Nitrogen Loading Rate Research Articles

Iron-containing carriers stimulate nitrogen conversions in one-stage reactors treating N-rich digester supernatant

Iron incorporation in biomass carriers (0%, 1%, 5%, and 10% of carrier weight) at nitrogen loading rates (NLR) from 0.08 to 0.30 g/(g MLVSS·d) was tested during the treatment of nitrogen-rich digester supernatant in one-stage reactors, in which hybrid biomass (suspended/attached) was inhabited by ammonia-oxidizing bacteria, Anammox bacteria, and denitrifiers. The Anammox process dominated at the highest NLR and increased the volumetric nitrogen removal rate to about 500 g/(m3·d). Total microbial composition was most strongly affected by NLR, however, Anammox bacteria abundance was also affected by the iron content. These bacteria predominated in reactors with 5%-iron carriers, which ensured the highest nitrogen removal efficiency (up to 75%) and kinetics: the average ammonium removal rate was at least 40% higher than in the reactor without iron. The presence of 10%-iron carriers in the reactor inhibited the ammonium oxidation rate; an increase in ammonium removal rate with increasing initial ammonium concentration was the lowest. The contribution of Anammox to nitrogen removal was demonstrated by the simultaneous increase in biomass heme c content to about 0.1 µmol/mg protein along with increasing iron content to 5% and NLR. The incorporation of iron into the carrier structure allowed for a long-term release of mostly ferrous iron to the supernatant, thus accelerating its treatment.

Low-intensity electromagnetic field as a new engineering oriented bioaugmentation strategy for anammox granules

Improving the relative abundance of bacteria and their activity is still the basis for the efficient operation of anammox process. Here, biomagnetic effect was used to promote anammox granules. Batch test results show that the application of an electromagnetic field (EMF) with a strength of 0.09 μT increased the nitrogen removal performance of anammox by 32.44% while higher strength EMF of 0.20 and 0.25 μT inhibited the activity of anammox bacteria. Long-term experiment indicated that the addition of EMF with a strength of 0.09 μT greatly improved nitrogen removal performance of the granular sludge, especially the total nitrogen removal performance increased by 15.3%. After 120 days of reactor operation, the nitrogen loading rate was increased to 6.4 kg N/m3/d, and the total nitrogen removal rate of the reactors with and without EMF addition reached 4.92 kg N/m3/d and 4.25 kg N/m3/d, respectively. Throughout the experiment, the removal rate of NH4+-N and NO2−-N of anammox reactor with 0.09 μT EMT addition was always higher than that without EMF addition. The high-throughput sequencing analysis showed that the proportion of Candidatus Brocadia in reactors with and without EMF addition were 21.3% and 15.8%, respectively. The application of EMF with an intensity of 0.09 μT increased the relative abundance of the main anammox bacteria. 70 kos were enriched under EMF conditions, including ko00780 (Biotin metabolism), ko00540 (Lipopolysaccharide biosynthesis), ko00590 (Arachidonic acid metabolism). 51 kos like ko03030 (DNA replication) decreased after EMF addition. This study demonstrates the feasibility of EMF to promote anammox and expands the application of EMF in wastewater treatment.

Start-up of the combined anaerobic ammonium oxidation and solid phase denitrification process and microbial characterization analysis

To improve the nitrogen removal performance of anaerobic ammonia oxidation (anammox)-based processes, a modified anaerobic baffled reactor (ABR) equipped with a packed bed of poly-3-hydroxybutyrate-cohyroxyvelate (PHBV) was employed to start up the combined anammox and solid phase denitrification (SPD) process for the treatment of nitrogen-rich wastewater. Results showed that a stable removal of total inorganic nitrogen (TIN) of 98.5 % was achieved with a nitrogen loading rate of 0.46 kg·(m3·d)−1, decreasing the effluent TIN concentration to <2 mg·L−1. Throughout the operation period of 180 days, sludge granulation in three compartments of the ABR was promoted by a stepwise decrease in the hydraulic retention time. The anammox reaction and endogenous denitrification mainly occurred in the first two compartments with inorganic feeding and contributed >86 % of TIN removal. 16S rRNA gene amplicon sequencing showed that anammox communities, dominated by genera Candidatus Kuenenia and Candidatus Brocadiaceae, were enriched in granular sludges with symbiotic heterotrophic bacteria. Co-cultures of hydrolytic bacteria (Burkholderiales, Kapabacteriales, and Clostridium-sensu-stricto-7) and denitrifying bacteria (Comamonadaceae, Rhodocyclaceae, and Denitratisoma) were detected within the biofilm on the surface of PHBV particles. PHBV hydrolysate input effectively drove heterotrophic denitrification in the successive compartment and increased the complexity of microbial co-occurrence networks. These findings provide insight into the synergistic mechanisms between anammox and SPD and present a feasible combined process application for advanced biological nitrogen removal.

Combined partial denitrification-anammox with urea hydrolysis (U-PD-Anammox) process: A novel economical low-carbon method for nitrate-containing wastewater treatment

For the sake of exploring a new economical and low-carbon alternative for real nitrate-containing wastewater treatment, a new combined partial denitrification-anammox with urea hydrolysis (U-PD-Anammox) process was developed. The nitrogen removal performance of this process was investigated through long-term operation in a sequencing batch reactor (SBR) and two submerged anaerobic biological filters (SABF). Results showed that the average NO3−-N to NO2–N transformation ratio improved to 82.6% with organic carbon source to NO3–N ratio of 1.8, and urea hydrolysis provided sufficient NH4+-N and inorganic carbon to anammox process for nitrogen removal. The influent NH4+-N/NO2−-N ratio for subsequent anammox reactor could be adjacent to the optimal ratio of 1.32 during the whole operation. The combined process showed efficient nitrogen removal performance with 85% NO3−-N removal, 93.8% total nitrogen removal and total nitrogen loading rate as 1.1 ± 0.5 kg N/(m3·d). High-throughput sequencing analysis results revealed that Genera Thauera, Hyphomicrobium and Candidatus Brocadia were the dominant species responsible for partial denitrification, urea hydrolysis and anammox, respectively. The proposed process was more economically and environmental-friendly than the traditional denitrification process with 51.7% operational cost reduction, 99.7% N2O and 60% CO2 emission decrement, facilitating the sustainable development of the nitrate-containing wastewater treatment industry in the future.

Using an innovative umbrella-shape membrane module to improve MBR for PN-ANAMMOX process.

Membrane fouling has been a key factor limiting the applications of membrane bioreactor (MBR). In this study, a novel umbrella-shape membrane module was applied to construct two MBRs for two-stage partial nitrification-anaerobic ammonia oxidation (PN-ANAMMOX) process. After 55days operation, the ANAMMOX process was started and the PN process was well controlled. Then, the ANAMMOX and PN process were successfully coupled to run the PN-ANAMMOX process. On 103days, the best nitrogen removing effect was achieved with the maximum nitrogen loading rate (NLR) of 0.4kgN·(m3·d)-1 and the corresponding maximum total nitrogen removal rate (TNRR) of 75.23%.The umbrella-shape membrane module in both reactors only needed to be cleaned once during the operation for 105days, indicating that the membrane module had better resistance to membrane fouling. The functional bacteria were cultivated in suspension state; moreover, the cell densities of ammonia oxidizing bacteria (AOB) and ANAMMOX bacteria (AnAOB) reached 58.32 × 1012 copies/g sludge and 28.39 × 1012 copies/g sludge. Their abundances reached 73.25% and 57.80% of the total bacteria, respectively. MBR improved by umbrella-shape membrane module could realize the rapid start-up of ANAMMOX process, effective control of PN process, and stable operation of PN-ANAMMOX process. This study provided a novel approach to control membrane fouling by optimizing the membrane module shape and widened applications of MBRs in PN-ANAMMOX process.

Autotrophic denitrification of nitrate rich wastewater in fluidized bed reactors using pyrite and elemental sulfur as electron donors

This study compared denitrification performances and microbial communities in fluidized bed reactors (FBRs) carrying out autotrophic denitrification using elemental sulfur (S 0 ) and pyrite (FeS 2 ) as electron donors. The reactors were operated for 220 days with nitrate loading rates varying between 23 and 200 mg N-NO 3 − /L ⋅ d and HRT between 48 and 4 h. The highest denitrification rates achieved were 142.2 and 184.4 mg N-NO 3 − /L ⋅ d in pyrite and sulfur FBRs, respectively. Pyrite-driven denitrification produced less SO 4 2 − and no buffer addition was needed to regulate the pH. The sulfur FBR needed instead CaCO 3 to maintain the pH neutral and consequentially more sludge was produced (CaSO 4 precipitation). The active community of pyrite-based systems was investigated and Azospira sp ., Ferruginibacter sp. , Rhodococcus sp. and Pseudomonas sp. were the predominant genera, while Thiobacillus sp. and Sulfurovum sp. dominated the active community in the sulfur FBR. However, Thiobacillus sp. became more dominant when operating at elevated nitrogen loading rate. Patterns of diversity and microbial community assembly were assessed and revealed three distinct stages of microbial community succession which corresponded with the operation of a period of high influent nitrate concentration (135 mg N-NO 3 − /L). It is proposed that a high degree of functional redundancy in the initial microbial communities may have helped both reactors to respond better to such high influent nitrate concentration. • Max denitrification rates were 142.2 and 184.4 mgN-NO 3 − / L ⋅ d in the FeS 2 and S 0 FBRs. • FeS 2 -driven denitrification produced low SO 4 2 − and no buffer addition was needed. • Microbial community succession was observed in response to NLR increased. • Functional redundancy in the AD microbiome resulted in resilience to increased NLRs. • The active community of FeS 2 FBR had Azospira and Pseudomonas as dominant genera.

Increasing nitrogen and organic matter removal from swine manure digestate by including pre-denitrification and recirculation in single-stage partial nitritation/anammox

A novel two-stage process comprising pre-denitrification and single-stage partial nitritation/anammox was developed to treat swine manure digestate with a constant nitrogen loading rate of 1.0 gN/L/d. As the influent NH4+-N concentration increased from 500 to 1500 mg/L, a nitrogen removal efficiency of 88 %–96 % and 5-day biochemical oxygen demand removal efficiency of 93 %–97 % were achieved. Owing to the high influent chemical oxygen demand (COD)/nitrates and nitrites (NOX) ratio of 8.2–9.2 and high COD utilization of denitrifying bacteria (DB), the NO2−-N and NO3−-N removal efficiencies in the denitrification reactor reached 96 %–99 % and 97 %–99 %, respectively. The contribution of anammox bacteria to nitrogen removal was 70.9 %–84.3 %, whereas that of DB was 11.7 %–18.3 %. The contributions of DB and ordinary heterotrophic organisms to COD removal were 19.5 %–49.3 % and 17.9 %–39 %, respectively. This study will help guide the anammox process in swine wastewater treatment.

Long-term performance, microbial evolution and spatial microstructural characteristics of anammox granules in an upflow blanket filter (UBF) treating high-strength nitrogen wastewater

Granule formation, microstructure and microbial spatial distribution are crucial to granule stability and nitrogen removal. Here, an upflow blanket filter (UBF) reactor with porous fixed cylinder carriers was fabricated and operated for 234 days to investigate overall performance and the formation mechanism of anammox granules. Results showed that the UBF performed the highest nitrogen removal efficiency of 93.19 ± 3.39% under nitrogen loading rate of 3.6 kg-N/m3/d and HRT of 2 h. The tryptophan-like proteins as the key component in EPS were vital for granules formation. Further 16 s rRNA analysis indicated that SBR1031 with a relative abundance of 40.5% played an important role in cell aggregation. Thus, anammox granules were developed successfully with a two-layered spatial structure where outer-layer was ammonia oxidizing bacteria and inner-core was anaerobic ammonia oxidizing bacteria. Together, introduction of porous fixed cylinder carriers is a valid method to avoid biomass loss and floatation.

Starting up anammox system with high efficiency nitrogen removal at low temperatures: Performance optimization, sludge characterization and microbial community analysis

Anaerobic ammonia oxidation (anammox) has potential advantages for nitrogen removal when operating at medium temperatures, but the increased operation costs of heating limit its application. It would be advantageous to start and operate anammox at low temperatures, the feasibility of which was studied here on a lab scale. Two identical expanded granular sludge bed (EGSB) reactors were inoculated at 35 ± 1 °C (Amed) and 15 ± 3 °C (Alow). Results showed that anammox was successful after 138 d for Alow, only 7 d longer than Amed. Stable operation to 194 d in Alow, the nitrogen loading rate (NLR) increased to 1.01 kg m−3·d−1, giving a high nitrogen removal efficiency (NRE) of 85%, which was only slightly lower than that of Amed (90%). More extracellular polymeric substance (EPS) was produced by the microbes of Alow compared to Amed, which prevented anaerobic ammonia oxidizing bacteria (AnAOB) against low temperature stress. Microbial community revealed presence of Candidatus Jettenia in Amed with relative abundance 7.4%, while the “cold-tolerant” Candidatus Kuenenia with 4% was the dominant anammox bacteria in Alow. The anammox granules adapted well to low temperatures and demonstrated high efficiency in anammox process without heating. Therefore, constructing an energy-saving and cost-effective anammox system in high latitudes or high altitudes can be considered.

Metagenomics-based interpretation of selective bioaugmentation promoting partial-denitrification coupling with anammox process reactivation in suspended sludge system

The partial-denitrification coupled to anammox process (PD/A) has been emerging as a potential alternative for cost-efficient nitrogen removal from wastewater. Although there has been intensive study on startup and optimization, efficient reactivation and controlling strategy after disturbance of this process still lack essential information. Here, a selective bioaugmentation strategy with low dosage for stepwise recovery of PD and anammox activity were proposed and demonstrated for the first time, and the mechanism of coupling process reactivation was revealed based on metagenomic analysis. A significant increase in nitrite (NO2-N) production was obtained after introducing PD inoculum by weight ratio of 7.7 %, with nitrate (NO3−-N)-to-NO2−-N transformation ratio (NTR) increasing from 15.7 % to 45.0 %, while anammox activity stayed at a relatively low level. The ammonia (NH4+-N) removal rate significantly increased by 4.0 times after supplying PD/A biomass by only 1.2 % due to sufficient substrate NO2−-N for anammox. Consequently, nitrogen removal efficiency was remarkably improved to 99.2 % and kept stable with low-strength wastewater. Metagenomics analysis revealed that the abundances of genes nar and nap encoding NO3−-N reductase were kept at much higher level than nir for NO2−-N reductase. Significantly, higher diversity and abundance of genes responsible for carbon metabolism could accelerate the electron generation and transfer to PD, thus stimulating anammox activity, which was the key reason for the rapid reactivation of PD/A process. Furthermore, the substate ratio, nitrogen loading rates and morphological characteristics of sludge have crucial influence on the recovery of biomass activity. The dominant genus Thauera responsible for PD and Candidatus Brocadia for anammox coexisted stably after bioaugmentation. These results provide a comprehensive understanding of reactivating and regulating a novel PD/A process towards application and microbial interaction.

Development of a post-treatment system using a downflow hanging sponge reactor – an upflow anaerobic reactor for natural rubber processing wastewater treatment

This study aimed to evaluate the nitrogen removal of a post-treatment system for natural rubber processing wastewater (NRPW) under low chemical oxygen demand to total nitrogen (COD/TN) ratios without any supplemental external carbon source. The system including a downflow hanging sponge (DHS) reactor and an upflow anaerobic reactor (UAR) was operated in two phases. In phase 1 (day 0–102), under a nitrogen loading rate (NLR) of 0.23 ± 0.06 kgN m−3 d−1 and COD/TN ratio of 0.63 ± 0.47, the DHS-UAR system removed 82.5 ± 11.8% and 83.9 ± 7.6% of TN and ammonium concentrations, respectively. In phase 2 (day 103–229), higher COD/TN ratio of 1.96 ± 0.28 was applied to remove increasing NLRs. At the highest NLR of 0.51 kgN m−3 d−1, the system achieved TN and ammonium removal efficiencies of 93.2% and 93.7%, respectively. Nitrogen profiles and the 16S rRNA high-throughput sequencing data suggested that ammonium, a major nitrogen compound in NRPW, was utilized by nitrifying and ammonium assimilation bacteria in DHS, then removed by heterotrophic denitrifying and anammox bacteria in the UAR. The predominance of Acinetobacter detected in both reactors suggested its essential role for the nitrogen conversion.

Anammox biofilter with denitrification sludge as seed in treating low nitrogen strength wastewater

Deficient seed sludge, low substrate concentrations are recognized as the major barriers for the application of anaerobic ammonia oxidation (Anammox) to treat mainstream wastewater. In this work, anammox biofilter (A-BF) was started up by inoculating denitrification sludge at low nitrogen strength at 25 °C. The total nitrogen removal efficiency (TNRE) and nitrogen removal rate (NRR) reached 74.8 ± 3.4% and 0.81 kg-N m−3 d−1 under nitrogen loading rate (NLR) of 1.20 kg-N m−3 d−1 with 7.00 mg-NH4+-N L−1 and 10.00 mg-NO2--N L−1 as influent. 1.00–2.00 mg-DO L−1 negatively impacted effluent, but the total nitrogen of effluent (TNeff) was 10.65 ± 2.76 mg L−1, in limit of the standard of Class 1A for municipal WWTP discharge (GB18918-2002). The abundance of Planctomycetes increased from 0.6% to 1.4–2.6%, in which, Candidatus_Brocadia was the dominant genera. The results establish the application feasibility of A-BFs as advanced nitrogen removal technique in treating mainstream wastewater.

Anammox in a biofilter reactor to treat wastewater of high strength nitrogen

An anammox biofilter reactor (A-BFR) under high total nitrogen (TN) concentration and high nitrogen loading rate (NLR) was operated for 283 days and the biomass characteristics were investigated at the end of the experiment to discuss the origin of strong impact resistance of A-BFR. The result showed TN removal rate of A-BFR reached 81.76 % averagely under the influent concentration of 525 mg/L and the NLR of 6.30 kg N/m3/d. Furthermore, A-BFR was partitioned as the core zone and the polish zone spontaneously according to the water quality along the height of reactor due to the characteristics of plug flow. Although the core zone bore an actual NLR of 17.71 kg N/m3/d, and an average free ammonia (FA) concentrations of 13.35 mg/L as well as a mean free nitrous acid (FNA) concentrations of 36.89 μg/L, it still obtained the TN removal of >80 %, which could be attributed to the high biomass of 30.67 gVSS/L comprised of biofilm and granular sludge aggregates, the high specific anammox activity up to 49.24 mg N/g VSS/d, and high extracellular polymeric substances of 148.69 mg/gVSS. In addition, the enrichment of anammox bacteria in the core zone attained over 50 %, and the dominant bacteria were unclassified_Candidatus_Brocadiaceae and Candidatus Kuenenia after the operation of 283 days. These findings revealed the unique characteristics of biomass in the core zone decided the robust capacity of A-BFR to resist high NLR and the inhibition of FA and FNA from high TN concentration, which would enrich the knowledge and understanding of anammox with plug flow reactor under higher FA and FNA concentrations, implying BFR was a robust and resilient reactor for anammox.

Start-up characteristics and microbial nitrogen removal mechanisms in ANAMMOX systems with different inoculations under prolonged starvation

The characteristics of lab-scale ANAMMOX system for efficient nitrogen removal were tested by different inoculations (anaerobic granular sludge (AGS) + anammox sludge (AMS), R1; AGS alone, R2) in continuous flow reactors following start-up under starvation. TN removal rates were above 90 % in both reactors. Microbial community analysis showed that the nitrogen removal was the combined results of anammox and partial denitrification (PD), Higher microbial growth rate triggered by quorum-sensing (QS) caused R1 to secrete more extracellular polymeric substances (EPS) and promoted the growth of its particle size. However, the overproduction of EPS destroyed the particle structure with time, and led to a deterioration of operational stability in R1. R2 showed better nitrogen removal stability to high nitrogen loading rate (NLR). This was due to higher endogenous organics within R2, which inhibited cell aggregation and EPS overproduction. But undeniably, R1 had higher specific anammox activity (SAA) with higher anammox bacteria (AAOB) abundance (The abundance of Planctomycetota in R1 and R2 were 21.2 %, 7.71 %). The results suggest that the operational stability was influenced by a combination of particle properties and microbial metabolism, and that the inoculation of AGS is more conducive to efficient and economic nitrogen removal in wastewater treatment under starvation.

Continuous plug-flow anammox system for mature landfill leachate treatment: Key zone for anammox pathway

This study established the one-stage partial nitrification coupled anammox and partial denitrification coupled anammox process in an anoxic/oxic continuous plug-flow system and operated for 465 days to treat mature landfill leachate. 97.9 %–98.1 % of inorganic nitrogen was removed when the nitrogen loading rate was maintained at 0.33–0.36 kg N/m3/d, and a high anammox contribution to nitrogen removal (89.8 %–92.4 %) was achieved. The long-term in-situ free ammonia (FA) anoxic treatment contributed to the stable performances of partial nitrification and in-situ fermentation. The employed integrated fixed-film activated sludge technology favored the enrichment of hzsA, hzsB, hdh, amoA, hao, narG, and napA functional genes. The oxic zone, particularly oxic biofilm, was the key zone for anammox pathway, where Candidatus_Kuenenia (from 1.6 % to 8.3 %) with high tolerance to FA and salinity stress outcompeted Candidatus_Brocadia (from 18.3 % to 0.1 %) as the dominant anammox bacteria. This study could provide guidance for anammox-mediated landfill leachate treatment in practical projects.

Low strength wastewater anammox start-up and stable operation by inoculating sponge-iron sludge: Cooperation of biological iron and iron bacteria

The application of anaerobic ammonium oxidation (Anammox) technology in low-strength wastewater treatment still faces difficult in-situ start-ups and unstable operations. Sponge-iron sludge (R1) was used as a novel inoculum to provide a promising solution. Conventional activated sludge (R0) was used as the control. However, little is known about the feasibility and performance during the start-up and operation of Anammox combined with biological iron and iron bacteria in an iron sludge system. Anammox was successfully started both in R1 (87 days) and R0 (89 days) with a low-strength influent (with a nitrogen loading rate (NLR) of 43.64 ± 0.41 g N/(m3⋅d)). During long-term operation, the R0 nevertheless produced higher nitrates (9.7 ± 0.1 mg/L) than expected. In contrast, R1 presented no excess nitrate production (2.1 ± 0.06 mg/L). The total inorganic nitrogen (TIN) removal efficiency increased from 78.2 ± 7.1% in R0 to 86.1 ± 4.3% in R1. The iron sludge in R1 was divided equally into three parts and three different nitrogen-feeding methods were used over the 34 days of operation, as follows: first using a mixture of ammonium (27.15 ± 1.0 mg/L) and nitrite (32.7 ± 1.7 mg/L), then only ammonium (27.15 ± 1.0 mg/L) and lastly only nitrite (32.7 ± 1.7 mg/L) as the influent. R1 was a coupled system composed of Anammox, Feammox, and NOx−-dependent Fe(II) oxidation (NDFO). The contribution of Feammox and NDFO to TIN removal was 27.1 ± 1.2% and 31.9 ± 0.7%. However, Anammox was the primary nitrogen transformation pathway. X-ray diffraction (XRD) analysis shows that iron hydroxide (Fe(OH)3) and iron oxide hydroxide (FeOOH) were generated in R1. The produced Fe(OH)3 and FeOOH were capable of participating in Feammox and formed a Fe(II)/Fe(III) cycle which further removed nitrogen. Therefore, a highly stable and impressive nitrogen removal performance was demonstrated in the iron sludge Anammox system under the cooperation of biological iron and iron bacteria. The study considered the enrichment of norank_c_OM190, Desulfuromonas, and Thiobacillus and their contribution to the Anammox, Feammox, and NDFO processes, respectively. This study provides a new perspective for the start-up and stable operation of low-strength wastewater Anammox engineering applications.

Rapid proliferation of anaerobic ammonium oxidizing bacteria using anammox-hydroxyapatite technology in a pilot-scale expanded granular sludge bed reactor

The practical application of anaerobic ammonium oxidation (anammox) technology was seriously limited by lack of anammox seeding sludge. In this work, a pilot-scale expanded granular sludge bed (EGSB) reactor was used for rapid proliferation of anaerobic ammonium oxidizing bacteria (AnAOB) using anammox-hydroxyapatite (anammox-HAP) technology. The excellent settleability of anammox-HAP granular sludge (with an excellent settling velocity of 395 m/h) supported the up-flow velocity of 9.6 m/h with recirculation ratio of 19. A high nitrogen loading rate (NLR) of 26.4 g N/L/d was achieved in the pilot-scale reactor, with a cell yield of 0.23 g VSS/g NH4+-N. The high recirculation ratio and up-flow velocity brought about the efficient mass transfer for anammox, eliminating free ammonia inhibition, resulting in the high NLR and cell yield. Results of microbial community revealed that the relative abundance of unclassified Brocadiaceae increased from 18.55% to 82.80%, illustrating the rapid proliferation of AnAOB.

Relationships of pulsed frequency and anammox bacteria growth rate, at low temperatures

ABSTRACT This study explored pulsed frequency that could enhance the anammox bacteria growth rate and TN removal rate at low temperatures (16 ± 1°C). The results showed that the growth rate of anammox bacteria in R1 (1000 Hz) was significantly higher than in R2 (30 Hz) and R3 (106Hz). The relative abundance values of anammox bacteria R1 were higher by 52.21% and 172.41% than R2 and R3, while that of MLSS were as high as 241.07% and 471.36% than R2 and R3, with the nitrogen loading rate was 6.84 kg-N/m³/d. Besides, the dynamics also showed that the specific anammox activity (SAA) and the cellular yield of R1 were higher than R2 and R3. The intermediate frequency could enhance the cell division by stimulating the anammoxosome and reduce the ionic hydration layer to accelerate the ion migration rate, further improving the number of anammox bacteria even at low temperatures. The pulsed frequency could enhance the anammox growth rate and the doubling time is just 5 d.

Response of the mainstream anammox process to the biodegradable carbon sources in the granule-based systems: The difference in self-stratification of the microbial community

The inevitable introduction of biodegradable carbon sources (such as monosaccharides and volatile fatty acids) originating from pretreatment units might affect the performance of the mainstream anaerobic ammonium oxidation (anammox) process. Two model carbon sources (glucose and acetate) were selected to investigate their effects on granule-based anammox systems under mainstream conditions (70 mg total nitrogen (TN) L−1, 15 °C). At a nitrogen loading rate of 2.87 ± 0.80 kg N m−3 d−1, a satisfactory effluent quality (TN < 10 mg L−1) was achieved in the presence of glucose or acetate at a chemical oxygen demand (COD/N) ratio of 0.5. The contribution of anammox to nitrogen removal decreased with increasing COD/N ratio to 1.0 because the expression of anammox functional genes was inhibited, whereas the expression of denitrifying functional genes was promoted. However, the nitrogen removal efficiency of the two considered reactors was maintained above 80 %. Self-stratification of the microbial community along the reactor height facilitated a functional balance through the retention of anammox bacteria in granules but resulted in washout of denitrifying bacteria in flocs under a high-flow pattern. These findings highlighted the advantages of granule-based systems in the mainstream anammox process due to their inherent biomass self-segregation property and the need for the development of targeted biomass retention strategies.

Insights into rapidly recovering the autotrophic nitrogen removal performance of single-stage partial nitritation-anammox systems: Reconstructing granular sludge and its functional microbes synergy

Partial nitritation-anammox (PNA) deteriorates easily and is difficult to recover. After an airlift inner-circulation partition bioreactor was impacted by low NH4+–N wastewater containing organic matter, Nitrospira and Denitratisoma propagated rapidly, granular sludge disintegrated, and the total nitrogen removal efficiency (TNRE) decreased from 68.27 % to 5.97 %. This study used a unique strategy to recover deteriorated single-stage PNA systems and explored the mechanism of rapid performance recovery. The TNRE of the system recovered up to 61.77 % in 43 days. The high nitrogen loading rate and hydraulic shear force from the airlift caused the sludge in the reactor to granulate again. The microbial community structure recovered, with a decrease in the abundance of Nitrospira (0.05 %) and enrichment of Candidatus Brocadia (8.82 %). A favorable synergy among functional microbes in the reactor was thus re-established, promoting the rapid recovery of the nitrogen removal performance. This study provides a feasible recovery strategy for PNA processes.