Treatment of decabromodiphenyl ether (BDE209) contaminated soil by solubilizer-enhanced electrokinetics coupled with ZVI-PRB

Effects of Pretreatment and Polarization Shielding on EK-PRB of Fe/Mn/C-LDH for Remediation of Arsenic Contaminated Soils

In this study, coupling electrokinetic (EK) with the permeable reactive barriers (PRB) of Fe/Mn/C-LDH composite was applied for the remediation of arsenic-contaminated soils. By using self-made Fe/Mn/C-LDH materials as PRB filler, the effects of pretreatment and polarization shielding on EK-PRB of Fe/Mn/C-LDH for remediation of arsenic contaminated soils were investigated. For the pretreatment, phosphoric acid, phosphoric acid and water washing, and phosphate were adopted to reduce the influence of iron in soil. The addition of phosphate could effectively reduce the soil leaching toxicity concentration. The removal rate of the soil pretreated with phosphoric acid or phosphoric acid and water washing was better than with phosphate pretreatment. For the polarization shielding, circulating electrolyte, electrolyte type, anion and cation membranes, and the exchange of cathode and anode were investigated. The electrolyte circulates from the cathode chamber to the anode chamber through the peristaltic pump to control the pH value of the electrolyte, and the highest arsenic toxicity removal rate in the soil reaches 97.36%. The variation of total arsenic residue in soil using anion and cation membranes is the most regular. The total arsenic residue gradually decreases from cathode to anode. Electrode exchange can neutralize H⁺ and OH^- produced by electrolyte, reduce the accumulation of soil cathode area, shield the reduction of repair efficiency caused by resistance polarization, enhance current, and improve the removal rate of arsenic in soil.

Efficient removal of TBBPA with a Z-scheme BiVO4-(rGO-Cu2O) photocatalyst under sunlight irradiation

In this study, reduced graphene oxide (rGO) was used to fabricate a Z-scheme BiVO₄-(rGO-Cu₂O) photocatalyst for the degradation of Tetrabromobisphenol A (TBBPA) under sunlight irradiation. The photocatalyst was synthesized using a three-step method BiVO₄-(rGO-Cu₂O) photocatalyst with an rGO loading of 1% and (rGO-Cu₂O) to BiVO₄ ratio of 50% achieved the best degradation effect for TBBPA removal. Electron paramagnetic resonance spectroscopy (EPR) confirmed that the charge transfer path of BiVO₄-(rGO-Cu₂O) follows that of Z-scheme photocatalysts. Moreover, the addition of rGO increases the charge transfer efficiency. High performance liquid chromatography-mass spectrometry (HPLC-MS) was used to detect and analyze intermediate products, allowing the proposal of the main degradation pathway of TBBPA. Photogenerated electrons of BiVO₄-(rGO-Cu₂O) were then transferred into the conduction band of Cu₂O. Cu₂O is located in the surface layer, which has the most effective contact area with pollutants, and therefore has a good outcome for the photocatalytic reduction of TBBPA. Photogenerated electrons (e^-) and hydroxyl radicals (∙OH) are the main factors affecting TBBPA degradation. The degradation process of TBBPA includes electron reduction debromination, hydroxylation, and β-cleavage. In our work, BiVO₄-(rGO-Cu₂O) was successfully synthesized to degrade TBBPA; this study brings forth a novel approach for the degradation of halogenated organic pollutants using a Z-scheme photocatalytic composite.

Removal of lindane using electrokinetic soil flushing coupled with air stripping

This paper evaluates the remediation of soil spiked with lindane using a combined treatment consisting of electrokinetic soil flushing (EKSF) with air stripping to elucidate the main processes occurring in the soil when electric fields of 0.75 V cm−1 and 1.50 V cm−1 are applied. The results demonstrate that lindane is efficiently transported to the anodic and cathodic wells using flushing fluids containing sodium dodecyl sulfate (SDS). Additionally, an important amount is volatilized and stripped with the injected air. In the cathodic well, lindane is rapidly transformed into other species because of the strongly alkaline media. These other species are also found in the portions of soil next to this well, confirming the efficient transport of chlorinated organics with SDS. After 14 days of operation, nearly 50% of the spiked lindane can be removed from the soil. Operation with large electric fields does not improve the performance of the treatment technology and results in lower current intensities and electro-osmotic fluxes and in higher evaporated water, despite the water content in the soil matrix, indicating the coexistence of multiple inputs in these processes.

Graphical abstract

Chelating surfactant N-lauroyl ethylenediamine triacetate enhanced electrokinetic remediation of copper and decabromodiphenyl ether co-contaminated low permeability soil: Applicability analysis

In this study, chelating surfactant N-lauroyl ethylenediamine triacetate (N-LED3A) was used as strengthening agent for electrokinetic (EK) remediation of copper (Cu) and decabromodiphenyl ether (BDE209) co-contaminated low permeability soil. The results indicated that negligible amount of N-LED3A would be adsorbed on the experimental soil. The synchronous elution efficiencies (SEEs) of Cu and BDE209 had reached 65.4% and 49.9%, respectively, when the concentration of N-LED3A was 4000 mg/L, and they kept almost unchanged as the concentration of N-LED3A further increased. Meanwhile, the optimal SEEs were obtained at the pH condition within 6-8. The removal efficiencies of Cu (55.3%-65.8%) and BDE209 (31.4%-46.4%) would be increased with the applied voltage gradient and concentration of N-LED3A. In addition, BDE209 and Cu contaminants were also detected in the catholyte and anolyte, respectively, and their concentrations still showed an uptrend by the end of the experiments. While in the control experiments, the removal efficiency of Cu was in the range of 18.2%-23.6%, and almost no BDE209 was migrated out. The electric current would be increased with N-LED3A concentration increased, further resulting in the enhancement of cumulative electro-osmotic flow (EOF). However, the increment of EOF was limited after an 8-day treatment due to the declined capacity of the soil water supply, and the removal efficiency of BDE209 did not change proportionally to the cumulative EOF as a consequence. The accumulated (21 days) energy consumption under the optimal operation conditions (voltage gradient 1 V/cm, N-LED3A 1 g/L) was 377.28 KWh/m³. Efficiently synchronous removal of BDE209 and Cu could be achieved by the N-LED3A enhanced EK technique, exhibiting a promising application potential in the organic pollutant and heavy metal co-contaminated soil remediation.

Compound-specific carbon isotope analysis for mechanistic characterization of debromination of decabrominated diphenyl ether

RATIONALE

Decabrominated diphenyl ether (BDE-209) is a notorious persistent organic pollutant widely found in the environment. Developing a compound-specific isotope analysis (CSIA) method is much needed in order to trace its transport and degradation processes and to evaluate the effectiveness of the remediation of BDE-209 in the environment. However, the conventional CSIA method, i.e. gas chromatography (GC) combustion isotope ratio mass spectrometry, is not appropriate for BDE-209 because of its high thermal instability and incomplete combustion.

METHODS

We developed a high-performance liquid chromatography (HPLC) method for the separation and purification of BDE-209 that prevents its thermal reactivity as occurred in prior GC-based methods. The δ¹³ C value of the purified BDE-209 was determined using offline elemental analyzer isotope ratio mass spectrometry (EA/IRMS). This two-step method was applied to determine the δ¹³ C values of BDE-209 in two commercial samples and to characterize carbon isotope fractionation associated with the debromination of BDE-209 via nanoscale zero-valent iron.

RESULTS

The mean values of daily δ¹³ C analyses of six replicates of a BDE-209 standard varied from -27.66‰ to -27.92‰, with a standard deviation ranging from 0.07‰ to 0.16‰, indicating a good reproducibility of EA/IRMS. The EA/IRMS analysis of the purified BDE-209 standard indicated no obvious isotope fractionation during the sample purification. The impurity content in commercial BDE-209 samples may contribute additional variation of the δ¹³ C values of BDE-209. The δ¹³ C values of BDE-209 gradually changed from -27.47 ± 0.37‰ to -24.59 ± 0.19‰ when 74% of the BDE-209 standard was degraded within 36 h. The estimated carbon isotope enrichment factor was -1.72 ± 0.18‰.

CONCLUSIONS

The two-step method based on HPLC and EA/IRMS avoids the thermal instability of BDE-209 in the traditional CSIA method. It offers a novel approach for elucidating the degradation mechanisms of BDE-209 in the environment and for source identification in contaminated sites.

Complex systems that incorporate cyclodextrins to get materials for some specific applications

Cyclodextrins (CDs) are a family of biodegradable cyclic hydrocarbons composed of α-(1,4) linked glucopyranose subunits, the more common containing 6, 7 or 8 glucose units are named α, β and γ-cyclodextrins respectively. Since the discovery of CDs, they have attracted interest among scientists and the first studies were about the properties of the native compounds and in particular their use as catalysts of organic reactions. Characteristics features of different types of cyclodextrins stimulated investigation in different areas of research, due to its non-toxic and non-inmunogenic properties and also to the development of an improved industrial production. In this way, many materials with important properties have been developed. This mini-review will focus on chemical systems that use cyclodextrins, whatever linked covalently or mediated by the non covalent interactions, to build complex systems developed mainly during the last five years.

Evaluation of electrokinetics coupled with a reactive barrier of activated carbon loaded with a nanoscale zero-valent iron for selenite removal from contaminated soils

The range between dietary deficient and toxic levels for selenium is quite narrow. In this study, the synergistic effects of electrokinetics (EK) and a permeable reactive barrier (PRB) on the reductive sequestration of Se(IV) oxyanions from spiked soils were investigated in detail. Activated charcoal (AC)-supported Fe(II) and nanoscale zero-valent iron (nZVI) were prepared as the PRB media for use in an electrolyzer. In aqueous equilibrium adsorption tests, the AC-supported nZVI medium had a higher adsorption capacity than that of the other adsorbents. The Se(IV) removal isotherms were well-fitted using the Langmuir model. The Se(IV) removal rates were accurately predicted by both pseudo-first- and pseudo-second-order kinetic models. For the coupled systems, a moderate increase in the number of PRBs and decrease in the PRB thickness in the electrolyzer enhanced the removal and catalytic recovery of Se(IV) from the spiked soil samples. A Se(VI) removal efficiency of approximately 95% and Se(VI) reduction efficiency of 90% were achieved in the optimized electrochemical system. The Se(IV) species were reduced to Se° and FeSe by the AC-supported nZVI regardless of the pH distribution. The experimental results provide guidance for the multichannel recovery of Se from abandoned ore tailings or solid wastes.

Remediation of nitrate-contaminated groundwater by PRB-Electrokinetic integrated process

Activated carbon is used as a reactive media in Permeable Reactive Barrier (PRB) for the removal of inorganic contaminants such as nitrate from groundwater. Since removal rate by this media decreases by time and due to the high costs of excavation and replacement of new media, the usage of activated carbon as an adsorbent in PRB is limited. The present study aimed to solve this defect by integrating electrokinetic process and PRB, using in-situ regeneration of activated carbon. This research was carried out on a laboratory scale using synthetically contaminated water and modified activated carbon as a reactive media in PRB. The effects of pH, nitrate concentration, carbon to sand ratio, and also electric gradient on the performance of the process were evaluated, and optimal conditions were determined, to increase the system longevity. According to the results, by applying an electric gradient of 1.25 V cm^-1 to the PRB alone process in optimum operating condition (135 mg L^-1 initial nitrate concentration, flow rate of 2.3 L min^-1, pH = 6.8, and carbon to sand ratios of 1:1) the adsorbent capacity increased by 90%. Under these conditions, the integrated process could keep nitrate concentration in the effluent below the standard limit for about 111 h, while the PRB alone process could do the same job for about 59 h. Also, SEM analysis showed that by applying electrokinetic process, activated carbon was regenerated. Integration of electrokinetic process and PRB was also caused nitrate to transfer from activated carbon media into the soil layer above the system. This nitrate-rich soil has the potential for reuse in agricultural activities.