Effects of water flow on performance of soil microbial fuel cells: Electricity generation, benzo[a]pyrene removal, microbial community and molecular ecological networks.

Soil microbial fuel cells with water flow (W-SMFCs) as a driven force of substrate transport were constructed. Electricity generation, benzo[a]pyrene (BaP) removal, microbial communities and microbial molecular ecological networks were compared between W-SMFCs and their control reactors (without water flow, C-SMFCs) in 240 days of operation. The W-SMFCs started up faster than C-SMFCs (37 days vs. 50 days) and output higher startup voltage (148.45 mV vs. 111.90 mV). The water flow caused higher removal efficiency of BaP at sites >1 cm from the anode (S > 1 cm) than at sites <1 cm from the anode (S < 1 cm) in W-SMFCs, whereas in C-SMFCs, the removal efficiency of BaP at S< 1 cm was higher than that at S> 1 cm. The removal efficiency of BaP at S> 1 cm in W-SMFCs was up to 1.7 times higher than that at S> 1 cm in C-SMFCs on the 91st day. After 240 days of operation, the biodegradation efficiency of absolute BaP amount was 45.95% in W-SMFCs, being 20% higher than that in C-SMFCs (38.17%). Moreover, the water flow caused highly tight interaction among the microbial species, which could be beneficial to BaP biodegradation. Conclusively, the water flow in soil was very beneficial for startup and biodegradation of BaP in SMFCs.

Organic matter composition, BaP biodegradation and microbial communities at sites near and far from the bioanode in a soil microbial fuel cell.

Bioanodes in a soil microbial fuel cell (SMFC) can serve as sustainable electron acceptors in microbial metabolism processes; thus, SMFCs are considered a promising in situ bioremediation technology. Most related studies have focused on the removal efficiency of contaminants. Relatively few efforts have been made to comprehensively investigate the organic matter composition and biodegradation metabolites of organic contaminants and microbial communities at various distances from the bioanode. In this study, the level and composition of dissolved organic matter (DOM), biodegradation metabolites of benzo[a]pyrene (BaP), and microbial communities at two sites with different distances (S1cm and S11cm) to the bioanode were investigated in an SMFC. The consumption efficiency of dissolved organic carbon (RDOC) and removal efficiency of BaP (RBaP) at S1cm were slightly higher than those at S11cm after 100 days (RDOC 47.82 ± 5.77% at S1cm and 44.98 ± 10.76% at S11cm; RBaP 72.52 ± 1.88% at S1cm and 68.50 ± 4.34% at S11cm). More fulvic acid-like components and more low-molecular-weight metabolites (indicating a higher biodegradation degree) of BaP were generated at S1cm than at S11cm. The microbial community structures were similar at the two sites. Electroactive bacteria (EAB) and some polycyclic aromatic hydrocarbon degraders were both enriched at the bioanode. Energy metabolism at the bioanode could be upregulated to generate more adenosine triphosphate (ATP). In conclusion, the bioanode could modulate the metabolic pathways in the adjacent soil by strengthening the contact between the EAB and BaP degraders, and providing more ATP to the BaP degraders.

Electron donating capacities of DOM model compounds and their relationships with chlorine demand, byproduct formation, and other properties in chlorination.

Electron donating capacity (EDC) is a promising parameter to characterize the antioxidant properties and oxidant consumption of dissolved organic matter (DOM). To assess the potential of EDC in rapidly predicting the chlorine demand during chlorination, the EDC values were measured for ten DOM model compounds, including phenol, quinol, resorcinol, vanillin, tannic acid, l-phenylalanine, l-tryptophan, l-tyrosine, l-cysteine, and reduced glutathione. The EDC values varied according to the functional moieties present in the model compounds and the pH. At pH 7.0, the order of EDC values of the ten model compounds was (mol e-/mol C): 0.843 (cysteine) > 0.538 (tyrosine) > 0.522 (tannic acid) > 0.516 (resorcinol) > 0.452 (phenol) ≈ 0.450 (tryptophan) > 0.257 (vanillin) > 0.226 (reduced glutathione) > 0.160 (quinol) > 0.00035 (phenylalanine). The EDC values correlated well (R2 = 0.93) with the 24 h Cl2 demand of the model compounds (except for phenol and tannic acid). By contrast, there was poor correlation between the EDC values and the 24 h formation potentials of chlorination byproducts (trihalomethanes, haloacetic acids and haloacetonitriles). The levels and variation of the EDC values were not significantly correlated with the total organic carbon, specific UV absorbance at 254 nm, or assimilable organic carbon of the model compounds.

Carbon nanomaterial-modified graphite felt as an anode enhanced the power production and polycyclic aromatic hydrocarbon removal in sediment microbial fuel cells.

Sediment microbial fuel cells (SMFCs) can be used to generate electricity and remove organic contaminants. For electricity generation and contaminant removal, the anode material is one of important factors influencing the performance of SMFCs. In this study, graphene (GR), graphene oxide (GO) and carbon nanotubes (CNTs) were applied to modify the graphite felt (GF) anode in SMFCs during 110 d operation. An economical and easy modification method with the carbon nanomaterials was applied. The carbon nanomaterials increased the electrochemically active surface areas and biomass content of the anodes and correspondingly effectively enhanced the generation of electricity and the removal rates of loss on ignition (LOI) and polycyclic aromatic hydrocarbons (phenanthrene and pyrene). During the steady period from 50 d to 110 d, the GO-SMFCs favored the enrichment of EAB and thus output the highest voltages of 30.60-48.61 mV. The GR-SMFCs and GO-SMFCs generated high electric power of approximate 0.98 ± 0.14 kJ and 0.87 ± 0.04 kJ, followed by CNT-SMFCs (0.57 ± 0.06 kJ) and GF-SMFCs (0.49 ± 0.07 kJ) during the 110 d operation. The PAH degradation was not directly related to the electric current in the SMFCs. Near the anodes, the order of the phenanthrene removal rates was CNT-SMFCs (78.1%) > GR-SMFCs (73.0%) ≈ GO-SMFCs (71.2%) > GF-SMFCs (45.6%), and the order of the pyrene removal rates was GO-SMFCs (69.6%) ≈ GR-SMFCs (68.2%) ≈ CNT-SMFCs (66.7%) > GF-SMFCs (42.3%). The three carbon nanomaterials increased the microbial community diversity and slightly changed the microbial community distribution of biofilms on the anodes. Correlation analysis indicated that the degradation of phenanthrene was positively correlated with the abundances of Pseudomonas, Thauera, Diaphorobacter, Tumebacillus and Lysobacter. Pyrene degradation was strongly correlated with LOI degradation.

Metallo-supramolecular complexes from mPEG/PDPA diblock copolymers and their self-assembled strip nanosheets.

Herein we designed and synthesized mPEG/PDPA copolymers containing two 4-([2,2':6',2''-terpyridin]-4'-yl) phenyl (Tpyp) groups at the junction point of the two blocks (mPEG(-b-Tpyp)2-b-PDPA x , x = 23, 33, and 44). Interestingly, after a hierarchical pattern from the coordination of mPEG(-b-Tpyp)2-b-PDPA x with Ru(ii) ions followed by the self-assembly in water, 2D strip nanosheets with a monomolecular layer were obtained. In contrast, mPEG(-b-Tpyp)2-b-PDPA x without coordination self-assembled into spherical micelles in the similar condition. The formation of the rigid and charged ⋯Tpyp-Ru(ii)⋯ chain, the brush-shaped polymer architecture and the presence of the hexafluorophosphate (PF6 -) counterions should be responsible for the unique self-assembly behavior of the metallo-supramolecular complexes. It is expected that the hierarchical self-assembly pattern can provide a new strategy for preparation of self-assemblies with different morphologies.

Increased power production and removal efficiency of polycyclic aromatic hydrocarbons by plant pumps in sediment microbial electrochemical systems: A preliminary study.

The low mass transfer of sediment substrates has limited the efficiency and application of a sediment microbial electrochemical system (SMES) as a power generator and as a practical bioremediation technology. In this study, we designed a new plant-driven SMES (New-PSMES) with a separated sand-filled anode column in order to improve the mass transfer and thereby enhance the microorganism activity, power generation and bioremediation range and efficiency for polycyclic aromatic hydrocarbons (PAHs). Because of the mass flow driven by the plants, the New-PSMESs started up approximately 7 d earlier and produced voltages 30-70 mV higher than the planted SMESs, and had greater enzyme activities and residual organic carbon than the unplanted and planted SMESs. In the New-PSMES, the total mass removal rates of phenanthrene and pyrene were 62.98% and 57.02% after 82 d, and these values were 1.5-2 times higher than those of the unplanted and planted SMESs. The removal of PAHs in the sediment was primarily attributed to nonelectrochemical biodegradation at sites far from the anode and to electrochemical reactions on the anode. The top three most abundant phyla in all samples were Proteobacteria, Chloroflexi, and Bacteroidetes. Aerobic bacteria, such as Nautella, were enriched in the biofilms of the New-PSMESs.

Preliminary study on the dynamics of heavy metals in saline wastewater treated in constructed wetland mesocosms or microcosms filled with porous slag.

This study aims to evaluate the practical potential of using constructed wetlands (CWs) for treating saline wastewater containing various heavy metals. The results demonstrated that CWs growing Canna indica with porous slag as substrate could efficiently remove heavy metals (Cu, Zn, Cd, and Pb) from saline wastewater at an electrical conductivity (EC) of 7 mS/cm, especially under low influent load. Salts with salinity level (characterized as EC) of 30 mS/cm suppressed the removal of some heavy metals, dependent on heavy metal species and their influent concentrations. The presence of salts in CWs can improve the accumulation of Cu, Zn, and Pb in plant tissues as compared to control treatment, irrespective of metal concentrations in solution. The influence of salts on Cd accumulation depended on both salinity levels and Cd concentrations in solution. Although more heavy metals were accumulated in roots than in shoots, the harvesting of aboveground plant materials is still efficient addition for heavy metal removal due to the greater biomass and growth rate of aboveground plant material. Furthermore, replacing all plants instead of preserving roots from harvested plants in CWs over a period of time is essential for heavy metal removal, because the continued accumulation by roots can be inhibited by the increasing accumulated heavy metals from saline wastewater.

Influence of vegetation type and temperature on the performance of constructed wetlands for nutrient removal.

In this study, the influence of vegetation type and environmental temperature on performance of constructed wetlands (CWs) was investigated. Results of vegetation types indicated that the removal of most nutrients in polyculture was greater than those in monoculture and unplanted control. The greatest removal percentages of NH4+-N, total nitrogen (TN) and total phosphorus (TP) in polyculture were 98.7%, 98.5%, and 92.6%, respectively. In experiments of different temperatures, the removal percentages of NH4+-N, NO3--N, TN and TP in all CWs tended to decrease with the decline of temperature. Especially, a sharp decline in the removal percentages of NO3--N (decreased by above 13.8%) and TN (decreased by above 7.9%) of all CWs was observed at low temperature (average temperature of 8.9 °C). Overall, the performance of CWs was obviously influenced by temperature, and the polyculture still showed best performance in the removal of nitrogen when the average temperature dropped to 19.8 °C. Additionally, the variations of urease activities in rhizosphere soil tended to decrease with the decreasing temperature. Overall, a substantial enhancement for nitrogen and TP removal in polyculture (Canna indica + Lythrum salicaria) was observed. In conclusion, CW cultivated with polyculture was a good strategy for enhancing nutrient removal when temperature was above 19.8 °C.

Removal of nutrients in saline wastewater using constructed wetlands: Plant species, influent loads and salinity levels as influencing factors.

This study aims to evaluate how plant species, influent loads and salinity levels affect the removal of nutrients from saline wastewater using constructed wetlands (CWs). CWs planted with Canna indica showed the greatest removal percentages among the four tested species for nitrogen (N) (∼100%) at both low and high influent loads, and ∼100% and 93.8% for phosphorus (P) at low and high influent loads, respectively at an electrical conductivity (EC) of 7 mS/cm (25 °C). The influence of different salinity levels on plant assimilation of N and P varied with their respective concentrations; salinity (e.g., EC at 7, 10 and 15 mS/cm) even enhanced plant absorption of N and P under specific conditions. In conclusion, CWs planted with selected species can be used for the removal of N and P under a range of different salinity levels (e.g., EC at 7, 10 and 15 mS/cm, 25 °C).

Impacts of vegetation and temperature on the treatment of domestic sewage in constructed wetlands incorporated with Ferric-Carbon micro-electrolysis material.

Ferric-Carbon Micro-Electrolysis (Fe/C-M/E) material had been widely used for the pretreatment of wastewater. Therefore, we hypothesized that Fe/C-M/E material could enhance the treatment of domestic sewage when it was integrated into constructed wetlands (CWs). In this study, CWs integrated with Fe/C-M/E material were developed. Druing the experiment of effect of vegetation on the performance of CWs, percentages of NH4+-N, NO3--N, total nitrogen (TN), and Chemical Oxygen Demand (COD) removed in polyculture (W1) were up to 91.8%, 97.0%, 92.3%, and 85.4%, respectively, which were much higher than those in Lythrum salicaria monoculture (W2) and Canna indica monoculture (W3). In the experiment of temperature influences on the removal efficiency of CWs, temperature substantially influenced the performance of CWs. For example, NO3--N removal percentages of W1, W2, and W3 at high temperature (25.5°C and 19.8°C) were relatively stable and greater than 85.4%. At 8.9°C, however, a sharp decline of NO3--N removal percentage was observed in all CWs. Temperature also influenced the Chemical Oxygen Demand (COD) removal and soil microbial activity and biomass. Overall, the polyculture (Lythrum salicaria +Canna indica) showed the best performance during most of the operating time, at an average temperature ≥ 19.8°C, due to the functional complementarity between vegetation. All the CWs consistently achieved high removal efficiency (above 96%) for TP in all experiments, irrespective of vegetation types, phosphorous loadings, and temperatures. In conclusion, polyculture was an attractive solution for the treatment of domestic sewage during most of the operating time (average temperature ≥ 19.8°C). Furthermore, CWs with Fe/C-M/E material were ideally suitable for domestic sewage treatment, especially for TP removal.