Anaerobic Ammonium Oxidation Activity Research Articles

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 4.3-4.9mg/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.

Study on Long-term Effect of Oxytetracycline on ANAMMOX Nitrogen Removal Performance in the Treatment of Salt-containing Wastewater

The effects of oxytetracycline on anaerobic ammonium oxidation (ANAMMOX) were analyzed in this study. Meanwhile, the change of specific ANAMMOX activity (SAA) and the content of heme c were also revealed. The performance of ANAMMOX reactor decreased gradually when the increase of OTC concentration from 2mg/L to 10mg/L under 10‰ salinity. The nitrogen removal performance almost collapsed until the elevation to 10 mg/L OTC, observed with a huge decrease of SAA of 77.71% and heme c content of 88.04%. After no addition of OTC into the ANAMMOX reactor, the system performance recovered within 20 days. At the end of this phase, NH4+-N was completely removed, NO2--N was removed above 99%, and total nitrogen removal efficiency recovered to 85.33%.

Control parameters in three-stage deammonification process for a mature leachate treatment based on a traditional Modified Ludzack-Ettinger process

This study evaluated a three-stage deammonification process consisting of a sequentially Modified Ludzack-Ettinger (denitritation (DN) and partial nitritation (PN)) and anaerobic ammonium oxidation (ANAMMOX) for the treatment of mature leachate. In the initial stage, the nitrogen removal performance by two-stage deammonification was evaluated without an internal recycle (IR). The results showed that the ANAMMOX activity was severely inhibited from 0.19 to 0.03 gN/gVSS/d despite the stable partial nitritation. As inhibitors of ANAMMOX activity, the toxic effects of Refractory organic matter (ROM) and nitrite were found to deteriorate the stability of the process, and in particular, the ROM severely inhibited the activity. A three-stage deammonification process with the IR was implemented to alleviate the inhibition effects. As the IR was increased from 0 to 2Q, the ROM and nitrogen loads decreased by 35.3% and 27.8%, respectively. In addition, improved DN efficiency with external carbon sources allowed the ROM to serve as a potential electron donor for denitritation. With stabilization of ANAMMOX activity, the nitrogen removal performance rapidly stabilized. A nitrogen removal rate of 0.49 ± 0.02 kg/m3/d could be achieved with a nitrogen removal efficiency of 92.1 ± 2.1%.

Evaluation of Non-Biodegradable Organic Matter and Microbial Community’s Effects on Achievement of Partial Nitrification Coupled with ANAMMOX for Treating Low-Carbon Livestock Wastewater

After the anaerobic digestion of livestock manure, high concentrations of nutrients still remain. Treatment of livestock wastewater through partial nitrification coupled with anaerobic ammonium oxidation (ANAMMOX) could be a useful technology depending on the investigation of microorganism enrichment and partial nitrification coupled with achievement of the ANAMMOX process. The results show 78.4% and 64.7% nitrite accumulation efficiency was successfully obtained in an intermittent aeration sequencing batch reactor and a continuous aeration sequencing batch reactor, respectively, at a loading rate of 0.93 kg ammonium/(m3·d). The main reason for the high nitrite accumulation efficiency was the intermittent aeration strategy which generated a 20–30 min lag reaction for nitrite oxidation and promoted the growth of the dominant ammonium oxidation bacteria (Nitrosomonas). Non-biodegradable organic matter in the effluents of partial nitrification did not have obvious influence on ANAMMOX activity at low loading rates (118 ± 13 mg COD/L and 168 ± 9 mg COD/L), and up to 87.4% average nitrite removal rate was observed. However, with the influent COD concentration increasing to 242 ± 17 mg/L, the potential inhibition of ANAMMOX activity was exerted by non-biodegradable organic matter.

Microbial community and performance of a partial nitritation/anammox sequencing batch reactor treating textile wastewater

Implementation of onsite bioremediation technologies is essential for textile industries due to rising concerns in terms of water resources and quality. Partial nitritation-anaerobic ammonium oxidation (PN/A) processes emerged as a valid, but unexplored, solution. In this study, the performance of a PN/A pilot-scale (9 m3) sequencing batch reactor treating digital textile printing wastewater (10–40 m3 d−1) was monitored by computing nitrogen (N) removal rate and efficiencies. Moreover, the structure of the bacterial community was assessed by next generation sequencing and quantitative polymerase chain reaction (qPCR) analyses of several genes, which are involved in the N cycle. Although anaerobic ammonium oxidation activity was inhibited and denitrification occurred, N removal rate increased from 16 to 61 mg N g VSS−1 d−1 reaching satisfactory removal efficiency (up to 70%). Ammonium (18–70 mg L−1) and nitrite (16–82 mg L−1) were detected in the effluent demonstrating an unbalance between the aerobic and anaerobic ammonia oxidation activity, while constant organic N was attributed to recalcitrant azo dyes. Ratio between nitrification and anammox genes remained stable reflecting a constant ammonia oxidation activity. A prevalence of ammonium oxidizing bacteria and denitrifiers suggested the presence of alternative pathways. PN/A resulted a promising cost-effective alternative for textile wastewater N treatment as shown by the technical-economic assessment. However, operational conditions and design need further tailoring to promote the activity of the anammox bacteria.

Effects of Temperature and Substrate Concentration on N2O Release of ANAMMOX Process

The greenhouse gas N2O is released during the biological nitrogen removal process. ANAMMOX (anaerobic ammonium oxidation) is regarded as a promising nitrogen removal process for treating municipal wastewater, and the N2O emission patterns and mechanisms need further investigation. In this study, batch tests were performed to study the release of N2O at different temperatures and substrate concentrations, and the microbial mechanisms of N2O emission were discussed. The results showed that the increase of the influent substrate concentration of the ANAMMOX process promoted the release of N2O. At 35℃, when the influent nitrite increased from 40 mg·L-1 to 60 mg·L-1, 120 mg·L-1, the maximum accumulated concentration of N2O increased from 0.5 mg·L-1 to 1.5 mg·L-1 and 2.4 mg·L-1, accounting for 0.85%, 1.43%, and 1.11% of the total nitrogen removal, respectively. Lowering temperature had an obvious inhibitory effect on ANAMMOX activity. The specific ANAMMOX activity at 15℃ was only 6% of that at 30℃. Furthermore, the intracellular ATP concentration was reduced. At 15℃, the intracellular ATP concentration was 4% of that at 30℃. The decrease in temperature led to a decrease in the release of N2O in the ANAMMOX process. When the temperature decreased, the denitrification rate would decrease, leading to a lower N2O production rate and lower N2O accumulation. 16S rRNA amplicon sequencing showed that ANAMMOX bacteria Candidatus Brocadia and Ca. Jettenia were enriched, accounting for 6.9%-13.8% and 1.4%-2.6% of microbial community, respectively. Abundant heterotrophic bacteria were also found in the microbial community. The accumulation of N2O in the ANAMMOX process was mainly attributed to denitrifying bacteria producing and consuming N2O. This study provides support for controlling N2O emission during the ANAMMOX process for treating municipal wastewater.

Effect of Hydroxylamine on Community of ANAMMOX Sludge

At present, the anaerobic ammonium oxidation (ANAMMOX) process has the advantages of high efficiency, low energy consumption, and low sludge quantity, and it therefore has broad application prospects in sewage nitrogen removal. Hydroxylamine is not only an intermediate product of ANAMMOX metabolism but also an inhibitor. However, the effect of hydroxylamine on the activity of ANAMMOX is not clear. Therefore, we investigated the ANAMMOX activity under the condition of adding different concentrations of hydroxylamine (40-80 mg·L-1) through a hydroxylamine batch experiment. It was found that hydroxylamine can inhibit ANAMMOX activity. However, it was impossible to determine the threshold of ANAMMOX bacteria to hydroxylamine. Next, the mRNA levels of hydrazine oxidase (HZO) in different reactors were detected by real-time fluorescent quantitative polymerase chain reaction (RT-qPCR), and it was found that the expression levels of HZO peak and then decrease with an increase of hydroxylamine concentration. It was suggested that the tolerated hydroxylamine concentration was within 60-70 mg·L-1 for 3.12 g·L-1 ANAMMOX granular sludge. Moreover, a 16S rRNA high-throughput sequencing method was used to analyze the structure and function of ANAMMOX granules in microbial communities in the reactor. It was found that the addition of an appropriate concentration of hydroxylamine (50 mg·L-1) helped to enhance the cellular motility of bacteria and promoted the composition of ANAMMOX bacteria, providing a better ecological balance.

Effect of Ni(Ⅱ) on Anaerobic Ammonium Oxidation and Changes in Kinetics

Anaerobic ammonium oxidation (ANAMMOX) is widely used for treatment of ammonium-rich wastewater because of its economic and environmental benefits. However, ANAMMOX bacteria are sensitive to environmental conditions, especially to heavy metals. The short-term and long-term effects of Ni(Ⅱ) on ANAMMOX were studied by batch and continuous flow experiments, respectively. Results showed that low concentrations of Ni(Ⅱ) had promoted nitrogen removal by ANAMMOX and high concentrations inhibited ANAMMOX performance during a short-term period. Compared with the specific anaerobic ammonium oxidation activity (SAA) without Ni(Ⅱ) addition, SAA with 1 mg·L-1 Ni(Ⅱ) addition increased by 11.14% and the SAA with 100 mg·L-1 Ni(Ⅱ) addition reduced by 49.55%. The IC50 of Ni(Ⅱ) for ANAMMOX was determined to be 83.86 mg·L-1. In contrast, long-term Ni(Ⅱ) addition significantly suppressed nitrogen removal of ANAMMOX, and the suppression threshold of Ni(Ⅱ) on ANAMMOX was 15 mg·L-1. The Monod model was applied to simulate the kinetics of ANAMMOX without Ni(Ⅱ) addition. The qmax0(TN/VSS) and KS0 values were 12.25 mg·(g·h)-1 and 405.36 mg·L-1, respectively. The modified Haldane model was suitable to describe the kinetics of ANAMMOX with 50 mg·L-1 Ni(Ⅱ) addition. The qmax(TN/VSS), KS, and Ki values were 6.78 mg·(g·h)-1, 313.2 mg·L-1, and 1.32, respectively. The inhibition of ANAMMOX by Ni(Ⅱ) is anticompetitive inhibition. In addition, the inhibition of Ni(Ⅱ) on ANAMMOX was mainly related to the content of intracellular Ni(Ⅱ). The IC50intracellular Ni(Ⅱ)(VSS) of intracellular Ni(Ⅱ) was 0.072 mg·g-1.

Innovative start-up strategies for single-stage deammonification with conventional activated sludge: Results of a pilot-scale demonstration

This study investigated innovative start-up strategies of a pilot-scale sequencing batch reactor (SBR) for single-stage deammonification using activated sludge as the sole inoculum source. In 24 m3 aerobic oxidizing bacteria cultivation plant, nitrogen loss efficiency was suggested to be an indicator for determining duration of cultivation. In 12 m3 ANAMMOX (ANaerobic AMMonium OXidation) cultivation plant, combined strategy (sequential fed-batch and continuous modes) was adopted to promote ANAMMOX activity from activated sludge. Both the cultivated sludge were inoculated in 24 m3 pilot-plant for single-stage SBR with deammonification. The feed distribution strategy was used to cultivate ANAMMOX bacteria selectively resulting in nitrogen removal rate of 0.73 kg/m3/d and nitrogen removal efficiency of 86.5 ± 1.9% within 254 days. Candidatus Brocadia sp. 40 was enriched from undetectable to 22.7% relative abundance. These findings indicated that fast start-up of the deammonification process was possible without ANAMMOX seed sludge in pilot-scale reactor with various variables.

Comparative study on pilots between ANAMMOX favored conditions in a partially saturated vertical flow constructed wetland and a hybrid system for rural wastewater treatment

The objective of this research was to evaluate the nitrogen removal in a single stage rural wastewater treatment system. It was a modified subsurface vertical flow (SSVF) constructed wetland. The so-called Anaerobic Ammonium Oxidation(ANAMMOX) process is favored by imposing a saturated zone at the bottom of the basin. The nitrogen removal performances of this modified SSVF were compared to those of a conventional hybrid system where the well-known nitrification-denitrification process is performed. This study was carried out using three lab-scale pilots of constructed wetlands during four months: (1) a hybrid constructed wetlands with a reed-Phragmites australis SSVF bed in serial with a cattail-Typha angustofolia SSHF bed (SSVFp + SSHF). (2) A reed-Phragmites australis SSVF bed partially saturated at 40% of its depth (SSVFPS); (3) A cattail-Typha angustofolia SSVF bed partially saturated at 40% of its depth (SSVFTS). The results showed that the three configurations used in this study were efficient for most of the pollutants reduction. In fact, single-stage reactors have achieved similar chemical oxygen demand (COD) removal in comparison to the two-stage reactor independently of the macrophytes species. However, for Total Kjeldahl Nitrogen (TKN), a slightly higher nitrogen removal efficiency was recorded for (SSVF p + SSHF) with an average removal rate of 53% versus 48% and 51% for SSVF PS and SSVFTS respectively. These findings were highlighted with fluorescent in situ hybridization (FISH) analysis, which demonstrated the presence of major differences in the community composition and abundance of the bacteria involved with denitrification and nitrification in the three systems. In fact, SSVFP of the hybrid system was characterized by highest relative abundance of nitrifying bacteria (13% Nitrosomonas, 11% Nitrosospira, 14% Nitrospira and 10% Nitrobacter). While, the SSHF of hybrid system had larger number of denitrifying species than SSVF, with relative abundances of pseudomonas (3%), Paracoccus (9%), Zoogloea (6%), Thauera (4%), Thiobacillus (2%) and Aeromonas (1%). Interestingly, in the SSVFST (planted with Thypha angustofolia) where the relative abundance of nitrifying bacteria was very low (4% Nitrosomonas, 4% Nitrosospira, 4% Nitrospira and 1% Nitrobacter), we have detected the presence of ANAMMOX bacteria (3%). Accordingly SSVFST in the presence of Thypha angustofolia have favored the development of ANAMMOX activity in comparison to the other configurations.

Successful start-up of pilot-scale single-stage ANAMMOX reactor through cultivation of ammonia oxidizing and ANAMMOX bacteria

The lack of seed sludges for Ammonium Oxidizing Bacteria (AOB) and slow-growing ANaerobic AMMonium OXidation (ANAMMOX) bacteria is one of the major problem for large-scale application. In this study, 24m3 of single-stage SBR (Sequencing Batch Reactor) was operated to remove nitrogen from reject water using AOB and ANAMMOX bacteria cultivated from activated sludge in the field. The ANAMMOX activity was found after 44 days of cultivation in the ANAMMOX cultivation reactor, and then 0.66 kg N/m3/d of the nitrogen removal rate was achieved at 0.78 kg N/m3/d of the nitrogen loading rate at 153 days of cultivation. The AOB cultivation reactor showed 0.2 kg N/m3/d of nitrite production rate at 0.4 kg N/m3/d of nitrogen loading rate after 36 days of operation. The cultivated ANAMMOX bacteria and AOB was mixed into the single-stage SBR. The feed distribution was applied to remove total nitrogen stably in the single-stage SBR. The nitrogen removal rate in the single-stage SBR was gradually enhanced with an increase of specific activities of both AOB and ANAMMOX bacteria by showing 0.49 kg N/m3/d of the nitrogen removal rate at 0.56 kg N/m3/d of the nitrogen loading rate at 54 days of operation.

Key operating parameters affecting nitrogen removal rate in single-stage deammonification

The key operating parameters for improving the nitrogen removal rate (NRR) in a sequencing batch reactor (SBR) for deammonification were investigated. The major operating strategies were the coexistence between deammonification and denitrification with a carbon/nitrogen (C/N) ratio of 0.5 and the control of the number of sub-cycles based on substrate concentration for anaerobic ammonium oxidation (ANAMMOX) and ammonium oxidizing bacteria (AOB). In the study, denitrification with the addition of an organic source was beneficial for improving the NRR from 0.5 ± 0.01 kg N m−3 d−1 to 0.53 ± 0.01 kg N m−3 d−1 by removing the nitrate produced as a by-product of ANAMMOX. Unlike the gradual increase of the specific activity for AOB, the specific ANAMMOX activity (SAA) was maximized when an ammonium concentration supplied after sub-feeding phase was increased from 20 to 100 mg L−1, which increased the NRR from 0.53 ± 0.01 kg N m−3 d−1 to 0.79 ± 0.01 kg N m−3 d−1. This result suggested that the SAA is more important than the specific activity for AOB as a parameter for controlling the NRR in the single-stage deammonification. In the whole experimental period, the granule size smaller than 100 μm accounted for 52.5 ± 0.9%, making the largest contribution to the activity for AOB and denitrifiers. However, the granule size larger than 100 μm made the greatest contribution (83.8 ± 0.5%) to SAA. The feasibility of using the derivate of pH and OPR as indirect parameters to control the NRR was verified.

Performance and kinetics of ANAMMOX granular sludge with pH shock in a sequencing batch reactor.

As an efficient and cost-effective nitrogen removal process, anaerobic ammonium oxidation (ANAMMOX) could be well operated at suitable pH condition. However, pH shock occurred in different kinds of wastewater and affected ANANNOX process greatly. The present research aimed at studying the performance and kinetics of ANAMMOX granular sludge with pH shock. When influent pH was below 7.5, effluent [Formula: see text]-N and [Formula: see text]-N increased with decreasing pH. At Ph 6.0, effluent [Formula: see text]-N approached 100mg/L, and the ratios of [Formula: see text] approached 2.2 and 1.3, respectively. Both greatly deviated from theoretical values. When influent pH was above 7.5, effluent [Formula: see text]-N and [Formula: see text]-N increased with increasing pH. At pH 9.0, ammonium removal rate (ARR) and nitrite removal rate (NRR) decreased to 0.011±0.004 and 0.035±0.004kg/(m3·d), respectively. Besides, [Formula: see text]-N:[Formula: see text]-N deviated from theoretical value. Longer recovery time from pH 9.0 than from pH 6.0 indicated that alkaline surroundings inhibited anaerobic ammonium oxidizing bacteria (AAOB) greater. The sludge settling velocity was 2.15cm/s at pH 7.5. However, it decreased to 2.02cm/s when pH was 9.0. Acidic pH had little effect on sludge size, but disintegration of ANAMMOX granule was achieved with pH of 9.0. The Bell-shaped (A) model and the Ratkowsky model were more applicable to simulate the effect resulting from pH shock on ANAMMOX activity (R2>0.95), and both could describe ANAMMOX activity well with pH shock. They indicated that qmax was 0.37 kg [Formula: see text]-N/(kgMLSS·d) at the optimum pH value (7.47) in present study. The minimum pH during which ANAMMOX occurred was 5.68 while the maximum pH for ANAMMOX reaction was 9.26. Based on nitrogen removal performance with different pH, strongly acidic (pH≤6.5) or alkaline (pH≥8.5) inhibited ANAMMOX process. Besides, ANAMMOX appeared to be more susceptible to alkaline wastewater. Compared to extremely acidic condition (low pH), extremely alkaline condition (high pH) affected ANAMMOX granules much more.

Nitrogen Removal Performance of ANAMMOX with Different Organic Carbon Sources

Anaerobic ammonium oxidation (ANAMMOX) has been regarded as an efficient process to treat high-strength wastewater without organic carbon source. To investigate the nitrogen removal performance of ANAMMOX in the presence of organic carbon source can broaden its application in organic wastewater treatment. In this work, an anaerobic sequencing batch reactor (ASBR) was used to study the effect of organic carbon source on ANAMMOX process. The experimental results indicated that the activity of anaerobic ammonia oxidizing bacteria (AAOB) decreased by 84.2% when 200 mg·L-1 COD of glucose was added. When sodium acetate was added, the activity of AAOB was affected little. Besides, it even promoted the activity with COD less than 120 mg·L-1. The effect of sucrose on ANAMMOX process was similar to that of sodium acetate and the maximum specific ANAMMOX activity (SAA) increased by 25.0% with 80 mg·L-1 COD. When citric acid was added, the maximum SAA peaked with 80 mg·L-1 COD. The order of ANAMMOX promotion resulted from organic carbon source was sucrose, sodium acetate, citric acid and glucose. With addition of organic carbon source, nitrate could also be removed through the synergy of ANAMMOX and denitrification, and the total nitrogen removal efficiency increased.

In situ nitrogen management in landfill bioreactors using combined sharon and anammox processes

Landfill bioreactors (LFBR) are gaining significant attention as sustainable alternative for conventional landfilling. Nitrogen management is an important issue in landfill bioreactors. The present study is to establish the combined SHARON (single reactor system for high activity ammonia removal over nitrite) and ANAMMOX (anaerobic ammonium oxidation) processes in landfill bioreactors for in situ nitrogen management. Laboratory scale landfill bioreactors (43 L volume capacity) as SHARON-ANAMMOX LFBR were loaded with mined municipal solid waste operated for 147 days at a nitrogen loading rate of 1.2 kg N/m3/d. The results showed a nitrogen removal efficiency of 84% with maximum partialnitritation efficiency of 56% and specific ANAMMOX activity of 0.7 mg Amm-N/mg MLVSS/d was achieved in the LFBR. Nitrogen transformations, biomass development and, hydrazine and hydroxylamine formation authenticated the aerobic ammonium oxidising bacteria (AOB) and anaerobic ammonium oxidising bacteria (AnAOB/ANAMMOX) activities responsible for combined SHARON-ANAMMOX processes in LFBR. 99% of the biogas in LFBR as N2 the end product confirmed the combined SHARON-ANAMMOX processes. The study successfully demonstrated the combined SHARON-ANAMMOX processes for in situ nitrogen management in landfill bioreactors with shorter start-up time and stable operation.

Specific ANAMMOX activity (SAA) in a sequencing batch reactor: optimization test with statistical comparison

A sequencing batch reactor (SBR) is a suitable system for evaluating an anaerobic ammonium oxidation (ANAMMOX) process. Response surface analysis was employed to optimize the specific ANAMMOX activity (SAA) and evaluate its technical features in a SBR with a range of total nitrogen (TN) concentration as NH4 +–N and NO2 −–N at 1:1 ratio and an appropriate pH. A partial cubic model adequately fit the response surface with high statistical significance. SAA was optimized at 1.77 mg-N/mg-VSS day with 155.9 mg-N/L TN concentration and pH at 7.34. The inhibition factors of free ammonia, free nitrous acid (FNA), and nitrite gave specific rise to the SAA responses of over 1.4 mg-N/mg-VSS day in square-like boundaries. However, the toxic effect of 2.4 mg-N/L of FNA was identified to induce a drastic decrease at the lowest pH of 5.6. For the most optimized fed-batch mode for ANAMMOX-SBRs, this study found that TN was 100–200 mg/L and pH was 6.5–8, which can become controlling factors for physicochemical reactions at the time of substrate feeding and microbial reacting stages.

Effect of increase in salinity on ANAMMOX–UASB reactor stability

ABSTRACTThe effect of salinity on the anaerobic ammonium oxidation (ANAMMOX) process in a UASB reactor was investigated by analysing ammonium, nitrite, nitrate and TN concentrations, and TN removal efficiency. Extracellular polymeric substances (EPSs) and specific ANAMMOX activity (SAA) were evaluated. Results showed the effluent deteriorated after salinity was increased from 8 to 13 g/L and from 13 to 18 g/L, and TN removal efficiency decreased from 80% to 30% and 80% to 50%, respectively. However, ANAMMOX performance recovered and TN removal efficiency increased to 80% after 40 days when the influent concentrations of and were 200 mg/L and salinity levels were at 13 and 18 g/L, respectively. The amount of EPSs decreased from 58.9 to 37.1 mg/g volatile suspended solids (VSS) when the reactor was shocked by salinity of 13 g/L, and then increased to 57.2 mg/g VSS when the reactor recovered and ran stably at 13 g/L. The amount of EPSs decreased from 57.2 to 49.1 mg/g VSS when the reactor was shocked by salinity of 18 g/L, and then increased to 60.7 mg/g VSS when the reactor recovered and ran stably at 18 g/L. The amount of EPS and the amounts of polysaccharide, protein and humus showed no evident difference when the reactor recovered from different levels of salinity shocks. Batch tests showed salinity shock load from 8 to 38 g/L inhibited the SAA. However, when the reactor recovered from salinity shocks, SAA was higher compared to that when the reactor was subjected to the same level of salinity shock.

The phenological stage of rice growth determines anaerobic ammonium oxidation activity in rhizosphere soil

Anaerobic oxidation of ammonium (anammox) plays an important role in nitrogen (N) loss from agricultural systems. Recently, the rice rhizosphere was demonstrated to be a hotspot for anammox, yet the dynamics of anammox activity and the distribution of anammox bacteria in rhizosphere soil at different phenological stages of rice growth are still unknown. In this study, the activity, diversity and abundance of anammox bacteria in both rhizosphere and bulk soils were investigated over the entire rice growth season. From tillering to ripening stage, significantly higher anammox bacterial abundance was detected in rhizosphere soils compared to bulk soils. The rhizosphere soils also had significantly higher anammox rates at tillering and booting stages (0.71 and 0.32 nmol N g−1 dry soil h−1, respectively) compared to bulk soils. The anammox rate in rhizosphere soil was positively correlated to the concentrations of NOx− (total of nitrate and nitrite) and acetate. The abundance of anammox bacteria was significantly correlated with the concentration of succinate in rhizosphere soils. A total of five anammox genera of Brocadia, Kuenenia, Anammoxoglobus, Jettenia and Scalindua were detected, with Brocadia predominating in all examined samples. The distribution of anammox bacteria in rhizosphere and bulk soils varied with phenological stages. Statistical analysis indicated that C/N ratio, formate, citrate and ammonium were key factors influencing the composition of anammox bacteria. Variations in activity, abundance and distribution of anammox bacteria in rhizosphere were observed over the phenological progression, demonstrating that the root exudates might be influential for the anammox process. This study implies that future efforts in estimating the rate of anammox should consider the temporal variation during plant life cycles.

Enhancement of anammox performance by Cu(II), Ni(II) and Fe(III) supplementation

This study explored the influence of metal ion addition on specific anaerobic ammonium oxidation activity (SAA). Batch assays were used to demonstrate the enhancement of the SAA upon the addition of Cu2+, Ni2+ and Fe3+. The SAA was enhanced by 41.0% when the Cu2+ concentration was below 1mgL−1, while it was improved by 63.5% at Ni2+ concentrations below 1.74mgL−1. An enhancement of 533.2% was obtained when 3.68mgL−1 Fe3+ was supplied. The effects of Fe3+, Cu2+ and Ni2+ on the SAA were analyzed and optimized by a response surface methodology, which demonstrated that the interaction between Fe3+ and Cu2+ was significant and that 6.61mg Fe3+ L−1, 1.18mgCu2+L−1 and 1.11mgNi2+L−1 were the optimal values for metal dosing. Subsequently, an Fe3+–Cu2+–Ni2+ continuous test was carried out under optimal conditions and revealed that the addition of Fe3+, Cu2+ and Ni2+ could stimulate the reactor potential at ambient temperature. The maximum nitrogen removal rate (NRR) of the test reactor was 52.8% higher than that of the control reactor (8.1 versus 5.3kgNm−3d−1). Moreover, a continuous test conducted by adding Fe3+ achieved an average nitrogen removal efficiency and maximum NRR of 67.4% and 4.9kgNm−3d−1, respectively, while the corresponding values of the control test were 64.7% and 4.1kgNm−3d−1, respectively. Altogether, appropriate dosages of Cu2+, Ni2+ and Fe3+ can significantly enhance the SAA and improve the reactor capacity at ambient temperature.

Mechanisms of ultrasound irradiation for enhancing the ANAMMOX process

The feasibility and mechanisms of anaerobic ammonium oxidation (ANAMMOX) pathway stimulation by ultrasound irradiation were explored. A response surface methodology (RSM) was chosen to optimize ultrasonication parameters according to specific ANAMMOX activity (SAA), and optimum conditions were attained at an ultrasound intensity (UI) of 0.7W/cm2 and an exposure time (ET) of 1.9min. Compared with ET, UI significantly affected the SAA. Dehydrogenase enzyme activity measured after ultrasonication was 61% higher compared to the control sludge not exposed to ultrasound. After ultrasound irradiation, the half-saturation constant decreased from 174.5 to 168.5mgTN/L (TN represents total nitrogen), and the IC50 (half-maximal inhibitory concentration) decreased from 633.4 to 571.4mgTN/L. The dehydrogenase enzyme activity and kinetic analysis of sludge after ultrasound irradiation confirmed that ultrasound treatment under optimal conditions increased sludge activity.