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The feasibility of a simultaneous nitrification, denitrification and fermentation process (SNDF) under electric stirrer agitation conditions was verified in a single reactor. Enhanced activated sludge for phenol degradation and denitrification in pharmaceutical phenol-containing wastewater under low dissolved oxygen conditions, additional inoculation with Comamonas sp. BGH and optimisation of co-metabolites were investigated. At a hydraulic residence time (HRT) of 28 h, 15 mg/L of substrate as strain BGH co-metabolised substrate degraded 650 ± 50 mg/L phenol almost completely and was accompanied by an incremental increase in the quantity of strain BGH. Strain BGH showed enhanced phenol degradation. Under trisodium citrate co-metabolism, strain BGH combined with activated sludge treated phenol wastewater and degraded NO2−-N from 50 ± 5 to 0 mg/L in only 7 h. The removal efficiency of this group for phenol, chemical oxygen demand (COD) and TN was 99.67%, 90.25% and 98.71%, respectively, at an HRT of 32 h. The bioaugmentation effect not only promotes the degradation of pollutants, but also increases the abundance of dominant bacteria in activated sludge. Illumina MiSeq sequencing research showed that strain BGH promoted the growth of dominant genera (Acidaminobacter, Raineyella, Pseudarcobacter) and increased their relative abundance in the activated sludge system. These genera are resistant to toxicity and organic matter degradation. This paper provides some reference for the activated sludge to degrade high phenol pharmaceutical wastewater under the action of biological enhancement. [ABSTRACT FROM AUTHOR]

• Complete nitrification (NH 4 + to NO 3 −) was achieved under DO below 0.1 mg/L. • Nitrifiers maintain a high nitrification rate and oxygen affinity under low DO. • Extremely low DO favors autotrophic nitrifiers enrichment over heterotrophs. • Genome-level phylogenetics revealed species succession within nitrifier genera. Nitrification, a process carried out by aerobic microorganisms that oxidizes ammonia to nitrate via nitrite, is an indispensable step in wastewater nitrogen removal. To facilitate energy and carbon savings, applying low dissolved oxygen (DO) is suggested to shortcut the conventional biological nitrogen removal pathway, however, the impact of low DO on nitrifying communities within activated sludge is not fully understood. This study used genome-resolved metagenomics to compare nitrifying communities under extremely low- and high-DO. Two bioreactors were parallelly operated to perform nitrification and DO was respectively provided by limited gas-liquid mass transfer from the atmosphere (AN reactor, DO < 0.1 mg/L) and by sufficient aeration (AE reactor, DO > 5.0 mg/L). Low DO was thought to limit nitrifiers growth; however, we demonstrated that complete nitrification could still be achieved under the extremely low-DO conditions, but with no nitrite accumulation observed. Kinetic analysis showed that after long-term exposure to low DO, nitrifiers had a higher oxygen affinity constant and could maintain a relatively high nitrification rate, particularly at low levels of DO (<0.2 mg/L). Community-level gene analysis indicated that low DO promoted enrichment of nitrifiers (the genera Nitrosomonas and Nitrospira , increased by 2.3- to 4.3-fold), and also harbored with 2.3 to 5.3 times higher of nitrification functional genes. Moreover, 46 high-quality (>90 % completeness and <5 % contamination) with 3 most abundant medium-quality metagenome-assembled genomes (MAGs) were retrieved using binning methods. Genome-level phylogenetic analysis revealed the species succession within nitrifying populations. Surprisingly, compared to DO-rich conditions, low-DO conditions were found to efficiently suppressed the ordinary heterotrophic microorganisms (e.g., the families Anaerolineales, Phycisphaerales , and Chitinophagales), but selected for the specific candidate denitrifiers (within phylum Bacteroidota). This study provides new microbial insights to demonstrate that low-DO favors the enrichment of autotrophic nitrifiers over heterotrophs with species-level successions, which would facilitate the optimization of energy and carbon management in wastewater treatment. [Display omitted] [ABSTRACT FROM AUTHOR]

Excessive aeration in wastewater treatment plants (WWTPs) will lead to energy waste. A large number of studies have shown that the control of low dissolved oxygen (DO) operation in WWTPs not only achieves considerable wastewater treatment effects, but also reduces energy waste. In this study, the transfer regulation of substrates and oxygen inside activated sludge flocs was measured under different equipment conditions (particle size of flocs, wastewater quality and sludge retention time of the treatment system) by using a microelectrode. A diffusion–reaction model based on the Monod kinetic model and Fick's first law of diffusion was established by considering both the internal diffusion resistance and the diffusion rate of oxygen and substrates inside the activated sludge flocs, and the critical DO (DOc) was calculated by MATLAB software. The results showed that the attenuation of DO concentration in activated sludge flocs increased slightly with the increasing particle size, but it decreased with increasing external DO concentration. A critical DO as low as 0.3 mg/L could be achieved in flocs with low DO concentrations. This study provides strong support to carry out effective and feasible process design and process optimization. In addition, it can further guide WWTPs to achieve energy savings and consumption under stable operation. [ABSTRACT FROM AUTHOR]

Abstract Low condition of dissolved oxygen (DO) is commonly associated with sludge bulking problem that was able to disrupt the efficiency of wastewater treatment performances. Relatively, very little attention was paid to the possibility of applying magnetic field in controlling the bulking problem. Hence, this study aims to investigate the performance of magnetic field on biomass properties and its effect on biodegradation under low condition of DO. Two continuous laboratory-scale sequencing batch reactors—Reactor A (SBRA) and Reactor B (SBRB)—were setup. SBRA was equipped with the magnetic device to exhibit magnetic field of 88 mT, while SBRB acted as a control system. The results showed that the biomass concentration in SBRA was higher compared to SBRB. High biomass concentration in SBRA resulted to better settleability with mean SVI of less than 30 mL/g. SBRA also showed consistently high removal performances of organic and inorganic contents compared to SBRB. These observations confirmed that the magnetic field was able to enhance the biomass properties, which further enhance the biodegradation ability of the aerobic bacteria under low DO condition. This also indicates that under the sludge bulking circumstances, the use of magnetic field stands a great chance in maintaining high biodegradation of the treatment system.

Low condition of dissolved oxygen (DO) is commonly associated with sludge bulking problem that was able to disrupt the efficiency of wastewater treatment performances. Relatively, very little attention was paid to the possibility of applying magnetic field in controlling the bulking problem. Hence, this study aims to investigate the performance of magnetic field on biomass properties and its effect on biodegradation under low condition of DO. Two continuous laboratory-scale sequencing batch reactors—Reactor A (SBRA) and Reactor B (SBRB)—were setup. SBRA was equipped with the magnetic device to exhibit magnetic field of 88 mT, while SBRB acted as a control system. The results showed that the biomass concentration in SBRA was higher compared to SBRB. High biomass concentration in SBRA resulted to better settleability with mean SVI of less than 30 mL/g. SBRA also showed consistently high removal performances of organic and inorganic contents compared to SBRB. These observations confirmed that the magnetic field was able to enhance the biomass properties, which further enhance the biodegradation ability of the aerobic bacteria under low DO condition. This also indicates that under the sludge bulking circumstances, the use of magnetic field stands a great chance in maintaining high biodegradation of the treatment system. [ABSTRACT FROM AUTHOR]

This study evaluated the properties and pollutant removal ability of sludge from low-strength synthetic wastewater during the formation of aerobic granules at low dissolved oxygen (DO) (1.0 ± 0.2 mg L–1). After 141 d operations, the aerobic granules were successfully cultivated. The removal efficiencies of chemical oxygen demand, NH4 +, total nitrogen and total phosphorus were 91.0%, 98.6%, 77.6% and 92.5%, respectively. The morphology of the mature granules was almost spherical, with an average granule size of 436.5 ± 12 μm. Filamentous bacteria on the surface were embedded in extracellular polymeric substances. The protein amount (190.4 mg g–1 VSS) was greater than that of polysaccharide (30.0 mg g–1 VSS). Aerobic granule at low DO (1.0 ± 0.2 mg L–1) consumed a 27.9% less aeration rate compared with conventional biological treatment methods. The good removal performance of aerobic granule at low DO could be suitably applied in wastewater treatment with low energy consumption. [ABSTRACT FROM AUTHOR]

Forecasts from climate models and oceanographic observations indicate increasing deoxygenation in the global oceans and an elevated frequency and intensity of hypoxic events in the coastal zone, which have the potential to affect marine biodiversity and fisheries. Exposure to low dissolved oxygen (DO) conditions may have deleterious effects on early life stages in fishes. This study aims to identify thresholds to hypoxia while testing behavioral and physiological responses of two congeneric species of kelp forest fish to four DO levels, ranging from normoxic to hypoxic (8.7, 6.0, 4.1, and 2.2 mg O2/L). Behavioral tests identified changes in exploratory behavior and turning bias (lateralization), whereas physiological tests focused on determining changes in hypoxia tolerance (pCrit), ventilation rates, and metabolic rates, with impacts on the resulting capacity for aerobic activity. Our findings indicated that copper rockfish (Sebastes caurinus) and blue rockfish (Sebastes mystinus) express sensitivity to hypoxia; however, the strength of the response differed between species. Copper rockfish exhibited reduced absolute lateralization and increased escape time at the lowest DO levels, whereas behavioral metrics for blue rockfish did not vary with oxygen level. Both species exhibited decreases in aerobic scope (as a function of reduced maximum metabolic rate) and increases in ventilation rates to compensate for decreasing oxygen levels. Blue rockfish had a lower pCrit and stronger acclimation response compared to copper rockfish. The differences expressed by each species suggest that acclimatization to changing ocean conditions may vary, even among related species that recruit to the same kelp forest habitat, leading to winners and losers under future ocean conditions. Exposure to hypoxia can decrease individual physiological fitness through metabolic and aerobic depression and changes to anti‐predator behavior, with implications for the outcome of ecological interactions and the management of fish stocks in the face of climate change. [ABSTRACT FROM AUTHOR]

Hypoxia and mercury contamination often co-occur in tropical freshwater ecosystems, but the interactive effects of these two stressors on fish populations are poorly known. The effects of mercury (Hg) on recorded changes in the detailed form of the electrocardiogram (ECG) during exposure to progressive hypoxia were investigated in two Neotropical freshwater fish species, matrinxã, Brycon amazonicus and traíra, Hoplias malabaricus. Matrinxã were exposed to a sublethal concentration of 0.1 mg L−1 of HgCl2 in water for 96 h. Traíra were exposed to dietary doses of Hg by being fed over a period of 30 days with juvenile matrinxãs previously exposed to HgCl2, resulting in a dose of 0.45 mg of total Hg per fish, each 96 h. Both species showed a bradycardia in progressive hypoxia. Hg exposure impaired cardiac electrical excitability, leading to first-degree atrioventricular block, plus profound extension of the ventricular action potential (AP) plateau. Moreover, there was the development of cardiac arrhythmias and anomalies such as occasional absence of QRS complexes, extra systoles, negative Q-, R- and S-waves (QRS complex), and T wave inversion, especially in hypoxia below O2 partial pressures (PO2) of 5.3 kPa. Sub-chronic dietary Hg exposure induced intense bradycardia in normoxia in traira, plus lengthening of ventricular AP duration coupled with prolonged QRS intervals. This indicates slower ventricular AP conduction during ventricular depolarization. Overall, the data indicate that both acute waterborne and sub-chronic dietary exposure (trophic level transfer), at sublethal concentrations of mercury, cause damage in electrical stability and rhythm of the heartbeat, leading to myocardial dysfunction, which is further intensified during hypoxia. These changes could lead to impaired cardiac output, with consequences for swimming ability, foraging capacity, and hence growth and/or reproductive performance. [ABSTRACT FROM AUTHOR]

Treating low C/N domestic sewage is one of the difficult tasks in wastewater treatment. This study investigated the treatment of low C/N domestic sewage under low dissolved oxygen condition via self-built biological contact oxidation reactor with composite packing and polyurethane suspension packing. Meanwhile, MiSeq high-throughput sequencing was performed on the microbial communities on the surface of the packing to analyze the changes in microbial community structure. The results showed that polyurethane suspension packing reactor had better removal efficacy on NH4 +-N, TN and COD than the combined packing reactor, and only the effluent indexes of polyurethane suspension packing reactor could reach the first-class A emission standard of Discharge standard of pollutants for municipal wastewater treatment plant (GB 18918-2002). The removal of biological phosphorus of the single-contact oxidation process was not ideal and could be combined with anaerobic reactor. The richness and diversity of the bacterial community in polyurethane suspension packing reactor was higher than those of composite packing reactor. Polyurethane suspension packing reactor contained relatively richer nitrification-related flora Nitrospira, which provide better growth and reproduction conditions for the denitrification-related flora Betaproteobacteria and Denitratisoma. The large amount of facultative heterotrophic bacteria in Proteobacteria had a significant effect on the removal of organic pollutants. This study provides a theoretical basis for subsequent in-depth research and practical application. [ABSTRACT FROM AUTHOR]

Published PCR primers targeting the ammonia monooxygenase gene (amoA) were applied to samples from activated sludge systems operated with low dissolved oxygen (DO) to quantify total and clade-level Nitrospira that perform complete ammonium oxidation (comammox); however, we found these existing primers resulted in significant artifact-associated non-target amplification. This not only overestimated comammox amoA copies but also resulted in numerous false positive detections in the environmental samples tested, as confirmed by gel electrophoresis. Therefore, instead of attempting to quantify comammox diversity, we focused on accurately quantifying the candidate comammox species. We designed specific and sensitive primers targeting 3 candidate species: Candidatus (Ca.) Nitrospira nitrosa, Ca. N. inopinata, and Ca. N. nitrificans. The primers were tested with amoA templates of these candidate species and used to quantify comammox at the species level in low DO activated sludge systems. We found that comammox related to Ca. N. nitrosa were present and abundant in the majority of samples from low DO bioreactors and were not detected in samples from a high DO system. In addition, the greatest abundance of Ca. N. nitrosa was found in bioreactors operated with a long solids retention time. Ca. N. inopinata and Ca. N. nitrificans were only detected sporadically in these samples, indicating a minor role of these comammox in nitrification under low DO conditions.

Published PCR primers targeting the ammonia monooxygenase gene (amoA) were applied to samples from activated sludge systems operated with low dissolved oxygen (DO) to quantify total and clade-level Nitrospira that perform complete ammonium oxidation (comammox); however, we found these existing primers resulted in significant artifact-associated non-target amplification. This not only overestimated comammox amoA copies but also resulted in numerous false positive detections in the environmental samples tested, as confirmed by gel electrophoresis. Therefore, instead of attempting to quantify comammox diversity, we focused on accurately quantifying the candidate comammox species. We designed specific and sensitive primers targeting 3 candidate species: Candidatus (Ca.) Nitrospira nitrosa, Ca. N. inopinata, and Ca. N. nitrificans. The primers were tested with amoA templates of these candidate species and used to quantify comammox at the species level in low DO activated sludge systems. We found that comammox related to Ca. N. nitrosa were present and abundant in the majority of samples from low DO bioreactors and were not detected in samples from a high DO system. In addition, the greatest abundance of Ca. N. nitrosa was found in bioreactors operated with a long solids retention time. Ca. N. inopinata and Ca. N. nitrificans were only detected sporadically in these samples, indicating a minor role of these comammox in nitrification under low DO conditions. [ABSTRACT FROM AUTHOR]

Controlling dissolved oxygen (DO) at low level can save energy for wastewater treatment plants (WWTPs), but it is easy to induce filamentous sludge bulking. Through establishing the kinetic equation of sludge settleability, ammonia nitrogen (NH4+-N) load and organic load (food-to-microbe ratio, F/M), the mechanism of the competitive relationship between filamentous and floccular bacteria under low DO was analyzed. The results showed when DO, NH4+-N load and F/M were in the range of 0.15-0.35 mg/L, 0.035-0.15 d-1 and 0.12-0.42 d-1, respectively, the mass transfer limitation of organic matter was the main factor determining the dominant growth of filamentous bacteria. When DO, NH4+-N load and F/M were in the range of 0.35-0.65 mg/L, 0.035-0.065 d-1 and 0.12-0.22 d-1, respectively, the mass transfer limitation of NH4+-N was the main factor determining the dominant growth of filamentous bacteria. When DO was low, no matter how NH4+-N load and F/M changed, the growth of filamentous bacteria was promoted. When DO and F/M were in the range of 0.35-0.65 mg/L and 0.22-0.42 d-1, respectively, no matter how NH4+-N load and F/M changed, the growth of filamentous bacteria was inhibited. Therefore, in actual operation, ensuring relatively low DO and high F/M was beneficial for the sludge settleability improvement. [ABSTRACT FROM AUTHOR]

[Display omitted] • The INPDA process obtained high NRR of 0.224 kg N/(m3·d) from municipal wastewater. • Nitrosospira has all nitrification genes to achieve complete nitrification at low DO. • Low DO and low nitrogen concentrations might selectively cultivate comammox. • Nitrosospira , Thauera , Ca. Brocadia coordinated N removal through step-feed. To achieve high-rate nitrogen removal in municipal wastewater treatment through anaerobic ammonia oxidation (Anammox), the nitrification, partial denitrification, and Anammox processes were integrated by a step-feed strategy. An exceptional nitrogen removal load of 0.224 kg N/(m3·d) was achieved by gradient-reducing the hydraulic retention time (HRT) to 5 h. Metagenomic analysis demonstrated that Nitrosospira could express all genes encoding ammonia oxidation under low nitrogen and dissolved oxygen conditions (less than 0.5 mg/L), enabling complete nitrification. With the short of HRT, the relative abundance of Thauera increased from 2.8 % to 6.4 %. Frequent substrate exchanges at such extremely short HRT facilitated enhanced synergistic interactions among Nitrosospira , Thauera , and Candidatus Brocadia. These findings provide a comprehensive understanding of the utilization of Anammox combined processes for high-speed nitrogen removal in municipal wastewater treatment and the microbial interactions involved. [ABSTRACT FROM AUTHOR]

Estuarine oxygen depletion is one of the worldwide problems, which is caused by the freshwater-input-derived severe stratification and high nutrients loading. In this study we presented the horizontal and vertical distributions of dissolved oxygen (DO) in the Pearl River estuary, together with temperature, salinity, chlorophyll a concentration and heterotrophic bacteria abundance obtained from two cruises during the summer (wet) and winter (dry) periods of 2015. In surface water, the DO level in the summer period was lower and varied greater, as compared to the winter period. The DO remained unsaturated in the summer period if salinity is < 12 and saturated if salinity is > 12; while in the winter period it remained saturated throughout the estuary. In subsurface (> 5 m) water, the DO level varied from 0.71 to 6.65 mg L − 1 and from 6.58 to 8.20 mg L − 1 in the summer and winter periods, respectively. Particularly, we observed an area of ~ 1500 km 2 low DO zone in the subsurface water with a threshold of 4 mg DO L − 1 during this summer period, that located at the fresh- and saline-water intersection where is characterized with severe stratification and high heterotrophic bacteria abundance. In addition, our results indicate that spatial DO variability in surface water was contributed differently by biological and physio-chemical variables in the summer and winter periods, respectively. [ABSTRACT FROM AUTHOR]

[Display omitted] • A low oxygen energy consumption method proposed to treat DSW with low COD/TN ratio. • Low-DO gradient control is the key to achieving efficient nitrogen removal. • Simultaneous nitrification & denitrification facilitated in 4 micro-oxygen reactors. • Advanced nitrogen removal efficiency (∼93%) obtained at SW addition ratio of 20%. This study developed an innovative step-feed anaerobic coupled four-stage micro-oxygen gradient aeration process to treat digested swine wastewater. An anaerobic zone was used for prepositive denitrification; four micro-oxygen reactors (zones O1–O4) were used for simultaneous partial nitrification and denitrification through low-dissolved oxygen gradient control, step-feed, and swine wastewater-digested swine wastewater distribution. The nitrogen-removal efficiency was satisfactory (93 ± 3 %; effluent total nitrogen, 53 ± 19 mg/L). Mass balance coupled with quantitative polymerase chain reaction analysis revealed that simultaneous partial nitrification and denitrification was achieved in four micro-oxygen zones. Zones O1 were the major denitrification zones for nitrogen removal; nitrification was primary happened in zones O2 and O3. Correlation analysis confirmed that low-dissolved oxygen gradient control was the key to achieving efficient nitrogen removal. This study provides a low oxygen energy consumption method to treat digested swine wastewater with a low carbon/nitrogen ratio (<3). [ABSTRACT FROM AUTHOR]

Low-oxygen tolerance is important for aquaculture species, because exposure to hypoxia can result in heavy mortalities. This study evaluated the effects of strain, body weight, and gender on low-oxygen tolerance in channel catfish ( Ictalurus punctatus) exposed to a lethal concentration of dissolved oxygen (0.1 mg/L). The variation in low-oxygen tolerance, assessed as the time to loss of equilibrium, of channel catfish from six strains (103KS, Kansas, KMix, Marion, Marion S, and Thompson) was examined. Catfish (15-179 g) showed a large variation in resistant time to hypoxia, ranging from 8 to 104 min, and both strain and body weight contributed significantly to this variation ( P < 0.05). 103KS and Marion S strains had higher low-oxygen tolerance than the other strains, while the Marion strain had the poorest low-oxygen tolerance ( P < 0.05). In addition to genetic background, body weight positively correlated with low-oxygen tolerance, but there were no significant differences between female and male catfish in low-oxygen tolerance. The results indicate that genetic background and body weight are important factors that contribute variations in low-oxygen tolerance. [ABSTRACT FROM AUTHOR]

To assess the effects of hypoxia, macrobenthic communities along an estuarine gradient of the Changjiang estuary and adjacent continental shelf were analyzed. This revealed spatial variations in the communities and relationships with environmental variables during periods of reduced dissolved oxygen (DO) concentration in summer. Statistical analyses revealed significant differences in macrobenthic community composition among the three zones: estuarine zone (EZ), mildly hypoxic zone (MHZ) in the continental shelf, and normoxic zone (NZ) in the continental shelf (Global R =0.206, P =0.002). Pairwise tests showed that the macrobenthic community composition of the EZ was significantly different from the MHZ (pairwise test R =0.305, P =0.001) and the NZ (pairwise test R =0.259, P =0.001). There was no significant difference in macrobenthic communities between the MHZ and the NZ (pairwise test R =0.062, P =0.114). The taxa included small and typically opportunistic polychaetes, which made the greatest contribution to the dissimilarity between the zones. The effects of mild hypoxia on the macrobenthic communities are a result not only of reduced DO concentration but also of differences in environmental variables such as temperature, salinity, and nutrient concentrations caused by stratification. [ABSTRACT FROM AUTHOR]

To investigate the applicability of ratio control strategy to other systems, a continuous floccular sludge reactor was used in this study. It was found that nitrite accumulation was barely detected throughout 70 days’ investigation, being the average concentration in the effluent of 0.7 ± 0.4 mg/L. Batch experiments indicated that low dissolved oxygen (DO < 0.3 mg·L −1 ) greatly repressed the ammonium oxidizing bacteria (AOB) but only slightly inhibited the nitrite oxidizing bacteria (NOB). However, high-throughput sequencing revealed that the ratio of abundance between Nitrospira and Nitrosomonas , being the dominant NOB and AOB respectively, was considerably low (1.2%/18.7%). The weak oxygen gradients in floccular sludge and the selectively enriched K-strategist NOB Nitrospira under oxygen-limited conditions were both contributed to the failure of achieving partial nitritation; therefore, the rapid start-up of partial nitritation process based on proposed ratio control strategy is not feasible for continuous floccular sludge systems treating low-strength wastewater. [ABSTRACT FROM AUTHOR]

This study developed a novel integrated nitrification, partial denitrification (PD), and anammox (INPDA) process in micro-aerobic sequencing batch reactor using step-feed strategy treating municipal wastewater. The results showed that the INPDA could achieve a 94.5 ± 1.1% total inorganic nitrogen (TIN) removal efficiency with effluent TIN concentration as low as 2.3 mg/L. The micro-aerobic with low dissolved oxygen concentration of 0.36 ± 0.01 mg/L allowed complete ammonium oxidation to nitrate. The applied step-feed by optimizing influent distribution ratio to 5:3 provided sufficient organics for nitrate reduction to nitrite. According to mass balance analysis, anammox was the dominant nitrogen removal pathway (87.9%). Microbial analysis indicated that aerobic nitrifiers Nitrosomonas (1.2%) and Nitrospira (0.9%) ensured full nitrification, while PD bacteria Thauera (27.1%) conducted labor metabolism coordination with anammox bacteria Candidatus Brocadia (1.3%) for nitrogen removal. These findings demonstrate that the INPDA has a good prospect for energy-efficient municipal wastewater treatment. [Display omitted] • The INPDA process obtained high NRE of 94.5 ± 1.1% from municipal wastewater. • Anammox dominated nitrogen removal with 87.9% contribution in INPDA system. • NH 4 +-N was oxidized to NO 3 −-N at low DO concentration of 0.36 mg/L. • Thauera and Ca. Brocadia were the core bacteria responsible for nitrogen removal. [ABSTRACT FROM AUTHOR]

Controlling of low dissolved oxygen (DO) levels (0.1–0.5 mg/L), a cost-effective strategy, was applied to a pilot-scale anoxic-oxic-oxic-anoxic process for partial nitrification and denitrification of mature landfill leachate. High ammonium removal efficiency, stable nitrite accumulation rate and total nitrogen removal efficiency was higher than 95.0%, 90.0% and 66.4%, respectively, implying potential application of this process for nitrogen removal of mature landfill leachate. Efficient nitrite accumulation in the first oxic reactor depended on low DO conditions and sufficient alkalinity. However, operational limit was mainly decided by actual hydraulic retention time (AHRT) of the first oxic reactor and appeared with AHRT less than 13.9 h under DO of 0.3–0.5 mg/L. High-throughput sequencing analysis demonstrated significant change of bacterial diversity in the first oxic reactor after a long-term operation and dominant bacteria genus Nitrosomonas was shown to be responsible for NH 4 + -N removal and nitrite accumulation under low DO levels. [ABSTRACT FROM AUTHOR]

The Minjiang River, a typical tidal channel in Southeast China, plays an important role in the supply of drinking water, flood control and drought relief, farming and navigation, as well as shipping and other functions. Dissolved oxygen (DO), as a basic living condition for aquatic biota, has been deteriorating in the Minjiang River in recent years. In order to understand how the spatial distribution of DO responds to river discharge, nutrient loading and water temperature, a three-dimensional Environmental Fluid Dynamics Code model was used to simulate water age and the distribution of DO in the Minjiang River. The model presented in this paper was used for water resource and water quality simulations under various physical, chemical, and biological scenarios. Sensitivity simulation results indicated that the three factors had a significant impact on the spatial distribution variation of DO in the Minjiang River. Increased river discharge or split ratio of the North Channel resulted in decreased water age and increased DO. Increased nutrient loading and water temperature caused lower DO. In order to protect coastal environments in the Minjiang River, river discharge should be increased and pollutants of local cities should be reduced during the high temperature and drought period. [ABSTRACT FROM AUTHOR]

Blooms of moon jellyfish Aurelia aurita s.l. occur in various vertical distribution patterns within the water column. Reasons for these distribution patterns have remained obscure. To quantify the influence of pycnocline and low dissolved oxygen (DO) on the vertical distribution of A. aurita aggregations, we investigated temperature, salinity, DO, and observed densities of A. aurita at 1-2 m depth intervals via video camera in a eutrophicated, enclosed bay, Mikawa Bay, Japan, for 3 years. During the observed period, stratification and hypoxic status of the bay varied seasonally and interannually due to climatic events, such as rainy season and typhoon passage. Both sharp pycnocline and low DO limited A. aurita vertical distribution. The more strongly stratified the water column, the more the upper boundary of A. aurita distribution was restricted. Bottom hypoxic water limited the lower boundary of A. aurita distribution. The DO threshold for in situ distribution was estimated to be ~2.5 mg l, which is much higher than the experimentally obtained, sublethal values identified in previous studies. Our results show that climatic events affect A. aurita vertical distribution through changes in the physical characteristics of the water column. [ABSTRACT FROM AUTHOR]

Quantifying the different sources of nitrogen (N) within the N cycle is crucial to gain insights in oceanic phytoplankton production. To understand the controls of primary productivity and the associated capture of CO2 through photosynthesis in the southeastern Indian Ocean, we compiled the physical and biogeochemical data from four voyages conducted in 2010, 2011, 2012, and 2013. Overall, higher NH4+ assimilation rates (~530 µmol m−2 h−1) relative to NO3− assimilation rates (~375 µmol m−2 h−1) suggest that the assimilation dynamics of C are primarily regulated by microbial regeneration in our region. N2 fixation rates did not decline when other source of dissolved inorganic nitrogen were available, although the assimilation of N2 is a highly energetic process. Our data showed that the diazotrophic community assimilated ~2 nmol N L−1 h−1 at relative elevated NH4+ assimilation rates ~12 nmol L−1 h−1 and NO3− assimilation rates ~6 nmol L−1 h−1. The small diffusive deep water NO3− fluxes could not support the measured NO3− assimilation rates and consequently point toward another source of dissolved inorganic NO3−. Highest NO2− values coincided consistently with shallow lower dissolved O2 layers (100-200 m; 100-180 µmol L−1). These results suggest that nitrification above the pycnocline could be a significant component of the N cycle in the eastern Indian Ocean. In our analysis we provide a conceptual understanding of how NO3− in the photic zone could be derived from new N through N2 fixation. We conclude with the hypothesis that N injected through N2 fixation can be recycled within the photic zone as NH4+ and sequentially oxidized to NO2− and NO3− in shallow lower dissolved oxygen layers. [ABSTRACT FROM AUTHOR]

Ammonia-oxidizing microbial communities involved in ammonia oxidation under low dissolved oxygen (DO) conditions (<0.3 mg/L) were investigated using chemostat reactors. One lab-scale reactor (NS_LowDO) was seeded with sludge from a full-scale wastewater treatment plant (WWTP) not adapted to low-DO nitrification, while a second reactor (JP_LowDO) was seeded with sludge from a full-scale WWTP already achieving low-DO nitrifiaction. The experimental evidence from quantitative PCR, rDNA tag pyrosequencing, and fluorescence in situ hybridization (FISH) suggested that ammonia-oxidizing bacteria (AOB) in the Nitrosomonas genus were responsible for low-DO nitrification in the NS_LowDO reactor, whereas in the JP_LowDO reactor nitrification was not associated with any known ammonia-oxidizing prokaryote. Neither reactor had a significant population of ammonia-oxidizing archaea (AOA) or anaerobic ammonium oxidation (anammox) organisms. Organisms isolated from JP_LowDO were capable of autotrophic and heterotrophic ammonia utilization, albeit without stoichiometric accumulation of nitrite or nitrate. Based on the experimental evidence we propose that Pseudomonas , Xanthomonadaceae , Rhodococcus , and Sphingomonas are involved in nitrification under low-DO conditions. [ABSTRACT FROM AUTHOR]

Membrane bioreactor (MBR) operation under low dissolved oxygen (DO) condition can potentially minimize the operational costs without compromising nitrification. In this study, the influence of periodic low DO condition to the overall removal of ammonia (NH3) in a lab-scale hypoxic/oxic (H/O) MBR was investigated. Performance evaluation of activated sludge ammonia oxidizing bacteria (AOB) shows that significant concentration of NH3 is initially oxidized in the hypoxic bioreactor and only trace amount of NH3 can be detected in the effluent. This high NH3 oxidizing activity can be supported by the high ATP value measured in the hypoxic activated sludge and from the following results of batch experiments. Similar potential for NH3 removal was observed in both activated sludge but the rate was higher in hypoxic activated sludge (2.50 mgNH3-N/L/h) than in oxic activated sludge (1.39 mgNH3-N/L/h). Under alternating hypoxic/oxic condition, simultaneous nitrification and denitrification was also observed. The results strongly support the hypothesis that stable and complete nitrification in H/O MBR is more of the adaptive response of AOB to changing environmental condition rather than the selection of specific AOB lineage. The response occurs within short time period (hydraulic retention time: 3 h and 40 min) and the same mixed AOB community is present in both hypoxic and oxic activated sludge which are related to Nitrosomonas eutropha, Nitrosomonas europaea, and Nitrosomonas oligotropha. The results suggest that periodic low DO through alternating hypoxic/oxic condition significantly contributes to efficient nitrification in H/O MBR as it renders the mixed activated sludge AOB the adaptability to DO limitation. [ABSTRACT FROM AUTHOR]

This laboratory research investigated a possible cause of filamentous bulking under low level of dissolved oxygen conditions (dissolved oxygen value in aerobic zone maintained between 0.6–0.8 mg O 2 /L) in an airlift inner-circular anoxic-aerobic reactor. During the operating period, it was observed that low nitrate concentrations affected sludge volume index significantly. Unlike the existing hypothesis, the batch tests indicated that filamentous bacteria (mainly Thiothrix sp.) could store nitrate temporarily under carbon restricted conditions. When nitrate concentration was below 4 mg/L, low levels of carbon substrates and dissolved oxygen in the aerobic zone stimulated the nitrate-storing capacity of filaments. When filamentous bacteria riched in nitrate reached the anoxic zone, where they were exposed to high levels of carbon but limited nitrate, they underwent denitrification. However, when nonfilamentous bacteria were exposed to similar conditions, denitrification was restrained due to their intrinsic nitrate limitation. Hence, in order to avoid filamentous bulking, the nitrate concentration in the return sludge (from aerobic zone to the anoxic zone) should be above 4 mg/L, or alternatively, the nitrate load in the anoxic zone should be kept at levels above 2.7 mg NO − 3 -N/g SS. [ABSTRACT FROM AUTHOR]

Abstract: A continuous anaerobic–aerobic–anoxic (AOA) process was established to remove nutrients from domestic wastewater without the addition of external carbon source. The AOA process was based on an enhanced biological phosphorous removal (EBPR) system with influent COD, and concentrations of 300, 50 and 3.8mg/L, respectively. Nitrogen and phosphorous were removed simultaneously driven by internal carbon sources under low dissolved oxygen (DO) condition. The removal efficiencies of total nitrogen (TN) and reached above 90% and 99% when the DO concentration of the aerobic unit was controlled at 1.2±0.2mg/L and the HRT of the aerobic and anoxic units were at 2h and 4h, respectively. Denitrification was mainly driven by poly-β-hydroxybutyrate (PHB), which increased via shortening the aerobic HRT. Results demonstrated that TN was removed via simultaneous nitrification and denitrification (SND) and denitrifying phosphorous removal in the continuous AOA process. [Copyright &y& Elsevier]

The hydrogen-induced cracking of X70 pipeline steel was investigated in low-temperature and low-dissolved-oxygen seawater by means of potentiodynamic polarization, slow strain rate tests (SSRT), and hydrogen permeation measurements. The results showed that the hydrogen evolution potential of X70 steel in low-temperature and low-dissolved-oxygen seawater decreased compared with the normal-temperature seawater. The susceptibility to hydrogen embrittlement increased as the potential shifted in the negative direction. When the polarization potentials were below -1,050 mV vs. saturated calomel electrode (SCE) in low-temperature and low-dissolved-oxygen seawater, the fracture surfaces exhibited quasi-cleavage fracture. [ABSTRACT FROM AUTHOR]