Simultaneous Removal of Trivalent Chromium and Hexavalent Chromium from Soil Using a Modified Bipolar Membrane Electrodialysis System.

In this study, a modified bipolar membrane electrodialysis system equipped with a "back-to-back" soil compartment was fabricated for simultaneous removal of trivalent chromium (Cr(III)) and hexavalent chromium (Cr(VI)) from contaminated soils. The results showed that the soil solution pH had a significant effect on the Cr(III) and Cr(VI) desorption, and the desorption data fit well with the Elovich kinetic model. Current density had an obvious effect on Cr(III) and Cr(VI) removal, cell voltage, soil pH, current efficiency, and specific energy consumption, and the optimal current density was 2.0 mA/cm2. The removal efficiencies of Cr(III) and Cr(VI) were both 99.8%, while Cr(III) and Cr(VI) recoveries were somewhat lower at 87 and 90%, respectively, because some Cr(III) and Cr(VI) were adsorbed by the membranes. An energy consumption analysis indicates that the back-to-back soil compartment equipped system increased the current efficiency and decreased the specific energy consumption. When a system equipped with two back-to-back soil compartments was used to remove chromium from soil, the current efficiency increased to 28.8% and the specific energy consumption decreased to 0.048 kWh/g. The experimental results indicate that the proposed process has the potential to be an effective technique for the treatment of soil contaminated with heavy metals.

Recovering chromium from electroplating sludge using an integrated technology of bipolar membrane electrodialysis and H2O2 oxidation.

Chromium electroplating produces Cr(III)-containing electroplating sludge (EPS) in large volumes, which is easily oxidised to Cr(Ⅵ) and is harmful to the environment and human health. This study recovered Cr(III) as Na2CrO4 from EPS using an integrated bipolar membrane electrodialysis (BMED)-H2O2 oxidation technology. During the treatment process, Cr(III) was oxidised to Cr(VI) using H2O2 in an alkaline environment, BMED was used to separate and recover Cr(VI). Experimental results showed that H2O2 dosage and pH affected Cr(III) oxidation-the highest Cr(III) oxidation ratio of 68.4% was observed when H2O2 dosage and pH were 5.5 mL and 12.0, respectively. The current density, solid/liquid ratio and sludge particle size affected Cr(III) recovery, energy consumption and current efficiency. Under a current density of 20.0 mA/cm2, solid/liquid ratio of 1.0:45 and sludge particle size of 100 mesh, 58.2% of Cr(III) was recovered. When the number of the equipped EPS compartments was increased from one to two and three, the specific energy consumption decreased from 1.04 to 0.87 and 0.81 kW h/g, respectively, but the current efficiency remained almost constant. After EPS treatment, the Cr(III) remaining in the sludge was mainly in the residual state, which is less environmentally harmful. The obtained Na2CrO4 had similar properties according to X-ray diffraction analysis. Thus, the proposed integrated technology effectively recovers Cr(III) from EPS and other chromium-containing solid wastes.

Nickel recovery from electroplating sludge via bipolar membrane electrodialysis.

In this study, nickel (Ni) was recovered from electroplating sludge in the form of Ni(OH)2 using a bipolar membrane electrodialysis (BMED) system. The results showed that the H+ generated by the bipolar membrane could effectively desorb Ni from the sludge to the solution and the solution pH considerably affected Ni desorption. The desorption process can be described using the first-order kinetic model. The current density and solid/liquid ratio (m/v) considerably affected Ni recovery. Moreover, 100% of Ni was removed from the electroplating sludge and 93.5% of Ni was recovered after 28 h under a current density of 20 mA/cm2, a solid/liquid ratio of 1.0:15 and an electroplating-sludge particle size of 100 mesh. As the number of electroplating compartments increased from one to two and three, the current efficiency for recovering Ni changed from 12.1% to 11.8% and 11.9%, respectively, and the specific energy consumption decreased from 0.064 to 0.048 and 0.039 kW·h/g, respectively. Fourier-transform infrared spectroscopy and Raman spectroscopy showed that the precipitate obtained in this study is similar to commercial Ni(OH)2 and the purity of Ni(OH)2 in the obtained precipitate was 79%. Thus, the results showed that the BMED system is effective for recovering Ni from electroplating sludge.

Recovery of nickel in the form of Ni(OH)2 from plating wastewater containing Ni-EDTA using bipolar membrane electrodialysis.

Ni is often present in plating wastewater as a complexing state. It is difficult to remove this Ni using traditional chemical precipitation technology. In this study, a bipolar membrane electrodialysis system was used to recover Ni in the form of Ni(OH)2 from plating wastewater containing Ni-ethylenediaminetetraacetic acid (Ni-EDTA) without adding chemical reagents. The stable structure of Ni-EDTA can be destroyed by H+ produced by the bipolar membrane to obtain free Ni2+, which can combine with OH- produced by the bipolar membrane to form Ni(OH)2. When the electrolyte Na2SO4 concentration, current density and initial Ni-EDTA concentration were 0.2 mol/L, 16 mA/cm2 and 1000 mg/L, respectively, 99.0% of Ni-EDTA was removed after 32 h. When the system was used to treat actual plating wastewater, 92.1% of Ni-EDTA was removed and 88.7% was recovered. When the number of wastewater compartments in the system was increased from one to three, the current efficiency increased from 1.7% to 5.8%, and the specific energy consumption decreased from 0.39 to 0.19 kW h/g. The results of an X-ray diffraction study indicate that the Ni(OH)2 obtained in this study is similar to commercial Ni(OH)2. Moreover, the recovery mechanism of Ni-EDTA was analysed. Thus, bipolar membrane electrodialysis can be regarded as an effective method to recover Ni from wastewater containing Ni-EDTA.

Recovery of copper from electroplating sludge using integrated bipolar membrane electrodialysis and electrodeposition.

Electroplating sludge, though a hazardous waste, is a valuable resource as it contains a large amount of precious metals. In this study, copper was recovered from the electroplating sludge using a technology that integrates bipolar membrane electrodialysis (BMED) and electrodeposition. The experimental results showed that Cu2+ in the electroplating sludge was successfully separated and concentrated in the BMED system without adding any chemical reagents; the concentrated Cu2+ was recovered in the form of copper foil in an electrodeposition system. Current density clearly affected the Cu2+ separation and concentration in the BMED system; the current density, solution pH and Cu2+ concentration drastically affected the Cu2+ electrodeposition ratio and the morphology and purity of the obtained copper foil. Under the optimised experimental conditions, 96.4% of Cu2+ was removed from the electroplating sludge and 65.4% of Cu2+ was recovered in the foil form. On increasing the number of electroplating sludge compartments from one to two and three, the current efficiency for recovering Cu2+ increased from 17.4% to 28.5% and 35.2%, respectively, and the specific energy consumption decreased from 11.3 to 6.7 and 5.3 kW h/kg of copper, respectively. The purity of the copper foil was higher than 99.5%. Thus, the integrated technology can be regarded as an effective method for recovering copper from electroplating sludge.

Application of Bipolar Membrane Electrodialysis in Environmental Protection and Resource Recovery: A Review.

Bipolar membrane electrodialysis (BMED) is a new membrane separation technology composed of electrodialysis (ED) through a bipolar membrane (BPM). Under the action of an electric field, H2O can be dissociated to H+ and OH-, and the anions and cations in the solution can be recovered as acids and bases, respectively, without adding chemical reagents, which reduces the application cost and carbon footprint, and leads to simple operation and high efficiency. Its application is becoming more widespread and promising, and it has become a research hotspot. This review mainly introduces the application of BMED to recovering salts in the form of acids and bases, CO2 capture, ammonia nitrogen recovery, and ion removal and recovery from wastewater. Finally, BMED is summarized, and future prospects are discussed.

Separation and Concentration of Nitrogen and Phosphorus in a Bipolar Membrane Electrodialysis System.

Struvite crystallization is a successful technique for simultaneously recovering PO43- and NH4+ from wastewater. However, recovering PO43- and NH4+ from low-concentration solutions is challenging. In this study, PO43-, NH4+, and NO3- were separated and concentrated from wastewater using bipolar membrane electrodialysis, PO43- and NH4+ can then be recovered as struvite. The separation and concentration of PO43- and NH4+ are clearly impacted by current density, according to experimental findings. The extent of separation and migration rate increased with increasing current density. The chemical oxygen demand of the feedwater has no discernible impact on the separation and recovery of ions. The migration of PO43-, NH4+, and NO3- fits zero-order migration kinetics. The concentrated concentration of NH4+ and PO43- reached 805 mg/L and 339 mg/L, respectively, which demonstrates that BMED is capable of effectively concentrating and separating PO43- and NH4+. Therefore, BMED can be considered as a pretreatment method for recovering PO43- and NH4+ in the form of struvite from wastewater.

Recovery of trivalent and hexavalent chromium from chromium slag using a bipolar membrane system combined with oxidation.

Chromium slag (CS) with large quantities of multivalent Cr species (III and VI) generated during chromium salt production is hazardous to nature and living organisms. Furthermore, CS discharge leads to considerable resource wastage. Herein, a bipolar membrane electrodialysis (BMED) system was employed along with hydrogen peroxide (H2O2) oxidation for simultaneously recovering Cr(III) and Cr(VI) from CS in the form of Na2CrO4. A bipolar membrane was used to produce OH- under a direct electric field, providing an alkaline environment for the oxidative conversion of Cr(III) to Cr(VI) in the presence of H2O2, followed by the recovery of Cr(III) and Cr(VI) as Na2CrO4. The effect of H2O2content on Cr(III) oxidation and that of the current density on chromium recovery, current efficiency and specific energy consumption were investigated. Moreover, the morphology of chromium in CS before and after the BMED treatment was analysed. The H2O2 content affected the Cr oxidation rate from Cr(III) to Cr(VI). The current density affected chromium removal, current efficiency and specific energy consumption. At a current density of 2 mA/cm2, the total chromium recovery exceeded 67% and the remaining chromium was mainly in the residual state (RES). When the number of CS compartments increased, the current efficiency was enhanced and the specific energy consumption decreased. Binding state analysis show that Cr(III) and different species of Cr(VI) could be transformed into exchangeable Cr(VI) after H2O2 oxidation and BMED treatment. After the treatment, 92% of the remaining chromium in CS was in the RES. Thus, the employed method can effectively recover chromium from CS and other chromium-contaminated solid waste.

Recovery of phosphate and ammonium nitrogen as struvite from aqueous solutions using a magnesium-air cell system.

The addition of alkaline and magnesium sources during the recovery of NH4+ and PO43- in the form of struvite using the traditional struvite precipitation method increases the production cost. To solve this problem, a magnesium-air cell (MAC) system was used herein to recover NH4+ and PO43- as struvite from wastewater using a magnesium strip (Mg2+) and the oxygen adsorbed on the surface of a titanium plate (OH-) as the anode and cathode, respectively. Experimental parameters (i.e. initial solution pH, temperature, NH4+/PO43- molar ratio, NH4+ and PO43- initial concentrations and stirring intensity) were found to affect the removal rate of NH4+ and PO43-. The presence of Ca2+ decreased the struvite purity. At Ca2+/PO43- ratios of 0:1 and 0.5:1, the purity of the obtained struvite after 6 h was 93.8% and 58.9%, respectively. Struvite with a purity of 95.7%, electricity with an average output power of 2.53 mW, and an energy density of 1.05 W/m2 were obtained when the proposed system was used to recover NH4+ and PO43- from an actual supernatant of domestic sludge anaerobic digestion. Scanning electron microscopy-energy-dispersive X-ray spectroscopy, X-ray diffraction, Fourier transform infrared spectroscopy, Raman spectroscopy and thermogravimetric analyses showed that the obtained struvite exhibited almost the same physicochemical properties as commercial struvite. Thus, the MAC system can be regarded as an effective method for recovering NH4+ and PO43- in the form of struvite from wastewater.

Electrochemical disinfection using a modified reticulated vitreous carbon cathode for drinking water treatment.

A reticulated vitreous carbon (RVC) cathode modified by anodic polarization in 20 wt% H2SO4 solution was used for drinking water disinfection under a neutral low electrolyte concentration (0.25 g/L Na2SO4) condition. The contribution of the modified RVC anode and the Ti/RuO2 cathode to disinfection was investigated. The influences of current, initial Escherichia coli load, temperature and water volume were studied. The results show that H2O2 generation increased to approximately three times using the modification of the RVC. E. coli was mainly deactivated by the H2O2 generated at the cathode. For water with about 106 CFU/mL E. coli, the detection limit (<4 CFU/mL) was reached under different conditions. Increasing current could simultaneously shorten the treatment time and increase the energy consumption (EC) simultaneously. Although decreasing the initial load reduced the treatment time, the EC for per log E. coli removal increased. The time required for disinfection shortened from 3.5 to 2.5 h and the EC for per log removal decreased from 218.5 to 123.2 Wh/m3 when the temperature increased from 20 to 40 °C. Although more time was required for disinfection, the EC decreased from 218.5 to 141.4 Wh/m3 when the volume was doubled.

2,4-Dichlorophenol removal from water using an electrochemical method improved by a composite molecularly imprinted membrane/bipolar membrane.

Low efficiency is often a problem in electrochemical reductive hydrodechlorination (ERHD) to remove chlorinated compounds such as 2,4-dichlorophenol (24DCP) from water. In this study, a composite molecularly imprinted membrane (MIM)/bipolar membrane (BPM) was introduced onto a palladium-coated titanium mesh electrode (BPM/MIM@Pd/Ti) to increase the concentration of 24DCP on the surface of electrode and ERHD efficiency. The efficiency of ERHD of 24DCP increased from 70 to 88% by introduction of the two membranes, from 71 to 89% by increasing current density from 5.0 to 30 mA/cm2, and from 80 to 94% by increasing the electrolyte concentration from 0.25 to 1.00 mol/L. Treatment with Fenton's reagent after ERHD achieved 100% 24DCP removal, with chemical oxygen demand and total organic carbon reductions of 91 and 87%, respectively. Notably, these reductions were greater than obtained from the direct oxidation of the 24DCP solution by Fenton's reagent alone (i.e., 98, 84, and 72%, respectively). No products were detected in solution by GC-MS after treatment with the proposed combination technology. The mechanism of 24DCP removal and degradation involved adsorption, electrochemical hydrodechlorination via Hads, and Fenton oxidation. Results show the process has high potential for removing 24DCP from aqueous solution.

High-load domestic wastewater treatment using a combined anaerobic-aerobic bio-filter with coal cinder as medium.

A combined anaerobic-aerobic bio-filter technology was used for field treatment of high-organic-load domestic wastewater with coal cinder as the bio-filter medium. The effects of parameters, including hydraulic retention time (HRT) and backflow ratio, on the decrease in the chemical oxygen demand (COD), NH3-N, total nitrogen (TN), total phosphorus (TP), and turbidity were investigated. The results showed the obvious influence of the HRT and ratio of backflow on wastewater treatment. Under the optimal HRT condition of 18 h, the removal efficiencies of COD, NH3-N, TN, TP, and turbidity were 67.9%, 95.6%, 30.4%, 65.6%, and 83.8%, respectively. When the backflow ratio (2:1) was added to the treatment system, the TN removal obviously increased, and the removal efficiencies of COD, NH3-N, TN, TP, and turbidity were 88.1%, 91.7%, 69.9%, 69.6%, and 97.5%, respectively. These results indicated that the combined technology has the potential as a treatment method for high-organic-load domestic wastewater.

Detection of Avian H7N9 Influenza A Viruses in the Yangtze Delta Region of China During Early H7N9 Outbreaks.

Since the first H7N9 human case in Shanghai, February 19, 2013, the emerging avian-origin H7N9 influenza A virus has become an epizootic virus in China, posing a potential pandemic threat to public health. From April 2 to April 28, 2013, some 422 oral-pharyngeal and cloacal swabs were collected from birds and environmental surfaces at five live poultry markets (LPMs) and 13 backyard poultry farms (BPFs) across three cities, Wuxi, Suzhou, and Nanjing, in the Yangtze Delta region. In total 22 isolates were recovered, and six were subtyped as H7N9, nine as H9N2, four as H7N9/H9N2, and three unsubtyped influenza A viruses. Genomic sequences showed that the HA and NA genes of the H7N9 viruses were similar to those of the H7N9 human isolates, as well as other avian-origin H7N9 isolates in the region, but the PB1, PA, NP, and MP genes of the sequenced viruses were more diverse. Among the four H7N9/H9N2 mixed infections, three were from LPM, whereas the other one was from the ducks at one BPF, which were H7N9 negative in serologic analyses. A survey of the bird trading records of the LPMs and BPFs indicates that trading was a likely route for virus transmission across these regions. Our results suggested that better biosecurity and more effective vaccination should be implemented in backyard farms, in addition to biosecurity management in LPMs.

Reverse flow injection analysis method for catalytic spectrophotometric determination of iron in estuarine and coastal waters: a comparison with normal flow injection analysis.

A method for determining iron in seawater had been developed by coupling reverse flow injection analysis (rFIA) and catalytic spectrophotometric detection with N,N-dimethyl-p-phenylenediamine dihydrochloride (DPD). With a seawater sample or a standard solution as the carrier, the mixture of DPD and buffer was injected into the carrier stream quantitatively and discretely. After mixing with H(2)O(2), the DPD was oxidized to form two pink semiquinone derivatives that were monitored at 514 nm wavelength with a reference at 700 nm. The method detection limit was 0.40 nmol L(-1), lower than half of that of normal flow injection analysis (nFIA) method. The sample throughput was 10h(-1) with triplicate determination, compared with 4h(-1) for nFIA-DPD method. The analysis results of the certified seawaters CASS-4 (12.33 ± 0.18 nmol L(-1)) and NASS-5 (3.47 ± 0.23 nmol L(-1)) well agreed with the certified values (12.77 ± 1.04 and 3.71 ± 0.63 nmol L(-1), respectively). The typical precision of the method for a 2.97 nmol L(-1) iron sample was 4.49% (n=8). Interferences from copper and salinity were investigated. An instrument was assembled based on the proposed method and applied successfully to analyze total dissolvable iron (TDFe) in surface seawater samples collected from the Pearl River Estuary, the results of which revealed non-conservative behavior of TDFe during the estuarine mixing. Results for these samples with both rFIA-DPD and nFIA-DPD methods showed good agreement with each other. The proposed method was superior to the currently used nFIA-DPD method, particularly when it is adapted for field and in situ deployment, due to its lower reagent consumption, higher sample throughput and keeping the manifold tubing clean.

Electrochemical removal of chromium from aqueous solutions using electrodes of stainless steel nets coated with single wall carbon nanotubes.

An electrochemical technique was adopted to investigate the removal of Cr(VI) species and total chromium (TCr) from aqueous solution at a laboratory scale. The electrodes of stainless steel nets (SSNE) coated with single wall carbon nanotubes (SWCNTs@SSNE) were used as both anode and cathode. Three parameters, including solution pH, voltage and electrolyte concentration, were studied to explore the optimal condition of chromium removal. The optimal parameters were found to be pH 4, voltage 2.5 V and electrolyte concentration 10 mg/L. Under these conditions, the Cr(VI) and TCr removal had a high correlation with the amount of SWCNTs coated on the electrodes, with coefficients of the regression equations 0.953 and 0.928, respectively. The mechanism of Cr(VI) removal was also investigated. X-ray photoelectron spectroscopy (XPS) study and scanning electron microscope (SEM) picture showed that the process of chromium removal involved the reduction of Cr(VI) to Cr(III) on the cathode, and then the adsorption of Cr(III) by SWCNTs on the cathode. The study results indicated that the proposed method provided an interesting means to remove chromium species from aqueous solution, especially Cr(VI) in acidic condition.

Mercury distribution in seawater discharged from a coal-fired power plant equipped with a seawater flue gas desulfurization system.

BACKGROUND AND PURPOSE: More and more coal-fired power plants equipped with seawater flue gas desulfurization systems have been built in coastal areas. They release large amount of mercury (Hg)-containing waste seawater into the adjacent seas. However, very limited impact studies have been carried out. Our research targeted the distribution of Hg in the seawater, sediment, biota, and atmosphere, and its environmental transportation. METHODS: Seawater samples were collected from five sites: 1, sea areas adjacent to the power plant; 2, near discharge outlets; 3, the aeration pool of the power plant; and 4 and 5, two reference sites. The total gaseous Hg was determined in situ with a Tekran 2537B. Analyses of total Hg (TM) followed the USEPA methods. RESULTS: In most part of the study area, TM concentrations were close to the reference values and Hg transfer from the seawater into the sediment and biota was not obvious. However, in the aeration pool and near the waste discharge outlets, atmospheric and surface seawater concentrations of TM were much higher, compared with those at a reference site. The concentration ranges of total gaseous Hg and TM in seawater were 3.83-8.60 ng/m(3) and 79.0-198 ng/L near the discharge outlets, 7.23-13.5 ng/m(3) and 186-616 ng/L in the aeration pool, and 2.98-4.06 ng/m(3) and 0.47-1.87 ng/L at a reference point. CONCLUSIONS: This study suggested that the Hg in the flue gas desulfurization waste seawater was not only transported and diluted with sea currents, but also could possibly be transferred into the atmosphere from the aeration pool and from the discharge outlets.