Long-term effects of heavy metals and antibiotics on granule-based anammox process: granule property and performance evolution

Nano-Fe3O4/FeCO3 modified red soil-based biofilter for simultaneous removal of nitrate, phosphate and heavy metals: Optimization, microbial community and possible mechanism

The pollution of nitrogen, phosphorus and heavy metals in surface water is becoming more and more serious, affecting the safety of water quality. In this study, three biofilters were constructed using iron-modified red soil-based filler carriers (RSC, nano-Fe3O4@RSC, and FeCO3@RSC) combined with strain Zoogloea sp. ZP7 to simultaneously remove nitrate (NO3--N), phosphate (PO43--P), copper (Cu2+), and zinc (Zn2+). The long-term operation results showed that the three groups of biofilters could remove 85.0 %, 90.0 %, and 89.8 % of NO3--N, respectively. Furthermore, the addition of iron compounds enhanced the removal of PO43--P and the resistance to the stress of Cu2+ and Zn2+ in the biofilter. The analysis illustrated that iron modification improved the redox activity and zeta potential of RSC surface. The secondary structure analysis of the protein showed that the microbial secreted proteins were more compact on the surface of the iron-modified RSC, which facilitated the formation of biofilm on the carrier surface. In addition, the iron-modified RSC-based biofilter also showed excellent NO3--N and PO43--P removal efficiency in the treatment of actual surface water. The microbial community analysis results showed that Zoogloea became the dominant species in the biofilter. On the other hand, the presence of iron-reducing bacteria and the expression iron cycle-related genes may contribute to denitrification under low nutrient conditions.

The presence of copper ions alters tetracycline removal pathway in aerobic granular sludge: Performance and mechanism

This study investigated the removal characteristics of tetracycline (TC) in the presence of copper ions (Cu2+) in aerobic granular sludge by analyzing the TC removal pathway, composition and functional group changes of extracellular polymeric substances (EPS), and microbial community structure. The TC removal pathway changed from cell biosorption to EPS biosorption, and the microbial degradation rate of TC was reduced by 21.37% in the presence of Cu2+. Cu2+ and TC induced enrichment of denitrifying bacteria and EPS-producing bacteria by regulating the expression of signaling molecules and amino acid synthesis genes to increase the content of EPS and -NH2 groups in EPS. Although Cu2+ reduced the content of acidic hydroxyl functional groups (AHFG) in EPS, an increase in TC concentration stimulated the secretion of more AHFG and -NH2 groups in EPS. The long-term presence of TC presence of the relative abundances of Thauera, Flavobacterium and Rhodobacter and improved the removal efficiency.

Accelerating the granulation of anammox sludge in wastewater treatment with the drive of "micro-nuclei": A review

Anammox granule sludge (AnGS) has great potential in the field of wastewater nitrogen removal, but its development and promotion have been limited by the slow granulation speed and fragile operating stability. Based on the reviews about the AnGS formation mechanism in this paper, "micro-nuclei" was found to play an important role in the granulation of AnGS, and adding "micro-nuclei" directly into the reactor may be an efficient way to accelerate the formation of AnGS. Then, accelerating AnGS granulation with inert particles, multivalent positive ions, and broken granule sludge as "micro-nuclei" was summarized and discussed. Among inert particles, iron-based particles may be a more advantageous candidate for "micro-nuclei" due to their ability to provide attachment sites and release ferric/ferrous ions. The precipitations of multivalent positive ions are also a potential option for "micro-nuclei" that can be generated in-situ, but a suitable dosing strategy is necessary. About broken granular sludge, the broken active AnGS may have advantages in terms of anaerobic ammonium oxidation bacteria-affinity and granulation speed, while using inactive granular sludge as "micro-nuclei" can avoid interfering bacterial invasion and has a higher cost performance than broken active AnGS. In addition, possible research directions for accelerating the formation of AnGS by dosing "micro-nuclei" were highlighted. This paper is intended to provide a possible pathway for the rapid start-up of AnGS systems, and references for the optimization and promotion of the AnGS process.

Efficient nitrogen removal from leachate by coupling Anammox and sulfur-siderite-driven denitrification

High concentrations of nitrate can be generated during anaerobic ammonium oxidation (Anammox) wastewater treatment processes. Addition of sulfur to Anammox reactors stimulates the growth of sulfur-driven denitrifying (SADN) bacteria that can reduce nitrate to nitrogen gas. However, protons released during the SADN process lower the pH of the system and inhibit Anammox activity. The system will keep stable when pH is in the range of 7.5-8.5. This study showed that addition of siderite stabilized the reactor system and significantly improved the nitrogen removal process. In fact, even when concentrations of total nitrogen were 477.15 ± 16.84 mg/L, the sulfur/siderite reactor maintained nitrogen removal efficiencies >90%, while efficiencies in the sulfur reactor were < 80%. Anammox accounted for 31% of the bacterial sequences in the sulfur/siderite reactor compared to only 14% in the sulfur reactor with the majority of sequences clustering with Ca. Brocadia. An abundance of c-type cytochromes in anammox aggregates in the sulfur-siderite reactor also indicated that anammox activity was higher in this system.

A review of heavy metals inhibitory effects in the process of anaerobic ammonium oxidation

Anaerobic ammonium oxidation (anammox) is a promising biological technology for treating ammonium-rich wastewaters. However, due to the high sensitivity of anammox bacteria, many external factors have inhibitory effects on this process. As one of the commonly found toxic substances in wastewater, heavy metals (HMs) are possible to cause inhibition on anammox sludge, which then results in a declined treatment performance. Getting insights into the response mechanism of anammox sludge to HMs is meaningful for its application in treating this kind of wastewater. This review summarized the effect of different HMs on treatment performance of anammox bioreactor. In addition, the mechanism of toxication raised by HMs was discussed. Also, the potential mitigation strategies were summarized and the future prospects were outlooked. This review might provide useful information for both scientific research on and engineering application of anammox process for treating HMs containing wastewater.

A review on characterizing the metabolite property of anammox sludge by spectroscopy

As one of the most promising autotrophic biological nitrogen removal technology, anaerobic ammonia oxidation (anammox) has gained intense attention for the past decades and several full-scale facilities have been implemented worldwide. However, anammox bacteria are easily affected by disturbed external environmental factors, which commonly leads to the fluctuations in reactor performance. The response of anammox sludge to external stress results in changes in components and structural characteristics of intracellular and extracellular polymer substances. Real-time and convenient spectral analysis of anammox sludge metabolites can give early warning of performance deterioration under external stresses, which is of great significance to the stable operation of bioreactor. This review summarized the research progress on characterizing the intracellular and extracellular metabolites of anammox sludge through spectroscopic techniques. The correlation between anammox sludge activity and its key metabolites was analyzed. Also, the limitations and future prospects of applying spectral analytical techniques for anammox bioreactor monitoring were discussed and outlooked. This review may provide valuable information for both scientific study and engineering application of anammox based nitrogen removal technology.

Inhibition of anammox activity by municipal and industrial wastewater pollutants: A review

The use of the anammox process for nitrogen removal has gained popularity across the world due to its low energy consumption and waste generation. Anammox reactors have been used to treat ammonium-rich effluents such as chemical, pharmaceutical, semiconductor, livestock, and coke oven wastewater. Recently, full-scale installations have been implemented for municipal wastewater treatment. The efficiency of biological processes is susceptible to inhibitory effects of pollutants present in wastewater. Considering the increasing number of emerging contaminants detected in wastewater, the impacts of the different types of pollutants on anammox bacteria must be understood. This review presents a compilation of the studies assessing the inhibitory effects of different wastewater pollutants towards anammox activity. The pollutants were classified as antibiotics, aromatics, azoles, surfactants, microplastics, organic solvents, humic substances, biodegradable organic matter, or metals and metallic nanoparticles. The interactions between the pollutants and anammox bacteria have been described, as well as the interactions between different pollutants leading to synergistic effects. We also reviewed the effects of pollutants on distinct species of anammox bacteria, and the main toxicity mechanisms leading to irreversible loss of anammox activity have been identified. Finally, we provided an analysis of strategies to overcome the inhibitory effects of wastewater pollutants on the nitrogen removal performance. We believe this review will contribute with essential information to assist the operation and design of anammox reactors treating different types of wastewaters.

Resistance genes and extracellular proteins relieve antibiotic stress on the anammox process

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.

Interrelationships between tetracyclines and nitrogen cycling processes mediated by microorganisms: A review

Due to their broad-spectrum antibacterial activity and low cost, tetracyclines (TCs) are a class of antibiotics widely used for human and veterinary medical purposes and as a growth-promoting agent for aquaculture. Interrelationships between TCs and nitrogen cycling have attracted scientific attention due to the complicated processes mediated by microorganisms. TCs negatively impact the nitrogen cycling; however, simultaneous degradation of TCs during nitrogen cycling mediated by microorganisms can be achieved. This review encapsulates the background and distribution of TCs in the environment. Additionally, the main nitrogen cycling process mediated by microorganisms were retrospectively examined. Furthermore, effects of TCs on the nitrogen cycling processes, namely nitrification, denitrification, and anammox, have been summarized. Finally, the pathway and microbial mechanism of degradation of TCs accompanied by nitrogen cycling processes were reviewed, along with the scope for prospective studies.

A critical review on the effects of antibiotics on anammox process in wastewater

Anaerobic ammonium oxidation (anammox) has recently become of significant interest due to its capability for cost-effective nitrogen elimination from wastewater. However, anaerobic ammonia-oxidizing bacteria (AnAOB) are sensitive to environmental changes and toxic substances. In particular, the presence of antibiotics in wastewater, which is considered unfavorable to the anammox process, has become a growing concern. Therefore, it is necessary to evaluate the effects of these inhibitors to acquire information on the applicability of the anammox process. Hence, this review summarizes our knowledge of the effects of commonly detected antibiotics in water matrices, including fluoroquinolone, macrolide, β-lactam, chloramphenicol, tetracycline, sulfonamide, glycopeptide, and aminoglycoside, on the anammox process. According to the literature, the presence of antibiotics in wastewater could partially or completely inhibit anammox reactions, in which antibiotics targeting protein synthesis or DNA replication (excluding aminoglycoside) were the most effective against the AnAOB strains.

Biogas-driven complete nitrogen removal from wastewater generated in side-stream partial nitritation

Anaerobic digestion is an attractive process in wastewater treatment plants (WWTPs) to achieve simultaneous sludge reduction and energy recovery. While converting the majority of organic carbon to biogas (mainly consisting 60%CH₄ + 40%CO₂), the high-strength anaerobic digestion liquor consists of a high level of nitrogen concentration. The feasibility of utilizing biogas produced in-situ to achieve satisfactory nitrogen removal performance from partially nitrified anaerobic digestion liquor was examined in this study. To this end, a membrane biofilm reactor (MBfR) was used to couple nitrite- or nitrate-dependent anaerobic methane oxidation (n-DAMO) and anammox microorganisms, which was supplied with synthetic biogas and partially nitrified anaerobic digestion liquor (470 mg NH₄⁺-N/L + 560 mg NO₂^--N/L). The MBfR achieved not only nearly complete nitrogen removal (~99%), but also a practically useful nitrogen removal rate above 1 kg N/m³/d. Due to the acidification caused by excessive CO₂ supply from biogas, pH dropping was observed. Two corresponding strategies, i.e., intermittent alkali dosing and intermittent nitrogen gas flushing, were developed to control the pH at neutral. Mass balance based on batch tests and microbial community analysis by 16S rRNA gene amplicon sequencing both showed the joint contribution of anammox bacteria and anaerobic methane oxidizers to the nitrogen removal. This study proved the potential and capacity of MBfR to access complete nitrogen removal from high-strength wastewater by using biogas produced in-situ, thus leading to a significant reduction of external carbon addition in practice.

Struvite Precipitation for Sustainable Recovery of Nitrogen and Phosphorus from Anaerobic Digestion Effluents of Swine Manure

In this study, we propose the application of struvite precipitation for the sustainable recovery of nitrogen (N) and phosphorus (P) from anaerobic digestion (AD) effluents derived from swine manure. The optimal conditions for four major factors that affect the recovery of N and P were derived by conducting batch experiments on AD effluents obtained from four AD facilities. The optimal conditions were a pH of 10.0, NH4-N:Mg:PO4-P molar ratio of 1:1.4:1, mixing intensity of 240 s−1, and mixing duration of 2 min. Under these optimal conditions, the removal efficiencies of NH4-N and PO4-P were approximately 74% and 83%, respectively, whereas those of Cu and Zn were approximately 74% and 79%, respectively. Herein, a model for swine manure treatment that incorporates AD, struvite precipitation, and biological treatment processes is proposed. We applied this model to 85 public biological treatment facilities in South Korea and recovered 4722 and 51 tons/yr of NH4-N and PO4-P, respectively. The economic analysis of the proposed model’s performance predicts a lack of profitability due to the high cost of chemicals; however, this analysis does not consider the resulting protection of the hydrological environment. Field-scale studies should be conducted in future to prove the effectiveness of the model.

Resistance of anammox granular sludge to copper nanoparticles and oxytetracycline and restoration of performance

Nanoparticles and antibiotics, the two most frequently detected emerging pollutants from different wastewater sources, are eventually discharged into wastewater treatment plants. In this study, the widely used materials CuNPs and oxytetracycline (OTC) were selected as target pollutants to investigate their joint effects on anaerobic ammonium oxidation (anammox). The results indicated that the environmental concentration slightly inhibited the performance of the reactors, while the performance rapidly deteriorated within a week under high-level combined shocks (5.0 mg L^-1 CuNPs and 2.0 mg L^-1 OTC). After the second shock (2.5 mg L^-1 CuNPs and 2.0 mg L^-1 OTC), the resistance of anammox bacteria was enhanced, with an elevated relative abundance of Candidatus Kuenenia and absolute abundance of hzsA, nirS, and hdh. Moreover, the extracellular polymeric substance (EPS) content and specific anammox activity (SAA) showed corresponding changes. Improved sludge resistance was observed with increasing CuNP and OTC doses, which accelerated the recovery of performance.

Interactions between tetracycline and extracellular polymeric substances in anammox granular sludge

The effects of antibiotics on extracellular polymeric substances (EPS) using tetracycline as the model chemical were analyzed in terms of molecular property and structure. Results showed that three components, tryptophan, tryptophan type-proteins and polysaccharides in EPS of granular sludge from anaerobic ammonium oxidation (anammox) reactor can interacted with tetracycline, detected by the static quenching via the endogenous fluorescence quenching and transient fluorescence spectroscopy. Thermodynamic experiment confirmed that their interaction was dominated by the hydrophobic force. Combined with the synchronous fluorescence spectroscopy, it was found that tetracycline facilitated the extension degree of peptide chains in tryptophan type-proteins, leading to the enhancement of hydrodynamic diameter of the macromolecules in EPS when binding with tetracycline. EPS in AnGS demonstrated the resistance ability to tetracycline by converting from gel to sol state in rheological term. With the increase of tetracycline concentration, the stability of elastic structures in EPS declined, influencing the AnGS stability.

Deciphering the microbial and genetic responses of anammox biogranules to the single and joint stress of zinc and tetracycline

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 R₁ and 1.0 mg L^-1 in R₂, 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 R₃. The quantification results showed that the abundances of eight antibiotic resistance genes (ARGs), czcA and intI1 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.

Successful operation performance and syntrophic micro-granule in partial nitritation and anammox reactor treating low-strength ammonia wastewater

The stable operation of the partial nitritation and anammox (PN/A) process is a challenge in the treatment of low-strength ammonia wastewater like sewage mainstream. This study demonstrated the feasibility of achieving stable operation in the treatment of 50 mg/L ammonia wastewater with a micro granule-based PN/A reactor. The long-term operation results showed nitrogen removal efficiencies of 71.8 ± 9.9% were stably obtained under a relatively short hydraulic retention time (HRT) of 2 h. The analysis on the physicochemical properties of the granules indicated most of the granules were in a size in a range of 265-536 μm, and the elementary composition of the granules was determined to be CH_1.61O_0.61N_0.17S_0.01P_0.03. The microbial analysis revealed Candidatus Kuenenia stuttgartiensis anammox bacteria and Nitrosomonas-like AOB were the two most dominant bacteria with 27.6% and 10.5% abundance, respectively, both of which formed spatially syntrophic co-immobilization within the micro-granules. The ex-situ activity tests showed the activity of NOB was well limited through DO regulation in the reactor. These results provide an alternative PN/A process configuration for low-strength wastewater treatment by sustaining microstate granules. Optimization of the nitrogen sludge loading rate and DO regulation are important for the successful performance.

Impacts of the heavy metals Cu (II), Zn (II) and Fe (II) on an Anammox system treating synthetic wastewater in low ammonia nitrogen and low temperature: Fe (II) makes a difference

In this study, the impacts of heavy metals (1 mg L^-1) on the nitrogen removal, bioactivity of anaerobic ammonia-oxidizing bacteria (AAOB) and the microbial community of anaerobic ammonium oxidation (Anammox) process were investigated. It was observed that short-term exposure in Cu (II) and Zn (II) both improved AAOB bioactivity, while long-term exposure significantly lowered the nitrogen removal to 0.218 and 0.302 kg m^-3 d^-1, when treated the wastewater with 100 mg L^-1 nitrogen under 14-16 °C. Fe(II) had slight impact on Anammox in short-term experiment but deeply enhanced nitrogen removal during the long-term contact, and finally increased the that to 0.58 kg m^-3 d^-1. The impact on Anammox was Cu(II) > Zn(II) > Fe(II). Cu(II) and Zn(II) lowered the share of Candidatus Kuenenia to 3.32% and 3.80%, while Fe(II) improved that to 11.30% from 7.99%. Extracellular polymeric substance in biofilm had prominent iron adsorption capacity, which was the key factor that help AAOB resist Fe(II).

Increased salinity improves the thermotolerance of mesophilic anammox consortia

While the application of anammox-based process for mesophilic sidestream treatment is at present the state of the art and mainstream treatment at ambient temperature is also in development, the feasibility of thermophilic anammox process is still unclear. This study investigated the effects of salinity on the thermotolerance of mesophilic anammox sludge. In batch activity tests, 45 °C seems to be the critical temperature for the tolerance of mesophilic anammox consortia without acclimatization or amendments. The optimal anammox activity at 40, 42.5, and 45 °C can be achieved with the amendment of salt at 5-8, 8-10, and ~12 g NaCl L^-1, respectively. However, this improvement effect was limited at 50 °C or when the shock duration was longer than 24 h even at 45 °C. In continuous-flow bioreactors, mesophilic anammox consortia could gradually adapt to 40-50 °C under a transition of 2.5 °C, and the performance was enhanced by an increase in salinity, which may be associated with the increase in extracellular polymeric substances. A nitrogen removal rate of 0.53 kgN m^-3 d^-1 was finally obtained at 50 °C. Overall, these interesting results facilitate further opportunities for thermophilic anammox process.

Influence of sulfadimethoxine (SDM) and sulfamethazine (SM) on anammox bioreactors: Performance evaluation and bacterial community characterization

The specific inhibitory effects of sulfonamides on anaerobic ammonium oxidation (anammox) process remain unknown. This study investigated the inhibitory characteristics of sulfadimethoxine (SDM) and sulfamethazine (SM) in two anammox bioreactors with NH₄⁺-N (160 mg/L) and NO₂^--N (210 mg/L) in influent. Results indicate that anammox bacteria in both bioreactors adapted to low antibiotic concentrations (less than 3 mg/L). At concentrations between 5 and 7 mg/L, SDM inhibited the growth of anammox bacteria and resulted in a decrease of Candidatus Brocadia abundance from 2.57% to 0.39%. In contrast, at concentrations of 5-9 mg/L, SM inhibited the denitrification process more severely than SDM, resulting in higher accumulation of nitrite and nitrate. The purpose of this study was to elucidate the inhibitory effects of sulfonamides on the anammox process and to provide a reference for the stable operation of anammox bioreactors for the treatment of sulfonamide-containing wastewater.

Acute and persistent toxicity of Cd(II) to the microbial community of Anammox process

In this study, the short- and long-term effects of Cd(II) on the bioactivity, nitrogen removal and microbial community of the anaerobic ammonia oxidation (Anammox) process were investigated by step-wise increasing Cd(II). The self-recovery ability of Anammox was also studied after long-term exposure in Cd(II). The bioactivity of anaerobic ammonia-oxidizing bacteria (AAOB) within short-term exposure of Cd(II) were detected by batch experiments. Results showed that Cd(II) had both acute and persistent toxicity to Anammox, the IC₅₀ in short-term exposure was calculated as 5.43 mg L^-1. Long-term exposure led to the microbial diversity increase, as well as the relative abundance decrease of AAOB in Anammox system. AAOB was continuously suppressed by Cd(II) in 1-20 mg L^-1, while it had self-adaption to Cd(II) in 1-10 mg L^-1. Anammox biofilm showed prominent adsorbing ability for cadmium, and the cadmium in biofilm was the key factor affecting Anammox.

Status, Challenges, and Perspectives of Mainstream Nitritation-Anammox for Wastewater Treatment

  The nitritation-anammox process is an efficient and cost-effective approach for biological nitrogen removal, but its application in treating mainstream wastewater remains a great challenge. Mainstream nitritation-anammox processes could create opportunities for achieving energy self-sufficient, or energy-generating water resource recovery facilities. Significant advancements have been achieved via pilot- and full-scale trials to overcome the major obstacles under mainstream conditions, such as repression of nitrite-oxidizing bacteria, limiting the overgrowth of denitrifiers, and effective selection and retention of ammonia-oxidizing bacteria and anammox bacteria. This review paper intends to provide a detailed update of research progress on mainstream nitritation-anammox processes, discuss metabolic interactions, and examine major challenges and possible solutions towards the future development.

Influence of elevated Zn (II) on Anammox system: Microbial variation and zinc tolerance

Nitrogen removal by anaerobic ammonium oxidation (Anammox) has attracted increasing attention in nowadays. An Anammox biofilter was subjected to a continuous loading of elevated Zn (II). The influence of Zn (II) on the nitrogen removal, microbial community and biofilm property was investigated in the condition of 23-26 °C and 3.5 h HRT. The nitrogen removal greatly decreased to 0.054 from the initial 0.502 kg m^-3 d^-1, with the Zn (II) addition. Anaerobic ammonia-oxidizing bacteria (AAOB) had self-adaption to Zn (II) in 1-10 mg L^-1 and was significantly enhanced after long-term acclimatization, while the suppression threshold was 20 mg L^-1. Soluble microbial products (SMP) increased correspondingly with Zn (II), while extracellular polymeric substance (EPS) climbed up initially and then decreased. Anammox biofilm performed the highest zinc adsorption as 158.27 mg g^-1 SS in biofilm. High Zn (II) improved the microbial diversity and lowered the Candidatus Kuenenia abuandance to 1.38% from 20.89%.

Long-term effects of combined divalent copper and tetracycline on the performance, microbial activity and community in a sequencing batch reactor

The long-term effects of combined divalent copper (Cu(II)) and tetracycline (TC) on the performance, microbial activity and community in a sequencing batch reactor (SBR) were investigated. The addition of Cu(II), TC or mixed Cu(II)/TC caused the decrease of the organics and nitrogen removal efficiencies, and their decreased degrees were the lowest at the addition of mixed Cu(II)/TC. The increase of mixed Cu(II)/TC concentrations in the influent did not change the antagonistic effects between Cu(II) and TC on nitrifying and denitrifying activities. Nitrifiers had higher tolerances to Cu(II), TC and mixed Cu(II)/TC than denitrifiers. Compared to the addition of Cu(II) or TC alone, the microbial community richness was higher at the addition of mixed Cu(II)/TC, while the microbial community diversity was lower. The increased protein (PN) in extracellular polymeric substances (EPS) was a protective response of bacteria to Cu(II), TC and mixed Cu(II)/TC.

Effect of zinc oxide nanoparticles on nitrogen removal, microbial activity and microbial community of CANON process in a membrane bioreactor

In this study, a membrane bioreactor (MBR) was adopted for completely autotrophic nitrogen removal over nitrite (CANON) process. Zinc oxide nanoparticles (ZnO NPs) was step-wise increased to analyze the influence on nitrogen removal, microbial activity and microbial communities. Finally ZnO NPs was removed to study its recovery capability. The bioactivities of ammonia-oxidizing bacteria (AOB), anaerobic ammonia-oxidizing bacteria (AAOB) and nitrite-oxidizing bacteria (NOB) were detected by batch experiments. Results showed that the ZnO NPs with low concentration (≤5mgL^-1) was profitable for nitrogen removal while the high concentration performed inhibition, and it lowered the abundance of both AOB and NOB while enhanced that of AAOB. ZnO NPs with high concentration (≥10mgL^-1) suppressed both AOB and AAOB, and long-term exposure within ZnO NPs led to microbial diversity decrease. The inhibition threshold of ZnO NPs on CANON process was 10mgL^-1, and the profitable concentration was 1mgL^-1.

Performance of autotrophic nitrogen removal from digested piggery wastewater

The performance of an autotrophic nitrogen removal process to treat digested piggery wastewater (DPW) was investigated by gradually shortening the HRT and enhancing the DPW concentration during 390days of operation. The results showed that the total nitrogen removal rate and efficiency reached 3.9kg-Nm^-3day^-1 and 73%, which were significantly higher than the levels reported previously. A high relative abundance of Nitrosomonas (4.2%) and functional microbes (12.15%) resulted in a high aerobic ammonium oxidizing activity (1.25±0.1g-NgVSS^-1d^-1), and a good settling ability (SVI, 78.42mLg^-1SS) resulted in a high sludge concentration (VSS, 11.01gL^-1), which laid a solid foundation for the excellent performance. High-throughput pyrosequencing indicated that, compared with synthetic wastewater, the DPW decreased the relative abundances of every functional group of nitrogen removal microbes, and increased relative abundances of anaerobes (15.7%), sulfur-oxidizing bacteria (9.4%) and methanogens (40.8%).

Susceptibility, resistance and resilience of anammox biomass to nanoscale copper stress

The increasing use of engineered nanoparticles (NPs) poses an emerging challenge to biological wastewater treatment. The long-term impact of CuNPs on anaerobic ammonium oxidation (anammox) process was firstly investigated in this study. The nitrogen removal capacity of anammox reactor was nearly deprived within 30days under the stress of 5.0mgL^-1 CuNPs and the relative abundance of anammox bacteria (Ca. Kuenenia) was decreased from 29.59% to 17.53%. Meanwhile, copper resistance genes associated with the Cus, Cop and Pco systems were enriched to eliminate excess intracellular copper. After the withdrawal of CuNPs from the influent, the nitrogen removal capacity of anammox biomass recovered completely within 70days. Overall, anammox biomass showed susceptibility, resistance and resilience to the stress of CuNPs. Therefore, the potential impacts of ENPs on anammox-based processes should be of great concern.

Short-term and long-term effects of Zn (II) on the microbial activity and sludge property of partial nitrification process

Autotrophic nitrogen removal was an innovative and economical nitrogen removal technology with less oxygen and no organics consumption, in which partial nitrification (PN) is the key component. It is necessary to clear the impact of metal ions on PN since the development of industry increased their opportunity for entering into wastewater. In this study, PN process was successfully started-up in an SBR, the short-term and long-term effects of Zn (II) on microbial bioactivity and the sludge adsorption ability for Zn (II) were investigated. Results suggested that low Zn (II) were favorable for AOB bioactivity, while the long-term effect also induced NOB bioactivity. The suppression threshold of Zn (II) on AOB in short-term effect was 10mgL^-1, which rose to 50mgL^-1 in the long-term effect due to the self-adaption. The PN sludge presented prominent absorbability for zinc and performed a quadratic relation with the Zn (II) concentration.