Robustness of the synergistic partial-denitrification, anammox, and fermentation process for treating domestic and nitrate wastewaters under fluctuating C/N ratios.

The synergistic partial-denitrification, anammox, and fermentation (SPDAF) process presents a promising solution to treat domestic and nitrate wastewaters. However, its capability to handle fluctuating C/N ratios (the ratios of COD to total inorganic nitrogen) in practical applications remains uncertain. In this study, the SPDAF process was operated for 236 days with C/N ratios of 0.7-3.5, and a high and stable efficiency of nitrogen removal (84.9 ± 7.8%) was achieved. The denitrification and anammox contributions were 6.1 ± 7.1% and 93.9 ± 7.1%, respectively. Batch tests highlighted the pivotal role of in situ fermentation at low biodegradable chemical oxygen demand (BCOD)/NO3- ratios. As the BCOD/NO3- ratios increased from 0 to 6, the NH4+ and NO3- removal rates increased, while the anammox contribution decreased from 100% to 80.1% but remained the primary pathway of nitrogen removal. The cooperation and balanced growth of denitrifying bacteria, anammox bacteria, and fermentation bacteria contributed to the system's robustness under fluctuating C/N ratios.

Facilitating effects of the synergy with zero-valent iron and peroxysulfate on the sludge anaerobic fermentation system: Combined biological enzyme, microbial community and fermentation mechanism assessment.

This study evaluated a synergetic waste activated sludge treatment strategy with environmentally friendly zero-valent iron nanoparticles (Fe0) and peroxysulfate. To verify the feasibility of the synergistic treatment, Fe0, peroxysulfate, and the mixture of peroxysulfate and Fe0 (synergy treatment) were added to different sludge fermentation systems. The study demonstrated that the synergy treatment fermentation system displayed remarkable hydrolysis performance with 435.50 mg COD/L of protein and 197.67 mg COD/L of polysaccharide, which increased 1.13-2.85 times (protein) and 1.12-1.49 times (polysaccharide) for other three fermentation system. Additionally, the synergy treatment fermentation system (754.52 mg COD/L) exhibited a well acidification performance which was 1.35-41.73 times for other systems (18.08-557.27 mg COD/L). The synergy treatment fermentation system had a facilitating effect on the activity of protease, dehydrogenase, and alkaline phosphatase, which guaranteed the transformation of organic matter. Results also indicated that Comamonas, Soehngenia, Pseudomonas, and Fusibacter were enriched in synergy treatment, which was beneficial to produce SCFAs. The activation of Fe0 on peroxysulfate promoting electron transfer, improving the active groups, and increasing the enrichment of functional microorganisms showed the advanced nature of synergy treatment. These results proved the feasibility of synergy treatment with Fe0 and peroxysulfate to enhance waste activated sludge anaerobic fermentation.

Insight into the potentiality of nano zero-valent iron on enhancing the nitrite accumulation and phosphorus removal performance of endogenous partial denitrification systems.

Endogenous partial denitrification (EPD) has drawn a lot of interest due to its abundant nitrite (NO2--N) accumulation capacity. However, the poor phosphate (PO43--P) removal rate of EPD restricts its promotion and application. In this study, the potentiality of various nano zero-valent iron (nZVI) concentrations (0, 20, 40, and 80 mg/L) on NO2--N accumulation and PO43--P removal in EPD systems had been investigated. Results showed that nZVI improved NO2--N accumulation and PO43--P removal, with the greatest nitrate-to-nitrite transformation ratio (NTR) and PO43--P removal rate of 97.74 % and 64.76 % respectively at the optimum nZVI level (80 mg/L). Microbial community analysis also proved that nZVI had a remarkable influence on the microbial community of EPD. Candidatus_Competibacter was contribute to NO2--N accumulation which was enriched from 24.74 % to 40.02 %. The enrichment of Thauera, Rhodobacteraceae, Pseudomonas were contributed to PO43--P removal. The chemistry of nZVI not only compensated for the deficiency of biological PO43--P removal, but also enhanced NO2--N enrichment. Therefore, nZVI had the huge potentiality to improve the operational performance of the EPD system.

Simultaneous phosphorus and nitrogen removal with different C/N ratios in a low oxygen aeration system: Microorganisms and mechanisms.

In this study, a combined system with simultaneous nitrification, denitrification, and phosphorus removal was operated in continuous low oxygen aeration mode, and the effect of lower oxygen aeration (dissolved oxygen [DO] 0.5-1.5 mg/L) on its performance was examined. The combined system consisted of sludge and high-efficiency biological packing and was operated using four carbon/nitrogen ratios (C/N) with being 10:1, 8:1, 6:1, 10:1. Experimental results showed that the combined system could perform an efficient nitrogen and phosphorus removal under low DO and C/N ratio of 8:1 condition, and removal efficiencies of chemical oxygen demand (COD), NH4 + -N, and PO4 3- -P were 80.01%, 99.03%, and 89.51%, respectively. High-throughput analysis indicated that the functional species of denitrifying bacteria, including Ferruginibacter Azospira, Comamonas, Bacilli, Hyphomicrobium, Thauera, and Comamonadaceae, were important participants in biological nutrient removal. Meanwhile, Acinetobacter was enriched in the combined system, which contributed to phosphorus removal. PRACTITIONER POINTS: A combined system was operated firstly under continuous low oxygen condition. The lower dissolved oxygen (DO) of the combined system was maintained at 0.50-1.5 mg/L level. The combined system could realize simultaneous phosphorus and nitrogen removal under C/N ratio of 8:1. Several functional bacteria were enriched in the coupled systems.

Rapid and stable achievement of mainstream nitritation at low temperature using the competitive inhibition caused by the organics.

The unstability of mainstream nitritation at low temperature has always been a limiting factor for the nitrogen removal from domestic wastewater by anammox. In this study, the competitive inhibition caused by the organics has been demonstrated as an effective strategy to rapidly and stably achieve mainstream nitritation. This strategy was based on our novel discovery that nitrite-oxidizing bacteria (NOB) was more susceptible to the organics inhibition than ammonia-oxidizing bacteria (AOB). Batch tests showed while NOB activity gradually decreased by 66.5%, AOB activity only decreased by 31.6% with the initial C/N ratio raising from 0.0 to 3.0. Furthermore, treating the actual domestic wastewater at 14-18 °C, mainstream nitritation was rapidly established within 12 days and then the nitrite accumulation ratio was stable at ∼92.1% during a long-term operation. This strategy could be easily and effectively applied in urban WWTPs through modifying the operation mode.

Synergistic partial denitrification, anammox and in-situ fermentation (SPDAF) process for treating domestic and nitrate wastewater: Response of nitrogen removal performance to decreasing temperature.

A synergistic partial denitrification, anaerobic ammonium oxidation (Anammox), and in-situ fermentation (SPDAF) system was established to solve problems of wastewater treatment plants (WWTPs) in combined treatment of domestic sewage, and nitrate wastewater discharged from industrial areas. The SPDAF system was started up at decreasing temperatures (26.8-18.9 ℃), and remained robust at abrupt temperature drop and drastic temperature fluctuations (20.7-14.1 ℃). The influent and effluent total inorganic nitrogen (TIN) were 97.0 ± 3.7 mg/L and 10.3 ± 4.0 mg/L, respectively. In-situ fermentation supplemented electron donors for NO3--N reduction. A high TIN removal efficiency, of 89.5 ± 3.9% was obtained. Specifically, Anammox contributed 90.9 ± 5.2% to TIN removal. Furthermore, the abundances of hydrolysis and acidogenesis bacteria were 14.02% and 29.47% in the low and high zones, respectively, which promoted fermentation and the use of complex organics. This study provided novel insights for actual operation of WWTPs.

Advanced nitrogen and phosphorus removal from municipal wastewater via simultaneous enhanced biological phosphorus removal and semi-nitritation (EBPR-SN) combined with anammox.

In this study, a novel laboratory-scale synchronous enhanced biological phosphorus removal and semi-nitritation (termed as EBPR-SN) combined with anammox process was put forward for achieving nutrient elimination from municipal wastewater at 27 ℃. This process consisted of two 10 L sequencing batch reactors (SBRs), i.e. EBPR-SN SBR followed by Anammox SBR. The EBPR-SN SBR was operated for 400 days with five periods and the Anammox SBR was operated starting on period IV. Eventually, for treating municipal wastewater containing low chemical oxygen demand/nitrogen (COD/N) of 3.2 (mg/mg), the EBPR-SN plus Anammox system performed advanced total inorganic nitrogen (TIN) and P removal, with TIN and P removal efficiencies of 81.4% and 94.3%, respectively. Further analysis suggested that the contributions of simultaneous partial nitrification denitrification, denitrification, and anammox to TIN removal were 15.0%, 45.0%, and 40.0%, respectively. The enriched phosphorus-accumulating organisms (PAOs) in the EBPR-SN SBR facilitated P removal. Besides, the EBPR-SN SBR achieved P removal and provided stable anammox substrates, suggesting a short sludge retention time (SRT 12 d) could achieve synergy between ammonia-oxidizing bacteria and PAOs. These results provided an alternative process for treating municipal wastewater with limited organics.

A novel partial nitrification-synchronous anammox and endogenous partial denitrification (PN-SAEPD) process for advanced nitrogen removal from municipal wastewater at ambient temperatures.

Mainstream anammox still faces the challenges of non-ideal NO2-/NH4+ ratios and excess nitrate resulted from the instability of partial nitrification (PN) in municipal wastewater. To address these problems, in this study, we developed a novel two-sludge process that combined PN with synchronous anammox and endogenous partial denitrification (SAEPD); the process was tested with pre-treated domestic sewage at ambient temperatures for 205 d. High nitrogen removal efficiency of 91.2% was achieved with an influent C/N ratio of 1.7 at 15.4 °C; the success was attributed to the fact that EPD replenished the deficient nitrite by reducing nitrate and the excess nitrite was further reduced to nitrogen gas. With a non-ideal NO2-/NH4+ ratio of 0.89, the contribution of the SAEPD-sequencing batch reactor (SBR) during the anoxic stage reached 98.2% and the proportional contributions of the anammox and denitrification pathways were 77.2% and 22.8%, respectively. Although the low nitrite accumulation (66.1%) caused 10.8 mg N/L of nitrate to be transported into the SAEPD-SBR and the anammox reaction also converted 20% of nitrite to nitrate, only 1.1 mg N/L of nitrate remained in the effluent. High-throughput sequencing analysis revealed that although NH2OH was added, some genera of nitrite-oxidizing bacteria (0.73%) remained in the PN-SBR and potentially resulted in the oxidation of nitrite to nitrate. In the SAEPD-SBR, anammox and endogenous denitrifying bacteria co-existed and synergistically achieved the removal of ammonium, nitrite, and nitrate. Overall, the PN-SAEPD process has great potential for achieving cost-effective and energy-efficient municipal wastewater treatment.

Synergistic Partial-Denitrification, Anammox, and in-situ Fermentation (SPDAF) Process for Advanced Nitrogen Removal from Domestic and Nitrate-Containing Wastewater.

This study presents a new method for energy-efficient wastewater treatment that synergizes the partial-denitrification, anammox, and in-situ fermentation (SPDAF) processes in an up-flow reactor. Nitrate-containing wastewater and actual domestic sewage were fed into this SPDAF system, which was operated for 180 days without the addition of external carbon sources and aeration. The total inorganic nitrogen (TIN) removal efficiency reached 93.1% with a low C/N ratio of 1.6, a NO3--N/NH4+-N ratio of 1.13 and a TIN concentration of 92.5 mg N/L. The contribution of anammox to nitrogen removal accounted for 95.6%. Batch tests demonstrated that the partial-denitrification process was able to use organics from either the influent or those produced by fermentation, thus providing nitrite for anammox. Significantly, fermentation played a key role in using the slowly biodegradable organics and provided adequate electron donor for partial-denitrification. Metagenomic sequencing analysis showed that the genera related to partial-denitrification, anammox, and fermentation bacteria were coexisted in this SPDAF system. The key functional genes of anammox bacteria (Hzs, 3986 hits; Hdh, 2804 hits) were highly detected in this study. The abundances of cytoplasmic nitrate reductase (58 706 hits) and periplasmic nitrate reductase (70 540 hits) were much higher than copper nitrite reductase (16 436 hits) and cytochrome cd1 nitrite reductase (14 264 hits), potentially contributing to the occurrence of partial-denitrification. Moreover, different abundances of genes involved in fermentation metabolism suggested that fermentation likely generated easily biodegradable organics for partial-denitrification.

A novel SNPR process for advanced nitrogen and phosphorus removal from mainstream wastewater based on anammox, endogenous partial-denitrification and denitrifying dephosphatation.

For achieving energy-efficient wastewater treatment, a novel simultaneous nitrogen and phosphorus removal (SNPR) process, which integrated anammox, endogenous partial-denitrification and denitrifying dephosphatation in a sequencing batch reactor with granular sludge was developed to treat mainstream wastewater. After 200 days of operation, a simultaneous high-level nitrogen and phosphorus removal of 93.9% and 94.2%, respectively was achieved with an average influent C/N ratio of 2.9. Anammox pathway contributed 82.9% of the overall nitrogen removal because of the stable nitrite production from nitrate via endogenous partial-denitrification. In addition, phosphorus was mainly removed via denitrifying dephosphatation utilizing nitrate as the electron acceptor, resulting in a significant saving of carbon sources and oxygen demands. Further, adsorption/precipitation of phosphorus occurred in this novel SNPR process, which displaced the energy source to the metabolism of glycogen accumulating organisms (GAOs) for nitrite production and alleviated competition between phosphorus accumulating organisms (PAOs) and anammox for electron acceptor. Using 16S rRNA gene amplicon sequencing analysis, the study found that anammox bacteria (8.4%), GAOs (1.5%) and PAOs (1.1%) co-existed in this system, potentially resulting in simultaneous endogenous partial-denitrification, anammox and denitrifying dephosphatation. The above results demonstrated that the novel SNPR process is a promising technique for energy-efficient wastewater treatment.

[Effect of Cu2+ on Denitrification Using NO2- as an Electron Acceptor].

The short-cut biological nitrogen removal process has been widely used in industrial wastewater treatment, and denitrification is a crucial step for removing nitrogen on which the effect of Cu2+, a common heavy metal ion in wastewater, has not been studied. In this study, sludge with good short-range biological nitrogen removal characteristics in an A/O reactor was selected to investigate the short-term and long-term effects of Cu2+ on denitrification using NO2- as an electron acceptor. The results showed that Cu2+ had a significant inhibitory effect on denitrification process using NO2- as an electron acceptor, and the semi-inhibitory concentration EC50 of sludge activity was 4.79 mg·L-1. In the long-term experiment, the concentration of Cu2+ was gradually increased. When the concentration of Cu2+ was 0.5 mg·L-1and 1 mg·L-1, the denitrification activity of the sludge could be restored to the original level after acclimation. When the concentration of Cu2+ was increased to 3 mg·L-1, the denitrification performance was destroyed and difficult to recover, at which point the NO2--N removal rate was reduced to less than 10% and the denitrification system was severely inhibited. However, there was some recovery of sludge denitrification capacity after the addition of Cu2+ had been stopped for 14 days. At the same time, during the long-term effect of Cu2+, the EPS content increased, which played an important role in protecting the microorganism against Cu2+ toxicity, and increased the sludge particle size and, as a result, sludge sedimentation.

Partial denitrification providing nitrite: Opportunities of extending application for anammox.

Anaerobic ammonium oxidation (anammox) has been extensively investigated for cost-efficient nitrogen removal from wastewater. However, the major issues of nitrate (NO3--N) residue and instability in the current combination of nitritation and anammox process necessitates being addressed efficiently. The recently proposed partial-denitrification (PD), terminating NO3--N reduction to nitrite (NO2--N), has been regarded as a promising alternative of NO2--N supplying for anammox bacteria. Given the engineering practices, the steadily high NO2--N production, alleviating organic inhibition, and reducing greenhouse gas of PD process offers a viable and efficient approach for anammox implementation. Moreover, it allows for the extending applications of anammox process due to the NO3--N removal availability. Here we comprehensively review the important new outcomes and discuss the emerging applications of PD-based anammox including the process development, mechanism understanding, and future trends. Significant greater stability and enhanced nitrogen removal efficiency have been demonstrated in the novel integrations of PD and anammox process, indicating a broad perspective in dealing with the mainstream municipal sewage, ammonia-rich streams, and industrial NO3--N contained wastewater. Furthermore, researches are still needed for the predictable and controllable strategies, along with the detailed microbiological information in future study. Overall, the achievement of PD process provides unique opportunity catalyzing the engineering applications of energy-efficient and environmental-friendly wastewater treatment via anammox technology.

Stable long-term operation and high nitrite accumulation of an endogenous partial-denitrification (EPD) granular sludge system under mainstream conditions at low temperature.

In this study, the robustness of an endogenous partial-denitrification (EPD) system was demonstrated during a 105 days operation under mainstream conditions at low temperature. The results showed a high nitrate-to-nitrite transformation ratio (NTR) of 88.7%, a suitable NO2--N/NH4+-N ratio of 1.09, and no residual NO3--N in the effluent, as reactor temperature was decreased from 25 °C to 13.5 °C. The stable morphology of the EPD granular sludge with high extracellular polymeric substance content (273.6-308.1 mg/g VSS) contributed to the steady performance of the EPD system. Bath tests revealed that the maximum NTRs (95.6% and 96.3%) were slightly higher at 10 °C and 15 °C than those (90.4% and 92.0%) at 20 °C and 30 °C, resulting from the lower poly-ß-hydroxyvalerate degradation rate or the negligible denitrifying dephosphatation activity at low temperatures. Thus, the EPD system has the potential to provide stable nitrite for mainstream anammox at low temperature.

Achieving advanced nitrogen removal from low C/N wastewater by combining endogenous partial denitrification with anammox in mainstream treatment.

Successful application of mainstream anammox would be favorable for energy- and resource-efficient sewage treatment. This study presents a new strategy to achieve mainstream anammox, which combined with endogenous partial denitrification (EPD) for treating sewage wastewater. In this EPD-Anammox system, nitrite was stably produced by EPD with a nitrate-to-nitrite transformation ratio of 80%. Through adjusting the volume exchange ratio of EPD-reactor after anaerobic reaction, a suitable NO2--N/NH4+-N ratio of ∼1.20 for anammox reaction was achieved. Further, results showed a stable, high nitrogen removal efficiency (90%) with an effluent total nitrogen of 5.8 mg N/L under low C/N (∼2.9). Anammox contributed 49.8% of the overall nitrogen removal owing to the steady nitrite supply from EPD. Denitrifying glycogen-accumulating organisms (GAOs, 36.6%) having potential for endogenous denitrification and Candidatus Brocadia (34.6%) were respectively dominated in the EPD-SBR and anammox-UASB and responsible for the high nitrite accumulation and anammox reaction.

Effects of salinity build-up on the performance and microbial community of partial-denitrification granular sludge with high nitrite accumulation.

High inorganic salts inevitably impose a toxic impact on biological treatment processes. In this study, the effect of salinity on the performance and microbial community structures of partial-denitrification (PD) was firstly investigated. Results showed the denitrifying activities of non-domesticated PD sludge were completely inhibited under a temporary high salinity (≥1.5 wt%). However, after domestication, denitrifying activities maintained above 50% of the maximum with salinity build-up step-by-step from 0.0 wt% to 3.0 wt%. High nitrite production was stably achieved during 120 days with nitrate-to-nitrite transformation ratio around 90%. Further investigation showed extracellular polymeric substances content of PD sludge increased from 184.59 mg gVSS-1 to 560.64 mg gVSS-1, accompanied by the elevation of average particle size. This occurred against high salinity as a protective response of PD bacteria. Moreover, Thauera, the functional bacteria of PD system, was still dominant with the relative abundance increasing to 83.36% (3.0 wt%) from 51.33% (0.0 wt%).

Achievement of high nitrite accumulation via endogenous partial denitrification (EPD).

This study proposed a novel strategy for achievement of partial denitrification driven by endogenous carbon sources in an anaerobic/anoxic/aerobic activated sludge system. Results showed that in the steady-stage, the nitrate-to-nitrite transformation ratio (NTR) was kept at around 87% without nitrate in the effluent. During the anaerobic period, exogenous carbon sources was completely taken up, accompanied by the consumption of glycogen and production of polyhydroxyalkanoates (PHAs). During the anoxic period, nitrate was reduced to nitrite by using PHAs as carbon sources, followed by the replenishment of glycogen. Thus, the phenotype of denitrifying GAOs was clearly observed and endogenous partial denitrification (EPD) occurred. Furthermore, results showed the nitrate reduction was prior to the nitrite reduction in the presence of nitrate, which led to the high nitrite accumulation.