Increased salinity triggers significant changes in the functional proteins of ANAMMOX bacteria within a biofilm community

Outstanding enrichment of ladderane lipids in anammox bacteria: Overlooked effect of pH

Ladderane lipids synthesised by anammox bacteria hold significant potential for applications in jet fuel, drug delivery, and optoelectronics. Despite the widespread use of anammox bacteria in nitrogen removal from wastewater, the optimal conditions for maximising ladderane production remain unclear, limiting their broader application. To address this, we operated a fed-batch bioreactor with anammox bacteria, gradually adjusting the pH from 6.5 to 7.5 while regularly sampling for microbial community composition (Illumina sequencing), proteins, and ladderane lipids (UHPLC-HRMS). Our findings reveal that ladderane production positively correlates with rising pH increasing nearly fivefold as pH rose from 6.5 to 7.5, with a notable shift towards lipids containing two ladderane alkyl chains at higher pH. However, the conditions at an alkaline pH range also induced mild stress in anammox bacteria, as evidenced by our proteomic and microbial community data. Therefore, we propose maintaining a pH above 7.5 to enrich ladderane-rich anammox biomass but emphasise the need for gradual adaptation. This approach could optimise anammox installations for producing high-value ladderane lipids from wastewater.

Improving microbial activity in high-salt wastewater: A review of innovative approaches

The Zero discharge technology has become an important pathroute for sustainable development of high salt wastewater treatment. However, the cohabitation of organic and inorganic debris can cause serious problems such membrane clogging and the formation of hazardous impurity salts that further restrict the recovery of all salt varieties by evaporating and crystallizing. In highly salinized wastewater, biological treatments offer advantages in terms of cost and sustainability when used as a pre-treatment step to eliminate organic debris. On the other hand, high salinity is always a major obstacle to microbial diversity, abundance, and activity, which can result in low organic matter removal effectiveness or the failure of the microbial treatment system. Biofortification techniques can attenuate the negative effects of salt stress and other unfavourable conditions on microorganisms, while the regulation mechanisms of microbial and community collaboration by fortification methods have been an open question. Therefore, a comprehensive summary of the types, mechanisms, and effects of the major biofortification techniques is proposed. This review dialyzes the characteristics and sources of hypersaline wastewater and the main treatment methods. Then, the mechanisms of microbial salt tolerance are summarized and discussed based on microbial characteristics and the protective effects provided by the processes. Finally, the research and application of the main bioaugmentation methods are developed in detail, describing the characteristics, advantages and disadvantages of the different enhancement methods in their implementation. This review provides a more comprehensive perspective on the future engineering applications of bioaugmentation technology, and explores in depth the possibilities of applying biological methods to high-salinity wastewater treatment.

Salinity Tolerance and Osmoadaptation Strategies in Four Genera of Anammox Bacteria: Brocadia, Jettenia, Kuenenia, and Scalindua

The salinity tolerance and osmoadaptation strategies in four phylogenetically distant anammox species, Brocadia, Jettenia, Kuenenia, and Scalindua, were investigated by using highly enriched cell cultures. The first-emerged "Ca. Scalindua sp." showed optimum growth at 1.5-3% salinity and was tolerant to ∼10% salinity (a slight halophile). The second-emerged "Ca. Kuenenia stuttgartiensis" was tolerant to ∼6% salinity with optimum growth at 0.25-1.5% (a halotolerant). These early-emerged "Ca. Scalindua sp." and ″Ca. K. stuttgartiensis" rapidly accumulated K+ ions and simultaneously synthesized glutamate as a counterion. Subsequently, part of the glutamate was replaced by trehalose. In contrast, the late-emerged "Ca. B. sinica" and "Ca. J. caeni" were unable to accumulate sufficient amounts of K+─glutamate and trehalose, resulting in a significant decrease in activity even at 1-2% salinity (nonhalophiles). In addition, the external addition of glutamate may increase anammox activity at high salinity. The species-dependent salinity tolerance and osmoadaptation strategies were consistent with the genetic potential required for the biosynthesis and transport of these osmolytes and the evolutionary history of anammox bacteria: Scalindua first emerged in marine environments and then Kuenenia and other two species gradually expanded their habitat to estuaries, freshwater, and terrestrial environments, while Brocadia and Jettenia likely lost their ability to accumulate K+─glutamate.

Rapid start-up of an innovative pilot-scale staged PN/A continuous process for enhanced nitrogen removal from mature landfill leachate via robust NOB elimination and efficient biomass retention

The start-up and stable operation of partial nitritation-anammox (PN/A) treatment of mature landfill leachate (MLL) still face challenges. This study developed an innovative staged pilot-scale PN/A system to enhance nitrogen removal from MLL. The staged process included a PN unit, an anammox upflow enhanced internal circulation biofilm (UEICB) reactor, and a post-biofilm unit. Rapid start-up of the continuous flow PN process (full-concentration MLL) was achieved within 35 days by controlling dissolved oxygen and leveraging free ammonia and free nitrous acid to selectively suppress nitrite-oxidizing bacteria (NOB). The UEICB was equipped with an annular flow agitator combined with the enhanced internal circulation device of the guide tube, which achieved an efficient enrichment of Candidatus Kuenenia in the biofilm (relative abundance of 33.4 %). The nitrogen removal alliance formed by the salt-tolerant anammox bacterium (Candidatus Kuenenia) and denitrifying bacteria (unclassified SBR1031 and Denitratisoma) achieved efficient nitrogen removal of UEICB (total nitrogen removal percentage: 90.8 %) and at the same time effective treatment of the refractory organic matter (ROM). The dual membrane process of UEICB fixed biofilm combined with post-biofilm is effective in sludge retention, and can stably control the effluent suspended solids (SS) at a level of less than 5 mg/L. The post-biofilm unit ensured that effluent total nitrogen (TN) remained below the 40 mg/L discharge standard (98.5 % removal efficiency). Compared with conventional nitrification-denitrification systems, the staged PN/A process substantially reduced oxygen consumption, sludge production, CO2 emissions and carbon consumption by 22.8 %, 67.1 %, 87.1 % and 87.1 %, respectively. The 195-day stable operation marks the effective implementation of the innovative pilot-scale PN/A process in treating actual MLL. This study provides insights into strategies for rapid start-up, robust NOB suppression, and anammox biomass retention to advance the application of PN/A in high-ammonia low-carbon wastewater.

A review of microbial nitrogen transformations and microbiome engineering for biological nitrogen removal under salinity stress

The osmotic stress caused by salinity exerts severe inhibition on the process of biological nitrogen removal (BNR), leading to the deterioration of biosystems and the discharge of nitrogen with saline wastewater. Feasible strategies to solve the bottleneck in saline wastewater treatment have attracted great attention, but relevant studies to improve nitrogen transformations and enhance the salt-tolerance of biosystems in terms of microbiome engineering have not been systematically reviewed and discussed. This work attempted to provide a more comprehensive explanation of both BNR and microbiome engineering approaches for saline wastewater treatment. The effect of salinity on conventional BNR pathways, nitrification-denitrification and anammox, was summarized at cellular and metabolic levels, including the nitrogen metabolic pathways, the functional microorganisms, and the inhibition threshold of salinity. Promising nitrogen transformations, such as heterotrophic nitrification-aerobic denitrification, ammonium assimilation and the coupling of conventional pathways, were introduced and compared based on advantages and challenges in detail. Strategies to improve the salt tolerance of biosystems were proposed and evaluated from the perspective of microbiome engineering. Finally, prospects of future investigation and applications on halophilic microbiomes in saline wastewater treatment were discussed.

Salinity determines performance, functional populations, and microbial ecology in consortia attenuating organohalide pollutants

Organohalide pollutants are prevalent in coastal regions due to extensive intervention by anthropogenic activities, threatening public health and ecosystems. Gradients in salinity are a natural feature of coasts, but their impacts on the environmental fate of organohalides and the underlying microbial communities remain poorly understood. Here we report the effects of salinity on microbial reductive dechlorination of tetrachloroethene (PCE) and polychlorinated biphenyls (PCBs) in consortia derived from distinct environments (freshwater and marine sediments). Marine-derived microcosms exhibited higher halotolerance during PCE and PCB dechlorination, and a halotolerant dechlorinating culture was enriched from these microcosms. The organohalide-respiring bacteria (OHRB) responsible for PCE and PCB dechlorination in marine microcosms shifted from Dehalococcoides to Dehalobium when salinity increased. Broadly, lower microbial diversity, simpler co-occurrence networks, and more deterministic microbial community assemblages were observed under higher salinity. Separately, we observed that inhibition of dechlorination by high salinity could be attributed to suppressed viability of Dehalococcoides rather than reduced provision of substrates by syntrophic microorganisms. Additionally, the high activity of PCE dechlorinating reductive dehalogenases (RDases) in in vitro tests under high salinity suggests that high salinity likely disrupted cellular components other than RDases in Dehalococcoides. Genomic analyses indicated that the capability of Dehalobium to perform dehalogenation under high salinity was likely owing to the presence of genes associated with halotolerance in its genomes. Collectively, these mechanistic and ecological insights contribute to understanding the fate and bioremediation of organohalide pollutants in environments with changing salinity.

A review of anammox metabolic response to environmental factors: Characteristics and mechanisms

Anaerobic ammonium oxidation (anammox) is a promising low carbon and economic biological nitrogen removal technology. Considering the anammox technology has been easily restricted by environmental factors in practical engineering applications, therefore, it is necessary to understand the metabolic response characteristics of anammox bacteria to different environmental factors, and then guide the application of the anammox process. This review presented the latest advances of the research progress of the effects of different environmental factors on the metabolic pathway of anammox bacteria. The effects as well as mechanisms of conventional environmental factors and emerging pollutants on the anammox metabolic processes were summarized. Also, the role of quorum sensing (QS) mediating the bacteria growth, gene expression and other metabolic process in the anammox system were also reviewed. Finally, interaction and cross-feeding mechanisms of microbial communities in the anammox system were discussed. This review systematically summarized the variations of metabolic mechanism response to the external environment and cross-feeding interactions in the anammox process, which would provide an in-depth understanding for the anammox metabolic process and a comprehensive guidance for future anammox-related metabolic studies and engineering applications.

Impact of N-butyryl-l-homoserine lactone-mediated quorum sensing on acidogenic fermentation under saline conditions: Insights into volatile fatty acids production and microbial community

Anaerobic fermentation is often inhibited under high salinity conditions. This study discovered a strong, positive association between N-butyryl-l-homoserine lactone (C4-HSL)-mediated quorum sensing (QS) and the production of volatile fatty acids (VFAs) under saline conditions. N-acyl-homoserine lactones were identified during acidogenic fermentation for VFA production. Only C4-HSL was detected at all salt concentrations, and a maximum C4-HSL concentration of 0.49 μg/L was observed at a salt concentration of 15 g/L. C4-HSL secretion was closely related to salinity, and a strong correlation was observed between C4-HSL and VFAs (p < 0.01), especially butyrate. Further experiments with C4-HSL addition indicated that exogenous C4-HSL promoted substrate hydrolysis and increased butyrate production by 1.5 times at 15 g/L NaCl. Microbial community analysis indicated that unclassified_f__Enterobacteriaceae and Clostridium_sensu_stricto_1, associated with QS genes and butyrate production, were positively associated with C4-HSL. This study demonstrates the positive effect of C4-HSL-mediated QS on acidogenic fermentation.

Anammox process for aquaculture wastewater treatment: operational condition, mechanism, and future prospective

Treatment of ammonia- and nitrate-rich wastewater, such as that generated in the aquaculture industry, is important to prevent environmental pollution. The anaerobic ammonium oxidation (anammox) process has been reported as a great alternative in reducing ammoniacal nitrogen concentration in aquaculture wastewater treatment compared to conventional treatment systems. This paper will highlight the impact of the anammox process on aquaculture wastewater, particularly in the regulation of ammonia and nitrogen compounds. The state of the art for anammox treatment systems is discussed in comparison to other available treatment methods. While the anammox process is viable for the treatment of aquaculture wastewater, the efficiency of nitrogen removal could be further improved through the proper use of anammox bacteria, operating conditions, and microbial diversity. In conclusion, a new model of the anammox process is proposed in this review.

Saline short-term shock and rapid recovery on anammox performance

Anaerobic ammonia oxidation (anammox) is an environmental-friendly biological nitrogen removal process, which has been developed as a promising technology in industrial wastewater treatment. However, anammox nitrogen removal under high saline conditions still faces many challenges. This study investigated the performance of anammox sludge under saline short-term shock and the strategy of rapid recovery. Salinity concentration, saline exposure time, and NaCl/Na₂SO₄ ratio were selected as three critical factors for short-term shock. The activity inhibition of anammox sludge were tested by using response surface methodology (RSM). Our results showed that, compared with the NaCl/Na₂SO₄ ratio, the salinity concentration and saline exposure time were the significant factor causing the anammox inhibition. The addition of glycine betaine (GB) in moderate amounts (0.1-5 mM) was found to help anammox to resist in relative low saline shock intensities (e.g., IC₂₅ and IC₅₀), with the activity retention rate of 94.7%. However, glycine betaine was not worked effectively under relatively high saline shock intensities (e.g., complete inhibition condition). Microbial community analysis revealed that Brocadiaceae accounted for only about 7.6%-13.2% at inhibited conditions. Interestingly, 16S rRNA analysis showed that the abundance of activated Brocadiaceae remarkably decreased with time after high-level saline shock. This tendency was consistent with the results of qPCR targeted hzsA gene. Finally, based on quorum sensing, the anammox activity was recovered to 93.5% of original sludge by adding 30% original sludge. The study realized the rapid recovery of anammox activity under complete inhibition, promoting the development and operation of salt-tolerant anammox process.

Co-metabolic biodegradation of structurally discrepant dyestuffs by Klebsiella sp. KL-1: A molecular mechanism with regards to the differential responsiveness

In this study, an attempt was made to decipher the underlying differential response mechanism of Klebsiella sp. KL-1 induced by exposure to disparate categories of dyestuffs in xylose (Xyl) co-metabolic system. Here, representative reactive black 5 (RB5), remazol brilliant blue R (RBBR) and malachite green (MG) belonging to the azo, anthraquinone and triphenylmethane categories were employed as three model dyestuffs. Klebsiella sp. KL-1 enabled nearly 98%, 80% or 97% removal of contaminants in assays Xyl + RB5, Xyl + RBBR or Xyl + MG after 48 h, which was respectively 16%, 11% or 22% higher than those in the assays devoid of xylose. LC-QTOF-MS revealed an increased formation of smaller molecular weight intermediates in assay Xyl + RB5, whereas more metabolic pathways were deduced in assay Xyl + RBBR. Metaproteomics analysis displayed remarkable proteome alteration with regards to the structural difference effect of dyestuffs by Klebsiella sp. KL-1. Significant (p-value<0.05) activation of pivotal candidate NADH-quinone oxidoreductase occurred after 48 h of disparate dyestuff exposure but with varying abundance. Dominant FMN-dependent NADH-azoreductase, Cytochrome d terminal oxidase or Thiol peroxidase were likewise deemed to be responsible for the catalytic cleavage of RB5, RBBR or MG, respectively. Further, the differential response mechanism towards the structurally discrepant dyestuffs was put forward. Elevated reducing force associated with the corresponding functional proteins/enzymes was transferred to the exterior of the cell to differentially decompose the target contaminants. Overall, this study was dedicated to provide in-depth insights into the molecular response mechanism of co-metabolic degradation of refractory and structurally discrepant dyestuffs by an indigenous isolated Klebsiella strain.

Glutamate Enhances Osmoadaptation of Anammox Bacteria under High Salinity: Genomic Analysis and Experimental Evidence

An osmoprotectant that alleviates the bacterial osmotic stress can improve the bioreactor treatment of saline wastewater. However, proposed candidates are expensive, and osmoprotectants of anammox bacteria and their ecophysiological roles are not fully understood. In this study, a comparative analysis of 34 high-quality public metagenome-assembled genomes from anammox bacteria revealed two distinct groups of osmoadaptation. Candidatus Scalindua and Kuenenia share a close phylogenomic relation and osmoadaptation gene profile and have pathways for glutamate transport and metabolisms for enhanced osmoadaptation. The batch assay results demonstrated that the reduced Ca. Kuenenia activity in saline conditions was substantially alleviated with the addition and subsequent synergistic effects of potassium and glutamate. The operational test of two reactors demonstrated that the reduced anammox performance under brine conditions rapidly recovered by 35.7-43.1% as a result of glutamate treatment. The Ca. Kuenenia 16S rRNA and hydrazine gene expressions were upregulated significantly (p < 0.05), and the abundance increased by approximately 19.9%, with a decrease in dominant heterotrophs. These data demonstrated the effectiveness of glutamate in alleviating the osmotic stress of Ca. Kuenenia. This study provides genomic insight into group-specific osmoadaptation of anammox bacteria and can facilitate the precision management of anammox reactors under high salinity.

Nitrogen Removal from Mature Landfill Leachate via Anammox Based Processes: A Review

Mature landfill leachate is a complex and highly polluted effluent with a large amount of ammonia nitrogen, toxic components and low biodegradability. Its COD/N and BOD5/COD ratios are low, which is not suitable for traditional nitrification and denitrification processes. Anaerobic ammonia oxidation (anammox) is an innovative biological denitrification process, relying on anammox bacteria to form stable biofilms or granules. It has been extensively used in nitrogen removal of mature landfill leachate due to its high efficiency, low cost and sludge yield. This paper reviewed recent advances of anammox based processes for mature landfill leachate treatment. The state of the art anammox process for mature landfill leachate is systematically described, mainly including partial nitrification–anammox, partial nitrification–anammox coupled denitrification. At the same time, the microbiological analysis of the process operation was given. Anaerobic ammonium oxidation (anammox) has the merit of saving the carbon source and aeration energy, while its practical application is mainly limited by an unstable influent condition, operational control and seasonal temperature variation. To improve process efficiency, it is suggested to develop some novel denitrification processes coupled with anammox to reduce the inhibition of anammox bacteria by mature landfill leachate, and to find cheap new carbon sources (methane, waste fruits) to improve the biological denitrification efficiency of the anammox system.

Adaptation and evolution of freshwater Anammox communities treating saline/brackish wastewater

The most common way to apply Anammox for saline wastewater treatment is via salt adaptation of freshwater Anammox bacteria (FAB). To better apply this process in practice, it's essential to understand the salt adaptation process of FBA, as well as the underlying mechanisms. This study investigated the long-term salt adaptation process of a fixed-film FAB culture in three reactors (namely R1-R3), under salinities of 2, 8, and 12 NaCl g/L, correspondingly. All three reactors were under stable operation and achieved 80-90% total inorganic nitrogen removal efficiency throughout the 425-day operation period. R1 servers as a blank control, based on the clear microbial community shifts in R2 and R3, the operation period was divided into 2 phases. During Phase 1, all FAB in the three reactors belonged to Ca. Brocadia sp.. The Anammox activity (AA) and the ratio of nitrite/ammonium (NO₂^--N/NH₄⁺-N) consumption in R2 and R3 decreased with the increase of salinity and did not recover to the initial levels. During Phase 2, the relative abundance of Ca. Kuenenia sp. in R2 and R3 increased from nearly 0 to about 60 and 77%, respectively. With the growth of Ca. Kuenenia sp., the AA and stoichiometry of R2 and R3 gradually recovered. AA of R2 and R3 both reached 1.0 g NH₄⁺-N/L/day at the end of this phase, which was about 80% of that in R1. These results indicated that the salt adaptation of FAB culture was achieved by species shift from a low salt-tolerance one to a high salt-tolerance one.

The application of glycine betaine to alleviate the inhibitory effect of salinity on one-stage partial nitritation/anammox process

One-stage partial nitritation/anammox (PN/A) has been proposed as a sustainable method for removing nitrogen from various wastewater. However, the activities of ammonium-oxidizing bacteria (AOB) and anammox bacteria are often inhibited by the exposure to salinity, thereby hindering their wide application in treating industrial wastewater with high salinity. This study reports that the addition of glycine betaine (GB), which is a compatible solute, could alleviate the inhibitory effects of salinity on both AOB and anammox, thereby improving nitrogen removal performance in a one-stage PN/A system. Short-term tests showed that with an addition of GB higher than 1 mM, the activity of AOB and anammox under salinity of 30 g/L could be increased by at least 45% and 51%, respectively. The half-inhibitory concentration of AOB and anammox rose with increasing GB concentration, with 1 mM GB being the optimal cost-effective dosage. Long-term experiments also demonstrated that 1 mM GB addition could enhance nitrogen removal performance and shorten recovery time by 42.9% under a salinity stress of 30 g/L. Collectively, GB addition was found to be a feasible and effective strategy to the counteract adverse effects of salinity on PN/A process. PRACTITIONER POINTS: Glycine betaine (GB) could improving performance of the PN/A process by alleviating the inhibitory effects of salinity on both AOB and anammox bacteria. A GB concentration of 1 mM was found to be optimum in terms of effectiveness and cost. GB addition was a feasible and effective strategy to remain stabilized in the community structure of PN/A sludge. GB could optimize the nitrogen removal performance and shorten the recovery time of PN/A process under saline stress.

Modeling of completely autotrophic nitrogen removal process with salt and glycine betaine addition

The susceptibility of the completely autotrophic nitrogen removal over nitrite (CANON) process to high salinity limits its widespread application. The addition of glycine betaine (GB), a type of compatible solutes that could resist osmotic stress, could be an effective strategy to enhance the salt tolerance ability of aerobic and anaerobic ammonium oxidizing bacteria (AOB and anammox bacteria) involved in the CANON process. This study aims to make use of mathematical modeling to systematically investigate the effects of salt and GB addition on the activities of AOB and anammox bacteria and the treatment performance of the CANON process. To this end, a series of dedicated batch tests and long-term experiments for the CANON process with salt and GB additions were conducted and the data was used to calibrate and validate the model established to consider the relationships between salt and GB concentrations and bacterial growth in the CANON process. The calibrated/validated CANON process model was then applied to simulate the long-term impacts of GB addition concentration and sludge retention time (SRT) on the CANON process. The results showed that 1 mM GB addition and a SRT of 50 days would be sufficient to protect AOB and anammox bacteria under the high salinity (30 g/L NaCl) conditions studied and therefore reduce the time needed to recover the treatment performance of the CANON process from exposure to salt inhibition by 35%-40%.

Correlation of microbial community with salinity and nitrogen removal in an anammox-based denitrification system

Anaerobic ammonium oxidation (anammox), a low-energy-consuming technology, can be used to remove nitrogen from industrial saline wastewater. However, high salinity inhibits anammox microbial activity. This study investigated the effect of salinity on nitrogen removal performance and microbial community structure. The experiment used an up-flow anammox reactor fed with synthetic wastewater with salinity increased from 0.5 to 2.5%. Results indicated that 80% nitrogen removal efficiency can be achieved at 2% salinity with a nitrogen loading rate of 2.0 kg-N/m³/d. Anammox performance significantly deteriorated at 2.5% salinity. High-throughput sequencing revealed that Planctomycetes (representative anammox bacteria) increased with salinity, replacing Proteobacteria (representative heterotrophic denitrifying bacteria) in the microbial community. qPCR analysis indicated that relative abundance of "Candidatus Kuenenia" within anammox bacteria increased from 3.96 to 83.41%, corresponding to salinity of 0.5-2.0%, and subsequently decreased to 63.27% at 2.5% salinity, correlating with nitrogen-removal performance. Thus, anammox has potential in nitrogen removal from wastewater with salinity up to 2%.

Successional Dynamics of Molecular Ecological Network of Anammox Microbial Communities under Elevated Salinity

Response of microbial interactions to environmental perturbations has been a central issue in wastewater treatment system. However, the interactions among anammox microbial community under salt perturbation is still unclear. Here, we used random matrix theory (RMT)-based network analysis to investigate the dynamics of networks under elevated salinity in an anammox system. Results showed that high salinity (20 and 30 g/L NaCl) inhibited anammox performance. Salinity led to closer and more complex networks for the overall network and subnetwork of Planctomycetes and Proteobacteria, especially under low salinity (5 g/L NaCl), which could serve as a strategy to survive under salt perturbation. Planctomycetes, most dominant phylum and playing crucial roles in anammox, possessed higher proportion of competitive relationships (64.3%) under 30 g/L NaCl. OTU 109 (closely related to Ignavibacterium), the only network hub detected in the anammox system, also had larger amount of competitive relationships (27.3%) than the control (0%) under 30 g/L NaCl. Similar result was found for the most abundant keystone bacteria Candidatus Kuenenia. These increasing competitions at different taxa level could be responsible for the deterioration of nitrogen removal. Besides, all the network topological features tended to reach the values of the original network, which showed the network of microbial community could gradually adapt to the elevated salinity. Microbial network analysis adds a different dimension for our understanding of the response in microbial community to elevated salinity.

Probing the dynamics of three freshwater Anammox genera at different salinity levels in a partial nitritation and Anammox sequencing batch reactor treating landfill leachate

Partial nitritation/Anammox was applied to treat NaCl-amended landfill leachate. The reactor established robust nitrogen removal of 85.7 ± 2.4% with incremental salinity from 0.61% to 3.10% and achieved 0.91-1.05 kg N/m³/d at salinity of 2.96%-3.10%. Microbial community analysis revealed Nitrosomonas, Nitrospira, and denitrifiers occupied 4.1%, <0.2% and 10.9%, respectively. Salinity variations impelled the dynamics of Anammox bacteria. Jettenia shifted to Brocadia and Kuenenia at salinity of 0.61%-0.81%. Kuenenia outcompeted Brocadia and occupied 51.5% and 50.9% at salinity of 1.48%-1.54% and 2.96%-3.10%, respectively. High nitrite affinity and fast growth rate were proposed as key factors fostering Brocadia overgrew Jettenia. Functionalities of sodium-motive-force facilitated energy generation and intracellular osmotic pressure equilibrium regulation crucially determined Kuenenia's dominance at elevated salinity. Co-occurrence network further manifested beneficial symbiotic relationships boosted Kuenenia's preponderance. Knowledge gleaned deepen understanding on survival niches of freshwater Anammox genera at saline environments and lead to immediate benefits to its applications treating relevant wastewaters.

The effect of sulfate on nitrite-denitrifying anaerobic methane oxidation (nitrite-DAMO) process

Sulfate is generally found in natural water and wastewater. Nitrite-DAMO bacteria live in natural water or wastewater containing different sulfates. To determine the effect of sulfate on the nitrite-DAMO process, we conducted batch tests and continuous tests to investigate the performance and microbial structure of the nitrite-DAMO system at different sulfate concentrations. The results indicated that the nitrogen removal performance of the nitrite-DAMO system was initially promoted and then inhibited at 0-200 mg SO₄^2-/L, and the denitrification rate was highest at 80 mg SO₄^2-/L which was 1.26 mgN/(L·d). When stimulated by sulfate, protein stabilized nitrite-DAMO bacteria. The denitrification kinetics conformed to the Edward equation, and the initial inhibitory concentration of the nitrite-DAMO system was 189.70 mg SO₄^2-/L. Changes in the proportion of unclassfied_c_ABY1 of the phylum Patescibacteria and norank_f_LD-RB-34 of the phylum Bacteroidetes were the main factors influencing how the nitrogen removal rate of the nitrite-DAMO system responded to sulfate.

Biphasic effect of nitrate on anaerobic ammonium oxidation (anammox) and related kinetic modeling

Nitrate is a byproduct of the anaerobic ammonium oxidation (anammox) process and is related to its electron transfer. However, little is known about the influence of nitrate on the anammox process. In this work, the biphasic effect of exogenous nitrate on the anammox process was investigated in an upflow biofilter (UBF) reactor with ammonium as the sole electron donor. The responses of anammox to increased nitrate were analyzed by one-way ANOVA test and found to be significantly different under a constant and decreased nitrite condition (p < 0.01). With a single increase in nitrate and constant ammonium and nitrite in the influent, the total nitrogen removal rate (TNRR) of anammox was uninhibited, but stoichiometry deviated and nitrate production always showed a linear decrease. In contrast, anammox exhibited a range of activity with constant ammonium and simultaneously increased nitrate and decreased nitrite in the influent, including a continuous reduction of TNRR, a nonpersistent ammonium overconsumption and a pronounced nonlinear response of nitrate production. Correlation analysis shows that the lack of ammonium overconsumption was accompanied by the disappearance of nitrate underproduction. Kinetic models of product formation were effectively used to explore the nitrate production behavior of anammox subjected to increased nitrate, and the metabolite of nitrate was divided into a growth negative coupling type and growth (partial) coupling type under a constant and decreased nitrite condition, respectively. These findings collectively suggest that nitrate has a biphasic effect on the anammox process and is correlated with the availability of nitrite.

Performance of Anammox Processes for Wastewater Treatment: A Critical Review on Effects of Operational Conditions and Environmental Stresses

The anaerobic ammonium oxidation (anammox) process is well-known as a low-energy consuming and eco-friendly technology for treating nitrogen-rich wastewater. Although the anammox reaction was widely investigated in terms of its application in many wastewater treatment processes, practical anammox application at the pilot and industrial scales is limited because nitrogen removal efficiency and anammox activity are dependent on many operational factors such as temperature, pH, dissolved oxygen concentration, nitrogen loading, and organic matter content. In practical application, anammox bacteria are possibly vulnerable to non-essential compounds such as sulfides, toxic metal elements, alcohols, phenols, and antibiotics that are potential inhibitors owing to the complexity of the wastewater stream. This review systematically summarizes up-to-date studies on the effect of various operational factors on nitrogen removal performance along with reactor type, mode of operation (batch or continuous), and cultured anammox bacterial species. The effect of potential anammox inhibition factors such as high nitrite concentration, high salinity, sulfides, toxic metal elements, and toxic organic compounds is listed with a thorough interpretation of the synergistic and antagonistic toxicity of these inhibitors. Finally, the strategy for optimization of anammox processes for wastewater treatment is suggested, and the importance of future studies on anammox applications is indicated.

Co-inhibition of salinity and Ni(II) in the anammox-UASB reactor

Both nickel and salinity are often detected in the environment. Especially electroplating wastewater contains some salt and nickel, which affects microbial activity in biological wastewater treatment process. In this study, the effects of sustaining addition of a high-concentration salinity and Ni(II) on the anaerobic ammonium oxidation (anammox) process were examined. The results indicated that the anammox system had an acclimation ability to <0.2 mg L^-1 Ni(II) and 20 g L^-1 NaCl. After a recovery phase of approximately 70 days, the nitrogen removal efficiency and rate reached at 77.1% and 1.18 kg N m^-3 d^-1, respectively. The three-dimensional excitation-emission matrix fluorescence and Fourier transform infrared spectra results showed that the introduction of NaCl and Ni(II) caused a substantial variation in the quantity and composition of the bound EPS in the surface of anammox granules. The present study is the first to document the long-term effect of co-existence of salinity and Ni(II) on the performance of the freshwater-derived anammox bacteria in the upflow anaerobic sludge blanket reactor and to provide a reference for the stable operation of anammox bioreactors for the treatment of sulfonamide-containing wastewater.

Changes in nitrogen removal and microbiota of anammox biofilm reactors under tetracycline stress at environmentally and industrially relevant concentrations

Anammox-related processes are often applied for the wastewater treatment which contains both ammonium and antibiotics. Herein, the long-term effects of tetracycline (TC), at environmentally and industrially relevant concentrations, on the performance, anammox activity and microbial community of anammox reactors were investigated for 518 days. The control reactor (without TC exposure) was stable for nitrogen removal during the long-term operation (a nitrogen removal rate of 0.56 ± 0.05 kg-N·m^-3·d^-1). In the TC-added reactor, the nitrogen removal efficiency increased slightly at low TC levels (1-100 μg/L), whereas poor anammox performance occurred at high TC concentration (1000 μg/L). Furthermore, the concentrations of extracellular polymeric substances (EPS) were much higher at 10 μg/L than those in the control reactor (P < 0.01), whereas rapidly decreased at 1000 μg-TC/L. Furthermore, the reactor performance was highly consistent with the variations of the heme c contents. Consistently, exposure to TC changed the abundance of anammox bacteria, e.g., an increase in Candidatus Jettenia abundance occurred from 2.20 ± 0.97% (0-10 μg/L) to 12.13 ± 1.66% (100 μg/L). Similarly, the genus Denitratisoma, the most predominant denitrification bacteria, also had a higher abundance at a TC concentration of 100 μg/L (15.60 ± 6.42%) than other TC concentrations (5.40 ± 2.50% and 7.65 ± 0.55% at concentrations of 10 and 1000 μg/L, respectively). The results can explain why the exposure of anammox bacteria to a lower TC concentration (100 μg/L) resulted in a better nitrogen removal rate. In contrast, exposure to a high TC level (1000 μg/L) led to a decline in the abundance of anammox bacteria and denitrifiers (1.53 ± 0.64% and 8.18 ± 0.63%, respectively) but an increased abundance in the nitrifier population (8.07 ± 1.21%; P < 0.01). Therefore, this study can aid in the design and operation of anammox-based processes treating sewage and industrial wastewater.

Underlying mechanisms of ANAMMOX bacteria adaptation to salinity stress

Dealing with nitrogen-rich saline wastewater produced by industries remains challenging because of the inhibition of functional microorganisms by high salinity. The underlying mechanisms of anaerobic ammonium-oxidizing bacteria (AnAOB) exposed to salinity stress should be studied to investigate the potential of anaerobic ammonium oxidation (ANAMMOX) for applications in such wastewater. In this study, the total DNA from granular sludge was extracted from an expanded granular sludge bed (EGSB) reactor operated at 0, 15 and 30 g/L salinity and subjected to high-throughput sequencing. The nitrogen removal performance in the reactor could be maintained from 86.2 to 88.0% at less than 30 g/L salinity level. The microbial diversity in the reactor under saline conditions was lower than that under the salt-free condition. Three genera of AnAOB were detected in the reactor, and Candidatus Kuenenia was the most abundant. The predictive functional profiling based on the Clusters of Orthologous Groups of proteins (COGs) database showed that the inhibition of AnAOB under saline conditions was mainly characterised by the weakening of energy metabolism and intracellular repair. AnAOB might adapt to salinity stress by increasing their rigidity and intracellular osmotic pressure. The predictive functional profiling based on the Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway database revealed that the inhibition of AnAOB was mainly manifested by the weakening of intracellular carbohydrate and lipid metabolism, the blockage of intracellular energy supply and the reduction of membrane transport capacity. AnAOB might adapt to salinity stress by strengthening wall/membrane synthesis, essential cofactors (porphyrins) and energy productivity, enhancing intracellular material transformation and gene repair and changing its structure and group behaviour. The stability of the nitrogen removal performance could be maintained via the adaptation of AnAOB to salinity and their increased abundance.

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.