Oxic Phase Research Articles

Growth of sulfate-reducing Desulfobacterota and Bacillota at periodic oxygen stress of 50% air-O2 saturation

BackgroundSulfate-reducing bacteria (SRB) are frequently encountered in anoxic-to-oxic transition zones, where they are transiently exposed to microoxic or even oxic conditions on a regular basis. This can be marine tidal sediments, microbial mats, and freshwater wetlands like peatlands. In the latter, a cryptic but highly active sulfur cycle supports their anaerobic activity. Here, we aimed for a better understanding of how SRB responds to periodically fluctuating redox regimes.ResultsTo mimic these fluctuating redox conditions, a bioreactor was inoculated with peat soil supporting cryptic sulfur cycling and consecutively exposed to oxic (one week) and anoxic (four weeks) phases over a period of > 200 days. SRB affiliated to the genus Desulfosporosinus (Bacillota) and the families Syntrophobacteraceae, Desulfomonilaceae, Desulfocapsaceae, and Desulfovibrionaceae (Desulfobacterota) successively established growing populations (up to 2.9% relative abundance) despite weekly periods of oxygen exposures at 133 µM (50% air saturation). Adaptation mechanisms were analyzed by genome-centric metatranscriptomics. Despite a global drop in gene expression during oxic phases, the perpetuation of gene expression for energy metabolism was observed for all SRBs. The transcriptional response pattern for oxygen resistance was differentiated across individual SRBs, indicating different adaptation strategies. Most SRB transcribed differing sets of genes for oxygen consumption, reactive oxygen species detoxification, and repair of oxidized proteins as a response to the periodical redox switch from anoxic to oxic conditions. Noteworthy, a Desulfosporosinus, a Desulfovibrionaceaea, and a Desulfocapsaceaea representative maintained high transcript levels of genes encoding oxygen defense proteins even under anoxic conditions, while representing dominant SRB populations after half a year of bioreactor operation.ConclusionsIn situ-relevant peatland SRB established large populations despite periodic one-week oxygen levels that are one order of magnitude higher than known to be tolerated by pure cultures of SRB. The observed decrease in gene expression regulation may be key to withstand periodically occurring changes in redox regimes in these otherwise strictly anaerobic microorganisms. Our study provides important insights into the stress response of SRB that drives sulfur cycling at oxic-anoxic interphases.1UtHR5dBbf2f8WaGLBYUtHVideo

Improving organic and nutrient removal efficiencies in seafood processing wastewater using anaerobic membrane bioreactor (AnMBR) integrates with anoxic/oxic (AO) processes

Wastewater from seafood processing is a significant source of pollution, containing many harmful organic and inorganic compounds such as proteins, lipids, carbohydrates, nitrogen and phosphorus. This study investigated the enhancement of organic and nutrient removal efficiencies in seafood processing wastewater by integrating an Anaerobic Membrane Bioreactor (AnMBR) with an anoxic/oxic (AO) processes. A pilot-scale system was constructed with a capacity of 0.5 m3/day directly at the factory operated continuously, featuring an AnMBR process with a 24-hour hydraulic retention time (HRT) and an AO process with HRT values and internal recycle changes. The AnMBR system exhibited consistent and high-performance biochemical oxygen demand (COD) elimination, approximately 80 ± 5 %. However, this system demonstrated low-efficiency removal of total nitrogen (TN) at about 20 ± 5 %, and total phosphorus (TP) 15 ± 5 %, under organic loading rates (OLR) of 0.6 to 1.3 kg-COD/(L·d). The AO process was then continually employed to improve the treatment efficacy (at HRT, 5 h in the anoxic phase, and 8.3 h in the oxic phase, at a recycling rate of 300 %) resulting in the final post-treatment concentrations of COD 27–41 mg/L (removal 98.3 ± 0.3 %), TN 12–25 mg/L (90 ± 2 %), and TP 18 ± 2 mg/L (35 ± 5 %). The performance of the integrated AnMBR-AO system met the established Vietnamese discharge standards for seafood processing wastewater, as outlined in QCVN 11-MT: 2015/BTNMT.

Evaluación de la tasa de utilización de sustratos orgánicos y nitrogenados por los microorganismos en un reactor discontinuo secuencial

In this article, the utilization rate of organic and nitrogenous substrates contained in tannery wastewater by a sequential batch reactor is evaluated. Two factorial experimental designs (FEDs) were implemented. FED1 (22) used granular biomass, the aeration sequence (oxic, anaerobic-oxic) and cycle duration (6 and 24 h). FED2 (4 x 3) included suspended biomass, reaction phases (anoxic I, oxic, anoxic II (CND: conventional nitrification-denitrification) and (SND: simultaneous nitrification-denitrification), filling time (fast, slow and in stages). The substrates examined were chemical oxygen demand (COD), ammonium (NH4+-N) and total nitrogen Kjeldahl (TKN). The utilization rates were COD (-100 and -200 mg l-1 h-1) (FED1) and (-48 and -75 mg l-1 h-1) (FED2), being 1.5 to 2 times higher in FED1 than FED2. In TKN (-5 mg l-1 h-1), and NH4+-N (-30 mg l-1 h-1), they were significant in the anoxic I and oxic phases.

Organic mass and nitrogen removal kinetic modeling in sequencing batch reactor

In this paper, the novelty consists of determining kinetic parameters for sequencing batch reactor (SBR) operated for the experimental design Nº1 (ED-1) under single (oxic) and combined biological sequences in two phases (anaerobic-oxic) treating a Chemical Oxygen Demand (COD) influent around 5,466 mg/L. ED-2 comprised three phases (anoxic I-oxic-anoxic II) with the influent containing COD (1,119-1,598 mg L−1), NH4 +-N (63-94.5 mg L−1 and Total Kjeldahl Nitrogen (126 - 175 mg L−1). Kinetic parameters corresponded to the substrate maximum utilization rate r(m,S) and the half-saturation coefficient (K s) The r (m,COD) and K s was increased as the biological phases were increased from single oxic phase (−60 mg L−1 h−1; 2704 mg L−1), anaerobic-oxic phases (−100 mg L−1 h−1; 1,069.8 mg L−1) to the anoxic I –oxic-anoxic II phases (−250 mg L−1 h−1). The kinetic coefficients were significant in the first anoxic and the oxic phases of SBR, for conventional and simultaneous nitrification-denitrification.

Monitoring the galvanic corrosion of copper–steel coupling in bentonite slurry during the early oxic phase using coupled multielectrode arrays

AbstractIn the case of a two‐part container for spent nuclear fuel, consisting of an iron‐based inner structure with a copper coating, the potential perforation of copper through minor damage may result in intensive galvanic corrosion between copper and steel. The present work focuses on the corrosion of steel galvanically coupled to copper and exposed to a slightly saline environment under oxic conditions. The electrochemical processes on individual electrodes were monitored by coupled multielectrode arrays (CMEAs). The CMEAs were either in contact with groundwater saturated with bentonite or immersed in groundwater only. Very high galvanic corrosion currents were detected between carbon steel and pure copper in the early oxic phase. Additionally, the use of CMEAs further made it possible to monitor the distribution of cathodic currents around the steel electrode, which behaved anodically. Various microscopy and spectroscopy techniques were applied to identify the modes of corrosion and the type of corrosion products present at the end of the period of exposure.

Chromium biogeochemical cycling in basalt-derived paddy soils from the Leizhou Peninsula, South China

Although basalt-derived paddy soils contain high Cr levels and pose serious environmental risks, the mechanisms controlling Cr transformation during anoxic–oxic alternation remain unclear. In this study, the major geochemical processes controlling the release, geochemical speciation, and Cr redistribution during anoxic–oxic alternation were investigated in three basalt-derived paddy soils containing 114, 268, and 429 mg/kg of Cr. The exchangeable and carbonate-bound Cr (available Cr fractions) increased under anoxic phase but decreased under oxic phase, indicating the reversibility of Cr availability. The relationships between the dynamic changes in Fe/C/N/S and Cr transformations were also revealed. FeMn oxide-bound Cr remained relatively stable during anoxic–oxic alternation, indicating that Cr may be released through reductive dissolution of Fe(III) (hydr)oxides while it was incorporated into the structure of Fe(III) (hydr)oxides through Fe(II)-catalyzed recrystallization under anoxic phase. The organic matter and sulfide-bound Cr increased under anoxic phase but decreased under oxic phase. During the anoxic period, organic matter can form complexes with Cr, and sulfate reduction may induce the formation of Cr sulfide. Based on elementary reactions, kinetic models were established to quantitatively describe Cr transformation during anoxic–oxic alternation in basalt-derived paddy soils. This study revealed the vital factors controlling Cr transformation and redistribution, which are useful for Cr risk assessment of basalt-derived paddy soils.

The Transition from Used Fuel Container Corrosion Under Oxic Conditions to Corrosion in an Anoxic Environment

The internationally accepted plan for nuclear fuel waste disposal is to store used nuclear fuels within a multi barrier system in a deep geological repository (DGR). Similarly, the DGR concept proposed in Canada involves isolating the used nuclear fuel in copper-coated carbon steel vessels surrounded by bentonite clay buffer boxes and gapfill material. The repository environment is anticipated to evolve from early oxic conditions to later anoxic conditions. Likewise, degradation processes of the UFCs should transition from the initial oxygen-driven processes to those governed by the availability of sulfide as oxidant. This transition may involve the conversion of accumulated (hydr)oxide-type corrosion products produced during the oxic phase to copper sulfide compounds. During this conversion, sulfide species could interact with the UFC surface in several ways depending on the type of (hydr)oxide corrosion products present, the nature and concentration of sulfide species, and other factors: Chemical conversion: in this process substitution reactions replace oxy-anions in the corrosion product layers with sulfide anions. This conversion doesn’t involve redox reactions; therefore, until the conversion is complete, the sulfide species would not drive further corrosion of the Cu surface. Over time, the (hydr)oxide corrosion product layer would be replaced by a sulfide layer.Galvanically-coupled process: in this process sulfides react with Cu metal exposed at the base of pores or cracks in the accumulated corrosion product layer, causing the Cu in those locations to oxidize and copper sulfide to form, while simultaneously expelling oxy-anions and causing cupric or cuprous ions to be reduced elsewhere in the corrosion product layer. Although the conservation of charge in these reactions would mean that no net oxidation of the surface would occur, the spatial separation of the sites where copper is oxidized (on the metal surface) and the locations where reduction occurs (in/on the corrosion product layer) would result in further damage to the Cu layer on the UFC surface, possibly localized at the sites where Cu metal is exposed. Eventually the (hydr)oxide corrosion product layer would be replaced by a sulfide layer and any localization should cease.Direct corrosion: in this process, sulfide species react with the Cu exposed at the base of pores or cracks in the accumulated corrosion product layer, causing further corrosion at these locations without the existing (hydr)oxide species being converted (i.e. process a) or galvanically reduced (i.e. process b). These sulfide species would drive further corrosion of the UFC surface, possibly localized at the sites where Cu metal is exposed. Since this process would not contribute to the removal of the (hydr)oxide corrosion product layer, it is possible that localization, if present, could continue. The research work reported here uses electrochemical and surface characterization methods to evaluate the extent to which each of these possible conversion processes take place, and the timescale/rate of conversion of (hydr)oxide layers grown in different ways. Results so far indicate a fairly rapid and quantitative conversion of oxides according to processes a) and/or b), followed by direct corrosion of the Cu surface by sulfide.

Habitat expansion of a tropical chironomid by seasonal alternation in use of littoral and profundal zones

The consistent warming of tropical lakes at all depths causes rapid development and long persistence of seasonal hypoxia in the hypolimnion, which greatly reduces the biodiversity of hypolimnetic benthic invertebrates. Full mixing of the water column in a typically annual cool-season creates a benthic habitat suitable for invertebrates but offers little time for colonization before the return of anoxia. In Lake Alchichica, Mexico, the endemic midge Chironomus alchichica has evolved a life cycle consisting of reproduction in waters of the littoral zone, which is suboptimal for development, followed by colonization of the hypolimnetic benthic zone during its oxic phase. As shown by the sampling of both littoral and benthic habitats over an annual cycle, the development of Ch. alchichica in the profundal zone is favoured by minimal competition (only one other invertebrate species present) and no significant predation. The rapid maturation of the midge leads to a high density of pupation before the seasonal anoxia.

Mainstream nitritation and denitritation in a pilot-scale multi-cycle sequencing batch reactor

Addition of external carbon sources for deep nitrogen removal highly increased the cost of municipal wastewater treatment. In this study, a carbon-saving nitritation and denitritation process was developed in a pilot-scale multi-cycle sequential batch reactor over 230 days. In the first three stages, the effluent total nitrogen (TN) concentration of the pilot plant without external carbon addition was similar to that of the on-site cyclic activated sludge system with external carbon addition. A highest nitrite accumulation rate (57.3%) and TN removal rate (85.1%) was observed, respectively, under conditions that temperature of 28.3 °C, dissolved oxygen concentrations of 2.0 mg/L and COD/N ratios of 4.5:1 as well as a short oxic phase (32.8 min). As the influent TN decreased after heavy rain, NOB could still be suppressed by shortening oxic phase and lowering DO (1.5 mg/L). In winter, slight nitrite accumulation was still obtained by adding glucose in stage IV. Nitrite competition between NOB and denitrifiers was indeed the key to NOB suppression. It should be a good choice for wastewater treatment plants to achieve high discharge standard and save carbon source using such a proposed process.

Enrichment of phosphate-accumulating organisms (PAOs) in a microfluidic model biofilm system by mimicking a typical aerobic granular sludge feast/famine regime

Wastewater treatment using aerobic granular sludge has gained increasing interest due to its advantages compared to conventional activated sludge. The technology allows simultaneous removal of organic carbon, nitrogen, and phosphorus in a single reactor system and is independent of space-intensive settling tanks. However, due to the microscale, an analysis of processes and microbial population along the radius of granules is challenging. Here, we introduce a model system for aerobic granular sludge on a small scale by using a machine-assisted microfluidic cultivation platform. With an implemented logic module that controls solenoid valves, we realized alternating oxic hunger and anoxic feeding phases for the biofilms growing within. Sampling during ongoing anoxic cultivation directly from the cultivation channel was achieved with a robotic sampling device. Analysis of the biofilms was conducted using optical coherence tomography, fluorescence in situ hybridization, and amplicon sequencing. Using this setup, it was possible to significantly enrich the percentage of polyphosphate-accumulating organisms (PAO) belonging to the family Rhodocyclaceae in the community compared to the starting inoculum. With the aid of this miniature model system, it is now possible to investigate the influence of a multitude of process parameters in a highly parallel way to understand and efficiently optimize aerobic granular sludge-based wastewater treatment systems.Key points• Development of a microfluidic model to study EBPR.• Feast-famine regime enriches polyphosphate-accumulating organisms (PAOs).• Microfluidics replace sequencing batch reactors for aerobic granular sludge research.

Simultaneous nitritation and denitritation in a multi-cycle SBR treating low-strength wastewater

This study presents a novel control strategy to achieve simultaneous nitritation and denitritation in a multi-cycle sequencing batch reactor with integrated fixed-biofilm and activated sludge. 86.0% of total nitrogen was removed from synthetic wastewater with an average COD/N ratio of 3.3 at 15 °C–24 °C. Batch tests and high-throughput sequencing results showed that Nitrospira and Nitrosomonas genus mainly distributed in the biofilm, so some of the nitrite produced by Nitrosomonas could be simultaneously reduced by denitrifiers in the biofilm during aeration, leading to low nitrate accumulation. As such, nitrite could be removed by denitrifiers in both anoxic and oxic phases, and accordingly suspended Nitrospira was completely suppressed due to food shortage and easily washed out at a short solids retention time.

Effect of Temperature on Acetate Mineralization Kinetics and Microbial Community Composition in a Hydrocarbon-Affected Microbial Community During a Shift From Oxic to Sulfidogenic Conditions.

Aquifer thermal energy storage (ATES) allows for the seasonal storage and extraction of heat in the subsurface thus reducing reliance on fossil fuels and supporting decarbonization of the heating and cooling sector. However, the impacts of higher temperatures toward biodiversity and ecosystem services in the subsurface environment remain unclear. Here, we conducted a laboratory microcosm study comprising a hydrocarbon-degrading microbial community from a sulfidic hydrocarbon-contaminated aquifer spiked with 13C-labeled acetate and incubated at temperatures between 12 and 80°C to evaluate (i) the extent and rates of acetate mineralization and (ii) the resultant temperature-induced shifts in the microbial community structure. We observed biphasic mineralization curves at 12, 25, 38, and 45°C, arising from immediate and fast aerobic mineralization due to an initial oxygen exposure, followed by slower mineralization at sulfidogenic conditions. At 60°C and several replicates at 45°C, acetate was only aerobically mineralized. At 80°C, no mineralization was observed within 178 days. Rates of acetate mineralization coupled to sulfate reduction at 25 and 38°C were six times faster than at 12°C. Distinct microbial communities developed in oxic and strictly anoxic phases of mineralization as well as at different temperatures. Members of the Alphaproteobacteria were dominant in the oxic mineralization phase at 12–38°C, succeeded by a more diverse community in the anoxic phase composed of Deltaproteobacteria, Clostridia, Spirochaetia, Gammaproteobacteria and Anaerolinea, with varying abundances dependent on the temperature. In the oxic phases at 45 and 60°C, phylotypes affiliated to spore-forming Bacilli developed. In conclusion, temperatures up to 38°C allowed aerobic and anaerobic acetate mineralization albeit at varying rates, while mineralization occurred mainly aerobically between 45 and 60°C; thermophilic sulfate reducers being active at temperatures > 45°C were not detected. Hence, temperature may affect dissolved organic carbon mineralization rates in ATES while the variability in the microbial community composition during the transition from micro-oxic to sulfidogenic conditions highlights the crucial role of electron acceptor availability when combining ATES with bioremediation.

P.080 A translational Homer 1a-based network approach: imaging how haloperidol modulates glutamate system functional connectivity

The dynamic response mechanism of Candidatus Accumulibacter clades to environmental factors in enhanced biological phosphorus removal (EBPR) was unclear. This study investigated the relationship between the transcriptional responses of Candidatus Accumulibacter clades and environmental dynamics. Results suggested that Candidatus Accumulibacter clade IIA only responded in initial 20 and 30 min of P-release and P-uptake stage, respectively, and was also the first clade to stop responding among the six Candidatus Accumulibacter clades. Clade IIC and IID responded at rising stage of P-release and P-uptake rate. Clade IA and IIB responded at decreasing stage of P-release and P-uptake rate. The transcriptional response duration of clade IIF was the longest, which constantly responded throughout anaerobic, anoxic and oxic phase. The transcriptional responses of Candidatus Accumulibacter clades to environmental dynamics revealed the microorganisms actually working in P-release and P-uptake, and gave a new insight into the transcriptional responses related to the EBPR performance.

Regulation of the product stoichiometry of denitrification in intensively managed soils

AbstractCrop residue amendment in conjunction with synthetic nitrogen (N) fertilization is a common agricultural practice that increases soil fertility and crop yield. However, such a practice may also change soil denitrification process. Here, we conducted an incubation experiment with a robotized continuous flow N2 free incubation system [using helium (He) and oxygen (O2)] and measured fluxes of N2O and N2 at a high resolution in an intensively managed soil to examine the interaction effect of straw amendment and N fertilization on soil denitrification. Four treatments were set consisting of (a) a nonamended treatment (Control); (b) a Straw treatment (2 g straw kg−1 dry soil); (c) a KNO3 treatment (KNO3, 15 mM KNO3); and (d) a Straw + KNO3 treatment (2 g straw kg−1 dry soil and 15 mM KNO3). During the oxic phase (80% He plus 20% O2) of the experiment (initial 2 days), flux rates of N2O were 0.54 and 0.38 kg N/ha day−1 in the Control and KNO3 treatments, respectively. Meanwhile, straw amendment triggered N2O fluxes immediately after the onset of treatments, which was more evident in the Straw + KNO3 treatment. During the anoxic phase (100% He), both N2O and N2 emissions increased in all treatments, with the effect being more pronounced in the Straw and Straw + KNO3 treatments. In line with the observed differences in gas fluxes, the abundances of nirK, nirS, and nosZ genes increased clearly in these treatments. Overall, the mean N2O/(N2O + N2) ratio (0.69 ± 0.03) in the Control treatment was significantly lower compared to the KNO3 treatment (18.8%) and higher than the straw‐amended soils (31.9% and 17.4% compared to the Straw and Straw + KNO3 treatments, respectively). Taken together, our results suggest straw amendment significantly altered N2O and N2 fluxes by decreasing the N2O/(N2O + N2) ratio; however, the effects of straw amendment depended on soil nitrate content.

Integrated Omics Elucidate the Mechanisms Driving the Rapid Biodegradation of Deepwater Horizon Oil in Intertidal Sediments Undergoing Oxic-Anoxic Cycles.

Crude oil buried in intertidal sands may be exposed to alternating oxic and anoxic conditions but the effect of this tidally induced biogeochemical oscillation remains poorly understood, limiting the effectiveness of remediation and managing efforts after oil spills. Here, we used a combination of metatranscriptomics and genome-resolved metagenomics to study microbial activities in oil-contaminated sediments during oxic-anoxic cycles in laboratory chambers that closely emulated in situ conditions. Approximately 5-fold higher reductions in the total petroleum hydrocarbons were observed in the oxic as compared to the anoxic phases with a relatively constant ratio between aerobic and anaerobic oil decomposition rates even after prolonged anoxic conditions. Metatranscriptomics analysis indicated that the oxic phases promoted oil biodegradation in subsequent anoxic phases by microbially mediated reoxidation of alternative electron acceptors like sulfide and by providing degradation-limiting nitrogen through biological nitrogen fixation. Most population genomes reconstructed from the mesocosm samples represented uncultured taxa and were present typically as members of the rare biosphere in metagenomic data from uncontaminated field samples, implying that the intertidal communities are adapted to changes in redox conditions. Collectively, these results have important implications for enhancing oil spill remediation efforts in beach sands and coastal sediments and underscore the role of uncultured taxa in such efforts.

Transcriptional responses of Candidatus Accumulibacter clades to environmental dynamics in enhanced biological phosphorus removal

The dynamic response mechanism of Candidatus Accumulibacter clades to environmental factors in enhanced biological phosphorus removal (EBPR) was unclear. This study investigated the relationship between the transcriptional responses of Candidatus Accumulibacter clades and environmental dynamics. Results suggested that Candidatus Accumulibacter clade IIA only responded in initial 20 and 30 min of P-release and P-uptake stage, respectively, and was also the first clade to stop responding among the six Candidatus Accumulibacter clades. Clade IIC and IID responded at rising stage of P-release and P-uptake rate. Clade IA and IIB responded at decreasing stage of P-release and P-uptake rate. The transcriptional response duration of clade IIF was the longest, which constantly responded throughout anaerobic, anoxic and oxic phase. The transcriptional responses of Candidatus Accumulibacter clades to environmental dynamics revealed the microorganisms actually working in P-release and P-uptake, and gave a new insight into the transcriptional responses related to the EBPR performance.

Impact of cycle type on aerobic granular sludge formation, stability, removal mechanisms and system performance

This paper aimed to assess the impact of the cycle type on aerobic granular sludge (AGS) formation, stability and system performance. Six AGS reactors were operated either on A/O cycles (anaerobic followed by oxic phase) or A/O/A cycles (anaerobic, followed by oxic and anoxic phases), changing only the phase time distribution. Reactors with high percentage of aerobic phase (65% of the total cycle time) generated granules with better settleability and resistance, however denitrification was impaired. On the other hand, reactors with long anaerobic or anoxic phases presented excellent nutrients removals, but the granules were fluffy and unstable. The best results in terms of performance and stability were achieved in an A/O/A reactor with short anoxic phase (10% of the total cycle) and medium aerobic phase (55% of the total cycle). Therefore, in AGS reactors, it is indispensable to optimize the cycle, aiming at fast biomass formation, long-term granule stability and high-rate pollutants removal.

Hydrogen producing water treatment through mesoporous TiO2 nanofibers with oriented nanocrystals

The development of well-defined TiO2 nanoarchitectures is a versatile strategy to achieve high-efficiency photocatalytic performance. In this study, mesoporous TiO2 nanofibers consisting of oriented nanocrystals were fabricated by a facile vapothermal-assisted topochemical transformation of preformed H-titanate nanobelts. The vapothermal temperature is crucial in tuning the microstructures and photocatalytic redox properties of the resulting mesoporous TiO2 nanofibers. The microstructures were characterized with XRD, TEM, XPS and nitrogen adsorption-desorption isotherms, etc. The photocatalytic activities were evaluated by photocatalytic oxidation of organic pollutant (Rhodamine B as an example) as well as photocatalytic reduction of water to generate hydrogen (H2). The nanofibers vapothermally treated at 150°C showed the highest photocatalytic activity in both oxidation and reduction reactions, 2 times higher than that of P25. The oriented alignment and suitable mesoporosity in the resulting nanofiber architecture were crucial for enhancing photocatalytic performances. The oriented alignment of anisotropic anatase nanocrystals shall facilitate faster vectorial charge transportation along the nanofibers architecture. And, the suitable mesoporosity and high surface area would also effectively enhance the mass exchange during photocatalytic reactions. We also demonstrate that efficient energy-recovering photocatalytic water treatments could be accomplished by a cascading oxic-anoxic process where the dye is degraded in the oxic phase and hydrogen is generated in the successive anoxic phase. This study showcases a novel and facile method to fabricate mesoporous TiO2 nanofibers with high photocatalytic activity for both clean energy production and environmental purification.

Performance of Two-Stage A/O Process on High-Strength Ammonia Nitrogen Wastewater

In order to understand the two-stage A/O process which contained two independent A/O (Anoxic/Oxic) subsystems when applied to treat high-strength ammonia nitrogen wastewater, connection mode of the two A/O subsystems and DO concentration of oxic phase were selected as the influencing factors in this paper. The connection modes of the two independent A/O subsystems were parallel-connected and tandem-connected. Initially, the performance of two-stage A/O process in different connection modes were investigated by comparing the ability to remove COD, NH4+-N and TN. It was observed that tandem-connected two-stage A/O system was suitable for the treatment of high-strength ammonia nitrogen wastewater, and two-stage A/O system which was operated in parallel-connected mode failed to meet the direct emission standard of Discharge Standard of Water Pollutants for Ammonia Industry in China (GB13458-2013) with remanent COD, NH4+-N and final effluent TN concentration of 234.2mg/L, 25mg/L and 74.2mg/L, respectively. Following the above observation, five different levels of DO concentration (2, 3, 4, 5 and 6 mg/L) of stage-one and stage-two were varied to figure out the optimal DO concentration in tandem-connected two-stage A/O system. Examination of effluent quality indicated that 5.0mg/L was determined to be the optimal DO concentration for Stage-one and 2.0mg/L for Stage-two. In this case, the quality of effluent was perfectly satisfied the direct emission standard.

Chemical stress from Fe salts dosing on biological phosphorus and potassium behavior.

In simultaneous precipitation, interaction between chemical and biological P removal could not be ignored. This work investigated effects of ferrous sulfate and Fe precipitates on metabolic behavior of bio-P and its counter cation of potassium. After dosing, mixed liquid suspended solids (MLSS) increased 9%, pH decreased from 7.35 to 7.00, sludge volume index (SVI) decreased, electrical conductivity increased. Chemical oxygen demand (COD) and NH3 removal was not affected. Fe dosing initially showed synergistic effect, and then inhibition appeared at accumulative dose above 10 mgFe/gMLSS. Both precipitate FePO4 and Fe(OH)3 deteriorated effluent P. FePO4 dissolved 35% in anaerobic phase which failed to be totally reprecipitated in oxic phase, resulting in increased effluent P. FePO4 inhibited K uptake rather than bio-P uptake. Fe(OH)3 caused reduction of bio-P release, meanwhile, its inhibition on K and bio-P uptake was greater than FePO4. Phosphorus metabolism was inhibited when sludge contained 0.15 mM FePO4 or 0.10 mM Fe(OH)3. Increased K/P molar ratio and coefficient b could be indicators for Fe residual in sludge. Intermittent dosing was suggested for wastewater treatment plant (WWTP) operation.