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•Effluent TN as low as 4.0 mg N/L was achieved via PD-Anammox process.•Anammox was stable and accounted for 78.2% on nitrogen removal.•Low nitrous oxide (N2O) was produced in ...PD-Anammox process.•Oxygen consumption, COD demand and sludge production would be largely reduced.•PD-Anammox process can be easily retrofitted from existing plants.
High nitrate (NO3−-N) concentration in the effluent of wastewater treatment plants (WWTPs), cannot meet the increasing stringent discharge limits. Hence, the tertiary treatment is necessary to lower the total nitrogen concentration. In this study, an innovative partial denitrification (PD)-Anammox process was applied to remove the nitrate nitrogen (20–40 mg N/L) from secondary effluent. The nitrate wastewater were firstly fed to PD sequencing batch reactor (SBR, 10 L) to produce nitrite along with the low carbon/nitrogen ratio (C/N) municipal sewage (NH4+ of 57.8 mg N/L, COD of 175.8 mg/L), then the effluent from SBR was pumped to the anaerobic sludge blanket (UASB, 3.2 L) performing anammox for further nitrogen removal. The integrated process was operated for 224 days with the secondary effluent to municipal sewage volume ratio of 2.9–6. The results suggested that an excellent nitrate removal efficiency of 97.9% was achieved, and the mean removal efficiency of NH4+-N and COD from municipal sewage were 95.2% and 81.6%, respectively, leading to the total nitrogen and COD concentration in the final effluent as low as 4.0 mg N/L and 30.1 mg/L, respectively. Anammox was the main nitrogen removal pathway with a mean proportion of 78.2%, and Candidatus_Brocadia was identified as the dominating genus. Furthermore, it was found that a minor nitrous oxide (N2O) was produced in the integrated process. The PD-Anammox process was verified to be economically and environmentally feasible for retrofitting of existing plants.
Elimination of nitrogen pollution from wastewater containing high-strength nitrate (NO3−-N) is a significant issue to prevent deterioration of water quality and eutrophication of receiving water ...body. Traditional denitrification process faces several challenges including the huge organic carbon demand, intermediate products accumulation, and long acclimatization period. In this study, an efficient solution was given by a novel two-stage Partial Denitrification (PD)-Anammox process. High NO3−-N (1000 mg N/L) wastewater and municipal sewage (COD: 182.5 mg/L, ammonia (NH4+-N): 58.3 mg/L) were simultaneously introduced to the PD reactor for NO3−-N converting to NO2−-N. The NH4+-N and NO2−-N in effluent of PD were removed in subsequent anammox reactor. Results showed that a satisfactory nitrogen removal was achieved by optimizing the volume ratios of influent NO3−-N and municipal sewage, as well as the external organic matter dosage. The NO3−-N removal efficiency reached up to 95.8% without accommodation period, along with the NH4+-N removal achieving 92.8%. Anammox contributed to 78.9% of TN removal despite the high COD (76.5–98.6 mg/L) in PD effluent was introduced, indicating the significant stability of the integrated process. The microbial analysis suggested that the Candidatus Brocadia, identified as anammox bacteria, cooperated stable with denitrifying bacteria in 215-day operation. The PD-Anammox process offers an economically and technically attractive approach in the high NO3−-N wastewater treatment since it has great advantages of much low carbon demand, minimal sludge production, enabling simultaneous treatment of municipal sewage, and avoiding the common issues in traditional denitrification process.
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•Simultaneous treatment of high-strength nitrate and municipal sewage was demonstrated.•Nitrate removal efficiency reached up to 95.8% at influent nitrate of 1000 mg/L.•Municipal sewage was treated with nitrogen removal efficiency of 92.8%.•Anammox and denitrifying bacteria cooperated for advanced nitrogen removal.•Partial-denitrification combining with anammox is an economic and efficient option.
In this study, a novel DEAMOX (DEnitrifying AMmonium OXidation) process coupling anammox with partial-denitrification generated nitrite (NO2−-N) from nitrate (NO3−-N) was developed for simultaneously ...treating ammonia (NH4+-N) and NO3−-N containing wastewaters. The performance was evaluated in sequencing batch reactors (SBRs) with different carbon sources for partial-denitrification: acetate (R1) and ethanol (R2). Long-term operation (180 days) suggested that desirable nitrogen removal was achieved in both reactors. The performance maintained stably in R1 despite the seasonal decrease of temperature (29.2 °C–12.7 °C), and high nitrogen removal efficiency (NRE) of 93.6% on average was obtained with influent NO3−-N to NH4+-N ratio (NO3−-N/NH4+-N) of 1.0. The anammox process contributed above 95% to total nitrogen (TN) removal in R1 with the nitrate-to-nitrite transformation ratio (NTR) of 95.8% in partial-denitrification. A little lower NRE was observed in R2 with temperature dropped from 90.0% at 22.7 °C to 85.2% at 16.6 °C due to the reduced NTR (87.0%–67.0%).
High-throughput sequencing analysis revealed that Thauera genera were dominant in both SBRs (accounted for 61.53% in R1 and 45.17% in R2) and possibly played a key role for partial-denitrification with high NO2−-N accumulation. The Denitratisoma capable of complete denitrification (NO3−-N→N2) was found in R2 that might lead to lower NTR. Furthermore, different anammox species was detected with Candidatus Brocadia and Candidatus Kuenenia in R1, and only Candidatus Kuenenia in R2.
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•Two novel DEAMOX were established for simultaneously treating NH4+-N and NO3−-N.•Stable nitrogen removal efficiency of 93.6% was achieved in acetate-driven DEAMOX.•Nitrogen removal efficiency declined from 90.0% to 85.2% in ethanol-driven DEAMOX.•Genera Thauera (61.53% and 45.17%) would play key role in partial-denitrification.•Brocadia and Kuenenia were identified in acetate-SBR, only Kuenenia in ethanol-SBR.
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•First systematically investigated PN-SBR/SFDA using high-throughput sequencing.•Observed long-term stable partial nitrification in the PN-SBR.•Identified key functional ...microorganisms contributing to simultaneous SFDA.
A combined process including a partial nitritation SBR (PN-SBR) followed by a simultaneous sludge fermentation, denitrification and anammox reactor (SFDA) was established to treat low C/N domestic wastewater in this study. An average nitrite accumulation rate of 97.8% and total nitrogen of 9.4mg/L in the effluent was achieved during 140days’ operation. The underlying mechanisms were investigated by using Illumina MiSeq sequencing to analyze the microbial community structures in the PN-SBR and SFDA. Results showed that the predominant bacterial phylum was Proteobacteria in the external waste activated sludge (WAS, added to the SFDA) and SFDA while Bacteroidetes in the PN-SBR. Further study indicated that in the PN-SBR, the dominant nitrobacteria, Nitrosomonas genus, facilitated nitritation and little nitrate was generated in the PN-SBR effluent. In the SFDA, the co-existence of functional microorganisms Thauera, Candidatus Anammoximicrobium and Pseudomonas were found to contribute to simultaneous sludge fermentation, denitrification and anammox.
•Change of pH during ES fermentation under different conditions has yet to be reported.•SCFAs, NH4+ and cations contributed to pH change under alkaline condition.•Under acidic and neutral condition, ...SCFAs and NH4+ played a role in pH change.•For alkaline fermentation, pH can predict whether SCFAs reach a stable stage.
The change in pH during excess sludge (ES) fermentation of varying sludge concentrations was investigated in a series of reactors at alkaline, acidic, and neutral pHs. The results showed that the changes were significantly affected by fermentative conditions. Under different conditions, pH exhibited changing profiles. When ES was fermented under alkaline conditions, pH decreased in a range of (10±1). At the beginning of alkaline fermentation, pH dropped significantly, at intervals of 4h, 4h, and 5h with sludge concentrations of 8665.6mg/L, 6498.8mg/L, and 4332.5mg/L, then it would become moderate. However, under acidic conditions, pH increased from 4 to 5. Finally, under neutral conditions pH exhibited a decrease then an increase throughout entire fermentation process. Further study showed short-chain fatty acids (SCFAs), ammonia nitrogen and cations contributed to pH change under various fermentation conditions. This study presents a novel strategy based on pH change to predict whether SCFAs reach their stable stage.
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•The increasing influent COD could stimulate the production of EPS.•TB-EPS were higher than LB-EPS, benefitting the formation of biofilms.•Carbohydrates, proteins, phenols and ...alcohols were the main components of EPS.•The abundance variation of Anammox bacteria was similar with the EPS contents.•Candidatus Kuenenia was the dominant genus of Anammox, rising from 3.26% to 12.38%.
The biofilm system is beneficial for Anammox process designed to treat landfill leachate. In this study, the composition of extracellular polymeric substances (EPS) and the microbial community in an Anammox biofilm system were analyzed to determine the functions driving the biofilm’s ability to treat landfill leachate. The results demonstrated that increasing influent carbon oxygen demand (COD) could stimulate EPS production. EPS helped enrich Anammox bacteria and supplied them with nutrients and enzymes, facilitating effective nitrogen removal (approximately 95%). The variation in Anammox bacteria was similar to the variation in EPS composition. In the tested Anammox Sequencing Biofilm Batch Reactor (SBBR) system, Candidatus Kuenenia was dominant among known Anammox genus, because of its high substrate affinity and because it adapts better to landfill leachate. The relative abundance of Candidatus Kuenenia in the biofilm rose from 3.26% to 12.38%, illustrating the protection and enrichment offered by the biofilm in carrying out Anammox.
•A novel PD-ANAMMOX was developed for treating nitrate and domestic wastewater.•NO3−-N, NH4+-N and COD removal efficiencies achieved 96.7%, 99.5% and 69.6%.•The nitrogen removal increased when the ...ANAMMOX influent contained more nitrate.•ANAMMOX maintained as the dominant pathway with over 70% total nitrogen removal.•Candidatus Jettenia species, present at 2.7%, dominated the ANAMMOX performance.
The simultaneous treatment of nitrate (NO3−-N∼50mgL−1) and domestic wastewater (ammonia (NH4+-N)∼60.6mgL−1, COD∼166.3mgL−1) via a novel partial denitrification (PD)-ANaerobic AMMonium OXidation (ANAMMOX) process was investigated at low temperature (12.9∼15.1°C). Results showed that desirable performance was achieved with average NO3−-N, NH4+-N and COD removal efficiencies of 89.5%, 97.6% and 78.7%, respectively. However, deteriorated sludge settleability in PD reactor was observed during operation, which bulked with serious sludge wash-out, leading to excess NO3−-N remaining in PD effluent. Fortunately, a satisfactory nitrogen removal was still achieved due to the occurrence of partial denitrification in ANAMMOX reactor. This was demonstrated by high-throughput sequencing, which revealed that the high nitrite (NO2−-N) production denitrifying bacteria of Thauera was detected (6.1%). ANAMMOX (above 70%) maintained the dominant pathway for nitrogen removal, and Candidatus Jettenia was identified as the major ANAMMOX species accounted for 2.7%.
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•Continuously fed PD coupling with anammox process was established in UASB reactor.•TN removal achieved 89.1% with effluent TN as low as 6.56 mg/L at 17.5 °C.•Capability of NO2–-N ...production by PD maintained stable with NTR over 90% in UASB.•Protein and tightly-bound layer of EPS had important role in sludge settleability.
In this study, the synergy of high nitrite (NO2–-N) accumulated partial-denitrification (PD) and anammox in a continuously fed upflow anaerobic sludge blanket (UASB) reactor was verified for simultaneous nitrate (NO3–-N) and ammonia (NH4+-N) removal. A 225-days operation demonstrated that the relatively low total nitrogen (TN) concentration of 6.56 mg/L in effluent could be achieved with influent NH4+-N and NO3–-N both of 30 mg/L, resulting in a high TN removal of 89.1% at 17.5 °C. Batch tests revealed that the NO3–-N-to-NO2–-N transformation ratio (NTR) of PD stabilized at 90% during the whole operation, which played a crucial role in the desirable performance. However, the PD and anammox activity was negatively impacted by the limited mass transfer with serious sludge flotation. Significantly, hydrodynamic mixing optimization by adjusting liquid recirculation ratio effectively enhanced the nitrogen removal. Moreover, protein composition and tightly-bound structure of EPS played an important role in the sludge stability.
The conversion pathway of NH4+ in deterioration and restoration periods. Display omitted
•Intermittent aeration restored single-stage PN/A process from nitrate build-up.•NOB accumulated under ...continuous aeration mode, Nitrospira was the dominant NOB.•Reducing DO to 0.17±0.08mg/L was failed to inhibited the NOB activity.•Sewage PN/A reactor was quickly started up by inoculating anammox sludge.
A single-stage partial nitrification-anammox (PN/A) reactor treating low-strength swage was operated for 288days to investigate the recovery of nitrogen removal from nitrate accumulation. The reactor was quickly started up by inoculating anammox sludge. However, nitrite oxidizing bacteria (NOB) abundance gradually increased on day 25, leading to high effluent nitrate concentration. Two strategies were executed to control the effluent nitrate. In strategy I, dissolved oxygen (DO) concentration was kept low (0.17±0.08mg/L), but nitrate production increased from 4.71 to 38.18mg-N/L. In strategy II, intermittent aeration operation mode (aeration 7min/anoxic 21min) was adopted, which significantly lowered the nitrate concentration to 1.3mg-N/L, indicating the NOB was inhibited. The high nitrogen removal rate of 73mg-N/(L·d) was achieved. The evolution of bacterial activity and abundance verified the changes of the nitrogen removal performance and proved the intermittent aeration strategy could successfully solve the problem of nitrate build-up in the PN/A process.
Coronavirus disease 2019 (COVID-19) is associated with a high mortality rate, especially in patients with severe illness. We conducted a systematic review and meta-analysis to assess the potential ...predictors of mortality in patients with COVID-19. PubMed, EMBASE, the Cochrane Library, and three electronic Chinese databases were searched from December 1, 2019 to April 29, 2020. Eligible studies reporting potential predictors of mortality in patients with COVID-19 were identified. Unadjusted prognostic effect estimates were pooled using the random-effects model if data from at least two studies were available. Adjusted prognostic effect estimates were presented by qualitative analysis. Thirty-six observational studies were identified, of which 27 were included in the meta-analysis. A total of 106 potential risk factors were tested, and the following important predictors were associated with mortality: advanced age, male sex, current smoking status, preexisting comorbidities (especially chronic kidney, respiratory, and cardio-cerebrovascular diseases), symptoms of dyspnea, complications during hospitalization, corticosteroid therapy and a severe condition. Additionally, a series of abnormal laboratory biomarkers of hematologic parameters, hepatorenal function, inflammation, coagulation, and cardiovascular injury were also associated with fatal outcome. We identified predictors of mortality in patients with COVID-19. These findings could help healthcare providers take appropriate measures and improve clinical outcomes in such patients.
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