Antibiotic resistance genes (ARGs) including extracellular ARGs (eARGs) and intracellular ARGs (iARGs), are recognized as emerging environmental contaminants. Despite extensive efforts to profile ...ARGs in their “hotspots” wastewater treatment plants (WWTPs), the contribution of eARGs to antibiotic resistance spread remains unclear. Here, we applied metagenomic sequencing to investigate the distribution, mobility and microbial hosts of eARGs in activated sludge from five WWTPs. The total relative abundance eARGs ranged from 9.5 × 10−6 to 1.3 × 10−4, mainly encompassing elfamycin, dual drug, and aminoglycoside resistance genes. Multiple eARGs (e.g., EF-Tu, ropB, and rpsL mutants) were shared among the five WWTPs, and some clustered in the same genetic element (e.g., EF-Tu-rpsJ). eARGs were found to frequently co-localize with the eMGEs (e.g., sul1-3′CS-TnAs3, sul2-intI1-ISVsa3, and tetX-p63039), which may facilitate the mobilization of eARGs. Most eARGs likely originated from the genera Mycobacterium (6.7%), Nitrosomonas (5.3%), Steroidobacter (5.3%), Nitrospira (5.2%) and Pseudomonas (5.1%). No significant difference in the diversity, abundance, and mobility was observed between eARGs and iARGs. The host composition of eARGs and iARGs from municipal WWTPs are consistently dominated by Nitrosomonas, Steroidobacter, Nitrospira and Pseudomonas, while some differentially enriched genera (especially Nitrospira) in the hosts of iARGs compared with those of eARGs from the swine WWTP were identified. Our findings corroborate the mobile eARGs reservoir in WWTPs, thereby laying foundation for mitigating widespread antibiotic resistance.
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•Metagenomic approach was used to study the eARGs in activated sludge for the first time.•The total eARGs abundance ranged from 9.5 × 10−6 to 1.3 × 10−4.•Co-location of eARGs and eMGEs may facilitate eARGs mobilization.•Most eARGs originated from Mycobacterium, Nitrosomonas, Steroidobacter, Nitrospira and Pseudomonas.•eARGs and iARGs showed similar profile and mobility, but differed in microbial hosts.
Micro/nanoplastics have raised worldwide concern with extensive research on its transfer, toxicity and removal. However, the primary environmental process-adsorption of nanoplastics has not been ...uncovered since the discovery of nanosized plastics. Here, we synthesized nanoscale polystyrene (PS) particles with mean diameter of ∼40 nm to avoid unknown properties from purchased ones, and thoroughly investigated its adsorption towards two typical pharmaceuticals and personal care products (PPCPs) with distinct characteristics, which are antibiotic (ciprofloxacin) and endocrine disruptor (bisphenol-A). Moreover, UV radiation is applied to simulate aging process in natural cases, and the carbonyl index derived from FTIR spectra increased clearly from 0.183 to 0.387. The adsorption capacity at equilibrium of CIP and BPA increased from 0.15 to 4.07 to 4.92 and 8.71 mg/g after weathering, respectively. Besides, the effect of environmental factors (pH, humic acid, salinity and cations) was also studied. Furthermore, electrosorption technology is applied to remove nanoplastics in solution for the first time, with the capacity of 0.707 g nano-polystyrene/g AC and 0.322 g aged-nano-polystyrene/g AC, suggesting that adsorption under electric field is presumably a feasible tertiary treatment method targeted at nanoplastics in wastewater treatment plants (WWTPs).
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•Nanoscale PS particles with mean diameter of ∼40 nm were synthesized.•UV radiation is applied to simulate aging process in natural cases.•Adsorption behavior of PPCPs on micro/nanoplastics were compared systematically.•Effect of environmental factors (pH, humic acid, salinity and cations) was also studied.•Electrosorption technology is applied to remove nanoplastics in solution.
•Two-stage PN-anammox processes were efficient to treat reject water.•53% COD was removed in PN process including oxygen-containing volatile organics, proteins and humic acids.•The effluent COD ...consisted mainly of recalcitrant hydrocarbons.•Organics in reject water stimulated the growth of denitrifying bacteria, Ottowiaand Denitratisoma.
Reject water contains complex components of organic compounds, which have significant influences on the nitrogen removal performance when treated using biological autotrophic nitrogen removal technology. In this study, a two-stage partial nitritation (PN)-anammox (floc-granule) system was established to treat reject water (COD/NH4+-N = 0.97 ± 0.15), and the evolution of organic compounds along PN and annamox bioreactors was investigated using gas chromatography–mass spectrometry and excitation-emission matrix. Also, the variation of PN and anammox sludge properties relating to COD reduction was examined. The PN-anammox system removed approximately 80% of total inorganic nitrogen and COD with hydraulic reaction time of 16 h. The influent organics (330–600 mg COD/L) in reject water were primarily composed of volatile, protein-like and humic acid-like organic compounds. PN process contributed 53 ± 18% of the overall COD removal, primarily including oxygen-containing organics (e.g. phenol), proteins and humic acids. Anammox process contributed 22 ± 15% of the overall COD removal, but large molecule acids (e.g. lactic acid) and small molecule alcohols (e.g. glycerol) were reoccurred, contributing to the effluent COD with recalcitrant hydrocarbons (e.g. n-Octadecane). Reject water increased the extracellular proteins/polysaccharides ratio of PN and anammox sludge, promoting the adsorption and degradation of organic compounds. High-throughput sequencing results showed that denitrifying bacteria of Ottowia increased from 0.03% to 14.4% in PN reactor, and of Denitratisoma increased from 9.6% to 15.4% in anammox reactor. The occurrence of these denitrifiers might mitigate the negative impact of organics to functional organisms. This study highlights the organics fate during PN-anammox treatment system, which is important to maintain the robust nitrogen removal when treating organics-containing and high ammonium concentration wastewater.
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•Microbiome and EPS are the hottest topics in the study of NRGS properties.•NRGS displays satisfactory nitrogen removal efficiency in most cases.•NRGS properties are strongly associated with the ...performance.•Technological advancements provide in-depth insights into NRGS characterization.•Future prospects for research and application of NRGS are proposed.
Nitrogen-removal granular sludge (NRGS) is a promising technology in wastewater treatment, with advantages of efficient nitrogen removal, less footprint, lower sludge production and energy consumption, and is a way for wastewater treatment plants to achieve carbon–neutrality. Aerobic granular sludge (AGS) and anammox granular sludge (AnGS) are two typical NRGS technologies that have attracted extensive attention. Mounting evidence has shown strong associations between NRGS properties and the status of NRGS systems; however, a holistic view is still missing. The aim of this article is to provide an overview of NRGS with an emphasis on characterization. Specifically, the integrated nitrogen transformation pathways inside NRGS and the performance of NRGS treating various wastewaters are discussed. NRGS properties are categorized as physical-, chemical-, biological- and systematical ones, presenting current advances and corresponding characterization technologies. Finally, the future prospects for furthering the mechanistic understanding and engineering application of NRGS are proposed. Overall, the technological advancements in characterization have greatly contributed to understanding NRGS properties, which are potential factors for optimizing the performance and evaluating the working status of NRGS. This review will provide guidance in characterizing NRGS properties and boost the introduction of novel characterization technologies.
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A laboratory-scale anaerobic–anoxic/nitrification sequencing batch reactor (A
2N-SBR) fed with domestic wastewater was operated to examine the effect of varying ratios of influent COD/P, COD/TN and ...TN/P on the nutrient removal. With the increased COD/P, the phosphorus removals exhibited an upward trend. The influent TN/P ratios had a positive linear correlation with the phosphorus removal efficiencies, mainly because nitrates act as electron acceptors for the phosphorus uptake in the A
2N-SBR. Moreover, it was found that lower COD/TN ratio, e.g. 3.5, did not significantly weaken the phosphorus removal, though the nitrogen removal first decreased greatly. The optimal phosphorus and nitrogen removals of 94% and 91%, respectively were achieved with influent COD/P and COD/TN ratios of 19.9 and 9.9, respectively. Additionally, a real-time control strategy for A
2N-SBR can be undertaken based on some characteristic points of pH, redox potential (ORP) and dissolved oxygen (DO) profiles in order to obtain the optimum hydraulic retention time (HRT) and improve the operating reliability.
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•ANAMMOX could tolerate a high salinity of 500 mmol/L NaCl with NRR of 9.72 kg/(m3·d).•Unclassified Brocadiaceae was supposed to be more salt-tolerant than Ca. Kuenenia.•160 mmol/L ...NaCl was the threshold value for the succession of salt-tolerant AnAOB.•Up/down regulations of PS/ζ potential in EPS were positive strategies for ANAMMOX.•240 mmol/L NaCl was the threshold value for PS and ζ potential regulations in EPS.
The application of anaerobic ammonium oxidation (ANAMMOX) process to industrial wastewater treatment usually faces the challenge of high salinity. However, most of the current ANAMMOX sludge was enriched from low-salinity water, resulting in the critical gap between the inoculum and saline wastewater. In this work, an ANAMMOX reactor fed with inoculum enriched from low-salinity water successfully adapted to saline wastewater (500 mmol/L NaCl, 2.92%) after a long-term stepwise acclimatization. The nitrogen removal rate and total nitrogen removal efficiency reached 9.72 kg·m−3·d−1 and 80.90%, respectively. However, further salinity increase to 600 mmol/L caused a collapse of reactor performance. The proportion of inorganic matters improved along with the increase of salinity, which might be attributed to the compact particles observed in the microstructure of ANAMMOX sludge. A microbial community succession occurred in response to the increase of salinity. When the salinity increased to 160 mmol/L, the dominant functional bacteria shifted from Candidatus Kuenenia to unclassified Brocadiaceae, which was supposed to be salt-tolerant. The up and down regulations of polysaccharides and ζ potential in EPS were positive strategies for salinity adaptation of ANAMMOX bacteria. However, the barrier of seawater salinity (3–5%) could not be overcome. The present work would provide a holistic view for the enrichment of salt-tolerant ANAMMOX bacteria and help in the selection of seeding sludge for the treatment of saline wastewater by ANAMMOX process.
Although anammox bacteria are commonly exposed to long-term starvation during transportation and preservation process, physiological changes in these organisms during long-term starvation are not ...well understood, nor are the molecular bases of their starvation survival strategies. To reveal survival mechanisms during long-term anaerobic and anoxic starvation (60 days at 20 ± 1 °C), metaproteomic technology was utilized to identify differentially expressed proteins in Candidatus Kuenenia stuttgartiensis. Our results showed that Candidatus Kuenenia stuttgartiensis exhibits a capacity to withstand long-term starvation stress. Although activity decay rates of 0.0129 d−1 and 0.0049 d−1 were observed for anammox sludge in anoxic and anaerobic starvation, the relative abundance of Candidatus Kuenenia stuttgartiensis, the shape of anammox granules, and the fraction of viable cells remained constant under both anaerobic and anoxic starvation conditions. Metaproteomics results illustrated that Candidatus Kuenenia stuttgartiensis maintained stable levels of most intracellular proteins, especially enzymes involved in principal metabolic pathways after 60-d of anaerobic or anoxic starvation, thereby allowing cells to regain metabolic activities once substrates became available. Induction of starvation proteins could be a survival strategy employed by Candidatus Kuenenia stuttgartiensis to resist long-term starvation stresses. During anaerobic starvation, 34 proteins were upregulated, five of which were associated with carbohydrate catabolism and oxidation of organic compounds, thereby increasing potential for utilization of endogenous carbon sources to produce energy. During anoxic starvation, only two proteins were upregulated, which may be attributed to insufficient energy for the synthesis of starvation-induced proteins.
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•Anammox bacteria has a good capacity to resist long-term starvation at 20 ± 1 °C.•Most intracellular proteins remain stable during the 60 days' starvation.•Lower activity decay rate occurred under anaerobic starvation than that of anoxic anaerobic.•The abundance of anammox bacteria remains stable during 60-d starvation.
As obligate anaerobes, anammox bacteria are sensitive to oxygen, which might hinder the maximization of anammox activity. However, there are very few effective strategies to rapidly recover anammox ...activity after its deterioration under exposure of oxygen. In this study, the activity recovery of anammox bacteria encountering dissolved oxygen (DO) exposure (0.2 and 2.0 mg L−1) were compared by three strategies in short-term experiments, nZVI, Fe(II) dosing, and N2 purging. nZVI is more effective in recovering anammox activity with a high DO exposure (2 mg L−1), compared to a low DO exposure (0.2 mg L−1). After inhibiting by 2.0 mg L−1 DO, anammox activity recovery (normalized to the control) was ranked in the order of nZVI (5 mg L−1) addition (63 ± 8.2%) > Fe(II) (5 mg L−1) addition (41 ± 8.0%) >N2 purging (39 ± 4.0%). In contrast to Fe(II) ion additions, the shell structure of nZVI combined with the buffering effect of biomass-extracellular polysaccharide (EPS) prevented the sharp pH variation and excessive dissolved Fe(II)/Fe(III) in solution. Under such circumstances, nZVI addition (5 and 25 mg L−1) increased the intracellular reactive oxygen species (ROS) to a moderate level (<200%), which might be responsible for the better activity recovery of anammox than that of Fe(II) addition and N2 purging. Specifically, 5 mg L−1 nZVI dosage moderately enhanced the intracellular O2− production (∼150% of the control) after scavenging 2.0 mg L−1 DO, and the anammox activity recovered better than that of both 5 and 25 mg L−1 Fe(II) ions additions. However, high dosage nZVI (75 mg L−1) inhibited anammox activity in spite of low or high DO exposure. Our findings elucidate that appropriate amount of nZVI (short-term dosing) can rapidly recover anammox activity when anammox bacteria encountering oxygen exposure accidentally and could be useful in facilitating the robust operation of anammox-based processes.
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•Ranking of anammox recovery was nZVI > Fe(II) >N2 after 2 mg L−1 DO shocks.•Low dose nZVI promotes anammox activity by moderate O2− increase and DO depletion.•High dose of nZVI/Fe(II) inhibits anammox activity by severe O2− increase.•Free Fe(II)/Fe(III) ions regulate intracellular Fenton reaction and O2− level.•Mechanism of intracellular O2− production after adding nZVI/Fe(II) was proposed.
Antibiotic resistance genes (ARGs) are an emerging concern in wastewater treatment plants (WWTPs), as dissemination of ARGs can pose a serious risk to human health. Few studies, however, have ...quantified ARGs in membrane bioreactors (MBRs), although MBRs have been widely used for both municipal and industrial wastewater treatment. To reveal the capacity of MBRs for removal of ARGs and the response of membrane fouling after antibiotic exposure, five typical ARG subtypes (sulI, sulII, tetC, tetX and ereA) and int1 were quantified affiliated by systematic membrane foulants analysis in a laboratory-scale anoxic/aerobic membrane bioreactor (A/O-MBR). Sulfamethoxazole and tetracycline hydrochloride additions increased ARG abundances by 0.5–1.4 orders of magnitude in the activated sludge, while the ARG removal performance of the membrane module remained stable (or even increased with ARG absolute abundance in several cases), with the abundance of removed ARGs ranging from 0.6 to 5.6 orders of magnitude. Specifically, the distribution of ARGs in membrane foulants accounted for 13%–25% of the total absolute abundance of all tested MBR samples. Indeed, substantial fouling occurred after the antibiotic additions, with the mean concentrations of soluble microbial product (SMP) and extracellular polymeric substance (EPS) increasing by 340% and 220%, respectively, in a membrane fouling cycle; moreover, the contents of EPS and SMP in the membrane foulants were significantly correlated with the ARG absolute abundance of membrane foulants (p < 0.05), among which more significant correlations occurred between both the protein and polysaccharide of foulants than that with humic acid. The dense membrane fouling layer and the membrane itself constituted dual barriers that effectively avoided the leakage of ARGs from the membrane module. Our findings provide fundamental insights into the proliferation and removal of ARGs in MBR systems, and highlight the contribution of membrane fouling to ARG removals in terms of the potential of MBR as an effective strategy to reduce ARG levels in WWTP effluent.
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•Five ARG subtypes and int1 were quantified by qPCR along the MBR process.•Antibiotic additions increased both membrane foulant contents and ARG abundance.•ARG removal capacity by the MBR was not affected by increased ARG abundance.•In membrane foulants, SMP and EPS contents correlated with the ARG abundance.•The dense fouling layer of the membrane module enhanced ARGs removal.
•Inactivation and adaptation of AOB and NOB to FNA was investigated.•FNA caused a stronger inactivation effect on NOB than on AOB.•This inactivation increased as the FNA increased and exposure time ...lengthened.•AOB did not adapt to the FNA treatment. In contrast, NOB did adapt to FNA.•NOB adaptation may be due to its shift from Nitrospira to Candidatus Nitrotoga.
Inactivation and adaptation of ammonia-oxidizing bacteria (AOB) and nitrite-oxidizing bacteria (NOB) to free nitrous acid (FNA) was investigated. Batch test results showed that AOB and NOB were inactivated when treated with FNA. After an 85-day operating period, AOB in a continuous pre-denitrification reactor did not adapt to the FNA that was applied to treat some of the return activated sludge. In contrast, NOB did adapt to FNA. NOB activity in the seed sludge was only 11% of the original activity after FNA batch treatment, at 0.75mg HNO2-N/L. NOB activity in the pre-denitrification reactor was not affected after being exposed to this FNA level. Nitrosomonas was the dominant AOB before and after long-term FNA treatment. However, dominant NOB changed from Nitrospira to Candidatus Nitrotoga, a novel NOB genus, after long-term FNA treatment. This adaptation of NOB to FNA may be due to the shift in NOB population makeup.
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