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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]

The potential application of anaerobic ammonium oxidation (anammox) to treat antibiotic-containing wastewaters has attracted public attentions. The responses of anammox to a typical antibiotic (spiramycin, SPM) with different exposure strategies (elevating-concentration strategy in R 1 and repeated-exposure strategy in R 2) were evaluated on the aspects of general performance, microbial community and genes. Results showed that anammox bacteria could adapt to low concentrations (≤1 mg L−1) of SPM, while high-concentration (≥3 mg L−1) SPM showed inhibitory influences. The nitrogen removal efficiency (NRE) quickly decreased from 90.21% to 76.29% when R 1 was exposed to 5 mg L−1 SPM, and then returned to a higher level within a short period. On the contrary, R 2 could not recover with the inhibition of 5 mg L−1 SPM, and the abundance of Planctomycetes declined from 18.96% to 15.41% on Day 105. Combined with the changes in key genes and functional bacteria, R 1 had a relatively stable performance and higher resistance to SPM, indicating the elevating-concentration strategy might be more effective to gain the tolerance of anammox process to high-concentration antibiotics. The present study provides a guide for the stable operation of anammox process treating antibiotic-containing wastewaters. Image 1 • High-concentration (≥3 mg L−1) spiramycin (SPM) could inhibit anammox activity. • SPM changed the microbial community structure in the anammox systems. • Abundances of antibiotic resistance genes changed with the SPM concentrations. • Elevating concentration strategy was more efficient to gain the SPM resistance. • Anammox process could be applied to treat the SPM-containing wastewaters. [ABSTRACT FROM AUTHOR]

The extensive application of antibiotics, and the occurrence and spread of antibiotic resistance genes (ARGs) shade health risks to human and animal. The long-term effects of sulfamethoxazole (SMX) and tetracycline (TC) on denitrification process were evaluated in this study, with the focus on nitrogen removal performance, microbial community and ARGs. Results showed that low-concentration SMX and TC (<0.2 mg L−1) initially caused a deterioration in nitrogen removal performance, while higher concentrations (0.4–20 mg L−1) of both antibiotics had no further inhibitory influences. The abundances of ARGs in both systems generally increased during the whole period, and most of them had significant correlations with int I1, especially efflux-pump genes. Castellaniella , which was the dominant genus under antibiotic pressure, might be potential resistant bacteria. These findings provide an insight into the toxic effects of different antibiotics on denitrification process, and guides future efforts to control antibiotics pollution in ecosystems. • Denitrification performance deteriorated at low concentrations of antibiotics. • The antibiotic inhibition on denitrification was reversible. • Castellaniella was mainly devoted to denitrification under antibiotics pressures. • Antibiotics addition promoted the increase in antibiotic resistance genes (ARGs). • Most ARGs were significantly correlated to int I1, especially efflux-pump ARGs. [ABSTRACT FROM AUTHOR]

The feasibility of using anaerobic ammonium oxidation (anammox) process to treat wastewaters containing antibiotics and heavy metals was evaluated in this study. The nitrogen removal performance and characteristic parameters were monitored during the whole experimental period of 258 d. The single and joint effects of zinc and tetracycline on the microbial community were studied in upflow anaerobic sludge blanket (UASB) reactors. The anammox performance remained at levels comparable with the initial state at the lower inhibitor concentrations (zinc, 0–2.26 mg L−1; tetracycline, 0–0.5 mg L−1). When the concentrations of zinc and tetracycline increased to 3.39 mg L−1 in R 1 and 1.0 mg L−1 in R 2 , an obvious deterioration in performance was observed. Dual inhibitors with a total concentration of ≥3 mg L−1 caused dramatic decreases in the nitrogen removal efficiency of R 3. The quantification results showed that the abundances of eight antibiotic resistance genes (ARGs), czc A and int I1 in the experimental reactors generally increased under stress from metals or/and antibiotics, with final values higher than in the control, while the functional gene abundances were lower. Moreover, most genes exhibited significant correlations. Microbial community analysis indicated that Planctomycetes (represented by Candidatus Kuenenia) was inhibited by both zinc and tetracycline, but still held the dominant position. Furthermore, Caldilinea (belonging to Chloroflexi) maintained a higher abundance during the inhibitory period, implying its potential resistance to both inhibitors. These findings suggested that anammox could be inhibited by metals and antibiotics, but it has the potential to remove nitrogen from wastewaters containing both of them within the concentration threshold. • The inhibition thresholds of zinc and tetracycline on anammox were 3.39 and 1 mg L−1, respectively. • The joint inhibition of zinc and tetracycline on anammox was stronger than the single inhibition. • Caldilinea was the potential resistance bacteria. • Anammox has the potential to treat wastewaters containing small amounts of metals and antibiotics. [ABSTRACT FROM AUTHOR]

The anaerobic ammonium oxidation (anammox) process has the advantages of a high nitrogen removal rate, low operational cost, and small footprint and has been successfully implemented to treat high-content ammonium wastewater. However, very little is known about the toxicity of the heavy metal element Ni(II) to the anammox process. In this study, the short- and long-term effects of Ni(II) on the anammox process in an upflow anaerobic sludge blanket (UASB) reactor were revealed. The results of the short-term batch test showed that the half maximal inhibitory concentration (IC 50) of Ni(II) on anammox biomass was 14.6 mg L−1. A continuous-flow experiment was performed for 150 days of operation, and the results illustrated that after domestication, the achieved nitrogen removal efficiency was up to 93±0.03% at 10 mg L−1 Ni(II). The settling velocity, specific anammox activity and EPS content decreased as the Ni(II) concentration increased. Nevertheless, the content of heme c increased as the Ni(II) increased. These results indicate that short-term exposure to Ni(II) has an adverse impact on anammox process, but the anammox system could tolerate 10 mg L−1 Ni(II) stress after acclimation during continuous-flow operation for 150 days. High-throughput sequencing results indicated that the presence of Ni(II) had an impact on the microbial community composition in the anammox reactor, especially Candidatus Kuenenia. At Ni(II) concentrations of 0-10 mg L−1, the relative abundance of Candidatus Kuenenia decreased from 36.23% to 28.46%. • The IC50 of Ni(II) on anammox biomass was 14.64 mg L−1 in short-term assay. • The effect of Ni(II) on substrate removal kinetic behavior of anammox was studied. • The long-term effects of Ni(II) in anammox UASB reactor were evaluated. [ABSTRACT FROM AUTHOR]

The difficulties of enrichment and preservation of anaerobic ammonium oxidation bacteria (AnAOB) greatly limit their application in practice. Herein, traditional and emerging preservative agents (e.g., EPS + N 2 H 4, betaine, glycerol and trehalose) were evaluated for their preservation of AnAOB-dominant sludge at different temperatures (e.g., 4 °C and room temperature). In addition, the effects of substrates on preservation were also considered. The results showed that adding betaine or glycerol at 4 °C was the optimal strategy for preserving anammox granular sludge. The relative anammox activities (rAA) increased by 145.26% and 158.30% at the recovery phase, respectively. Moreover, the absolute abundances of functional gene hzs A increased by 339% and 46%, respectively. Although the granular properties and microbial community structures changed during the preservation, the general performance of anammox granules could effectively restored. Collectively, this study provides the optimal strategies for anammox sludge preservation at low temperatures. [Display omitted] • Preservation with betaine or glycerol at 4 °C was optimal for the anammox sludge. • The addition of both preservation agents led to a better recovery performance. • The absolute abundances of hzs A and nir S increased after the recovery phase. • The relative abundance of Denitratisoma also showed an increasing tendency. [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]

• Cd(II) at 2 mg L−1 enhanced anammox performance. • Cd(II) at 5 mg L−1 inhibited anammox performance. • The relative abundance of Candidatus kuenenia increased at ≤2 mg L−1 Cd(II). • The SAA, EPS and microbial community could be recovered after withdrawing Cd(II). • Anammox biomass displayed a certain adaption to Cd(II) suppression. Cadmium (Cd) can cause the deterioration of biological systems through inhibiting the enzymes activity and disturbing the microbial metabolism. Although the influence of Cd on conventional wastewater treatment process has been studied, the response of anammox to Cd exposure still remains unclear. This study firstly investigated the adaption and restoration of anammox biomass to Cd(II) stress. Results showed that long-term exposure of anammox bacteria to 2 mg L−1 Cd(II) was beneficial for the reactor performance, while 5 mg L−1 Cd(II) would cause the decline of SAA, extracellular polymeric substance content and relative abundance of Candidatus kuenenia by 40%, 25% and 31%, respectively. Furthermore, these indexes could approximately recover to the initial status after withdrawing Cd(II) from the influent. Overall, the anammox biomass exhibited a certain adaption and restoration ability to the suppression of Cd(II). This study may provide key valuable information for the biological treatment of wastewater containing Cd(II). [ABSTRACT FROM AUTHOR]