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•A novel PN/Anammox system with low ammonia and no temperature control was developed.•Low sludge is advantageous for the suppression of NOB activity by light.•Stable nitrification was ...achieved by light irradiation under mainstream conditions.•Ellin6067 of light-resistant AOB bacteria enhances nitrification system performance.•PN/Anammox achieves a total nitrogen removal rate of > 90 % under mainstream conditions.
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.
Hepatic lipidome has been given emphasis for years since hepatic steatosis is the most remarkable character of nonalcoholic fatty liver diseases, an increasingly serious health issue worldwide. ...Nobiletin (NOB), one of the citrus flavonoids, exerted outstanding effect on lipid metabolism disorder. However, the underlying mechanism of NOB exerting effect on hepatic lipid alternation remains unclear. In this study, the animal model was built by feeding APOE−/− mice with high fat diet (HFD). The results of Oil Red O-stained liver section and the biochemical assay of lipid parameters confirmed the protective effect of NOB on hepatic steatosis and global lipid metabolism disorder in APOE−/− mice. The hepatic lipidomic study revealed a total of 958 lipids significantly altered by HFD and a total of 86, 116, 212 lipid metabolites changed by L-NOB (50 mg/kg/d NOB), M-NOB (100 mg/kg/d NOB) and H-NOB (200 mg/kg/d NOB) respectively. In the further screening analysis, an amount of 60 lipids were identified as the potential lipid markers of NOB treatment, most of which belonged to glycerophospholipids lipid categories and exhibited obvious correlation with each other and the lipid parameters related to hepatic steatosis. Taken together, our data demonstrated that glycerophospholipids metabolism played an indispensable role in the progression of hepatic steatosis and the protective effect of NOB. Besides, the modulation towards genes involved in lipid synthesis was observed after NOB administration in this study. These finding illustrated the antihepatic steatosis effect of NOB based on altering hepatic lipidome, particularly the glycerophospholipids metabolism, and provided a new insight in the pathogenesis of hepatic steatosis.
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•Mainstream PN was quickly established by sludge treatment using high salinity.•High NAR (95.69 ± 2.65 %) was maintained stable in the mainstream CSTR.•Salinity increased the relative ...abundance of Nitrosomonas from 5.98% to 38.08%.•NOB activity was almost undetectable after sludge treatment using high salinity.•The absolute activity change of NOB should be given attention for sludge treatment.
The difficulty of the start-up and maintenance the stability of partial nitritation (PN) was considered as a key challenge for mainstream anammox. This study demonstrated a novel approach for achieving rapid start-up of mainstream PN by sludge treatment using high salinity based on the phenomenon which high salinity is far more biocidal to nitrite-oxidising bacteria (NOB) than to ammonia-oxidising bacteria (AOB) in short-term (within 24 h). In this study, one-third of the nitrifying sludge from the continuous stirred tank reactor (CSTR) fed by mainstream wastewater was suppressed at 70 g NaCl/L for 24 h every day. The treated nitrifying sludge was afterwards returned back to the CSTR. Mainstream PN with high nitrite accumulation ratio (NAR) was rapidly established (in 14 d) after optimizing the suppression conditions and maintained stable (NAR = 95.69 ± 2.65 %) more than 45 days in the mainstream reactor, indicating the establishment of PN process. After long-term high salinity treatment, NOB activity in the reactor was almost undetectable, while AOB activity significantly increased. Microbial community analysis revealed that the sludge treatment using high salinity could significantly reduce Nitrospira abundance while the relative abundance of Nitrosomonas increased by an order of magnitude. Moreover, the relationship between the absolute activity change of nitrifying sludge and inhibition strength was explored based on the activity batch assays and quantitative polymerase chain reaction assays analysis. The approach of achieving mainstream PN by sludge treatment using high salinity is economically and environmentally attractive because salt is an easily obtainable substance.
•A continuous flow reactor for treating actual municipal wastewater was studied•Nitritation was quickly initiated in 15 d via UL-SRT during seasonal warming•Stable nitritation could be achieved by ...using joint UL-SRT and tapered aeration•The AOB (amoA) abundance increased approximately 50 times after nitritation
Rapid achievement of nitritation of mainstream municipal wastewater in a continuous-flow process is attractive since it favors the involvement of the anammox process and reduces the operational costs. In this study, a feasible and economical strategy is proposed to rapidly achieve the nitritation of municipal wastewater. By aggressively discharging excess sludge during the seasonal warming period (temperature increasing from 18°C to 22°C), nitritation was established in 15 days with a nitrite accumulation ratio of 85.09% in a continuous-flow anaerobic/oxic (An/O) reactor. Meanwhile, qPCR results revealed that amoA abundance increased from (1.78±0.10) × 108 copies/(g VSS) to (1.05±0.11) × 1010 copies/(g VSS) while the abundance of nitrite-oxidizing bacteria decreased from (1.1±0.02) × 1010 copies/(g VSS) to (5.01±0.02) × 108 copies/(g VSS). The temperature gradually stabilized at 26°C during the following operational period and stable nitritation was maintained with a nitrite accumulation ratio above 90%, which was mainly attributed to a short sludge retention time (SRT) of 4.3 days and a low dissolved oxygen of 0.86 ± 0.5 mg/L. Falling temperature negatively impacted the stability of nitritation, but nitritation could be restarted by aggressively discharging excess sludge during another temperature increase period. Overall, this study provides a feasible strategy to start-up nitritation that has great potential applications for municipal wastewater treatment.
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•An integrated strategy for stabilizing NOB inhibition was successfully established.•Nutrient conversion pathways that PNA coupled with EPDA were specified.•Advanced nitrogen and ...phosphorus removal was achieved in mainstream PNA system.•Functional microbial activities, composition, and variations were investigated.•Anammox-related functional genes had higher expression at the transcriptome level.
Partial nitrification anammox (PNA) is a promising technology for energy saving and nitrogen removal. The bottlenecks limiting the widespread application of PNA in mainstream municipal wastewater treatment include the difficulty in stably suppressing nitrite-oxidizing bacteria (NOB) and failure to meet discharge standards for total nitrogen (TN) due to high nitrate concentration in the effluent. To this end, this study aims to stably suppress NOB using integrated strategies (including the inoculated activated sludge pretreatment with FNA, low DO, residual ammonia nitrogen, and floc sludge discharge) while also investigating the feasibility and performance of coupling PNA with endogenous partial denitrification/anammox (EPDA) in a PNA granular hybrid system. During the 300 days of operation, the integrated strategies effectively stabilized the suppression of NOB, decreasing its abundance from 1.22 % to 0.55 %, and the final activity was reduced to 0.36 ± 0.12 mg-N/L/h. Meanwhile, the relative abundance of AnAOB as the dominant microbial community increased from 9.16 % to 24 %, with its activity reaching 2.84 ± 0.16 mg-N/L/h, limiting the supply of nitrite and ensuring the stable suppression of NOB. Typical cycle tests showed that EPDA and PNA were successfully coupled during the aeration stage with a nitrogen removal contribution rate of 80.55 %, ultimately achieving the average effluent TN and PO43--P were 4.22 mg/L and 0.09 mg/L, respectively. The metagenomic and metatranscriptomic sequencing results revealed that anammox bacteria (AnAOB) coexisted with ammonia-oxidizing bacteria (AOB), NOB, and endogenous denitrifying bacteria (EDB), and AnAOB played a primary role in the nitrogen removal process of mainstream PNA. This study brings mainstream PNA closer to widespread application and provides significant technical support for its engineering implementation.
•PN/AMX pilot plant treated municipal wastewater without temperature control.•Stable two-stage system coping with wastewater characteristic fluctuations.•NOB suppression was rapidly started up by ...overloading and maintained by FNA.•NOB were inactive but still present in the nitritation unit.•Nitrogen removal efficiencies of 80 % were achieved in the anammox reactor.
Two-stage partial nitritation (PN) and anammox (AMX) systems showed promising results for applying autotrophic nitrogen removal under mainstream conditions. In this study, a pilot-scale (600 L per reactor) two-stage PN/AMX system was installed in a municipal wastewater treatment plant (WWTP) provided with a high-rate activated sludge (HRAS) system for organic carbon removal. The PN/AMX system was operated without temperature control (ranging from 11 to 28 °C) and was subjected to the same variations in wastewater characteristics as the WWTP (22 to 63 mg NH4+- N/L). The developed strategy is simple, does not require the addition of chemicals and is characterised by short start-up periods. The PN process was established by applying a high hydraulic load and maintained by in situ accumulated free nitrous acid (FNA) of 0.015–0.2 mg HNO2-N/L. Based on pH value, a controlled aeration strategy was applied to achieve the target nitrite to ammonium ratio in the effluent (1.1 g NO2–-N/g NH4+-N) to feed the AMX reactor. Although NOB were not fully washed out from the system, nitrite accumulation remained (>99 %) stable with no evidence of NOB activity. In the AMX reactor, an overall nitrogen removal efficiency of 80 % was achieved. Regarding effluent quality, 12 ± 3 mg TN/L was obtained, but 5 mg NO3–-N/L was already in the HRAS effluent. The relative abundance of NOB showed a strong negative correlation with the FNA concentration, providing a good strategy for establishing PN under mainstream conditions.
•Inactivation and adaptation of AOB and NOB to FNA was investigated.•FNA caused a stronger inactivation effect on NOB than on AOB.•This inactivation increased as the FNA increased and exposure time ...lengthened.•AOB did not adapt to the FNA treatment. In contrast, NOB did adapt to FNA.•NOB adaptation may be due to its shift from Nitrospira to Candidatus Nitrotoga.
Inactivation and adaptation of ammonia-oxidizing bacteria (AOB) and nitrite-oxidizing bacteria (NOB) to free nitrous acid (FNA) was investigated. Batch test results showed that AOB and NOB were inactivated when treated with FNA. After an 85-day operating period, AOB in a continuous pre-denitrification reactor did not adapt to the FNA that was applied to treat some of the return activated sludge. In contrast, NOB did adapt to FNA. NOB activity in the seed sludge was only 11% of the original activity after FNA batch treatment, at 0.75mg HNO2-N/L. NOB activity in the pre-denitrification reactor was not affected after being exposed to this FNA level. Nitrosomonas was the dominant AOB before and after long-term FNA treatment. However, dominant NOB changed from Nitrospira to Candidatus Nitrotoga, a novel NOB genus, after long-term FNA treatment. This adaptation of NOB to FNA may be due to the shift in NOB population makeup.
Microbial nitrite oxidation is the primary pathway that generates nitrate in wastewater treatment systems and can be performed by a variety of microbes: namely, nitrite-oxidizing bacteria (NOB). ...Since NOB were first isolated 130 years ago, the understanding of the phylogenetical and physiological diversities of NOB has been gradually deepened. In recent endeavors of advanced biological nitrogen removal, NOB have been more considered as a troublesome disruptor, and strategies on NOB suppression often fail in practice after long-term operation due to the growth of specific NOB that are able to adapt to even harsh conditions. In line with a review of the history of currently known NOB genera, a phylogenetic tree is constructed to exhibit a wide range of NOB in different phyla. In addition, the growth behavior and metabolic performance of different NOB strains are summarized. These specific features of various NOB (e.g., high oxygen affinity of Nitrospira, tolerance to chemical inhibitors of Nitrobacter and Candidatus Nitrotoga, and preference to high temperature of Nitrolancea) highlight the differentiation of the NOB ecological niche in biological nitrogen processes and potentially support their adaptation to different suppression strategies (e.g., low dissolved oxygen, chemical treatment, and high temperature). This review implicates the acquired physiological characteristics of NOB to their emergence from a genomic and ecological perspective and emphasizes the importance of understanding physiological characterization and genomic information in future wastewater treatment studies.
The high energy consumption and excessive waste activated sludge (WAS) production have become the major concerns on the municipal wastewater treatment with conventional biological processes. To ...tackle these emerging issues, this study demonstrated the feasibility of a novel process integrating an upflow anaerobic fixed-bed reactor (UAFBR) followed by a continuous step-feed reactor for mainstream deammonification towards improved energy efficiency, minimized sludge production and cost-effective ammonium removal. The results showed that 48.8% of the influent chemical oxygen demand (COD) was directly converted to methane gas in UAFBR with minimized sludge production, while 80% of total nitrogen (TN) was removed in the step-feed reactor. Mass balance on the step-feed reactor revealed that the oxic chambers contributed 51.6% of the removed ammonium oxidation to mainly nitrite, while the produced nitrite was immediately removed via anammox with the ammonium supplied by the step-feed in the following anoxic chambers where about 87.1% TN removal occurred. Moreover, it was found that sustainable repression of nitrite oxidizing bacteria (NOB) was achieved without compromising the activity of ammonia oxidizing bacteria (AOB). The anammox bacteria were effectively retained in the anoxic chambers and showed a high specific anammox activity of 0.42 g N/(g VSS·day). These suggest that the step-feed configuration can offer a feasible engineering option towards single-stage mainstream deammonification. It appears that the integrated process developed in this study sheds light on the possible way towards sustainable, energy self-sufficient municipal wastewater reclamation.
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•An integrated process was developed for sustainable wastewater reclamation.•Step-feed configuration was favorable for stable mainstream deammonification.•Effective NOB repression was observed without affecting AOB and anammox activity.•80% of nitrogen was autotrophically removed via mainstream anammox.•The process offered a feasible engineering solution for stable mainstream anammox.
Morphological evolution of layered double hydroxides (LDHs) with preferential crystal facets has appealed gigantic attention of research community. Herein, we prepare hierarchical hybrid material by ...structurally integrating fusiform-like CuNiAl LDHs petals on conductive backbone of CF (CF@CuNiAl LDHs) and investigate electrocatalytic behavior in nitrate reduction over a potential window of ˗0.7 V to +0.7 V. The CF@CuNiAl LDHs electrode exhibits remarkable electrocatalytic aptitude in nitrate sensing including broad linear ranges of 5 nM to 40 µM and 75 µM to 2.4 mM with lowest detection limit of 0.02 nM (S/N = 3). The sensor shows sensitivity of 830.5 ± 1.84 µA mM1- cm2- and response time within 3 s. Owing to synergistic collaboration of improved electron transfer kinetics, specific fusiform-like morphology, presence of more catalytically active {111} facets and superb catalytic activity of LDHs, CF@CuNiAl LDHs electrode has outperformed as electrochemical sensor. Encouraged from incredible performance, CF@CuNiAl LDHs flexible electrode has been applied in real-time in-vitro detection of nitrite oxidizing bacteria (NOB) through the sensing of nitrate because NOB convert nitrite into nitrate by characteristic metabolic process to obtain their energy. Further, CF@CuNiAl LDHs based sensing podium has also been employed in in-vitro detection of nitrates from mineral water, tap water and Pepsi drink.
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•The hierarchical CF@CuNiAl LDH nanohybrids are synthesized by facile methods.•Maximum interfacial collaborations are resulted from fusiform-like CF@CuNiAl LDH.•CF@CuNiAl LDH hybrids show excellent electrochemical activity for nitrate reduction.•Real-time in-vitro detection of NOB through the sensing of nitrate as biomarker.
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