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[Display omitted] • The anammox process could tolerate to the stress of 10 mg/L ciprofloxacin (CIP). • The performance of anammox system deteriorated under 20 mg/L CIP. • The strategy of starvation and shock was effective to mitigate the CIP inhibition. • Upregulating ARG expression and key metabolic pathways promoted process recovery. • Isolated ARB showed multidrug resistance, particularly Pseudomonas. Ciprofloxacin (CIP) poses a high risk of resistance development in water environments. Therefore, comprehensive effects and recovery strategies of CIP in anaerobic ammonia oxidation (anammox) process were systematically elucidated from consortia and pure strains perspectives. The anammox consortia was not significantly affected by the stress of 10 mg L-1 CIP, while the higher concentration (20 mg L-1) of CIP caused a dramatic reduction in the nitrogen removal performance of anammox system. Simultaneously, the abundances of dominant functional bacteria and corresponding genes also significantly decreased. Such inhibition could not be mitigated by the recovery strategy of adding hydrazine and hydroxylamine. Reducing nitrogen load rate from 5.1 to 1.4 kg N m-3 d-1 promoted the restoration of three reactors. In addition, the robustness and recovery of anammox systems was evaluated using starvation and shock strategies. Simultaneously, antibiotic resistance genes and key metabolic pathways of anammox consortia were upregulated, such as carbohydrate and energy metabolisms. In addition, 11 pure stains were isolated from the anammox system and identified through phylogenetic analysis, 40 % of which showed multidrug resistance, especially Pseudomonas. These findings provide deep insights into the responding mechanism of anammox consortia to CIP stress and promote the application of anammox process for treating wastewater containing antibiotics. [ABSTRACT FROM AUTHOR]

As a key component of extracellular polymeric substances (EPS), extracellular deoxyribonucleic acid (eDNA) acts as a bridge in maintaining the structural stability of granular sludge. However, its ability of carrying antibiotic resistance genes (ARGs) promotes the gene horizontal transfer, raising a high risk for human health. In this study, a series of batch tests were performed to elucidate the response of anammox granular sludge (AnGS) with different sizes (S-AnGS with diameters lower than 0.9 mm and L-AnGS with diameters of 0.9–2 mm) to the removal of eDNA and corresponding mechanism. The results showed that the highest bioactivity of S-AnGS and L-AnGS was achieved by adding DNase I, and the absolute abundance of hzs A in the systems also increased. The dominant microorganism in each sludge was Candidatus Kuenenia, which maintained a higher relative abundance of 24% in S-AnGS. Settling experiments demonstrated that the permeability of AnGS was positively correlated with the addition of DNase I. The permeability index of granular sludge, Г , rose by 58.54% in S-AnGS and 11.79% in L-AnGS. The absence of eDNA is conducive to the increase in the permeability and porosity of AnGS. Similarity in the functional genes and microbial communities of intracellular and extracellular DNA implied the occurrence of gene transmembrane transfer. The findings enrich our knowledge of eDNA in anammox granules and provide a guidance for the specific control of gene transfer through reducing eDNA. [Display omitted] • Responses of different-sized anammox granular sludge (AnGS) to DNase I varied. • Removal of extracellular DNA (eDNA) by DNase I is beneficial for AnGS. • DNase I increased the permeability, porosity and mass transfer of AnGS. • L-AnGS exhibited a relatively stable performance by removing eDNA. • Gene transfer occurred between eDNA and intracellular DNA (iDNA). [ABSTRACT FROM AUTHOR]

• Microbial and genetic responses of anammox process to ETC and SMZ were different. • The combined effects of ETC and SMZ was more significant than that of the single. • Increase in ARGs and EPS probably relieved the selection pressures of antibiotics. • Proteins in EPS provided binding sites for two antibiotics via hydrogen bonds. The anaerobic ammonium oxidation (anammox) process is regarded as a promising approach to treat antibiotic-containing wastewater. Therefore, it is urgent to elucidate the effects of various antibiotics on the anammox process. Moreover, the mechanism of extracellular polymeric substance (EPS) as protective barriers to relieve antibiotic stress remain unclear. Therefore, the single and combined effects of erythromycin (ETC) and sulfamethoxazole (SMZ), and interactions between EPS and antibiotics were investigated in this study. Based on a 228-day continuous flow experiment, high concentrations of ETC and SMZ had significant inhibitory effects on the nitrogen removal performance of the anammox process, with the abundances of corresponding antibiotic resistance genes (ARGs) increasing. In addition, the combined inhibitory effect of the two antibiotics on the anammox process was more significant and longer-lasting than that of the single. However, the anammox process was able to quickly recover from deterioration. The tolerance of anammox granules to the stress of low-concentration antibiotics was probably attributed to the increase in ARGs and secretion of EPS. Molecular docking simulation results showed that proteins in EPS could directly bind with SMZ and ETC at the sites of GLU-307, HYS-191, ASP-318 and THR-32, respectively. These findings improved our understanding of various antibiotic effects on the anammox process and the interaction mechanism between antibiotics and proteins in EPS. [Display omitted] [ABSTRACT FROM AUTHOR]

[Display omitted] • The responses of two different anammox granules to CuNPs were investigated. • Antibiotic-exposed anammox granules were more sensitive to the CuNPs stress. • CuNPs induced the co-selection of multiple resistance genes in the anammox system. • The mechanism through which CuNPs affected the anammox granules was speculated. Two types of anaerobic ammonium oxidation (anammox) seed sludge were selected to evaluate their responses to copper nanoparticles (CuNPs) exposure. Antibiotic-exposed anammox granules (R 1) were more likely to be inhibited by 5.0 mg L-1 CuNPs than the normal anammox granules (C 1). The nitrogen removal efficiency (NRE) of C 1 decreased by 9.00% after two weeks of exposure to CuNPs, whereas that of R 1 decreased by 20.32%. Simultaneously, the abundance of Candidatus. Kuenenia decreased by 27.65% and 36.02% in C 1 and R 1 under CuNPs stress conditions, respectively. Generally, R 1 was more susceptible to CuNPs than C 1. The correlation analysis indicated that the horizontal transfer of antibiotic resistance genes and cop A triggered by int I1 facilitated the generation of multiresistance in the anammox process. Moreover, the potential multiresistance mechanism of anammox bacteria was hypothesized based on previous results. The results will generate new ideas for the treatment of complex wastewater using the anammox process. [ABSTRACT FROM AUTHOR]

The wide existence of saline wastewater has attracted public attention due to its environmental destructiveness. The potential of anammox to treat saline wastewater was systematically evaluated in this study. Three bioreactors with different salinity increasing strategies (R 1 : inhibition kinetic; R 2 : gradient increasing; R 3 : pulsed increasing) were operated to identify the optimal acclimation mode. The results showed that the inhibition of anammox activity by salinity was mainly caused by the loss of enzyme activity. Under the condition of 25.0 g NaCl L−1, the highest nitrogen removal rate of R 3 (2.36 ± 0.14 kg N m−3 d−1) indicated that the pulsed strategy might be optimal. Changes in microbial community might be the primary reason lead to different acclimatization results. The relative abundance of anammox bacteria increased by 37.19% in R 1 and by 46.81% in R 3 , but remained stable in R 2 with increasing salinity. Dynamic varations in bacterial interactions, proteins, and functional genes revealed the potential resistance mechanisms of bacteria to salinity. The present work provides a novel approach and guidance for the treatment of nitrogen-rich saline wastewater by the anammox process. Image 1 • Three acclimation strategies for salt-tolerant anammox process were proposed for the first time. • The inhibition of FAB by salinity was mainly caused by the loss of enzyme activity. • High abundance of anammox bacteria led to the excellent acclimatization results. • Corresponding strategies can be selected based on the wastewater characteristics. [ABSTRACT FROM AUTHOR]

• Sulfide (20 mg L−1) could reduce the specific anammox activity by 61.7%. • Protein-like substances were quenched due to sulfide stress. • Sulfide addition led Candidatus Kuenenia decrease while Thiobacillus increase. • Functional gene abundances significantly decreased with 20 mg L−1 sulfide. Sulfide has attracted increasing attention due to its odor nuisance, toxicity and corrosion. Although variations in the nitrogen removal performance of anammox under sulfide stress have been reported previously, understanding the microorganisms at the molecular level is of greater significance. This study first deciphered the microbial community and functional gene response of anammox sludge to sulfide stress. Results showed that 20 mg L−1 sulfide could reduce specific anammox activity by 61.7%. The protein-like substances within extracellular polymeric substances were quenched at the end of the experiment. Moreover, the relative abundance of Candidatus Kuenenia significantly decreased from 28.7% to 6.4% while Thiobacillus increased from 0 to 7.2% due to sulfide stress. Furthermore, the abundances of functional genes (hzs A, hdh , nir K and nir S) significantly decreased when the sulfide concentration reached 20 mg L−1. These findings provide a further theoretical basis for the anammox process for nitrogen removal from wastewater containing sulfide. [ABSTRACT FROM AUTHOR]

To achieve the efficient treatment of high-strength ammonium wastewaters, a two-stage anammox process was proposed in this study. The nitrogen loading rates (NLR) of two anammox reactors were increased to 60.19 g N L−1 d−1 (R 1) and 24.32 g N L−1 d−1 (R 2), through reducing hydraulic retention time (HRT) and increasing ammonium concentration. Afterwards, the reactors were operated in series at variable temperatures (6.15–34.13 °C) for 240 days to treat the synthetic high-ammonium containing wastewater, with the effluent of R 1 pumping into R 2 as influent. Finally, the advanced treatment of the high-strength ammonium wastewater (490 mg NH 4 +-N L−1 and 980 mg TN L−1) was successfully achieved, and nitrogen removal efficiency (NRE) maintained at 83.25 ± 9.48%. During the whole operational period (400 days), the richness and diversity of microbial community in two reactors generally increased, and Candidatus Kuenenia was identified as the dominant anammox bacterium. In serial-operation phase, the dominant phylum changed from Planctomycetes to Proteobacteria, and the average relative abundance of Proteobacteria 39.61% in R 1 and 48.32% in R 2. Variations in bacterial abundances and distributions were closely related to the substrate concentration and temperature. Correspondingly, the expression levels of most functional genes were reduced by low temperature, and were slightly different in settling, middle and floating sludge. Nitrogen transformation pathway in each phase was also determined based on the gene expression levels, and main pathways in both reactors included anammox and first step of denitrification (NO 3 −→NO 2 −). All findings of this study provide new insights into the potential application of the two-stage anammox process to treat high-strength ammonium wastewater under variable temperature conditions. Image 1 • A novel anammox process was proposed to treat high-strength ammonium wastewater. • The two-stage anammox process could maintain efficient and stable for a long term. • Microbial community composition and distribution changed. • Expression levels of functional genes were slightly affected by low temperature. • Main nitrogen transformation pathways included anammox and NO 3 −.→NO 2 −. [ABSTRACT FROM AUTHOR]