Simultaneous nitrogen and phosphorus removal from municipal wastewater by Fe(III)/Fe(II) cycling mediated partial-denitrification/anammox.

The efficient removal of nitrogen and phosphorus remains challenging for traditional wastewater treatment. In this study, the feasibility for enhancing the partial-denitrification and anammox process by Fe (III) reduction coupled to anammox and nitrate-dependent Fe (II) oxidation was explored using municipal wastewater. The nitrogen removal efficiency increased from 75.5 % to 83.0 % by adding Fe (III). Batch tests showed that NH4+-N was first oxidized to N2 or NO2--N by Fe (III), then NO3--N was reduced to NO2--N and N2 by Fe (II), and finally, NO2--N was utilized by anammox. Furthermore, the performance of phosphorus removal improved by Fe addition and the removal efficiency increased to 78.7 %. High-throughput sequencing showed that the Fe-reducing bacteria Pseudomonas and Thiobacillus were successfully enriched. The abundance of anammox bacterial increased from 0.03 % to 0.22 % by multiple nitrite supply pathways. Fe addition presents a promising pathway for application in the anammox process.

Advanced nitrogen removal from real municipal wastewater by multiple coupling nitritation, denitritation and endogenous denitritation with anammox in a single suspended sludge bioreactor.

Achieving advanced nitrogen removal based on anammox for treating mainstream municipal wastewater in a single suspended sludge bioreactor is a challenging research topic. In this study, multiple coupling nitritation, denitritation and endogenous denitritation with anammox (PNA-(E)PDA) was simultaneously achieved in a 10 L step-feed bioreactor, which enhanced stable nitrogen removal. After 223 days of operation, the total nitrogen concentrations of the influent and effluent were 70.7 ± 6.1 and 4.3 ± 1.8 mg/L, respectively, when treating municipal wastewater even at C/N ratio of 2.24 with only 5 h of aerobic time (DO: 0.5-0.8 mg/L). After the evolution of nitritation/anammox to PNA-(E)PDA, the contribution of anammox to nitrogen removal increased to 78.6% and the anammox activity increased from 4.3 ± 0.2 to 15.2 ± 0.7 mg NH4+-N/gVSS/d. qPCR results showed that the abundance of anammox bacteria increased from 4.1 × 109 to 4.5 × 1010 copies/ (g VSS). High-throughput sequencing further revealed that the relative abundance of Candidatus Brocadia, the dominant anammox genus, increased from 0.09 to 0.46%. Based on the strong competitiveness of anammox on nitrite, this novel PNA-(E)PDA process provides a potential strategy for enriching anammox bacteria in municipal wastewater treatment plants.

Mutual boost of granulation and enrichment of anammox bacteria in an anaerobic/oxic/anoxic system as the temperature decreases when treating municipal wastewater.

Low temperature is an important factor affecting the municipal wastewater treatment systems. The aim of this study was tracking the variations in the abundance of anammox bacteria (AnAOB) and the sludge form as the temperature decreased. Mutual boost of granulation and enrichment of AnAOB was achieved even though the temperature dropped from 20.4 °C to 12.9 °C. The average particle size of the sludge increased from 128.5 µm to 245.6 µm. With low dissolved oxygen (DO) aeration (0.2-0.5 mg/L) and short oxic hydraulic retention time (HRT) (5 h), nitritation in the anaerobic/oxic/anoxic (AOA) system was stable enough to provide NO2- for AnAOB. Ca. Brocadia, a type of typical AnAOB, was enriched from 0.03% to 0.24% in the suspended sludge and reached 16.09% in the granular sludge. Overall, this study presents the prospects of anammox and granule technologies when treating municipal wastewater at a low temperature.

Study on the nonfatigue and fatigue states of orchard workers based on electrocardiogram signal analysis.

In recent years, fatigue has become an important issue in modern life that cannot be ignored, especially in some special occupations. Agricultural workers are high-risk occupations that, under fatigue conditions over a long period, will cause health problems. In China, since very few studies have focused on the fatigue state of agricultural workers, we were interested in using electrocardiogram (ECG) signals to analyze the fatigue state of agricultural workers. Healthy agricultural workers were randomly recruited from hilly orchards in South China. Through the field experiment, 130 groups of 5-min interval ECG signals were collected, and we analyzed the ECG signal by HRV. The time domain (meanHR, meanRR, SDNN, RMSSD, SDSD, PNN20, PNN50 and CV), frequency domain (VLF percent, LF percent, HF percent, LF norm, HF norm and LF/HF) and nonlinear parameters (SD1, SD2, SD1/SD2 and sample entropy) were calculated and Spearman correlation coefficient analysis and Mann-Whitney U tests were performed on each parameter for further analysis. For all subjects, nine parameters were slightly correlated in nonfatigue and fatigue state. Six parameters were significantly increased and ten HRV parameters were significantly decreased compared the nonfatigue state. As for males, fifteen parameters were significantly different, and for females, eighteen parameters were significantly different. In addition, the probability density functions of SDNN, SDSD, VLF%, HFnorm and LF/HF were significantly different in nonfatigue and fatigue state for different genders, and the nonlinear parameters become more discrete compared the nonfatigue state. Finally, we obtained the most suitable parameters, which reflect the fatigue characteristics of orchard workers under different genders. The results have instructional significance for identifying fatigue in orchard workers and provide a convincing and valid reference for clinical diagnosis.

Effect of low salinity on nitrogen removal from municipal wastewater via a double-anammox process coupled with nitritation and denitratation: Performance and microbial structure.

Saline wastewater present in municipal pipe networks poses challenges to biological nitrogen removal due to its inhibition on microorganisms. This study focuses on the effects of low salinity (0.0%, 0.4%, 0.7% and 1.0%) on a system featuring a combination of nitritation/anammox in oxic stage and denitratation/anammox in anoxic stage (double-anammox) in a step-feed SBR for municipal wastewater over a period of 130 days. The results showed that a maximum nitrogen removal efficiency of 81.2% was achieved at a salinity of 1.0% with anammox contribution of 76.5%. Analysis of anammox contribution and sludge activities discovered that low salinity promoted both nitritation and denitratation, further enhancing the coupling with anammox. Further, microbial analysis confirmed that Ca. Brocadia was enriched on biofilms from 0.21% to 0.51% and Nitrosomonas was enriched in flocs from 0.50% to 1.04%. Overall, the double-anammox process appears to be a promising method for the treatment of saline wastewater.

Mainstream partial denitrification-anammox (PD/A) for municipal sewage treatment from moderate to low temperature: Reactor performance and bacterial structure.

Anammox is sensitive to temperature, which can limit its practical application in wastewater treatment. In this study, a step-feed anoxic-oxic (A/O) process coupled with PD/A was operated steadily from 26.8 °C to 13.1 °C for wastewater treatment for 200 days. The effluent total inorganic nitrogen (TIN) and phosphorus concentrations were 10.2 mg/L and 0.29 mg/L at C/N ratio of 4.6 and 15.0 °C even with increasing nitrogen loading rate (NLR). The anammox activity was 5.60 mg NH4+-N/gMLSS/d even at 14 °C, moreover, anammox abundance on the biocarriers increased with decreasing temperature. It was observed that the effect of partial denitrification (PD) was enhanced under low temperature, thus the contribution of anammox for nitrogen removal was improved. The pathway of anammox for nitrogen removal accounted for 48% and the effect of effluent did not deteriorate under low temperature. This study states that PD/A has advantages under low temperature operation, which is suitable for treatment of wastewater with low C/N ratio.

Sustainable upgrading of biological municipal wastewater treatment based on anammox: From microbial understanding to engineering application.

Anaerobic ammonium oxidation (anammox) has drawn increasing attention as a promising option to energy-neutral wastewater treatment. While anammox process still faces challenges in the low-strength and organics-contained municipal wastewater due to its susceptibility and the technical gaps in substrate supply. Effective strategies for extensive implementation of anammox in municipal wastewater treatment plants (WWTPs) remain poorly summarized. In view of the significance and necessity of introducing anammox into mainstream treatment, the growing understanding not only at level of microbial interactions but also on view of upgrading municipal WWTPs with anammox-based processes need to be considered urgently. In this review, the critical view and comprehensive analysis were offered from the perspective of microbial interactions within partial nitrification- and partial denitrification-based anammox processes. To minimize the microbial competition and enhance the cooperation among anammox bacteria and other functional bacteria, targeted control strategies were systematically evaluated. Based on the comprehensive overview of recent advances, the combination of flexible regulation of input organic carbon with anaerobic/oxic/anoxic process and the integration of sludge fermentation with anoxic biofilms in anaerobic/anoxic/oxic process were proposed as promising solutions to upgrade municipal WWTPs with anammox technology. Furthermore, a new perspective of coupling anammox with denitrifying dephosphatation was proposed as a promising method for in-depth nutrients removal from carbon-limit municipal wastewater in this study. This review provides the critical and comprehensive viewpoints on anammox engineering in municipal wastewater and paves the way for the anammox-based upgrading of municipal WWTPs.

Mainstream double-anammox driven by nitritation and denitratation using a one-stage step-feed bioreactor with real municipal wastewater.

A novel double-anammox process for advanced mainstream nitrogen removal was established using step-feed sequencing batch reactor (SBR) system with integration of suspend sludge and biofilms. Following optimization of influent distribution ratio, the effluent total inorganic nitrogen (TIN) was < 10.2 mg N/L, with influent TIN of 43.4 mg N/L, and anammox contributed 71.4% to TIN removal. Biological processes and batch tests revealed that gradient C/N reduction promoted denitratation/anammox in anoxic stage, and simultaneous nitritation and anammox were achieved in oxic stage. Specially, anammox maintained on biofilms with abundance over 109 copies/ (g dry sludge). High-throughput sequencing revealed that Thauera and Nitrosomonas were enriched in flocs. Furthermore, metagenomic sequencing confirmed that Thauera owns narG and napA (NO3-→NO2-) and Nitrosomonas owns amoA (NH4+→NO2-), support stable NO2- supply for double-anammox. This mainstream anammox-dominant process could potentially be used for stable nitrogen removal in municipal wastewater treatment plants.

Improving performance and efficiency of partial anammox by coupling partial nitrification and partial denitrification (PN/A-PD/A) to treat municipal sewage in a step-feed reactor.

Improving contribution and nitrogen removal efficiency (NRE) of partial anammox in municipal wastewater is a researching hotspot. This study developed an innovative PN/A-PD/A process with fixed biocarriers in anaerobic/anoxic chambers for actual sewage treatment in a typical step-feed reactor over 390 days. Two coupled pathways providing continuous NO2- (partial nitrification in oxic chambers and partial denitrification in anaerobic/anoxic chambers) for anammox were introduced to the process, achieving 47% nitrogen loss by anammox in stable phase. The influent and effluent total inorganic nitrogen (TIN) were 51.3 and 11.0 mg/L, respectively, even with chemical oxygen demand (COD)/TIN ratio of 2.9. Anammox activity improved from 6.52 to 9.68 mg NH4+-N/gMLSS/d and abundance on the biocarriers raised to 3.16 × 1010 gene copies/g dry sludge. Overall, this study confirmed partial anammox, spatially coupled with partial nitrification and partial denitrification via oxic/anoxic distribution with step feed mode, as an alternative for application of mainstream anammox.

Nutrients removal from low C/N actual municipal wastewater by partial nitritation/anammox (PN/A) coupling with a step-feed anaerobic-anoxic-oxic (A/A/O) system.

In this study, a novel combined strategy was successfully established by partial nitritation/anammox (PN/A) within a step-feed A/A/O process integrated with fixed-biocarriers to treat municipal sewage for 200 days. The excellent nutrients removal performance of this system compared with national level of discharging standard were achieved: low total inorganic nitrogen (7.1 mg/L) and phosphorus (0.3 mg/L) in the effluent with the influent (51.1 and 4.2 mg/L) at C/N ratios of 3.4 ± 0.5, mainly attributed to the stable PN (oxic zone) and subsequently anammox effect (anoxic zone). Nitrogen mass balance indicated that anammox contribution in anoxic zones to nitrogen loss could be up to 42% at stable phase. Therefore, aeration and carbon cost could be greatly reduced under low DO, low C/N and aerobic hydraulic retention time (HRT) of 7.4 h condition. The low DO and anammox bacteria retention in anoxic chambers promoted the washout of NOB and combination of anammox and partial nitritation process. During long-term operation, the activity of AOB effectively maintained while that of NOB drastically reduced to 0.1 mg N / g MLSS / h resulting in high and stable nitrite accumulation ratios (about 90%). The achievement of partial nitritation was mainly due to low DO (0.4-0.5 mg/L) and effective retention of anammox bacteria even with a low temperature (14.5 °C). Notedly, anammox activity gradually increased both on the biocarriers and in the flocs while a higher anammox abundance was observed on the biocarriers (2.48%) than that in suspend flocs (0.03%). As above, this study indicated that the novel combined strategies could be applicable to mainstream anammox, and a pilot-scale reactor will be established to verify and promote the industrial application of mainstream anammox.

Evaluation of tractor driving vibration fatigue based on multiple physiological parameters.

The vibration generated by tractor field operations will seriously affect the comfort and health of the driver. The low frequency vibration generated by the engine and ground excitation is similar to the natural frequency of human organs. Long term operation in this environment will resonate with the organs and affect drivers' health. To investigate this possibility, in this paper we carried out a collection experiment of human physiological indicators relevant to vibration fatigue. Four physiological signals of surface electromyography, skin electricity, skin temperature, and photoplethysmography signal were collected while the subjects experienced vibration. Several features of physiological signals as well as the law of signal features changing with fatigue are studied. The test results show that with the increase of human fatigue, the overall physiological parameters show the following trends: The median frequency of the human body surface electromyography and the slope of skin surface temperature decreases, the value of skin conductivity and the mean value of the photoplethysmography signal increases. Furthermore, this paper proposes a vibration comfort evaluation method based on multiple physiological parameters of the human body. An artificial neural network model is trained with test samples, and the prediction accuracy rate reaches 88.9%. Finally, the vibration conditions are changed by the shock-absorbing suspension of a tractor, verifying the effectiveness of the physiological signal changing with the vibration of the human body. The established prediction model can also be used to objectively reflect the discomfort of the human body under different working conditions and provide a basis for structural design optimization.

Highly enriched anammox within anoxic biofilms by reducing suspended sludge biomass in a real-sewage A2/O process.

This study proposes a novel strategy of stably enriching anammox in mainstream, based on the competitive difference to NO2- between anoxic biofilms and suspended sludge. A modified anaerobic-anoxic-oxic (A2/O) process run for 500 days with actual municipal wastewater. Microbial analysis revealed that anoxic-carrier biofilms had a significantly higher abundance of anammox (qPCR: 0.74% - 4.34%) than suspended sludge (P< 0.001). Batch tests showed that anammox within anoxic-carrier biofilms contributed to significant nitrogen removal, coupled with partial-denitrification (NO3- â†’ NO2-). The anammox genus, Ca. Brocadia, was highly enriched when suspended sludge was accidentally lost. Further batch tests found that reducing suspended biomass helped anammox enrichment in anoxic-carrier biofilms, because the suspended sludge had strong NO2- competition (NO2- â†’ N2) with anammox (increased nirK). Metagenomic sequencing revealed that Ca. Brocadia dominates in the anoxic-carrier biofilms, and is the most important narG contributor to NO3- â†’ NO2-, which could have promoted the competition of NO2- with heterotrophic bacteria. For this A2/O process, the low effluent total nitrogen (8.9 mg ± 1.0 mg N/L) was attributed to partial-denitrification coupling with anammox, demonstrating that this process is applicable to the general influent N-concentration range (30 mg - 50 mg NH4+-N/L) of municipal wastewater treatment plants (WWTPs). Based on the special competitive preference of anammox for NO2-, this study provides a promising and practical alternative for enriching anammox bacteria in municipal WWTPs.

Enhanced simultaneous nitrogen and phosphorus removal from low COD/TIN domestic wastewater through nitritation-denitritation coupling improved anammox process with an optimal Anaerobic/Oxic/Anoxic strategy.

Advanced nitrogen and phosphorus removal in a single-stage suspending-sludge system was achieved by employing a novel Anaerobic/Oxic/Anoxic (AOA) strategy over 200 days. Satisfactory total inorganic nitrogen (TIN) removal efficiency of 90.4% was achieved and effluent phosphorus was below 0.5 mg/L when treating domestic wastewater with the chemical oxygen demand (COD)/TIN as low as 2.98 ± 1.26. Stable nitritation was maintained with the ammonia residual and low dissolved oxygen of 0.2-0.5 mg/L at aerobic stage following by a post anoxic stage. The much higher activity of ammonia oxidation bacteria (12.99 mgN/gVSS/h) was achieved than the nitrite oxidation bacteria (0.09 mgN/gVSS/h). Notably, improved anammox performance was obtained without initial inoculation, contributing 47.4% to TIN removal. The abundance of Nitrosomonas increased from 0.12% to 0.95% (P < 0.001) and self-enrichment of anammox bacteria Ca. Brocadia was confirmed. It provided new insight into the advanced nutrient removal with comprehensible regulation and less aeration requirement.

[Advanced Denitrification of Municipal Wastewater Achieved via Partial ANAMMOX in Anoxic MBBR].

Anoxic MBBR is a process to achieve advanced denitrification from municipal wastewater. Here, anoxic MBBR was applied as a post-denitrification SBR to achieve advanced denitrification by partial anammox (anaerobic ammonium oxidation). During a 250-day operation, denitrification performance gradually improved and the total nitrogen concentration of the effluent was approximately 5 mg·L-1. The average nitrate, ammonia, and total inorganic nitrogen removal efficiencies were (97.7±2.9)%, (93.3±2.9)%, and (94.3±2.7)%, respectively, between day 211 and 250. The simultaneous removal of ammonia and nitrate was observed in the anoxic reactor. Analysis of the ammonia removal pathway revealed that assimilation and nitrification were poor in the anoxic MBBR. The anammox activity test and the denitrification performance showed that anammox occurred and played a not insignificant role in the anoxic MBBR. The results of real-time quantitative PCR showed that anammox bacteria enriched in anoxic MBBR, especially in the anoxic carrier biofilms, where the abundance of anammox bacteria increased from 4.37×107 copies·g-1 to 2.28×1010 copies·g-1. This study demonstrates that anoxic carrier biofilms may have potential applications in anammox bacterial enrichment to enhance denitrification from municipal wastewater.

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.

Quantify the contribution of anammox for enhanced nitrogen removal through metagenomic analysis and mass balance in an anoxic moving bed biofilm reactor.

In this study, enhanced nitrogen removal through in situ enrichment of anammox bacteria was successfully obtained in a full-scale municipal wastewater treatment plant (WWTP). The WWTP was an anaerobic-anoxic-oxic (AAO) process and upgraded by adding moving carriers into the anoxic zone. Enhanced nitrogen removal was obtained during almost two years of operation. The significant nitrogen removal might be associated with the in situ enrichment of anammox bacteria on the adding carriers, as revealed by the comprehensive results of molecular analysis and 15N-stable isotope tracing tests. Quantitative PCR results indicated that anammox bacteria in the anoxic-carrier biofilms presented a higher abundance than flocculent sludge (16S rRNA: P < 0.005; HzsB: P < 0.042). The 16S rRNA amplicon sequencing showed significant differences in the phylum Planctomycetes (P < 0.001) between anoxic-carrier biofilms and flocculent sludge. And metagenomic sequencing analysis further revealed the anammox relative abundance in the anoxic-carrier biofilms was significantly higher than the reported level in the flocculent sludge of conventional WWTPs. In addition, 15N-stable isotope tracing tests showed that anammox could be combined with nitrate reduction by the anoxic-carrier biofilms. Thus, enriched anammox bacteria might contribute to nitrogen loss and lead to improvements in the nitrogen removal, which was also supported by the mass balance analysis of organic carbon, nitrogen, and phosphorus of the WWTP. Overall, this study suggests that anoxic-carrier biofilms might be a candidate to enhance nitrogen removal through partial anammox in municipal WWTPs.

A critical review of one-stage anammox processes for treating industrial wastewater: Optimization strategies based on key functional microorganisms.

The one-stage nitritation/anammox (anaerobic ammonium oxidation) process is an energy-saving technology, which has been successfully developed and widely applied to treat industrial wastewaters. For the one-stage nitritation/anammox process, key functional microbes generally include anaerobic ammonia oxidation bacteria (AnAOB), ammonia-oxidizing bacteria (AOB), nitrite oxidizing bacteria (NOB), and heterotrophic bacteria (HB). Cooperation and competition among the key functional microbes are critical to the stability and performance of anammox process. Based upon key functional microorganisms, this review summarizes and discusses the optimized strategies that promote the operation of one-stage nitritation/anammox process. In particular, the review focuses on strategies related to: (1) the retention of anammox biomass through granular sludge or biofilm, (2) the balanced relationship between AOB and AnAOB, (3) the NOB suppression and (4) the HB management by controlling the influent organic matter. In addition, the review proposes further research to address the existing challenges.