Nitrite Oxidizing Bacteria Activity Research Articles

Mechanism of stable autotrophic nitrogen removal and NOB inhibition in low-sludge PN-Anammox system under non-temperature control and low ammonia environment

PN/Anammox, as an economical and effective nitrogen removal process, is of great significance for reducing carbon emission in municipal wastewater treatment. However, municipal wastewater has mainstream characterized of low temperature and low NH4+-N concentration, and NOB activity is difficult to inhibit, so achieving a stable PN process is the biggest challenge in the application of PN/Anammox to mainstream wastewater. This study developed a method for stable and efficient PN/Anammox based on very low sludge volume (MLVSS = 65 mg/L). Even when the temperature dropped to 15℃ or there was exogenous nitrite-oxidizing bacteria (NOB) interference, the system still had good inhibition of NOB activity. The total stable operation time was 386 days, and the NO2–-N accumulation efficiency could reach more than 90 %. Ellin6067, Nitrosomonas and Candidatus_Brocadia were the dominant functional microorganisms in the system. Nitrospira was the dominant genera of NOB with very low relative abundance (<0.04 %). The mechanism of the long-term stable mainstream PN/Anammox system showed that low sludge content was beneficial to light irradiation on microorganisms in the reactor, while nxrA, the functional gene of NOB, had weak light resistance and oxidation resistance, which makes the system had strong inhibition effect on NOB. The construction of this new system which does not depend on activated sludge volume and complex NOB activity inhibition strategy can better promote the practical application of PN/Anammox under mainstream conditions.

Effective recovery of the nitritation process through hydrogen peroxide.

This study successfully achieved stable nitritation by adding hydrogen peroxide (H2O2) to the nitrification sludge whose nitritation stability had been destroyed. The batch experiment demonstrated that, the activity of ammonia-oxidizing bacteria (AOB) was restored more rapidly than that of nitrite oxidizing bacteria (NOB) after the addition of H2O2, thereby selectively promoting AOB enrichment and NOB washout. When the H2O2 concentration was 6.25 mg/L, the NOB activity was significantly reduced and the nitrite accumulation rate (NAR) was more than 95% after 18 cycles of nitrifying sludge restoration. As a result, H2O2 treatment enabled a nitrifying reactor to recover stable nitritation performance via H2O2 treatment, with the NAR and ammonia removal efficiency (ARE) both exceeding 90%. High-throughput sequencing analysis revealed that H2O2 treatment was successful in restoring nitritation, as the relative abundance of Nitrosomonas in the nitrifying reactor increased from 6.43% to 41.97%, and that of Nitrolancea decreased from 17.34% to 2.37%. Recovering nitritation by H2O2 inhibition is a low operational cost, high efficiency, and non-secondary pollution nitritation performance stabilization method. By leveraging the varying inhibition degrees of H2O2 on AOB and NOB, stable nitrification can be efficiently restored at a low cost and without causing secondary pollution.

Urea Fertilization Significantly Promotes Nitrous Oxide Emissions from Agricultural Soils and Is Attributed to the Short-Term Suppression of Nitrite-Oxidizing Bacteria during Urea Hydrolysis.

The application of urea in agricultural soil significantly boosts nitrous oxide (N2O) emissions. However, the reason for nitrite accumulation, the period of nitrite-oxidizing bacteria (NOB) suppression, and the main NOB species for nitrite removal behind urea fertilization have not been thoroughly investigated. In this study, four laboratory microcosm experiments were conducted to simulate urea fertilization in agricultural soils. We found that within 36 h of urea application, nitrite oxidation lagged behind ammonia oxidation, leading to nitrite accumulation and increased N2O emissions. However, after 36 h, NOB activity recovered and then removed nitrite, leading to reduced N2O emissions. Urea use resulted in an N2O emission rate tenfold higher than ammonium. During incubation, Nitrobacter-affiliated NOB growth decreased initially but increased later with urea use, while Nitrospira-affiliated NOB appeared unaffected. Chlorate suppression of NOB lasted longer, increasing N2O emissions. Urease inhibitors effectively reduced N2O emissions by slowing urea hydrolysis and limiting free ammonia production, preventing short-term NOB suppression. In summary, short-term NOB suppression during urea hydrolysis played a crucial role in increasing N2O emissions from agricultural soils. These findings revealed the reasons behind the surge in N2O emissions caused by extensive urea application and provided guidance for reducing N2O emissions in agricultural production processes.

Competitive bio-augmentation overcoming unusual direct inhibitor inefficacy in mainstream nitrite-oxidizing bacteria suppression: Unveiling the underpinnings in microbial and nitrogen metabolism aspects

The long-stabilized mainstream partial nitritation/Anammox (PN/A) process continues to encounter significant challenges from nitrite-oxidizing bacteria (NOB). Therefore, this study aimed to determine an efficient, rapid, and easily implementable strategy for inhibiting NOB. A laboratory-scale reactor was operated continuously for 325 days, experiencing NOB outbreak in mainstream and recovery with simulated sidestream support. The results show that direct inhibitory strategies including intermittent aeration and approximately 35 mg/L free ammonia had unusual weak inhibitory effects on NOB activity. Subsequently, the exogenous Anammox from sidestream employed as a competitive bio-augmentation approach rapidly inhibited NOB dynamics. Evidence suggests that the damaged hydroxyapatite granules under low pH conditions might have contributed to NOB dominance by diminishing Anammox bacteria activity, thereby creating a substrate-rich environment favoring NOB survival. In contrast, the introduction of exogenous Candidatus Kuenenia facilitated the nitrogen removal efficiency from 32.5 % to over 80 %. This coincided with a decrease in the relative abundance of Nitrospira from 16.5 % to 2.7 % and NOB activity from 0.34 to 0.07 g N/(g mixed liquor volatile suspended solid)/d. Metagenomic analysis reveals a decrease in the functional potential of most nitrite transport proteins, coupled with a significant increase in eukaryotic-like serine/threonine-protein kinase involved in cellular regulation, during the Anammox activity recovery. This study's findings reveal the feasibility of the bio-augmentation based on substrate competition, wherein sidestream processes support the mainstream PN/A integration, offering significant potential for practical applications.

Achieving mainstream partial nitritation with aerobic granular sludge treating high-rate activated sludge effluent

New configurations for wastewater treatment plants (WWTPs) are under development to increase their self-sufficiency and sustainability. One is the A-B process, in which the A-stage is designed to maximize the redirection of influent chemical oxygen demand (COD) to the production of biogas. A promising A-stage alternative is the high-rate activated sludge (HRAS). B-stage, on the other hand, can consist of the combined partial nitritation (PN)-anaerobic ammonium oxidation (anammox). In this study, PN with aerobic granular sludge (AGS) was attempted under mainstream conditions at pilot scale. The effluent of a HRAS system – ideally operating at 2 g/L of total suspended solids, 0.5 mg/L of dissolved oxygen and 1 h of hydraulic retention time (52 ± 13 % COD removal) – was fed to the PN-AGS reactor initially inoculated with floccular sludge. Granulation and PN were studied with daily/seasonal fluctuations and without adding external reagents. Selective wasting from the top of the settled sludge bed was found a successful strategy to trigger granular sludge formation. The maintenance of a low sludge volume index (SVI < 100 mL/g) was helpful enough for improved operation of the system (i.e., COD removal and PN). Stable PN was achieved due to the suppression of the nitrite oxidizing bacteria activity by inhibitory levels of free nitrous acid. Finally, working with fast settling biomass at long settling times reduced the influent-biomass-nitrite contact and, thus, denitritation.

Achieving partial nitrification in a continuous-flow bioreactor by free ammonia treatment combined with low dissolved oxygen

Partial nitrification (PN) is still difficult to achieve in continuous-flow bioreactors. In this study, free ammonia (FA) treatment combined with low dissolved oxygen (DO) were applied to achieve PN in an A/O bioreactor. Batch tests showed 200 mg/L FA with 12 h treatment time could effectively expand the activity difference between ammonia oxidizing bacteria (AOB) and nitrite oxidizing bacteria (NOB), with an 24.86% falling of AOB activity and an 54.34% decrease of NOB activity. Furthermore, AOB activity can be recovered in a shorter time after once FA treatment than NOB. FA treatment combined with low DO could effectively establish AOB advantage and achieved PN with the nitrite accumulation ratio (NAR) with 86.95% and the ammonia removal efficiency (ARE) with 93.11% in our A/O reactor. FA treatment caused a decrease of extracellular polymeric substance (EPS) secretion, among which the protein reduction may be a key factor that prevented NOB activity recovered. Meanwhile, Nitrospira abundance with FA treatment once a day decreased by 79.1%, while Nitrosomonas abundance dropped by 16.4% only. Amo and hao abundance increased while nxr abundance reduced by 71.8%. The decreased abundance of Nitrospira and nxr was the key to achieve PN. This study demonstrated critical regulating factors for PN achievement in continuous-flow bioreactors using FA and DO, and may provide a new insight for PN in engineering applications.

Single-stage partial nitrification/anammox process performance restoration by bio-augmenting nitrifiers with or without nitrite oxidizing bacteria suppression

The use of low dissolved oxygen (DO) is common to suppress the growth of nitrite oxidizing bacteria (NOB) in the partial nitrification/anammox (PN/A) process. However, this approach can negatively impact the activity of ammonium oxidizing bacteria (AOB) and reduce the oxygen consumption rate, disrupting the essential low DO environment required for anammox bacteria (AMX) and leading to a decline in PN/A performance. We innovatively harnessed the strategy of common nitrifiers (AOB + NOB) bioaugmentation in an impaired single-stage PN/A reactor after operation for a period of time. The results demonstrated an immediate improvement, with the total nitrogen removal efficiency increasing from approximately 60 % to 80 %. This enhancement was attributed to decreased NOB activity and increased AMX activity, which occurred at reduced DO level (0.24 to 0.12 mg O2/L) following nitrifiers bioaugmentation. Partial nitrification (PN) and PN/A batch experiments with nitrifiers bioaugmentation further supported these findings. This strategy pioneered a fresh perspective that the diversion of nitrite from NOB to AMX was the pivotal underlying mechanism. Mathematical simulations complemented these results by demonstrating that nitrifiers bioaugmentation broadened the optimal oxygen supply window.

Deregulation of Ribosome Biogenesis in Nitrite-Oxidizing Bacteria Leads to Nitrite Accumulation.

Nitrite (NO2-) accumulation caused by nitrite-oxidizing bacteria (NOB) inhibition in nitrification is a double-edged sword, i.e., a disaster in aquatic environments but a hope for innovating nitrogen removal technology in wastewater treatment. However, little information is available regarding the molecular mechanism of NOB inhibition at the cellular level. Herein, we investigate the response of NOB inhibition on NO2- accumulation established by a side-stream free ammonia treatment unit in a nitrifying reactor using integrated metagenomics and metaproteomics. Results showed that compared with the baseline, the relative abundance and activity of NOB in the experimental stage decreased by 91.64 and 68.66%, respectively, directly resulting in a NO2- accumulation rate of 88%. Moreover, RNA polymerase, translation factors, and aa-tRNA ligase were significantly downregulated, indicating that protein synthesis in NOB was interfered during NO2- accumulation. Further investigations showed that ribosomal proteins and GTPases, responsible for bindings between either ribosomal proteins and rRNA or ribosome subunits, were remarkably downregulated. This suggests that ribosome biogenesis was severely disrupted, which might be the key reason for the inhibited protein synthesis. Our findings fill a knowledge gap regarding the underlying mechanisms of NO2- accumulation, which would be beneficial for regulating the accumulation of NO2- in aquatic environments and engineered systems.

The successful application of light to the system of simultaneous nitrification/endogenous denitrification and phosphorus removal: Promotion of partial nitrification and glycogen accumulation metabolism

Partial nitrification (PN) and high glycogen accumulating metabolism (GAM) activity are the basis for efficient nitrogen (N) and phosphorus (P) removal in simultaneous nitrification endogenous denitrification and phosphorus removal (SNDPR) systems. However, achieving these processes in practical operations is challenging. This study proposes that light irradiation is a novel strategy to enhance the nutrient removal performance of the SNDPR system with low carbon to nitrogen ratios (C/N of 3.3–4.1) domestic wastewater. Light energy densities (Es) of 55–135 J/g VSS were found to promote the activity of ammonia-oxidizing bacteria (AOB) and GAM, while inhibiting the activity of nitrite-oxidizing bacteria (NOB) and polyphosphate accumulating metabolism (PAM). Long-term exposure to different light patterns at Es of 55–135 J/g VSS revealed that continuous light rapidly achieved PN by inhibiting NOB activity and promoted the growth of glycogen accumulating organisms (GAOs), allowing the removal of above 82 % N and below 80 % P. Intermittent light maintained stable PN by inhibiting the activity and growth of NOB and promoted the growth of polyphosphate accumulating organisms (PAOs) with high GAM activity (Accmulibacer IIC-ii and IIC-iii), allowing the removal of above 82 % N and 95 % P. Flow cytometry and enzyme activity assays showed that light promoted GAM-related enzyme activity and the metabolic activity of partial Accmulibacer II over other endogenous denitrifying bacteria, while inhibiting NOB translation activity. These findings provide a new approach for enhancing nutrient removal, especially for achieving PN and promoting GAM activity, in SNDPR systems treating low C/N ratio domestic wastewater using light irradiation.

Effect of ultrasound on the stability of partial nitrification: Under the interference of aeration rate

The fluctuation of dissolved oxygen is one of the primary cause of disruptions to the consistent operation of partial nitrification, and the level of dissolved oxygen is mainly controlled by the aeration rate. This study investigated the influence of ultrasonic treatment on the stability of partial nitrification of activated sludge under different aeration conditions. After being treated with ultrasound (energy density = 0.20 W·mL−1, treatment time = 10 min), partial nitrification process operated stably for 67 days, with the nitrite accumulation rate above 83.89 %. The effluent contained 42.50 mg·L−1 of nitrite, much higher than the control reactor (0.30 mg·L−1). The gap between the specific ammonia and nitrite oxidation rates widened continuously as the aeration rate increased, and nitrite-oxidizing bacteria activity did not recover even under conditions with a very high oxygen content. Further analysis showed that ultrasonic treatment had obvious stripping effect on excess extracellular polymeric substances (EPS), especially loosely bound EPS and protein. Additionally, long-term ultrasonic treatment promoted the enrichment of Nitrosomonas and strongly inhibited Nitrotoga. Based on these findings, it appears that under conditions of high aeration rate, ultrasound effectively suppress the recovery of Nitrotoga activity and improve the stability of partial nitrification.

Using sulfide as nitrite oxidizing bacteria inhibitor for the successful coupling of partial nitrification-anammox and sulfur autotrophic denitrification in one reactor

The partial nitrification-anammox (PNA) process, as a new “green” biological nitrogen removal technology, is completely autotrophic and has great economic and environmental benefits. However, the applied bottleneck of this process is the inability to inhibit nitrite oxidizing bacteria (NOB) activity and the low total nitrogen removal efficiency (TNRE) due to nitrate accumulation. In this study, the addition of sulfide was utilized to selectively screen NOB while promoting the sulfur autotrophic denitrification (SAD) process in one sequencing batch biofilter granular reactor. The results showed that when the influent concentration of NH4+-N and S2− were 184.6 ± 4.4 mg/L and 153.9 ± 3.1 mg/L, the average TNRE reached 89.6 ± 3.6 %. At this stage, aerobic ammonia oxidizing bacteria (AOB) and anaerobic ammonium oxidation bacteria (AnAOB) showed good activities (specific oxygen uptake rate of AOB and specific anammox activity could reach to 0.09 ± 0.00 mg O2/g SS/h and 0.47 ± 0.06 mg TN/g SS/h, respectively), while NOB activity was significantly suppressed by sulfide, with specific oxygen uptake rate of 0.003 ± 0.00 mg O2/g SS/h, which further demonstrating the feasibility and long-term application of this sustainable and efficient process. Anammox was the predominant nitrogen removal pathway contributing approximately 89.0 % of nitrogen removal. Typical AOB (Nitrosomonas), AnAOB (Candidatus Kuenenia), and SAD bacteria (Thiobacillus, Pseudoxanthomonas, and Limobacter) coexisted in the PNA-SAD system. The syntrophic interactions among sulfur-oxidizing, sulfate-reducing, and anammox bacterial populations of this system were revealed by PICRUST2 and network analysis. Sulfides were most likely oxidized to biologically produced elemental sulfur first and then converted to sulfate via the Sox system. Our study provided a new reaction scheme and theoretical reference for efficient nitrogen and sulfur removal in a single reactor.

Nitrite accumulation in activated sludge through cyclic anaerobic exposure with acetate

Achieving nitrite accumulation still remains challenging for efficient short-cut biological nitrogen removal in municipal wastewater treatment. To tackle the problem of insufficient carbon in incoming wastewater for biological nutrient removal, a return activated sludge (RAS) fermentation method has been proposed and demonstrated to enable producing supplemental volatile fatty acids (VFAs) and enhance biological phosphorus removal via sludge cycling between mainstream and a sidestream anaerobic reactor. However, the impacts of long anaerobic exposure with acetate on nitrifying bacteria, known as the aerobic chemoautotrophic microorganisms, remains unexplored. In this study, the activated sludge underwent a cyclic anaerobic treatment with the addition of acetate (Ac), the effects on nitrification rate, abundance and microdiversity of nitrifying communities were comprehensively assessed. Firstly, batch activity tests proved the direct addition of high acetate (above 1000 mg/L) could cause inhibition on the nitrification rate, moreover, the inhibitory effect was stronger on nitrite-oxidizing bacteria (NOB) activity than that of ammonia-oxidizing bacteria (AOB). Then, a sequencing batch reactor (SBR) was applied to test the nitrogen conversion performance for low-strength ammonium wastewater. Nitrite accumulation could be achieved via the cyclic anaerobic exposure with 1000–5000 mg Ac/L. The maximum effluent concentration of nitrite was 40.8 ± 3.5 mg N/L with nitrite accumulation ratio (NAR) of 67.6 ± 3.5%. The decrease in NOB activity (72.7%) was greater than AOB of 42.4%, promoting nitrite accumulation via nitritation process. Furthermore, the cyclic anaerobic exposure with acetate can largely reshape the nitrifying communities. As the dominant AOB and NOB, the abundance of Nitrosomonas and Nitrospira were both decreased with species-level microdiversity in the nitrifying communities. However, the heterotrophic microorganism, Thauera, were found to be highly enriched (from 0 to 17.3%), which may act as the potential nitrite producer as proved by the increased nitrate reduction gene abundance. This study can provide new insights into achieving mainstream nitrite accumulation by involving sidestream RAS fermentation towards efficient wastewater treatment management.

Comparison of typical nitrite oxidizing bacteria suppression strategies and the effect on nitrous oxide emissions in a biofilm reactor

In mainstream partial nitritation/anammox (PN/A), suppression of nitrite oxidizing bacteria (NOB) and mitigation of N2O emissions are two essential operational goals. The N2O emissions linked to three typical NOB suppression strategies were tested in a covered rotating biological contactor (RBC) biofilm system at 21 °C: (i) low dissolved oxygen (DO) concentrations, and treatments with (ii) free ammonia (FA), and (iii) free nitrous acids (FNA). Low emerged DO levels effectively minimized NOB activity and decreased N2O emissions, but NOB adaptation appeared after 200 days of operation. Further NOB suppression was successfully achieved by periodic (3 h per week) treatments with FA (29.3 ± 2.6 mg NH3-N L−1) or FNA (3.1 ± 0.3 mg HNO2-N L−1). FA treatment, however, promoted N2O emissions, while FNA did not affect these. Hence, biofilm PN/A should be operated at relatively low DO levels with periodic FNA treatment to maximize nitrogen removal efficiency while avoiding high greenhouse gas emissions.

Effect of initial ammonium concentration on a one-stage partial nitrification/anammox biofilm system: Nitrogen removal performance and the microbial community

One-stage partial nitrification coupled with anammox (PN/A) technology effectively reduces the energy consumption of a biological nitrogen removal system. Inhibiting nitrite-oxidizing bacteria (NOB) is essential for this technology to maintain efficient nitrogen removal performance. Initial ammonium concentration (IAC) affects the degree of inhibited NOB. In this study, the effect of the IAC on a PN/A biofilm was investigated in a moving bed biofilm reactor. The results showed that nitrogen removal efficiency decreased from 82.49% ± 1.90% to 64.57% ± 3.96% after the IAC was reduced from 60 to 20 mg N/L, while the nitrate production ratio increased from 13.87% ± 0.90% to 26.50% ± 3.76%. NOB activity increased to 1,133.86 mg N/m2/day after the IAC decreased, approximately 4-fold, indicating that the IAC plays an important inhibitory role in NOB. The rate-limiting step in the mature biofilm of the PN/A system is the nitritation process and is not shifted by the IAC. The analysis of the microbial community structure in the biofilm indicates that the IAC was the dominant factor in changes in community structure. Ca. Brocadia and Ca. Jettenia were the main anammox bacteria, and Nitrosomonas and Nitrospira were the main AOB and NOB, respectively. IAC did not affect the difference in growth between Ca. Brocadia and Ca. Jettenia. Thus, modulating the IAC promoted the PN/A process with efficient nitrogen removal performance at medium to low ammonium concentrations.

Increasing specific biomass nitrogen load facilitated nitrite accumulation in mainstream wastewater treatment

By regulating influent nitrogen loading rate (NLR) and solids retention time (SRT), the effect of specific biomass nitrogen load (BNL) on the start-up of mainstream partial nitrification (PN) was investigated in five parallel sequencing batch reactors inoculated with ordinary nitrification sludge. The results showed that increasing BNL by both methods could achieve nitrite accumulation. Moreover, a high initial activity of ammonium oxidizing bacteria (AOB) accelerated nitrite accumulation. Increasing influent NLR (ammonium: 55–70 mg N/L) achieved only 30%–40% of nitrite accumulation ratio (NAR) and gradually decreased with reactor operation. By increasing BNL via controlling SRT (30 days), desirable PN with an average NAR of 81.7 ± 4.4% (effluent nitrite: ∼10 mg N/L) was obtained. Nitrite oxidizing bacteria (NOB) were effectively inhibited, and the AOB to NOB activity ratio increased from 1.5 to 7.8, promoting efficient nitrite accumulation. Overall, increasing BNL by regulating SRT was a potential method for start-up of mainstream PN.

Nitrification of the liquid phase of digestate: The transfer of the process from laboratory to pilot plant and full scale conditions

This paper aimed to verify the laboratory research results related to the liquid phase of digestate (LPD) treatment using nitrification at pilot scale conditions and to suggest an optimal method for full-scale system start-up. A reactor applying the nitrification of LPD was operated for 358 days. Significant free ammonia and free nitrous acid inhibition towards nitrite-oxidizing bacteria (NOB) increased N-NO2− concentrations up to 2300 mg/L in LPD. As a result of pH and a nitrogen loading rate control combined with the re-inoculation of the reactor, NOB activity was fully restored after 90 days, where the nitrogen oxidation rate and nitrogen oxidation efficiency reached up to 0.26 kg/(m3⋅d) and 99.9%, respectively, at N-NO2− concentrations not exceeding 45 mg/L. Thus, the feasibility of stable operation of the system even without any dilution of LPD was confirmed. The procedure of full-scale reactor start-up consisting of a separate unit serving to produce nitrifying biomass was suggested. It was shown that the volume of such a reactor could be divided into three compartments to optimize the start-up. Simple modeling proved the possibility of completing the start-up process in 34 days under specific conditions (total ammonia concentrations in LPD 2 kg/m3, daily production of LPD 20 m3/d, nitrogen loading rate reaching 0.25 kg/(m3⋅d)). The results could be used to accelerate the method transfer into practice.

Achieving robust and highly efficient nitrogen removal in a mainstream anammox reactor by introducing low concentrations of readily biodegradable organics.

In this study, an anammox reactor was operated to treat low-strength (NH4+ + NO2-, 25-35 mg/L) wastewater without (phase I) or with (phase II) readily biodegradable chemical oxygen demand (rbCOD). In phase I, although efficient nitrogen removal was achieved at the beginning, nitrate accumulated in the effluent after long-term operation (75 days), resulting in a decrease in the nitrogen removal efficiency to 30%. Microbial analysis revealed that the abundance of anammox bacteria decreased from 2.15 to 1.78%, whereas that of nitrite-oxidizing bacteria (NOB) increased from 0.14 to 0.56%. In phase II, rbCOD, in terms of acetate, was introduced into the reactor with a carbon/nitrogen ratio of 0.9. The nitrate concentration in the effluent decreased within 2 days. Advanced nitrogen removal was achieved in the following operation, with an average effluent total nitrogen of 3.4 mg/L. Despite the introduction of rbCOD, anammox pathway still dominated to the nitrogen loss. High-throughput sequencing indicated that high anammox abundance (2.48%) further supports its dominant position. The improvement in nitrogen removal was attributed to the enhanced suppression of NOB activity, simultaneous nitrate polishing through partial denitrification and anammox, and promotion of sludge granulation. Overall, the introduction of low concentrations of rbCOD is a feasible strategy for achieving robust and efficient nitrogen removal in mainstream anammox reactors.

Performance of rotating cage biological contactors based on the partial nitrification of immobilized bioactive fillers

The rotating cage biological contactors (RCBC) is based on the partial nitrification immobilization of bioactive fillers, incorporating the advantages of traditional the rotating biological contactor (RBC). The RCBC is more energy-efficient, with higher ammonia oxidation rate (AOR) and nitrite accumulation rate (NAR) levels compared to the RBC Under the conditions of different rotational speeds and immersion rates of an RCBC, the volumetric oxygen transfer coefficient (KLa) was measured. The experimental results show that these two factors significantly affected the KLa of the reactor, which ranged from 1.08 to 42.02 h−1. Regarding long-term ammonia oxidation performance, the RCBC can successfully start partial nitrification in only 5 days. After stable operation, the AOR was 23.34 ± 0.55 mg (L·h)−1, with an NAR of 93.42 ± 0.84 %. This indicates a good adaptability to variations in influent ammonia nitrogen (NH4+-N) in the range of 95.92–403.14 mg·L−1 and good resistance to free nitrous acids (FNA). In addition, high-throughput sequencing analysis showed that the operation mode of the RCBC could effectively inhibit the growth of nitrite-oxidizing bacteria (NOB) in immobilized bioactive fillers, and the internal oxygen-limited environment provided favorable conditions for reducing the relative abundance and activity of NOB. In this study, a partial nitrification device was established by immobilized bioactive fillers in the form of an RCBC for the first time, providing a partial nitrification technology without aeration.

Design strategy and mechanism of nitrite oxidation suppression of elevated loading rate partial nitritation system.

There is a current need for a low operational intensity, effective and small footprint system to achieve stable partial nitritation for subsequent anammox treatment at mainstream municipal wastewaters. This research identifies a unique design strategy using an elevated total ammonia nitrogen (TAN) surface area loading rate (SALR) of 5 g TAN/m2.d to achieve cost-effective, stable, and elevated rates of partial nitritation in a moving bed biofilm reactor (MBBR) system under mainstream conditions. The elevated loaded partial nitritation MBBR system achieves a TAN surface area removal rate (SARR) of 2.01 ± 0.07 g TAN/m2.d and NO2 --N: NH4 +-N stoichiometric ratio of 1.15:1, which is appropriate for downstream anammox treatment. The elevated TAN SALR design strategy promotes nitrite-oxidizing bacteria (NOB) activity suppression rather than a reduction in NOB population as the reason for the suppression of nitrite oxidation in the mainstream elevated loaded partial nitritation MBBR system. NOB activity is limited at an elevated TAN SALR likely due to thick biofilm embedding the NOB population and competition for dissolved oxygen (DO) with ammonia-oxidizing bacteria for TAN oxidation to nitrite within the biofilm structure, which ultimately limits the uptake of DO by NOB in the system. Therefore, this design strategy offers a cost-effective and efficient alternative for mainstream partial nitritation MBBR systems at water resource recovery facilities.

Nitrification potential of daily-watered biofiltration designs for high ammonium wastewater treatment

The vegetated biofiltration systems (VBS), also known as bioretentions or rain gardens, are well-established technology for treatment of urban stormwater and recently greywater, offering multiple benefits to urban environments. However, the impact of high ammonium strength wastewater (60 mg/L) on the nitrification process in these systems is not well understood. Hence, a laboratory-based column study was conducted to uncover dominant nitrification mechanisms, based on the learnings from similar onsite wastewater treatment systems. The experimental columns tested the effect of contact time (filter media depth, 150 mm, 300 mm and 700 mm), media oxygenation (active and passive) and alkalinity/pH (marble chips 5 % weight), as well as optimal operational conditions (inflow loading, concentrations, and dissolved oxygen (DO)). All nitrogen species (NH4+, NO3−, NO2−), chemical oxygen demand (COD) and physical parameters (DO, pH, electrical conductivity) were monitored across seven events over thirteen weeks. The results show that dosing with 30 and 60 mg/L of NH4+ resulted in 700 mm sand column depth to perform almost complete nitrification of NH4+ to NO3− (< 90 %), while 300 mm designs achieved partial nitrification of NH4+ to NO2−, likely due to limited contact time and inefficient nitrite oxidizing bacteria activity. Nitrification potential of all designs further supported that appropriate aerobic contact time is necessary for effective nitrification. Inflow concentration of NH4+ and DO did not significantly impact nitrification performance, while reducing daily volume loading reduced NO3− and NO2− leaching. Active and passive aeration and alkalinity buffering did not positively affect ammonium removal. While there is a potential to apply both nitrification-denitrification and anammox processes to future VBS design, further understanding of aeration and alkalinity on microbially driven nitrification processes is needed.