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The widespread use of renewable energy remains a challenging and complex multidisciplinary problem. Developing alternatives using new technology such as nanotechnology is necessary to increase renewable energy’s scalability. Microbial fuel cells (MFCs) combined with nanotechnology can improve bioelectricity generation during wastewater treatment. In this study, hollow carbon nanofibers (H-CNF) were decorated with manganese oxide (MnO2) via a simple chemical reduction method. MnO2-decorated H-CNF prepared with varying concentrations of manganese precursor (MnO2@H-CNF) were characterized via different spectroscopic and microscopic techniques. The cathode catalyst performance of the MnO2@H-CNF was investigated in an //-type constructed MFC system using Shewanella Oneidensis MR1. The MnO2@H-CNF-1 in the assembled MFC displayed excellent power density of 25.7 mW/m2, which is higher than pure H-CNF (8.66 mW/m2), carbon cloth (5.10 mW/m2), and MnO2@H-CNF-3 (16 mW/m2). The maximum power generated in the MFC coupled with MnO2@H-CNF as a cathode catalyst may have been due to the synergistic effect of the MnO2@H-CNF, which increased the electric conductivity and catalytic activity in the MFC’s cathode chamber. These results demonstrate that the developed MnO2@H-CNF cathode catalyst could improve the MFC’s performance and reduce the operational costs of practical applications.

Many design variables and constraints, such as operating temperature and pressure of existing batch distillation or operating temperature of existing cooling and heating media, must be verified and satisfied during design and optimization when an existing batch distillation column is utilized for new mixture. The convergence of batch distillation simulation is sensitive with the initial values of these variables. Thus, a new systematic methodology was proposed to design and optimize separation of a new mixture using an existing batch column. The systematic methodology was based on an industrial case study of dichlorodifluoromethane (R-12) reclamation from a waste refrigerant mixture. Based on a comparison of the Pxy diagram with experimental data, “REFerence fluid PROPerties” was selected as the thermodynamic model. After design and optimization using shortcut and rigorous methodologies, the existing batch distillation unit was operated to validate the proposed methodology. The experimented performance match well with the simulated results. Under the optimized operating condition, complete purification of R-12 (purity=99.5%) was achieved experimentally after 28.3 h. The advantages and disadvantages of the proposed methodology were then discussed.

This paper reports the simultaneous synthesis of gold nanoparticles (AuNPs) with a spherical and stable structure using microbial fuel cell (MFC) biofilms. The green, facile, chemical stabilizers and capping-agent free AuNPs synthesis allow the binder-free in situ decoration of AuNPs on MFC anode electrode with the help of special interactions of biofilm. The MFC with AuNPs decorated carbon foam anode electrode produced 62.5% higher (46.37 Wm-3) power density than that of the MFC equipped with plain carbon foam anode (control). The AuNPs facilitated the good adhesion of bacteria, amplified the conductivity, and reduced the internal resistance, resulting in improved overall MFC performance. In addition, the peroxide-mimicking activity was evaluated and the MFC-synthesized AuNPs exhibited significantly higher peroxidase mimicking activity than the chemically synthesized AuNPs, thereby, allowing the easy and rapid colorimetric detection of hydrogen peroxide with a detection limit of 20 uM.

In this study, highly graphitic nitrogen-doped carbon nano-onions (N-CNOs) were prepared by a one-step, direct, in situ flame synthesis technique and their potential applications as catalysts for oxygen reduction reaction (ORR) in a microbial fuel cell (MFC) were evaluated for the first time. The ORR activity of the CNO, N-CNO, and the commercial Pt/C were measured using a rotating ring-disk electrode (RRDE). The reaction mechanism for the N-CNO was found to follow a four-electron transfer pathway and possess a higher onset potential in RRDE measurement than CNOs. The ORR activity of N-CNO was 5.4 times better than that of CNO, which was attributed to the introduction of nitrogen to the carbon faramework. The MFC fabricated with the N-CNO cathode produced a maximum power density of 49.6 mW m–2, which was approximately double the performance of the CNO-based MFC. The performance of N-CNO was low compared to Pt/C but the cost per power was only 1/310th. These results confirmed that N-CNOs could be used as a low-cost alternative and an energy-efficient metal-free ORR catalyst for practical MFC applications.

Ag nanoparticles (NPs) grafted on TiO2 nanorods (NRs) using electroactive biofilms (EABs) were assessed as photoanodes for water splitting under solar light irradiance. EABs-assisted bio-reduction leads to the uniform decoration of spherical Ag NPs (10–40 nm) and stronger attachment to the Ag–TiO2 interface due to the prior adsorption of Ag+ ions. Plasmonic interaction of Ag NPs with TiO2 NRs showed stronger adsorption in visible range due to surface plasmon resonance. Compared to TiO2 NRs, Ag–TiO2 NRs/FTO exhibited 8 times higher current density under solar light irradiation due to enhanced visible light absorption, SPR effect, and efficient electron-hole separation.

The contribution ratio of autotrophic and heterotrophic metabolism in the mixotrophic culture of Chlorella sorokiniana (C. sorokiniana) was investigated. At the early stage of mixotrophic growth (day 0–1), autotrophy contributed over 70% of the total metabolism, however, heterotrophy contributed more than autotrophy after day 1 due to the rapid increase in cell density, which had a shading effect in the photo-bioreactor. Heterotrophy continued to have a higher contribution until the available organic carbon was depleted at which point autotrophy became dominant again. Overall, the increase in algal biomass and light conditions in the photo-bioreactor are important factors in determining the contribution of autotrophy and heterotrophy during a mixotrophic culture.

Noble-metal silver (Ag) nanoparticles (NPs) anchored/decorated onto polymeric graphitic carbon nitride (g-C3N4) as nanostructures (NSs) were prepared using modest and environment-friendly synthesis method with a developed-single-strain biofilm as a reducing implement. The as-fabricated NSs were characterized using standard characterization techniques. The nanosized and uniform AgNPs were well deposited onto the sheet-like matrix of g-C3N4 and exhibited good antimicrobial activity and superior photodegradation of dyes methylene blue (MB) and rhodamine B (RhB) dyes under visible-light illumination. The Ag@g-C3N4 NSs exhibited active and effective bactericidal performance and a survival test in counter to Escherichia coli, Staphylococcus aureus, and Pseudomonas aeruginosa. The as-fabricated NSs also exhibited superior visible-light photodegradation of MB and RhB in much less time as compared to other reports. Ag@g-C3N4 NSs (3 mM) showed superior photocatalytic measurements under visible-light irradiation: ∼1...

Microbial fuel cells (MFCs) are a potential sustainable energy resource by converting organic pollutants in wastewater to clean energy. The performance of MFCs is influenced directly by the electrode material. In this study, a ternary PANI-TiO2-GN nanocomposite was used successfully to improve the performance of both the cathode and anode MFC. The PANI-TiO2-GN catalyst exhibited better oxygen reduction reaction activity in the cathode, particularly as a superior catalyst for improved extracellular electron transfer to the anode. This behavior was attributed to the good electronic conductivity, long-term stability, and durability of the composite. The immobilization of bacteria and catalyst matrix in the anode facilitated more extracellular electron transfer (EET) to the anode, which further improved the performance of the MFCs. The application of PANI-TiO2-GN as a bifunctional catalyst in both the cathode and anode helped decrease the cost of MFCs, making it more practical.

This paper reports the synthesis of N-doped carbon foams (NCFs) using simple, environment-friendly, and self-developed freezing method. A robust structure of NCFs along with high surface area, hierarchical pore structure, and nitrogen/oxygen functionalities allows their application as free-standing electrode. Microbial fuel cell equipped with differently prepared NCFs as free-standing anode and metal-free cathode generates significantly higher power density, 35.74 W m−3 than conventional electrodes. Furthermore, NCF with an optimized resorcinol-formaldehyde content shows significantly high-charge storage capacity, 799 F g−1, at 0.25 A g−1 and also delivers a high energy density, 111 Wh kg−1, equivalent to that of a Li-ion battery.

Colonies of electrochemically active microorganisms called electroactive biofilms (EABs) have potential applications in bioenergy and chemical production. In the present study, an EAB was used as a reducing tool to synthesize Ag-decorated ZnO@C core–shell (Ag–ZnO@C) ternary plasmonic photocatalysts. A simple thermal decomposition route was followed to synthesize ZnO@C nanoparticles using a zinc aniline nitrate complex. The simultaneous adsorption of Ag+ in the carbon shell of the ZnO@C particles during reduction using an EAB allowed the direct contact among Ag nanoparticles, the ZnO core, and the carbon shell. Therefore, the synthesized Ag–ZnO@C ternary photocatalysts showed a stronger interconnection among all the components, which allowed the easy transfer of photogenerated charges and provided enhanced charge carrier separation. Optical characterization showed that the enhanced absorption of visible light along with a decrease in the band gap and a red shift in the valence band maximum occurred due to the decoration of Ag-nanoparticles on ZnO@C. Ag–ZnO@C exhibited higher photocatalytic activity for the degradation of rhodamine blue and 4-nitrophenol under visible light irradiation than ZnO@C and bare ZnO without any significant loss after five successive cycles. Finally, a possible photocatalytic mechanism for charge transfer was proposed to explain the enhanced photocatalytic performance of the Ag–ZnO@C ternary photocatalyst. This study provides insights into the ternary photocatalytic system with a core–shell material and offers a biogenic route for the facile fabrication of Ag–ZnO@C photocatalysts.

Nutrient removal from artificial wastewater in autotrophic condition by the co-culture consortium of Scenedesmus dimorphus and nitrifiers was investigated. The batch experiments of co-culture, S. dimorphus- and nitrifiers-only treatments were conducted and compared for 9 days. As a result, the co-culture system showed enhancement in both nitrogen (N) and phosphorous (P) removal compared to each single culture. Especially, total N removal efficiency and P removal efficiency in co-culture reactor were enhanced 3.4 and 6.5 times compared to nitrifiers-only reactor, respectively. This result implies that post-treatment systems such as denitrification of nitrate and luxury uptake of P can be deducted by using the co-culture consortium of Scenedesmus dimorphus and nitrifiers. In addition, unlike nitrifiers-only reactor, the co-culture maintained high Dissolved Oxygen (DO) without external aeration. Thus it is suggested that co-culture of Scenedesmus dimorphus and nitrifiers is an efficient and economic method to removal nutrient from wastewater.

Distillation for R-410A reclamation from a waste refrigerant is an energy-intensive process. Thus, various heat pump configurations were proposed to enhance the energy efficiency of existing conventional distillation columns for separating R-410A and R-22. One new heat pump configuration combining a vapor compression (VC) heat pump with cold water and hot water cycles was suggested for easy operation and control. Both advantages and disadvantages of each heat pump configuration were also evaluated. The results showed that the mechanical vapor recompression heat pump with top vapor superheating saved up to 29.5%, 100.0%, and 10.5% of the energy required in the condenser duty, reboiler duty, and operating cost, respectively, compared to a classical heat pump system, and 85.2%, 100.0%, and 60.8%, respectively, compared to the existing conventional column. In addition, this work demonstrated that the operating pressure of a VC heat pump could be lower than that of the existing distillation column, allowing for an increase in capacity of up to 20%. In addition, replacing the throttle valve with a hydraulic turbine showed isentropic expansion can decrease the operating cost by up to 20.9% as compared to the new heat pump configuration without a hydraulic turbine. Furthermore, the reduction in carbon dioxide emission was investigated to assess the environmental impact of all proposed sequences.

The synergistic effects of a co-culture of Chlorella vulgaris (C. vulgaris) and activated sludge in Volatile Fatty Acids (VFAs) treatment were examined by constructing and comparing the performance of the three reactors (only algae, only activated sludge, coculture). As a result, the addition of the activated sludge stimulated the growth of C. vulgaris up to 2.6-fold, even though the initial algae concentration in the co-culture was only 30% of that in the only algae reactor. The treatment efficiency, which was indicated by the degradation of both the VFAs and nutrients, increased due to the symbiotic relationship of the co-culture of C. vulgaris and activated sludge. For the co-culture of algae and activated sludge, the propionate removal rate was enhanced by approximately 29.5- fold and 2.2-fold, respectively, compared to only algae and only sludge; the butyrate removal rate was also enhanced 6-fold and 1.5- fold, respectively. Both the NH4+–N and PO43––P removal rate of the reactor with the co-culture was approximately 2 times higher than that of the reactor with the only algae and only sludge. Within 88 h, the removal efficiency of the co-culture reactor reached 98.2%, whereas the removal efficiency was 59.3% and 49.8% for only algae and only sludge reactor, respectively.

This paper reports a simple methodology for the synthesis of a polyaniline/titanium oxide/graphene hybrid (Pani/TiO2/GN) using a simple methodology, and their application as a supercapacitor electrode material for energy storage. The Pani/TiO2/GN hybrid was prepared by a simple approach by simultaneous generation of Pani and TiO2 in situ from aniline and titanium iso-propoxide, respectively, in the presence of GN under ice bath conditions. The incorporation of GN improved the electrical conductivity of Pani and helped to decrease the charge transfer resistance, whereas TiO2 generation by an in situ method increased the surface area considerably and enhanced the capacitance of the Pani/TiO2/GN hybrid. TEM showed that Pani and TiO2 were well incorporated and coated on the GN successfully. The shift of the peaks in the FTIR spectrum and XRD pattern of the Pani/TiO2/GN hybrid compared to their pure counterparts suggested that TiO2 and Pani had been perfectly coated on the GN, and there was a strong interaction among Pani, GN, and TiO2 particles. The electrochemical performance of the as-prepared Pani/TiO2/GN hybrid electrode showed a high specific capacitance of 403.2 F g−1 at a current density of 2 A g−1 and excellent cycling stability for up to 1000 cycles. This suggested that the effective incorporation of GN and TiO2 into Pani and the high surface area could simultaneously increase the electrochemical capacitance and cyclic stability of the Pani/TiO2/GN hybrid, leading to superior electrochemical performance.

Fibrous Pani-MnO2 nanocomposite were prepared using a one-step and scalable in situ chemical oxidative polymerization method. The formation, structural and morphological properties were investigated using a range of characterization techniques. The electrochemical capacitive behavior of the fibrous Pani-MnO2 nanocomposite was examined by cyclic voltammetry and galvanostatic charge-discharge measurements using a three-electrode experimental setup in an aqueous electrolyte. The fibrous Pani-MnO2 nanocomposite achieved high capacitance (525 F g(-1) at a current density of 2 A g(-1)) and excellent cycling stability of 76.9% after 1000 cycles at 10 A g(-1). Furthermore, the microbial fuel cell constructed with the fibrous Pani-MnO2 cathode catalyst showed an improved power density of 0.0588 W m(-2), which was higher than that of pure Pani and carbon paper, respectively. The improved electrochemical supercapacitive performance and cathode catalyst performance in microbial fuel cells were attributed mainly to the synergistic effect of Pani and MnO2 in fibrous Pani-MnO2, which provides high surface area for the electrode/electrolyte contact as well as electronic conductive channels and exhibits pseudocapacitance behavior.

Three-dimensional (3D) N-doped open-porous carbon foam was fabricated using the simple procedure of calcining a melamine sponge. The properties of the fabricated carbon foam and its performance in microbial fuel cells (MFCs) using Shewanella oneidensis MR-1 (S. oneidensis) were compared with those of commercial graphite felt. The MFC with the carbon foam anode produced approximately 2 times higher power density than the commercial graphite felt. The superior performance of the as-prepared carbon foam in MFC was attributed to the higher surface area (687.19 m2 g−1) and open-porous scaffold structure. Moreover, the appearance of the hydrophilic functional groups such as CN–C, N–CO on the surface of the as-prepared carbon foam facilitated extracellular electron transfer, resulting in a decrease in charge transfer resistance and an increase in biocompatibility. Owing to the excellent biocompatibility, a large amount of microbial biomass colonized both the surface and inside the carbon foam, which helped enhance the performance of the MFC.

Platinum nanoparticles (PtNPs) have long been regarded as the benchmark catalyst for the oxygen reduction reaction (ORR) in the cathode of microbial fuel cells (MFCs). On the other hand, the practical applications of these catalysts are limited by the high cost and scarcity of Pt. Therefore, developing an alternative catalyst to PtNPs for efficient ORR activity is essential for meeting the future demands for practical applications in MFCs. In this study, sulfur-doped graphene (S-GN) was synthesized via the environmental friendly, economical and facile one pot electrochemical exfoliation of graphene in a unique combination of electrolytes, which both catalyzed the exfoliation reaction and acted a sulfur source. The initial activity of S-GN as an ORR active catalyst was examined by cyclic voltammetry (CV), which showed that the as-synthesized S-GN exhibited better ORR activity than the plain material. Furthermore, the application of S-GN as a cathode material was also studied in MFCs. The results showed that the MFC equipped with the S-GN cathode produced a maximum power density of 51.22 ± 6.01 mW m−2, which is 1.92 ± 0.34 times higher than that of Pt/C. The excellent performance of S-GN as a cathode catalyst in MFCs could be due to the doping of graphene with heteroatoms, which increased the surface area and improved the conductivity of graphene through a range of interactions. Based on the above MFC performance, the as-synthesized S-GN catalyst could help reduce the cost and scale up the design of MFCs for practical applications in the near future.

The effects of several light conditions (various light/dark cycles, light intensities, and light frequencies) of a mixture of intermittent red and blue light on nitrogen and phosphorus removal from wastewater using Scenedesmus dimorphus were evaluated. The nitrogen removal rates were almost the same (~ 10 mg/L/day) during light/dark cycles of 16:8, 20:4, and 24:0, and were two-fold higher than those observed during light/dark cycles of 12:12 and 8:16. The phosphorous removal rate also reached its highest value (~ 1.5 mg/L/day) during the light/dark cycles of 20:4 and 24:0. These results suggest that microalgae should be illuminated for at least 16 and 20 h for the efficient removal of nitrogen and phosphorous, respectively. Moreover, both the nitrogen and phosphorous removal rates were significantly enhanced when the light intensity was raised from 50 to 400 µmol/m2/sec. Increasing the light intensity above 400 µmol/m2/sec caused photo-inhibition, such that microalgae production decreased. Besides the light/dark cycle and light intensity, flashing frequency also controls the growth and nutrient removal rate of Scenedesmus dimorphus. It was found that the most appropriate flashing frequency was 2,500 Hz.

Microbial fuel cells (MFCs) and related bioelectrochemical systems (BESs) have shown impressive developments for many purposes over the past decade (Kalathil et al. 2012; Han et al. 2013, 2014, 2016). Even with the noticeable improvements in power density, the large-scale application of MFCs is still limited due to the low power generation and high cost (Wei et al. 2011). To take this technology from laboratory-scale research to commercial applications, the cost and the performance of these systems need to be optimized further. The anode electrode plays an important role in the performance and cost of MFCs. The electrode materials in MFCs have some general and individual characteristics. In general, electrode materials must have good conduction, excellent biocompatibility, good chemical stability, high mechanical strength and low cost. The anode material design has attracted an enormous number of studies over the past decade.

VFAs like acetate are the major soluble metabolites of food waste leachates after digested. Therefore this study investigates the effect of acetate on growth rate and nutrient removal efficiency of Chlorella vulgaris to treat digested food waste leachates. The initial acetate concentration varied from 0 to 20 mM. As a result, Chlorella vulgaris growth rate was increased as high as the concentrations ranged from 0 to 20 mM. The same trend was observed with -N and -P consumption. The highest growth rate and the highest -N, -P removal rate were observed at acetate concentration of 20 mM. The microalgae growth rate and -N, -P removal rates were 1.5, 1.8, 2.3 times higher than the condition without acetate.

The synthesis of (+)AuNPs procedure using a stainless-steel mesh was optimized. The optimal synthetic parameters were found to be one piece of stainless-steel mesh (22.5 cm 2 in surface area) in 100 mL of a 1 mM precursor, precursor solution pH 4, and reaction temperature of 30 °C. Under the optimal conditions, the as-synthesized (+)AuNPs were highly positively charged (+24.2 mV). Therefore, the as-synthesized (+)AuNPs act as a peroxidase mimic and provide a simple, fast, highly sensitive and selective colorimetric method for H 2 O 2 detection with a detection limit of 0.06 mM in the linear range from 0.06 mM to 4.29 mM.

Microbial fuel cells (MFCs) generate electricity from the oxidation of dissolved organic matter. A variety of Gram-positive and Gram-negative bacteria, including Escherichia coli, produce a large quantity of indole, which functions as an extracellular signal molecule. This work explored the role of indole in a mediatorless E. coli catalyzed MFC. Although the presence of indole alone did not affect power generation, indole oxidation by the indole-oxidizing enzyme toluene-o-monooxygenase (TOM) enhanced power density by 9-fold. Open circuit voltage and polarization curve showed that indole oxidation by TOM produced a maximum power density of 5.4 mW/m2 at 1,000 ohm. Cyclic voltammetric results suggested that indole oxidation resulted in the production of redox compounds. This study provides a novel means of enhancing power generation in E. coli-catalyzed MFCs.

A simple and scalable method to synthesize N-doped carbon (NC) based on a carbothermal reduction of a ZnO/carbon composite (ZCC) obtained from the decomposition of a zinc aniline nitrate complex is reported. The present study examined the effects of the structural characteristics of NC, such as electrical conductivity and surface area, more precisely without altering the other structural features of NC. A carbothermal reduction of ZCC allowed the production of hierarchically porous NC with a low sheet resistance of 0.432 kΩ □−1 without any post-treatment with Zn nanorods as a valuable byproduct. The resulting NC exhibited ultra-high stability and rate capability, i.e., 100% stability after 200,000 cycles up to 300 A g−1 with a high capacitance of 229 F g−1 at 0.5 A g−1. The 288% increase in surface area with a similar % contribution from micro and mesopores and similar electrical conductivity increased the electrochemical charge storage capacity of NC by 266%. Similarly, NC materials possessing a similar surface area but a large difference in electrical conductivity resulted in a 1539% difference in charge storage capacity. Enhancement of both the surface area and electrical conductivity improved the capacitance of NC drastically to 4098% higher than the base product. A prototype flexible solid-state supercapacitor fabricated from the obtained NC delivered a very high areal capacitance of 363.6 mF cm−2 (at 0.5 mA cm−2) with ultra-high stability (82%) even after 70,000 cycles (at 25 mA cm−2).

A novel, rapid, one-pot, and facile approach was developed to synthesize positively charged gold nanoparticles [(+) AuNPs] by employing an aqueous solution of HAuCl4 x 3H2O as a precursor at 30 degrees C and a stainless-steel mesh as a reducing agent. The penetration of Cl- ions into the stainless-steel surface results in corrosion on the stainless-steel surface and excretion of electrons which are used for reduction of Au3+ --Au0. As a result, (+) AuNPs 5-20 nm in size, mostly monodispersed, were synthesized within 3 h. The as-synthesized AuNPs were charaterized by UV-vis, DLS, XRD, TEM, HR-TEM, EDX and SAED. The utilization of non-toxic chemicals and easily available materials, and the non-requirement of energy input, make this methodology easy, inexpensive, and efficient. The new findings about the role of the stainless-steel mesh, which provides electrons in the presence of Cl- ions, for the reduction of Au3+ --Au0, makes it a novel material for (+) AuNPs synthesis.

This study examined the effect of positively charged gold nanoparticles [(+)AuNPs] on the enhancement of methylene blue (MB) degradation in a microbial fuel cell (MFC) cathode. Complete MB degradation and a maximum electricity production of 36.56 mW/m2 were achieved simultaneously. The MFC performance and MB degradation were found to be strictly dependent on the cathodic conditions, such as N2 bubbling, air bubbling, and addition of H2O2. MB was reduced rapidly under anaerobic conditions, whereas complete oxidative mineralization of MB occurred in the presence of dissolved oxygen (DO) or H2O2. (+)AuNPs enhanced the electricity generation in the MFCs involving MB degradation owing to its electron-relay effect. The presence of both (+)AuNPs and H2O2 produced the greatest enhancement in MB degradation. After 5 h, almost all of the MB (98%) and chemical oxygen demand (COD) (96%) had been removed in the presence of (+)AuNPs, whereas only 57.4% of the MB and 40% of the COD had been removed in the absence of (+)...

Microbial fuel cells (MFCs) are a promising green approach for wastewater treatment with the simultaneous advantage of energy production. Among the various limiting factors, the cathodic limitation, with respect to performance and cost, is one of the main obstacles to the practical applications of MFCs. Despite the high performance of platinum and other metal-based cathodes, their practical use is limited by their high cost, low stability, and environmental toxicity. Oxygen is the most favorable electron acceptor in the case of MFCs, which reduces to water through a complicated oxygen reduction reaction (ORR). Carbon-based ORR catalysts possessing high surface area and good electrical conductivity improve the ORR kinetics by lowering the cathodic overpotential. Recently, a range of carbon-based materials have attracted attention for their exceptional ORR catalytic activity and high stability. Doping the carbon texture with a heteroatom improved their ORR activity remarkably through the favorable adsorption of oxygen and weaker molecular bonding. This review provides better insight into ORR catalysis for MFCs and the properties, performance, and applicability of various metal-free carbon-based electrocatalysts in MFCs to find the most appropriate cathodic catalyst for the practical applications. The approaches for improvement, key challenges, and future opportunities in this field are also explored.

1,4-Dioxane is one of the by-products from the polyester manufacturing process, which has been carelessly discharged into water bodies and is a weak human carcinogen. In this study, a laboratory-scale, up-flow biological aerated filter (UBAF), packed with tire chips, was investigated for the treatment of 1,4-dioxane. The UBAF was fed with effluent, containing an average of 31 mg/L of 1,4-dioxane, discharged from an anaerobic treatment unit at H Co. in the Gumi Industrial Complex, South Korea. In the batch, a maximum of 99.5 % 1,4-dioxane was removed from an influent containing 25.6 mg/L. In the continuous mode, the optimal empty bed contact time (EBCT) and air to liquid flow rate (A:L) were 8.5 hours and 30:1, respectively. It was also found that the removal efficiency of 1,4-dioxane increased with increasing loading rate within the range 0.04 to 0.31 kg 1,4-dioxane/m(3)·day. However, as the COD:1,4-dioxane ratio was increased within the range 3 to 46 (mg/L COD)/(mg/L 1,4-dioxane), the removal efficiency unexpectedly decreased.

The cyclic ether 1,4-dioxane is a synthetic industrial chemical that is used as a solvent in producing paints and lacquers. The EPA and the International Agency for Research on Cancer(IARC) classified 1,4-dioxane as a GROUP B2(probable human) carcinogen. 1,4-dioxane is also produced as a by-product during the manufacture of polyester. In this research, a polyester manufacturing company (i.e. K Co.) in Gumi, Korea was investigated regarding the release of high concentrations of 1,4-dioxane (about 600 mg/L) and whether treatment prior to release should occur to meet with the level of the regulation standard (e.g., 5 mg/L in 2010). A 10 ton/day pilot-scale treatment system using photo-Fenton oxidation was able to remove approximately 90% of 1,4-dioxane under the conditions that concentrations of 2800 ppm H2O2 and 1,400 ppm FeSO4 were maintained along with 10 UV-C lamps (240 μW/cm2) installed and operated continuously during aeration. However, the effluent concentration of 1,4-dioxane was still high at about 60 mg/L where TOC concentration in the effluent had been moreover increased due to decomposed products such as aldehydes and organic acids. Thus, further investigation is needed to see whether the bench scale (reactor volume, 8.9 L) of activated sludge could facilitate the decomposition of 1,4-dioxane and their by-products (i.e., TOC). As a result, 1,4-dioxane in the effluent has been decreased as low as 0.5 mg/L. The optimal conditions for the activated sludge process that were obtained are as follows: DO, 3-3.5 mg/L; HRT, 24 h; SRT 15 d; MLSS, 3,000 mg/L. Consequently, photo-Fenton oxidation coupled with activated sludge can make it possible to efficiently decompose 1,4-dioxane to keep up with that of the regulation standard.

Positively charged gold nanoparticles [(+) AuNPs] of 5–20 nm were synthesized by using electrochemically active biofilm (EAB) formed on a stainless steel mesh, within 30 minutes, in aqueous solution containing HAuCl4 as a precursor and sodium acetate as an electron donor. Electrochemically active bacteria present on biofilm oxidize the sodium acetate by producing electrons. Simultaneously, stainless steel also provides electrons because of the Cl − ions penetration into the stainless steel. Combined effect of both the EAB and stainless steel mesh enhances the availability of electrons for the reduction of Au 3+ in the solution, which makes this synthesis efficient and fast. Therefore, small size, positively charged (+ 32.72 mV), monodispersed, controlled, easy separation and extracellular synthesis of (+) AuNPs makes this protocol highly significant. As-synthesized AuNPs were characterized by UV-vis, DLS, XRD, TEM, HRTEM, EDX and SAED. (+) AuNPs shows remarkable enhancement in the rate of reduction of methyl orange by NaBH4 because of the electron relay effect.

A variety of both Gram-positive and Gram-negative bacteria produce large quantities of indole as an intercellular signal in microbial communities. Biosynthesis of indole is well-studied, and while carbon sources and amino acids are important environmental cues for indole production in Escherichia coli, other environmental factors affecting indole production for this strain are less clear. This study demonstrates that the environmental cue pH is an important factor for indole production that further controls biofilm formation of E. coli. Moreover, E. coli produced a higher level of extracellular indole in the presence of the antibiotics ampicillin and kanamycin, and the increased indole enhanced cell survival during antibiotic stress. Additionally, we found here that temperature is another important factor for indole production; E. coli produces and accumulates a large amount of indole at 50 °C, even at low cell densities. Overall, our results suggest that indole is a stable biological compound, and E. coli may utilize indole to protect itself against other microorganisms.