Removal and degradation of phenol in a saturated flow by in-situ electrokinetic remediation and Fenton-like process.

In this laboratory study, a sandy loam soil saturated with phenol solution was treated by in-situ electrokinetics-Fenton process incorporated with a permeable reactive wall of scrap iron powder (SIP). The soil was contaminated and saturated with aqueous phenol solution of 90-115 mg/kg in concentration. It was then placed in a soil cell. The soil cell was assembled with an anode reservoir and a cathode reservoir at its ends. A bed of SIP (1.05-32.69 g) was inserted in the soil cell at a distance of 5 cm from the anode reservoir compartment. For the test runs, 0.3% H(2)O(2) was used as the anode reservoir fluid, whereas de-ionized water was used as the cathode reservoir fluid. An electric gradient of 1 V/cm was applied to enhance the saturated flow in the soil cell for a period of 10 days. Experimental results have shown that the electroosmotic (EO) flow quantity decreased as the amount of SIP increased. This phenomenon was in good agreement with the results showing the value of EO permeability increased with a decreasing amount of SIP. Results also showed that throughout the test period the cumulative, consumed mass of H(2)O(2) in the anode reservoir increased as the amount of SIP decreased. On the other hand, the cumulative, increased mass of phenol in the cathode reservoir was found to increase with a decreasing amount of SIP. Meanwhile, the residual phenol concentration in the soil cell was found to decrease with a decreasing amount of SIP. When 1.05 g scrap iron powder was used, an overall removal and destruction efficiency of phenol of 99.7% was obtained. Therefore, it is evident that an in-situ combined technology of electrokinetic remediation and Fenton-like process is capable of simultaneously removing and degrading the phenol in a saturated flow.     

The effect of critical operational parameters on the circulation-enhanced electrokinetics

Electrokinetics (EK) is a technique for soil remediation. However, the acid produced due to the water electrolysis at the anode will cause soil acidification, which may destroy the soil constituents, and reduce contaminant removal efficiency. The formation of a base front produced at the cathode will result in the precipitation of metal hydroxides and a concomitant clogging of pore space. In this study, a circulation-enhanced EK (CEEK) system is designed to neutralize the pH of the working solution and soils for avoiding the above problems. Experiments are conducted by controlling different voltage gradients, electrode materials, and electrode emplacement, respectively. According to the experimental results, the CEEK system could effectively stabilize the current and the pH of processing solution at a neutral range. The strength of voltage gradient is proportional to the current magnitude of the CEEK system. The graphite electrode for CEEK is the better choice than the metal electrodes because graphite electrodes can achieve the lower electricity consumption. The electrode installed in the reservoir without attachment on soils can decrease the pH deviation of the soil matrix.     

The remediation performance of a specific electrokinetics integrated with zero-valent metals for perchloroethylene contaminated soils

This research was conducted to evaluate an integrated technique, combination of the electrokinetics (EK) and zero-valent metal (ZVM), for remediation of the perchloroethylene (PCE) contaminated soils. Various experimental conditions were controlled such as different voltage gradients, the position of ZVM, and ZVM species. The appropriate operational parameters are concluded as follows: (1) 0.01 M sodium carbonate serves as the working solution; (2) the voltage gradient is controlled at 1.0 V/cm; (3) ZVM wall is settled close to the anode. Based on the above operation conditions, the pH value of working solution can maintain at neutral range for avoiding the soil acidification. Neutral pH also causes the system to stay at a stable status of electricity consumption. The removal efficiency reaches 99% and 90% for decontaminating the PCE in the pore-water and the soil, respectively, after a 10-day treatment. The zero-valent zinc performs better PCE degradation than zero-valent iron. Moreover, the soils treated by EK+ZVM still possess their original properties.     

Integration of electrokinetics and chemical oxidation for the remediation of creosote-contaminated clay

Remediation of clayey soils that are contaminated with polycyclic aromatic hydrocarbons (PAHs) is a challenging task that may require integration of several technologies. The benefits of integrating in situ electrokinetic remediation with chemical oxidation were evaluated in laboratory-scale experiments lasting for 8 weeks. A voltage gradient of 48 V/m of direct current and 4.7 V/m of alternating current and periodic additions of chemical oxidants were applied to creosote-contaminated soil. Electrokinetically enhanced oxidation with sodium persulphate resulted in better PAH removal (35%) than either electrokinetics (24%) or persulphate oxidation (12%) alone. However, the improvement was shown only within 1/3 (5 cm) of the soil compartment. Electrokinetics did not improve the performance of Fenton oxidation. Both chemical oxidants created more positive oxidation-reduction potential than electrokinetic treatment alone. On the other hand, persulphate treatment impaired the electroosmotic flow rate. Elemental analyses showed reduction in the natural Al and Ca concentrations, increase in Zn, Cu, P and S concentrations and transfer of several metal cations towards the cathode. In conclusion, the results encourage to further optimisation of an integrated remediation technology that combines the beneficial effects of electrokinetics, persulphate oxidation and Fenton oxidation.     

Application of a new electrolyte circulation method for the ex situ electrokinetic bioremediation of a laboratory-prepared pentadecane contaminated kaolinite

Ex situ electrokinetic (EK) bioremediation of a laboratory-prepared pentadecane-contaminated kaolinite was carried out. Extraneous bacteria and ionic nutrients were continuously supplied to the soil specimen by a new electrolyte circulation method, which controlled electrical pH change of electrolyte solution to keep bacterial activity. During the EK bioremediation the anode region showed the highest colony forming unit (CFU) due to electrical attraction between anode and bacteria. Simultaneous increases of CFU and uniform pentadecane removal in most soil regions demonstrated that electro-osmosis as well as electrophoresis affected the bacterial transport in soil. At 3.13 mA/cm2, increase in soil temperature to above 45 degrees C inhibited bacterial activity, which caused the decrease of removal efficiency. The removal amount of pentadecane increased with initial pentadecane concentration at the same current densities (0.63 and 1.88 mA/cm2) because of the increased amount of weakly bound pentadecane onto the soil surface. The highest removal efficiency (77.6%) was obtained at 0.63 mA/cm2 for 1000 mg/kg pentadecane after 14 days. Consequently, the present methods of EK bioremediation demonstrated superiority over the conventional bioremediation, which had inherent demerits of slow degradation and low removal efficiency.     

Electrodialytic remediation of copper mine tailings

Mining activities in Chile have generated large amounts of solid waste, which have been deposited in mine tailing impoundments. These impoundments cause concern to the communities due to dam failures or natural leaching to groundwater and rivers. This work shows the laboratory results of nine electrodialytic remediation experiments on copper mine tailings. The results show that electric current could remove copper from watery tailing if the potential gradient was higher than 2 V/cm during 21 days. With addition of sulphuric acid, the process was enhanced because the pH decreased to around 4, and the copper by this reason was released in the solution. Furthermore, with acidic tailing the potential gradient was less than 2 V/cm. The maximum copper removal reached in the anode side was 53% with addition of sulphuric acid in 21 days experiment at 20 V using approximately 1.8 kg mine tailing on dry basis. In addition, experiments with acidic tailing show that the copper removal is proportional with time.     

Electro-kinetic dewatering of oily sludges

An oily sludge from a rendering facility was treated using electro-kinetic (EK) techniques employing two different experimental designs. The bench scale used vertical electrodes under different operational conditions, i.e. varied electrode spacing at 4, 6 and 8 cm with electric potential of 10, 20 and 30 V, respectively. The highest water removal efficiency (56.3%) at bench scale was achieved at a 4 cm spacing and 30 V. Comparison of the water removal efficiency (51.9%) achieved at the 20 V at 4 cm spacing showed that power consumption at 30 V was 1.5 times larger than that at 20 V, suggesting a further increase of electric potential is unnecessary. The solids content increased from an initial 5 to 11.5 and 14.1% for 20 and 30 V, respectively. The removal of oil and grease (O&G) was not significant at this experimental design. Another larger scale experiment using a pair of horizontal electrodes in a cylinder with 15 cm i.d. was conducted at 60 V at an initial spacing of 22 cm. More than 40.0% of water was removed and a very efficient oil separation from the sludge was achieved indicating the viability of electro-kinetic recovery of oil from industrial sludge.     

Interfacial evolution in Sn–58Bi solder joints during liquid electromigration

For Sn–58Bi low temperature solder alloy, local molten induced from electromigration Joule heating might change the atomic diffusion and interfacial behavior. In this paper, the diffusion behavior and interfacial evolution of Cu/Sn–58Bi/Cu joints were studied under liquid–solid (L–S) electromigration in molten solder and were compared with the interfacial behaviors in solid–solid (S–S) electromigration in solid solder. L–S or S–S electromigration was realized by applying a current density of 1.0?×?10⁴ A/cm² to molten solder at 150 °C or solid solder at 25 °C, respectively. During S–S electromigration, Bi atoms were driven towards anode side under electromigration induced flux and then accumulated to form Bi-rich layer near anode interface with current stressing time increasing. During L–S electromigration, Bi atoms were reversely migrated from anode to cathode to produce Bi segregation at cathode interface, while Cu atoms were rapidly dissolved into molten solder from cathode and migrated to form large amounts of Cu₆Sn₅ rod-like phases near anode interface. The reversal in the direction of Bi atoms may be attributed to the reversal in the direction of electromigration induced flux and correspondingly the change on effective charge number of Bi atoms from negative to positive.     

Evaluation of electrokinetic removal of heavy metals from sewage sludge

The presence of heavy metals is one of the main obstacles for agricultural use of million tonnes of dewatered sewage sludge produced in wastewater treatment plants. Electrokinetic (EK) treatment can be applied to remove heavy metals from sludge. The aim of this study was to increase the efficiency of electrokinetic removal of heavy metals from dewatered sewage sludge. EK experiments were carried out with and without pH adjustment in cathode chamber of acidified sewage sludge. The selective sequential extraction (SSE) was used to determine the fractionation of heavy metals in sewage sludge. The mobility of heavy metals in sludge significantly increased after its acidification at pH 2.7 and followed the order: Ni, Zn, Cu, As, Cr, Pb. Removal efficiencies of heavy metals in the experiment with acidified sewage sludge and pH adjustment at cathode chamber at 2.0 were: 95% for Zn, 96% for Cu, 90% for Ni, 68% for Cr, 31% for As and 19% for Pb. The concentrations of Zn, Cu, Ni, Cr and Pb after EK treatment were below the United States Environmental Protection Agency limits for biosolids applied to agricultural land, forest, public contact sites or reclamation sites.     

Biosorption of palladium(II) from aqueous solution by moss (Racomitrium lanuginosum) biomass: equilibrium, kinetic and thermodynamic studies

Arsenite (As(III)) and arsenate (As(V)) removal by direct contact membrane distillation (DCMD) were investigated with self-made polyvinylidene fluoride (PVDF) membranes in the present work. Permeability and ion rejection efficiency of the membrane were tested before the arsenic removal experiments. A maximum permeate flux 20.90 kg/m(2)h was obtained, and due to the hydrophobic property, the PVDF membrane had high rejection of inorganic anions and cations which was independent of the solution pH and the temperature. The experimental results indicated that DCMD process had higher removal efficiency of arsenic than pressure-driven membrane processes, especially for high-concentration arsenic and arsenite removal. The experimental results indicated that the permeate As(III) and As(V) were under the maximum contaminant limit (10 microg/L) until the feed As(III) and As(V) achieved 40 and 2000 mg/L, respectively. The 250 h simultaneous DCMD performance of 0.5mg/L As(III) and As(V) solution was carried out, respectively. The permeate arsenic was not detected during the process which showed the PVDF membrane had stable arsenic removal efficiency. Membrane morphology changed slightly after the experiments, however, the permeability and the ion rejection of the membrane did not change.     

Remediation of TCE contaminated soils by in situ EK-Fenton process

The treatment performance and cost analysis of in situ electrokinetic (EK)-Fenton process for oxidation of trichloroethylene (TCE) in soils were evaluated in this work. In all experiments, an electric gradient of 1V/cm, de-ionized water as the cathode reservoir fluid and a treatment time of 10 days were employed. Treatment efficiencies of TCE were evaluated in terms of the electrode material, soil type, catalyst type, and catalyst dosage and granular size if applicable. Test results show that graphite electrodes are superior to stainless steel electrodes. It was found that the soil with a higher content of organic matter would result in a lower treatment efficiency (e.g. a sandy loam is less efficient than a loamy sand). Experimental results show that the type of catalyst and its dosage would markedly affect the reaction mechanisms (i.e. "destruction" and "removal") and the treatment efficiency. Aside from FeSO4, scrap iron powder (SIP) in the form of a permeable reactive wall was also found to be an effective catalyst for Fenton reaction to oxidize TCE. In general, the smaller the granular size of SIP, the lower the overall treatment efficiency and the greater the destruction efficiency. When a greater quantity of SIP was used, a decrease of the overall treatment efficiency and an increase of percent destruction of TCE were found. Experimental results have shown that the quantity of electro-osmotic (EO) flow decreased as the quantity of SIP increased. It has been verified that the treatment performances are closely related to the corresponding EO permeability. Results of the cost analysis have indicated that the EK-Fenton process employed in this work is very cost-effective with respect to TCE destruction.     

Use of solar cell in electrokinetic remediation of cadmium-contaminated soil

This preliminary study used a solar cell, instead of direct current (DC) power supply, to generate electric field for electrokinetic (EK) remediation of cadmium-contaminated soil. Three EK tests were conducted and compared; one was conducted on a cloudy and rainy day with solar cell, one was conducted on a sunny day with solar cell and another was conducted periodically with DC power supply. It was found that the output potential of solar cell depended on daytime and was influenced by weather conditions; the applied potential in soil was affected by the output potential and weather conditions, and the current achieved by solar cell was comparable with that achieved by DC power supply. Solar cell could be used to drive the electromigration of cadmium in contaminated soil, and removal efficiency achieved by solar cell was comparable with that achieved by DC power supply. Compared with traditional DC power supply, using solar cell as power supply for EK remediation can greatly reduce energy expenditure. This study provided an alternative to improve the EK soil remediation and expanded the use of solar cell in environmental remediation.     

Electrokinetic removal of 2,6-dichlorophenol and diuron from kaolinite and humic acid-clay system

This paper presents the results of a study on the electrokinetic treatment of kaolinite and humic acid kaolinite complexes spiked with 2,6-dichlorophenol or 3-(3,4-dichlorophenyl)-1,1-dimethylurea (diuron). In particular, the attention was paid to the interaction between solid surface and dissolved organics: the effects of contaminant sorption as well as the physicochemical reactions on the efficiency of electrokinetic remediation were investigated. Using a 3V/cm voltage gradient, approximately 90% of diuron was removed from kaolinite after one water pore volume was collected in the cathode reservoir, but much lower efficiency was obtained in the electrokinetic removal of this compound from humic acid-coated kaolinite. The results also showed that partial degradation of the contaminant occurred during electrokinetic treatment of kaolinite clay spiked with 2,6-dichlorophenol: the contamination in the clay could be remediated by the combination of electrokinetic extraction and electrochemical reactions.     

Removal of As(V) and As(III) by reclaimed iron-oxide coated sands

This paper aims at the feasibility of arsenate and arsenite removal by reclaimed iron-oxide coated sands (IOCS). Batch experiments were performed to examine the adsorption isotherm and removal performance of arsenic systems by using the IOCS. The results show that the pH(zpc) of IOCS was about 7.0 +/- 0.4, favoring the adsorption of As(V) of anion form onto the IOCS surface. As the adsorbent dosage and initial arsenic concentration were fixed, both the As(V) and As(III) removals decrease with increasing initial solution pH. Under the same initial solution pH and adsorbent dosage, the removal efficiencies of total arsenic (As(V) and As(III)) were in the order as follows: As(V)>As(V)+As(III)>As(III). Moreover, adsorption isotherms of As(V) and As(III) fit the Langmuir model satisfactorily for the four different initial pH conditions as well as for the studied range of initial arsenic concentrations. It is concluded that the reclaimed IOCS can be considered as a feasible and economical adsorbent for arsenic removal.     

Surface complexation modeling of the removal of arsenic from ion-exchange waste brines with ferric chloride

Brine disposal is a serious challenge of arsenic (V) removal from drinking water using ion-exchange (IX). Although arsenic removal with ferric chloride (FeCl(3)) from drinking waters is well documented, the application of FeCl(3) to remove arsenic (V) from brines has not been thoroughly investigated. In contrast to drinking water, IX brines contain high ionic strength, high alkalinity, and high arsenic concentrations; these factors are known to influence arsenic removal by FeCl(3). Surface complexation modeling and experimental coagulation tests were performed to investigate the influence of ionic strength, pH, Fe/As molar ratios, and alkalinity on the removal of arsenic from IX brines. The model prediction was in good agreement with the experimental data. Optimum pH range was found to be between 4.5 and 6.5. The arsenic removal efficiency slightly improved with higher ionic strength. The Fe/As ratios needed to treat brines were significantly lower than those used to treat drinking waters. For arsenic (V) concentrations typical in IX brines, Fe/As molar ratios varying from 1.3 to 1.7 were needed. Sludge solid concentrations varying from 2 to 18 mg L(-1) were found. The results of this research have direct application to the treatment of residual wastes brines containing arsenic.     

Electrochemical degradation of amaranth aqueous solution on ACF

The degradation of Amaranth, a kind of azo dye, has been studied under galvanostatic model with activated carbon fiber (ACF) electrode in aqueous solution with electrochemical method. The ACF was used as anode and cathode, respectively for the decolorization process. The onset oxidation potential and reduction potential for Amaranth on ACF were respectively ascertained at 0.6 and -0.4 V. During the range of -1.1 to 0.50 mA cm(-2), the decolorization was clarified into three processes as electroreduction, adsorption and electrooxidation. There were little contributions to the color and COD removals for the process of adsorption. The color removal can be up to 99% when the current density was 0.50 mA cm(-2). The maximum COD removal was 52% for the process of electrooxidation. Hundred percent color removal was obtained when the current density of -1.0 mA cm(-2) was applied. The maximum COD removal was 62% for the electroreduction. The COD removal results from the adsorption of products for the decolorization process of electrooxidation or electroreduction.     

Assessment of electrokinetic removal of heavy metals from soils by sequential extraction analysis

Electrokinetic remediation of metal-contaminated soils is strongly affected by soil-type and chemical species of contaminants. This paper investigates the speciation and extent of migration of heavy metals in soils during electrokinetic remediation. Laboratory electrokinetic experiments were conducted using two diverse soils, kaolin and glacial till, contaminated with chromium as either Cr(III) or Cr(VI). Initial total chromium concentrations were maintained at 1000mg/kg. In addition, Ni(II) and Cd(II) were used in concentrations of 500 and 250mg/kg, respectively. The contaminated soils were subjected to a voltage gradient of 1 VDC/cm for over 200h. The extent of migration of contaminants after the electric potential application was determined. Sequential extractions were performed on the contaminated soils before and after electrokinetic treatment to provide an understanding of the distribution of the contaminants in the soils. The initial speciation of contaminants was found to depend on the soil composition as well as the type and amounts of different contaminants present. When the initial form of chromium was Cr(III), exchangeable and soluble fractions of Cr, Ni, and Cd ranged from 10 to 65% in kaolin; however, these fractions ranged from 0 to 4% in glacial till. When the initial form of chromium was Cr(VI), the exchangeable and soluble fractions of Cr, Ni and Cd ranged from 66 to 80% in kaolin. In glacial till, however, the exchangeable and soluble fraction for Cr was 38% and Ni and Cd fractions were 2 and 10%, respectively. The remainder of the contaminants existed as the complex and precipitate fractions. During electrokinetic remediation, Cr(VI) migrated towards the anode, whereas Cr(III), Ni(II) and Cd(II) migrated towards the cathode. The speciation of contaminants after electrokinetic treatment showed that significant change in exchangeable and soluble fractions occurred. In kaolin, exchangeable and soluble Cr(III), Ni(II), and Cd(II) decreased near the anode and increased near the cathode, whereas exchangeable and soluble Cr(VI) decreased near the cathode and increased near the anode. In glacial till, exchangeable and soluble Cr(III), Ni(II), and Cd(II) were low even before electrokinetic treatment and no significant changes were observed after the electrokinetic treatment. However, significant exchangeable and soluble Cr(VI) that was present in glacial till prior to electrokinetic treatment decreased to non-detectable levels near the cathode and increased significantly near the anode. In both kaolin and glacial till, low migration rates occurred as a result of contaminants existing as immobile complexes and precipitates. The overall contaminant removal efficiency was very low (less than 20%) in all tests.     

Electrochemical treatment of anionic surfactants in synthetic wastewater with three-dimensional electrodes

The electrochemical oxidation of anionic surfactants (sodium dodecyl benzene sulfonate, DBS) contained in simulated wastewater treated by three-dimensional electrode system with combined modified kaolin served as packed bed particle electrodes and Ti/Co/SnO(2)-Sb(2)O(3) anode was studied, the chemical oxygen demand (COD) removal of pollutants in the solutions was also investigated. The results showed that the three-dimensional electrodes in combined process could effectively decompose anionic surfactants. The COD removal efficiency can reach 86%, much higher than that of Ti/Co/SnO(2)-Sb(2)O(3) electrodes used singly or modified kaolin employed singly (graphite as anode and cathode) on the same condition of pH 3 and 38.1 mA/cm(2) current density. The current efficiency and kinetic constant were calculated and energy consumption was studied. At the same time the influence of pH and current density on COD removal efficiency with combined three-dimensional electrodes was also investigated, respectively. The optimal initial pH value of degradation is 3 (acid condition), and a minor COD removal increase follows higher current density.     

电场对Au/SiO_2及Au-Ag/SiO_2表面结构与原子迁移特性的影响

利用扫描俄歇微探针（SAM）和原子力显微镜（AFM）研究了SiO2衬底上在外加直流电场作用下沉积的Au薄膜及Au－Ag复层薄膜的表面形貌、结构变化及电迁移扩散行为。结果表明：①在衬底表面施加水平方向电场辅助沉积制备的Au薄膜其表面显示出平整的椭球形晶粒，并沿外电场方向呈织构取向。与未加电场的热蒸发沉积膜相比，具有较为均匀、有序的表面微观结构。②SiO2表面Au-Ag复层薄膜在直流电场作用下，Au，Ag物种同时向负极方向作走向迁移扩散，这与Au－Ag复层薄膜在Si（111）表面电迁移时Au，Ag分别向两极扩散的特点不同，反映了衬底性质对表面原子电迁移的影响。③Au－Ag复膜在电迁移过程中还发生了表面原子聚集状态的变化，原来沉积排布的细小晶粒在电迁移扩散过程中出现不均匀长大，导致薄膜表面粗糙度显著增加。     

Observations on the electromigration in various thin films of group I–IV

The transport of ions under the influence of a direct current has been found to be directed towards the cathode in thin films of silver, copper and gold, and towards the anode in aluminum, magnesium, indium, tin and lead films. The direction of electromigration in silver, copper and gold films is opposite to the one usually found in bulk samples of these metals. In silver films with large as well as with small grains the direction of electrotransport is the same. The experiments show that electromigration in single-crystalline silver films is small. This suggests that grain boundary electrotransport predominates in silver films over surface and volume electrotransport, which is also true for aluminum films.