Development Of Permeable Reactive Barriers Research Articles

Improved Electron Efficiency of Zero-Valent Iron towards Cr(VI) Reduction after Sequestering in Al2O3 Microspheres.

Zero-valent iron (ZVI) is widely used for groundwater remediation, but suffers from high electron consumption because of its free contact with non-target substrates such as O2. Here, ZVI-ALOX particles were prepared via in situ NaBH4 aqueous-phase reduction of ferrous ions (Fe2+) preabsorbed into Al2O3 microspheres. The electron efficiency (EE) and long-term performance of the material were improved by sequestering ZVI in the interspace of the Al2O3 microspheres (ZVI-ALOX). During long-term (350 days) continuous flow, Cr(VI) was removed to below the detection limit for over 23 days. Based on the high reactivity of ZVI towards Cr(VI), the EE of ZVI-ALOX was evaluated by measuring its Cr(VI) removal efficiency at neutral pH and comparing it with that of ZVI. The results showed that the EE of ZVI-ALOX during long-term continuous flow could reach 39.1%, which was much higher than that of ZVI (8.68%). The long-term continuous flow results also demonstrated that treatment of the influent solution achieved higher EE values than in the batch mode, where the presence of dissolved oxygen reduced EE values. At lower pollutant concentrations, the sequestering of ZVI was beneficial to its performance and long-term utility. In addition, measurement of the acute toxicity of treated column effluent using the indicator organism Photobacterium phosphoreum T3 showed that ZVI-ALOX could reduce the toxicity of 5 mg/L Cr(VI) solution by ~70% in 350 d. The results from this study provide a basis for the development of permeable reactive barriers for groundwater remediation based on sequestered ZVI.

A systematic mapping study on the development of permeable reactive barrier for acid mine drainage treatment

Acid mine drainage is a result of exposure of sulfide ore and minerals to water and oxygen. This environmental pollutant has been considered the second biggest environmental problem after global warming. On the other hand, permeable reactive barrier is an emerging remediation technology which can be used to treat acid mine drainage. However, the effectiveness of this proposed remediation technology greatly depends on the reactive media. Also, treatment of acid mine drainage using permeable reactive barrier is still in the infancy stage, and long-term performance is still unknown. Hence, this study was conducted to identify what have been studied, addressed and what are currently the biggest challenges and limitations on the use of permeable reactive barrier for acid mine drainage treatment. Through systematic mapping approach, the results have shown that the reactive media used in permeable reactive barrier can be categorized into five namely iron-based, organic-based, inorganic minerals-based, industrial waste-based, and combined media. The data revealed that majority of the papers which is about 40% use combined media as the reactive substrate. The future direction is toward the use of combined media as a reactive material for AMD treatment, for instance, use of geopolymer with mine tailings and silts as reactive media in combination with organic-based media

Combination of Fe(0) with additional reactive materials in fixed bed reactors for TCE removal

Declines of reactivity and permeability due to mineral and gas accumulations are considered as major risks of Fe(0) fixed bed reactors (permeable reactive barriers) for passive treatment of contaminated aquifers. Reducing the Fe(0) content per volume unit is a simple but effective modification that might enhance longevity. Reducing passivating build-ups on the Fe(0) surface by attracting precipitation on non-Fe(0) surfaces might enhance the long-term reactivity. Calcite and granular ferric hydroxide (GFH) as potential crystallization seeds were combined with Fe(0). Wood in combination with Fe(0) was tested for enhanced microbial activity with potentially positive effects on gas clogging and contaminant removal. Calcite revealed decreased effluent concentration of calcium and inorganic carbon, probably due to initiation of CaCO3 crystallization on its surface. Differing effects were observed for the combination of GFH and Fe(0) in the initial period: Anion exchange caused high chloride effluent concentrations, sulfate retention and subsequent sulfate release and acidic conditions with comparably high corrosion rates. No chlorinated compounds were found in the effluent of the GFH containing column. An increase of cDCE was observed in the effluent of calcite and wood containing columns representing a failure of the tested remediation approach. The combination of different reactive materials as a potential further development of permeable reactive barriers is discussed.

Development of Permeable Reactive Barrier for Phosphorus Removal

Permeable reactive barriers were developed for phosphorus removal. The barrier consists in an organic-inorganic hybrid material, which allows water and others species to flow through it, while selectively removes the contaminants. Polyethylene oxide (POE) and aluminium oxide (Al2O3) were used as the organic and the inorganic parts, respectively. The hybrid material was obtained by sol-gel reaction, using aluminium isopropoxide as inorganic percursor in order to attain Al2O3. The hybrid material produced was characterized by FT-IR spectroscopy and thermogravimetry. The previous tests for phosphorus removal have shown the effectiveness capacity of the developed material to remove it.

Assessing performance of a permeable biobarrier

While the past 15 years have seen rapid development of permeable reactive barriers and other in situ systems for the treatment of groundwater contamination, assessing performance has not received the same attention. In some cases the long-screened monitoring wells installed as part of initial site investigations are used to monitor treatment, while in others a few additional wells may be installed to serve as sentinels. Performance is assessed based on differences in contaminant concentrations, which is unreliable where plumes are spatially complex and/or temporally unstable. In this work, a standard concentration performance metric is compared with that based on mass flux, using data collected during an evaluation of a discontinuous aerobic biobarrier treating a near-source (and spatially complex) BTEX plume. The data were derived from high-resolution multilevel samplers installed up- and down-gradient of the treatment system. Concentrations in screened monitoring wells of various lengths were approximated by interval-weighted concentrations from these multilevels. The accuracy of the different performance assessment methods was measured based on estimated uncertainty generated as a result of observed spatial plume complexity. While more data intensive, mass flux proved to be a more reliable performance metric. Assessment using data from few long-screened wells could not reliably match that of the flux fences, but did come within acceptable limits when the number of wells approached the number of multilevels.