Speciation of nickel and zinc, its short-term inhibitory effect on anammox, and the associated microbial community composition

Inhibition effect of Cu(II) on nitrogen removal in anammox-denitrification couple system

Due to the wide application in industries, copper can be detected in some nitrogen-rich wastewater. In this research, short-term and long-term experiments were conducted to explore the effects of Cu(II) on the anammox-denitrification couple system. It concluded that the half inhibition concentration (IC50) of Cu(II) was 35.54 mg/L. The system in reactor could tolerate low concentrations of Cu(II) (≤5 mg/L), while the total nitrogen removal efficiency decreased from 93 % to 33 % under 10 mg/L of Cu(II). After 45 days exposure to Cu(II) (1-10 mg/L), 14.54 mg/g SS copper accumulated in the sludge, which largely inhibited the microbial activity. More extracellular polymeric substances (EPS) were secreted to defend against copper toxicity. Proteobacteria (19.18 %-44.04 %) was the dominant phylum and showed excellent tolerance and adaptability to Cu(II). The dominant anammox bacteria, Candidatus_Brocadia, was slightly enhanced under low concentrations of Cu(II), but was highly inhibited under 10 mg/L of Cu(II). PICRUSt2 results showed that some metabolic activities were suppressed under the exposure of copper while defensive responses were also induced. Metabolic disorders eventually led to the death of some microbes, resulting in unrecoverable deterioration in microbial activity. Overall, this study explores the effect of Cu(II) on the anammox-denitrification process and provides a possible inhibition mechanism.

Feasibility of anaerobic ammonium oxidation process for treatment of pretreated printed circuit board wastewater

The treatment of pretreated printed circuit board (PCB) wastewater by anaerobic ammonium oxidation (anammox) process has been rarely reported. This study sought to investigate the performance of the anammox process during various phases of pretreated PCB wastewater treatment. The nitrogen removal efficiency (NRE) reached 90 ± 10% at a Cu2+ concentration of 2.5 mg·L-1, but declined to 22 ± 11% as the Cu2+ level increased to 10.3  mg·L-1. During phase III, there was a 38% increase in the relative abundance of Candidatus Kuenenia compared to phase I. By adjusting the substrate concentration and introducing synthetic wastewater into the reactor, the anammox performance was nearly restored to that of phase I. These findings underscore the potential of the anammox process for treating pretreated PCB wastewater and expanding its practical applications to industrial wastewater treatment.

Effects of Heavy Metals on the Performance and Mechanism of Anaerobic Ammonium Oxidation for Treating Wastewater

Persistence of ammonium nitrogen and heavy metals in wastewater still remains a challenge, and many wastewater treatment plants face the challenge of removing nitrogen under heavy metal stresses. There is no preferred method for the biological treatment of wastewater containing nitrogen and heavy metals with the possible exception of the anaerobic ammonium oxidation (anammox), since it has shown promise for removing nitrogen under heavy metal stresses. This article reviews the recent research results of the nitrogen-removal performance and mechanism by the anammox process under heavy metal stresses, mainly discussing the enhancing and inhibition effects of heavy metals on the performance of the Anammox reactor. The influencing mechanism of heavy metals on the microbial community and extracellular polymeric substances is also presented, and examples are given for explanation. The main problems of the present research are pointed out, and it is proposed that unifying the metal ion concentrations of inhibiting or promoting anammox activity is necessary for the development and industrial application of the anammox process. The information of this review can offer a great possibility for achieving desired nitrogen removal in wastewater treatment under heavy metal stresses and with significant energy savings.

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.

Application of metagenomics to biological wastewater treatment

Biological wastewater treatment is a process in which the microbial metabolism of complex communities transforms pollutants into low- or non-toxic products. Due to the absence of an in-depth understanding of the diversity and complexity of microbial communities, it is very likely to ignore the potential mechanisms of microbial community in wastewater treatment. Metagenomics is a technology based on molecular biology, in which massive gene sequences are obtained from environmental samples and analyzed by bioinformatics to determine the composition and function of a microbial community. Metagenomics can identify the state of microbes in their native environments more effectively than traditional molecular methods. This review summarizes the application of metagenomics to assess microbial communities in biological wastewater treatment, such as the biological removal of phosphorus and nitrogen by bacteria, the study of antibiotic resistance genes (ARGs), and the reduction of heavy metals by microbial communities, with an emphasis on the contribution of microbial diversity and metabolic diversity. Technical bottlenecks in the application of metagenomics to biological wastewater treatment are elucidated, and future research directions for metagenomics are proposed, among which the application of multi-omics will be an important research method for future biological wastewater treatment.

Evaluation of the joint effects of Cu2+, Zn2+ and Mn2+ on completely autotrophic nitrogen-removal over nitrite (CANON) process

The completely autotrophic nitrogen-removal over nitrite (CANON) process has merits in energy saving and consumption reducing, thus being considered as an attractive alternative over the common denitrification technology. In this study, the effects of three common heavy metals (Cu²⁺, Zn²⁺ and Mn²⁺) in wastewater to the CANON process were evaluated comprehensively. A central composite design with response surface methodology was utilized to investigate the joint effect of these three metal ions on the nitrogen removal performance of CANON process. In accordance with the determined optimal dosage in batch tests, four bioreactors were established with different amounts of heavy metal dosage in long-term operation, which determined the optimal concentrations for Cu²⁺, Zn²⁺ and Mn²⁺ to be 0.25, 0.81 and 1.00 mg/L, respectively. However, the optimal dosing level determined in batch tests showed no promotion during long-term experiment. This indicated that the actual concentration of heavy metals in bioreactors during long-term operation could be higher than expectation, leading to the difference between short-term tests and long-term experiment. The distribution of metal ions revealed that Mn²⁺ was mainly absorbed in anammox bacteria cells while Cu²⁺ and Zn²⁺ were mostly identified inside AOB cells. Moreover, the addition of heavy metals consistently showed positive effects for the relative abundance of AOB, while only a low level of dosage could promote the abundance of anammox bacteria. Furthermore, a mathematical model was established to simulate the CANON system considering the impacts of heavy metals, which was calibrated and validated using independent dataset in this study.

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.

Microbiologically induced calcite precipitation technology for mineralizing lead and cadmium in landfill leachate

As a new bioremediation technology for toxic metals, microbiologically induced calcite precipitation (MICP) is gradually becoming a research focus. This study investigated the application of MICP to mineralize toxic metals (lead and cadmium) in landfill leachate for the first time. In the experiment of remediating synthetic landfill leachate (SLL) contaminated by Pb²⁺, 100% of the 20 mg/L Pb²⁺ was removed when the maximum urease activity was only 20.96 U/ml. Scanning electron microscopy and energy dispersive spectroscopy (SEM-EDS) and laser particle size characterizations of the precipitates indicate the formation of agglomerated square particles, 76.9% of which had sizes that ranged from 33.93 to 57.06 μm. Fourier transform infrared spectroscopic and X-ray diffraction analyses confirmed that the precipitates consisted predominantly of calcite crystals, and the unit cell lattice constants of the precipitates (a = b = 4.984 Å, c = 17.171 Å) matched those of calcite, while lead was fixed as hydrocerussite. In addition, the Pb-MICP precipitates were stable under continuous acid degradation (pH = 5.5), and only 1.76% of the lead was released after 15 days. In the verification test of toxic metals remediation in a real landfill leachate (RLL), all of the Pb²⁺ and Cd²⁺ (initial concentrations: Pb²⁺ = 25 mg/L; Cd²⁺ = 5.6205 mg/L) was mineralized simultaneously, which further confirmed the feasibility of MICP for toxic metal remediation in landfill leachate. However, optimizing the urea dosage and combining the ammonium recovery are necessary strategies required for improving the economic and environmental benefits of the MICP process.

Short- and long-term effects of copper on anammox under gradually increased copper concentrations

This study aims to determine both short- and long-term response of enriched anammox culture to Cu. Assessment of short-term inhibition is based both on total applied Cu concentration and potential bioavailable fractions like intracellular, surface-bound, soluble and free Cu ion. The half maximal inhibitory concentration (IC50) values for total applied, soluble, intracellular and cell-associated concentrations were determined as 4.57 mg/L, 1.97 mg/L, 0.71 mg/L, 1.11 mg/L, respectively. Correlation between the surface-bound fraction of Cu and inhibition response was weak, suggesting that Cu sorbed to biomass was not directly responsible for the effects on anammox activity. There was a disparity between the results of short- and long-term experiments in terms of inhibition threshold concentration (i.e. short-term IC50 = 4.57 mg/L vs long-term IC50 = 6.74 mg/L). Candidatus Kuenenia (59.8%) and Candidatus Brocadia (40.2%) were the two main anammox genera within the initial biomass sample. One of the most interesting finding of the study is the demonstration that a complete wash-out of C. Brocadia genus at an applied Cu concentration of 6.5 mg/L. This strongly indicates that C. Brocadia were not able to tolerate high copper concentrations and all nitrogen conversion was carried out by C. Kuenenia during the Cu exposure period.

Assessment of Anammox process against acute and long-term exposure of ZnO nanoparticles

The impacts of nanoparticles (NPs) on wastewater treatment have become a great concern because of their widespread applications. Although the acute responses of anammox bacteria to NPs have enhanced the knowledge about the potential risks of them, deep understanding of the cumulative impacts of NPs must be assessed. The purpose of this research was therefore to further extend the current knowledge by evaluating both acute and long-term effects of Zinc oxide (ZnO) NPs on Anammox process based on nitrogen removal performance, self-recovery ability and microbial community structure. The acute exposure tests indicated that, the median inhibition concentration (IC50) of ZnO NPs on Anammox process was 84.7 mg/L (54.82 mg ZnO NPs/g VSS). Acute exposure of 200 mg/L ZnO NPs (117.54 mg Zn/g VSS) caused 80% inhibition in batch assays while the long-term inhibition dosage was 100 mg/L ZnO NPs (187.50 mg ZnO NPs/g VSS) corresponding to 1022 mg/L total Zn (1916.27 mg Zn/g VSS) in the reactor due to the accumulation of NPs. Total, soluble and biomass-associated Zn concentrations were measured throughout the long-term exposure to observe the behavior of ZnO NPs in the reactor. Total Zn in the reactor was cumulatively increased and mostly originated from biomass-associated Zn. Following the long-term inhibition tests, self-recovery of Anammox process within 120 days demonstrated that, the ZnO NPs inhibition is reversible for the applied dose. Furthermore, next generation sequencing results indicated a symbiotic relationship between the microbial groups in the anammox bioreactor while relative abundance of Candidatus (Ca.) Brocadiaceae family showed a decrease parallel to the deterioration in nitrogen removal performance of bioreactor. At the end of the long-term exposure studies, 48.76% decline on anammox quantity was detected.

Anammox and partial denitrification coupling: a review

As a new wastewater biological nitrogen removal process, anammox and partial denitrification coupling not only plays a significant role in the nitrogen cycle, but also holds high engineering application value. Because anammox and some denitrifying bacteria are coupled under harsh living conditions, certain operating conditions and mechanisms of the coupling process are not clear; thus, it is more difficult to control the process, which is why the process has not been widely applied. This paper analyzes the research focusing on the coupling process in recent years, including anammox and partial denitrification coupling process inhibitors such as nitrogen (NH₄⁺, NO₂⁻), organics (toxic and non-toxic organics), and salts. The mechanism of substrate removal in anammox and partial denitrification coupling nitrogen removal is described in detail. Due to the differences in process methods, experimental conditions, and sludge choices between the rapid start-up and stable operation stages of the reactor, there are significant differences in substrate inhibition. Multiple process parameters (such as pH, temperature, dissolved oxygen, redox potential, carbon-to-nitrogen ratio, and sludge) can be adjusted to improve the coupling of anammox and partial denitrification to modify nitrogen removal performance.

As a new wastewater biological nitrogen removal process, anammox and partial denitrification coupling not only plays a significant role in the nitrogen cycle, but also holds high engineering application value.

Effect of divalent nickel on the anammox process in a UASB reactor

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 (IC₅₀) 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%.

Simultaneous removal of ammonia and nitrate by coupled S0-driven autotrophic denitrification and Anammox process in fluorine-containing semiconductor wastewater

To achieve the simultaneous removal of NH₄⁺-N and NO₃^--N in F^--containing semiconductor wastewater by coupled S⁰-driven autotrophic denitrification and Anammox process, the effect of variable F^- concentration on the Anammox process was investigated by batch experiments. The denitrifying ammonium oxidation (Deamox) reactor was then started-up to explore the feasibility of the coupling of Anammox and sulfur autotrophic denitrification (SADN) for the treatment of semiconductor wastewater. Short-term variation of F^- concentration has an obviously effect on the activity of Anammox sludge, but didn't affect the nitrogen conversion rate. The activity of Anammox obviously decreased after long-term operation of the Deamox reactor when influent F^- concentrations reached 552 mg/L. The sensitivity of Anammox bacteria to F^- concentration is stronger than that of SADN bacteria. Total nitrogen removal efficiency of 98% and total nitrogen removal rate of 4.11 kg/(m³·d) were achieved in the Deamox reactor, when the F^- was pre-treated by calcium ions. Moreover, the high-throughput 16S rRNA gene sequence analysis indicated that variation in F^- concentrations could influence the structure and functional of microbial communities in the Deamox process. Candidatus Kuenenia, Thiobacillus and Sulfurimonas were main functional bacteria that achieved symbiotic.

Aerobic co-composting degradation of highly PCDD/F-contaminated field soil. A study of bacterial community

This study investigated bacterial communities during aerobic food waste co-composting degradation of highly PCDD/F-contaminated field soil. The total initial toxic equivalent quantity (TEQ) of the soil was 16,004 ng-TEQ kg^-1 dry weight. After 42-day composting and bioactivity-enhanced monitored natural attenuation (MNA), the final compost product's TEQ reduced to 1916 ng-TEQ kg^-1 dry weight (approximately 75% degradation) with a degradation rate of 136.33 ng-TEQ kg^-1 day^-1. Variations in bacterial communities and PCDD/F degraders were identified by next-generation sequencing (NGS). Thermophilic conditions of the co-composting process resulted in fewer observed bacteria and PCDD/F concentrations. Numerous organic compound degraders were identified by NGS, supporting the conclusion that PCDD/Fs were degraded during food waste co-composting. Bacterial communities of the composting process were defined by four phyla (Proteobacteria, Actinobacteria, Bacteroidetes and Firmicutes). At the genus level, Bacillus (Firmicutes) emerged as the most dominant phylotype. Further studies on specific roles of these bacterial strains are needed, especially for the thermophiles which contributed to the high degradation rate of the co-co-composting treatment's first 14 days.