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In this paper, the acidified multi-walled carbon nanotubes (MWCNTs) film was coated on the quartz crystal microbalance (QCM) to prepare a high-performance sensor for the real-time detection of organic acid gases. The material characteristics of the thin films were analysed by field emission scanning electro microscopy (FESEM), Raman spectra and X-ray photoelectron spectroscopy (XPS). The organic acid vapours' sensing results indicated that acidized-MWCNTs thin film exhibited good frequency response, repeatability, reversibility and stability. There is a clear linear relationship between the frequency offset and the organic acid vapours with concentration below 5.0 ppm, and the detection limit of 0.77 and 0.73 ppm for formic and acetic acid vapours, respectively. The sensor shows the highest response to formic acid vapour than acetic acid vapour which may be ascribed to molecular polarity. Furthermore, a sensing mechanism model was introduced to understand the adsorption reaction between organic acid molecules and acidized-MWCNTs. This paper proves that acidized-MWCNTs is a potential and suitable material for organic acid vapour detection when combined with a QCM sensor.

Calcium silicate (CS) composite materials are widely applied in cementitious materials and bone tissue engineering. Extensive studies focused on the traditional organic templates (e.g., surfactant)...

The potential coexistence and interaction of bromine and polyamide membranes during membrane-based water treatment prompts us to investigate the effect of bromine on membrane performance. For fully aromatic polyamide membrane NF90 exposed under a mild bromination condition (10 mg/L), bromine incorporation resulted in more negatively charged (-13 vs -25 mV) and hydrophobic (55.2 vs 58.9°) surfaces and narrower pore channels (0.3 vs 0.29 nm). The permeabilities of water and neutral solutes were reduced by 64 and 69-87%, respectively, which was attributed to the decreased effective pore radius and hydrophilicity. NaCl permeability was reduced by 90% as a synergistic result of enhanced size exclusion and charge repulsion. The further exposure (100 and 500 mg/L bromine) resulted in a more hydrophobic surface (61.7 and 65.5°) and the minor further reduction for water and solute permeabilities (1-9%). Compared with chlorine, the different incorporation efficiency and properties (e.g., atomic size, hydrophilicity) of bromine resulted in opposite trends and/or different degrees for the variation of physicochemical properties and filtration performance of membranes. The bromine incorporation, the shift and disappearance of three characteristic bands, and the increased O/N ratio and calcium content indicated the degradation pathways of N-bromination and bromination-promoted hydrolysis under mild bromination conditions (480 mg/L·h). The further ring-bromination occurred after severe bromine exposure (4800-24,000 mg/L·h). The semi-aromatic polyamide membrane NF270 underwent a similar but less significant deteriorated filtration performance compared with NF90, which requires a different explanation.

Ionic liquids have a number of excellent applications such as a kind of promising lubricants which have attracted considerable attention. In this work, we investigated corrosion properties which were found in the use of ILs formed by a 1-butyl-3-methylimidazolium cation and a fluorine-containing anion as lubricants of AISI E52100 steel. Electrochemical tests were used to study the anodic behavior of AISI E52100 steel, and surface analysis was performed to study the surface morphology. The electrochemical results showed that increasing temperature accelerates corrosion of the alloy in two kinds of ionic liquids. The data obtained from polarization curves and EIS suggested that the anodic process of the E52100 steel showed generally an active dissolution and increasing temperature can accelerate the corrosion of the steel. At the same time, the main difference as revealed by SEM–EDS plots was that localized corrosion with some irregular etch pits occurred in [Bmim]BF4 ionic liquid; however, a product layer covered uniformly on the surface of metal in [Bmim]PF6. The results of XPS spectrum indicated that the corrosion products formed on the surface of the AISI E52100 steel are mainly composed of FeO, Fe2O3, FeF2 and FeF3.

The co-presence of haloacetic acids (HAAs) and Mg2+ in swimming pool waters and the potential interaction among Mg2+, HAAs, and membranes prompted a systematic investigation of membrane performance...

The corrosion processes of bare bronze and three types of patina-bearing tin bronze in the presence of formic acid have been explored through laboratory exposure. Following exposure time of 4, 14 and 28 days, the morphology and composition of the corrosion products on the sample were characterized to investigate their evolution by using SEM, XRD and Raman. The results indicated that Cu2O was first generated on the bare bronze surface, then Cu(OH)2 was formed at the early stage of the corrosion and as the exposure time increased, Cu(OH)(HCOO) and Cu(HCOO)2 were further generated. Bronze with Cu2O layer was destroyed by formic acid and converted into Cu(HCOO)2, which was similar to the conversion process of corrosion products of bare bronze, except that, the account of products of bronze patinated with Cu2O was more than that of bare bronze, indicating that the Cu2O layer on the sample surface was destroyed and further transformed. The main corrosion product of bronze with CuCl patina was Cu2(OH)3Cl, which was consistent with the reaction process of powdery rust. For bronze with mixed patina, two corrosion processes of Cu2O patina and CuCl patina proceed at the same time, and the corrosion products were Cu(HCOO)2 and Cu2(OH)3Cl, which were basically consistent with the corrosion behavior of bronze covered with a Cu2O and a CuCl patina.

Wastewater from olaquindox-producing factories contains high levels of salts and organics. In this study, we investigated the multiple freeze-thaw technology to recover olaquindox from wastewater and decrease its chemical oxygen demand (COD) and salinity. Results suggested that under lower ice formation rate, the removal efficiencies of COD, electric conductivity, ammonia nitrogen and total nitrogen could reach 99.4%, 98.2%, 98.7% and 98.5% respectively. Higher ice formation rate, however, promoted wastewater concentration and volume reduction. A liter of wastewater concentrate can recover 11.5 g solid through a simple crystallization step at 4 °C for 12 h. This substance contained mostly olaquindox based on Raman infrared spectroscopy, scanning electron microscopy, and energy dispersive spectrometry. An industrial-scale wastewater treatment process, which the theoretical cost is one seventh that of conventional technologies, was then proposed to recover olaquindox and treat wastewater.

Reduction in and recovery of precious metals are research hotspots in the environmental engineering field. In this study, we investigated the transformation and distribution of platinum in microbial fuel cells (MFCs) and demonstrated a feasible approach to recover platinum (Pt) from wastewater with less than 16.88 mg/L platinum through charring biofilms in MFCs and generate Pt/C catalyst. The optimal reaction condition was identified, and charred biofilms were analyzed via SEM-EDS, XRD and XPS. Results showed that less than 10% of Pt was in MFC effluents, and less than 0.5% was in the cathode chamber when the influent concentration was below 16.88 mg/L. Close to 40% of Pt could be recovered. The recovery efficiency could be higher should the reactions run longer. SEM-EDS and XRD results indicated that the metallic form Pt0 is one of the reduction products in MFCs. XPS results induced that Pt (IV) was reduced to Pt (II) and Pt0. Keywords: Microbial fuel cells, Platinum, Bio-reduction, Recovery, Sludge

The long-term effectiveness concern of municipal solid waste incineration (MSWI) fly ash (FA) disposal has been placed more emphatic recently, however, few studies worked on the control of leaching risk of heavy metals under the long-term stability. In this study, the leaching properties and risk assessment of two representative solidified/stabilized (S/S) FA wastes, i.e., sodium dithiocarbamate (DTC) chelator treated and Portland cement + chelator combining treated, were evaluated by a long-term cycles assessment method which coupled multifaceted environmental stresses (e.g., freezing-thawing, drying-wetting, accelerated carbonation). The results showed that the cement/chelator had a better long-term stability and exhibited ~55% lower cumulative overall pollution toxicity index (OPTI) than chelator treatment after the test, which was always rated as “low risk” during the cycles. In addition, the cement/chelator exhibited ~23.3% smaller cumulative mass release rate than the chelator treatment after 6 cycles and restrained the transformation of Pb and Cd from stable states to removable fractions, which attributes to its great erosion resistance and compact pore structure. Under the cumulative external factors and carbon dioxide attacks, the decalcification of hydrate products (e.g., C-S-H, hydrocalumite), as well as deterioration of pore structure are the critical factors increasing the local erosion, cracking and heavy metals release. Thus, the optimization of S/S waste microstructure (e.g., enhancing binder system) and landfill site conditions (e.g., reducing rainfall impact) could be propitious to the S/S waste risk control and management.

Four plant–sediment microbial fuel cells (plant-SMFCs) with four plant species, Oryza sativa, Acorus calamus, Spathiphyllum petite and Chamaedorea elegans, were built to investigate sulfide concentrations, pH and oxidation–reduction potential (ORP) in the sediment as well as plant growth. Sulfide concentrations at 1 and 2 cm depth of sediment in plant-SMFCs and their control reactors were 1.66 ± 0.30, 9.29 ± 3.46, 2.38 ± 0.10 and 24.20 ± 1.02 μmol g−1, respectively. The ORP in water and sediment of 1 and 2 cm depth in plant-SMFCs was 106.0 ± 7.7, − 142 ± 30 and − 209 ± 9 mV, respectively. The ORP in the three control reactors was 119.0 ± 11.5, − 209 ± 9 and − 386 ± 2 mV, respectively. Harvest of O. sativa, A. calamus, Spathiphyllum petite and C. elegans was 0.218 ± 0.009, 0.136 ± 0.007, 0.127 ± 0.007 and 0.340 ± 0.007 gDW g−1GW in the plant-SMFCs, while that of their control reactors was 0.179 ± 0.011, 0.127 ± 0.008, 0.102 ± 0.007 and 0.318 ± 0.006 gDW g−1GW, respectively. The results showed that sulfide concentrations decreased in sediments of plant-SMFCs, while the ORPs in both the overlying water and sediments increased. Moreover, plant growth due to operating plant-SMFCs was promoted. Running plant-SMFCs abates the toxicity of sulfide to the emerged plants as well as decreases the sulfide emission in water–plant–sediment systems.

Sodium dimethyldithiocarbamate (SDDC) is a widely used heavy metal chelating agent in harmless treatment of wastewater and hazardous waste, but SDDC and its heavy metal chelates may leak into the environment and bring potential ecological risks. In this study, the model organism Caenorhabditis elegans was used to evaluate the toxic effect of SDDC and its heavy metal Cu, Pb chelates. Multiple endpoints were investigated by subacute exposure to SDDC (0.01–100 mg/L) and micro-sized Cu, Pb chelates of SDDC (1–100 mg/L). Our data indicated that the LC50 value of SDDC was 139.39 mg/L (95% Cl: 111.03, 174.75 mg/L). In addition, SDDC was found that concentration of 1 mg/L is a safe limit value for nematode C. elegans, and concentration above 1 mg/L caused adverse effects on the survival, growth, locomotion behaviors and reactive oxygen species (ROS) production of exposed nematodes. Furthermore, all tested SDDC-Cu and SDDC-Pb chelates had obviously lower toxic effect than untreated Cu, Pb metals. These two chelates also had a lower toxic effect than SDDC agent due to its more stable structure. Moreover, SDDC-Cu had a higher toxic effect than SDDC-Pb at the same concentration. Thus, our results suggest that SDDC as a kind of chelating agent applied in harmless treatment of heavy metals, the safe addition limit should not be exceeded.

In order to further protect the bronze products, we investigated the corrosion process and behavior of bronze materials under organic acid‐containing thin electrolyte layer.

Two kinds of thioureas, 1-N-(1′-(1′,2′,4′-triazole))acetyl-4-N-benzoylthiosemicarbazide (TBU) and 1-N-(1′-(1′,2′,4′-triazole))Methyl-4-N-(3″,5″-dimethyl)benzoylthiosemicarbazide (TDBU) were synthesized and characterized as corrosion inhibitors in 1 mol/L hydrochloric acid to mild steel by weight loss measurement, electrochemical measurement, quantum chemistry calculation and molecular dynamics simulation. The results demonstrate that TBU and TDBU are good inhibitors that could reduce anodic dissolution and retard the hydrogen evolution reaction with the order TBU > TDBU, and that the corrosion inhibition efficiency increases with the increasing thiourea concentration. TBU has a remarkably high inhibition efficiency of 97.5% at a concentration of 1.0 × 10−3 mol/L. The adsorptions of TBU and TDBU on mild steel accord with the Langmuir model. The results of quantum chemical study indicate that the S atom contributes to the adsorption of the corrosion thiourea molecules. The steric hindrance of the methyl group, not an electronic effect, was suggested as the main influencing factor on the inhibition efficiency of the two thioureas, which is relatively rare in literature reports.

A set of experiments was conducted so as to detect the influences of concerned factors including freezing temperature, stirring speed and pH adjustment on combined method of suspension crystallization and freeze-thaw technique for waste cutting fluid treatment and oil recovery. The optimal operating conditions of freezing temperature and stirring speed were confirmed by the experiment result to be −8 °C and 300 rpm respectively, while the chemical oxygen demand (COD) removal efficiency was above 90% without pH adjustment. The concentrates from the suspension crystallization were further treated by freeze-thaw method, and the oil recovery rate could reach to 95%. The micrograms of concentrates from suspension crystallization showed that the size of oil droplets in concentrates was about 148 μm in diameter, which became significantly larger after the suspension crystallization process. As a consequence, higher possibility for oil droplets to gather and separate was provided by their expanded size. The results of infrared spectroscopy studies indicated that the oil recovered from waste cutting fluid precipitates was mainly composed of esters. Up to 2.85 kg fat was recovered from 1 m 3 of waste cutting fluid, while the required power of the combined freezing process is theoretically 42 kW h. Based on the results, a freezing/concentration concept for oil recovery from waste cutting fluid is proposed.

The effective disposal of waste cutting fluid has received increasing attention in recent years. This study focuses on the treatment of waste cutting fluid by freeze-thaw method. The influences of freezing medium, freezing temperature, freezing time, NaCl content and pH on treatment efficiency were studied. The COD removal rate of waste cutting fluid was about 80% and oil recovery reached 3700 mg/L at the freezing temperature of −8 °C for 8 h without NaCl addition or pH adjustment. The micrograms of initial and treated waste cutting fluid showed that the particles of oil droplets in wastewater were significantly larger after freeze-thaw process and easier to gather and separation. Infrared spectroscopy studies indicated that the oil recovered from waste cutting fluid precipitation was mainly composed of esters. Up to 3.7 kg fat extract was recovered from 1 m3 of waste cutting fluid, while the required power of this freezing process is 42.90 kW h by theoretical calculation. Thus, freeze-thaw method appears to be effective and feasible for waste cutting fluid treatment.

Freezing methods, progressive freezing and suspension crystallization, were examined for treating Grignard reagent wastewater containing tetrahydrofuran (THF) used as a solvent. The effect of freezing temperature, addition of seed ice crystals, and stirring speed on performance were investigated. The addition of seed ice with appropriate temperature contributed to enhance the purity. The optimal operating conditions of freezing temperature and stirring speed were −6 °C and 300 rpm respectively while the removal efficiency of COD was above 90%. The suspension crystallization is superior to progressive freezing in terms of performance and energy consumption, with an estimation of about 38.26 kW h per ton of wastewater treated. Based on these results, a freezing/concentration concept for THF recovery from Grignard reagent wastewater is proposed.

Several newly synthesized triazoles including 1-(2″-nitrobenzyl)methenylideneamino-2-mercapto-5-(1′-(1′,2′,4′-triazol)) methenyl-1,3,4-triazole (NMTT), 1-(2″-methoxybenzyl)methenylideneamino-2-mercapto-5-(1′-(1′,2′,4′-triazol)) methenyl-1,3,4-triazole (MMTT), and 1-((4″-chlorobenzyl)methenylideneamino-2-mercapto-5-(1′-(1′,2′,4′-triazol)) methenyl-1,3,4-triazole (CMTT) were studied as corrosion inhibitors of mild steel in 1 M HCl by weight loss measurements, electrochemical experiments, and quantum-chemical calculations. The experimental results show that these compounds have high inhibition efficiency in the order CMTT > MMTT > NMTT. CMTT at concentration of 1.0 × 10−3 M showed the highest inhibition efficiency of 96.4 %. The adsorption of the inhibitors on the metal surface obeyed the Langmuir isotherm, and the basic adsorption mechanism is proposed based on quantum-chemical calculations.

Natural magnetite and hematite were explored to decrease sulfide in sewage, compared with iron salts (FeCl3 and FeSO4). A particle size of magnetite and hematite ranging from 45 to 60 μm was used. The results showed that 40 mg L− 1 of powdered magnetite and hematite addition decreased the sulfide in sewage by 79%and 70%, respectively. The achieved decrease of sulfide production capacities were 197.3, 210.6, 317.6 and 283.3 mg S g− 1Fe for magnetite, hematite, FeCl3 and FeSO4 at the optimal dosage of 40 mg L− 1, respectively. Magnetite and hematite provided a higher decrease of sulfide production since more iron ions are capable of being released from the solid phase, not because of adsorption capacity of per gram iron. Besides, the impact on pH and oxidation-reduction potential (ORP) of hematite addition was negligible; while magnetite addition resulted in slight increase of 0.3–0.5 on pH and 10–40 mV on ORP. Powdered magnetite and hematite thus appear to be suitable for sulfide decrease in sewage, for their sparing solubility, sustained-release, long reactive time in sewage as well as cost-effectiveness, compared with iron salts. Further investigation over long time periods under practical conditions are needed to evaluate the possible settlement in sewers and unwanted (toxic) metal elements presenting as impurities. Capsule abstract Powdered magnetite and hematite were more cost-effective at only 30% costs of iron salts, such as FeCl3 and FeSO4 for decreasing sulfide production in sewage.

Electricity generation in microbial fuel cells can be restricted by a few factors, such as the effective area of the anode for biofilm attachment, diffusion limitation of substrates and internal resistance. In this paper, a suspended anode (carbon-based felt granule)-type microbial fuel cell was developed to make full use of the volume of the anode chamber and provide a larger surface area of the anode for the growth of exoelectrogenic bacteria. The current collector was rotated in the anodic chamber to contact with the suspended granules intermittently and achieve better mixing. The open-circuit voltage reached steady state at around 0.83 V. The maximum power density obtained from each scenario increased steadily with the increase in mixing rate. The internal resistance decreased when the rotational rate and the content of the carbon granules were increased. The maximum power density reached 951 ± 14 mW m−3 with a corresponding minimum internal resistance of 162.9 ± 3.5 Ω when the mass of carbon granules was 50 g and the rotational rate was 300 rpm. The suspended microbes made negligible contribution to the power density. The microbial fuel cell with a higher content of carbon granules had lower coulombic efficiency and lower relative abundance of exoelectrogenic bacteria.

Recently, innocent treatment of heavy metals in hazardous waste has become a hot topic in China. In particular, lead (Pb) as a typical heavy metal, is one of the easiest leaching heavy metal elements for municipal solid waste incineration (MSWI) fly ash. In this paper, different dosages of gelatinized sticky rice (SR) as green additives were added into the mixture of MSWI fly ash (FA) and ordinary Portland cement (OPC) to solidify/stabilize Pb in an attempt to optimize cement solidification. The leaching behaviour of Pb, hydration phases and hydration microstructure were determined by Toxicity Characteristic Leaching Procedures (TCLP) leaching test, Tessier sequential extraction method, XRD, BET and SEM. The results showed that Pb leaching concentration significantly decreased when adding 10% OPC and 30% gelatinized SR solution compared to only OPC treatment, and increasing dosage of SR also reduced Pb leaching concentration and met the criteria of landfill after curing 28 days. Additionally, increase of gelatinized SR dosage made Pb in fraction of Fe–Mn oxides more easily transformed into the stable crystal and organic matter structure of FA solidified products, and the growth of hydration products were restricted and particle size became finer. The addition of gelatinized SR also reduced initial/final setting times and increased compressive strength. The data suggest that the addition of gelatinized SR provides a new and clean approach to enhance the FA/OPC solidification/stabilization and reduce the leaching concentration of heavy metals in MSWI fly ash.

Attention is drawn to the freezing method for separating organic contaminants from industrial wastewater and simultaneously recovering valuable materials, but the mechanism regarding functional group of organic contaminants how affect ice purity remains unclear. In this work, four types of organics, including hexane, hexanoic acid, N-hexanol and N-hexanal, with various oxygen functional groups were selected as organic contaminants and studied to be separated from aqueous solutions by the suspension freezing method. Experimental results revealed that their separation efficiencies were 67.07%, 87.75%, 94.71% and 95.32%, respectively, after freezing 30 min at 200 rpm and −0.9 °C. The presented theoretical work reveals that hexane, as a non-polar organic contaminant without function group, unable to form hydrogen bonds with water clusters, making it more readily to precipitate and stick on ice surface during freezing, which significantly increased ice impurities with the lowest separation efficiency. Presence of functional group promotes organics to solute in concentrate via forming H-bond with water clusters, and thus improves ice purity by avoiding of precipitation. Hexanoic acid with the largest absorption energy with ice crystal tend to adsorb on ice surface but not stay in concentrate and showed the highest ice impurity corresponding to lowest separation efficiency. This work provides new sight for understanding declination of ice purity and separation efficiency caused by functional group of organic contaminants during freezing.

In search of a cost effective cathode material for microbial fuel cells (MFCs), graphite was chemically treated with H3PO4, HNO3, ZnCl2, urea or melamine, and the effect of chemical activations on the oxygen reduction reaction (ORR) was examined. The performance of MFCs with activated graphite as the catalyst-free cathodes was then compared to those with untreated graphite. Results suggested that H3PO4 and HNO3 activations could improved ORR, showing the highest ORR activity in graphite treated with 14.62 M H3PO4 for 12 h at 30–50 °C. MFCs with H3PO4 and HNO3 activated graphite cathodes generated maximum power densities (7.9 W/m³ and 6.5 W/m³, respectively) 2.4 and 1.8 times higher than that of the untreated control. The chemical activation process involves just a simple immersion step, and it does not require heating, electrochemical process or expensive chemicals. Therefore, it is a highly cost-effective approach to improve the performance of MFCs. We recommend an in-situ modification of graphite cathodes in scale-up MFCs with either H3PO4 or HNO3 to optimize MFCs' various industrial applications.

Although plant-microbial fuel cells (PMFCs) have been considered as an alternative approach to utilize plants as an energy source, the application of a conventional PMFC coupled with rhizodeposits is immensely limited by environmental factors and plant species. In this research, we suggested a new concept for a device that can directly generate continuous bioelectricity from the plant stem associated with microbial fuel cells (MFCs), in which Pachira macrocarpa and Populus alba were employed. Compared with a conventional PMFC, the novel PMFC coupled with the plant stems produced more stable and continuous bioelectricity without oscillatory behaviour as well as a much shorter start-up period. The stem-coupled PMFCs produced bioelectricity that were operated at least 40 days. P. alba coupled PMFC showed higher power output compared to P. macrocarpa counterparts and the maximal power densities were 7.61 mW m−2 and 3.60 mW m−2 anode surface, respectively. Besides, we explored the response of the novel PMFC to different substrate concentrations and observed that the cell voltage effectively increased after the injection of moderate substrate concentrations. Moreover, the anodic bacteria formed a commensal relationship with the plant.

A novel electrochemical micromembrane technology coupling membrane and electric method was developed to demulsify oily wastewater and recover oil. The diameter of the oil droplets increased to 55.0 μm from the initial 7.0 μm after treating the emulsion with the electrochemical micromembrane technology. Chemical oxygen demand removal rate and oil recovery reached 87.89% and 5173 mg/L, respectively, after cycling for 90 min at 10.0 V voltage with a 10.0 mm electrode distance, a 5.0 μm micromembrane pore size and a 0.5 L/min flow rate. Micromembrane pore sizes of 1.0 and 5.0 μm were both effective for decreasing chemical oxygen demand and recovering oil. The recovered oil was the mixture of mineral oil and ester according to the Raman infrared spectroscopy analysis. Surface charge redistribution and electrogenerated destruction for hydrophilic groups of surfactant molecules are responsible for oil coalescence. The electrochemical micromembrane technology used in this study offer an attractive treatment option to demulsify oily wastewater.

Pulsed electrochemical process was explored to remove sulfide in municipal sewage, which successfully achieved higher removal rate of 93.2% compared with 73.2% by direct current (DC) power supply. The sulfur content on the electrode was 0.21% by pulsed electrochemical process compared with that of 1.05% on anode by DC electrochemical process, indicating that pulsed electrochemical process can inhibit anodic passivation resulting from sulfur deposition compared with DC electrochemical process. Besides, the electrode scaling can also be effectively controlled during pulsed electrochemical process. Moreover, the process optimization was investigated for pulsed electrochemical treatment, which obtained the highest removal rate of 97.8% at pH 7–8, cell voltage of 7 V, duty cycle of 60%, pulse frequency at 1000 Hz and electrode spacing of 2.5–3.0 cm. These results indicate that pulsed electrochemical process is a promising method of efficient and sustainable electrochemical sulfide removal from sewage.

Bioelectrochemical systems (BESs) have been focused on by many researchers to treat wastewater and recover energy or valuable chemicals from wastes. In BESs, metal ions play an important role in the conductivity of solution, reactors' internal resistance, power generation, chemical production and activity of microorganisms. Additionally, the metal ions are also involved in anodic or cathodic reaction processes directly or indirectly in BESs. This paper reviews the behavior of metal ions in BESs, including (1) increase of the conductivity of electrolyte and decrease of internal resistance, (2) transfer for desalination, (3) enhancement or inhibition of the biocatalysis in anode, (4) improvement of cathodic performance by metal ions through electron acceptance or catalysis in cathodic process and (5) behavior of metal ions on membranes. Moreover, the perspectives of BESs removing heavy metal ions in wastewater or solid waste are discussed to realize recovery, reduction and detoxification simultaneously.

Hydrogen sulfide emission in sewer systems is associated with toxicity, corrosion, odour nuisance and high costs treatment. In this study, a novel method to inhibit sulfide generation from sewage by means of glutaraldehyde supplementation has been suggested and evaluated under anaerobic conditions. Different concentrations of glutaraldehyde at 10, 15, 20, 30 and 40 mg·L−1 have been investigated. Besides, the possible impacts of glutaraldehyde supplementation on an activated sludge system and an appraisal of the economic aspects are presented as well. As observed from the experimental results, a dosage of 20 mg·L−1 glutaraldehyde resulted in a significant decrease of the sulfide production by 70%–80% in the simulated sewage. Moreover, the impacts of additional glutaraldehyde at 20 mg·L−1 on activated sludge, in terms of chemical oxygen demand removal and oxygen uptake rates, were negligible. From an economical point of view, the cost of the commercial glutaraldehyde products required in the operation, which was calculated on the basis of activated sulfide removal avoidance, was around €3.7–4.6 S·kg−1. Therefore it is suggested that glutaraldehyde supplementation is a feasible technique to abate the sulfide problems in sewer systems. Yet further research is required to elucidate the optimum “booster” dosage and the dosing frequency in situ accordingly.

A rotating disk electrode (RDE) was used to investigate the concentration loss and impedance characteristics of anodic biofilms in microbial fuel cells (MFCs). Amperometric time-current analysis revealed that at the rotation rate of 480 rpm, a maximum current density of 168 µA cm(-2) can be achieved, which was 22.2 % higher than when there was no rotation. Linear sweep voltammetry and electrochemical impedance spectroscopy tests showed that when the anodic potential was set to -300 mV vs. Ag/AgCl reference, the power densities could increase by 59.0 %, reaching 1385 mW m(-2), the anodic resistance could reduce by 19 %, and the anodic capacitance could increase by 36 %. These results concur with a more than 85 % decrease of the diffusion layer thickness. Data indicated that concentration loss, diffusion layer thickness, and the mixing velocity play important roles in anodic resistance reduction and power output of MFCs. These findings could be helpful to the design of future industrial-scale MFCs with mixed bacteria biofilms.

A polyaniline-modified quartz crystal microbalance (QCM) sensor was obtained through immobilizing the polyaniline film on the silver electrode surface of quartz crystal resonator by an electrochemical method. The sensor was studied for detecting the formic acid gas of different concentrations, and the results showed that the resonant frequency of QCM decreased quickly in the beginning and tended to be constant in the end when exposed to formic acid gas. The frequency shifts decreased faster as the concentration of formic acid gas increased. And the frequency shifts of the QCM sensors were found to be linearly related to the concentration of formic acid gas, which might be used to estimate the concentration level of the formic acid gas within the range of experimental concentrations. The result of on-line monitoring test fully indicated that the QCM sensor responded effectively to the increasing concentration of formic acid and had important practical significance and broad application prospect in real-time detection of antique conservation environment in the museum.

Hydrogen sulphide emission in sewers is associated with toxicity, corrosion and odour and also yields considerable costs. The purpose of this study was to evaluate whether the soluble sulphide concentration in raw sewage can be controlled by dosing an iron-rich waste-activated sludge (WAS) or an iron-rich aerated waste-activated sludge (AWAS). An average soluble sulphide elimination of 99% was achieved at an iron-rich AWAS to sewage ratio (v/v) of 16%, whereas dosage of iron-poor AWAS at the same ratio decreased the soluble sulphide in the raw sewage by only 53%. Our lab-scale tests suggest that dosing iron-rich AWAS to sewage did not affect the chemical oxygen demand (COD) and total ammonia nitrogen (TAN) removal as well as the nitrification efficiency in the receiving activated sludge system. The results indicate that iron-rich AWAS dosage is a feasible technique to remediate the sulphide problem in sewers.

The abiotic cathodes usually require a catalyst such as Pt to enhance power production, increasing the cost and lowering the operational sustainability. In this paper, the performance of a biocathode microbial fuel cell biocatalyzed by ferro/manganese-oxidizing bacteria was investigated. A scanning electron microscopy with an energy-dispersive spectrometer (SEM-EDS) was used to characterize the cathode and analyze the element of cathode. The amount of ferro/manganese-oxidizing bacteria in the biocathode was examined. In batch-fed systems, the maximum open circuit voltage (OCV) was between 700 and 800 mV and the maximum cell potential difference was higher than 600 mV with an external resistance of 100 Ω. The maximum power density was 32 W m −3 MFC for batch-fed systems (20–40% Coulombic yield) and 28 W m −3 MFC for a continuous system with an acetate loading rate of 1.0 kg COD m −3 day −1 . The results of SEM-EDS clearly showed that cathode was impregnated with iron and manganese. The amount of ferro/manganese-oxidizing bacteria was (7.5–20.0) × 10 5 MPN mL −1 in the biocathode. Biocathodes alleviate the need to use noble catalysts for the reduction of oxygen, which step forward towards large-scale application of MFCs.

The purines and its derivatives, such as, guanine, adenine, 2,6-diaminopurine, 6-thioguanine and 2,6-dithiopurine, were investigated as corrosion inhibitors for mild steel in 1 M HCl solution by weight loss measurements, electrochemical tests and quantum chemical calculations. The polarization curves of mild steel in the hydrochloric acid solutions of the purines showed that both cathodic and anodic processes of steel corrosion were suppressed. The Nyquist plots of impedance expressed mainly as a depressed capacitive loop with different compounds and concentrations. For all these purines, the inhibition efficiency increased by increasing the inhibitor concentration, and the inhibition efficiency orders are 2,6-dithiopurine > 6-thioguanine > 2,6-diaminopurine > adenine > guanine with the highest inhibiting efficiency of 88.0% for 10(-3) M 2,6-dithiopurine. The optimized structures of purines, the Mulliken charges, molecular orbital densities and relevant parameters were calculated by quantum chemical calculations. The quantum chemical calculation results inferred that the adsorption belong to physical adsorption, which might arise from the pi stacking between the pi electron of the purines and the metal surface. (C) 2008 Elsevier Ltd. All rights reserved.

It is known that cell potential increases while anode resistance decreases during the start-up of microbial fuel cells (MFCs). Biological capacitance, defined as the apparent capacitance attributed to biological activity including biofilm production, plays a role in this phenomenon. In this research, electrochemical impedance spectroscopy was employed to study anode capacitance and resistance during the start-up period of MFCs so that the role of biological capacitance was revealed in electricity generation by MFCs. It was observed that the anode capacitance ranged from 3.29 to 120 mF which increased by 16.8 % to 18–20 times over 10–12 days. Notably, lowering the temperature and arresting biological activity via fixation by 4 % para formaldehyde resulted in the decrease of biological capacitance by 16.9 and 62.6 %, indicating a negative correlation between anode capacitance and anode resistance of MFCs. Thus, biological capacitance of anode should play an important role in power generation by MFCs. We suggest that MFCs are not only biological reactors and/or electrochemical cells, but also biological capacitors, extending the vision on mechanism exploration of electron transfer, reactor structure design and electrode materials development of MFCs.

This work focused on studying the effect of the chemical oxidation demand to sulfide ratio (COD/S) on power generation and sulfide oxidation in microbial fuel cells treating sulfide-rich wastewater containing organic contaminants. The maximum power density achieved was 20 +/- 1 W m(-3) V(Anode) and the C(oulombic) yield was 20 +/- 2%. The COD/S ofinfluent played an important role in elemental sulfur and sulfate production because of competition between acetate oxidation and element sulfur oxidation to sulfate in the anode. When the COD/S was 12.50/1, more than 74.0% of sulfide was converted into elemental sulfur after 24 hours of operation. The effect of the COD/S on power generation was negligible when the COD/S ranged between 4.85/l and 18.53/l. After 24 hours, the COD removals were 110 +/- 6, 213 +/- 9, 375 +/- 8 and 410 +/- 10 mgl(-1) when the COD/S was 4.85/1, 8.9/1, 12.5/1 and 18.53/1, respectively. The COD removal increased with the increasing COD of the influent, which fitted to the model of first-order reaction kinetics.