been widely detected in the municipal wastewater and wastewater treatment solids in wastewater treatment plants (WWTPs), the discharge and agricultural application of which represent a primary source of environmental HFRs contamination. This review seeks to provide a current overview on the occurrence, fate, and impacts of HFRs in WWTPs around the globe. We first summarize studies recording the occurrence of representative HFRs in wastewater and wastewater treatment solids, revealing temporal and geographical trends in HFRs distribution. Then, the efficiency and mechanism of HFRs removal by biosorption, which is known to be the primary process for HFRs removal from wastewater, during biological wastewater treatment processes, are discussed. Transformation of HFRs via abiotic and biotic processes in laboratory tests and full-scale WWTPs is reviewed with particular emphasis on the transformation pathways and functional microorganisms responsible for HFRs biotransformation. Finally, the potential impacts of HFRs on reactor performance (i.e., nitrogen removal and methanogenesis) and microbiome in bioreactors are discussed. This review aims to advance our understanding of the fate and impacts of HFRs in WWTPs and shed light on important questions warranting further investigation.

Highly enriched anammox within anoxic biofilms by reducing suspended sludge biomass in a real-sewage A2/O process

This study proposes a novel strategy of stably enriching anammox in mainstream, based on the competitive difference to NO₂^- between anoxic biofilms and suspended sludge. A modified anaerobic-anoxic-oxic (A²/O) process run for 500 days with actual municipal wastewater. Microbial analysis revealed that anoxic-carrier biofilms had a significantly higher abundance of anammox (qPCR: 0.74% - 4.34%) than suspended sludge (P< 0.001). Batch tests showed that anammox within anoxic-carrier biofilms contributed to significant nitrogen removal, coupled with partial-denitrification (NO₃^- → NO₂^-). The anammox genus, Ca. Brocadia, was highly enriched when suspended sludge was accidentally lost. Further batch tests found that reducing suspended biomass helped anammox enrichment in anoxic-carrier biofilms, because the suspended sludge had strong NO₂^- competition (NO₂^- → N₂) with anammox (increased nirK). Metagenomic sequencing revealed that Ca. Brocadia dominates in the anoxic-carrier biofilms, and is the most important narG contributor to NO₃^- → NO₂^-, which could have promoted the competition of NO₂^- with heterotrophic bacteria. For this A²/O process, the low effluent total nitrogen (8.9 mg ± 1.0 mg N/L) was attributed to partial-denitrification coupling with anammox, demonstrating that this process is applicable to the general influent N-concentration range (30 mg - 50 mg NH₄⁺-N/L) of municipal wastewater treatment plants (WWTPs). Based on the special competitive preference of anammox for NO₂^-, this study provides a promising and practical alternative for enriching anammox bacteria in municipal WWTPs.

Seasonal Prevalence of Ammonia-Oxidizing Archaea in a Full-Scale Municipal Wastewater Treatment Plant Treating Saline Wastewater Revealed by a 6-Year Time-Series Analysis

Although several molecular-based studies have demonstrated the involvement of ammonia-oxidizing archaea (AOA) in ammonia oxidation in wastewater treatment plants (WWTPs), factors affecting the persistence and growth of AOA in these engineered systems have not been resolved. Here, we show a seasonal prevalence of AOA in a full-scale WWTP (Shatin, Hong Kong SAR) over a 6-year period of observation, even outnumbering ammonia-oxidizing bacteria in the seasonal peaks in 3 years, which may be due to the high bioavailable copper concentrations. Comparative analysis of three metagenome-assembled genomes of group I.1a AOA obtained from the activated sludge and 16S rRNA gene sequences recovered from marine sediments suggested that the seawater used for toilet flushing was the primary source of the WWTP AOA. A rare AOA population in the estuarine source water became transiently abundant in the WWTP with a metagenome-based relative abundance of up to 1.3% over three seasons of observation. Correlation-based network analysis revealed a robust co-occurrence relationship between these AOA and organisms potentially active in nitrite oxidation. Moreover, a strong correlation between the dominant AOA and an abundant proteobacterial organism suggested that capacity for extracellular polymeric substance production by the proteobacterium could provide a niche for AOA within bioaggregates. Together, the study highlights the importance of long-term observation in identifying biotic and abiotic factors governing population dynamics in open systems such as full-scale WWTPs.

Time to act-assessing variations in qPCR analyses in biological nitrogen removal with examples from partial nitritation/anammox systems

Quantitative PCR (qPCR) is broadly used as the gold standard to quantify microbial community fractions in environmental microbiology and biotechnology. Benchmarking efforts to ensure the comparability of qPCR data for environmental bioprocesses are still scarce. Also, for partial nitritation/anammox (PN/A) systems systematic investigations are still missing, rendering meta-analysis of reported trends and generic insights potentially precarious. We report a baseline investigation of the variability of qPCR-based analyses for microbial communities applied to PN/A systems. Round-robin testing was performed for three PN/A biomass samples in six laboratories, using the respective in-house DNA extraction and qPCR protocols. The concentration of extracted DNA was significantly different between labs, ranged between 2.7 and 328 ng mg^-1 wet biomass. The variability among the qPCR abundance data of different labs was very high (1-7 log fold) but differed for different target microbial guilds. DNA extraction caused maximum variation (3-7 log fold), followed by the primers (1-3 log fold). These insights will guide environmental scientists and engineers as well as treatment plant operators in the interpretation of qPCR data.

Sustained organic loading disturbance favors nitrite accumulation in bioreactors with variable resistance, recovery and resilience of nitrification and nitrifiers

Sustained disturbances are relevant for environmental biotechnology as they can lead to alternative stable states in a system that may not be reversible. Here, we tested the effect of a sustained organic loading alteration (food-to-biomass ratio, F:M, and carbon-to-nitrogen ratio, C:N) on activated sludge bioreactors, focusing on the stability of nitrification and nitrifiers. Two sets of replicate 5-L sequencing batch reactors were operated at different, low and high, F:M (0.19–0.36 mg COD/mg TSS/d) and C:N (3.5–6.3 mg COD/mg TKN) conditions for a period of 74 days, following 53 days of sludge acclimation. Recovery and resilience were tested during the last 14 days by operating all reactors at low F:M and C:N (henceforth termed F:M–C:N). Stable nitrite accumulation (77%) was achieved through high F:M–C:N loading with a concurrent reduction in the abundance of Nitrospira. Subsequently, only two of the three reactors experiencing a switch back from high to low F:M–C:N recovered the nitrite oxidation function, with an increase in Nitrobacter as the predominant NOB, without a recovery of Nitrospira. The AOB community was more diverse, resistant and resilient than the NOB community. We showed that functional recovery and resilience can vary across replicate reactors, and that nitrification recovery need not coincide with a return to the initial nitrifying community structure.

Complete nitrogen removal via simultaneous nitrification and denitrification by a novel phosphate accumulating Thauera sp. strain SND5

Bacteria capable of simultaneous nitrification and denitrification (SND) and phosphate removal could eliminate the need for separate reactors to remove nutrients from wastewater and alleviate competition for carbon sources between different heterotrophs in wastewater treatment plants (WWTPs). Here we report a newly isolated Thauera sp. strain SND5, that removes nitrogen and phosphorus from wastewater via SND and denitrifying-phosphate accumulation, respectively, without accumulation of metabolic intermediates. Strain SND5 simultaneously removes ammonium, nitrite, and nitrate at an average rate of 2.85, 1.98, and 2.42 mg-N/L/h, respectively. Batch testing, detection of functional genes, nitrogenous gas detection and thermodynamic analysis suggested that nitrogen gas, with hydroxylamine produced as an intermediate, was the most likely end products of heterotrophic ammonium oxidation by strain SND5. The generated end products and intermediates suggest a novel nitrogen removal mechanism for heterotrophic ammonium oxidation in strain SND5 (NH₄⁺→NH₂OH→N₂). Strain SND5 was also found to be a denitrifying phosphate-accumulating organism, capable of accumulating phosphate, producing and storing polyhydroxybutyrate (PHB) as an intracellular source of carbon while using nitrate/nitrite or oxygen as an electron acceptor during PHB catabolism. This study identifies a novel pathway by which simultaneous nitrogen and phosphorus removal occurs in WWTPs via a single microbe.

Abundance of organohalide respiring bacteria and their role in dehalogenating antimicrobials in wastewater treatment plants

Anthropogenic organohalide contaminants present in wastewater treatment plants (WWTPs) often remain untreated and can be discharged into the environment. Although organohalide respiring bacteria (OHRB) contribute to the elimination of anthropogenic organohalides in natural anaerobic environments, reductive dehalogenation by OHRB in mainstream WWTPs remains poorly understood. In this study, we quantified OHRB during a long-term operation of a municipal WWTP with short hydraulic and sludge retention times (3 h and 1.5-5 days, respectively). The obligate OHRB were detected at high levels (averaging 2.56 ± 1.73 × 10⁷ and 3.11 ± 1.16 × 10⁷ 16S rRNA gene copies/ml MLSS sludge in anoxic and aerobic zones, respectively) over the entire sampling period and throughout the wastewater treatment train. Microcosms derived from mainstream activated sludge contained an unidentified member of the Dehalococcoides genus that metabolically dechlorinated triclosan, used as a representative emerging organohalide antimicrobial, to diclosan, suggesting the potential of anaerobic degradation of emerging contaminants in WWTPs. To further understand the mechanisms for such antimicrobials' removal, an investigation of dechlorination of triclosan by Dehalococcoides strains was conducted. Dechlorination of environmentally relevant concentrations of triclosan to diclosan was observed in Dehalococcoides mccartyi strain CG1, yielding 4.59 ± 0.34 × 10⁸ cells/μmole Cl^- removed at a rate of 0.062 μM/day and a minimal inhibitory concentration of 0.5 mg/L. Notably, both the tolerance of strain CG1 to triclosan and the rate of triclosan dechlorination increased when CG1 was cultured in the presence of both triclosan and tetrachloroethene. Taken together, our results suggest that anaerobic degradation of organohalide antimicrobials might be more prevalent in mainstream WWTPs than previously speculated, though the low growth yields that are supported by triclosan dechlorination seem to indicate that other organohalide substrates could be necessary to sustain OHRB populations in these systems.

Abundance and diversity of nitrogen-removing microorganisms in the UASB-anammox reactor

Anaerobic ammonium oxidation is considered to be the most economical and low-energy biological nitrogen removal process. So far, anammox bacteria have not yet been purified from cultures. Some nitrogen-removing microorganisms cooperate to perform the anammox process. The objective of this research was to analyze the abundance and diversity of nitrogen-removing microorganisms in an anammox reactor started up with bulking sludge at room temperature. In this study, the ammonia-oxidizing archaea phylum Crenarchaeota was enriched from 9.2 to 53.0%. Nitrosomonas, Nitrosococcus, and Nitrosospira, which are ammonia-oxidizing bacteria, increased from 3.2, 1.7, and 0.1% to 12.8, 20.4, and 3.3%, respectively. Ca. Brocadia, Ca. Kuenenia, and Ca. Scalindua, which are anammox bacteria, were detected in the seeding sludge, accounting for 77.1, 11.5, and 10.6%. After cultivation, the dominant genus changed to Ca. Kuenenia, accounting for 82.0%. Nitrospirae, nitrite oxidation bacteria, decreased from 2.2 to 0.1%, while denitrifying genera decreased from 12.9 to 2.1%. The results of this study contribute to the understanding of nitrogen-removing microorganisms in an anammox reactor, thereby facilitating the improvement of such reactors. However, the physiological and metabolic functions of the ammonia-oxidizing archaea community in the anammox reactor need to be investigated in further studies.