Surfactant enhanced persulfate system for the synergistic oxidation and reduction of mixed chlorinated hydrocarbons.

Surfactant-enhanced in-situ chemical oxidation (S-ISCO) is widely applied in soil and groundwater remediation. However, the role of surfactants in the reactive species (RSs) transformation remains inadequately explored. This work introduced nonionic surfactant Tween-80 (TW-80) into a nano zero-valent iron (nZVI) activated persulfate (PS) system. The findings indicate that PS/nZVI/TW-80 system can realize the concurrent removal of trichloroethylene (TCE), tetrachloroethene (PCE), and carbon tetrachloride (CT), whereas CT cannot be eliminated without TW-80 presence. Further analysis unveiled that hydroxyl (HO•) and sulfate radicals (SO4－•) were the primary species for TCE and PCE degradation, while CT was reductively eliminated by surfactant radicals generated from TW-80. Moreover, the surfactant radicals were found to accelerate Fe(III)/Fe(II) cycle, reduce the production of iron sludge, and increase PS decomposition. The possible degradation routes of mixed chlorinated hydrocarbons (CHCs) and the decomposition pathways of TW-80 were proposed through the density function theory (DFT) calculation and intermediates analysis. Additionally, the effects of other nonionic surfactants on the simultaneous removal of TCE, PCE, and CT, and the practical applications using the actual contaminated groundwater were also evaluated. This study provides theoretical support for the simultaneous removal of CHCs, particularly those containing perchlorinated contaminants, using the S-ISCO techniques.

Detection of formic acid and acetic acid gases by a QCM sensor coated with an acidified multi-walled carbon nanotube membrane.

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.

Risk assessment of lead and cadmium leaching from solidified/stabilized MSWI fly ash under long-term landfill simulation test.

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.

Degradation of Polyamide Nanofiltration Membranes by Bromine: Changes of Physiochemical Properties and Filtration Performance.

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.

Enhanced solidification/stabilization of lead in MSWI fly ash treatment and disposal by gelatinized sticky rice.

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.

Ecotoxicity assessment of sodium dimethyldithiocarbamate and its micro-sized metal chelates in Caenorhabditis elegans.

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.

Suspended anode-type microbial fuel cells for enhanced electricity generation.

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.

Decrease of dissolved sulfide in sewage by powdered natural magnetite and hematite.

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 60µm was used. The results showed that 40mgL-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 283.3mgSg-1Fe for magnetite, hematite, FeCl3 and FeSO4 at the optimal dosage of 40mgL-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 10-40mV 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.

Anodic concentration loss and impedance characteristics in rotating disk electrode microbial fuel cells.

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.

Biological capacitance studies of anodes in microbial fuel cells using electrochemical impedance spectroscopy.

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.

Effect of the chemical oxidation demand to sulfide ratio on sulfide oxidation in microbial fuel cells treating sulfide-rich wastewater.

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.

Improvement of biological total phosphorus release and uptake by low electrical current application in lab-scale bio-electrochemical reactors.

The overall process enhancement by different electrical current application on the biological phosphorus release and uptake have been investigated. Five reactors were constructed for three experiments and activated sludge was used as inoculums. In Exp.1 by comparing the control and the bio-electrochemical reactors, it was found that the overall phosphorus removal efficiency could be enhanced at lower electrical current applications of 5mA and 10mA, but were restrained at higher than 20mA, although 20mA could be a sensitive turning point. Moreover, the electrochemical effects of the cathodic and the anodic reactions on the phosphorus release and uptake, respectively, have been further evaluated separately under an electrical current application of 10mA in Exp.2 and Exp.3, respectively. As observed, both of the biological release and uptake were improved by the cathodic reactions in the cathode reactor, but not by the anodic reactions in the anode reactor, and thus indicated that the cathodic reactions play an important role in the improvement of the biological phosphorus release and uptake.