Rapid achieving partial nitrification in domestic wastewater: Controlling aeration time to selectively enrich ammonium oxidizing bacteria (AOB) after simultaneously eliminating AOB and nitrite oxidizing bacteria (NOB)

Startup of a large height-diameter ratio bioreactor by alternate feeding: performance of partial nitrification and enrichment of ammonia-oxidizing bacteria (AOB)

In order to solve the complicated control of dissolved oxygen (DO) for partial nitrification in bioreactors treating high NH 4 + - N wastewater, a large height-diameter ratio anammox pre-reactor system was developed. And in this reactor, NO 2 - - N accumulation rate can reach 85.76% by alternate feeding with high NH 4 + - N wastewater (150 mg NH 4 + - N / L ) and low NH 4 + - N wastewater (50 mg c) with low DO (0.19 mg/L-0.62 mg/L). Based on 16S rRNA identification technology, it was found that Nitrosomonas had a significant effect on NH 4 + - N oxidization in this study. And when the reactor treated higher concentration wastewater (250 mg NH 4 + - N / L ), the growth rate of Nitrosomonas was higher than that of Nitrospira (nitrite-oxidizing bacteria, NOB), which was conducive to improving the NO 2 - - N accumulation rate and realizing partial nitrification stably. It was also found that the material exchange frequency of the microbial flora during alternate feeding with different NH 4 + - N concentration wastewaters was higher than that during feeding with higher NH 4 + - N concentration wastewater (250 mg/L) by Kyoto Encyclopedia of Genes and Genomes (KEGG) metabolism pathways analysis. This study can provide valuable insights and lay the foundation for building anammox pre-reactors.

Novel insights into the co-metabolism of pyridine with different carbon substrates: Performance, metabolism pathway and microbial community

Pyridine is a widely employed nitrogen-containing heterocyclic organic, and the discharge of pyridine wastewater poses substantial environmental challenges due to its recalcitrance and toxicity. Co-metabolic degradation emerged as a promising solution. In this study, readily degradable glucose and the structurally analogous phenol were used as co-metabolic substrates respectively, and the corresponding mechanisms were thoroughly explored. To treat 400 mg/L pyridine, all reactors achieved remarkably high removal efficiencies, surpassing 98.5%. And the co-metabolism reactors had much better pyridine-N removal performance. Batch experiments revealed that glucose supplementation bolstered nitrogen assimilation, thereby promoting the breakdown of pyridine, and resulting in the highest pyridine removal rate and pyridine-N removal efficiency. The high abundance of Saccharibacteria (15.54%) and the enrichment of GLU and glnA substantiated this finding. On the contrary, phenol delayed pyridine oxidation, potentially due to its higher affinity for phenol hydroxylase. Nevertheless, phenol proved valuable as a carbon source for denitrification, augmenting the elimination of pyridine-N. This was underscored by the abundant Thauera (30.77%) and Parcubacteria (7.21%) and the enriched denitrification enzymes (narH, narG, norB, norC, and nosZ, etc.). This study demonstrated that co-metabolic degradation can bolster the simultaneous conversion of pyridine and pyridine-N, and shed light on the underling mechanism.

Novel anammox granules formation from conventional activated sludge for municipal wastewater treatment through flocs management

The direct integration of anammox process into municipal wastewater treatment has caused widespread concern, but the lack of anammox seeds limited its real application. This study successfully cultivated anammox granules (322.0 μm) from conventional activated sludge treating municipal wastewater. Through ultra-low floc sludge retention times of 8d, nitrifiers on flocs were eliminated and partial nitrification was realized. Furthermore, highly bacteria-enriched granules were initially formed, with Nitrosomonas and Ca. Competibacter 4-fold higher than that of flocs. Specific staining results revealed the microbial interaction with Ca. Brocadia, considering that Ca. Competibacter and Nitrosomonas correspondingly identified in the inner and outer layers of granules. The percentage of Ca. Brocadia present on the granules increased substantially from 0.0 % to 3.0 %, accompanied by a nitrogen removal rate of 0.3 kg·m-3·d-1. Our findings revealed a valuable reference for the anammox bacteria in-situ enrichment under mainstream conditions, which provides theoretical guidance for anammox-based processes practical application.

Comparative assessment of different scenarios for upgrading activated sludge wastewater treatment plants in developing countries

Improvement of current wastewater treatment plants (WWTPs) to accommodate the growing influent flow rate and cope with the increasingly stringent regulations is hindered by the allowed space and the difficulty of changing the design parameters. Mathematical modeling is a useful tool for assessing the performance of WWTPs in light of broadening objectives. We herein explore the utilization of mathematical modeling to improve effluent quality in conventional activated sludge systems. BioWin was used to model Mansoura WWTP, one of the largest WWTPs in Egypt. Lab records, design reports, and additional analyses were conducted through site visits and a comprehensive sampling campaign. The wastewater was characterized, and the plant-wide model was calibrated following the protocol of the Dutch Foundation for Applied Water Research STOWA. Important kinetic and stoichiometric parameters were identified and adjusted during the calibration process. The model validity was assessed using different validation periods considering average relative deviation (ARD) values below 20 % as acceptable. The optimized nitrification and denitrification processes involved 16 scenarios with different operational conditions. By changing some zones in the aeration basin from aerobic to anoxic and increasing the return activated sludge, the average ammonia and nitrate concentrations were significantly reduced from 23.06 and 0.5 mg/L to 4.64 and 0.07 mg/L respectively. Furthermore, phosphorus removal optimization was carried out through biological and chemical processes. Chemical phosphorus removal was 85.76 % by using a coagulant dosage of 25 mg/L, resulting in an effluent concentration of 1.04 mg P/L. Biological phosphorus removal was increased to 85.43 % by modifying the volume of anaerobic and aerobic zones with lower power consumption. Overall, this study demonstrates the effectiveness of mathematical modeling in enhancing effluent quality and reducing energy consumption to meet stringent wastewater treatment regulations.

Optimizing ciprofloxacin removal through regulations of trophic modes and FNA levels in a moving bed biofilm reactor performing sidestream partial nitritation

The performance of partial nitritation (PN)-moving bed biofilm reactor (MBBR) in removal of antibiotics in the sidestream wastewater has not been investigated so far. In this work, the removal of ciprofloxacin was assessed under varying free nitrous acid (FNA) levels and different trophic modes. For the first time, a positive correlation was observed between ciprofloxacin removal and FNA levels, either in the autotrophic PN-MBBR or in the mixotrophic PN-MBBR, mainly ascribed to the FNA-stimulating effect on heterotrophic bacteria (HB)-induced biodegradation. The maximum ciprofloxacin removal efficiency (∼98 %) and removal rate constant (0.021 L g-1 SS h-1) were obtained in the mixotrophic PN-MBBR at an average FNA level of 0.056 mg-N L-1, which were 5.8 and 51.2 times higher than the corresponding values in the autotrophic PN-MBBR at 0 mg FNA-N L-1. Increasing FNA from 0.006 to 0.056 mg-N L-1 would inhibit ammonia oxidizing bacteria (AOB)-induced cometabolism and metabolism from 10.2 % and 6.9 % to 6.2 % and 6.4 %, respectively, while HB-induced cometabolism and metabolism increased from 31.2 % and 22.7 % to 41.9 % and 34.5 %, respectively. HB-induced cometabolism became the predominant biodegradation pathway (75.9 %-85.8 %) in the mixotrophic mode. Less antimicrobial biotransformation products without the piperazine or fluorine were newly identified to propose potential degradation pathways, corresponding to microbial-induced metabolic types and FNA levels. This work shed light on enhancing antibiotic removal via regulating both FNA accumulation and organic carbon addition in the PN-MBBR process treating sidestream wastewater.

Achieving partial nitrification: A strategy for washing NOB out under high DO condition

This study investigated the effect of high DO concentrations on PN. The experimental setup involved operating at high DO concentrations (1.5-2.5 mg/L) and environmental temperatures (15-20 °C) over a period of 180 days. Through a sludge enrichment process, the kinetic parameters of ammonia-oxidizing bacteria (AOB) and nitrite-oxidizing bacteria (NOB) were determined. Surprisingly, contrary to conventional reports, it was observed that NOB exhibited a stronger affinity for DO compared to AOB. As a result, high DO concentrations were necessary to provide favorable conditions for the growth of AOB. In order to establish PN, strategies including intermittent aeration, free ammonia (FA), and controlled sludge retention time (SRT) were employed. The successful PN was achieved with a specific ammonia oxidation rate of 24 mg N/g MLVSS/h and a specific nitrite oxidation rate below 0.10 mg N/g MLVSS/h. The nitrite accumulation rate (NAR) was maintained at 100% during stable operation. The abundance of Nitrosomonas, a typical genus of AOB, was found to be 68.62%, which surpasses previous studies in similar research. A slightly higher DO concentrations may increase energy consumption, but achieve higher efficiency and stability in PN. This study provided new insights into the application of PN in wastewater treatment.

Anaerobic starvation realizes partial nitrification and starts anammox bacteria self-enrichment in mainstream municipal sewage treatment in a low filling ratio sequencing batch reactor

The initiating and stable preservation of partial nitrification (PN) and achievement of anammox bacteria self-enrichment in domestic sewage is a purposeful subject. In this article, an originality tactics of anaerobic starvation for 100 days was adopted for rapidly achieving PN in actual wastewater, the nitrite accumulation rate (NAR) improved from 4.95% to 81.73% in 18 days. After anaerobic starvation was stopped, the stable PN effect furnished enough stroma for the growth of anammox bacteria. The abundance of Candidatus Brocadia grew from 0% to 0.42% in floc sludge and 0.43% in blank biofilm, which promoted nitrogen removal effect. Anaerobic starvation continuing 74 days generated further decrease in the abundance of Nitrobacter and Nitrospira of nitrite-oxidizing bacteria (NOB), indicating that anaerobic starvation can restore the destroyed partial nitrification. In conclusion, this article furnished a low-cost method for achieving anammox bacteria self-enrichment in mainstream municipal wastewater in 10% filling ratio without chemicals addition.

Extracellular polymeric substances and microbial community shift during the start-up of a single-stage partial nitritation/anammox process

A sequencing batch reactor (SBR) was operated to investigate variations of extracellular polymeric substances (EPS) and microbial community during the start-up of the single-stage partial nitritation/anammox (SPN/A) process at intermittent aeration mode. The SPN/A system was successfully started on day 34, and the nitrogen removal efficiency and total nitrogen loading rate were 82.29% and 0.31 kg N/(m3 ·day), respectively. Furthermore, the relationship between the protein secondary structures and microbial aggregation was strongly related. The α-helix/ (β-sheet + random coil) ratios increased obviously from 0.20 ± 0.03 to 0.23 ± 0.01, with the sludge aggregation mean size increased from 56 to 107 μm during the start-up of SPN/A. During the start-up of SPN/A, Candidatus Kuenenia was the primary anammox bacteria, whereas Nitrospira was the main functional bacteria of nitrite-oxidizing bacteria. Correlation between the microbial community and EPS components was performed. The EPS and microbial community played important roles in keeping stable nitrogen removal and the formation of sludge granules. PRACTITIONER POINTS: Intermittent aeration strategy promoted SPN/A system start-up. EPS composition and protein secondary structure were related with the sludge disintegration and aggregation. Microbial community shift existed and promoted the stability of sludge and reactor performance during SPN/A start-up.

Seasonal monitoring of microbial activity using conventional approaches in a full-scale urban biological wastewater treatment plant

Activated sludge processes contain various groups of microorganisms with different metabolic properties, which are responsible for contaminants removal. Therefore, it is important to elucidate the general structure and functional properties of biomass in activated sludge processes. For this purpose, a full-scale domestic biological wastewater treatment plant in Tunceli (Turkey), Tunceli WWTP (wastewater treatment plant), was monitored to observe seasonal variations in process performance and biomass properties for a year. It was observed that nitrifying bacteria developed abundantly in the rainy and cool spring season as they were suppressed in summer because their large losses took place due to an environment containing high alkalinity values. In September, aerobic heterotrophic, nitrify, denitrify, and anaerobic activities increased. It can be said that the biomass contained young and mature microorganism in this environment in which the sludge volume index (SVI) value increased to 196 mL/g. As a result of the improvement in the structural and functional properties of biomass, the nitrogen removal efficiency reached 99%. Throughout the whole study, the structural improvement observed in biomass was reflected in its removal activity. The amount of biomass and removal activity decreased with the abundance of organic matter in the influent at the period in which biomass was closer to being categorized in the aged sludge class. The results showed that as the lowest mixed liquid suspended solids (MLSS) and mixed liquid volatile suspended solids (MLVSS) values of the year were 530 and 400 mg/L, respectively, in November 2017, MLSS and MLVSS values reached the highest amount (1700 and 1400 mg/L, respectively) in December 2017 when aerobic heterotrophic activity accelerated with a decrease in organic matter level.

Rapid start-up of PN/A process and efficient enrichment of functional bacteria: A novel aerobic-biofilm/anaerobic-granular nitrogen removal system (OANRS)

Reactor configuration, control strategy and inoculation method were key factors affecting the rapid start-up of partial nitrification/anammox (PN/A) process and the efficient enrichment of functional bacteria (anammox and ammonia oxidizing bacteria). At present, PN/A process was generally operated through single factor rather than forming a system. In this study, a novel aerobic-biofilm/anaerobic-granular nitrogen removal system (OANRS) was constructed, which consisted of a multi-stage aerobic-biofilm/anaerobic-granular baffle reactor (MOABR) and a control strategy on pH/aeration time. PN process was started within 10d, and PN/A process was started on the basis of stable PN process within 41d. The simultaneous enrichment of functional bacteria was achieved by combining the advantages of single-stage and two-stage PN/A process. The results of high-throughput sequencing showed that Candidatus Kuenenia (20.42 ± 15.88%) was highly enriched in each compartment at day 98, and the relative abundance of Candidatus Kuenenia in the anaerobic compartment R4 was as high as 43.13%.

The coexistence and competition of canonical and comammox nitrite oxidizing bacteria in a nitrifying activated sludge system - Experimental observations and simulation studies

The second step of nitrification can be mediated by nitrite oxidizing bacteria (NOB), i.e. Nitrospira and Nitrobacter, with different characteristics in terms of the r/K theory. In this study, an activated sludge model was developed to account for competition between two groups of canonical NOB and comammox bacteria. Heterotrophic denitrification on soluble microbial products was also incorporated into the model. Four 5-week washout trials were carried out at dissolved oxygen-limited conditions for different temperatures (12 °C vs. 20 °C) and main substrates (NH₄⁺-N vs. NO₂^--N). Due to the aggressive reduction of solids retention time (from 4 to 1 d), the biomass concentrations were continuously decreased and stabilized after two weeks at a level below 400 mg/L. The collected experimental data (N species, biomass concentrations, and microbiological analyses) were used for model calibration and validation. In addition to the standard predictions (N species and biomass), the newly developed model also accurately predicted two microbiological indicators, including the relative abundance of comammox bacteria as well as nitrifiers to heterotrophs ratio. Sankey diagrams revealed that the relative contributions of specific microbial groups to N conversion pathways were significantly shifted during the trial. The contribution of comammox did not exceed 5 % in the experiments with both NH₄⁺-N and NO₂^--N substrates. This study contributes to a better understanding of the novel autotrophic N removal processes (e.g. deammonification) with nitrite as a central intermediate product.

Efficient partial nitrification with hybrid nitrifying granular sludge based on a simultaneous fill/draw SBR mode

In this study, a simultaneous fill/draw SBR was applied to investigate the feasibility of partial nitrification process with inoculation of matured aerobic granular sludge. The system operated stably over 120 days with the relatively high ammonium removal efficiency (≥ 98.83%) and nitrite accumulation rate (≥ 89.60%). Moreover, a hybrid flocs/granules system was formed stably after long-term operation. The nitrite-oxidizing bacteria (NOB) was suppressed effectively because of the combined effect of simultaneous fill/draw mode and intermittent aeration conditions. Furthermore, batch tests were separately tested with isolated granules (> 200 μm) and flocs (< 200 μm), showing that the specific ammonia oxidation rate of granules and flocs were 15.94 ± 2.85 and 66.77 ± 0.83 mg N/(g MLSS·h), respectively. Correspondingly, the abundance of Nitrosomonas as a typical AOB in granules (6.24%) and flocs (11.94%) was obtained via the microbial diversity analysis, while NOB was almost hardly detected in granules and flocs.

Achieving robust mainstream nitritation by implementing light irradiation: long-term performance and microbial dynamics

The effective inhibition of nitrite-oxidizing bacteria (NOB) is widely acknowledged to be a critical issue for mainstream short-cut biological nitrogen removal. This study demonstrated a stable mainstream nitritation by implementing light irradiation. A sequencing batch reactor with ultraviolet-A (UVA) irradiation was operated for 250 days, and a high nitrite accumulation ratio was achieved and stabilized at about 90 %. UVA irradiation also positively impacts denitrification activity, with total nitrogen removal up to 63 %. Microbial community analysis confirmed that the UVA effectively and stably decreased the abundance of Nitrospira (the only detected NOB) from 6.0 % to 0.1 %, while it showed no effect on Nitrosomonas. The enriched genus Rhodocyclaceae was the major contributor to the increase in denitrification activity in the light-induced nitritation system. The proposed UVA irradiation strategy has the potential to be integrated with an anoxic/aerobic (A/O) or integrated fixed-film activated sludge (IFAS) process for achieving mainstream short-cut biological nitrogen removal.

Response mechanism of microorganisms to the inhibition of endogenous pollution release by calcium peroxide

To further explore the response mechanism of microorganisms to the synchronous control of nitrogen and phosphorus release from sediments by CaO₂, the spatiotemporal changes in the physical, chemical and biological indicators of the overlying water, interstitial water and sediments in each reactor were measured in the experiment. The experiment results showed that CaO₂ could increase the ammonia monooxygenase activity, nitrite oxidase activity and Nitrospira abundance in the sediment near its dosing position, and enhanced the activities of nitrate reductase and nitrite reductase at a certain distance from the dosing position, thereby promoting nitrogen removal in sediments through the alternating process of nitrification and denitrification. At the same time, the increase of alkaline phosphatase activity and Saccharimonadales abundance in the test groups accelerated the hydrolysis of organic phosphorus, and the P immobilization in sediments was realized through the subsequent precipitation reaction of Ca²⁺ and PO₄^3- under alkaline conditions. In addition, the enhanced activities of dehydrogenase and catalase ensured that CaO₂ would not cause great killing effect on microorganisms when improving the hypoxic conditions and inhibiting endogenous release. As a result, the dissolved product of CaO₂ such as Ca(OH)₂ and H₂O₂ reduced the nutrients concentration and killed the algae, which kept the algae density and chlorophyll a concentration at a low level throughout the test groups. Therefore, this study systematically clarified the microbial mechanism of CaO₂ synchronously controlling the release of nitrogen and phosphorus from sediments, which provided a new idea for the remediation of endogenous pollution in the water system.

Stable enhanced nitrogen removal from low COD/N municipal wastewater via partial nitrification-anammox in the traditional continuous anoxic/oxic process through bio-augmentation of partial nitrification sludge under decreasing temperatures

The application of partial nitrification-anammox (PNA) in continuous flow processes for treating low COD/N (C/N) sewage remains a critical challenge. Here, a traditional continuous anoxic/oxic (A/O) process was operated to investigate nitrogen removal from municipal wastewater by the bio-augmentation of partial nitrification sludge combined with the inoculation of biocarriers under decreasing temperatures. Stable enhanced nitrogen removal via PNA was achieved. The average total inorganic nitrogen in influent and effluent was 44.3 and 7.1 mg N/L under a low C/N ratio (3.4) and a short hydraulic retention time (8.2 h). The bio-augmentation of partial nitrification sludge enhanced the PNA process under low temperatures (16.9 ± 0.6 °C). The nitrogen removal efficiency remained stable at 83.3 ± 5.7 % as the temperature decreased from 29.1 to 16.3 °C, and the relative abundance of Ca. Brocadia in carrier biofilms increased from 2.22 % to 4.31 % and 3.27 % in two aerobic chambers after 70 days of operation.

Recent progress in applications of Feammox technology for nitrogen removal from wastewaters: A review

Feammox process is crucial for the global nitrogen cycle and has great potentials for the treatment of low COD/NH₄⁺-N wastewaters. This work provides a systematic and comprehensive overview of the Feammox process. Specifically, underlying mechanisms and functional microbes mediating the Feammox process are summarized in detail. And key influencing factors including pH, temperature, dissolved oxygen, organic carbon, source of Fe(III) as well as various electron shuttles are discussed. Additionally, recent development trends and attempts of the Feammox technology in wastewater treatment applications are reviewed, and perspectives for future development are presented. A thorough review of the recent progress in Feammox process is expected to provide valuable information for further process optimization, which is helpful to achieve a more economical operation and better nitrogen removal performance in future field applications.

Comparison of inhibitory roles on nitrite-oxidizing bacteria by hydroxylamine and hydrazine during the establishment of partial nitrification

The inhibitory roles of hydroxylamine (NH₂OH) and hydrazine (N₂H₄) on nitrite-oxidizing bacteria were investigated in a comparative study. The results showed that nitrite accumulation was achieved by adding 5 mg-N/L NH₂OH or N₂H₄ to two parallel sequencing batch reactors, with nitrite accumulation rate reaching 95.83% and 86.58% within 15 days after adopting aeration time control, respectively. Correspondingly, the maximum level of NO in typical cycles caused by NH₂OH addition was 0.18 mg-N/L, which was higher than obtained for N₂H₄. NH₂OH or N₂H₄ showed strong inhibition on Nitrospira and promoted the enrichment of Nitrosomonas, with the effects of NH₂OH being more significant. However, nitritation began to deteriorate after the cessation of inhibitors addition. In conclusion, NH₂OH was a better inhibitor than N₂H₄ for Nitrospira. The inhibitory role of NH₂OH was primarily related to NO toxicity, while for N₂H₄ it was attributed to its own toxicity, with NO playing a smaller role.

Enhanced simultaneous partial nitrification and denitrification performance of aerobic granular sludge via tapered aeration in sequencing batch reactor for treating low strength and low COD/TN ratio municipal wastewater

The aerobic granular sludge simultaneous partial nitrification, denitrification and phosphorus removal (AGS-SPNDPR) process was carried out via tapered aeration in sequencing batch reactor (SBR) for treating low strength and low COD/TN ratio municipal wastewater. The results showed that aerobic granular sludge was successfully cultivated with good sedimentation performance when treating the municipal wastewater. Meanwhile, the median granule size increased to 270 (R1) and 257 (R2) μm on day 80. The excellent removal performance of COD (92%) and NH₄⁺-N (95%) were achieved under different aeration modes, while the higher TN removal efficiency (76%) was achieved by tapered aeration. The accumulation of NO₂^--N in R2 indicated that the tapered aeration was beneficial to achieve simultaneously partial nitrification and denitrification. Meanwhile, the high-efficiency phosphorus (95%) removal was realized via additional carbon source, and SPNDPR process was formed under tapered aeration. The bacterial community analysis indicated denitrifying glycogen-accumulating organisms (DGAOs) Candidatus_Competibacter and ammonia-oxidizing bacteria (AOB) Nitrosomonas were more effectively enriched via tapered aeration, while phosphorus-accumulating organisms (PAOs) Candidatus_Accumulibacter were effectively enriched under additional organic carbon. AOB, denitrifying bacteria and PAOs were simultaneously enriched by tapered aeration and additional carbon source, which was beneficial to nutrients removal. This study might be conducive to the application of AGS-SPNDPR system for treating low strength and low COD/TN ratio municipal wastewater under tapered aeration.

Bacterial Community Composition and Function in a Tropical Municipal Wastewater Treatment Plant

Bacterial diversity and community composition are of great importance in wastewater treatment; however, little is known about the diversity and community structure of bacteria in tropical municipal wastewater treatment plants (WWTPs). Therefore, in this study, activated sludge samples were collected from the return sludge, anaerobic sludge, anoxic sludge, and aerobic sludge of an A2O WWTP in Haikou, China. Illumina MiSeq high-throughput sequencing was used to examine the 16S ribosomal RNA (rRNA) of bacteria in the samples. The microbial community diversity in this tropical WWTP was higher than in temperate, subtropical, and plateau WWTPs. Proteobacteria, Bacteroidota, Patescibacteria, and Chloroflexi were the dominant phyla. Nitrification bacteria Nitrosomonas, and Nitrospira were also detected. Tetrasphaera, instead of Candidatus Accumulibacter, were the dominant polyphosphate accumulating organisms (PAOs), while, glycogen accumulating organisms (GAOs), such as Candidatus Competibacter and Defluviicoccus were also detected. The bacterial community functions predicted by PICRUSt2 were related to metabolism, genetic information processing, and environmental information processing. This study provides a reference for the optimization of tropical municipal WWTPs.

Variations of nitrogen-metabolizing enzyme activity and microbial community under typical loading conditions in full-scale leachate anoxic/aerobic system

Influent loading determines the performance of leachate treatment plant (LTP) facing the dynamic conditions, but enzyme expression in microbial community is unclear. Here, six nitrogen-metabolizing enzymes were detected during nitrification failures (NF), high loading (HL), low loading (LL), and low carbon/nitrogen (LCN) in a 500 m³/d LTP. Nitrogen removal in LL was 15 ± 5% higher than that in HL. The activity of hydroxylamine oxidoreductase decreased by 90% as the influent total nitrogen increased from 2450 mg/L to 3100 mg/L, which might be a critical enzyme causing the nitrification failure. Denitrifying enzyme abated by 1.3% as the carbon/nitrogen dropped by 1% in LCN. With the influent chemical oxygen demand decreased from 22000 mg/L to 12000 mg/L, the relative abundance of norank_f_Saprospiraceae dropped from 33.66% to 11.94%, and finally disappeared, which seems to be an indicator of the high load operation. These findings provide the basis for improving the efficiency of LTPs.

Performance and bacterial community profiles of sequencing batch reactors during long-term exposure to polyethylene terephthalate and polyethylene microplastics

Microplastics (MPs) are ubiquitous in wastewater treatment plants (WWTPs), but much remains to be learned about their roles in WWTPs. Herein, polyethylene terephthalate (PET) and polyethylene (PE) particles were added into sequencing batch reactors (SBRs), and the sole impacts and co-impacts of MPs with other pollutants (phenol and Cu²⁺) on wastewater treatment processes were evaluated. Results indicated that MPs did not significantly affect SBR performance, either alone or co-occurrence with phenol, but the co-exposure to MPs and Cu²⁺ severely suppressed COD removal efficiency by 37.02%-64.70%. The functional groups of activated sludge had no changes after receiving MPs, but the MPs-Cu²⁺ co-exposure could greatly promote the secretion of extracellular polymeric substances. Furthermore, MPs had no negative impacts on diversity, richness and structure of bacterial communities, and PET and PE showed different preferences for enrichment of bacterial populations. Moreover, the MPs-Cu²⁺ co-exposure obviously reduced the overall abundances of Cu-related genes in SBRs.

The anammox coupled partial-denitrification process in an integrated granular sludge and fixed-biofilm reactor developed for mainstream wastewater treatment: Performance and community structure

This study describes an integrated granular sludge and fixed-biofilm (iGB) reactor innovatively designed to carry out the anammox/partial-denitrification (A/PD) process for nitrogen removal with mainstream municipal wastewater. The iGB-A/PD reactor consists of anammox granules inoculated in the lower region of reactor and an acclimated fixed-biofilm positioned in the upper region. Compared to the other reported A/PD systems for mainstream wastewater treatment, this iGB-A/PD reactor is notable due to its higher quality effluent with a total inorganic nitrogen (TIN) of ∼3 mg•L^-1 and operation at a high nitrogen removal rate (NRR) of 0.8 ± 0.1 kg-N•m^-3•d^-1. Reads-based metatranscriptomic analysis found that the expression values of hzsA and hdh, key genes associated with anammox, were much higher than other functional genes on nitrogen conversion, confirming the major roles of the anammox bacteria in nitrogen bio-removal. In both regions of the reactor, the nitrate reduction genes (napA/narG) had expression values of 56-99 RPM, which were similar to that of the nitrite reduction genes (nirS/nirK). The expression reads from genes for dissimilatory nitrate reduction to ammonium (DNRA), nrfA and nirB, were unexpectedly high, and were over the half of the levels of reads from genes required for nitrate reduction. Kinetic assays confirmed that the granules had an anammox activity of 16.2 g-NH₄⁺-N•kg^-1-VSS•d^-1 and a nitrate reduction activity of 4.1 g-N•kg^-1-VSS•d^-1. While these values were changed to be 4.9 g- NH₄⁺-N•kg^-1-VSS•d^-1and 4.3 g-N•kg^-1-VSS•d^-1 respectively in the fixed-biofilm. Mass flux determination found that PD and DNRA was responsible for ∼50% and ∼25% of nitrate reduction, respectively, in the whole reactor, consistent with high effluent quality and treatment efficiency via a nitrite loop. Metagenomic binning analysis revealed that new and unidentified anammox species, affiliated with Candidatus Brocadia, were the dominant anammox organisms. Myxococcota and Planctomycetota were the principal organisms associated with the PD and DNRA processes, respectively.

Mainstream double-anammox driven by nitritation and denitratation using a one-stage step-feed bioreactor with real municipal wastewater

A novel double-anammox process for advanced mainstream nitrogen removal was established using step-feed sequencing batch reactor (SBR) system with integration of suspend sludge and biofilms. Following optimization of influent distribution ratio, the effluent total inorganic nitrogen (TIN) was < 10.2 mg N/L, with influent TIN of 43.4 mg N/L, and anammox contributed 71.4% to TIN removal. Biological processes and batch tests revealed that gradient C/N reduction promoted denitratation/anammox in anoxic stage, and simultaneous nitritation and anammox were achieved in oxic stage. Specially, anammox maintained on biofilms with abundance over 10⁹ copies/ (g dry sludge). High-throughput sequencing revealed that Thauera and Nitrosomonas were enriched in flocs. Furthermore, metagenomic sequencing confirmed that Thauera owns narG and napA (NO₃^-→NO₂^-) and Nitrosomonas owns amoA (NH₄⁺→NO₂^-), support stable NO₂^- supply for double-anammox. This mainstream anammox-dominant process could potentially be used for stable nitrogen removal in municipal wastewater treatment plants.

Control of aeration time in the aniline degrading-bioreactor with the analysis of metagenomic: Aniline degradation and nitrogen metabolism

The strategy of adjusting aeration time (5 h/6 h/7 h) was applied to the sequential batch reactors to optimize the treatment of aniline wastewater (600 mg/L) conveniently and economically. Three reactors degraded aniline effectively. The nitrogen removal ability of system with 6 h aeration time was better, performing the similar denitrification property as 5 h and nitrification performance as 7 h. Meanwhile, longer aeration time potentially damaged the sludge structure. The metagenomic analysis explained the micro-mechanism for the better performance of the system with 6 h aeration time. Appropriate aeration time was conducive to the enrichment of synergistic microflora, including aniline degrading-bacteria, heterotrophic nitrifiers and denitrifiers. Then, the tilt of environmental resources to these floras in the system was beneficial to the maximum value utilization of living substrates. Accordingly, these bacteria were more closely related to genes, resulting in higher expression of functional genes in the system.

A novel simultaneous partial nitritation, denitratation and anammox (SPNDA) process in sequencing batch reactor for advanced nitrogen removal from ammonium and nitrate wastewater

This study presented a novel simultaneous partial nitritation (PN), denitratation and anammox (SPNDA) process for treating ammonium and nitrate wastewater. Results indicated that SPNDA could achieve a great total nitrogen (TN) removal of 97.6 ± 0.5%, leading to effluent TN concentration of only 3.4 mg/L. Mass balance indicated that nitrogen removal rates via anammox, simultaneous nitrification and denitrification were 96.7% and 3.3%, respectively. Extended aerobic duration (12 h) and low dissolved oxygen (DO) concentration (0.15 mg/L) could improve ammonia-oxidizing bacteria (AOB) activity and maintain PN stability. The stable suppression of nitrite-oxidizing bacteria activity was attributed to the low DO (0.15 mg/L) and high free ammonia (3.63 mg/L) in SPND. Besides, the nitrogen conversion mechanisms for SPNDA were revealed based on a typical operational cycle. Microbial analysis showed that AOB (Nitrosomonas) and partial denitrifying bacteria (Thauera and Denitratisoma) coexisted with anammox bacteria (Candidatus Brocadia and Candidatus Anammoxoglobus) in the mixotrophic bio-community.

Enhanced nitrogen removal by partial nitrification-anammox process with a novel high-frequency micro-aeration (HFMA) mode: Metabolic interactions among functional bacteria

A novel high-frequency micro-aeration (HFMA) mode with aeration frequency of 15 times/h and DO concentration lower than 0.5 mg/L was proposed. Advanced partial nitrification-anammox (PN-A) performance was achieved in a two-stage sequencing batch reactor-integrated fixed-film activated sludge reactor with the HFMA mode. When treating wastewater with carbon/nitrogen ratio of 3, the abundance of NO₂^--N oxidation related genes decreased, and the genes carried out NO₃^--N reduction and carbon source consumption were up-regulated. These variations in microbial metabolism brought more NO₂^--N substrate for the subsequent anammox process, and consumed part of the accumulated organic matter and NO₃^--N. Thus, the HFMA conditions eventually promoted the expression of anammox bacteria with NH₂OH as an intermediate metabolite and the substance exchange activity of anammox bacteria. The changes in microorganisms lead to increase in the nitrite accumulation rate, nitrogen removal efficiency and abundance of anammox bacteria (16.34%, 18.71% and 5.92%, respectively).

Rapidly achieving and optimizing simultaneous partial nitrification denitrification and anammox integrated process by hydroxylamine addition for advanced nitrogen removal from domestic wastewater

The achievement and stable maintenance of partial nitrification and partial anammox process for municipal sewage is a challenging research topic at present. In this study, a novel strategy of hydroxylamine (NH₂OH) addition under low DO condition was adopted for rapidly achieving simultaneous partial nitrification denitrification and anammox process (SPNDA) to deal with domestic wastewater, the nitrite accumulation ratio (NAR) increased from 1% to 82% in the first 4 days. After the addition of NH₂OH was stopped, the PN effect of SPNDA process remained relatively stable within 100 days. During the stable operation period with aerobic HRT of 5 h, the nitrogen removal efficiency was 87.9 ± 4.2%. Moreover, the abundance of denitrifying bacteria and Candidatus Brocadia increased from 1.79% and 0.062% to 22.49% and 0.38% respectively, which promoted nitrogen removal effect. Overall, this study provided a quickly way for achieving the cost-effective SPNDA process to enhance nitrogen removal with NH₂OH addition.

Achieving stable nitrogen removal performance of mainstream PN-ANAMMOX by combining high-temperature shock for selective recovery of AOB activity

This paper describes the new concept of the mainstream partial nitritation (PN)-anaerobic ammonium oxidation (ANAMMOX) combined with a high-temperature shock strategy for the selective recovery of ammonia-oxidizing bacteria (AOB) activity. In the preliminary test, the temperature shock condition for PN was optimized (60 °C and > 20 min). Based on this, the implementation strategy in a continuous stirred tank reactor (CSTR) system was studied further, and the polyvinyl alcohol (PVA)/sodium alginate carrier exposure ratio (ER) and dissolved oxygen (DO) concentration were considered as primary variables. The AOB activity was recovered selectively when the ER of the carrier ranged from 20 to 40%, and the DO was higher than 2.3 mg O₂/L. This was not the case for nitrite-oxidizing bacteria (NOB) (AOB: 1.17±0.1 gNH₄⁺-N/L_Carrier/d, NOB: 0.34±0.1 gNO₃^--N/L_Carrier/d). As a result, the activity of AOB was recovered selectively with a decrease in Nitrospira spp., which was verified by kinetic and microbial analyses for the AOB (K_{S, DO} = 3.89 mgO₂/L) and NOB (K_{S, DO} = 1.14 mgO₂/L). Eventually, the mainstream PN-ANAMMOX was achieved with a nitrogen removal efficiency of 81.5±3.3% for 95 days. The findings provide insight to establishing a stable mainstream PN-ANAMMOX process using a high-temperature shock strategy.