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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.
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.
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.
•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.
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.
•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.
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•A two-stage PN/A system successfully treated undiluted THP/AD dewatering liquor.•Startup by gradually reducing HRT from 20 to 9 h enabled to reach stable PN process.•PN unit operated ...for 778 days treating high loading rates up to 4.8 g NH4+-N/(L·d).•Inhibitory effects of THP/AD dewatering liquor are removed by the PN reactor itself.•No adverse effect related to the THP/AD process was observed in the anammox reactor.
A two-stage system (partial nitritation (PN) and anammox processes) was used to remove nitrogen from the dewatering liquor originating from the thermal hydrolysis/anaerobic digestion (THP/AD) of municipal WWTP sludge. Two strategies were tested to start up the PN reactor: 1) maintaining a fixed hydraulic retention time (HRT) and increasing the ammonium loading rate (ALR) by decreasing the feeding dilution ratio and 2) feeding undiluted dewatering liquor and gradually decreasing the HRT. With diluted feeding, the reactor performance had destabilization episodes that were statistically correlated with the application of high specific ammonium (> 0.6 g NH4+-N/(g TSS·d)) and organic (> 0.7 g COD/(g TSS·d)) loading rates. The second strategy allowed stable PN reactor operation while treating ALR up to 4.8 g NH4+-N/(L·d) and demonstrating that dilution of THP/AD effluents is not required. The operating conditions promoted the presence of free nitrous acid levels (> 0.14 mg HNO2-N/L) inside the PN reactor that inhibited the proliferation of nitrite oxidizing bacteria.
Batch activity tests showed that the inhibitory effects of organic compounds present in the THP/AD dewatering liquor on the ammonia oxidizing bacteria activity can be removed in the PN reactor. Thus, aerobic pretreatment would not be necessary when two-stage systems are used. The PN reactor effluent was successfully treated by an anammox reactor.
An economic analysis showed that using two-stage systems is advantageous for treating THP/AD dewatering liquor. The implementation of an aerobic pre-treatment unit is recommended for WWTPs capacities higher than 5·105 inhabitants equivalent when one-stage systems are used.
Autotrophic nitrogen removal in the main stream appears as a prerequisite for the implementation of energy autarchic wastewater treatment plants. To investigate autotrophic nitrogen removal a ...lab-scale gas-lift sequencing batch reactor with granular sludge was operated for more than 500 days. The reactor was operated at temperatures between 20 and 10 °C on autotrophic medium with ammonium (60 and 160 mg-N L−1) as only nitrogen compound at an HRT of 0.23–0.3 d. The dissolved oxygen (DO) concentration was shown to be an effective control parameter for the suppression of the undesired nitratation process. DO control guaranteed the effective suppression of the nitratation both at 20 and 15 °C, allowing nitrogen removal rates of 0.4 g-NTot L−1 d−1 at nitrogen removal efficiencies of 85-75%. Prolonged operation at 10 °C caused a slow but unrestrainable decrease in anammox activity and process efficiency. This study represents a proof of concept for the application of the autotrophic nitrogen removal in a single reactor with granular sludge at main stream conditions.
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•Proof of concept: autotrophic N-removal with granules at main stream conditions.•Effective suppression of nitratation at DO up to 2.5 mg-O2 L−1 with NOB presence.•Nitrogen removal rates of 0.4 g-NTot L−1 d−1 with high removal efficiencies.•Decreased anammox activity and process efficiency after prolonged operation at 10 °C.
The interaction of ammonia-oxidizing bacteria (AOB) and nitrite-oxidizing bacteria (NOB) is of considerable importance in nitrification process. Ecophysiological interactions between the communities ...of AOB and NOB were investigated by monitoring NO
2
−
as the intermediate compound in an organic carbon-depleted nitrifying activated sludge fed only NH
4
+
as a nitrogen source (40 mg/L). The presence of boom and bust (feast and famine) cycle successfully indicates the activity cycles of AOB and NOB through cultivation-dependent method. The maximum growth rate and yield for AOB in nitritation-dominant period were (0.67 day
−1
, 0.17 gVSS gN
−1
) and for NOB in nitratation-dominant period were (0.71 day
−1
, 0.072 gVSS gN
−1
). Soluble microbial products (SMP) and extracellular polymeric substances (EPS) generated by AOB were 1.2 and 1.8 mg/L, respectively, while NOB produced 0.6 mg/L of SMP and 1 mg/L of EPS. While NOB were low in utilization-associated products (UAP) (0.07 mg/L) and biomass-associated products (BAP) (0.12 mg/L), AOB were higher in UAP (0.15 mg/L) and BAP (0.3 mg/L). The continuation presence of zero C/N ratio, in either inlet ratio or net available ratio for the microbial community, can prolong and enhance nitratation process. NOB enrichment and nitratation intensification strategy through zero C/N ratio are able to reduce remarkably microbial metabolites 50% lower than conventional process and enhance nitrification efficiency in activated sludge-involved processes.
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