Achieving stable mainstream nitrogen and phosphorus removal assisted by hydroxylamine addition in a continuous partial nitritation/anammox process from real sewage

Space heterogeneity of nitrogen removal functional genes, nitrogen transformation pathways and mechanisms in MEBR treating mariculture wastewater

Membrane Electro-Bioreactor (MEBR), exhibited excellent nitrogen removal in mariculture wastewater treatment. However, the differences of microbial community and nitrogen transformation pathways on spatial scale caused by the mass transfer of reactive chlorine species (RCS) generated by electrooxidation were unclear. This study provided new insights into the space heterogeneity of ammonia transformation pathways and mechanisms. The results demonstrated an increase in the reduction of nitrate to nitrite through partial denitrification on the membrane. Coupling with dissimilatory nitrate reduction to ammonium and RCS, higher nitrate (0.3 mgN/L) and TN removal (2.6 mgN/L) was obtained in MEBR. Higher relative abundance of narGHI and nirB were obtained. Ammonia oxidation by biofilters was enhanced in MEBR, that ammonia removal contributed by biofilters was 32.0 %, 5.2 times higher than the membrane. Relative abundance of amoABC and Nitrosomonas in biofilters were the highest. The results will provide theoretical basis for reactor configuration and operation optimization.

Advanced N removal from low C/N sewage via a plug-flow anaerobic/oxic/anoxic (AOA) process: Intensification through partial nitrification, endogenous denitrification, partial denitrification, and anammox (PNEnD/A)

Achieving low-cost advanced nitrogen (N) removal from municipal wastewater treatment plants (WWTPs) remains a challenge. A plug-flow anaerobic/oxic/anoxic (AOA) system with a mixtures bypass (MBP) integrating partial nitrification (PN), endogenous carbon denitrification (EnD), partial denitrification (PD), and anaerobic ammonium oxidation (Anammox), was constructed to treat actual sewage with a low C/N ratio. The effluent concentrations and removal efficiency of total inorganic nitrogen (TIN) during stable operation were 2.9 ± 0.9 mg/L and 93.1 ± 2.0 %, respectively. EnD was enhanced by the MBP through the efficient utilization of polyhydroxyalkanoates generated in the anaerobic zone. PD was promoted by the addition of carries and sodium acetate to the anoxic tank and the subsequent implantation of the Anammox biofilm successfully coupled PD/A. Stable PN was obtained with a satisfactory nitrite accumulation ratio of 92.6 %, facilitated by carriers and the introduction of hydroxylamine in the oxic zone. Mass balance analysis revealed that EnD and Anammox contributed 40.8 % and 48.2 % of TIN removal, respectively. The enrichment and synergistic effects of ammonia-oxidizing bacteria, denitrifying bacteria, glycogen-accumulating organisms, and anaerobic ammonia-oxidizing bacteria formed a diverses bacterial basis for the establishment of PN, EnD, PD, and Anammox (PNEnD/A) in the AOA system. The successful integration of PNEnD/A into the AOA process provides an innovative approach for low-cost advanced N removal in WWTPs.

Revisit the role of hydroxylamine in sulfur-driven autotrophic denitrification

Through dedicated batch tests using the enriched sludge dominated by sulfur-oxidizing bacteria (SOB), the potential transformation of hydroxylamine (NH2OH) by SOB and the effects of NH2OH on the rate-limiting sequential reduction processes of sulfur-driven autotrophic denitrification (SDAD) were systematically explored in this study. The results indicated that NH2OH might be first converted to NO by SOB and then participate in the SDAD process, thus accelerating the utilization of S2- and contributing to the formation of N2O. Up to 3.5 mg-N/L NH2OH didn't affect the NO3- or NO2- reduction of SDAD, during which no significant changes were observed for the NH2OH concentration. Comparatively, even though NH2OH had no direct impact on the N2O reduction of SDAD, it could be consumed and therefore affect the depletion of N2O indirectly by regulating the toxic effect and electron supply of S2-. These findings provide novel implications for applying NH2OH to SDAD-based integrated processes for biological nitrogen removal.

Regulation mechanism of hydrazine and hydroxylamine in nitrogen removal processes: A Comprehensive review

As the new fashioned nitrogen removal process, short-cut nitrification and denitrification (SHARON) process, anaerobic ammonium oxidation (anammox) process, completely autotrophic nitrogen removal over nitrite (CANON) process, partial nitrification and anammox (PN/A) process and partial denitrification and anammox (PD/A) process entered into the public eye due to its advantages of high nitrogen removal efficiency (NRE) and low energy consumption. However, the above process also be limited by long-term start-up time, unstable operation, complicated process regulation and so on. As intermediates or by-metabolites of functional microorganisms in above processes, hydroxylamine (NH2OH) and hydrazine (N2H4) improved NRE of the above processes by promoting functional enzyme activity, accelerating electron transport efficiency and regulating distribution of microbial communities. Therefore, this review discussed effects of NH2OH and N2H4 on stability and NRE of above processes, analyzed regulatory mechanism from functional enzyme activity, electron transport efficiency and microbial community distribution. Finally, the challenges and limitations for nitric oxide (NO) and nitrous oxide (N2O) produced from regulation of NH2OH and N2H4 are discussed. In additional, perspectives on future trends in technology development are proposed.

Metagenomics reveals the microbial community and functional metabolism variation in the partial nitritation-anammox process: From collapse to recovery

Mainstream partial nitritation-anammox (PNA) process easily suffers from performance instability and even reactor collapse in application. Thus, it is of great significance to unveil the characteristic of performance recovery, understand the intrinsic mechanism and then propose operational strategy. In this study, we combined long-term reactor operation, batch tests, and metagenomics to reveal the succession of microbial community and functional metabolism variation from system collapse to recovery. Proper aeration control (0.10-0.25 mg O2/L) was critical for performance recovery. It was also found that Candidatus Brocadia became the dominant flora and its abundance increased from 3.5% to 11.0%. Significant enhancements in carbon metabolism and phospholipid biosynthesis were observed during system recovery, and the genes abundance related to signal transduction was dramatically increased. The up-regulation of sdh and suc genes showed the processes of succinate dehydrogenation and succinyl-CoA synthesis might stimulate the production of amino acids and the synthesis of proteins, thereby possibly improving the activity and abundance of AnAOB, which was conducive to the performance recovery. Moreover, the increase in abundance of hzs and hdh genes suggested the enhancement of the anammox process. Changes in the abundance of key genes involved in nitrogen metabolism indicated that nitrogen removal pathway was more diverse after system recovery. The achievement of performance recovery was driven by anammox, nitrification and denitrification coupled with dissimilatory nitrate reduction to ammonium. These results provide deeper insights into the recovery mechanism of PNA system and also provide a potential regulation strategy for the stable operation of the mainstream PNA process.

Anammox granule destruction and reconstruction in a partial nitrification/anammox system under hydroxylamine stress

Nitrite oxidizing bacteria (NOB) outcompeting anammox bacteria (AnAOB) poses a challenge to the practical implementation of the partial nitrification/anammox (PN/A) process for municipal wastewater. A granules-based PN/A bioreactor was operated for 260 d with hydroxylamine (NH2OH) added halfway through. qPCR results detected the different amounts of NOB among granules and flocs and the dynamic succession during operation. CLSM images revealed a unique layered structure of granules that NOB located inside led to the inhibition effect of NH2OH delayed. Besides, the physical and morphological characteristics revealed that anammox granules experienced destruction. AnAOB took the broken granules as an initial biofilm aggregate to reconstruct new granules. RT-qPCR and high throughput sequencing results suggested that functional gene expression and community structure were regulated for the AnAOB metabolism process. Correspondingly, the rapid proliferation (0.52 → 1.99%) of AnAOB was realized, and the nitrogen removal rate achieved a nearly quadruple improvement (0.21 → 0.83 kg-N/m3·d). This study revealed that anammox granules can self-reconstruct in the PN/A system when granules are disintegrated under NH2OH stress, broadening the feasibility of applying PN/A process.

Model-based development of strategies enabling effective enrichment and application of comammox bacteria in floccular sludge under mainstream conditions

The discovery of complete ammonium oxidation (comammox) has redefined the perception of the nitrification process which plays a vital part in biological nitrogen removal (BNR) from wastewater. Despite the reported detection or cultivation of comammox bacteria in biofilm or granular sludge reactors, limited attempts have been made to enrich or assess comammox bacteria in floccular sludge reactors with suspended growth of microbes, which are most extensively applied at wastewater treatment plants. Therefore, through making use of a comammox-inclusive bioprocess model reliably evaluated using batch experimental data with joint contributions of different nitrifying guilds, this work probed into the proliferation and functioning of comammox bacteria in two commonly-used floccular sludge reactor configurations, i.e., continuous stirred tank reactor (CSTR) and sequencing batch reactor (SBR), under mainstream conditions. The results indicated that compared with the studied SBR, the CSTR was observed to favor the enrichment of comammox bacteria through maintaining a sufficient sludge retention time (40-100 d) while avoiding an extremely low DO level (e.g., 0.05 g-O2/m3), irrespective of the varied influent NH4+-N of 10-100 g-N/m3. Meanwhile, the inoculum sludge was found to greatly influence the start-up process of the studied CSTR. By inoculating the CSTR with a sufficient amount of sludge, finally enriched floccular sludge with a high abundance of comammox bacteria (up to 70.5 %) could be rapidly obtained. These results not only benefitted further investigation and application of comammox-inclusive sustainable BNR technologies but also explained, to some extent, the discrepancy in the reported presence and abundance of comammox bacteria at wastewater treatment plants adopting floccular sludge-based BNR technologies.

Mainstream nitrogen removal from low temperature and low ammonium strength municipal wastewater using hydrogel-encapsulated comammox and anammox

Application of partial nitritation (PN)-anammox to mainstream wastewater treatment faces challenges in low water temperature and low ammonium strength. In this study, a continuous flow PN-anammox reactor with hydrogel-encapsulated comammox and anammox was designed and operated for nitrogen removal from mainstream wastewater with low temperature. Long-term operation with synthetic and real wastewater as the feed demonstrated nearly complete ammonium and total inorganic nitrogen (TIN) removal by the reactor at temperatures as low as 10 °C. A significantly decreased nitrogen removal performance and biomass activity was observed in the reactor at 4 °C before a selective heating strategy was employed. A novel heating technology using radiation to heat carbon black co-encapsulated in the hydrogel matrix with biomass was used to selectively heat biomass but not water in the treatment system. This selective heating technology enabled nearly complete ammonium removal and 89.4 ± 4.3 % TIN removal at influent temperature of 4 °C and reactor temperature 5 °C. Activity tests suggested selective heating brought the biomass activity at influent temperatures of 4 °C and reactor temperature 5 °C to a level comparable to that at 10 °C. Comammox and anammox were consistently present in the system and spatially organized in the hydrogel beads as revealed by qPCR and fluorescence in-situ hybridization (FISH). The abundance of comammox largely decreased by 3 orders of magnitude during the operation at 4 °C, and rapidly recovered after the application of selective heating. The anammox-comammox technology tested in this study essentially enabled mainstream shortcut nitrogen removal, and the selective heating ensured good performance of the technology at temperature as low as 5 °C.

Insights into the mechanism of the deterioration of mainstream partial nitritation/anammox under low residual ammonium

Residual ammonium is a critical parameter affecting the stability of mainstream partial nitritation/anammox (PN/A), but the underlying mechanism remains unclear. In this study, mainstream PN/A was established and operated with progressively decreasing residual ammonium. PN/A deteriorated as the residual ammonium decreased to below 5 mg/L, and this was paralleled by a significant loss in anammox activity in situ and an increasing nitrite oxidation rate. Further analysis revealed that the low-ammonium condition directly decreased anammox activity in situ via two distinct mechanisms. First, anammox bacteria were located in the inner layer of the granular sludge, and thus were disadvantageous when competing for ammonium with ammonium-oxidizing bacteria (AOB) in the outer layer. Second, the complete ammonia oxidizer (comammox) was enriched at low residual ammonium concentrations because of its high ammonium affinity. Both AOB and comammox presented kinetic advantages over anammox bacteria. At high residual ammonium concentrations, nitrite-oxidizing bacteria (NOB) were effectively suppressed, even when their maximum activity was high due to competition for nitrite with anammox bacteria. At low residual ammonium concentrations, the decrease in anammox activity in situ led to an increase in nitrite availability for nitrite oxidation, facilitating the activation of NOB despite the dissolved oxygen limitation (0.15-0.35 mg/L) for NOB persisting throughout the operation. Therefore, the deterioration of mainstream PN/A at low residual ammonium was primarily triggered by a decline in anammox activity in situ. This study provides novel insights into the optimized design of mainstream PN/As in engineering applications.

A critical review on microbial ecology in the novel biological nitrogen removal process: Dynamic balance of complex functional microbes for nitrogen removal

The novel biological nitrogen removal process has been extensively studied for its high nitrogen removal efficiency, energy efficiency, and greenness. A successful novel biological nitrogen removal process has a stable microecological equilibrium and benign interactions between the various functional bacteria. However, changes in the external environment can easily disrupt the dynamic balance of the microecology and affect the activity of functional bacteria in the novel biological nitrogen removal process. Therefore, this review focuses on the microecology in existing the novel biological nitrogen removal process, including the growth characteristics of functional microorganisms and their interactions, together with the effects of different influencing factors on the evolution of microbial communities. This provides ideas for achieving a stable dynamic balance of the microecology in a novel biological nitrogen removal process. Furthermore, to investigate deeply the mechanisms of microbial interactions in novel biological nitrogen removal process, this review also focuses on the influence of quorum sensing (QS) systems on nitrogen removal microbes, regulated by which bacteria secrete acyl homoserine lactones (AHLs) as signaling molecules to regulate microbial ecology in the novel biological nitrogen removal process. However, the mechanisms of action of AHLs on the regulation of functional bacteria have not been fully determined and the composition of QS system circuits requires further investigation. Meanwhile, it is necessary to further apply molecular analysis techniques and the theory of systems ecology in the future to enhance the exploration of microbial species and ecological niches, providing a deeper scientific basis for the development of a novel biological nitrogen removal process.

Enhancing nitrogen removal through directly integrating anammox into mainstream wastewater treatment: Advantageous, issues and future study

Anaerobic ammonium oxidation (anammox) has great potential to be applied to the process of nitrogen removal from mainstream wastewater. However, directly applying complete anammox to the mainstream is typically hindered by low temperatures, a low ammonia concentration, and high organic matter concentrations. Directly integrating anammox into mainstream treatment by enhancing the in-situ enrichment of anammox bacteria in wastewater treatment plants (WWTPs) could effectively improve the nitrogen removal efficiency and reduce the treatment cost. A certain anammox bacteria abundance in full-scale WWTPs provides the feasibility of directly integrating anammox into mainstream treatment and realizing partial mainstream anammox. The technical development status of partial anammox and the mechanisms of achieving partial mainstream anammox by aeration and organic control are summarized. This review provides an enhanced understanding of this novel technical route of partial mainstream anammox treatment for improving the quality, performance, and prospects for this technology to be used in upgrading WWTPs.

Rapidly recovering and maintaining simultaneous partial nitrification, denitrification and anammox process through hydroxylamine addition to advance nitrogen removal from domestic sewage

The collapse of simultaneous partial nitrification, denitrification and anammox (SPNDA) system, caused by the destruction of partial nitrification (PN), is the most likely phenomenon to occur. Therefore, recovering the process quickly and maintaining efficient nitrogen removal is a valuable topic for research. In the anaerobic/aerobic/anoxic operation mode, SPNDA process was used to treat domestic sewage in a sequencing batch biofilm reactor. After the deterioration of PN effect, with the addition of hydroxylamine, the activity of ammonia-oxidizing bacteria in the nitrobacteria increased (61.0-91.3 %), whereas the accumulation of nitrite quickly recovered to 90.4 % within 5 days. Meanwhile, the nitrogen removal efficiency improved (61.8-95.6 %) and the effluent TN was 2.1 mg/L. Furthermore, Candidatus Brocadia was enriched (0.50-1.82 %) in the system. The results indicated that the addition of hydroxylamine was an effective strategy to recover and economically maintain the SPNDA process for advanced nitrogen removal from domestic sewage.

Mechanisms of NO and N2O production by enriched nitrifying sludge in a sequencing batch reactor: Effects of hydroxylamine

NO and N₂O as important greenhouse gases andtheir production mechanisms during nitrification are not completely understood. This study aimed to analyze the effect of hydroxylamine (NH₂OH) on NO and N₂O produced by nitrifying bacteria from activated sludge in a sequencing batch reactor (SBR). Experimental results showed that when nitrite (NO₂^-) accumulated during aerobic ammonia (NH₄⁺) oxidation, N₂O was the main product. The total amount of NO and N₂O produced by NH₂OH oxidation was positively correlated with dissolved oxygen (DO) levels. The imbalance of NH₄⁺ oxidation caused by NH₂OH addition was more conducive to the generation of NO and N₂O under high DO conditions. When NH₂OH was added into the reactor with NO₂^- as the substrate, the production of NO and N₂O under high DO levels was mainly related to NH₂OH oxidation. Under low DO conditions, NO and N₂O from the biotic/abiotic hybrid pathways were more significant in the reactor of the coexistence of NO₂^- and NH₂OH, which could be mainly caused by the pathways of nitrifier denitrification and abiotic reaction. Besides, limited amount of NO and N₂O was generated by heterotrophic denitrification pathway during autotrophic nitrification. The implications for the above results are important for understanding the production of NO and N₂O under NH₂OH stress in nitrifying sludge reactor.

Alcaligenes ammonioxydans HO-1 antagonizes Bacillus velezensis via hydroxylamine-triggered population response

Antagonism is a common behavior seen between microbes in nature. Alcaligenes ammonioxydans HO-1 converts ammonia to nitrogen under aerobic conditions, which leads to the accumulation of extracellular hydroxylamine (HA), providing pronounced growth advantages against many bacterial genera, including Bacillus velezensis V4. In contrast, a mutant variant of A. ammonioxydans, strain 2-29, that cannot produce HA fails to antagonize other bacteria. In this article, we demonstrate that cell-free supernatants derived from the antagonistic HO-1 strain were sufficient to reproduce the antagonistic behavior and the efficiency of this inhibition correlated strongly with the HA content of the supernatant. Furthermore, reintroducing the capacity to produce HA to the 2-29 strain or supplementing bacterial co-cultures with HA restored antagonistic behavior. The HA-mediated antagonism was dose-dependent and affected by the temperature, but not by pH. HA caused a decline in biomass, cell aggregation, and hydrolysis of the cell wall in exponentially growing B. velezensis bulk cultures. Analysis of differential gene expression identified a series of genes modulating multicellular behavior in B. velezensis. Genes involved in motility, chemotaxis, sporulation, polypeptide synthesis, and non-ribosomal peptide synthesis were all significantly downregulated in the presence of HA, whereas autolysis-related genes showed upregulation. Taken together, these findings indicate that HA affects the population response of coexisting strains and also suggest that A. ammonioxydans HO-1 antagonize other bacteria by producing extracellular HA that, in turn, acts as a signaling molecule.

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.

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.

Nitrogen removal by a Hydroxyapatite-enhanced Micro-granule type One-stage partial Nitritation/anammox process following anaerobic membrane bioreactor treating municipal wastewater

Nitrogen removal from wastewater by the partial nitritation/anammox (PNA) technology is promising from both economic and environmental perspectives. However, this technology has not been popularized in the mainstream because of low biomass retention and the growth of the nitrite oxidizing bacteria. In this study, a one-stage PNA process with hydroxyapatite (HAP)-enhanced granules was used to treat effluent from a mainstream anaerobic membrane bioreactor. The HAP-enhanced reactor allowed an enriched high biomass of 6.9 ± 0.2 g/L at a low hydraulic retention time of 2 h. A nitrogen removal efficiency of 80 ± 6.0 %, a nitrogen removal rate of 0.36 ± 0.05 kg/m³/d and a COD removal efficiency of 54 ± 15 % were achieved stably, leading to a low total nitrogen concentration of 8.5 ± 2.7 mg/L and a low COD concentration of 19.7 ± 5.9 mg/L in the effluent. Anammox bacteria of Candidatus Kuenenia stuttgartiensis and ammonium oxidizing bacteria of Nitrosomonas were found to be the two most predominant bacteria.

In-situ fermentation coupling with partial-denitrification/anammox process for enhanced nitrogen removal in an integrated three-stage anoxic/oxic (A/O) biofilm reactor treating low COD/N real wastewater

Mainstream partial-denitrification with anammox (PD-anammox) process faced the challenge of complex organics involved in real sewage. Herein, PD-anammox coupled with in-situ fermentation was successfully achieved in a full biofilm system formed by three-stage anoxic/oxic reactor to treat real wastewater with low COD/N of 3.6. The total nitrogen (TN) removal efficiency was enhanced to 78.4% ± 3.6% with average TN and ammonium concentrations in effluent of 10.6 and 0.5 mg N/L, respectively. Batch tests confirmed that partial-denitrification was the major nitrite provider for anammox in the anoxic biofilm, while in-situ fermentation could decompose the complex organics to readily-biodegradable organics for full- or partial-denitrification. Additionally, a significant anammox bacteria (Candidatus Brocadia) population was detected in the second (3.53%) and third (4.46%) anoxic zones, while denitrifiers and fermentative bacteria were mainly enriched in the first anoxic zone. This study presents a feasible approach for PD-anammox process in practical application under mainstream condition.