Performance and microbial communities of completely autotrophic denitrification in a bioelectrochemically-assisted constructed wetland system for nitrate removal

Response of soil microbes after direct contact with pyraclostrobin in fluvo-aquic soil

Agricultural chemicals affect the daily life of food production. However, the abuse of pesticides led to the damage to the environment. Pyraclostrobin (PYR) is commonly used strobilurin fungicide which inhibits fungal respiration through mitochondrial cytochrome-b and c1 inhibition. There is increasing concerns that PYR may adversely impact the environment. Although impacts on ecological receptors have been detailed, little information is available regarding the toxicological impact of PYR on soil microbial community dynamics and functioning. Understanding the potential impact on soil microbial populations is important. The activity of enzymes (urease, dehydrogenase, and β-glucosidase) and diversity of microbial community structure using high-throughput 16S rRNA sequencing were evaluated at different soil-PYR concentrations (0.1, 1.0, and 2.5 mg/kg) over a 48 day exposure period. Urease activity remained stable in general. Pyraclostrobin inhibited dehydrogenase activity during the exposure period. The β-glucosidase activity was inhibited on day 28 and induced on day 48 at 1.0 and 2.5 mg/kg. The genera Gp6, Exiguobacterium, Gp4, and Gemmatimonas were both the dominant genera and significantly changed genera. Pyraclostrobin had different level of influence on soil microbes containg their enzyme activity and community structure. The purpose of the current study was to examine the impact of PYR addition on soil enzymes as an indicator of soil health and to have complementary data on the impact of microbial populations. Furthermore, the study may also be the guide for further rational pesticide selection.

Influence of suspended mariculture on vertical distribution profiles of bacteria in sediment from Daya Bay, Southern China

Mariculture is known to contribute to oxygen depletion, pH decline and accumulation of nutrients and organic matter in sediments. However, studies on the bacterial vertical distribution of mariculture area are very limited. The bacterial abundance in the non-culture site (3.8 ± 0.8 × 10⁹ copies g^-1) was significantly higher than that in the three mariculture sites (1.2 ± 0.2 × 10⁹ copies g^-1), and bacterial diversity in the non-culture site was significantly higher than that in fish cage-TF (p < 0.05). The vertical distribution profiles of bacteria in non-culture and oyster culture sites were similar but very different from that of fish cage-TF. In addition, significant downward trends in bacterial abundance and diversity were observed as sediment depth increased (p < 0.05), and the most relevant environmental factors were moisture content, total nitrogen, total organic carbon and carbon/nitrogen. The dominant bacterial phyla in sediment were Proteobacteria, Chloroflexi and Bacteroidetes.

Effect of corn cobs as external carbon sources on nitrogen removal in constructed wetlands treating micro-polluted river water

Micro-polluted river water is characterized as having limited biodegradability, low carbon to nitrogen ratio and little organic carbon supply, all of which makes it hard to further purify. Two bench scale constructed wetlands (CWs) with a horizontal subsurface flow mode were set up in the laboratory to evaluate their feasibility and efficiency on denitrification with and without corn cobs as external carbon sources. Micro-polluted river water was used as feed solution. The CW without corn cobs substrates possessed a good performance in removing chemical oxygen demand (COD, <40 mg/L) and ammonia nitrogen (NH₃-N, <0.65 mg/L), but less efficiency in removing total nitrogen (TN) and nitrate nitrogen (NO₃-N). In marked contrast, the CW with 1% (w/w) corn cobs substrates as external carbon sources achieved a significant improvement in the removal efficiency of TN (increased from 34.2% to 71.9%) and NO₃-N (increased from 19% to 71.9%). The incorporation of corn cobs substrates did not cause any obvious increase in the concentrations of COD and NH₃-N in the effluent. This improvement in the denitrification efficiency was owing to the released organic carbon from corn cobs substrates, which facilitated the growth of abundant microbes on the surface and pores of the substrate. The open area of the used corn chips is larger than that of the pristine ones, and corn cobs can continue to provide a carbon fiber source for denitrification.

Enhanced nitrate reduction in water by a combined bio-electrochemical system of microbial fuel cells and submerged aquatic plant Ceratophyllum demersum

High nitrate (NO₃^-) loading in water bodies is a crucial factor inducing the eutrophication of lakes. We tried to enhance NO₃^- reduction in overlying water by coupling sediment microbial fuel cells (SMFCs) with submerged aquatic plant Ceratophyllum demersum. A comparative study was conducted by setting four treatments: open-circuit SMFC (Control), closed-circuit SMFC (SMFC-c), open-circuit SMFC with C. demersum (Plant), and closed-circuit SMFC with C. demersum (P-SMFC-c). The electrochemical parameters were documented to illustrate the bio-electrochemical characteristics of SMFC-c and P-SMFC-c. Removal pathways of NO₃^- in different treatments were studied by adding quantitative ¹⁵NO₃^- to water column. The results showed that the cathodic reaction in SMFC-c was mainly catalyzed by aerobic organisms attached on the cathode, including algae, Pseudomonas, Bacillus, and Albidiferax. The oxygen secreted by plants significantly improved the power generation of SMFC-c. Both electrogenesis and plants enhanced the complete removal of NO₃^- from the sediment-water system. The complete removal rates of added ¹⁵N increased by 17.6% and 10.2% for SMFC-c and plant, respectively, when compared with control at the end of experiment. The electrochemical/heterotrophic and aerobic denitrification on cathodes mainly drove the higher reduction of NO₃^- in SMFC-c and plant, respectively. The coexistence of electrogenesis and plants further increased the complete removal of NO₃^- with a rate of 23.1%. The heterotrophic and aerobic denitrifications were simultaneously promoted with a highest abundance of Flavobacterium, Bacillus, Geobacter, Pseudomonas, Rhodobacter, and Arenimonas on the cathode.

Sulfur and iron cycles promoted nitrogen and phosphorus removal in electrochemically assisted vertical flow constructed wetland treating wastewater treatment plant effluent with high S/N ratio

Phosphate (PO₄^3--P) and nitrate (NO₃^--N) in the effluent of wastewater treatment plants are the predominant sources of eutrophication. In this study, a bench-scale electrochemically assisted vertical flow constructed wetland (E-VFCW) was developed, which exhibited favorable PO₄^3--P (89.7-99.4%), NO₃^--N (82.7-99.6%), and TN (51.9-93.7%) removal efficiency in tertiary wastewater treatment. In addition, little N₂O accumulation (0.32-2.19% of △NO₃^--N) was observed. The study further elucidated that PO₄^3--P was removed mainly in the anode chamber by co-precipitation (Fe⁽ⁿ⁺⁾OH-PO₄) and adsorption (FeOOH-PO₄) pathways. Multi-pathway of NO₃^--N reduction was proposed, with 13.9-30.2% of NO₃^--N predominantly eliminated in the anode chamber by ferrous-dependent NO₃^--N reduction bacteria. In the cathode chamber, electrons storage and resupply modes during S cycle exerted crucial roles in NO₃^--N reduction, which enhanced the resilience capabilities of the E-VFCW to shock loadings. Stoichiometric analysis revealed that 3.3-6.6 mmol e^-/cycle were stored in the form of S⁰, FeS, and FeS₂ in the E-VFCW under longer HRT or higher current density. However, the deposited S resupplied 19.6% and 28.3% of electrons for NO₃^--N reduction under shorter HRT (1 h) or lower current density (0.01 mA cm^-2). Moreover, ferrous-driven NO₃^--N-reducing or DNRA bacteria also promoted NO₃^--N elimination in the cathode chamber. These findings provide new insight into the coupling interactions among S, Fe and H cycles, as well as N and P transformations in electrochemically assisted NO₃^--N reduction systems.

Biokinetics of microbial consortia using biogenic sulfur as a novel electron donor for sustainable denitrification

In this study, the biokinetics of autotrophic denitrification with biogenic S⁰ (ADBIOS) for the treatment of nitrogen pollution in wastewaters were investigated. The used biogenic S⁰, a by-product of gas desulfurization, was an elemental microcrystalline orthorhombic sulfur with a median size of 4.69 µm and a specific surface area of 3.38 m²/g, which made S⁰ particularly reactive and bioavailable. During denitritation, the biomass enriched on nitrite (NO₂^-) was capable of degrading up to 240 mg/l NO₂^--N with a denitritation activity of 339.5 mg NO₂^--N/g VSS·d. The use of biogenic S⁰ induced a low NO₂^--N accumulation, hindering the NO₂^--N negative impact on the denitrifying consortia and resulting in a specific denitrification activity of 223.0 mg NO₃^--N/g VSS·d. Besides Thiobacillus being the most abundant genus, Moheibacter and Thermomonas were predominantly selected for denitrification and denitritation, respectively.

Simulated reactive zone with emulsified vegetable oil for the long-term remediation of Cr(VI)-contaminated aquifer: dynamic evolution of geological parameters and groundwater microbial community

Cr(VI), which is highly toxic and soluble, is one of the most challenging groundwater contaminants. Previous work has indicated that emulsified vegetable oil (EVO) is an effective in situ amendment for removing Cr(VI) from groundwater. However, the spatial and temporal changes in geological parameters and microbial community structures throughout the remediation period are poorly understood. In this study, a large laboratory-scale sand-packed chamber (reactive zone of 100 × 50 × 30 cm) was used to simulate the bioremediation of Cr(VI)-contaminated aquifer by EVO over a 512-day period. Various geological parameters and microbial communities were monitored during both the establishment and remediation stages. The results indicate that several biogeochemical reactions occurred in a specific sequence following the injection of EVO, creating an acidic and reducing environment. A shift in the community structure and a decrease in the community diversity were observed. The abundance of microbes involved in the degradation of EVO and reduction of electron acceptors significantly increased. Then, the EVO reactive zone was flushed with Cr(VI)-contaminated groundwater. Biogeochemical reactions were inhibited after the inflow of Cr(VI) and subsequently recovered a month later. The pH of the aquifer returned to the initial neutral condition (approximately 7.2). The EVO reactive zone could remediate Cr(VI)-contaminated groundwater at an efficiency exceeding 97% over 480 days. Biogeochemistry played a major role in the early period (0~75 days). In the later period (240~480 days), the remediation of Cr(VI) in the reactive zone depended mostly on bio-reduction by Cr(VI)-reducing bacteria.

Effects of process operating conditions on the autotrophic denitrification of nitrate-contaminated groundwater using bioelectrochemical systems

Nitrates have been detected in groundwater worldwide, and their presence can lead to serious groundwater use limitations, especially because of potential health problems. Amongst different options for their removal, bioelectrochemical systems (BESs) have achieved promising results; in particular, attention has raised on BES-driven autotrophic denitrification processes. In this work, the performance of a microbial electrolysis cell (MEC) for groundwater autotrophic denitrification, is assessed in different conditions of nitrate load, hydraulic retention time (HRT) and process configuration. The system obtained almost complete nitrate removal under all conditions, while nitrite accumulation was recorded at nitrate loads higher than 100mgNO₃^-L^-1. The MEC system achieved, in different tests, a maximum nitrate removal rate of 62.15±3.04gNO₃^--Nm^-3d^-1, while the highest TN removal rate observed was 35.37±1.18gTNm^-3d^-1. Characteristic of this process is a particularly low (in comparison with other reported works) energy consumption: 3.17·10^-3±2.26·10^-3kWh/gNO₃^-N removed and 7.52·10^-2±3.58·10^-2kWhm^-3 treated. The anolyte configuration in closed loop allowed the process to use less clean water, while guaranteeing identical performances as in other conventional configurations.

Performance and microbial communities in a combined bioelectrochemical and sulfur autotrophic denitrification system at low temperature

Combined bioelectrochemical and sulfur autotrophic denitrification (CBSAD) system had proven to be feasible for nitrate removal at low temperature. This system obtained excellent denitrification efficiency 96.55% at 10 ± 2 °C long term operation. Nitrate removal efficiency presented increased tendency with applied current increased from 50 to 200 mA and then decreased when the applied current was further increased to 300 mA. The CBSAD system owned the most abundant and rich communities at current 200 mA, and the community structures of the microbial samples at different current conditions were clearly different from each other. Phyla Firmicutes, Proteobacteria and classes Epsilonproteobacteria, Gammaproteobacteria, Betaproteobacteria, Clostridia dominated in all the communities in the system. The largest genus at current 50 mA was Arcobacter, whereas Pseudomonas was the most dominant genus at current 100-300 mA condition, suggesting that high current changed the bacterial structure in this CBSAD reactor.

High-throughput sequencing analysis of bacterial community spatiotemporal distribution in response to clogging in vertical flow constructed wetlands

The aim of this study was to characterize bacterial communities in vertical flow constructed wetlands (VFCWs) using Illumina high-throughput sequencing. The bacterial communities developed lower richness and diversity in response to clogging. Bacterial diversity did not overtly decrease with depth. A variety of bacterial phyla were found in VFCWs' bacterial communities, including Bacteroidetes, Actinobacteria and Acidobacteria, among which Proteobacteria was dominant. At the genus level, a spatiotemporal variation was illustrated in the diversity and structure of bacterial communities. Clustering analysis of bacterial composition in the operational taxonomic units (OTUs) at the phylum and genus levels had a consistent trend, namely, that bacterial communities were more similar at similar column depths.

Bacterial community and nitrate removal by simultaneous heterotrophic and autotrophic denitrification in a bioelectrochemically-assisted constructed wetland

To enhance nitrate removal in constructed wetlands (CWs), a bioelectrochemically-assisted CW (BECW) integrating a three-dimensional biofilm-electrode reactor (3D-BER) into the CW was evaluated for the effectiveness of combined autotrophic and heterotrophic denitrification in the presence of organic matter and applied current. The effects of COD/N ratios on nitrate removal were investigated, and the bacterial communities in the granular active carbon (GAC) and graphite felt (GF) in the reactor's cathode region were compared. The highest NO₃^--N and TN removal efficiencies of 91.3±7.2% and 68.8±7.9% were obtained at the COD/N ratio of 5. According to the results of high-throughput sequencing analysis, sample GAC was enriched with a high abundance of Pseudomonas (17.29%) capable of autotrophic and heterotrophic denitrification, whereas autotrophic bacteria Thiobacillus (43.94%) was predominant in sample GF. The synergy between heterotrophic and autotrophic denitrification bacteria is believed to cause the high and stable nitrogen removal performance.

Performance and microbial community dynamics of electricity-assisted sequencing batch reactor (SBR) for treatment of saline petrochemical wastewater

High-salinity wastewater is often difficult to treat by common biological technologies due to salinity stress on the bacterial community. Electricity-assisted anaerobic technologies have significantly enhanced the treatment performance by alleviating the impact of salinity stress on the bacterial community, but electricity-assisted aerobic technologies have less been reported. Herein, a novel bio-electrochemistry system has been designed and operated in which a pair of stainless iron mesh-graphite plate electrodes were installed into a sequencing batch reactor (SBR, designated as S1) to strengthen the performance of saline petrochemical wastewater under aerobic conditions. The removal efficiency of phenol and chemical oxygen demand (COD) in S1 were 94.1 and 91.2%, respectively, on day 45, which was clearly higher than the removal efficiency of a single SBR (S2) and an electrochemical reactor (S3), indicating that a coupling effect existed between the electrochemical process and biodegradation. A certain amount of salinity (≤8000 mg/L) could enhance the treatment performance in S1 but weaken that in S2. Illumina sequencing revealed that microbial communities in S1 on days 45 and 91 were richer and more diverse than in S2, which suggests that electrical stimulation could enhance the diversity and richness of the microbial community, and reduce the negative effect of salinity on the microorganisms and enrich some salt-adapted microorganisms, thus improve the ability of S1 to respond to salinity stress. This novel bio-electrochemistry system was shown to be an alternative technology for the high saline petrochemical wastewater.