Coupled reduction of chlorinated hydrocarbons and heavy metals by zerovalent silicon.

The feasibility of using zerovalent silicon (Si0) as a novel reductant to remove chlorinated compounds and heavy metals in contaminated sites was investigated. The kinetics and degradation mechanism of carbon tetrachloride (CT) by Si0 were also examined. Results showed that zerovalent silicon could effectively dechlorinate the chlorinated compounds. A nearly complete dechlorination of CT by Si0 was obtained within 14 h. The produced concentrations of chloroform (CF) accounted for 71-88% loss of CT, showing that reductive dechlorination is the major degradation pathway for the degradation of chlorinated hydrocarbons by Si0. The degradation followed pseudo first-order kinetics and the normalized surface reaction rate constant (k(sa)) for CT dechlorination ranged between 0.0342 and 0.0454 L m(-2) h(-1) when CT concentrations were in the range of 3-20 microM. A linear relationship between the k(sa) and pH value was also established. In addition, zerovalent silicon has a high capability in the removal of heavy metals. 83% of Cr(VI) was removed by 0.5g Si0 within 5 h, which is higher than that by Fe0. The removal efficiency of divalent metal ions by Si0 followed the order of Cu(II) > Pb(II) > Ni(II). This indicates that zerovalent silicon is an alternative reductant and can undergo coupled reduction of heavy metals and chlorinated hydrocarbons in contaminated groundwater.     

Synergetic degradation of Fe/Cu/C for groundwater polluted by trichloroethylene

This study investigated the enhancement of synergetic degradation of Fe/Cu/C (Fe: commercial iron, Cu: solid product of Fe reacted with CuSO(4), C: carbon powder) for simulated groundwater contaminated by trichloroethylene (TCE). Zero valent iron (ZVI) as a reducing agent was proved to be effective for TCE removal. The Fe/Cu/C system resulted in higher reduction efficiency as a result of the synergetic role of Fe/Cu and Fe/C microelectrode than the Fe (ZVI) or Fe/Cu system, and the half-life was only about 0.4 h. When m(Fe) achieved 12.5 g L(-1), the residual concentration of TCE almost leveled off. Fe:Cu = 10:1 or m(C) = 0.0086 g can induce the optimum function for TCE degradation. A neutral condition was appropriate for TCE degradation, and an acidic system slightly favored TCE dechlorination compared with an alkaline system. GC/MS analysis indicated that TCE was dechlorinated to 1,1-dichloroethene (1,1-DCE), cis-1,2-dichloroethene (cis-DCE) and vinyl chloride (VC), and 1,1-DCE might be the precursor. Fe/Cu/C reduction is a highly promising technique for TCE removal, and it is an excellent alternative to enhance TCE reductive dechlorination.     

Removal of hexavalent chromium in soil and groundwater by supported nano zero-valent iron on silica fume

Silica fume supported-Fe(0) nanoparticles (SF-Fe(0)) were prepared using commercial silica fume as a support. The feasibility of using this SF-Fe(0) for reductive immobilization of Cr(VI) was investigated through batch tests. Compared with unsupported Fe(0), SF-Fe(0) was significantly more active in Cr(VI) removal especially in 84 wt% silica fume loading. Silica fume had also been found to inhibit the formation of Fe(III)/Cr(III) precipitation on Fe nanoparticles' surface, which was increasing the deactivation resistance of iron. Cr(VI) was removed through physical adsorption of Cr(VI) onto the SF-Fe(0) surface and subsequent reduction of Cr(VI) to Cr(III). The rate of reduction of Cr(VI) could be expressed by pseudo first-order reaction kinetics. The rate constant increased with the increase in iron loading but decreased with the increase in initial Cr(VI) concentration. Furthermore, column tests showed that the SF-Fe(0) could be readily transported in model soil.     

Homogeneous (Fe(III)) and heterogeneous (TiO2) photocatalytic systems for pollutant removal from the aquatic compartment: comparison and complementarity.

Kinetics of the oxidative photodegradation of monuron (3-(4-chlorophenyl)-1-1-dimethylurea) in both homogeneous solution of Fe(ClO4)3 and heterogeneous suspension of TiO2, were investigated and compared. In the homogeneous system (Fe(II)), the speciation of Fe(III) aquacomplexes was shown to play an essential role in the rate of photodegradation. For high concentrations of TiO2 (> 500 mg L(-1)), the photodegradation rate was similar to the reaction rate obtained with a freshly prepared solution of Fe(II) (3 x 10(-4) mol L(-1)). In the combined system (TiO2 + Fe(III)), a synergy effect accelerating the monuron photodegradation was observed. Actually, in the presence of Fe(III) (in concentration compatible with a safe environment), a similar reaction rate for monuron photodegradation was obtained with a TiO2 concentration lower by a factor of 20.     

Selective separation of Cr(III) and Fe(III) from liquid effluents using a chelating resin

This study aimed to assess the selective separation of Cr(III) from Fe(III) from liquid solutions by using a chelating ion exchange resin, Diaion CR 11, from Mitsubishi Chemical Corporation, in the H(+) form. Equilibrium experiments with synthetic solutions of iron and chromium were carried out in batch mode. For both metals favorable adsorption isotherms were obtained, and the experimental data were well described by the Langmuir model. However, the resin exhibited higher affinity for iron than for chromium. The regeneration experiments revealed that, for both metals, HCl provided higher removal efficiencies than H(2)SO(4) and HNO(3). Moreover, precipitation with NaOH allows selectively separate chromium and iron to be stripped from the resin. Experiments in fixed bed operation were carried out to assess the dynamic behavior of the sorption of Cr(III) and Fe(III) into the tested resin by using synthetic and industrial solutions. The experiments with industrial effluent showed that the resin can remove low levels of contaminant transition metal ions, and thus the effluent can be purified for reuse of chromium during periods of 20-25 min. The resin regeneration was achieved with a sequential treatment with HCl and NaOH/H(2)O(2). High efficiencies were observed for both monocomponent and multicomponent systems. A global strategy for separating and recovering Cr(III) from an effluent that also contains Fe(III) is presented, involving the integration of ion exchange (saturation and regeneration phases) and precipitation processes. In conclusion, our approach demonstrates that efficient separation of chromium and iron is possible if ion exchange operation in a fixed bed configuration is optimized and combined with conventional processes such as precipitation.     

Mechanism of adsorption of ferric iron by extracellular polymeric substances (EPS) from a bacterium Acidiphilium sp

The aim of this study was to assess the sorption of Fe(III) by extracellular polymeric substances (EPS) of the Acidiphilium 3.2Sup(5) bacterium, which has promising properties for use in microbial fuel cells (MFC). The EPS of A. 3.2Sup(5) was extracted using EDTA. The sorption isotherms were determined using aliquots of purified EPS. The exosubstances loaded with metal were characterized by scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), X-ray diffraction spectroscopy (XRD) and Fourier transform infrared spectroscopy (FTIR). The sorption uptake approaches to 536.1 +/- 26.6 mg Fe(III) (g EPS)(-1) at an initial ferric concentration of 2.0 g l(-1). The sorption of Fe(III) by EPS can be fitted to the Freundlich model. The sorption process produces hydrated iron (III) oxalate [Fe(OH)(C2O4) x 2H2O] by a reversible reaction (log K = 1.06 +/- 0.16), indicating that a shift in the sorption of the cation can be easily achieved. Know the magnitude and form of iron sorption by EPS in MFC can foresee the potential impact on the metabolism of iron-reducing and iron-oxidazing bacteria and, therefore, on the feasibility of the system.     

Mechanistic evidence and efficiency of the Cr(VI) reduction in water by different sources of zerovalent irons.

The objective of this research was to assess the mechanism and effectiveness of the zerovalent iron (ZVI) to remediate the Cr(VI) contaminated water. The mechanism of Cr(VI) reduction by ZVI was evaluated by characterising surface properties and chemical compositions of Fe and Cr products using SEM-EDS, XRD and XPS analyses. The effectiveness of ZVI in Cr(VI) reduction was assessed by the luminescent bacteria (Photobacterium Phosphoreum). The Cr(VI) was reduced to Cr(III), when the reactive Fe(o) was oxidised to Fe(II, III), showing the presence of Fe2O3, (Fe-Cr)2O3 and FeOOH. The SEM-EDS analysis showed that ZVI with a higher reducing capacity was more subject to changes of surface and morphological properties due to ionisation of ZVI. The Cr and Fe in precipitates subsisted exclusively in the Cr(III) or Fe(III) states with the respective forms of Cr(OH)3 or Cr2O3 and FeOOH or Fe2O3. Electrons produced from ZVI oxidation reduced Cr(VI) to Cr(III), thus resultantly Cr(III) precipitated or co-precipitated with Fe(III) to form Fe(III)-Cr(III) hydroxide or Fe(III)-Cr(III) oxyhydroxide. Toxicity of water reacted with ZVI was significantly lower than that of the untreated water.     

Enhancing phosphorus removal in constructed wetlands with ochre from mine drainage treatment.

No single end-use has yet been identified that is capable of consuming the projected production of ochre (mainly iron (III) oxides) from mine drainage treatment. However, the high sorption capacity of ochre for phosphorus (up to 26 mg kg(-1)) means that it could be used in constructed wetlands to enhance phosphorus removal. Laboratory batch experiments showed that coarse-grained ochre removes 90% of all phosphorus forms from sewage effluent after 15 minutes of shaking. From a larger-scale experiment, it is estimated that constructed wetlands with an ochre substrate should remove phosphorus from sewage effluent for up to 200-300 years. The suitability of ochre for phosphorus removal is being investigated at the field scale in a wastewater constructed wetland (175 m2 area) in Berwickshire, UK. The hydraulic and treatment performance of the wetland were monitored for 15 months prior to installation at the inlet in November 2003 of a tank containing approximately 1200 kg ochre. Results so far show that improved hydraulic design is required for ochre to increase the mean phosphorus removal efficiency of the system (27 +/- 28%), but potentially toxic metals (Al, Cd, Cr, Cu, Fe, Ni, Pb, Zn) have not been released from the ochre into the wetland outflow.     

Evaluation of hybrid treatments to produce high quality reuse water

Four tertiary hybrid treatments to produce high quality reused water, fulfilling Brazilian drinking water regulations, from a slaughterhouse's secondary treated effluent were evaluated. The pilot plant with a capacity of 500 L h(-1) was set up and consisted of these stages: pre-filtration system (cartridge filter 50 micron, activated carbon filter, cartridge filter 10 micron), oxidation (H2O2) or second filtration (ceramic filter, UF) followed by UV radiation (90 L h(-1)). The best combination was T4: pre-filtration followed by H2O2 addition and UV radiation (AOP H2O2/UV). Disinfection kinetics by T4 followed pseudo first-order kinetics: k(T4) = 0.00943 s(-1) or 0.00101 cm2 mJ(-1). Three different zones (A, B, C) were observed in the UV254 degradation kinetics (pseudo-first order kinetics): k' decreased over time (k'(A) > k'(B) > k'(C)).     

New insights in the dihydroxybenzenes-driven Fenton reaction: electrochemical study of interaction between dihydroxybenzenes and Fe(III)

It has been reported that the dihydroxybenzene (DHB) driven Fenton reaction is more efficient to degrade recalcitrant substrates than the simple Fenton reaction. The enhanced reactivity of the DHB driven Fenton reaction is not clear, but it could be explained by the formation of oxidant species different from the ones formed by classical Fenton reaction or by the shift of the redox potential of the complex formed by DHB and Fe(III). The redox reaction between Fe(III) and the DHBs 1,2-dihydroxybenzene (catechol, CAT), 2,3-dihydroxybenzoic acid (2,3-DHBA), 3,4-dihydroxybenzoic acid (3,4-DHBA), and 1,2-dihydroxy-3,5-benzenedisulfonate (TIRON) was studied by cyclic voltammetry to better understand the enhanced reactivity of the DHB driven Fenton reaction. It was determined that the amount of Fe(II) produced by the redox reaction between Fe(III) and DHBs was insufficient to explain the enhanced reactivity. Cyclic voltammograms (CV) of the DHBs/Fe(III) systems show a quasi-reversible or irreversible behavior and also shifting and splitting the anodic peaks. This effect can be related to DHBs oxidation by Fe(III), but not to a real interaction.     

Geospeciation of arsenic using MINTEQA2 for a post-mining lake.

The objective of this study was to investigate the cycling of arsenic in the water column of a post-mining lake. This study is part of a research project to develop health risk assessment for the surrounding population. Inductively Coupled Plasma-Mass Spectrophotometer (ICP-MS) and Capillary Electrophoresis (CE) have been used to analyze the total amount and speciation, respectively. A computer program, called MINTEOA2, which was developed by the United States Environmental Protection Agency (USEPA) was used for predicting arsenic, iron, and manganese as functions of pH and solubility. Studying the pH values and cycle of arsenic shows that the percentage of bound arsenate, As(V) species in the form of HAsO4- increases with range pH from 5 to 7, as well as Fe(II) and Mn(III). As expected phases of arsenic oxides are FeAsO4 and Mn3(AsO4), as a function of solubility, however none of these phases are over saturated and not precipitated. It means that the phases of arsenic oxides have a high solubility.     

Removal of lead(II) and copper(II) from aqueous solution using foitite from Linshou mine in Hebei, China

Foitite from Linshou mine in China's Hebei province was investigated as an adsorbent to remove Pb(II) and Cu(II) from aqueous solution. The results showed that foitite can readily remove heavy metal ions from aqueous solution. The data shows that the metal uptake for Pb(II) increases rapidly, accounting for 74.47% when contact time was 2 min. In contrast to Pb(ll), there was a worse capability for adsorption of Cu(II). In the first 4 min, the metal uptake accounted for 34.7%. According to the analytical results obtained from X-ray diffraction, laser Raman spectrum, X-ray energy dispersive spectrometer, and Zeta potential, the removal mechanism of Pb(II) and Cu(II) by using foitite can be explained as following: firstly, the existence of an electrostatic field around foitite particles can attract heavy metal ions and consequently combine heavy metal ions with OH; secondly, heavy metal ions in the solution are exchanged with the Fe3+ and Al3+ in the foitite.     

Development and validation of a UPLC-MS/MS method for studying the degradation kinetics of ofloxacin and trimethoprim during the application of solar Fenton process in secondary treated sewage

In this work, a sensitive and highly selective method was developed and validated to study the degradation of two antibiotic compounds (ofloxacin (OFX) and trimethoprim (TMP)), spiked in secondary treated domestic effluents, by the solar Fenton process. Three different chromatographic columns were tested on a ultra performance liquid chromatography-tandem mass spectrometric (UPLC-MS/MS) instrument working in the electrospray ionization (ESI) mode with twelve combinations of eluting solvents. Samples were enriched prior to the analysis by solid phase extraction using the hydrophilic-lipophilic balanced (HLB) reversed phase polymeric sorbent. The method was optimized and showed very good performance characteristics and was successfully applied to study the degradation kinetics of the selected antibiotics during the solar Fenton process applied. The degradation was found to follow a pseudo first-order kinetics for both compounds at initial concentration of 100 μg L(-1) with k = 0.0345 min(-1) for OFX and k = 0.0768 min(-1) for TMP, whereas the complete removal was achieved after 120 min of treatment for both compounds.     

Biosorption of lead(ll) and copper(ll) from stormwater by brown seaweed Sargassum sp.: batch and column studies.

This study evaluated the potential use of brown seaweed Sargassum sp to sequester lead and copper (Pb(II) and Cu(ll)) from urban runoff based on batch as well as column experiments. The equilibrium data exhibited Langmuir isotherms. The adsorption capacity of this seaweed was found to be 196.1 mgg(-1) and 84.0 mg g(-1) for Pb(ll) and Cu(ll), respectively, which are in good agreement with those values obtained for the aqueous solution (188.6 mg g(-1) for Pb(ll) and 86.9 mg g(-1) for Cu(II)). The functional group analysis of the seaweed using FTIR demonstrated that the carboxyl functional groups are mainly responsible for biosorption. The cation exchange capacity of the biosorbent was 2.25 meq/g. This observation suggested that ion exchange mechanism is predominantly responsible for the metal ion uptake. The column study showed that the highest bed height and the lowest flow rate result in a substantial enhancement of the metals uptake with the biosorption uptake capacities being 264.3 mg Pb(ll) g(-1) and 86.0 mg Cu(ll) g(-1). In the binary system, the biosorption capacity was observed to be 208.7 mg Pb(ll) g(-1) and 61.0 mg Cu(II) g(-1). The predicted breakthrough curves by the Thomas adsorption model gave a good fit of the experimental data with r2 ranging from 0.92 to 0.99.     

Application of iron-coated sand and manganese-coated sand on the treatment of both As(III) and As(V).

In this study, manganese-coated sand (MCS) and iron-coated sand (ICS) were applied in the oxidation of As(III) and adsorption of As(V), respectively. ICS and MCS were prepared by mixing FeCl3 and Mn(NO3)2, respectively, with Joomoonjin sand at 150 degrees C. In the batch adsorption isotherms, adsorption of As(III) and As(V) onto ICS followed a Langmuir type. ICS showed a greater capacity in the removal of As(V) than As(III) and also in the removal of As(V) compared with MCS. Three different configurations of ICS and MCS were used to investigate the oxidation of As(III) and adsorption of As(V) in a column. In the homogenised system, arsenic breakthrough was approximately two-times delayed compared with the separately packed systems. After breakthrough of arsenic, concentration of As(III) in the effluents was below 40 ppb for the entire reaction period in all configurations, and most arsenic was identified as As(V) owing to near complete conversion of As(III) to As(V) by MCS. The catalytic activity of MCS on the oxidation of As(III) was maintained up to 700 pore volumes, which corresponds to the treatment of at least 300 mg As(III) based on the 1 kg MCS. Compared with the homogenised column, the released Mn(II) concentration from two-staged and four-staged columns was great for the entire reaction period. In the case where the same amount of ICS and MCS was packed in a filtration system, the homogenised column was identified as a better configuration compared with the two-staged and four-staged columns when considering the arsenic breakthrough time as well as the released concentration of Fe(III) and Mn(II).     

Removal of toxic heavy metals by iron-coated starfish.

In this study, the applicability of calcined starfish (SF) and iron-coated SF (ICSF) as potential adsorbents for the treatment of wastewater containing heavy metal ions was evaluated. ICSF was prepared by mixing FeCl(3) solution previously adjusted to pH 7 approximately 9 with SF at 105 degrees C. From the dissolution test at pH 2, ICSF showed strong acid-proof properties. In the batch adsorption, Cu(II) adsorption onto ICSF was completed within 150 minutes, while 47% Cu(II) was removed with SF alone. This result clearly suggests that the coated Fe(III) serves additional adsorption sites, resulting in the enhanced removal of heavy metal ions. The removed fraction of both Cu(II) and Pb(II) increased with increasing solution pH and nearly complete removals of Pb(II) and Cu(II) were observed at around pH 6 and 8, respectively. From the adsorption isotherm of Cu(II) onto SF and ICSF at pH 3.0, the removed amount of Cu(II) by ICSF was greater than that by SF over the entire concentration range studied. In the column test, the breakthrough of Cu(II) in the ICSF column was greatly retarded compared to that in the SF column. Based on the drinking water regulations for Cu(II), SF and ICSF were able to remove 3400 and 8600 mg/kg of Cu(II) from the wastewater, respectively.     

Microbial Fe(II)-oxidation by nitrate in activated sludge

The oxidation of Fe(II) to Fe(III) by addition of nitrate and nitrite to activated sludge was studied to determine whether the process was biological or chemical (chemodenitrification). It was shown that the process was mainly biological, although the microorganisms involved have not yet been described. Investigations in a full scale treatment plant suggested that the process most likely took place m the anoxic (denitrification) tank. Details of the kinetics and stoichiometry have not yet been determined, but the process may he of significance for keeping Fe(III) oxidized, which is important for P-removal and for floc structure. Furthermore, in some treatment plants, the oxidation may also be of significance for nitrate removal (denitrification).     

氧气对零价铁去除三价砷过程的影响及其机制

为研究氧气对零价铁(Fe0)去除水中三价砷(As(Ⅲ))过程的影响,通过曝氮气、空气和氧气的实验研究了pH为4.0和6.0时As(Ⅲ)的去除动力学,并采用X射线精细吸收结构谱(XAFS)和X射线衍射谱(XRD)等表征手段探究其影响机制。结果表明:尽管高浓度的氧气有利于As(Ⅲ)被氧化为更容易被铁氧化物吸附的五价砷(As(Ⅴ)),但曝空气对于As(Ⅲ)的去除相对于曝氧气更为有利。在pH为4.0时,高浓度的氧气能够促进Fe0的溶解,从而抑制As(Ⅲ)的去除;而在pH为6.0时,高浓度的氧气会导致Fe0表面钝化,从而阻碍反应的进行。此外,曝氮气则几乎完全抑制了Fe0对水中As(Ⅲ)的去除,这是由于无氧条件不利于吸附性铁氧化物的生成;调控氧气的量可改进Fe0对As(Ⅲ)的去除效果。     

Photo-Fenton reaction using a nanocomposite.

A laponite RD clay-based Fe nanocomposite (Fe-Lap-RD) has been synthesized by the so-called pillaring technique. The X-ray diffraction (XRD) results reveal that the Fe-Lap-RD mainly consists of Fe2O3 (maghemite) crystallites and Fe2SiO10(OH)2 (iron silicate hydroxide) crystallites. The photo-catalytic activity of the Fe-Lap-RD for the degradation of an organic azo dye Orange II is examined. It is found that the rate of mineralization of Orange II is slower than that of discoloration. Under optimal conditions, 100% color and 70% total organic carbon (TOC) of 0.2 mM Orange II can be removed in 45 and 90 minutes, respectively. In addition, the performance of a strongly acidic type of ion exchange resin based catalyst as a heterogeneous photo-Fenton catalyst for the degradation of salicylic acid is also discussed.     

Use of iron(VI) and iron(V) in water and wastewater treatment.

Fe(VI) (Fe(VI)O4(2-)) and Fe(V) (Fe(V)O4(3-)) have high oxidizing power, selectivity, and upon decomposition produce a non-toxic by-product, Fe(III), which makes them potential oxidants in water and wastewater treatment. Rates of oxidation increase with a decrease in pH and are related to protonation of Fe(VI)O4(2-) and Fe(V)O4(3-). Oxidation of sulfur- and nitrogen-containing pollutants by Fe(VI) can be accomplished in seconds to minutes with formation of non-hazardous products. Fe(VI) can easily oxidize the amino acid components of microcystins and is a suitable disinfectant for detoxifying toxins in water. The oxidation of pollutants and amino acids with Fe(V) is 3-5 orders of magnitude faster than with Fe(VI). The use of ionizing radiation and photocatalytic techniques in the presence of Fe(VI) results in Fe(V) formation and may have synergistic effects on the oxidation of pollutants and removal of toxins in water and wastewater. This paper summarizes the results of multi-functional properties of Fe(VI) and Fe(V) to treat water and wastewater.