Enhancing anammox resistance to low operating temperatures with the use of PVA gel beads

A new strategy for accelerating recovery of anaerobic granular sludge after low-temperature shock: In situ regulation of quorum sensing microorganisms embedded in polyvinyl alcohol sodium alginate

Low-temperature could inhibit the performance of anaerobic granular sludge (AnGS). Quorum sensing (QS), as a communication mode between microorganisms, can effectively regulate AnGS. In this study, a kind of embedded particles (PVA/SA@Serratia) based on signal molecule secreting bacteria was prepared by microbial immobilization technology based on polyvinyl alcohol and sodium alginate to accelerate the recovery of AnGS system after low temperature. Low-temperature shock experiment verified the positive effect of PVA/SA@Serratia on restoring the COD removal rate and methanogenesis capacity of AnGS. Further analysis by metagenomics analysis showed that PVA/SA@Serratia stimulated higher QS activity and promoted the secretion of extracellular polymeric substance (EPS) in AnGS. The rapid construction of EPS protective layer effectively accelerated the establishment of a robust microbial community structure. PVA/SA@Serratia also enhanced multiple methanogenic pathways, including direct interspecies electron transfer. In conclusion, this study demonstrated that PVA/SA@Serratia could effectively strengthen AnGS after low-temperature shock.

Mechanism of gel immobilization driving efficient anammox in mainstream partial nitritation/anammox process: Structural characterization and multi-perspective microbial analysis

Here, the mechanism of encapsulated anammox bacteria (AnAOB) driving efficient nitrogen removal in the mainstream partial nitritation/anammox process is revealed. The results show that a high nitrogen removal rate (1.21±0.02 kgN·(m3·d)-1) was achieved due to the abundant micropore structure inside the anammox immobilized filler, ensuring good connectivity, and a stable aggregation capacity, reducing dependence on extracellular polymeric substances. AnAOB were uniformly distributed throughout all regions of the immobilized filler, and their abundance was higher than that of the control anammox granular sludge (AnGS). Conversely, cracks appeared on the surface of the AnGS, and hollows formed inside. The metagenome analysis revealed that the immobilized filler supported the coexistence of multiple AnAOB, and the appropriate niche enhanced coordination between the AnAOB and dominant companion microorganisms. In contrast, AnGS exhibited stronger NH4+-N and NO2--N loops, potentially reducing the total nitrogen removal efficiency. This study promotes the mainstream application of anammox.

Analyzing the nitrogen removal performance and cold adaptation mechanism of immobilized cold-acclimation ANAMMOX granules at low temperatures

To improve the treatment performance of anaerobic ammonium oxidation (ANAMMOX) processes at low temperatures, the immobilized cold-acclimation ANAMMOX granules (R3) were prepared and their low-temperature nitrogen removal ability as well as the cold adaptation mechanism were analyzed. The results indicated that the total inorganic nitrogen (TIN) removal efficiency of R3 was significantly higher than that of R2 (cold-acclimation granules without immobilization) and R1 (common granules), especially at 11 ± 2 and 7 ± 2°C (68% and 54%). These were attributed to the remarkable biomass retention capacity of R3, high up to 4.3-4.9 mg/gVSS even at 5-18°C. Besides, higher protein (PN) content of tightly bound extracellular polymeric substances (TB-EPS) also facilitated microbial aggregation in R3. Meanwhile, R3 granules retained higher ANAMMOX activity and heme c content at 5-25°C. The original dominant ANAMMOX genus (Candidatus Kuenenia) in R3 kept higher abundance (49%-57%) at 23 ± 2 and 16 ± 2°C, whereas Candidatus Brocadia became the dominant ANAMMOX genus (25%-32%) in R3 at 11 ± 2 and 7 ± 2°C. Notably, different ANAMMOX genera in R3 may adapt to cold environment by regulating the expression of cold-stress proteins (CspA, CspB, PpiD, and UspA). PRACTITIONER POINTS: Immobilized cold-acclimation ANAMMOX granules showed higher nitrogen removal efficiency at 23°C → 5°C. Immobilization method effectively retained biomass (Candidatus Kuenenia and Candidatus Brocadia). Immobilization facilitated TB-EPS release and biological aggregation in cold-acclimation granules. Expression of cold-stress proteins in immobilized cold-acclimation granules was more active.

Mainstream nitrogen removal from low temperature and low ammonium strength municipal wastewater using hydrogel-encapsulated comammox and anammox

Application of partial nitritation (PN)-anammox to mainstream wastewater treatment faces challenges in low water temperature and low ammonium strength. In this study, a continuous flow PN-anammox reactor with hydrogel-encapsulated comammox and anammox was designed and operated for nitrogen removal from mainstream wastewater with low temperature. Long-term operation with synthetic and real wastewater as the feed demonstrated nearly complete ammonium and total inorganic nitrogen (TIN) removal by the reactor at temperatures as low as 10 °C. A significantly decreased nitrogen removal performance and biomass activity was observed in the reactor at 4 °C before a selective heating strategy was employed. A novel heating technology using radiation to heat carbon black co-encapsulated in the hydrogel matrix with biomass was used to selectively heat biomass but not water in the treatment system. This selective heating technology enabled nearly complete ammonium removal and 89.4 ± 4.3 % TIN removal at influent temperature of 4 °C and reactor temperature 5 °C. Activity tests suggested selective heating brought the biomass activity at influent temperatures of 4 °C and reactor temperature 5 °C to a level comparable to that at 10 °C. Comammox and anammox were consistently present in the system and spatially organized in the hydrogel beads as revealed by qPCR and fluorescence in-situ hybridization (FISH). The abundance of comammox largely decreased by 3 orders of magnitude during the operation at 4 °C, and rapidly recovered after the application of selective heating. The anammox-comammox technology tested in this study essentially enabled mainstream shortcut nitrogen removal, and the selective heating ensured good performance of the technology at temperature as low as 5 °C.

Rapid start-up and long-term stable operation of the anammox reactor based on biofilm process: Status, challenges, and perspectives

Anammox-biofilm processes have great potential for wastewater nitrogen removal, as it overcomes the slow growth and easy loss of AnAOB (anaerobic ammonium oxidation bacteria). Biofilm carrier is the core part of the Anammox-biofilm reactor and plays a key role in the start-up and long-term operation of the process. Therefore, the research on the biofilm carrier of Anammox-based process was summarized and discussed in terms of configurations and types. In the Anammox-biofilm process, fixed bed biofilm reactor is a relatively mature biofilm carrier configuration and has advantages in terms of nitrogen removal and long-term operational stability, while moving bed biofilm reactor has advantages in terms of start-up time. Although the long-term operational stability of fluidized bed biofilm reactor is good, its nitrogen removal performance needs to be improved. Among the different biofilm carrier categories, the inorganic biofilm carrier has an advantage in start-up time, due to the enhancement of the growth and metabolic of AnAOB by inorganic materials (such as carbon and iron). Anammox-based reactors using organic biofilm carriers, especially suspension carriers, are well-established and more stable in long-term operation. Composite biofilm carriers combine the advantages of several materials, but their complex preparation procedures lead to high costs. In addition, possible research directions for accelerating the start-up and keeping the long-term stable operation of Anammox reactor by biofilm process were highlighted. It is hoped to provide a possible pathway for the rapid start-up of Anammox-based process, and references for the optimization and promotion of process.

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

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

Activity enhancement and the anammox mechanism under low temperature via PVA-SA and nano Fe2O3-PVA-SA entrapped beads

Anaerobic ammonia-oxidizing bacteria (AAOB) have a long growth time and low activity at low temperatures. In suspended systems, sludge is easily lost, which limits the mainstream application of anaerobic ammonia oxidation (anammox).Entrapment provides effective ideas for solving these problems. In this study, polyvinyl‑sodium alginate (PVA-SA) and nano Fe₂O₃-PVA-SA entrapment beads were prepared to discuss the effectiveness of entrapment enhanced anammox sludge at low temperatures. The differences in the entrapped beads and granules were compared to analyze the strengthening mechanism. The results show that the nitrogen removal performance of granules, PVA-SA and nano Fe₂O₃-PVA-SA entrapped beads, first decreased and then increased during the cooling and low-temperature operation. Nano Fe₂O₃-PVA-SA entrapped beads showed the smallest decline and the highest degree of recovery. Reaction metering ratio (△NO₂^--N/△NH₄⁺-N and △NO₃^--N/△NH₄⁺-N) showed that entrapment could realize Nitrite oxidizing bacteria (NOB) inhibition and improve the activity of denitrifying bacteria (DNB) to promote the removal of total nitrogen by providing a strict anaerobic environment. The results demonstrate that entrapment is beneficial for maintaining the content of heme c, specifically, nano Fe₂O₃ can stimulate its production, and is beneficial for alleviating the reduction of hydrazine dehydrogenase (HDH) enzyme activity. The extracellular polymeric substances (EPS) content and analysis showed that entrapment does not change the composition of EPS, and can maintain the EPS content. Nano Fe₂O₃ can stimulate AAOB to secrete more EPS to maintain sludge stability. From a molecular perspective, entrapment can maintain the expression of functional genes, promote the enrichment of AAOB, thus improving the nitrogen removal performance from the dual perspectives of "quality" and "quantity".

Nitrogen removal performance of anammox immobilized fillers in response to seasonal temperature variations and different operating modes: Substrate utilization and microbial community analysis

Four anaerobic ammonium oxidation (anammox) immobilized filler reactors (R1: 33 °C-normal, R2: seasonal temperature-normal, R3: seasonal temperature-feast, R4: seasonal temperature-starvation) were established to study the response of anammox immobilized fillers to seasonal temperature changes and different operating modes. The results showed that the anammox immobilized filler could better adapt to the seasonal temperature drop and maintain the activity potential by adjusting the hydraulic retention time (HRT). During the temperature rise phase, R2 activity increased rapidly with the highest nitrogen removal rate reaching 1.26 kgN·(m³·d)^-1, which was equivalent to control sample R1 (1.33 kgN·(m³·d)^-1). However, feasting and famine conditions severely impaired anammox performance and changed stoichiometric ratios; feasting, in particular, significantly lowered the nitrogen removal potential of R3. The specific anammox activity of R2, R3 and R4 was 92.2%, 52.6% and 67.9%, respectively, that of R1, respectively, where the accumulation of functional bacteria was the reason for the higher activity of R2. Degradation kinetics and NO₂^--N inhibition curves showed that R3 was less sensitive to high concentrations of NH₄⁺-N, while R4 responded earlier to low concentrations of NH₄⁺-N, and the reduction of IC50 at low temperature was the reason for the inhibition of R3 activity. Furthermore, seasonal temperature fluctuations had little effect on the microbial community structure but had a considerable impact on bacteria abundance. The anammox functional bacteria Candidatus Kuenenia was found to be the dominant genus in R1-R4; however, the relative abundance of most bacteria, including anammox bacteria, decreased in R3, while the proportion of fermentation bacteria and denitrifying bacteria increased in R4. These findings highlight the necessity of rational regulation of HRT for the adaptation of anammox immobilized fillers to seasonal temperature changes, which could enhance our understanding of the synergistic effect of seasonal temperature changes and different operating modes on nitrogen removal.

A mainstream anammox fixed-film membrane bioreactor with novel sandwich-structured carriers for fast start-up, effective sludge retention and membrane fouling mitigation

Novel sandwich-structured carriers were developed for fast immobilizing anammox sludge, with which a fixed-film membrane bioreactor was further established for treating municipal wastewater. Results showed that fast start-up of the fixed-film reactor with anammox bacteria could be achieved without lag phase, indicated by the respective nitrogen removal efficiency and rate of 70.58 ± 0.66% and 0.12 g N/(L·d). Meanwhile, low membrane fouling 0.0017 bar/hour was also observed. The activity of anammox sludge fixed in the novel carriers gradually stabilized at the level of 6.59 mg N/(g VSS·h), while Candidatus Kuenenia as the dominant anammox bacteria were enriched from the initial abundance of 15.16% to 39.12% after a long-term operation. Consequently, it was demonstrated that the sandwich-structured carriers developed in this study could offer a promising alternative for fast immobilization and start-up of mainstream anammox process.

Effect of the form of granular sludge and temperature on anammox immobilized fillers: From performance to microbial community analysis

The immobilized carrier was prepared with complete anaerobic ammonia oxidation granular sludge (AnGS) and crushed AnGS, respectively. We evaluated the effects of granular form and continuous temperature changes on nitrogen removal by immobilized anaerobic ammonium oxidation (anammox) filler. The results showed that the rate of nitrogen removal of crushed and encapsulated AnGS was 20% higher than that of direct encapsulated AnGS. However, the latter had higher thresholds of tolerance to Fe²⁺ and Cu²⁺. In addition, the immobilization reduced the activation energy of anammox. Above 12.5 °C, the immobilized filler was efficient at removing nitrogen removal through the dual adjustment of temperature-hydraulic retention time. From 12.5 °C to 23 °C, the temperature had a greater influence on the nitrogen removal effect than the HRT. In contrast, HRT had a dominant influence from 23 °C to 32 °C. Anammox activity was severely inhibited below 12.5 °C. High-throughput sequencing analysis showed that the community structure migrated with the changes in temperature. The anammox functional bacteria Candidatus Kuenenia (18.31-39.73%) were the dominant genus at medium and high temperatures, and it was replaced by Chryseobacterium (24.19%) at 8.5 °C. In addition, an RDA analysis showed that Candidatus Brocadia was more adaptable to low temperatures than Candidatus Kuenenia. In addition, Bellilinea was more sensitive to temperature than Candidatus Kuenenia. Thus, the temperature could be appropriately lowered to avoid overbreeding. The results of this study optimized the operation of an anammox immobilized system and promote its further application.

Can nitrifiers from the sidestream deammonification process be a remedy for the N-overload of the mainstream reactor?

The combination of sidestream deammonification and bioaugmentation of the mainstream reactor using ammonia oxidizers from partial nitritation (PN) was not achieved before. This novel solution not only enables the efficient sidestream nitrogen removal, but also improves mainstream resistance to stress situations such as biomass washout or nitrogen overload. This feature is important for wastewater treatment plants (WWTPs) equipped with reject water deammonification as its implementation leads to lower nitrifier mass in the mainstream reactor and therefore diminish ability to cope with rapid increase in the loading rate (i.e. due to sidestream process failure). The proposed approach presents the use of the excess sludge from a modified PN process to boost the mainstream nitrification in unfavourable conditions. In a long-term laboratory experiment, the operation of an existing WWTP at low temperature was simulated in two reactors using real wastewater fluxes. One of them was augmented with the excess sludge from a PN reactor that treats reject water containing 20% of the WWTP N-load. The treatment efficiency in both reactors was tested under different nitrogen loading rates, as well as in the case of the of biomass loss. The bioaugmentation intensity was set according to the actual nitrogen load balance of the modelled WWTP, resulting in a daily seed volume only equal to 0.28% of the reactors' influent. Two incidents were simulated, where the nitrogen load increased by about 24.5% and 34%. In both cases, the nitrification efficiency in the non-augmented reactor dropped by about 45%, while the augmented reactor maintained efficient ammonium removal. The bioaugmentation effect was also noticeable during biomass washout - only in the non-augmented reactor nitrification was insufficient for over 60 days. These results undoubtedly show the possibility of combining two different approaches for sidestream nitrogen removal into one technology demonstrating the advantages of both component solutions.