Enhanced degradation of pyrene and phenanthrene in sediments through synergistic interactions between microbial fuel cells and submerged macrophyte Vallisneria spiralis

Purpose Submerged macrophyte Vallisneria spiralis and sediment microbial fuel cell (SMFC) systems are cost-effective methods for the remediation of polycyclic aromatic hydrocarbon (PAH)-polluted sediments. This study evaluates whether the combination of these two ecological approaches could further improve the removal efficiency of PAHs from sediments and investigates the possible mechanisms of removal. Materials and methods Sediments, macrophytes, electrodes, and plexiglass columns were used to construct an experimental microcosm. A 65-day comparative study was performed with six treatments as follows: SMFC without PAH (SMFC); PAH only (PAH); SMFC with PAH (SMFC-PAH); V. spiralis without PAH (macrophyte); V. spiralis with PAH (macrophyte-PAH); V. spiralis with SMFC and PAH (M-SMFC-PAH). Pyrene and phenanthrene were added to raw sediments to obtain initial PAH concentrations of 10 mgkg(-1) dry sediment. The monitored parameters were sediment oxidation-reduction potential (ORP); low molecular weight organic acids (LMWOAs) and Fe (II) concentrations in pore water; electron acceptor (sulfate and Fe (III)), humic acid (HA), and PAH concentrations in sediments; and plant morphology and root physiology. High-throughput 16S rRNA gene sequencing was also performed to assist mechanistic understanding. Results and discussion The M-SMFC-PAH treatment obtained the highest sediment ORP and PAH removal efficiency. The average ORP level in M-SMFC-PAH was increased by 57.2, 59.1, and 168.4 mV, compared with the SMFC-PAH, macrophyte-PAH, and PAH-only treatments, respectively, with a mean value of 121.7 mV observed during the whole experimental period. The pyrene (phenanthrene) dissipation ratios at the end of the experimental period were 29.1% (35.4%), 45.5% (56.3%), 59.8% (67.3%), and 79.4% (88.2%) for PAH only, SMFC-PAH, macrophyte-PAH, and M-SMFC-PAH treatments, respectively. The highest correlation was observed between PAH concentration and sediment ORP value, in the coupled M-SMFC-PAH system. Conclusions Results suggest that the interactions between the anode and rhizosphere of V. spiralis were synergistic during PAH removal. The coexistence of anodic and rhizospheric oxygen loss in sediments had a synergistic effect on PAH degradation. Plant presence facilitated the electrogenic degradation of PAHs. The inhibited growth of V. spiralis due to PAH toxicity was reduced by electrogenesis, thus facilitating the removal of vegetable PAHs from sediments. Coordinated growth of anaerobic and aerobic PAH degrading bacteria on the anode was a key factor in the optimal removal of PAHs in coupled systems

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 (NO3-)-N-15 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 N-15 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. (c) 2018 The Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences. Published by Elsevier B.V

A comparison of the growth and photosynthetic response of Vallisneria natans (Lour.) Hara to a long-term water depth gradient under flowing and static water

In a mesocosm experiment, the growth and photosynthetic responses of Vallisneria natans (Lour.) Hara was studied monthly in different water depths under flowing and static water. Water depth showed a significant effect on the shoot length, below-ground: above-ground biomass, and total biomass, while water velocity showed only a significant effect on the total biomass. In addition, total biomass and shoot length at 45, 75 and 105 cm was higher in the flowing treatment than that in the static treatment, which suggested that total biomass and shoot length are promoted by water flow to some extent. All of the investigated photosynthetic showed different changes with different months. Water depth exhibited significant effects on the maximum photosynthetic efficiency Fv/Fm, the maximum electron transport rate rETRmax, Chla, Chla + b and Chla/b, while water velocity showed only significant effects on Chla, Chla + b, ETRmax. The rapid light response curves varied differently with the time periods. In October, the time-course of slow chlorophyll a fluorescence induction curves, Fm peak, in the flowing treatment in 45, 75 and 105 cm is higher than that in the static treatment. All the results demonstrated that the differences between flowing and static water resulted in the different life strategy

The physiological response of Arundo donax and characteristics of anodic bacterial community in BE-CW systems: Effects of the applied voltage

The performance of bioelectrochemically assisted constructed wetland systems planted with Arundo donax were evaluated at applied voltages of 1, 2, 3 and 5 V. The RGR and Proline (Pro) results implied a positive response at the proper applied voltage. In the 3-V group, the RGR sharply climbed to a maximum over two stages, and the Pro reached a higher level of 256.25 mu g/g at the end of the first stage without an additional organic carbon source. This result indicated that A. donax was attempting to adapt the 3-V stress via physiological self-regulation and the growth was nearly unaffected. However, in the 5-V group, the great increase in Pro and withering of the aboveground A. donax showed that the voltage stress had become lethal and the plant was not able to endure it through physiological regulation. In addition, Anodic microbial community compositions accumulating on graphite felts were analyzed via high-throughput sequencing. Results showed that there were two clear clusters at different applied voltages. One cluster was assembled from the anodic region of the 0-V and 1-V groups, and the other was collected from the 2-V and 3-V samples. At the phylum level, Proteobacteria, Firmicutes and Bacteroidetes were the most common phyla among the samples. However, at the genus level, the dominant genera varied with the applied voltage. The relative abundance of Desulfovibrio increased with increased applied voltage. The highest total nitrogen removal rate in the 2-V group was closely related to the high abundance of the Acinetobacter genus. Moreover, Exiguobacterium became dominant only in the 5-V sample, suggesting that this genus strongly depended on the interactive environment of exudes from A. donax and applied voltage

Application of dual stable isotopes in investigating the utilization of two wild dominant filamentous algae as food sources for Daphnia magna

In this study, we evaluated the effects of two dominant microfilamentous algae (i.e. Melosira granulata and Oscillatoria sp.), collected from the West Lake, on growth and metabolism of Daphnia magna. Our experiment utilized 13C and 15N dual labeling to calculate the carbon and nitrogen isotopic turnover rates and half-life times in D. magna. The two labeled types of filaments were offered to D. magna as sole food sources or as paired mixtures with the unlabeled Scenedesmus obliquus. Labeled S. obliquus served as the control. Combined results showed that D. magna had a higher grazing rate on Oscillatoria sp. than on M. granulate and a small percentage of unlabeled S. obliquus addition could improve the grazing rate in both filamentous algae, especially for Oscillatoria sp., which had the highest carbon and nitrogen isotopic turnover rates and the lowest half times, even superior to the sole S. obliquus treatment. Our study revealed that D. magna could utilize the two dominant filamentous algae as a food source for their growth and metabolism, and a small percentage addition of S. obliquus could ameliorate the negative impact of these two filamentous algae on D. magna

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&#39;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.</p

High performance of integrated vertical-flow constructed wetland for polishing low C/N ratio river based on a pilot-scale study in Hangzhou, China

We investigated the treatment efficiency of micro-polluted NO3--dominated river water with low C/N ratio by five parallel pilot-scale IVCWs with different plant and substrate collocation. When the mean concentration was 2.24 and 0.193mgL(-1) in influent, IVCWs achieved an average (mass) removal rate of (0.09gm(-2)day(-1)) 46.8% and (0.77gm(-2)day(-1)) 62.3% for TN and TP, respectively, during 1year of operation. Water quality was significantly improved from grade V to meet the criterion of grade IV of surface water. Through the comparison of removal rate by different IVCWs, we found that lack of carbon sources in influent limited the denitrification in the middle and bottom layers (ML, BL) of IVCW. Zeolites deployed in the upper layer (UL) of IVCW reduced the overall N removal efficiency compared with gravels, due to a stronger nitrification but weaker denitrification. Canna indica (C. indica) was superior to Arundo donax (A. donax) and Thalia dealbata (T. dealbata) for N removal in the UL of IVCW due to higher aboveground biomass accumulation and microbial removal during the first 10months. Stronger nitrification and denitrification were simultaneously facilitated near the rhizosphere of C. indica. When entered into Dec., A. donax performed higher N removal efficiency than the other two species. The internal replenishment of peats in the ML as carbon sources significantly improved N and P removal efficiency. Zeolites with stronger capacity of ammonium (NH4+) adsorption was more in favor of anammox in the BL, when compared with roseites, but both of them were not conducive to the growth of denitrifiers. However, the deployment of shale ceramisites obtained an opposite result. Gemmata and Pirellula as anammox bacteria were more enriched in the zeolite layer, whereas some anaerobic denitrifiers (Corynebacterium and Paludibacter) and heterotrophic denitrifiers including Bacillus, Geobacter, Pseudomonas, and Lactococcus were more found in shale ceramisite. Supply of peats as carbon sources in the ML was beneficial for the adhesion of anammox bacteria and denitrifiers in the BL of shale ceramisites. An ideal model composed of C. indica+A. donax (DFU)-gravel (UL)-anthracite+peat (ML)-zeolite+shale ceramsite (BL)-Acorus calamus (UFU) was proposed for treating this type of river water to achieve high efficiency

How Temperature Affects Wastewater Nitrate Removal in a Bioelectrochemically Assisted Constructed Wetland System

A novel bioelectrochemically assisted constructed wetland system (BECW) was investigated using a laboratory-scale experimental apparatus for treating nitrate-contaminated water without an organic carbon source. The BECW was operated at 29 +/- 1 and 18 +/- 1 degrees C, respectively, to explore the effects of temperature on the autotrophic denitrification process. The results showed that higher TN removal efficiency (76.30 +/- 5.08%) was obtained at higher temperature when compared to a lower temperature (48.18 +/- 4.40%). The effluent concentrations of NO2--N and NH4+-N at 18 +/- 1 degrees C were 0.40 +/- 0.11 and 0.50 +/- 0.42 mg N whereas those at 29 +/- 1 degrees C could be neglected. Besides, significant accumulations of NO2--N and NH4+-N were observed in the cathode region at 18 +/- 1 degrees C through quantifying different forms of nitrogen that varied along the flow path

Effects of salinity on the performance of bioflocs with activated sludge as inoculum

This study evaluated the feasibility of domesticating the bioflocs with activated sludge as inoculum at high salinity. By using the gradually increase salinity from 0.2 to 4.0%, the study evaluated the effectiveness of bioflocs in sustaining the water quality of aquaculture, the biofloc morphology characteristics and microbial community structure of bioflocs in order to discover the influence of salinity. From the perspective of sustaining the water quality of bioflocs, the COD removal efficiency dropped sharply from 63.9% to 3.7%, the NO3−-N was maintained below 0.5 mg/L but the NH4+-N exceeded the safety threshold of aquaculture at the salinity of 2.5–4.0%. From the pespective of flocculation of flocs, the biofloc volume index and content were maintained at about 30 ml/g and 7 g/L, while the floc particle size (45–200 um) tended to increase cumulatively, showing good agglomeration, sedimentation and stability. From the pespective of floc microbial community structure, Arenibacter, Thauera, Paracoccus and Denitromonas became the dominant genera with relative abundances of 4.8–7.5%, 4.9–17.1%, 3.0–4.7% and 5.3–14.1% at 3.0–4.0% salinity, respectively, however, the relative abundance of Candidatus Competibacter rapidly decreased from 15.0% to 2.5% with the increasing salinity from 1.0% to 4.0%. Furthermore, Redundancy analysis (RDA) indicated that salinity was a key environmental factor affecting floc community, and Functional Annotation of Prokaryotic Taxa (FAPROTAX) confirmed the promoted flocs denitrification as well as inhibited nitrification and hydrocarbon cycling in higher salinity to some extent. This study demonstrated the feasibility of using freshwater activated sludge as a base nucleus for biofloc formation for salinity up to 2% – 2.5%, which provided a useful reference for improving the taste and nutritional value of fish cultured by Biofloc Technology (BFT)

Enhanced phosphorus reduction in simulated eutrophic water: a comparative study of submerged macrophytes, sediment microbial fuel cells, and their combination

The phosphorus reduction in water column was attempted by integrating sediment microbial fuel cells (SMFCs) with the submerged macrophyte Vallisneria spiralis. A comparative study was conducted to treat simulated water rich in phosphate with a control and three treatments: SMFC alone (SMFC), submerged macrophytes alone (macophyte), and combined macrophytes and fuel cells (M-SMFC). All treatments promoted phosphorus flux from the water column to sediments. Maximum phosphorus reduction was obtained in proportion to the highest stable phosphorus level in sediments in M-SMFC. For the initial phosphate concentrations of 0.2, 1, 2, and 4mg/L, average phosphate values in the overlying water during four phases decreased by 33.3% (25.0%, 8.3%), 30.8% (5.1%, 17.9%), 36.5% (27.8%, 15.7%), and 36.2% (0.7%, 22.1%) for M-SMFC (macrophyte, SMFC), compared with the control. With macrophyte treatment, the obvious phosphorus release from sediments was observed during the declining period. However, such phenomenon was significantly inhibited with M-SMFC. The electrogenesis bacteria achieved stronger phosphorus adsorption and assimilation was significantly enriched on the closed-circuit anodes. The higher abundance of Geobacter and Pseudomonas in M-SMFC might in part explain the highest phosphorus reduction in the water column. M-SMFC treatment could be promising to control the phosphorus in eutrophic water bodies