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•Continuous aeration in membrane-aerated biofilms resulted in full nitrification.•Intermittent aeration suppressed nitrite oxidation and supported anammox process.•Biofilm pH ...presented periodic upshifts with aeration switches.•Free ammonia speciation likely caused the inhibition of nitrite-oxidizing bacteria.•Heterotrophs established nitrous oxide-reduction zones under intermittent aeration.
Membrane-aerated biofilm reactors (MABR) are being applied for autotrophic nitrogen removal, yet control of nitrogen turnover remains challenging in MABR counter-diffusion biofilms. In this study, we regulated microbial activities in two lab-scale MABRs by providing continuous versus intermittent aeration. Nitrogen consumption by different functional microbial groups was estimated from bulk measurements via a mass balance approach. Nitrite-oxidizing bacteria (NOB) proliferated under continuous aeration while they were significantly suppressed under intermittent aeration, and NOB suppression activated anaerobic ammonium oxidation. Nitritation performance in the MABR was studied through long-term bulk measurements and in situ biofilm microprofiles of dissolved oxygen (DO) and pH. During intermittent aeration pH effects rather than DO effects determined nitritation success, especially ammonia speciation, which serves as substrate and inhibitor in nitrification processes. Biofilm transition phases were monitored upon aeration switches. Canonical correspondence analysis suggested that the relative transition after anoxia and aeration intermittency were less decisive for biofilm performance than the relative aeration duration. Heterotrophic bacteria displayed minor denitrification rates with aeration control, but contributed to mitigation of nitrous oxide (N2O) emissions. N2O production hotspots were identified at the top of the anoxic biofilm zone under continuous aeration. Instead, under intermittent aeration an anoxic N2O reduction zone was established. Our observations support intermittent aeration control of MABRs as a simple strategy for energy-efficient nitrogen removal with low N2O emission. .
Nobiletin (Nob) is a major component among the most reported polymethoxyflavones (PMFs), which possesses multiple efficacious healthcare activities. Owing to its high melting point and poor water ...solubility, the oral bioavailability of Nob needs to be improved via loading Nob on carriers. To take full advantage of Nob, the interaction mechanism between Nob and vehicles should be clarified. Herein, β-lactoglobulin (β-LG) was selected as the vehicle and further investigated the binding mechanism between Nob and β-LG. The binding stoichiometry of complex was found to be 1:1 by analysis of intrinsic fluorescence experiment. The results also confirmed by isothermal titration calorimetry (ITC) measurement that the binding behavior between β-LG and Nob was a spontaneously endothermic process driving mainly by hydrophobic interaction. Moreover, competitive binding and molecular docking method indicated the Nob was primary bound to internal calyx of β-LG at neutral pH. UV spectrophotometry revealed that the solubility of Nob was enhanced to 3 times by forming complex. Furthermore, Nob could alter secondary structure of β-LG by a transition from α-helix to β-sheet and lead to small increase on surface hydrophobicity of β-LG. This work will provide some valuable information on clarifying the interaction between protein and PMFs, which contributing to improve the poor bioavailability of PMFs.
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•Nobiletin had influence on the secondary and tertiary structure of β-lactoglobulin.•The hydrophobic interaction played a vital role in the interaction between Nobiletin and β-lactoglobulin.•The formation of β-lactoglobulin/Nobiletin complex was a spontaneously endothermic process.•At neutral pH, Nobiletin was primary bound into internal calyx of β-lactoglobulin.•Nobiletin solubility could be improved up to 3 times by forming β-lactoglobulin/Nobiletin complex.
Sidestream sludge treatment approaches have been developed in recent years to achieve mainstream nitrite shunt or partial nitritation, where NOB are selectively inactivated by biocidal factors such ...as free nitrous acid (FNA) or free ammonium (FA) in a sidestream reactor. The existence of NOB in raw wastewater has been increasingly realized and could pose critical challenge to stable NOB suppressions in those systems. This study, for the first time, evaluated the impact of influent NOB on the NOB suppressions in a mainstream nitrite shunt system achieved through sidestream sludge treatment. An over 500-day sequential batch reactor operation with six experimental phases rigorously demonstrated the negative effects of influent NOB on mainstream NOB control. Continuously seeding of NOB contained in influent stimulated NOB community shifts, leading to different extents of ineffective NOB suppression. The role of primary wastewater treatment in NOB removal from raw wastewater was also investigated. Results suggest primary settling and High Rate Activated Sludge system could remove a large part of NOB contained in raw wastewater. Primary treatment for raw wastewater is necessary for ensuring stable mainstream NOB suppressions.
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•Influent NOB challenge NOB suppression by stimulating community shift and resistance.•Primary settling substantially reduces NOB in raw wastewater.•High-rate activated sludge treatment substantially reduces NOB in raw wastewater.•This study expanded the current knowledge of mainstream NOB suppression.
The partial nitritation-anammox (PNA) process is the most promising technique to treat municipal sewage; however, nitrite oxidizing bacteria (NOB) are a hindrance to achieve PNA. This study ...investigated the effects of selectively discharging flocs (<200 μm) to washout NOB in a sequencing batch reactor (SBR) over 200 d. The experiment was divided into three phases with different floc sludge retention times (SRTs; 30, 20 and 30 d). When the SRT of the flocs was reduced from 30 to 20 d to washout NOB, a significant reduction of ammonia oxidizing bacteria (AOB) and anaerobic ammonium-oxidizing (anammox) bacteria in the flocs was found. This indicates that a low floc SRT (20 d) leads to the loss of AOB and anammox bacteria in the flocs (<200 μm) and destroys PNA. Activity tests and qPCR analysis revealed the variations of functional bacteria in the granules and flocs, indicating that the enrichment of AOB, NOB, anammox bacteria in the granules is caused by the long-term discharging of flocs. High-throughput sequencing analysis revealed that the microbial shift of Tetrasphaera was significant in the flocs and may be connected to the enrichment of anammox bacteria and the stability of the PNA requires further research. All the obtained NOB sequences were affiliated with the genera Nitrospira and could further influence the PNA system. Overall, this study provides an in-depth understanding of the impact of discharging flocs to washout NOB and promotes the application of combing granules/floc PNA in sewage treatment.
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•Controlling floc SRTs of 30 d was beneficial to stable operation of PNA.•Floc SRTs of 20 d would result in the reduction of AOB and Anammox in flocs.•The distribution of NOB in granules and flocs was impacted by long-term discharging flocs.•The microbial community structure was seriously affected by discharging flocs.
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•A novel three-stage process, comprising PN/A, acidic PN, and anammox, is proposed.•The PN/A unit requires residual ammonium to suppress nitrite-oxidizing bacteria (NOB).•The acidic ...PN unit provides stable nitrite sources to the anammox unit.•The anammox unit removes the residual ammonium and nitrite from the PN/A and the acidic PN units.•The overall nitrogen removal efficiency is higher than 90% based on model simulation.
Sewage treatment with partial nitritation and anammox (PN/A, also termed as deammonification) has gained widespread attentions over the past decade, driven by the need of establishing energy-neutral/positive sewage treatment plants (STPs). However, a key challenge for the mainstream deammonification is to achieve stable suppression of nitrite-oxidizing bacteria (NOB). Deammonification can be configured in either one reactor or two reactors (where PN and anammox are separated), known as one-stage and two-stage configurations, respectively. This study first analyses the current bottlenecks in one-stage and two-stage deammonification. To address these issues, a new, three-stage configuration is proposed. Three-stage deammonification comprises three components, including a PN/A reactor, an acidic PN reactor, and an anammox reactor. The majority of sewage is allocated to the PN/A reactor, which produces an effluent with an elevated level of residual ammonium (2–40 mg N L−1), as required for NOB suppression in this reactor. The residual ammonium is removed in the anammox reactor, using the nitrite supplied from the acidic PN reactor. The acidic PN reactor is fed with a mixture of sewage and anaerobic digestion liquor with a ratio that allows the attainment of a low pH (<6.0) and NOB suppression. This three-stage process was shown applicable to a wide range of municipal wastewaters which have a HCO3–/ NH4+ mole ratio of 1.17–2.41, based on mass balance. Further, simulation indicates that this three-stage process can deliver a stable and high-quality effluent, with the total nitrogen < 10 mg N L−1 and the nitrogen removal efficiency > 90%.
The mainstream partial nitritation/anammox (PN/A) process has been intensively studied but its stability remains a key challenge. It is shown here that biofilm thickness can exhibit a critical role ...in controlling the process stability of mainstream PN/A against dissolved oxygen (DO) variation. In a laboratory moving bed biofilm reactor (MBBR), PN/A performance was initially established in 200 days by controlling a low DO of 0.13 ± 0.07 mg O2/L in the bulk liquid, which deteriorated with an increase of DO (0.35 ± 0.13 mg O2/L) for over two months, and then rapidly recovered in a month with the initial low DO level re-applied. Biofilm thickness of PN/A carriers was measured during the experiment, which became significantly thinner (367 ± 146 μm) at mainstream conditions. The thin thickness primarily decreased the in-situ consumption rate of nitrite, rather than ammonium, when DO increased from 0.1 to 0.4 mg O2/L, due to that the thin thickness can only restrict anammox capacity. These results illustrated the role of biofilm thickness in regulating PN/A performance and microbial activities. Further investigation using an established model revealed the joint contribution of biofilm thickness and DO concentration to PN/A process, while particularly, the biofilm thickness can determine the optimal DO level for maximizing the nitrogen removal efficiency and system robustness against DO variation. These results highlight the need of considering biofilm thickness in PN/A process optimization and stability improvement in low-strength wastewater treatment.
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•N-removal efficiency >80% is achieved via PN/A in a mainstream MBBR.•The mainstream PN/A is stably realized at DO concentration of 0.13 ± 0.07 mgO2/L.•Biofilm thickness controls the maximal capacity of anammox rather than AOB or NOB.•A narrow DO range (0.15-0.20 mgO2/L) is required for high N-removal in thin biofilm.
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•Manure application significantly increased both PAO and PNO.•Manure fertilization augmented nitrifier abundance.•Soil NH4+-N and TC are good indicators for NOB and comammox ...community.•Community composition of NOB and comammox was affected by both soil type and manure fertilizer.•Manure fertilizer made nitrifier community more closely linked and stimulated the function performance of nitrifiers.
Nitrification plays an important role in the soil nitrogen cycle. Here, we conducted an experiment in three different soil types (red soil, black soil, and alluvial soil) to evaluate the response of nitrifiers and nitrification to manure fertilizers. We found that long-term manure fertilization altered the soil physicochemical properties, increased soil organic matter and NO3－-N concentrations, and decreased NH4+-N concentrations. Both ammonia and nitrite oxidation potential were higher in the manured soils than those in the control soils. Long-term manure fertilization markedely increased the abundance of nitrifiers and the abundance of the complete ammonia oxidation (comammox) amoA gene copy number ranged from 0.78 × 106 to 2.18 × 106 g−1 dry soil, which was lower than that of canonical nitrifiers including ammonia‐oxidizing archaea, ammonia‐oxidizing bacteria, and nitrite‐oxidizing bacteria (NOB). The community composition of NOB and comammox was affected by both soil type and manure fertilizer. Soil NH4+-N concentration and total carbon content were the factors that were most strongly correlated with the microbial community composition. Manure fertilizers promoted the coupling linkages among soil Nitrobacter, Nitrospira, and comammox communities and created a more closely linked microbial community. The results suggest that long-term inputs of manure to agricultural soils influence the structure of NOB and increase nitrification rates.
The accumulation of nitrite is frequently overlooked, despite the fact that nitrification is the most essential phase of the entire nitrogen (N) cycle and that nitrifying bacteria play a significant ...role in nitrification. At present, the effects of different N application rates on soil nitrite-oxidizing bacteria (NOB) abundance, community composition, diversity, and its main influencing factors are still unclear. In this study, five N fertilizer application rates under film mulching and a drip irrigation system were studied in the semi-arid area of Northeast China. The treatments were 0 kg ha−1 (N0), 90 kg ha−1 (N1), 150 kg ha−1 (N2), 210 kg ha−1 (N3), and 270 kg ha−1 (N4). Fluorescent quantitative PCR and Illumina Miseq sequencing were used to analyze the abundance and community structure of NOB under different amounts of N application. The results showed that the increase in amounts of N application was strongly accompanied by an increase in the content of soil organic matter (SOM), total nitrogen (TN), nitrate nitrogen (NO3−-N), and ammonium nitrogen (NH4+-N), while the pH significantly reduced with an increase in N fertilization. N fertilization significantly increased soil nitrite oxidoreductase (NXR) activity, soil nitrification potential (PNR), and soil nitrite oxidation potential (PNO). A high N application rate significantly heightened the abundance of Nitrospira- and Nitrobacter-like NOB. N fertilizer considerably raised the Shannon index of Nitrospira-like NOB. The N application amount was the key factor affecting the community structure of Nitrospira-like NOB, and available nitrogen (AN) had the dominant influence on the community structure of Nitrospira-like NOB. N fertilizer can cause soil acidification, which affects NOB abundance and diversity. Nitrospira-like NOB may promote nitrite oxidation in different N application rates under a mulched fertigation system. The findings offered a crucial scientific foundation for further investigation into how nitrite-oxidizing bacteria respond to N fertilizer management strategies in farmland soil under film mulching drip irrigation in Northeast China.
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•NH2OH has a strong inhibition on NOB.•Inhibition of NOB by 5 mg-N/L NH2OH is reversible.•NH2OH addition caused production of NO and N2O to increase.•Inhibition of Nitrospira by NH2OH ...could be related to NO production.
This study investigated a strategy for hydroxylamine (NH2OH) addition for promoting the conversion of complete nitrification to partial nitrification in a sequencing batch reactor (SBR). The results showed that continuous dosing of 5 mg-N/L NH2OH into a complete nitrification reactor for 16 days led to an increase in the nitrite accumulation ratio (NAR) from 0.22% to 95.08% and a significant enhancement in the accumulation of NO and N2O in the liquid. The maximum concentration of NO in each cycle rose with the increase of NAR during NH2OH addition. With the stopping of NH2OH addition, the partial nitrification disappeared progressively in 21 days. The analysis for microbial community showed that Nitrospira was the main NOB and its relative abundance decreased with NH2OH addition and recovered after the cessation of NH2OH addition. Accordingly, NH2OH has a significant and reversible inhibition on Nitrospira and its essence might be related to NO toxicity.
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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.
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