Effect of different preservation conditions on the reactivation performance of anammox sludge

Effect of long-term dosage of hydrazine on mainstream anammox process: Biofilm characteristics and microbial community

The impact of the long-term trace hydrazine (N2H4) exogenous supplementation on activity of the anaerobic ammonium oxidation (anammox) biofilm was investigated in a moving bed biofilm reactor (MBBR) for mainstream wastewater treatment. The results of this study demonstrated that the addition of 2-5 mg/L N2H4 enhanced anammox biofilm activity, as evidenced by the augmented nitrogen removal rate (NRR), which increased from 113.4 g/(m3·d) to 126.7 g/(m3·d) with the introduction of 2 mg/L N2H4. However, a higher concentration of N2H4 (10 mg/L) suppressed anammox activity, leading to a reduced NRR of 91.5 g/(m3·d). Bioindicators revealed that the long-term addition of 2 mg/L N2H4 fostered the accumulation of anammox bacteria (AnAOB) biomass, elevating the volatile suspended solids (VSS) content by 12%. Moreover, the structural composition of extracellular polymeric substances (EPS) within the biofilm was altered, resulting in enhanced biofilm strength within the reactor. The protective mechanism of the biofilm was activated, and EPS secretion was stimulated by the continuous N2H4 supplementation. The introduction of an excess dosage of N2H4 led to alterations in the microbial communities, ultimately resulting in a decline in the performance of the reactor. These findings collectively illustrate that N2H4, as an intermediate product, can effectively enhance anammox activity within the MBBR for mainstream wastewater treatment. This study contributes to the understanding of the optimization strategies for anammox processes in wastewater treatment systems.

Efficient nitrogen removal and substrate usage in integrated fixed-film activated sludge-anammox system under seasonal temperature variation

To elucidate how integrated fixed-film activated sludge (IFAS) system favors nitrogen removal performance under seasonal temperature variations, two push-flow reactors were operated with and without carriers under the same operating conditions. The results show that the IFAS system had significant advantages in shock response and low temperature adaptation, with a nitrogen removal rate of 0.37-0.53 kg-N(m3·d)-1 at the temperature of 8-12 °C. Anammox bacteria on carriers were almost unaffected by temperature variation, and its nitrogen removal contribution rate stabilized at 55 % in the IFAS system. The Haldane model reveals that the specific anammox activity in the IFAS system was 28 % to 49 % higher than that in the control system at 13 °C. Candidatus_Jettenia, with the highest abundance of 45 %, was the dominant species in the IFAS system and preferred to attach to the carriers. This study provides a feasible scheme for the application of anammox process.

Evaluation the role of soluble microbial products for denitrification sludge characteristic under starvation stress

Physiological changes with the assist role of soluble microbial products (SMP) of preserved denitrifying sludge (DS) undergoing long-term stress of starvation under different storage temperature is extremely important. In this study, SMP extracted from DS were added into DS in starvation condition under room temperature (15-20 °C), 4 °C and -20 °C with three different bio-augmentation phases of 10, 15 and 30 days. Experimental results showed that added SMP in room temperature was optimal for preservation of DS under starvation stress with optimized dosage of 2.0 mL mL^-1 sludge and bio-augmentation phase of 10 d. SMP was more effective in maintaining the specific denitrification activity of DS, and it was nearly boosted to 94.1 % of control one due to assist of 2 times SMP addition with 10 days interval of each. Under assist of SMP, extracellular polymeric substances (EPS) secretion was enhanced as the defense layer to withstand starvation stress, and the protein may be utilized as an alternative substrate to gain energy, accelerate electron transport and transfer during denitrification process. This investigation revealed the feasibility of SMP as an economical and robust strategy for preservation of DS.

Gel-immobilized partial nitritation/anammox achieves reliable nitrogen removal at different concentrations of nitrogen and reactivation processes

A two-stage partial nitritation/anammox process based on microbial encapsulation (PN/A-E) was established. The nitrogen removal characteristics of PN/A-E under high and low ammonia nitrogen and after reactivation following a long-term shutdown were comprehensively investigated and compared with anammox granular sludge (AnGS). The stable PN process did not depend on high ammonia nitrogen, and the nitrite accumulation rate reached 95.2 ± 0.7 %. The overall nitrogen removal rate of encapsulated anammox bacteria was twice that of the AnGS, and it was more tolerant to external interference. Moreover, PN/A-E showed good reactivation performance, and the total nitrogen in the effluent was 10.0 ± 1.4 mg·L^-1 when the final hydraulic retention time was 2.18 h. The immobilized fillers support an increase in ammonia-oxidizing bacteria under restricted conditions and were more conducive to the dominance of functional bacteria and the stability of microbial community under low ammonia nitrogen. This study provides a positive method to achieve a reliable PN/A.

A critical review of exogenous additives for improving the anammox process

Anammox achieves chemoautotrophic nitrogen removal under anaerobic and anoxic conditions and is a low-carbon wastewater biological nitrogen removal process with broad application potential. However, the physiological limitations of AnAOB often cause problems in engineering applications, such as a long start-up time, unstable operation, easily inhibited reactions, and difficulty in long-term strain preservation. Exogenous additives have been considered an alternative strategy to address these issues by retaining microbes, shortening the doubling time of AnAOB and improving functional enzyme activity. This paper reviews the role of carriers, biochar, intermediates, metal ions, reaction substrates, redox buffers, cryoprotectants and organics in optimizing anammox. The pathways and mechanisms of exogenous additives, which are explored to solve problems, are systematically summarized and analyzed in this article according to operational performance, functional enzyme activity, and microbial abundance to provide helpful information for the engineering application of anammox.

Evaluation of long-term preservation and reactivation efficiency of anaerobic ammonium oxidation (anammox) microorganisms based on activation energy

The preservation efficiency of mainstream (M-ANA) and sidestream anaerobic ammonium oxidation (anammox) (S-ANA) were evaluated based on their activation energy (E_a). The E_a of M-ANA cultivated under low nitrogen loads was lower than that of S-ANA, which greatly contributed to enhancing the viability of anammox during preservation at 4 °C. After preservation for 140 d, the decay rate (b_AN) of M-ANA ranged from 0.0012 to 0.0013/d; the b_AN of S-ANA was 0.0036-0.0041/d. The addition of hydrazine, which requires minimal energy to activate anammox metabolism, is highly beneficial for the viability of microorganisms. The low E_a of anammox contributes to efficient reactivation with rapid reactivation of heme c, and the addition of hydrazine makes the process more beneficial. Although the specific nitrogen removal rate of the M-SNA seed sludge was much lower than that of S-ANA, the rate of M-ANA became higher after 48 days of reactivation.

Analyzing the effect of storage conditions on anammox recovery performance from the perspectives of time, temperature and biomass form

In this study, the effects of different storage conditions, such as temperature, storage time and biomass form, on the properties of anaerobic ammonia oxidation (anammox) were investigated along with the identification of the process mechanism. The results showed that the influence of storage time on anammox properties was stronger than that of storage temperature and biomass form. Also, the anammox recovery activity at 15 °C was better than that at 4 °C, and the anammox recovery activity of immobilized filler was better than that of anammox granular sludge (AnGS). Although cryogenic storage severely damaged anammox activity, lower loss of extracellular polymeric substances maintained the AnGS structure. The maximum recovery of specific anammox activity at 15 °C for the immobilized filler was observed to be 109%. In addition, intermittent substrate supplementation weakened the adverse effect of long-term storage on anammox activity, and was conducive to maintaining stable flora composition and promoting regeneration of anammox bacteria (AnAOB). High-throughput sequencing analysis showed that starvation resulted in increased community diversity, and the functional bacteria Candidatus Brocadia was observed to be more tolerant to starvation than Candidatus Kuenenia. Finally, principal component analysis was used to explain the complex relationship between process performance and preservation conditions. Based on the results of this work, it is recommended to preserve AnAOB in the form of immobilized filler at 15 °C and supplement substrate intermittently during long term storage. This study provides an economical and robust strategy for the short-term and long-term preservation of AnAOB.

Anammox sludge preservation: Preservative agents, temperature and substrate

The difficulties of enrichment and preservation of anaerobic ammonium oxidation bacteria (AnAOB) greatly limit their application in practice. Herein, traditional and emerging preservative agents (e.g., EPS + N2H4, betaine, glycerol and trehalose) were evaluated for their preservation of AnAOB-dominant sludge at different temperatures (e.g., 4 °C and room temperature). In addition, the effects of substrates on preservation were also considered. The results showed that adding betaine or glycerol at 4 °C was the optimal strategy for preserving anammox granular sludge. The relative anammox activities (rAA) increased by 145.26% and 158.30% at the recovery phase, respectively. Moreover, the absolute abundances of functional gene hzsA increased by 339% and 46%, respectively. Although the granular properties and microbial community structures changed during the preservation, the general performance of anammox granules could effectively restored. Collectively, this study provides the optimal strategies for anammox sludge preservation at low temperatures.

New Insight Into the Interspecies Shift of Anammox Bacteria Ca. "Brocadia" and Ca. "Jettenia" in Reactors Fed With Formate and Folate

The sensitivity of anaerobic ammonium-oxidizing (anammox) bacteria to environmental fluctuations is a frequent cause of reactor malfunctions. It was hypothesized that the addition of formate and folate would have a stimulating effect on anammox bacteria, which in turn would lead to the stability of the anammox process under conditions of a sharp increase in ammonium load, i.e., it helps overcome a stress factor. The effect of formate and folate was investigated using a setup consisting of three parallel sequencing batch reactors equipped with a carrier. Two runs of the reactors were performed. The composition of the microbial community was studied by the 16S rRNA gene profiling and metagenomic analysis. Among anammox bacteria, Ca. "Brocadia" spp. dominated during the first run. A stimulatory effect of folate on the daily nitrogen removal rate (dN) was identified. The addition of formate led to progress in dissimilatory nitrate reduction and stimulated the growth of Ca. "Jettenia" spp. The spatial separation of two anammox species was observed in the formate reactor: Ca. "Brocadia" occupied the carrier and Ca. "Jettenia"-the walls of the reactors. Biomass storage at low temperature without feeding led to an interspecies shift in anammox bacteria in favor of Ca. "Jettenia." During the second run, a domination of Ca. "Jettenia" spp. was recorded along with a stimulating effect of formate, and there was no effect of folate on dN. A comparative genome analysis revealed the patterns suggesting different strategies used by Ca. "Brocadia" and Ca. "Jettenia" spp. to cope with environmental changes.

Achieving rapid mainstream deammonification through inoculating long-term refrigerated sidestream sludge in plug-flow fixed-bed biofilm reactor

The start-up of a stable mainstream deammonification requires sufficient anaerobic ammonia-oxidizing bacteria (AnAOB). This study used a plug-flow fixed-bed reactor (PFBR) to verify the feasibility of establishing the mainstream deammonification system by inoculating the sidestream sludge after long-term refrigeration. A rapid resuscitation of the mainstream deammonification system was accomplished by controlling the front-end aeration rate of the PFBR. Results showed that the system was rapidly resuscitated in 44 days eventually with the nitrogen removal rate and nitrogen removal efficiency of 0.1 kg N·(m³·d)^-1 and 79.1%, respectively. Also, the efficient performance was secured by the proportionate approaching equilibrium of AnAOB and ammonia-oxidizing bacteria (AOB) activity of 2.35 ± 0.40 and 2.60 ± 0.29 mg N·(g VSS·h)^-1, respectively. In addition, Pearson correlation analysis revealed that AnAOB abundance (detected Candidatus Kuenenia) negatively correlated with the AOB (mainly Nitrosomonas)/AnAOB abundance ratio, while correlated positively with the residual ammonium concentration of a region. Furthermore, long-term refrigeration probably reduced the cross-feed relationship between AnAOB and other symbiotic organisms (Armatimonadetes and Chloroflexi) to maintain the basic metabolism. Meanwhile, extracellular polymeric substances produced by other genera (order Xanthomonadales and Pseudomonadales) decreased the mass transfer, protecting AnAOB from unfavorable conditions, thereby facilitating high AnAOB abundance during refrigeration. Thus, this study provides a promising perspective towards the practical applications of mainstream process.

Effect of temperature decrease on anammox granular sludge: Shock and adaptation

Cryopreservation is one of the effective methods for the preservation of anammox granular sludge (AnGS). However, the effects of cooling pretreatment on AnGS are still unclear. In this study, the effects of temperature decrease on AnGS property were investigated by designing different cooling modes: constant at room temperature 20-25 °C (CK), sharp cooling to 4 °C (S4), -20 °C (S20) and stepwise cooling to 4 °C (A4), -20 °C (A20). The results showed that compared with CK, the cooling modes in S4, S20, A4 and A20 improved the physical preservability of AnGS, slowing down the changes of color, shape and structure; and elevated the preservation rate of functional bacteria Planctomycetes (phylum level) and Candidatus Brocadia (genus level). The preservation rate of live cells in different experimental groups was 48.4 ± 1.8%(CK), 61.1 ± 3.3%(S4), 37.8 ± 0.8%(S20), 81.7 ± 4.8%(A4), 61.9 ± 3.1%(A20), respectively. The Anaerobic Ammonium Oxidation Bacteria (AnAOB) in the stepwise cooling mode (A4 and A20) were found to enter the dormant state and form "dormant zoogloea", while the AnAOB in the sharp cooling mode (S4 and S20) were observed to enter the shock state with a little change. The findings in this work (especially the dormant state of AnAOB) are helpful to understand the effect of temperature decrease on AnGS and to promote the development of AnGS preservation technology.

Exogenous extracellular polymeric substances as protective agents for the preservation of anammox granules

The preservation of anammox granules is of great significance for the rapid start-up of the anammox process and improvement of performance stability. Therefore, it is necessary to explore an economical and stable preservation strategy. Exogenous extracellular polymeric substances (EPS) were used as protective agents for the preservation of anammox granules in this study. In brief, EPS from anammox sludge (A-EPS) and denitrifying sludge (D-EPS) were added to preserve anammox sludge at 4 °C and room temperature (15-20 °C). The results showed that A-EPS addition at 4 °C was the optimal condition for the preservation of anammox granules. After 90 days of preservation, the specific anammox activity (SAA) of the anammox granules remained at 92.7 ± 2.2 mg N g^-1 VSS day^-1 (remaining ratio of 33.4%), while that of the sludge with D-EPS addition at the same temperature was only 77.1 ± 3.2 mg N g^-1 VSS day^-1 (remaining ratio of 27.8%). The nitrogen removal efficiency of the experimental group with D-EPS at room temperature was 85.9%, and that of the A-EPS group reached 90.6% under the same temperature conditions. The abundance of the functional genes hzsA, hdh and nirS of the sludge (4 °C; A-EPS addition) after recovery were 138.5%, 317.1%, and 375.9%, respectively, of those of sludge from the D-EPS-added group at the same temperature. RDA revealed the contribution of proteins to the preservation process. Overall, this study provides an economical and robust strategy for the preservation of anammox granules.

Genome-based analysis to understanding rapid resuscitation of cryopreserved anammox consortia via sequential supernatant addition

Simple cryopreservation of anaerobic ammonium-oxidation (anammox) consortia has become a promising preservation technology for the fast start-up of the anammox process. Here, we use genome-resolved metagenomics and metatranscriptomics to understand of the microbial interaction in a simple and effective resuscitation process for long-term cryopreserved anammox consortia by sequential addition of anammox SBR supernatant. Performance results showed that sequential addition of anammox supernatant significantly reduced the resuscitation time of the granule-based anammox process from 40 to 20 days. Genome-centric metagenomics were used to recover 19 high-quality draft genomes of anammox and heterotrophic bacteria. Comparative metatranscriptomic analysis was conducted to examine the gene expression of Candidatus Kuenenia stuttgartiensis, the dominant anammox bacterium, and heterotrophic bacteria to better understand their potential interactions. Proteobacteria-affiliated bacteria found in the supernatant were highly active in producing the secondary metabolites molybdopterin cofactor and folate which are needed for growth of the auxotrophic anammox bacteria. In addition, the significantly higher expression levels of hzsA and CO₂-fixtion genes in the Candidatus Kuenenia genome indicated the anammox bacteria were likely more active and growing faster after sequential anammox supernatant addition during the resuscitation process. The resuscitation treatment pulse assays confirmed that sequential addition of supernatant was an effective way for the rapid resuscitation of anammox consortia. Our findings offer the first evidence of cross-feeding during the rapid resuscitation of cryopreserved anammox consortia.

Comparison of Preservation Methods of Staphylococcus aureus and Escherichia coli Bacteria

One of the most important problems faced by microbiologists is to preserve bacterial isolates in the best state to study and further diagnosis. The current study aims to provide a summary of experimental results to maintain two species of bacteria alive after being stored by using some additives. This study found that the best temperature to preserve Staphylococcus aureus was -20°C for a year, while for Escherichia coli it was the same temperature except in using Glycerol (G) 100% and Food oil (FO) methods. The optimum method to preserve S. aureus was by using Normal Saline (NS), while Distilled Water (DW) was the optimum method to preserve E. coli at temperatures (4, 25 and -20)°C for a year, the phenotypic patterns for examining bacteria were maintained except in NS at 4°C for S. aureus after a year ago. Glycerol was used alone at concentrations (100, 50, 30 and 15)%, and another group used G+NS in the same volumes, good results were achieved when it used alone or with NS to preserve bacteria for six months at 4°C except for methods of G100% and (G100% + NS) for examining bacteria. FO has never been used as preservation liquid, it is successful to survive S. aureus at -20°C for a year, and when it was added to NS, E. coli survived for a year at three temperatures (4, 25 and -20)°C, while S. aureus didn’t survive for a year when FO+NS method used at room temperature. The precipitation method was used for bacterial suspension, then added the preserving liquid, but the results were not effective compared to the First method.

A novel strategy for anammox consortia preservation: Transformation into anoxic sulfide oxidation consortia

The preservation of anaerobic ammonia oxidation (anammox) consortia is crucial for the rapid start-up and the process stability of the anammox based bioreactor. This work proposed and evaluated the feasibility of an anammox consortia preservation strategy, in which the anammox sludge was transformed into intermediate anoxic sulfide oxidation (ASO) functional microorganisms. Initially, the ASO process was successfully started up by inoculating anammox sludge and the overall sulfide and nitrate removal rates stabilized at 57.5 ± 0.22 and 10.0 ± 0.18 kg m^-3 day^-1, respectively. Then, the bioreactor function was reversely transformed into anammox, whose nitrogen removal rate reached 1.68 kg m^-3 day^-1. Granule characteristics analysis revealed that both biomass and extracellular polymeric substance content returned to their original states after the reverse start-up. Although the population of Candidatus_Kuenenia was greatly declined during ASO process, its richness was successfully recovered after the reverse start-up of the anammox process. The inferred metagenomes analysis demonstrated that the shifts in functional microorganisms were related to variation in the main metabolic pathways. The specific activities of anammox and ASO both are regarded as key indicators for the successful start-up of bioreactor. This work revealed a novel technique for the preservation of anammox consortia and might be a potential strategy for overcoming the drawback of long start-up time.

A novel anammox reactor with a nitrogen gas circulation: performance, granule size, activity, and microbial community

Anammox process was regarded to be one of the vital links to achieve energy-saving or energy-producing wastewater treatment plant. In the study, an anammox reactor with the nitrogen gas circulation was constructed to culture anammox granules, and the performance, granule size distribution, and microbial community were investigated. Dissolved oxygen loading is found to be an important factor for the start-up of the anammox process, and the nitrogen removal rate of 2.12 kg N m^-3 day^-1 was achieved under the average nitrogen loading rate of 2.6 kg N m^-3 day^-1. The activity test showed that the highest specific anammox activity of 345.9 mg N gVSS^-1 day^-1 was achieved for granules with size of 0.5-1.0 mm. The Illumina high-throughput sequencing analysis revealed the consistent variation of Candidatus Brocadia and Denitratisoma abundance in granues of all sizes, suggesting possible synergistic mechanism between heterotrophic bacteria Denitratisoma and anammox bacteria Ca. Brocadia. Furthermore, the results indicated the reactor with the nitrogen gas circulation is an efficient strategy to start-up anammox.

Effects of biomass and environmental factors on nitrogen removal performance and community structure of an anammox immobilized filler

In order to reduce the loss of anaerobic ammonia oxidation (anammox) sludge and stabilize the reaction microenvironment, polyvinyl alcohol - polypropylene (PVA-PP) was used to encapsulate anammox bacteria on a filler. The influence of different inoculation amounts (2, 4, 6 and 8%) on the overall nitrogen removal process was first compared and then the anammox characteristics of the immobilized filler under the influence of different environmental factors were evaluated through batch experiments. The results show that the biomass only affected the growth rate of the activity during the logarithmic phase, while the total nitrogen removal rate (NRR) tended to be similar after 99 d of culture. The NRR reached 1.83 kg·(m³·d)^-1 on day 140, which was 9.4 times that of suspended sludge before encapsulation, and the structure of embedding filler was complete without shedding. Scanning electron microscopy (SEM) showed that the internal porous network structure formed channels and a large number of anammox bacteria were observed around. Microbial community analysis of the 16S rDNA gene showed that the diversity was maintained in the entrapped carrier. Furthermore, the effective enrichment of the anammox functional bacteria Candidatus Kuenenia (AF375995.1) increarsed from 11.06% to 32.55%. The PVA-PP immobilized filler fit well with the biological nitrogen removal kinetic model and could also achieve coupling of anammox and denitrification. The inhibition effect of the organic carbon source interference and starvation on anammox bacteria was significantly weakened.

Vacuum lyophilization preservation and rejuvenation performance of anammox bacteria

The storage of anaerobic ammonia oxidizing bacteria (anammox) plays an important role in the application of anammox. Glycerol, sodium alginate and DMSO were used as the cryoprotectant, and vacuum lyophilization was used to prepare the anammox bacteria powder. Simultaneously, the control experiment was set up with the same protectant and preservation time. Bacteria powders were preserved using vacuum lyophilization and preserved at 4 °C for 60 days. During the 54 days of rejuvenation, the reactors that were inoculated with bacteria powder preserved by different methods showed significant difference. The results show that the anammox bacteria powder with 3 wt% DMSO as the cryoprotectant and without the substrate solution presented the best rejuvenation effect. The average specific anammox activity was 115.84 mg-N·(g VSS·d)^-1 with an activity recovery rate of 89%, and its stoichiometric ratio (Rs and Rp) was 1.33 and 0.21, which were very close to the theoretical values. The vacuum lyophilization method for the long-term preservation of anammox bacteria was effective.

Effect of storage conditions on maintaining anammox cell viability during starvation and recovery

Anammox bacteria can easily undergo starvation due to fluctuations in feed flowrate and concentration in wastewater treatment plants. In this study, we analyzed the effects of different types of storage conditions (presence of ammonium (R_a), nitrite (R_n), hydrazine (R_h), and no substrate (R_c)) in aiding the viability of anammox bacteria during starvation and recovery. After starvation, the bacteria were subjected to a 15-week recovery period. Anammox bacteria showed better results during starvation and recovery in R_h as compared to other conditions. Decay rate values obtained after starvation in R_a, R_n, R_h, and R_c were 0.032/day, 0.042/day, 0.019/day, and 0.037/day, respectively. Meanwhile, µ_max values obtained in R_h, R_a, R_n, and R_c on the 15th week of recovery were 0.092, 0.075, 0.011, and 0.067 d^-1, respectively. This indicated that the availability of hydrazine helps to reduce the mortality rate of anammox bacteria during starvation and enhances the recovery of anammox process.

Investigation of the process stability of different anammox configurations and assessment of the simulation validity of various anammox-based kinetic models

Over the last 30 years, the successful implementation of the anammox process has attracted research interest from all over the world. Various reactor configurations were investigated for the anammox process. However, the construction of the anammox process is a delicate topic in regards to the high sensitivity of the biological reaction. To better understand the effects of configurations on the anammox performance, process-kinetic models and activity kinetic models were critically overviewed, respectively. A significant difference in the denitrification capabilities was observed even with similar dominated functional species of anammox with different configurations. Although the kinetic analysis gained insight into the feasibility of both batch and continuous processes, most models were often applied to match the kinetic data in an unsuitable manner. The validity assessment illustrated that the Grau second-order model and Stover–Kincannon model were the most appropriate and shareable reactor-kinetic models for different anammox configurations. This review plays an important role in the anammox process performance assessment and augmentation of the process control.

Over the last 30 years, the successful implementation of the anammox process has attracted research interest from all over the world.

Physico-chemical and microbial characterization of compartment-wise profiles in an anammox baffled reactor

In this study, compartment-wise investigation of an anammox baffled reactor (AnBR) was performed. The AnBR achieved steady-state conditions after a start-up period of ∼50 days and achieved NH₄ and NO₂ conversion percentages of 88.5 and 99.3%, respectively. Examination of the nitrogen mass balance revealed that an AnBR with a two-compartment configuration was sufficient for nitrogen loading rates (NLRs) ranging from 0.125 to 1.975 kg N/m³/d and resulted in a nitrogen removal efficiency (NRE) of 86.7-93.7%. Higher NLRs (4.04-5.05 kg N/m³/d) required four compartments to achieve an NRE of 82.2-87.1%. Further, an overall NLR increase of up to 5.93 ± 0.23 kg N/m³/d resulted in complete AnBR failure. The maximum nitrogen removal rate was consistently recorded in the 1^st compartment for all NLRs examined; as a result, this compartment exhibited the highest bacterial activity. Biomass concentration, specific anammox activity, extracellular polymeric substances, and average granule diameter in the 1^st compartment with an overall NLR of 0.05 kg N/m³/d were estimated to be 11.2 g_VSS/L, 0.03 mg N/g_VSS/h, 84.3 mg/g_VSS, and 0.65 mm, respectively. These values increased to 26.1 g_VSS/L, 11.80 mg N/g_VSS/h, 242.1 mg/g_VSS, and 2.31 mm, respectively, when the overall NLR was incremented to 4.04 kg N/m³/d. However, a gradual reduction in bacterial activity was observed from the 1^st to the 5^th compartment. The microbial community analysis indicated that the dominant phyla in the 1^st compartment (NLR of 0.252 kg N/m³/d) with the highest nitrogen removal were Chloroflexi (38.13%), Planctomycetes (22.62%), and Proteobacteria (14.75%).

Preservation and reactivation of Candidatus Jettenia asiatica and Anammoxoglobus propionicus using different preservative agents

Anaerobic ammonium oxidation (anammox) bacteria have peculiar characteristics that make them difficult to cultivate. The conservation of these microorganisms in culture collections or laboratories requires successful preservation and reactivation techniques. Furthermore, studies have shown that successful reactivation may be preservative dependent. Considering this, the present study aimed to evaluate the preservation and reactivation of anammox consortia enriched from swine manure treatment lagoons, by using different preservative agents at different temperatures: KNO₃ (at 4 °C), glycerol (-20 °C, -80 °C), and skimmed cow milk (-20 °C, -80 °C, -200 °C). After 4 months, the biomass was thawed (except for KNO₃), and the reestablishment of anammox activity was evaluated by stoichiometric coefficients. Microbial community transformation during the reactivation process was also studied by 16S rDNA sequence analysis. The results showed that the anammox biomass preserved with glycerol or skimmed cow milk at -80 °C recovered activity, while the biomass preserved with other methodologies did not reestablish activity during the studied time (90 days). The bacterial community from the biomass with anammox activity was characterized and showed the presence of Candidatus Brocadia anammoxidans, Candidatus Jettenia asiatica, and Candidatus Anammoxoglobus propionicus. Preservation with skimmed cow milk at -80 °C favored the selection of Candidatus Anammoxoglobus propionicus, while preservation with glycerol at -80 °C was successful for Candidatus Jettenia asiatica. The present study was effective on anammox sludge preservation and reactivation using low-cost processes for anammox cultures preservation, which is important for biomass transport and deammonification reactor start up.

Highly efficient long-term storage of carrier-bound anammox biomass

The anammox process is a potential alternative to the conventional nitrogen removal from wastewater. However, due to large generation times of anammox bacteria, the start-up of treatment reactors may be impeded. An efficient storage technique can handle this drawback and may be also suitable for seasonally operated treatment plants like in touristic areas. In the current study, several storage techniques were investigated with respect to its suitability for the preservation of the specific anammox activity after long-term storage. Storing conditions differed in terms of temperature, redox buffer and nutrient supplementation. The specific activity of immobilized anammox bacteria (Candidatus Kuenenia stuttgartiensis) was determined three times during a long-term preservation of 78 days and 106 days, respectively. The highest activity was ensured at a storing temperature of 4 °C, providing nitrate as redox buffer and a nutrient supplement every 23 days. Thus, 91.4% of the initial anammox activity could be preserved after a storage of 106 days. Superiority of the presented treatment condition was confirmed by a calculated nitrate-ammonium consumption rate close to the optimal ratio of 1.32. This technique provided an economical and simple method suitable for long-term storage of immobilized anammox biomass.