Nitrite Process Research Articles

Influence of Low Air Pressure on the Combined Nitritation and Anaerobic Ammonium Oxidation Process

Influence of Low Air Pressure on the Combined Nitritation and Anaerobic Ammonium Oxidation Process

Application of data reconciliation to a dynamically operated wastewater treatment process with off-gas measurements

Data reconciliation was applied to a full-scale SHARON partial nitritation process. Adding off-gas analysis allowed to identify more key variables, facilitated gross error detection and led to more reliable information on N2O emissions.

The short- and long-term effects of cold-temperature shock on partial nitritation - improved assessment methodology

This research sheds light on the gap in knowledge concerning the effect of temperature shock on nitrifiers. This phenomenon was analysed in context of mainstream bioaugmentation with nitrifiers cultivated in a sidestream partial nitritation process, which was recently experimentally confirmed to be beneficial in municipal wastewater treatment plants. In this study, using respirometric activity measurements and a simple mathematical model of nitritation, it has been proven that fluctuations in nitrifier concentration in long term tests affect the value of the estimated temperature correction coefficient (θ). Furthermore, this leads to underestimation of its value and thus, results in inaccurate prediction of the scale of the temperature shock effect. During the first days following the shock occurrence, the estimated process rate using the new approach was equal to only 64.1 ± 9.7% of the value calculated using previously preferred methods. Moreover, faster biomass acclimatisation to lower temperature in the following days was observed. These observations clearly indicate the need for change in the current approach and confirm the validity of the proposed improvements. It can be assumed, that the presented insights concerning the method of temperature effect assessment are transferrable to other microbial communities involved in biological wastewater treatment processes.

Achieving high-rate partial nitritation with aerobic granular sludge at low temperatures.

Partial nitritation is necessary for the implementation of the mainstream anammox (anaerobic ammonium oxidation) process in wastewater treatment plants. However, the difficulty in outcompeting nitrite-oxidizing bacteria (NOB) at mainstream conditions hinders the performance of partial nitritation. The present work aimed to develop a high-rate partial nitritation process for low-ammonium wastewater treatment at low temperatures by seeding aerobic granules. Experimental results suggested that both stratified structure of nitrifiers developed in the granules and sufficient residual ammonium concentration (18-35mgN L-1) in the bulk liquid contributed to efficient NOB repression. With the hydraulic retention time progressively shortened from 1.0 to 0.17h, the influent nitrogen loading rate of the partial nitritation process reached 6.8 ± 0.4kgN m-3 d-1 even at 10-15°C. The high concentration (7.5 gVSS L-1) and activity (0.48gN g-1 VSS d-1 at 11°C) of granular sludge made the reactor possess an overcapacity evaluated by the ratio between the actual ammonium oxidation rate of the granules and their maximum potential. The overcapacity helped the reactor to face the adverse effect of decreasing temperatures. Overall, this work indicated the great potential of applying aerobic granules to achieve high-rate partial nitritation at mainstream conditions. Moreover, anammox bacteria with a relative abundance of 2.8% was also identified in the partial nitritation granules at the end of this study, suggesting that the granules provided a habitable niche for anammox bacteria growth. Note that these results cannot fully relate to the treatment of real domestic/municipal wastewater, they are a source of important information increasing the knowledge about low temperature partial nitrification.

Impact of the nitrifying community dynamics on the partial nitritation process performed by an AOB-enriched culture in a granular sludge airlift reactor

One of the main challenges for the full-scale implementation of the autotrophic biological nitrogen removal process is to achieve a stable long-term partial nitritation under the mainstream conditions of urban wastewater treatment plants. Here, the performance of partial nitritation process under mainstream conditions was investigated based on the change of the nitrifying community developed. A lab-scale airlift reactor was operated for 430 days with a granular sludge highly enriched in ammonia oxidizing bacteria (AOB) performing partial nitritation treating a mainstream-mimicked synthetic influent. The changes in solid retention time (SRT), dissolved oxygen (DO) concentration and temperature strongly affected to the microbial community developed, especially to the dynamics of the nitrite oxidizing bacteria (NOB) population, which triggered to instabilities in the partial nitritation process. The extremely high values of SRT applied (SRT = ∞) and long-term exposure to low temperature (10 °C) promoted the growth of NOB Nitrotoga genus and development of nitratation activity; and the subsequent variability in temperature (between 10 and 30 °C) and in DO concentration (between 0.4 ± 0.1 and 1.4 ± 0.3 mg O2 L−1) influenced the competitiveness between nitrifiers and the growth of species previously undetected in the culture, as Nitrospira genus. Anaerobic ammonia oxidizing bacteria were also identified during cultivation and assisted to the repression of the NOB activity at 25–15 °C. The results of the present study uphold that understanding the niche differentiation and competitiveness of NOB will be key to develop strategies for NOB repression in order to make possible full-scale implementation of partial nitritation process at mainstream conditions.

Effect of humic acid on the single-stage nitrogen removal using anammox and partial nitritation (SNAP) process: performance and bacterial communities

The present research investigated the effect of humic acid on nitrogen removal performance and microbial community structure in a single-stage nitrogen removal using anammox and partial nitrification (SNAP) reactor. The results showed that 576 mg·L−1 humic acid enhanced nitrogen removal efficiency maximally to 96% and nitrogen removal rate to 1.61 kgN·m−3·d−1. COD concentration (provided by humic acid) of 120–233 mg·L−1, the nitrogen removal rate (NRR) was 1.27 kgN·m−3·d−1. COD concentration (provided by humic acid) of 259–658 mg·L−1 enhanced the NRR above 1.5 kgN·m−3·d−1, and COD concentration increased to 691–1637 mg·L−1, the average NRR decreased to 1.45 kgN·m−3·d−1. The results indicated COD concentration of 691–1637 mg·L−1 has the strongest positive effect on the anammox reaction. The analysis of high throughput sequencing presented COD concentration of 500 mg·L−1 promoted the growth of Candidatus_brocadia, and 1500 mg·L−1 COD concentration improved Candidatus kuenenia growth. Functional genes from KEGG and COG database showed that the expressions of nitrate reductase and nitrite reductase were highly promoted with the increase of humic acid concentration, which proved the nitrification enhanced by humic acid. All findings in this study were inferred that humic acid enhanced nitrogen removal in SNAP reactor. This result will improve the practical and effective use of the SNAP process to treat landfill leachate in engineering application.

Effects of fulvic acid on the denitrification performance of completely autotrophic nitrogen removal over nitrite (CANON) process for the treatment of landfill leachate

Ammonia reduction treatment in landfill leachate is primarily necessary to prevent toxic impacts for environmental concerns on aquatic life in surface waters. Fulvic acid (FA) is one of the refractory organic humus in landfill leachate. In this present study, the potential effects of FA on completely autotrophic nitrogen removal over nitrite (CANON) systems were studied. This study focuses on the CANON reaction startup in a short time. Effects of FA on denitrification performance, sludge properties and microbial community of CANON process. The CANON process was started in a short period of time. Ammonia nitrogen (NH4+-N) and total nitrogen (TN) removal efficiency was 98% and 80%, respectively. In the CANON process, part of the nitrification and anaerobic ammonia oxidation reaction proceed simultaneously and reach the maximum rate in the aerobic aeration stage at the initial stage of the reaction. After reaching the stable operation stage, FA was added 50 mg/L, 100 mg/L, 150 mg/L and 200 mg/L, respectively. As the FA concentration reached 200 mg/L, FA addition was stopped and the recovery was observed for a period of time. Nitrogen removal performance, sludge properties and microbial communities of the CANON process, was becoming more and more obvious with the stepwise increase in Humic acid (HA) and FA concentration. With the FA concentration increased from 50 mg/L to 200 mg/L, NH4+-N and TN removal efficiency decreased from 98.00% to 80.00%–71.32% and 48.18%, respectively. Sludge concentration decreased from 3.291 g/L to 2.245 g/L. Abundance of both ammonia-oxidizing bacteria (AOB) and anaerobic ammonia-oxidizing bacteria (AnAOB) decreased gradually, while nitrite-oxidizing bacteria (NOB) increased. After the addition of FA was stopped, the denitrification performance and granular sludge activity of CANON process were evaluated. This study can be used for application of CANON process for the treatment of landfill leachate.

Research on Biological Fluidized Bed System Treatment Performance and Nitrogen Removal Process for Seafood Processing Wastewater with Different Operation Conditions

In this study, the biological fluidized bed system was used to treat seafood processing wastewater. The sludge was collected from the secondary sedimentation tank of a municipal wastewater treatment plant and acclimated for 200 days before the experiment. The treatment efficiencies of simulated seafood processing wastewater by biological fluidized bed system with different sludge concentrations, different hydraulic retention times (HRTs) and different bio-carriers were studied. The results showed that the removal efficiency of nitrogen and phosphorus increased with the increasing sludge concentration and by extending hydraulic retention time, and the higher removal efficiency of nitrogen and phosphorus could be obtained with the higher specific surface area of the bio-carrier. The nitrogen removal process analysis showed that the nitrification and denitrification activity of sludge could be changed with different operation conditions resulting in different nitrogen removal efficiency in the biological fluidized bed system. This was mainly because the change tendency of the ammonia nitrogen oxidizing process, nitrite oxidizing process, nitrite reduction process and nitrate reduction process was different with different operation conditions in a high salinity environment. Theoretically, the difference of the inhibitory effect of a high-salt environment on different nitrification and denitrification processes could be used to realize shortcut nitrification denitrification by controlling a certain operation condition.

Modeling granule-based completely autotrophic nitrogen removal over the nitrite (CANON) process in an SBR

AbstractBased on the simplified activated sludge model No. 1 (ASM1), a 1D biofilm model containing autotrophic and heterotrophic microorganisms was developed to describe the microbial population dynamics and reactor dynamics of completely autotrophic nitrogen removal over the nitrite in sequencing batch reactor (CANON SBR). After sensitivity analysis and calibration for parameters, the simulation results of NH4+-N concentration and NO2−-N concentration were consistent with the measured results, while the simulated NO3−-N concentration was slightly lower than the measured. The simulation results showed that the soluble microbial products had an extremely low concentration. The aerobic ammonia oxidation bacteria and anaerobic ammonia oxidation bacteria were the dominant microbial populations of the CANON system, while nitrite oxidization bacteria and heterotrophic bacteria were eliminated completely. The optimal ratio of air aeration load to influent NH4+-N load was about 0.18 L air/mgN. The operating condition of the reactor was optimized according to the simulation results, and the total nitrogen removal rate and the total nitrogen removal efficiency increased from 0.312 ± 0.015 to 0.485 ± 0.013 kg N/m3/d and from 71.2 ± 4.3 to 85.7 ± 1.4%, respectively.

Evaluation of the joint effects of Cu2+, Zn2+ and Mn2+ on completely autotrophic nitrogen-removal over nitrite (CANON) process

The completely autotrophic nitrogen-removal over nitrite (CANON) process has merits in energy saving and consumption reducing, thus being considered as an attractive alternative over the common denitrification technology. In this study, the effects of three common heavy metals (Cu2+, Zn2+ and Mn2+) in wastewater to the CANON process were evaluated comprehensively. A central composite design with response surface methodology was utilized to investigate the joint effect of these three metal ions on the nitrogen removal performance of CANON process. In accordance with the determined optimal dosage in batch tests, four bioreactors were established with different amounts of heavy metal dosage in long-term operation, which determined the optimal concentrations for Cu2+, Zn2+ and Mn2+ to be 0.25, 0.81 and 1.00 mg/L, respectively. However, the optimal dosing level determined in batch tests showed no promotion during long-term experiment. This indicated that the actual concentration of heavy metals in bioreactors during long-term operation could be higher than expectation, leading to the difference between short-term tests and long-term experiment. The distribution of metal ions revealed that Mn2+ was mainly absorbed in anammox bacteria cells while Cu2+ and Zn2+ were mostly identified inside AOB cells. Moreover, the addition of heavy metals consistently showed positive effects for the relative abundance of AOB, while only a low level of dosage could promote the abundance of anammox bacteria. Furthermore, a mathematical model was established to simulate the CANON system considering the impacts of heavy metals, which was calibrated and validated using independent dataset in this study.

Nutrients removal from low C/N actual municipal wastewater by partial nitritation/anammox (PN/A) coupling with a step-feed anaerobic-anoxic-oxic (A/A/O) system

In this study, a novel combined strategy was successfully established by partial nitritation/anammox (PN/A) within a step-feed A/A/O process integrated with fixed-biocarriers to treat municipal sewage for 200 days. The excellent nutrients removal performance of this system compared with national level of discharging standard were achieved: low total inorganic nitrogen (7.1 mg/L) and phosphorus (0.3 mg/L) in the effluent with the influent (51.1 and 4.2 mg/L) at C/N ratios of 3.4 ± 0.5, mainly attributed to the stable PN (oxic zone) and subsequently anammox effect (anoxic zone). Nitrogen mass balance indicated that anammox contribution in anoxic zones to nitrogen loss could be up to 42% at stable phase. Therefore, aeration and carbon cost could be greatly reduced under low DO, low C/N and aerobic hydraulic retention time (HRT) of 7.4 h condition. The low DO and anammox bacteria retention in anoxic chambers promoted the washout of NOB and combination of anammox and partial nitritation process. During long-term operation, the activity of AOB effectively maintained while that of NOB drastically reduced to 0.1 mg N / g MLSS / h resulting in high and stable nitrite accumulation ratios (about 90%). The achievement of partial nitritation was mainly due to low DO (0.4–0.5 mg/L) and effective retention of anammox bacteria even with a low temperature (14.5 °C). Notedly, anammox activity gradually increased both on the biocarriers and in the flocs while a higher anammox abundance was observed on the biocarriers (2.48%) than that in suspend flocs (0.03%). As above, this study indicated that the novel combined strategies could be applicable to mainstream anammox, and a pilot-scale reactor will be established to verify and promote the industrial application of mainstream anammox.

Achieving biogas production and efficient pollutants removal from nitrogenous fertilizer wastewater using combined anaerobic digestion and autotrophic nitrogen removal process

Nitrogenous fertilizer was massively utilized during agricultural production process, which led to the discharge of large amount of nitrogenous wastewater with low C/N ratio. In this study, anaerobic digestion combined with subsequent Completely autotrophic nitrogen removal over nitrite (CANON) process was adopted for treating nitrogenous fertilizer wastewater. The reactor performances and the microbial community structure were analyzed. Results showed that COD was mainly removed by anaerobic digestion, with the COD removal efficiency as 98.4%, and nitrogen was effectively removed via CANON integrating with partial denitrification, with the removal efficiency as 96.3%. The COD, ammonia and total nitrogen in the effluent of the combined process were 3.7, 2.9 and 7.4 mg L−1, respectively. Methanothrix (43.2%) and Methanomassiliicoccus (34.0%) were detected as the dominant methane production archaea, while Nitrosomanas (10.4%), Candidatus Kuenenia (13.8%) and Truepera (2.8%) were detected as the functional bacteria for nitrogen removal, when treated the nitrogenous fertilizer wastewater.

Nitrogen removal performance and microbiological characteristics of a three-stage series of vertical flow constructed wetlands.

In this study, the treatment performance and underlying molecular mechanisms of nitrogen transformation in a three-stage series of vertical flow constructed wetlands (T-VFCWs) treating rural domestic sewage were investigated at three different hydraulic loading rates (HLRs). Specifi-cally, the T-VFCWs composed of three sequential vertical flow constructed wetlands (termed V-1, V-2 and V-3), which were built according to the topography. The results showed that high pollutant removal rates could be achieved when the T-VFCWs was operated to treat rural domestic sewage, even though the HLR increased from 0.10 to 0.20 m3·m-2·d-1. Effluent quality of the T-VFCWs could reach Discharge Standard of Pollutants for Municipal Wastewater Treatment Plant (GB 18918-2002) class A standard. Regarding to the T-VFCWs operated under the oxygen-limiting conditions, three different pathways for nitrogen transformation could be respectively formed in V-1, V-2 and V-3, owing to the specific influent quality of each subunit. Consequently, the T-VFCWs were effective in nitrogen removal as a result of the collaboration of the three subunits. When the T-VFCWs ran constantly during the test, nitrogen removal in V-1, V-2, and V-3 respectively relied on the nitritation/denitrification process, the completely autotrophic nitrogen removal over nitrite (CANON) process, and the denitrification process. The contributions of three subunits for total nitrogen (TN) and NH4+-N removal were (51.3±4.4)% and (63.7±2.6)%, (30.9±4.8)% and (35.5±4.5)%, (17.8±5.0)% and (0.8±0.1)%, respectively. This study could provide scientific basis and technical support for the research and the engineering application of hybrid constructed wetlands.

The benefits of autotrophic nitrogen removal from high concentration of urea wastewater through a process of urea hydrolysis and partial nitritation in sequencing batch reactor

For the sake of high efficiency and saving operational cost for high-concentration urea wastewater treatment, a novel two-stage partial nitritation (PN)-anammox process containing simultaneous urea hydrolysis and PN in sequencing batch reactor (SBR) was investigated. Although the influent urea concentration increased from 500 to 1200 mg/L, the SBR simultaneously achieved urea removal efficiency higher than 98% and stable PN with effluent NO2−-N/NH4+-N ratio of 1.0–1.3 without any extra alkalinity addition. The intracellular hydrolysis was the dominant mechanism for urea removal and persistent free ammonia inhibition on nitrite-oxidizing bacteria was the main reason for nitrite accumulation of 97.92% in SBR. The subsequent anammox reactor showed efficient nitrogen removal performance with average ammonium removal efficiency, nitrogen removal efficiency and maximum nitrogen removal loading rate of 98.08%, 81.45% and 1.05 kg N·m−3·d−1 respectively. High-throughput sequencing results indicated Gemmatimonadetes became the most abundant bacterial phylum related to potential intracellular urea hydrolysis and displayed obvious ammonium-oxidizing bacteria enrichment and nitrite-oxidizing bacteria inhibition in SBR, and the dominant anammox bacteria (Candidatus_Kuenenia) in anammox reactor. The proposed process was proven to be promising for high-concentration urea wastewater treatment, facilitating the sustainable development of the urea industry in the future.

Evaluation of Partial Nitritation/Anammox Process for Reduction of Pollutants from Sanitary Landfill Leachate

A proposed combined process (partial nitritation process followed by anaerobic ammonia oxidation process (anammox)) was used to treat municipal landfill leachate with high amount of pollutants. This process remains under the considerable scope to increase the treatment ability of hazardous leachate. This proposed treatment will conserve surface water and ground water and save energy as well. Leachate used in this study was provided from a drainage system of a landfill in Borg El-Arab city, Egypt. The leachate produced from the studied landfill has a high concentration of ammonia that ranged from 115 mM to 160 mM. Batch laboratory experiments were performed using synthetic wastewater composed of ammonia and nitrite in the theoretical stoichiometric molar relationship ratio (1:1.32) to enrich anammox granules. This experiment was followed by using real sanitary landfill leachate produced from partial nitritation process (PN). Partial nitritation reactor was operated at constant hydraulic retention time (24 h), using three different leachate concentrations, namely, 5.9%, 25%, and 50%. The results showed that the partial nitritation process ranged from 30% to 50.8% over the study period due to the inhibition of nitrite-oxidizing bacteria by free ammonia and free nitrous acid. Ammonia reduction up to 85% has been achieved in the anammox reactor. Corresponding nitrite reduction was almost 99% in the anammox reactor. This study revealed that Broccadia species in the anammox reactor was demonstrated to be responsible for the anammox process.

N2O generation via nitritation at different volumetric oxygen transfer levels in partial nitritation-anammox process

Volumetric oxygen transfer coefficient (KLa) is an important parameter affecting oxygen transfer and nitrogen conversion during biological wastewater management. However, how the generation of nitrous oxide (N2O) responds to the variation of KLa levels is unclear. In this study, N2O generation via the main pathway, which was confirmed to be nitritation, at different KLa levels was investigated in a partial nitritation-anammox (PN-A) reactor run as a sequencing batch reactor. The results showed that N2O generation in the PN-A process, which was described using the maximum N2O generation rate (MGR), the duration of N2O generation (DG), and the N2O generation factor, was affected by KLa levels and the limiting factors of the nitritation process, i.e., oxygen transfer and nitritation activity. DG always decreased with the increase of KLa, indicating that the process of N2O generation lasted for a shorter time at higher KLa. With the increase of KLa, MGRs remarkably increased when oxygen transfer was the limiting factor, while slightly reduced when nitritation activity became the limiting factor. As a result, with the increase of KLa levels, the N2O generation factor remarkably increased at lower KLa levels when oxygen transfer was the limiting factor, but significantly reduced at higher KLa levels when nitritation activity became the limiting factor. These results revealed how N2O generation via nitritation responded to different KLa levels and the limiting factors of the nitritation process. Based on these results, practical suggestions to mitigate the N2O generation in PN-A process operated in a batch mode were recommended.

Robust Nitritation Sustained by Acid-Tolerant Ammonia-Oxidizing Bacteria

Oxidation of ammonium to nitrite rather than nitrate, i.e., nitritation, is critical for autotrophic nitrogen removal. This study demonstrates a robust nitritation process in treating low-strength wastewater, obtained from a mixture of real mainstream sewage with sidestream anaerobic digestion liquor. This is achieved through cultivating acid-tolerant ammonia-oxidizing bacteria (AOB) in a laboratory nitrifying bioreactor at pH 4.5-5.0. It was shown that nitrite accumulation with a high NO2-/(NO2- + NO3-) ratio of 95 ± 5% was stably maintained for more than 300 days, and the obtained volumetric NH4+ removal rate (i.e., 188 ± 14 mg N L-1 d-1) was practically useful. 16S rRNA gene sequencing analyses indicated the dominance of new AOB, "Candidatus Nitrosoglobus," in the nitrifying guild (i.e., 1.90 ± 0.08% in the total community), with the disappearance of typical activated sludge nitrifying microorganisms, including Nitrosomonas, Nitrospira, and Nitrobacter. This is the first identification of Ca. Nitrosoglobus as key ammonia oxidizers in a wastewater treatment system. It was found that Ca. Nitrosoglobus can tolerate low pH (<5.0), and free nitrous acid (FNA) at levels that inhibit AOB and nitrite-oxidizing bacteria (NOB) commonly found in wastewater treatment processes. The in situ inhibition of NOB leads to accumulation of nitrite (NO2-), which along with protons (H+) also produced in ammonium oxidation generates and sustains FNA at 3.0 ± 1.4 mg HNO2-N L-1. As such, robust PN was achieved under acidic conditions, with a complete absence of NOB. Compared to previous nitritation systems, this acidic nitritation process is featured by a higher nitric oxide (NO) but a lower nitrous oxide (N2O) emission level, with the emission factors estimated at 1.57 ± 0.08 and 0.57 ± 0.03%, respectively, of influent ammonium nitrogen load.

Effect of Filter Medium on the Enhancement of Complete Autotrophic Nitrogen Removal over Nitrite Process in a Tidal Flow Constructed Wetland

This study attempted to shorten the time wasted at the startup of a complete autotrophic nitrogen removal over nitrite (CANON) process in a tidal flow constructed wetland (TFCW) to achieve higher nitrogen removal rates. Thus, the starting performance and the related microbiological characteristics of different kinds of filter media filling the TFCW were explored at an appropriate drainage rate. The results showed that the physicochemical properties of the filter medium could significantly affect the quantity and activity of the functional microbes (especially ANAMMOX bacteria) enriched in the TFCWs, leading to fluctuations of the starting time and nitrogen transformation rates of the systems filled with five different kinds of filter media. Compared with that of gravel, the quantity and activity of ANAMMOX bacteria in the bed could be enhanced to different degrees as the TFCW was filled with ceramsite, zeolite, broken bricks, and lobster shells. Correspondingly, the starting times of the TFCWs with the CANON process were shortened, and their nitrogen removal performances could also be optimized. When the hydraulic loading rate of the TFCW was 0.96 m3·(m2·d)-1, the initiation of the CANON process could be accomplished successfully in the system filled with lobster shells within 300 cycles, since AOB and ANAMMOX bacteria could become dominant quickly in the packing bed. Moreover, the TN and NH4+-N removal rates could reach up to (88.37±1.19)% and (91.03±0.66)%, respectively, followed by those of broken bricks, zeolite, ceramsite, and gravel.

Nitrogen removal and microbial community characteristics of CANON process enhanced by static magnetic field at ambient temperature

In this study, a completely autotrophic nitrogen-removal over nitrite (CANON) process was started in a membrane bioreactor at ambient temperature, to which a static magnetic field (SMF) at a 20 ​mT intensity was applied to evaluate the enhancement of the CANON process by SMF. The results indicated that the SMF was capable of enhancing the nitrogen removal rate and shortening the start-up period of the CANON process. After running for about 8 months, the average nitrogen removal rate of the CANON process with SMF exposure was 324.8 ​± ​64.8 gN/m3/d, which was 30.4% higher than that of the control. Moreover, the SMF has the potential to protect the CANON process from being inhibited by low temperatures. Importantly, the SMF induced the synthesis and secretion of the extracellular polymeric substance (EPS) of the activated sludge and simultaneously reduced the zeta potential. This was conducive to the aggregation of the sludge material and the formation of an oxygen gradient in the sludge flocs, which promoted the coexistence of ammonium-oxidizing bacteria (AOB) and anaerobic ammonium-oxidizing bacteria (AnAOB). The high-throughput 16S rRNA gene sequence analysis confirmed that the abundances of the Nitrosomonas and Candidatus Brocadia genera, respectively the main AOB and AnAOB, were enhanced by SMF exposure.

A Novel Stable Nitritation Process Based on Linear Regression: Sludge Treatment by Alternating Free Nitrous Acid (FNA)/Heat Shock

A Novel Stable Nitritation Process Based on Linear Regression: Sludge Treatment by Alternating Free Nitrous Acid (FNA)/Heat Shock