Treatment of simulated wastewater from in situ leaching uranium mining by zerovalent iron and sulfate reducing bacteria

Batch and column experiments were conducted to determine whether zerovalent iron (ZVI) and sulfate reducing bacteria (SRB) can function synergistically and accelerate pollutant removal. Batch experiments suggest that combining ZVI with SRB can enhance the removal of U(Ⅵ) synergistically. The removal rate of U(Ⅵ) in the ZVI+SRB combining system is obviously higher than the total rate of ZVI system and SRB system with a difference of 13.4% at t=2 h and 29.9% at t=4 h. Column experiments indicate that the reactor filled with both ZVI and SRB biofilms is of better performance than the SRB bioreactor in wastewater basification, desulfurization and U(Ⅵ) fixation. The results imply that the ZVI+SRB permeable reactive barrier may be a promising method for treating subsurface uranium contamination.

SYNTHESIS AND CHARACTERIZATION OF ZEROVALENT PALLADIUM COMPLEXES

A series of nine Pd(0)complexes(L)Pd(L')[L=bis(diphenylphosphino) methane(dppm),1,2-bis(diphenylphosphino)ethane(dppe),and 1,1'-bis(diphenyl- phosphino)ferrocene(dppf),respectively;L=dibenzylideneacetone(dba),2,3,5, 6-tetrachloro-1.4-benzoquinone(q)and 2,3-dichloro-1,4-naphthoquinone(nq)] were synthesized and characterized by means of elemental analyses,IR,UV, 1~H-NMR and^(31)P-NMR spectra.The redox wave peak potentials of the ferrocenyl group of complexes with dppf were measured by using CV method.Results showed that all the diphosphorus ligands behaved as chelating bidentate ligand and dba,q,nq were coordinated to the Pd(0)atom through their C=C moieties,not their carbonyl ones.Analytical data also showed that there were interactions between the two different ligands in each complex.

Partial aging can counter-intuitively couple with sulfidation to improve the reactive durability of zerovalent iron

Sulfated zero-valent iron(SZVI)has shown promising applications in wastewater treatment.However,the rapid decline in the reactivity of SZVI with time limits its real practice.To mediate this problem,partial aging was proposed to improve the reactive durability of SZVI.Taking Cr(VI)as the target contaminant,we found that the aged ZVI(AZVI)gradually lost reactivity as aging time increased from 0.5 to 2 d.Counter-intuitively,the partially aged SZVI(ASZVI)showed greater reactivity than SZVI when exposed to oxygenated water for a period ranging from 0.5 to 14 d.In addition,the ASZVI with 0.5 d of aging time(ASZVI-0.5)not only maintained reactivity in successive runs but also increased the Cr(VI)removal capacity from 9.1 mg/g by SZVI to 19.1 mg/g by ASZVI-0.5.Correlation analysis further revealed that the electron transfer from the Fe0 core to the shell was mediated by the conductive FeS and FeS2 in the subshell of ASZVI.Meanwhile,the lepidocrocite and magnetite on the surface of ASZVI facilitated Cr(VI)adsorption and subsequent electron transfer for Cr(VI)reduction.Moreover,the iron(hydr)oxide shell could retain the conductive FeS and FeS2 in the subshell,allowing ASZVI to reduce Cr(VI)efficiently and sustainably.In general,partial aging can enhance the reactive durability of ZVI when coupled with sulfidation and this synergistic effect will be beneficial to the application of SZVI-based technology for wastewater treatment.

Removal of decabromodiphenyl ether （BDE-209） by sepiolite-supported nanoscale zerovalent iron

Nanoscale zerovalent iron （nZVI） synthesized using sepiolite as a supporter was used to investigate the removal kinetics and mechanisms of decabromodiphenyl ether （BDE-209）. BDE-209 was rapidly removed by the prepared sepiolite-supported nZVI with a reaction rate that was 5 times greater than that of the conventionally prepared nZVI because of its high surface area and reactivity. The degradation of BDE-209 occurred in a stepwise debromination manner, which followed pseudo- first-order kinetics. The removal efficiency of BDE-209 increased with increasing dosage of sepiolite-supported nZVI particles and decreasing pH, and the efficiency decreased with increasing initial BDE-209 concentrations. The presence of tetrahydrofuran （THF） as a cosolvent at certain volume fractions in water influenced the degrada- tion rate of sepiolite-supported nZVI. Debromination pathways of BDE-209 with sepiolite-supported nZVI were proposed based on the identified reaction intermedi- ates, which ranged from nona- to mono-brominated diphenylethers （BDEs） under acidic conditions and nonato penta-BDEs under alkaline conditions. Adsorption on sepiolite-supported nZVI particles also played a role in the removal of BDE-209. Our findings indicate that the particles have potential applications in removing environ- mental pollutants, such as halogenated organic contami- nants.

Biochar-supported nano-scale zerovalent iron activated persulfate for remediation of aromatic hydrocarbon-contaminated soil:an in-situ pilot-scale study

Biochar supported nano-scale zerovalent iron(nZVI/BC)for persulfate(PS)activation has been studied extensively for the degradation of pollutants on the lab scale,but it was rarely applied in practical soil remediation in the field.In this research,we developed a facile ball-milling method for the mass production of nZVI/BC,which was successfully applied to activate persulfate for the remediation of organic polluted soil on an in-situ pilot scale.In-situ high-pressure injection device was developed to inject nZVI/BC suspension and PS solution into the soil with a depth of 0-70 cm.The removal efficiency of target pollutants such as 2-ethylnitrobenzene(ENB,1.47-1.56 mg/kg),biphenyl(BP,0.19-0.21 mg/kg),4-(methylsulfonyl)toluene(MST,0.32-0.43 mg/kg),and 4-phenylphenol(PP,1.70-2.46 mg/kg)at different soil depths was 99.7%,99.1%,99.9%and 99.7%,respectively,after 360 days of remediation.The application of nZVI/BC significantly increased the degradation rates of contaminants by 11-322%,ascribed to its relatively higher efficiency of free radical generation than that of control groups.In addition,it was found that nZVI/BC-PS inhibited soil urease and sucrase enzyme activities by 1-61%within 55 days due to the oxidative stress for microbes induced by free radicals,while these inhibition effects disappeared with remediation time prolonged(>127 days).Our research provides a useful implementation case of remediation with nZVI/BC-PS activation and verifies its feasibility in practical contaminated soil remediation.

Nano-Phytotechnological Remediation of Endosulfan Using Zero Valent Iron Nanoparticles

Endosulfan, an organochlorine pesticide, is known for its toxicity and ability to accumulate in the environment. In India endosulfan was banned only in 2011 and hence toxic residues are still persistent in the environment. The abilities of three plant species Chittaratha (Alpinia calcarata), Tulsi (Ocimum sanctum), and Lemongrass (Cymbopogon citratus) to remove endosulfan from soil in the absence and presence of zerovalent iron nanoparticles (nZVIs) (1000 mg/Kg of soil), i.e., by phytoremediation and nano-phytoremediation, were determined. Extracted soil samples from the experimental plot were analyzed using Gas Chromatograph with Electron Capture Detector (GC-ECD) and final dehalogenated product was confirmed by Mass Spectrometer (MS). A. calcarata had the best efficiency compared to the other two plant species and the efficiency decreased in the order A. calcarata > O. sanctum> C. citrates. The initial endosulfan removal rate was high (82% was removed within 7 days) when nano phytoremediation experiments were conducted with A. calcarata but then gradually decreased, probably because the activity of nZVI decreased over time. The nZVI endosulfan degradation mechanism appears to involve hydrogenolysis and sequential dehalogenation which was confirmed by GC-MS analysis. Only small amounts of endosulfan were accumulated in the plants because the added nZVIs might have promoted the reductive dechlorination of endosulfan.

Agroecosystem modeling of reactive nitrogen emissions from U.S.agricultural soils with carbon amendments

Fertilizer-intensive agriculture is a leading source of reactive nitrogen(Nr)emissions that damage climate,air quality,and human health.Biochar has long been studied as a soil amendment,but its influence on Nr emissions remains insufficiently characterized.More recently,the pyrolysis of light hydrocarbons has been suggested as a source of hydrogen fuel,resulting in a solid zero-valent carbon(ZVC)byproduct whose impact on soil emissions has yet to be tested.We incorporate carbon amendment algorithms into an agroecosystem model to simulate emission changes in the year following the application of biochar or ZVC to the US.fertilized soils.Our simulations predicted that the impacts of biochar amendments on Nr emissions would vary widely(−17%to+27%under 5 ton ha^(−1) applications,−38%to+18%under 20 ton ha^(−1) applications)and depend mostly on how nitrification is affected.Low-dose biochar application(5 ton ha^(−1))stimulated emissions of all three nitrogen species in 75%of simulated agricultural areas,while high-dose applications(20 ton ha^(−1))mitigated emissions in 76%of simulated areas.Applying zero-valent carbon at 20 ton ha^(−1) exhibited similar effects on nitrogen emissions as biochar applications at 5 ton ha^(−1).Biochar amendments are most likely to mitigate emissions if applied at high rates in acidic soils(pH<5.84)with low organic carbon(<55.9 kg C ha^(−1))and inorganic nitrogen(<101.5 kg N ha^(−1))content.Our simulations could inform where the application of carbon amendments would most likely mitigate Nr emissions and their associated adverse impacts.

Sorption of lanthanide ions on biochar composites

Sorption of lanthanum（Ⅲ）, cerium（Ⅲ and neodymium（Ⅲ） ions from the aqueous solutions of mixtures through adsorption on the biochar composites was investigated as a function of sorbent mass, pH, phase contact time and initial concentration of solutions at 295 K. The maximum removal of lanthanide ions takes place under the following conditions： 0.1 g of sorbent mass, pH 4 and 360 rain contact time for all studied initial concentrations of solutions. Kinetics of La（Ⅲ）, Ce（Ⅲ） and Nd（Ⅲ） ions sorption proceeded by a fast initial uptake reached equilibrium. This process was modelled by means of the pseudo first order, pseudo second order, intraparticle diffusion and Elovich models. The desorption of three lanthahide ions by nitric, hydrochloric and sulfuric acids at a concentration of 1 mol/L from biochar composites was also studied. In order to investigate the sorption mechanism FFIR, XRD and XPS analyses were performed after sorption of ions from the mixture.

Removing polybrominated diphenyl ethers in pure water using Fe/Pd bimetallic nanoparticles

Polybrominated diphenyl ethers （PBDEs） have been widely used as fire-retardants. Due to their high production volume, widespread usage, and environmental persistence, PBDEs have become ubiquitous contaminants in various environments.Nanoscale zero-valent iron （ZVI） is an effective reductant for many halogenated organic compounds. To enhance the degradation efficiency, ZVI/ Palladium bimetallic nanoparticles （nZVI/Pd） were synthe- sized in this study to degrade decabromodiphenyl ether （BDE209） in water. Approximately 90% of BDE209 was rapidly removed by nZVI/Pd within 80 min, whereas about 25% of BDE209 was removed by nZVL Degradation of BDE209 by nZVI/Pd fits pseudo-first-order kinetics. An increase in pH led to sharply decrease the rate of BDE209 degradation. The degradation rate constant in the treatment with initial pH at 9.0 was more than 6.8 x higher than that under pH 5.0. The degradation intermediates of BDE209 by nZVI/Pd were identified and the degradation pathways were hypothesized. Results from this study suggest that nZV//Pd may be an effective tool for treating polybromi- nated diphenyl ethers （PBDEs） in water.

Effect of humic acid and metal ions on the debromination of BDE209 by nZVM prepared from steel pickling waste liquor

As a promising in situ remediation technology, nanoscale zero-valent iron （nZVI） can remove polybromi- nated diphenyl ethers such as decabromodiphenyl ether （BDE209） effectively, However its use is limited by its high production cost. Using steel pickling waste liquor as a raw material to prepare nanoscale zero-valent metal （nZVM） can overcome this deficiency. It has been shown that humic acid and metal ions have the greatest influence on remediation. The results showed that nZVM and nZVI both can effectively remove BDE209 with little difference in their removal efficiencies, and humic acid inhibited the removal efficiency, whereas metal ions promoted it. The promoting effects followed the order Ni2＋ 〉 Cu2＋ 〉 Co2＋ and the cumulative effect of the two factors was a combination of the promoting and inhibitory individual effects. The major difference between nZVM and nZVI lies in their crystal form, as nZVI was found to be amorphous while that of nZVM was crystal. However, it was found that both nZVM and nZVI removed BDE209 with similar removal efficiencies. The effects and cumu- lative effects of humic acid and metal ions on nZVM and nZVI were very similar in terms of the efficiency of the BDE209 removal.

Novel synthesis of aluminum hydroxide gel-coated nano zero-valent iron and studies of its activity in flocculation-enhanced removal of tetracycline

A newly designed aluminum hydroxide gel-coated nanoscale zero-valent iron(AHG@NZVI)with enhanced activity and dispersibility of NZVI was successfully synthesized.The AHG@NZVI composite was synthesized via control of the surface AHG content.AHG@NZVI-1,AHG@NZVI-2 and AHG@NZVI-3 were prepared under centrifugal mixing speeds of 1000,2000 and 4000 r/min,respectively.The activity of AHG@NZVI was evaluated by its tetracycline(TC) removal efficiency.The effects of AHG content,pH value,reaction temperature,and presence of competitive anions on TC removal were investigated.TC could be removed by both adsorption and chemical reduction on AHG@NZVI-2(centrifugal speed 2000 r/min) in a short time with high removal efficiency(≥98.1%) at the optimal conditions.Such excellent performance can be attributed to a synergistic interaction between aluminum hydroxide gel and NZVI:(1) AHG could enhance the stability and dispersity of NZVI;(2) aluminum hydroxide gel could absorb a certain amount of TC and Fe^2+/Fe^3+,which facilitated the mass transfer of TC onto the NZVI surface,resulting in acceleration of the reduction rate of TC by the AHG@NZVI composite;and(3) AHG-Fe^2+/Fe^3+could absorb a certain amount of TC by flocculation.The kinetics of TC removal by AHG@NZVI composite was found to follow a two-parameter pseudo-first-order model.The presence of competitive anions slightly inhibited the activity of AHG@NZVI systems for TC removal.Overall,this study provides a promising alternative material and environmental pollution management option for antibiotic wastewater treatment.

Poly[β-(1→4)-2-amino-2-deoxy-D-glucopyranose] based zero valent nickel nanocomposite for efficient reduction of nitrate in water

Chemical reduction of nitrate using metal nanoparticles has received increasing interest due to over-dependence on groundwater and consequence health hazard of the nitrate ion. One major drawback of this technique is the agglomeration of nanoparticles leading to the formation of large floes. A low cost biopolymeric material, poly [β-（1-4）-2-amino-2-deoxy-D-glucopyranose] （β-PADG） obtained from deacetylated chitin was used as stabilizer to synthesize zero valent nickel （ZVNi） nanoparticles. The β-PADG-ZVNi nanocomposite was characterized using infra red （IR）, UV-Vis spectrophotometric techniques and Scanning Electron Microscope （SEM）. The morphology of the composite showed that β-PADG stabilized-ZVNi nanoparticles were present as discrete particles. The mean particle size was estimated to be （7.76 ± 2.98） nm and surface area of 87.10 m2/g. The stabilized-ZVNi nanoparticles exhibited markedly greater reactivity for reduction of nitrate in water with 100% conversion within 2 hr contact owing to less agglomeration. Varying the β-PADG-to-ZVNi ratio and the ZVNi-to-nitrate molar ratio generally led to a faster nitrate reduction. About 3.4-fold difference in the specific reaction rate constant suggests that the application of the β-PADG-stabilizer not only increased the specific surface area of the resultant nanoparticles, but also greatly enhanced the surface reactivity of the nanoparticles per unit area.