Due to the key role of nitrite in novel nitrogen removal systems, nitrite oxidizing bacteria (NOB) have been receiving increasing attention. In this study, the coexistence and interactions of ...nitrifying bacteria were explored at decreasing solids retention times (SRTs). Four 5-week washout experiments were carried out in laboratory-scale (V = 10 L) sequencing batch reactors (SBRs) with mixed liquor from two full-scale activated sludge systems (continuous flow vs SBR). During the experiments, the SRT was gradually reduced from the initial value of 4.0 d to approximately 1.0 d. The reactors were operated under limited dissolved oxygen conditions (set point of 0.6 mg O2/L) and two process temperatures: 12 °C (winter) and 20 °C (summer). At both temperatures, the progressive SRT reduction was inefficient for the out-selection of both canonical NOB and comammox Nitrospira. However, the dominant NOB switched from Nitrospira to Ca. Nitrotoga, whereas the dominant AOB was always Nitrosomonas. The results of this study are important for optimizing NOB suppression strategies in the novel N removal processes, which are based on nitrite accumulation.
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•Variable N2H4 concentration dosage make mainstream deammonification process stable.•The inhibit effect of N2H4 on AnAOB and AnAOB self-regulate mechanism was found.•Variable N2H4 ...concentration dosage was beneficial for most microorganisms.
In this study, an expanded granular sludge blanket reactor (EGSB) was proposed to achieve stable mainstream deammonification process by adding hydrazine (N2H4). Two N2H4 addition methods consisted of constant concentration (strategy A) and variable concentration (strategy B) both can inhibit nitrite oxidizing bacteria. A efficient performance was achieved with higher total nitrogen removal efficiency (82 ± 6%) and nitrogen removal rate (0.32 ± 0.02 kg N/(m3·d)) under strategy B. For strategy A, anaerobic ammonia oxidizing bacteria (AnAOB) in-situ activity was decreased from 2.76 to 0.68 mg N/(g VSS·h) at 42 mg/L NH4+-N. Candidatus Brocadia abundance increase from 14.62% to 20.07% under the strategy may indicated the self-regulate mechanism of AnAOB. Aerobic ammonia oxidizing bacteria (AOB, mainly Nitrosomonas) and AnAOB (mainly Candidatus Brocadia) were always dominated under two strategies. Strategy B provided better environment for most microorganisms (mainly Chloroflexri, Planctomycetes, Proteobacteria and Chlorobi).
•Higher NH4+-N load led to higher oxygen transfer rate and lower NOB activity.•NOB was inhibited by low DO concentration in the limited space of aerobic biofilm.•Closed-end aeration mode favored ...Nitrosomonas and inhibited Nitrospira.•A strategy was proposed for quick start-up and stable mainstream PN in MABR.
The proliferation of nitrite oxidizing bacteria (NOB) still remains as a major challenge for nitrogen removal in mainstream wastewater treatment process based on partial nitrification (PN). This study investigated different operational conditions to establish mainstream PN for the fast start-up of membrane aerated biofilm reactor (MABR) systems. Different oxygen controlling strategies were adopted by employing different influent NH4+-N loads and oxygen supply strategies to inhibit NOB. We indicated the essential for NOB suppression was to reduce the oxygen concentration of the inner biofilm and the thickness of aerobic biofilm. A higher NH4+-N load (7.4 g-N/(m2·d)) induced higher oxygen utilization rate (14.4 g-O2/(m2·d)) and steeper gradient of oxygen concentration, which reduced the thickness of aerobic biofilm. Employing closed-end oxygen supply mode exhibited the minimum concentration of oxygen to realize PN, which was over 46% reduction of the normal open-end oxygen mode. Under the conditions of high NH4+-N load and closed-end oxygen supply mode, the microbial community exhibited a comparative advantage of ammonium oxidizing bacteria over NOB in the aerobic biofilm, with a relative abundance of Nitrosomonas of 30–40% and no detection of Nitrospira. The optimal fast start-up strategy was proposed with open-end aeration mode in the first 10 days and closed-end mode subsequently under high NH4+-N load. The results revealed the mechanism of NOB inhibition on the biofilm and provided strategies for a quick start-up and stable mainstream PN simultaneously, which poses great significance for the future application of MABR.
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•A new Fe-dosing strategy proposes centralized dosage into returned sludge than sewage.•Centralized Fe-dosing acidifies sludge and resulted in free nitrous acid accumulation.•The new strategy ...achieves less biomass production and shortcut nitrogen removal.•The new strategy still provides the same benefits as common mainstream Fe-dosing.
Iron salts (i.e. FeCl3) are the most used chemicals in the urban wastewater system. Iron is commonly dosed into sewage or the mainstream system, which provides multiple benefits such as enhanced phosphorus removal and improved sludge settleability/dewaterability. This study reported and demonstrated a new approach that dosed FeCl3 into returned sludge in order to bring two more benefits to wastewater management: short-cut nitrogen removal via the nitrite pathway and less biomass production. This approach is achieved based on our findings that with similar amount of FeCl3, centralized iron dosing into a sidestream sludge unit generated iron concentration two orders of magnitude higher than the common mainstream dosing (e.g. 10–40 mg Fe/L-wastewater), leading to sludge acidification (pH = 2.1) with Fe (III) hydrolysis. Together with accumulated nitrite in the supernatant of the sludge, ppm-level of free nitrous acid was generated and thus enabled sludge disintegration, cell lysis, and selective elimination of nitrite-oxidizing bacteria (NOB). Long-term effects on nitrifying bacteria and overall reactor performance were evaluated using two laboratory reactor experiments for over one year. The experimental reactor showed stable nitrite accumulation with an average NO2−/(NO2− + NO3−) ratio above 80% and ∼30% observed biomass yield reduction compared to those in control reactors. In addition, the centralized sludge dosing strategy still provided benefits such as improved settleability and dewaterability of sludge and enhanced phosphorus removal.
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Chronic hepatitis B virus (HBV) infection is a serious problem due to its extensive worldwide distribution and poor prognosis including cirrhosis and/or hepatocellular carcinoma. The hepatitis B ...surface antigen(HBsAg) is a vital serum marker in HBV infection and a major obstacle for effective and subsequently virus clearance. However, Current anti-HBV drugs, such as nucleos(t)ide analogs (NA) and PegIFN, do not meet ideal result of sustained HBsAg loss (defined as functional cure). Therefore, there is an urgent need to identify a new compound targeting HBsAg. In this study, nobiletin was screened out from 1500 compounds due to its low cytotoxicity and high antiviral activity. The effect of nobiletin on HBV was determined in HepG2.2.15 and HepG2-NTCP cells. Furthermore, the antiviral capability of nobiletin was also verified in vivo. Unlike entecavir (ETV) therapy, which reduced HBV DNA but do not lead to an effective reduction in HBsAg, nobiletin significantly reduced the level of HBsAg as well as lowered HBV DNA in vivo and in vitro. Meanwhile, combination of nobiletin and ETV led to broad reductions of both HBV DNA and HBsAg level. This study may shed light on the development of a novel class of anti-HBV agents.
•Nobiletin was screened out from 1500 compounds due to its low cytotoxicity and high antiviral activity.•Nobiletin significantly reduced the level of HBsAg and HBV DNA in vivo and in vitro.•Combination of nobiletin and ETV generated a much stronger loss of HBsAg and HBV DNA than monotherapy.•Nobiletin could be used as a novel class of anti-HBV agent targeting HBsAg and contribute to “functional cure”.
•High-salinity treatment as an ex situ NOB inactivation strategy was first proposed.•High salinity presented greater inactivation of NOB than AOB.•NAR was above 33% during nitrification after one ...high-salinity treatment.•Sludge characteristics remained almost unchanged after inhibition.•A novel process for achieving mainstream PN was proposed and evaluated.
The difficulty in achieving stable partial nitritation (PN) is a challenge that limits the application of mainstream anaerobic ammonium oxidation (anammox). This study proposes high-salinity treatment as a novel strategy for inactivating nitrite-oxidising bacteria (NOB). The study indicated that NOB are more sensitive to high salinity than ammonia-oxidising bacteria (AOB). The inhibitory effect on the nitrifier gradually increased with increasing salinity from 0 to 100 g NaCl/L. After 24 h and 35 g NaCl/L inhibition, the AOB and NOB activities were 36.65% and 7.15% of their original activities, respectively. After one high-salinity treatment, nitrite accumulation rate (NAR) was above 33% during nitrification. Moreover, the sludge characteristics remained almost unchanged after suppression. A novel process for achieving mainstream PN was proposed and evaluated based on the results. An energy consumption analysis showed that mainstream PN/anammox based on the ex situ high-salinity treatment can achieve higher energy self-sufficiency compared with activated sludge.
In this study, the conventional two-step nitrification model was extended with complete ammonia oxidation (comammox) and heterotrophic denitrification on soluble microbial products. The data for ...model calibration/validation were collected at four long-term washout experiments when the solid retention time (SRT) and hydraulic retention time (HRT) were progressively reduced from 4 d to 1 d, with mixed liquor suspended solids (MLSS) of approximately 2000 mg/L at the start of each trial. A new calibration protocol was proposed by including a systematic calculation of the initial biomass concentrations and microbial relationships as the calibration targets. Moreover, the impact assessment of initial biomass concentrations (X) and maximum growth rates (μ) for ammonia-oxidizing bacteria (AOB), nitrite-oxidizing bacteria (NOB), comammox Nitrospira, and heterotrophs on the calibration accuracy were investigated using the response surface methodology (RSM). The RSM results revealed the strongest interaction of XAOB and μAOB on the model calibration accuracy. All the examined model efficiency measures confirmed that the extended model was accurately calibrated and validated. The estimated μ values were as follows: μAOB = 0.38 ± 0.005 d−1, μNOB = 0.20 ± 0.01 d−1, μCMX = 0.20 ± 0.01 d−1, μHET = 1.0 ± 0.03 d−1. For comparison, when using the conventional model, μAOB and μNOB increased respectively by 26 and 15 % (μAOB = 0.48 ± 0.02 d−1 and μNOB = 0.23 ± 0.005 d−1). This study provides better understanding of the effects of the initial biomass composition and the accompanying processes (comammox and heterotrophic denitrification) on modeling two-step nitrification.
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•Two-step nitrification model was expanded with comammox and heterotrophic activity.•The model was evaluated against data from long-term washout experiments in an SBR.•The model accurately predicted behavior of N species and microbial relationships.•The initial biomass concentrations strongly influenced model predictions over time.•Denitrifying heterotrophs grew only on SMP but remained the dominant microbial group.
Conventional nitrification/denitrification process is gradually being replaced with partial-nitritation/anammox (PN/A) processes due to its installation and running cost. However, high ...ammonia-oxidizing bacteria (AOB) and anaerobic ammonia-oxidizing (anammox) bacteria activity as well as optimum out-selection of nitrite-oxidizing bacteria (NOB) are necessary to achieving efficient PN/A process. Consequently, to enhance PN process via nitrifying bacteria enrichment/out-selection within psychrophilic environment, a novel pH-DO (dissolved oxygen) control strategy was proposed and the response of PN, kinetics, AOB enrichment, and NOB out-selection efficiency was investigated during start-up and long-term operation. With DO of 0.7 mg/L and pH of 7.5–7.9, quick start-up of the PN process was established within 34d as NO2−-N accumulation ratio (NAR) reached 90.08 ± 1.4%. Again, when NLR was elevated to 0.8 kg/m3·d (400mgNH4+-N/L), DO curtailed to 0.2 mg/L, pH maintained at 7.7 and free ammonium at 6.5 mg/L, NAR and NH4+-N removal rate could still reach 97.04 ± 2.4% and 97.84 ± 1.5%, respectively. After optimum control factors had been established, real nitrogen-rich-mine-wastewater was fed (DO, 0.2 mg/L, pH, 8.9, and free ammonia, 6.5 mg/L) and NAR and NH4+-N removal rate reached was 97.33 ± 0.5% and 97.76 ± 1.1%, respectively. Estimated kinetic parameters including maximum degradation rate (Vmax = 1.58/d), half-rate constant (Km = 33.8 mg/L), and inhibition constant (Ki = 201.6 mg/L) suggested that inhibition on NH4+-N oxidation was most feasible at higher concentration of NH4+-N. To elucidate biological mechanisms, 16S rRNA high-throughput revealed that AOB (Nitrosomonas) enrichment had increased from 0.08% to 49% whereas NOB (Nitrospira) abundance reduced from 1% to 0.034%, indicating pH-DO control efficiently enriched AOB and out-selected NOB. Conversely, when influent NH4+-N was curtailed to about 200 mg/L and free ammonia concentration maintained at 6.5 mg/L, the population of AOB was observably reduced by 6% within a period of 14 days, indicating control strategies including pH-DO control and substrate availability were the key factors which substantially influenced and promoted the activities and growth of AOBs in the present SBR.
Schematic of the sequencing batch reactor, performance and microbial community evolution: (1) Influent feed tank; (2) Feed pump; (3) Effluent pump; (4) Effluent tank; (5) Mechanical stirrer; (6) Air distribution disc; (7) Air flow meter; (8) Air pump; (9) Timer; (10) Automatic control system; (11) Dissolved oxygen monitor; (12) DO probe; (13) pH probe (14) pH controller; (15) Peristaltic pump; (16) Alkaline solution for pH adjustment. Display omitted
•Rapid and high-rate partial nitritation was achieved within 34d.•Performance of NAR and ANR were satisfactory as efficiency of both exceeded 97%.•pH-DO control was the major driver to out-select NOB and promote AOB activities.•With DO of 0.2 mg/L and pH of 7.7, Nitrosomonas (AOB) increased from 0.08% to 49%.•Kinetics revealed that inhibition on NH4+-oxidation was feasible at higher NH4 conc.
We investigated the density and distribution of total bacteria, canonical Ammonia Oxidizing Bacteria (AOB) (Nitrosomonas plus Nitrosospira), Ammonia Oxidizing Archaea (AOA), as well as Nitrobacter ...and Nitrospira in rapid sand filters used for groundwater treatment. To investigate the spatial distribution of these guilds, filter material was sampled at four drinking water treatment plants (DWTPs) in parallel filters of the pre- and after-filtration stages at different locations and depths. The target guilds were quantified by qPCR targeting 16S rRNA and amoA genes. Total bacterial densities (ignoring 16S rRNA gene copy number variation) were high and ranged from 109 to 1010 per gram (1015 to 1016 per m3) of filter material. All examined guilds, except AOA, were stratified at only one of the four DWTPs. Densities varied spatially within filter (intra-filter variation) at two of the DWTPs and in parallel filters (inter-filter variation) at one of the DWTPs. Variation analysis revealed random sampling as the most efficient strategy to yield accurate mean density estimates, with collection of at least 7 samples suggested to obtain an acceptable (below half order of magnitude) density precision. Nitrospira was consistently the most dominant guild (5–10% of total community), and was generally up to 4 orders of magnitude more abundant than Nitrobacter and up to 2 orders of magnitude more abundant than canonical AOBs. These results, supplemented with further analysis of the previously reported diversity of Nitrospira in the studied DWTPs based on 16S rRNA and nxrB gene phylogeny (Gülay et al., 2016; Palomo et al., 2016), indicate that the high Nitrospira abundance is due to their comammox (complete ammonia oxidation) physiology. AOA densities were lower than AOB densities, except in the highly stratified filters, where they were of similar abundance. In conclusion, rapid sand filters are microbially dense, with varying degrees of spatial heterogeneity, which requires replicate sampling for a sufficiently precise determination of total microbial community and specific population densities. A consistently high Nitrospira to bacterial and archaeal AOB density ratio suggests that non-canonical pathways for nitrification may dominate the examined RSFs.
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•Microbial density in RSFs are high (upto109 to 1010 per gram (1015 to 1016 per m3) but vary spatially.•Acceptable mean precision of density estimates requires 7 random samples.•Nitrospira were more abundant than Nitrobacter and AOBs.•Nitrospira abundance is likely caused by their NH4+ oxidation capability (comammox).•AOB consistently exceed AOAs in RSFs, except in RSFs with strong stratification.
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