Viral community distribution, assembly mechanism, and associated hosts in an industrial park wastewater treatment plant.

Viruses manipulate bacterial community composition and impact wastewater treatment efficiency. Some viruses pose threats to the environment and human populations through infection. Improving the efficiency of wastewater treatment and ensuring the health of the effluent and receptor pools requires an understanding of how viral communities assemble and interact with hosts in wastewater treatment plants (WWTPs). We used metagenomic analysis to study the distribution, assembly mechanism, and sensitive hosts for the viral communities in raw water, anaerobic tanks, and returned activated sludge units of a large-scale industrial park WWTP. Uroviricota (53.42% ± 0.14%) and Nucleocytoviricota (26.1% ± 0.19%) were dominant in all units. Viral community composition significantly differed between units, as measured by ß diversity (P = 0.005). Compared to raw water, the relative viral abundance decreased by 29.8% in the anaerobic tank but increased by 9.9% in the activated sludge. Viral community assembly in raw water and anaerobic tanks was predominantly driven by deterministic processes (MST <0.5) versus stochastic processes (MST >0.5) in the activated sludge, indicating that differences in diffusion limits may fundamentally alter the assembly mechanisms of viral communities between the solid and liquid-phase environments. Acidobacteria was identified as the sensitive host contributing to viral abundance, exhibiting strong interactions and a mutual dependence (degree = 59). These results demonstrate the occurrence and prevalence of viruses in WWTPs, their different assembly mechanism, and sensitive hosts. These observations require further study of the mechanisms of viral community succession, ecological function, and roles in the successive wastewater treatment units.

Variations in antibiotic resistance genes during long-term operation of an upflow anaerobic sludge blanket reactor.

Antibiotic resistance genes (ARGs) have been widely detected in the environment. Anaerobic digestion (AD) has the potential ability to remove ARGs, and a comprehensive study is needed on the variations in ARGs during AD. In this study, variations in antibiotic resistance genes (ARGs) and microbial communities were investigated during the long-term operation of an upflow anaerobic sludge blanket (UASB) reactor. An antibiotic mixture of erythromycin, sulfamethoxazole and tetracycline was added to the UASB influent and the operation period was 360 days. The abundances of 11 ARGs and class 1 integron-integrase gene were detected in the UASB reactor, and the correlation between the ARGs and the microbial community was analyzed. The composition of ARGs indicated that the main ARGs in the effluent were sul1, sul2, and sul3, whereas the main ARG in the sludge was tetW. Correlation analysis indicated a negative correlation between microorganisms and ARGs in the UASB. In addition, most of ARGs showed a positive correlation with norank_f_Propionibacteriaceae and Clostridum_sensu_stricto_6, which were identified as potential hosts. These findings may help develop a feasible strategy for removing ARGs from aquatic environments during anaerobic digestion.

A landfill serves as a critical source of microplastic pollution and harbors diverse plastic biodegradation microbial species and enzymes: Study in large-scale landfills, China.

Microplastics (MPs) are emerging pollutants. Landfills store up to 42% of worldwide plastic waste and serve as an important source of MPs. However, the study of MPs distribution and the plastic biodegradation potential in landfills is limited. In this study, the distribution of abundance, size, morphology and polymer type of MPs and plastics biodegradation species in refuse samples along landfill depths were extensively investigated within a large-scale landfill in Shenzhen, China. In addition, plastics biodegradation enzymes were evaluated in seven Chinese large-scale landfills leachate. MPs distribution pattern was investigated in all refuse samples. The abundance of MPs in refuse samples varied between 81 and 133 items/g. The size of MPs in all samples varied between 0.03 and 5 mm, and the average sizes were 1.2 mm ± 0.1 mm. The main morphology and polymer type were fragments and cellophane, respectively. Landfill depth was significantly negatively correlated with the relative abundance of MPs size 1-5 mm (p < 0.05) and was positively correlated with the relative abundance of MPs size < 0.2 mm (p < 0.05), suggesting that plastics were broken down during municipal solid waste decomposition. The multiple regression on matrices analysis further showed the landfill depths and plastic morphology significantly impact the MPs distribution. The strains, Lysinibacillus massiliensis (with relative abundance of 1.8%) for low-density polyethylene and polystyrene biodegradation, and Pseudomonas stutzeri (0.1%) for low density polythene and polypropylene biodegradation, were detected on the plastic surface with high relative abundance. Furthermore, 75 plastic degradation species and their associated 31 enzymes (breakdown 24 plastics) were discovered in seven landfills leachate samples.

Rapid simultaneous removal of nitrogen and phosphorous by a novel isolated Pseudomonas mendocina SCZ-2.

Nitrogen (N) and phosphorous (P) removal by a single bacterium could improve the biological reaction efficiency and reduce the operating cost and complexity in wastewater treatment plants (WWTPs). Here, an isolated strain was identified as Pseudomonas mendocina SCZ-2 and showed high performance of heterotrophic nitrification (HN) and aerobic denitrification (AD) without intermediate accumulation. During the AD process, the nitrate removal efficiency and rate reached a maximum of 100% and 47.70 mg/L/h, respectively, under optimal conditions of sodium citrate as carbon source, a carbon-to-nitrogen ratio of 10, a temperature of 35 °C, and shaking a speed of 200 rpm. Most importantly, the strain SCZ-2 could rapidly and simultaneously eliminate N and P with maximum NH4+-N, NO3--N, NO2--N, and PO43--P removal rates of 14.38, 17.77, 20.13 mg N/L/h, and 2.93 mg P/L/h, respectively. Both the N and P degradation curves matched well with the modified Gompertz model. Moreover, the amplification results of functional genes, whole genome sequencing, and enzyme activity tests provided theoretical support for simultaneous N and P removal pathways. This study deepens our understanding of the role of HN-AD bacteria and provides more options for simultaneous N and P removal from actual sewage.

Optimization of Fe/Ni organic frameworks with core-shell structures for efficient visible-light-driven reduction of carbon dioxide to carbon monoxide.

To address CO2 emissions caused by the overuse of fossil fuels, photocatalytic CO2 reduction from metal-organic frameworks (MOFs) to valuable chemicals is critical for energy conversion and storage. Core-shell MOFs improve interfacial interactions, increasing the number of active sites in the catalyst, thereby improving the photocatalytic reduction. In this work, the catalytic performance of Fe/Ni-MOFs toward photocatalytic CO2 reduction was improved using a bimetallic strategy. We successfully synthesized a series of Fe/Ni-MOFs with a core-shell structure using a single-step approach combined with hydrothermal synthesis. By altering the synthesis conditions of the bimetallic organic skeleton and contrasting it with a single MOF, we successfully synthesized Fe/Ni-T120 through an efficient photocatalytic reduction of CO2. The results of photocatalytic CO2 reduction experiments indicated that upon using [Ru(bpy)3]Cl2·6H2O as a photosensitizer and triethanolamine (TEOA) and acetonitrile (MeCN) as sacrificial agents, the CO evolution rate of Fe/Ni-T120 reached 9.74 mmol g-1 h-1 and the CO2 to CO selectivity reached up to 92.1%. Additionally, Fe/Ni-T120 has a broad response range to visible light, a high photocurrent intensity, good chemical stability, and strong photocatalytic efficiency, even after repeated cycles. This study proposes a straightforward method for producing adaptable and stable MOFs for effective photocatalytic CO2 reduction that is driven by visible light.

Viral community in landfill leachate: Occurrence, bacterial hosts, mediation antibiotic resistance gene dissemination, and function in municipal solid waste decomposition.

A municipal solid waste (MSW) landfill is a significant source of antibiotic resistance, pathogens and viruses and also a habitat for microbial consortia that perform MSW decomposition. Viruses are of great significance in ecological interactions such as MSW decomposition and antibiotic resistance gene (ARG) transmission. In this study, the viral community structure and the associated driver, the linkage of viruses and their bacterial hosts, the virus-associated ARG dissemination and virtual community function on MSW decomposition were investigated in landfill leachate from seven cities, China. The seven cities include four megacities, two large-scale cities and one small-scale city, representing the leachate characters of China. The results showed that the leachates were dominated by the phage families Siphoviridae, Myoviridae and Podoviridae (91.7 ± 3.6) %. Their putative hosts were the important MSW decomposers Lactobacillus, Pseudomonas, Clostridium, Proteiniphilum, and Bacteroides. The structure of the viral community was significantly affected by pH (P = 0.007, analyzed by RDA) and the bacterial community (R = 0.83, P < 0.001, analyzed by Mantel test). The relative abundance of ARGs showed a strong correlation (R > 0.8, P < 0.01) with viral family, suggesting that viruses play an important role in ARGs dissemination. Phage regulate bacterial population abundance through top-down effects, thus participating in MSW decomposition. These results demonstrate that viral community are involve in ARGs transmission and dissemination and mediate MSW decomposition in landfill.

Simultaneous recovery of nutrients and improving the biodegradability of waste algae hydrothermal liquid.

The ever-increasing algae biomass due to eutrophication brings an enormous destruction and potential threat to the ecosystem. Hydrothermal carbonization (HTC) is a potential means converting algae to value added products such as sustainable bioenergy and biomaterials. However, the waste aqueous phase (AP) produced during the HTC of algae biomass needs to be treated carefully in case of the second pollution to environment. In this study, a model microbe (E. coli) was adopted for the microbial pretreatment of AP, by which the bioavailability of AP could be improved, and the nutrients could be reclaimed though struvite precipitation. Three-dimensional fluorescence spectra and GC-MS results illustrated that E. coli pretreatment could convert a large number of organic nitrogenous compounds to ammonia nitrogen by degrading aromatic protein substances and deaminating nitrogenous heterocyclic compounds. Afterwards, a serious of characterizations confirmed that 81.13% of ammonia nitrogen could be recovered as struvite though precipitation. Life cycle assessment indicates the cost of the two-step treatment process was much lower than that of conventional wastewater treatment processes, and is beneficial to environment. This work provides an environment-friendly strategy for the comprehensive utilization of algae, which may contribute to alleviating the algal disasters and bring certain economic benefits though algal treatment.

Unveiling the chemotactic response and mechanism of Shewanella oneidensis MR-1 to nitrobenzene.

Bioreduction by electroactive bacteria (EAB) is considered as a potential and cost-effective approach for the removal of nitroaromatic compounds (NACs). However, little is known about how the widespread EAB sense and respond to slightly soluble NACs in aquatic environments. Here, the chemotactic behaviors of Shewanella oneidensis MR-1, a model EAB, toward several NACs were examined and their underlying molecular mechanism was elucidated. S. oneidensis MR-1 was found to exhibit a strong chemotactic response to nitrobenzene (NB), but not to other selected NACs under aerobic conditions. To sense NB, this bacterium requires both the histidine kinase (CheA-3)-involved chemotactic signal transduction pathway and an inner-membrane c-type cytochrome CymA. Such a chemotactic response is mediated by an energy taxis mechanism. Additionally, external riboflavin was shown to greatly enhance the Shewanella taxis toward NB, implying a feasible way to increase the bioavailability of NACs. The present study deepens our understanding of the role of microbial chemotaxis in the removal of NACs and provides more options for the bioremediation of NAC-contaminated sites.

Effect of antibiotic mixtures on the characteristics of soluble microbial products and microbial communities in upflow anaerobic sludge blanket.

Two upflow anaerobic sludge blanket reactors (UASBs) were used to investigate the effects of three antibiotic mixtures (erythromycin, sulfamethoxazole, and tetracycline) on reactor performance, soluble microbial products (SMPs) composition and microbial community. One reactor (UASBantibiotics) was fed with antibiotic mixtures, whereas another reactor (UASBcontrol) was used as a control without the addition of antibiotic mixtures. Compared with those in UASBcontrol, UASBantibiotics show lower chemical oxygen demand removal efficiency and biogas content. A higher removal efficiency of antibiotic mixtures was obtained in first few stages in UASBantibiotics. The SMPs composition of effluent from the two reactors did not differ significantly, and the main components were protein-like substances, which produced higher fluorescence intensity in UASBantibiotics. Gas chromatography-mass spectrometry analysis revealed that the main compounds identified as SMPs (<580 Da) were alkanes, aromatics and esters, with only 20% similarity of SMPs between UASBantibiotics and UASBcontrol. Antibiotics had a significant effect on the microbial community structure. Notably, in UASBcontrol, hydrogenotrophic methanogens, key microorganisms in anaerobic digestion, had an obvious advantage at all stages compared with UASBantibiotics, whereas acetoclastic methanogen exhibited the opposite pattern. The above results demonstrated that antibiotic mixtures influenced the effluent quality during anaerobic treatment of synthetic wastewater, resulting in changes in the microbial community structure. This study clarified the effect of antibiotic mixtures on the operation of UASBs. It could contribute to identifying potential strategies for improving effluent quality in anaerobic treatment.

Efficient Photocatalytic Reduction of CO2 to CO Using NiFe2O4@N/C/SnO2 Derived from FeNi Metal-Organic Framework.

Use of light is considered an effective approach to convert CO2 into usable chemical energy. In the present study, an iron- and nickel-containing bimetallic metal-organic framework (MOF) was synthesized via a simple solvothermal route. SnO2 was then composited with the said MOF, and the obtained material was calcined and annealed to fabricate a series of nanophotocatalysts. The annealed sample displayed superior photocatalytic activity to the calcined sample, possibly due to the carbon-nitrogen layer formed after annealing mediating the charge-transfer process. The results of photocatalytic experiments indicated that using [Ru(bpy)3]Cl2·6H2O as a photosensitizer and triethanolamine (TEOA) and acetonitrile (MeCN) as sacrificial agents, the catalyst sample was annealed at 450 °C (NiFe2O4@N/C/SnO2-450) to afford the highest CO yield from CO2 (2057.41 µmol g-1 h-1). The increase in the photocatalytic ability of the nanocomposites is basically attributed to multiple synergistic effects between NiFe2O4 and SnO2, which reduce the recombination probability of the photo-induced electrons and holes. Ultimately, a photocatalytic reaction mechanism is proposed for NiFe2O4@N/C/SnO2 in the reduction of CO2.

Cobalt-based metal-organic frameworks for the photocatalytic reduction of carbon dioxide.

Metal-organic frameworks (MOFs) are porous materials composed of metal centers and organic connectors. They are formed by complexation reactions and exhibit characteristics of both polymers and coordination compounds. They exhibit numerous advantageous features, including a large specific surface area, adjustable pore size/shape, and modifiable pore wall functional groups. Consequently, MOFs have been extensively applied in the photocatalytic reduction of carbon dioxide (CO2). Despite considerable research on cobalt-based MOFs, the photocatalytic reduction of CO2 in the presence of these materials remains challenging. The present review summarizes the current studies concerning the utilization of cobalt-based MOFs in the photocatalytic reduction of CO2. Additionally, approaches used to enhance the catalytic reduction performance are evaluated and the challenges associated with Co-based MOFs are discussed.

Correlating the chemical properties and bioavailability of dissolved organic matter released from hydrochar of walnut shells.

Large amounts of lignocellulosic biomass are discarded, whereas the carbon source of sewage is deficient. This situation greatly impairs the efficiency of wastewater treatment. To address this concern, we evaluate the feasibility of using hydrochar as a potential carbon source by systematically investigating the effects of hydrothermal carbonization (HTC) conditions on the composition, content, and chemical structure of dissolved organic matter (DOM) released from hydrochar. Results show that the most important factor that affects the properties of hydrochar and DOM is temperature, followed by heating rate. Under optimal HTC conditions, the growth of Bacillus subtilis increased by 18.32% in hydrochar aqueous solution in comparison with the 6.64% growth of the untreated biomass group. Excitation emission matrix-parallel factor analysis and UV-vis analyses confirm that the DOM released by hydrochar produced at a low temperature mainly contains protein substances, which promote the growth of microorganisms. The DOM released by hydrochar at a high temperature mainly contains humic substances with an aromatic structure; such substances are toxic to microorganisms. This study demonstrates that hydrochar obtained under optimized conditions can be a potential carbon source of wastewater treatment plants.

Single-Atom Gadolinium Anchored on Graphene Quantum Dots as a Magnetic Resonance Signal Amplifier.

A single-atom metal doped on carbonaceous nanomaterials has attracted increasing attention due to its potential applications as high-performance catalysts. However, few studies focus on the applications of such nanomaterials as nanotheranostics for simultaneous bioimaging and cancer therapy. Herein, it is pioneeringly demonstrated that the single-atom Gd anchored onto graphene quantum dots (SAGd-GQDs), with dendrite-like morphology, was successfully prepared. More importantly, the as-fabricated SAGd-GQDs exhibits a robustly enhanced longitudinal relaxivity (r1 = 86.08 mM-1 s-1) at a low Gd3+ concentration of 2 µmol kg-1, which is 25 times higher than the commercial Gd-DTPA (r1 = 3.44 mM-1 s-1). In vitro and in vivo studies suggest that the obtained SAGd-GQDs is a highly potent and contrast agent to obtain high-definition MRI, thereby opening up more opportunities for future precise clinical theranostics.

Adsorption characteristics and mechanism of p-nitrophenol by pine sawdust biochar samples produced at different pyrolysis temperatures.

Biochar is becoming a low-cost substitute of activated carbon for the removal of multiple contaminants. In this study, five biochar samples derived from pine sawdust were produced at different pyrolysis temperatures (300 °C-700 °C) and used adsorbents to remove p-nitrophenol from water. Results indicate that, as the pyrolysis temperature increases, the surface structure of biochar grows in complexity, biochar's aromaticity and number of functional group decrease, and this material's polarity increases. Biochar's physiochemical characteristics and dosage, as well as solution's pH and environmental temperature significantly influence the p-nitrophenol adsorption behavior of biochar. p-nitrophenol adsorption onto biochar proved to be an endothermic and spontaneous process; furthermore, a greater energy exchange was observed to take place when biochar samples prepared at high temperatures were utilized. The adsorption mechanism includes physical adsorption and chemisorption, whereas its rate is mainly affected by intra-particle diffusion. Notably, in biochar samples prepared at low temperature, adsorption is mainly driven by electrostatic interactions, whereas, in their high-temperature counterparts, p-nitrophenol adsorption is driven also by hydrogen bonding and π-π interactions involving functional groups on the biochar surface.

Biosynthesis of Ag2S/TiO2 nanotubes nanocomposites by Shewanella oneidensis MR-1 for the catalytic degradation of 4-nitrophenol.

Biosynthesized nanocomposites are attracting growing interests because they are environmentally friendly. Ag2S nanoparticles (Ag2S NPs) are deposited in situ on the surfaces of TiO2 nanotubes (TNTs) via Shewanella oneidensis MR-1 to form Ag2S/TNT nanocomposites. The prepared Ag2S/TNTs nanocomposites are characterized using high-resolution transmission electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, and energy-dispersive X-ray spectroscopy. The results show that Ag2S NPs smaller than 8 nm are successfully synthesized and fabricated on the TNT surfaces with relatively uniform distribution. The catalytic performance of the Ag2S/TNT nanocomposites is evaluated for catalytic reduction in the presence of NaBH4 and the photocatalytic degradation of 4-nitrophenol (4-NP) under visible light. The Ag2S/TNT nanocomposites show excellent catalytic activity and good stability in the 4-NP reduction process. The 4-NP degradation ratio reaches 98.3% in 50 min, and 87% conversion was achieved after eight cycles. The Ag2S/TNT nanocomposites also exhibit excellent photocatalytic activity for 4-NP at a rate of 0.69 h-1, and the complete degradation of 4-NP was observed within 5 h. Therefore, this study offers an environmentally friendly approach to synthesize nanocomposites for practical applications.

Dual application of Shewanella oneidensis MR-1 in green biosynthesis of Pd nanoparticles supported on TiO2 nanotubes and assisted photocatalytic degradation of methylene blue.

Biosynthesised nanocomposites have attracted growing interests attributed to their 'green' synthesis nature in recent years. Shewanella oneidensis MR-1, a dissimilatory metal-reducing bacterium, was used to reduce palladium (II) nitrate to palladium (0) nanoparticles (Pd NPs) under anaerobic conditions, resulting in the in situ formation of Pd NPs immobilised on TiO2 nanotubes (TNTs) (Pd/TNTs nanocomposites). The Pd/TNTs nanocomposites were characterised by transmission electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, energy dispersive X-ray, and electron spin resonance, respectively. The results indicated that Pd NPs are successfully grown on the TNTs without aggregation. Photocatalytic degradation of methylene blue (MB) by Pd/TNTs nanocomposites under simulated sunlight was also investigated. Pd/TNTs nanocomposites had photocatalytic efficiency superior to that of single TiO2 nanomaterials. The photocatalytic activity of Pd/TNTs nanocomposites can be enhanced by S. oneidensis MR-1. The results showed that after only 10 min, the degradation ratio of MB reached 98.7% by Pd/TNTs nanocomposites when simultaneously assisted with S. oneidensis MR-1.

Taxonomic structure and function of seed-inhabiting bacterial microbiota from common reed (Phragmites australis) and narrowleaf cattail (Typha angustifolia L.).

The present study investigated the endophytic bacterial communities in the seeds of mature, natural common reed (Phragmites australis) and narrowleaf cattail (Typha angustifolia L.). Additionally, seed endophytic bacterial communities were compared with rhizospheric and root endophytic bacterial communities using Illumina-based sequencing. Seed endophytic bacterial communities were dominated by Proteobacteria (reed, 41.24%; cattail, 45.51%), followed by Bacteroidetes (reed, 12.01%; cattail, 10.41%), Planctomycetes (reed, 10.36%; cattail, 9.09%), Chloroflexi (reed, 8.72%; cattail, 6.45%), Thermotogae (reed, 5.43%; cattail, 6.11%), Tenericutes (reed, 3.63%; cattail, 3.97%) and Spirochaetes (reed, 3.32%; cattail, 3.90%). The dominant genera were Desulfobacter (reed, 8.02%; cattail, 8.96%), Geobacter (reed, 2.74%; cattail, 2.81%), Thiobacillus (reed, 2.71%; cattail, 2.41%), Sulfurimonas (reed, 2.47%; cattail, 2.31%), Methyloversatilis (reed, 2.29%; cattail, 2.05%) and Dechloromonas (reed, 1.13%; cattail, 1.48%). Obvious distinctions were observed among the respective rhizospheric, root endophytic and seed endophytic bacterial communities. Principal coordinate analysis with weighted UniFrac distance and the heat map analysis demonstrated that the seed endophytic bacterial communities were distinct assemblages rather than a subgroup of rhizobacterial communities or root endophytic bacterial communities. These results provide new information regarding endophytic bacteria associated with seeds of wetland plants and demonstrate a variety of genera that have a strong potential to enhance phytoremediation in the wetland ecosystem.

Preparation of a synthetic seed for the common reed harboring an endophytic bacterium promoting seedling growth under cadmium stress.

Bacterial seed endophytes can facilitate germination and early plant development. Therefore, the introduction of seed-borne endophytes may improve selected plant characteristics across generations. In this study, regenerated plantlets of common reed (Phragmites australis) were inoculated with activated sludge to obtain a specific functional endophytic bacterium. Denaturing gradient gel electrophoresis demonstrated that abundant endophytic bacteria could be enriched in the roots. A siderophore-producing endophytic bacterium was isolated from the roots and identified as Herbaspirillum frisingense RE3-3 based on 16S rRNA sequences. This endophyte secrets indole-3-acetic acid to promote plant growth and cadmium-binding siderophores. The strain was successfully colonized into synthetic seeds using bacterium-propagule co-cultivation and transmitted to regenerated seedlings. These seedlings exhibited improved growth under cadmium stress. This study identifies Herbaspirillum colonization and transmission as a potentially valuable strategy to improve the phytotoxin resistance of reeds for constructed wetlands.

Bioreductive deposition of highly dispersed Ag nanoparticles on carbon nanotubes with enhanced catalytic degradation for 4-nitrophenol assisted by Shewanella oneidensis MR-1.

Biogenetic nanomaterials research provides insights and valuable implications for the green synthesis of nanomaterials and auxiliary biodegradation behaviors. Ag nanoparticles (Ag NPs) fabricated on multiwalled carbon nanotubes (MWNTs) (Ag/MWNTs nanocomposites) are prepared in situ assisted by Shewanella oneidensis MR-1 (S. oneidensis MR-1) that provide respiratory pathway to transmit electrons. The Ag/MWNTs nanocomposites are characterized by a scanning electron microscopy (SEM), an energy dispersive X-ray (EDX), a transmission electron microscopy (TEM), an X-ray diffraction (XRD), and an X-ray photoelectron spectroscopy (XPS), respectively. The results indicate that Ag NPs (less than 20 nm in diameter) are successfully formed on the MWNTs without an aggregation. In application studies, the catalytic activities of the Ag/MWNTs nanocomposites towards the reduction of 4-nitrophenol (4-NP) by sodium borohydride (NaBH4) are tracked by a UV-visible spectroscopy. It is suggested that the Ag/MWNTs nanocomposites exhibit a satisfactory catalytic efficiency, which might be ascribed to the high dispersion of Ag NPs on MWNT surfaces. Moreover, the final results indicate that only after 10 min of reaction, the catalytic degradation ratio of 4-NP reaches 94.0% in the presence of Ag/MWNTs nanocomposites assisted by S. oneidensis MR-1.

Electricity generation from mixed volatile fatty acids using microbial fuel cells.

Fermentative hydrogen production, as a process for clean energy recovery from organic wastewater, is limited by its low hydrogen yield due to incomplete conversion of substrates, with most of the fermentation products being volatile fatty acids (VFAs). Thus, further recovery of the energy from VFAs is expected. In this work, microbial fuel cell (MFC) was applied to recover energy in the form of electricity from mixed VFAs of acetate, propionate, and butyrate. Response surface methodology was adopted to investigate the relative contribution and possible interactions of the three components of VFAs. A stable electricity generation was demonstrated in MFCs after the enrichment of electrochemically active bacteria. Analysis showed that power density was more sensitive to the composition of mixed VFAs than coulombic efficiency. The electricity generation could mainly be attributed to the portion of acetate and propionate. However, the two components showed an antagonistic effect when propionate exceeded 19%, causing a decrease in coulombic efficiency. Butyrate was found to exert a negative impact on both power density and coulombic efficiency. Denaturing gradient gel electrophoresis profiles revealed the enrichment of electrochemically active bacteria from the inoculum sludge. Proteobacteria (Beta-, Delta-) and Bacteroidetes were predominant in all VFA-fed MFCs. Shifts in bacterial community structures were observed when different compositions of VFA mixtures were used as the electron donor. The overall electron recovery efficiency may be increased from 15.7% to 27.4% if fermentative hydrogen production and MFC processes are integrated.