Aerobic Layer Research Articles

Peatland warming influences the abundance and distribution of branched tetraether lipids: Implications for temperature reconstruction

Branched glycerol dialkyl glycerol tetraethers (brGDGTs) are bacterial membrane lipids whose distribution in peatland soils serves as an important proxy for past climate changes due to strong linear correlations with temperature in modern environments. However, commonly used brGDGT-based temperature models are characterized by high uncertainty (ca. 4 °C) and these calibrations can show implausible correlations when applied at an ecosystem level. This lack of accuracy is often attributed to our limited understanding of the exact mechanisms behind the relationship between brGDGTs and temperature and the potential effect of temperature-independent factors on brGDGT distribution. Here, we examine the abundance and distribution of brGDGTs in a boreal peatland after four years of in-situ warming (+0, +2.25, +4.5, +6.75 and +9 °C). We observed that with warming, concentrations of total brGDGTs increased. Furthermore, we determined a shift in brGDGT distribution in the surface aerobic layers of the acrotelm (0–30 cm depth), whereas no detectable change was observed at deeper anaerobic depths (>40 cm), possibly due to limited microbial activity. The response of brGDGTs to warming was also reflected by a strong increase in the methylation index of 5-methyl brGDGTs (MBT′5Me), classically used as a temperature proxy. Further, the relationship between the MBT′5Me index and soil temperature differed between 0–10, 10–20 and 20–30 cm depth, highlighting depth-specific response of brGDGTs to warming, which should be considered in paleoenvironmental and paleoecological studies. As the bacterial community composition was generally unaltered, the rapid changes in brGDGT distribution argue for a physiological adaptation of the microorganisms producing these lipids. Finally, soil temperature and water table depth were better predictors of brGDGT concentration and distribution, highlighting the potential for these drivers to impact brGDGT-based proxies. To summarize, our results provide insights on the response of brGDGT source microorganisms to soil warming and underscore brGDGTs as viable temperature proxies for better understanding of climatic perturbation in peatlands.

Wheat straw biochar as an additive in swine manure Composting: An in-depth analysis of mixed material particle characteristics and interface interactions

In recent research, biochar has been proven to reduce the greenhouse gases and promote organic matter during the composting. However, gas degradation may be related to the microstructure of compost. To investigate the mechanism of biochar additive, composting was performed using swine manure, wheat straw and biochar and representative solid compost samples were analyzed to characterize the mixed biochar and compost particles. We focused on the microscale, such as the particle size distributions, surface morphologies, aerobic layer thicknesses and the functional groups. The biochar and compost particle agglomerations gradually became weaker and the predominant particle size in the experiment group was < 200 μm. The aerobic layer thickness (Lp) was determined by infrared spectroscopy using the wavenumbers 2856 and 1568 cm−1, which was 0–50 μm increased as composting proceeded in both groups. The biochar increased Lp and facilitated oxygen penetrating the compost particle cores. Besides, in the biochar-swine manure particle interface, the aliphatic compound in the organic components degraded and the content of aromaticity increased with the composting process, which was indicated by the absorption intensity at 2856 cm−1 decreasing trend and the absorption intensity at 1568 cm−1 increasing trend. In summary, biochar performed well in the microscale of compost pile.

Seasonal response of nitrogen exchange fluxes to crab disturbance at sediment–water interface in coastal tidal wetlands

Coastal wetlands are hotspots for nitrogen (N) cycling, and crab burrowing is known to transform N in intertidal marsh soils. However, the underlying mechanisms remain unclear. This study conducted field experiments and used indoor control test devices to investigate the seasonal response of nitrogen to crab disturbance at the sediment–water interface in coastal tidal flat wetlands. The results showed that crab disturbance exhibited significant seasonality with large seasonal differences in cave density and depth. Due to crab disturbance, nitrogen fluxes at the sediment–water interface were much greater in the box with crabs than in the box without crabs. In summer, NH4+-N showed a positive flux from the sediment to the overlying water, but NO2−-N and NO3−-N showed positive fluxes from the sediment to the overlying water only in early stages. In winter, NH4+-N showed a positive flux from the sediment to the overlying water, but NO2−-N and NO3−-N both exhibited positive and negative fluxes. These results indicated that the presence of crab burrows can cause the aerobic layer to move downward by approximately 8–15 cm in summer and directly promote nitrification at the sediment surface.

Effects of carbon to nitrogen ratio on oxygen mass transfer characteristics in wastewater and biofilms

Systematic elucidation of the oxygen mass transfer (OMT) mechanism is the key to improving aeration and oxygenation efficiency. In this study, an aerobic fluidized bed biofilm reactor (AFBBR) was established to evaluate the OMT in the wastewater phase [macroscopic (reactor) scale] and diffusion kinetic parameters in the biofilm phase (microbiological scale) under different carbon-nitrogen(C:N) ratios. A model relating the oxygen concentration and the aerobic layer thickness of the biofilm was established based on oxygen mass balance theory and Fick's second law. The results showed that the average DO concentration decreased from 7.68 mg/L to 5.85 mg/L with increasing C:N ratio (from 4.79 to 13.94). The oxygen transfer rate (OTR) was consistent with the distribution of the total biomass (total suspended solids, TSS), which was the largest (9.74 ± 0.33 mg/(L·h) and 8178 ± 87 mg/L) under the highest C:N ratio (13.94). Additionally, the α-factor, as a key parameter for evaluating OMT efficiency, had an exponential correlation with chemical oxygen demand (CODcr). The oxygen concentration exhibited in a Gaussian distribution (0.9963 ≤R2 ≤0.9998) relative to the thickness of the aerobic layer. The mass transfer efficiency (ki) and diffusion coefficient (Di) of oxygen in the boundary layer both reached maxima [(8.1 ± 3.2)× 10−5 cm2/s and (2.0 ± 0.1)× 10−3 cm/s] under the condition of C:N = 9.49. However, under the lowest C:N ratio, the biofilm thickness (LF=2422 ± 411 µm) and oxygen diffusion coefficient (Db) both reached maxima. These results have important theoretical significance for improving OMT theory and reducing the energy consumption of the aeration process.

Effects of freeze-thaw intensities on N2O release from subsurface wastewater infiltration system

Subsurface wastewater infiltration system (SWIS) is a low-investment and cost-effective wastewater treatment technology. Nitrous oxide (N2O), an important greenhouse and ozone-depleting gas, is a major by-product of biological denitrification processes within SWIS. Although SWIS has been widely applied in varying zones, until now, whether and how periodical freeze-thaw cycles (FTCs) occurring in aerobic layers affect N2O release still remain unclear? In this study, two runs were arranged, which covered two freeze-thaw (FT) intensities of − 5 °C/5 °C and − 15 °C/5 °C, respectively. An in-situ simulation system of SWIS was carried out to monitor N2O release and microbial community structure in different profiles. The result revealed that raising FT intensity decreased the rate of nitrogen removal of SWIS. Average removal rate of TN under strong FTCs was 88.65–88.97%, which was 1.32–2.47% lower than that under weak FTCs conditions. In addition, a positive correlation was found between FT numbers and N2O release. The contribution of anaerobic zone increased from 29.24% to 75.16% with extending the FT cycles from 1 to 9. High-throughput sequencing results showed that different FT intensities had distinct effects on microbial communities. Euryarchaeota abundance increased significantly under strong FT treatment, while Proteobacteria abundance sharply decreased from 49.5% to 7.6% at day 27 of stable operation. PCA analysis shows that bacterial community composition of samples treated with weak FT and CK is similar. While significant differences in sample composition were found between strong and weak FT treatments, which was the main reason resulting in different N2O release patterns.

Eukaryotic Community Structure and Interspecific Interactions in a Stratified Acidic Pit Lake Water in Anhui Province.

The stratified acidic pit lake formed by the confluence of acid mine drainage has a unique ecological niche and is a model system for extreme microbial studies. Eukaryotes are a component of the AMD community, with the main members including microalgae, fungi, and a small number of protozoa. In this study, we analyzed the structural traits and interactions of eukaryotes (primarily fungi and microalgae) in acidic pit lakes subjected to environmental gradients. Based on the findings, microalgae and fungi were found to dominate different water layers. Specifically, Chlorophyta showed dominance in the well-lit aerobic surface layer, whereas Basidiomycota was more abundant in the dark anoxic lower layer. Co-occurrence network analysis showed that reciprocal relationships between fungi and microalgae were prevalent in extremely acidic environments. Highly connected taxa within this network were Chlamydomonadaceae, Sporidiobolaceae, Filobasidiaceae, and unclassified Eukaryotes. Redundancy analysis (RDA) and random forest models revealed that Chlorophyta and Basidiomycota responded strongly to environmental gradients. Further analysis indicated that eukaryotic community structure was mainly determined by nutrient and metal concentrations. This study investigates the potential symbiosis between fungi and microalgae in the acidic pit lake, providing valuable insights for future eukaryotic biodiversity studies on AMD remediation.

Strengthening in microbiota dynamics and C, N, S transformation induced by novel synthesized pyrite/PHBV composites for advanced nitrogen and phosphate removal: Overlooked sulfate reduction process

Fine-grained pyrites are difficult to be denitrified under natural environment due to chemical oxidation with O2. In this study, the pyrite/PHBV composites were synthesized through high-temperature melting and realized nitrogen and phosphate removal under natural aerobic conditions. Results showed that pyrite/PHBV-40 composites had the highest denitrification rate of 0.61 mg NO3−–N /(L·h) with low SO42− production, and its removal efficiency of nitrogen and phosphorus was 98% and 41%, respectively. Microbial community structure analysis revealed that the enrich sulfate-reducing bacteria (SRB) on the pyrite/PHBV-40 composites demonstrated that the sulfate reduction driven by SRB enhanced denitrification process, and thereby the S cycle could underpin the potential self-sustainability of pyrite/PHBV-40 composites. Co-occurrence network analysis showed that Fe oxidizers/reducers (e.g., Ferruginibacter/Geobacter) and SRB (e.g., Desulfovibrio) were the keystone species in microbial community. Bugbase analysis showed that formed biofilms mainly consisted of aerobic and facultative anaerobic strains, which was corresponding to structure of biofilm including aerobic and anoxic layer. Partial mantel test revealed the total Fe and nutrients (e.g., N and P) are the drivers in OTU and phenotype composition, respectively. Metabolic pathway analysis suggested that pyrite/PHBV composites may not only accelerate glycolysis with rapid hydrolysis of PHBV, but also enhance the TCA cycle with high production of ATP and NADH. The final product of nitrate reduction is N2O or NO, and the cysJ gene play an important role in sulfate reduction in pyrite/PHBV systems. Overall, the novel synthesized pyrite/PHBV composites are an ideal functional material with high denitrification rate, no secondary pollution and long service life. Our study highlights pyrite/PHBV-induced strength in microbiota dynamics and C, N, S transformation, therein, the sulfate reduction process cannot be overlooked.

Improved closed test setup for biodegradation testing of slightly volatile substances in water-sediment systems (OECD 308)

Standardized biodegradation testing methods, like the OECD 308 Aerobic and Anaerobic Transformation in Aquatic Sediment Systems, generate data on biodegradation required during environmental risk and hazard assessment of chemicals under different European and international regulations. However, difficulties arise when applying the OECD 308 guideline for testing hydrophobic volatile chemicals. Especially the use of a co-solvent (like acetone) as a measure to facilitate the application of the test chemical in combination with a closed setup to reduce losses due to volatilization tend to deplete/restrict the amount of oxygen in the test system. The result is a low oxygen or even anoxic water column in the water-sediment system. Thus, the degradation half-lives of the chemical generated from such tests are not directly comparable to the regulatory half-life values for Persistence assessment of the test chemical. The aim of this work was to further develop the closed setup to improve and maintain aerobic conditions in the water phase of the water-sediment systems for testing slightly volatile hydrophobic test chemicals. This improvement was attained by optimizing the test system geometry and agitation technique to maintain aerobic conditions in the water phase in a closed test setup, investigating appropriate co-solvent application strategy, and trialing the resulting test setup. This study shows that when using a closed test setup for OECD 308 tests, agitation of the water phase overlaying the sediment and the test item application using low co-solvent volume is critical for maintaining an aerobic water layer.

Enhanced carbon emission driven by the interaction between functional microbial community and hydrocarbons: An enlightenment for carbon cycle

Soil microbial communities are usually regarded as one of the key players in the global element cycling. Moreover, an important consequence of oil contamination altering the structure of microbial communities is likely to result in an increased carbon emission. However, understanding of the complex interactions between environmental factors and biological communities is clearly lagging behind. Here it showed that the flux of carbon emissions increased in oil-contaminated soils, up to 13.64 g C·(kg soil)−1·h−1. This phenomenon was mainly driven by the enrichment of rare degrading microorganisms (e.g., Methylosinus, Marinobacter, Pseudomonas, Alcanivorax, Yeosuana, Halomonas and Microbulbifer) in the aerobic layer, rather than the anaerobic layer, which is more conducive to methane formation. In addition, petroleum hydrocarbons and environmental factors are equally important in shaping the structure of microbial communities (the ecological stability) and functional traits (e.g., fatty acid metabolism, lipid metabolism and amino acid metabolism) due to the different ecological sensitivities of microorganisms. Thus, it can be believed that the variability of rare hydrocarbon degrading microorganisms is of greater concern than changes in dominant microorganisms in oil-contaminated soil. Undoubtedly, this study could reveal the unique characterization of bacterial communities that mediate carbon emission and provide evidence for understanding the conversion from carbon stores to carbon gas release in oil-contaminated soils.

Environmental Characteristics of Nutrients and Recent Changes in Blue-green Algae in the Aerobic Layer of Meromictic Lake Abashiri

Environmental Characteristics of Nutrients and Recent Changes in Blue-green Algae in the Aerobic Layer of Meromictic Lake Abashiri

Methane and carbon dioxide emissions from the forest floor of a black spruce forest on permafrost in interior Alaska

High-latitude warming has stimulated CO2 and CH4 emissions from permafrost peatland. This study evaluated growing season CH4 and CO2 emissions from a forest floor of a lowland black spruce forest on permafrost in interior Alaska using automated-closed chambers, anaerobic incubation of peat soils and next-generation sequencing. The CH4 emissions from May to October were 723 ± 432 mg C m−2 and 829 ± 628 mg C m−2 from the two Carex wet plots, 124 ± 76 mg C m−2 from the Sphagnum moss plot, and 11 mg C m−2 from the lichen plot (± denotes standard deviation of different years). The CH4 emissions in the peak season showed diurnal variations with a single peak around noon or double peaks depending on the plots. The CH4 emissions were an order of magnitude lower than those for other northern wetlands, possibly because deep, cold peats regulated CH4 production and oxidation at the dry aerobic surface layer. Low water table positions strongly inhibited CH4 emissions in 2018, suggesting the importance of dissolved CH4 pool at the bottom of the active layer. The future trajectory of CH4 emissions could substantially change with water conditions, deep soil temperatures, and sedge compositions.

Biotic and Abiotic Control Over Diurnal CH4 Fluxes in a Temperate Transitional Poor Fen Ecosystem

To understand the variability of methane (CH4) fluxes between a temperate mid-altitude Sphagnum-dominated peatland and the atmosphere, we monitored simultaneously eddy covariance, hydrometeorological and physical parameters between April 2019 and December 2021. The site was a CH4 source for the atmosphere, with a cumulative emission of 23.9 ± 0.6 g C m−2 year−1. At the interannual scale, deeper water table during vegetation growth periods resulted in lower CH4 fluxes (FCH4), and reciprocally. Furthermore, the seasonal temperature variation in the anaerobic peat layer was a good predictor for FCH4. However, while the lowest temperatures occurred between December and February, the lowest FCH4 were observed between March and May, with around 30% of negative FCH4. Indeed, the fastest increase in temperature of the aerobic layer likely stimulated methanotrophy at the expense of methanogenesis. Negative FCH4, systematically observed at midday, were concurrent with high photon flux densities, latent heat fluxes and net negative ecosystem CO2 exchanges, suggesting the control of photosynthesis over CH4 oxidation. Moreover, our results highlighted marked diurnal cycles with FCH4 maximal at night and minimal at midday for all seasons. This diurnal cyclicity is in opposition to what is typically known for peatlands dominated by vascular plants. Physical parameters, such as soil surface temperature and sensible heat fluxes, likely contribute to this diurnal FCH4 cyclicity and require further investigation. Our study thus demonstrates that diurnal variations in FCH4 must be considered before upscaling to seasonal or annual cycles, along with the effect of vegetation on CH4 transfer and oxidation processes.

Does the repeated freezing and thawing of the aerobic layer affect the anaerobic release of N2O from SWIS?

Subsurface wastewater infiltration systems (SWIS) is an efficient, economical, and less temperature affected sewage treatment technology. Pollutants are removed by physical, chemical, and biological reactions such as filtration, adsorption, oxidation, and degradation. Under the conditions of limited carbon source and inactivation of nitrous oxide reductase, N2O, an important greenhouse gas, is released from the anaerobic layers of SWIS. However, is N2O release affected by repeated freeze-thawing of the upper aerobic layer? How does microbial population structure and denitrogenate activity in different profiles respond to the freeze-thaw cycle (FTC)? These questions have not yet been revealed. In this study, a SWIS simulator with in-situ regulation of FTC was first constructed. The re-distribution of N2O, microbial composition and denitrogenate activity were analyzed in response to FTC. Furthermore, potential bio-markers were screened and identified. The results revealed that the release of N2O was correlated with FTC, with the anaerobic layer being the main contributor throughout, accounting for 73.32–75.8 % of the total release. The limiting factor for N2O emissions was the NO3−-N concentration in the anaerobic zone, and there were no simple linear communications between total nitrogen and N2O generations. High throughput sequencing results showed the main markers of SWIS were Proteobacteria, Gemmatimonadetes, Firmicutes, Acidobacteria, Actinobacteria, Bacteroidetes, Chloroflexi and Nitrospirae, accounting for 97.4 %–98.1 % of the total relative abundance. A significant positive correlation between Firmicutes and anaerobic release of N2O was observed, where Firmicutes abundance increased from 5 % to 21 % during the experimental cycle, while N2O concentration increased from 2.65 mg·L−1 to 18.88 mg·L−1. The results indicated that Firmicutes was an important biomarker of N2O release under freeze-thaw conditions.

Biofilm stratification in counter-diffused membrane biofilm bioreactors (MBfRs) for aerobic methane oxidation coupled to aerobic/anoxic denitrification: Effect of oxygen pressure

Aerobic methane oxidation coupled with denitrification (AME-D) executed in membrane biofilm bioreactors (MBfRs) provides a high promise for simultaneously mitigating methane (CH4) emissions and removing nitrate in wastewater. However, systematically experimental investigation on how oxygen partial pressure affects the development and characteristics of counter-diffusional biofilm, as well as its spatial stratification profiles, and the cooperative interaction of the biofilm microbes, is still absent. In this study, we combined Optical Coherence Tomography (OCT) with Confocal Laser Scanning Microscopy (CLSM) to in-situ characterize the development of counter-diffusion biofilm in the MBfR for the first time. It was revealed that oxygen partial pressure onto the MBfR was capable of manipulating biofilm thickness and spatial stratification, and then managing the distribution of functional microbes. With the optimized oxygen partial pressure of 5.5 psig (25% oxygen content), the manipulated counter-diffusional biofilm in the AME-D process obtained the highest denitrification efficiency, due mainly to that this biofilm had the proper dynamic balance between the aerobic-layer and anoxic-layer where suitable O2 gradient and sufficient aerobic methanotrophs were achieved in aerobic-layer to favor methane oxidation, and complete O2 depletion and accessible organic sources were kept to avoid constraining denitrification activity in anoxic-layer. By using metagenome analysis and Fluorescence in situ hybridization (FISH) staining, the spatial distribution of the functional microbes within counter-diffused biofilm was successfully evidenced, and Rhodocyclaceae, one typical aerobic denitrifier, was found to survive and gradually enriched in the aerobic layer and played a key role in denitrification aerobically. This in-situ biofilm visualization and characterization evidenced directly for the first time the cooperative path of denitrification for AME-D in the counter-diffused biofilm, which involved aerobic methanotrophs, heterotrophic aerobic denitrifiers, and heterotrophic anoxic denitrifiers.

Coupled modeling of peatlands carbon cycle and carbon dioxide emission from their peat deposits

COmplex Model of BOg LAndscapes (COMBOLA) is a set of dynamic models of carbon and nitrogen turnover, net ecosystem exchange, water balance, heat and water transport, generation and transfer of CO2 and CH4 in a peat deposit on a number of time scales. Combined modeling of carbon turnover and carbon dioxide emission from peat deposits on an annual time scale is carried out as part of COMBOLA for several bog landscapes in Western-Siberian south taiga. One-dimensional vertical reaction-diffusion model for carbon dioxide emission from peat deposit is combined with compartment carbon cycle model allowing estimate both bog type vegetation changes and greenhouse gases balance under probable climate change or perturbations initiated by human activities. Water table level (WTL) separating aerobic peat layer from the anaerobic one is calculated by means of the whole peat layer depth and its water balance relations. Minimal statistical information is used for calibrating temperature dependencies together with coefficients of heat and water transfer equations. The stationary states of carbon cycle are accompanied by steady average profiles of carbon dioxide concentration and can loose stability under human or climatic perturbations. The model dynamics is simulated with several climatic projections of the IPSL atmospheric circulation model for 21st century with anthropogenic scenarios RCP-2.6 and RCP-8.5.

Landfill leachate biological treatment: perspective for the aerobic granular sludge technology.

Landfill leachates are high-strength complex mixtures containing dissolved organic matter, ammonia, heavy metals, and sulfur species, among others. The problem of leachate treatment has subsisted for some time, but an efficient and cost-effective universal solution capable of ensuring environmental resources protection has not been found. Aerobic granular sludge (AGS) has been considered a promising technology for biological wastewater treatment in recent years. Granules' layered structure, with an aerobic outer layer and an anaerobic/anoxic core, enables the presence of diverse microbial populations without the need for support media, allowing simultaneous removal of different pollutants in a single unit. Besides, its strong and compact arrangement provides higher tolerance to toxic pollutants and the ability to withstand large load fluctuations. Furthermore, its good that settling properties allow high biomass retention and better sludge separation. Nevertheless, AGS-related research has focused on carbon-nitrogen-phosphorus removal, mainly from sanitary sewage. This review aims to summarize and analyze the main findings and problems reported in the literature regarding AGS application to landfill leachate treatment and identify the knowledge gaps for future applications.

Hydraulic Resistance and Macromolecular Structure of Aerobic and Anaerobic Mixed-Culture Extracellular Polymeric Substances Gel Layers: Opportunities and Challenges

Soluble Extracellular Polymeric Substances (sEPS) are a mixture of microbial soluble polymers produced during aerobic or anaerobic treatment of wastewater. Gel layers mainly consisting of sEPS are usually present in the fouling layers of membrane bioreactors (MBRs) and in the dynamic membranes (DMs) of dynamic membrane bioreactors (DMBRs), and their properties have not been thoroughly investigated over the years. In this study, sEPS fractions recovered from aerobic and anaerobic reactors were analyzed and tested to build-up EPS gel layers on a 0.2 µm pore size polycarbonate carrier. Dead-end filtration experiments showed that anaerobic sEPS layers, which have a low polysaccharide:protein (PS:PN) ratio, had a lower hydraulic resistance than the aerobic sEPS gel layers, which show a high PS:PN ratio. Optical Coherence Tomography (OCT) and Confocal Laser Scanning Microscopy (CLSM) analyses highlighted that both layers had similar thicknesses and 3D structural organizations. Fluorescent staining of organics and biovolume analysis revealed that for the anaerobic sEPS (low PS:PN), the abundance of proteins appears to destabilize the polysaccharide network increasing the water permeability through the layer. Additionally, the polysaccharides present in the anaerobic sEPS were mainly of the α-linked type, contributing to a more open crosslinked network within the layer, resulting in the low filtration resistance measured. The filtration characteristics observed in this study for the sEPS layers from anaerobic mixed cultures are of interest for possible future application of those layers as dynamic membranes within anaerobic reactors.

Heteromastus similis Southern, 1921 (Polychaeta: Capitellidae) in Mar Chiquita brackish coastal lagoon, Argentina

This paper analyzes the spatial and vertical distribution and describes biological and ecological features o f the capitellid polychaete. He leromas lus similis, in the southern part of Mar Chiquita coastal lagoon, Argentina. Sampling was carried out in three intertidal sand-muddy areas from April 1993 to April 1994. Sediment composition and organic matter content were analysed in two different depths. Feeding activity of this head-down deposit feeder occurs below aerobic sediment layers. Galleries are not ventilated, remaining as grey-black as the sourrounding sediments. Average densities vary markedly between upper and lower layers, and over time. Juveniles are frequently recorded in gregarious settlements. Feeding type, morphology of juveniles and habitat are similar to those of other capitellids. Size, faecal pellet production and food availability for H. similis are compared w-ith the northern H. jiliformis.

Simultaneously enhanced removal of PAHs and nitrogen driven by Fe2+/Fe3+ cycle in constructed wetland through automatic tidal operation

The lack of dissolved oxygen and weak substrate removal capacity in constructed wetlands (CW) leads to terrible removal of nitrogen and polycyclic aromatic hydrocarbons (PAHs). In this study, automatic tidal flow CW microcosms were constructed by improving the oxygen environment (siphon and air-duct) and substrate (magnetite) to enhance purification performance and the mechanism was explored. The results showed that the addition of air-duct could improve the oxygen collection and thus improved the NH4+ removal efficiency. Additionally, nitrogen removal was improved greatly due to the simultaneous nitrification and denitrification in aerobic layer with the addition of magnetite. Mass balance indicated the microbial degradation dominated (32–62%) the removal of PAHs. Metagenomic analysis proved the existence of magnetite enhanced the number of PAHs-degrading bacteria, functional groups and metabolic pathways and thus greatly improved the microbial degradation of PAHs. Furthermore, Fe2+/Fe3+ cycle played an important role in promoting the anaerobic degradation of PAHs, which might be served as an electron conduit to establish the direct interspecies electron transfer between iron-reducing bacteria (e.g. Deltaproteobacteria bacterium) and Anaerolineae bacterium to degrade PAHs efficiently. This study provided better understanding of the simultaneous removal of PAHs and nitrogen in tidal flow CWs.

NirS-type denitrifying bacteria in aerobic water layers of two drinking water reservoirs: Insights into the abundance, community diversity and co-existence model

The nirS-type denitrifying bacterial community is the main drivers of the nitrogen loss process in drinking water reservoir ecosystems. The temporal patterns in nirS gene abundance and nirS-type denitrifying bacterial community harbored in aerobic water layers of drinking water reservoirs have not been studied well. In this study, quantitative polymerase chain reaction (qPCR) and Illumina Miseq sequencing were employed to explore the nirS gene abundance and denitrifying bacterial community structure in two drinking water reservoirs. The overall results showed that the water quality parameters in two reservoirs had obvious differences. The qPCR results suggested that nirS gene abundance ranged from (2.61 ± 0.12) × 105 to (3.68 ± 0.16) × 105 copies/mL and (3.01 ± 0.12) × 105 to (5.36 ± 0.31) × 105 copies/mL in Jinpen and Lijiahe reservoirs, respectively. The sequencing results revealed that Paracoccus sp., Azoarcus sp., Dechloromonas sp. and Thauera sp. were the dominant genera observed. At species level, Cupriavidus necator, Dechloromonas sp. R-28400, Paracoccus denitrificans and Pseudomonas stutzeri accounted for more proportions in two reservoirs. More importantly, the co-occurrence network analysis demonstrated that Paracoccus sp. R-24615 and Staphylococcus sp. N23 were the keystone species observed in Jinpen and Lijiahe reservoirs, respectively. Redundancy analysis indicated that water quality (particularly turbidity, water temperature, pH and Chlorophyll a) and sampling time had significant influence on the nirS-type denitrifying bacterial community in both reservoirs. These results will shed new lights on exploring the dynamics of nirS-type denitrifying bacteria in aerobic water layers of drinking water reservoirs.