Iron Column Research Articles

Evaluating an integrated nano zero-valent iron column system for emerging contaminants removal from different wastewater matrices – Identification of transformation products

The presence of micropollutants in water bodies has become a growing concern due to their persistence, bioaccumulation and potential toxicological effects on aquatic life and humans. In this study, the performance of a column system consisting of zero-valent iron nanoparticles (nZVI) incorporated into a cationic resin and synthesized from green tea extract with the addition of persulfate for the elimination of selected pharmaceuticals and endocrine disruptors from wastewater is evaluated. Ibuprofen, naproxen, diclofenac and ketoprofen were the target pharmaceuticals from non-steroidal anti-inflammatory drugs group, while bisphenol A was the target endocrine disruptor. In this context, different real wastewater effluent matrices were investigated: anaerobic membrane bioreactor (AnMBR), upflow anaerobic sludge blanket reactor (UASB) after microfiltration, tertiary treated by conventional activated sludge system and saturated vertical constructed wetland followed by a sand filtration unit effluent (hybrid). The transformation products of diclofenac and bisphenol A were also identified. The experimental results indicated that the performance of the R-nFe/PS system towards the removal efficiency of the target compounds was enhanced in the order of effluents: tertiary > AnMBR ≈ hybrid > UASB. More than 70% removal was obtained for almost all target compounds when conventional tertiary effluent was used, while the maximum removal efficiency was about 50% in the case of filtered UASB. As far as we know, this is the first time that nZVI has been assessed in combination with persulfate for the removal of micropollutants in a continuous flow system receiving various types of real wastewater with different matrix characteristics.

Effects of seepage velocity and concentration on chromium(VI) removal in abiotic and biotic iron columns.

Continuous-flow iron and bio-iron columns were used to evaluate the effects of seepage velocity and concentration on Cr(VI) removal from groundwater. Solid-phase analysis showed that microorganisms accelerated iron corrosion by excreting extracellular polymeric substances and generated highly reactive minerals containing Fe(II), which gave the bio-iron column a longer life span and enhanced capacity for Cr(VI) removal via enhanced adsorption and reduction by reactive minerals. The bio-iron column showed much higher Cr(VI) removal capacity than the iron column with increasing Cr(VI) loading, which was obtained by increasing the seepage velocity or influent Cr(VI) concentration from 95 to 1138m yr-1 and from 5 to 40mg L-1 , respectively. When the Cr(VI) loading varied in a range of 0 to 10mg L-1 h-1 , the bio-iron column had a 60% longer longevity and one- to sixfold higher Cr(VI) elimination capacity than the iron column. This result indicated that, under fluctuating hydraulic conditions [e.g., seepage velocity and Cr(VI) concentration], the presence of microorganisms can significantly boost Cr(VI) removal using Fe0 -based permeable reactive barriers.

Structural investigation of steel-reinforced epoxy granite machine tool column by finite element analysis

Higher damping with higher static stiffness is essential for improving the static and dynamic characteristics of machine tool structures. The structural vibration in conventional machine tools, which are generally made up of cast iron and cast steel, may lead to poor surface finish and the dimensional inaccuracy in the machined products. It leads to the investigation of alternative machine tool structural materials such as concrete, polymer concrete, and epoxy granite. Although epoxy granite has a better damping capacity, its structural stiffness (Young's modulus) is one-third as compared to cast iron. Therefore, the present work represents optimization of the structural design of the vertical machining center column by introducing various designs of steel reinforcement in the epoxy granite structure to improve its static and dynamic characteristics using experimental and numerical approaches. A finite element model of the existing cast iron vertical machining center column has been developed and validated against the experimental data obtained using modal analysis. Furthermore, finite element models for various epoxy granite column designs have been developed and compared with the static and dynamic characteristics of cast iron column. A total of nine design configurations for epoxy granite column with steel reinforcement are evolved and numerical investigations are carried out by finite element analysis. The proposed final configuration with standard steel sections has been modeled using finite element analysis for an equivalent static stiffness and natural frequencies of about 12–20% higher than cast iron structure. Therefore, the proposed finite element model of epoxy-granite-made vertical machining center column can be used as a viable alternative for the existing column in order to achieve higher structural damping, equivalent or higher static stiffness and, easy and environmental-friendly manufacturing process.

About problems with cast iron columns of the revitalized post-industrial buildings

The paper discusses examples of the use of cast iron columns in existing post-industrial buildings. The results of experimental investigations in which a cast iron column originating from an existing structure was subjected to compression, were presented. The load carrying capacity of the element was assessed in the light of historical design procedures, demonstrating their conservativeness resulting from material uncertainties. The examples of failures of cast iron columns, resulting from errors committed during modernization works, were also presented.

Cold gas in the early Universe

We present a survey for neutral atomic-carbon (C I) along gamma-ray burst (GRB) sightlines, which probes the shielded neutral gas-phase in the interstellar medium (ISM) of GRB host galaxies at high redshift. We compile a sample of 29 medium- to high-resolution GRB optical afterglow spectra spanning a redshift range through most of cosmic time from 1 < z < 6. We find that seven (≈25%) of the GRBs entering our statistical sample have C I detected in absorption. It is evident that there is a strong excess of cold gas in GRB hosts compared to absorbers in quasar sightlines. We investigate the dust properties of the GRB C I absorbers and find that the amount of neutral carbon is positively correlated with the visual extinction, AV, and the strength of the 2175 Å dust extinction feature, Abump. GRBs with C I detected in absorption are all observed above a certain threshold of logN(H I)/cm−2 + [X/H] > 20.7 and a dust-phase iron column density of logN(Fe)dust/cm−2 > 16.2. In contrast to the SED-derived dust properties, the strength of the C I absorption does not correlate with the depletion-derived dust properties. This indicates that the GRB C I absorbers trace dusty systems where the dust composition is dominated by carbon-rich dust grains. The observed higher metal and dust column densities of the GRB C I absorbers compared to H2- and C I-bearing quasar absorbers is mainly a consequence of how the two absorber populations are selected, but is also required in the presence of intense UV radiation fields in actively star-forming galaxies.

Experimental Determination of Dispersion Coefficient in Soil

Unsaturated soil dispersion experiment was done using three different soil samples which includes sand, clay and silt soil. The objective of the study is to determine experimentally dispersion coefficient in soil. Each sample was gradually introduced into a fabricated iron column, having a length of horizontal column 30cm and vertical part 60.96cm. A solution of silver nitrate was allowed to pass through the vertical column down to the horizontal part. Samples of soil were collected at a constant distance of 10cm and time interval of 5mins for 60mins .The concentration of nitrate was taken at a constant distance of 10cm .This was done three times for each of the soil sample. Thereafter, the dispersion coefficient was calculated, and a regression dispersion model developed as a function of permeability, average diameter of sieve, velocity of flow and time taken to flow. The model was calibrated and verified with experimental results and found to have a high correlation coefficient (r) of 0.943. Data obtained from the experiments were fitted into the two existing models and poor correlation coefficients of -0.529 and -0.524 were obtained respectively.

Study on 19th-century cast iron columns from the former financial office building in Kwidzyn

The article presents the results for cast iron columns used as floor supports in the former financial office building in Kwidzyn (Poland). The stocktaking drawings provided the general and detailed data about the 19th century designer’s decisions. During the research, architectural and structural analysis was carried out. The graphics were used as a starting material for preparing 3D calculation models. The FEM-based numerical simulations were conducted using ABAQUS software. It was shown that the selection of such a structural solution in the building allowed arranging the interior space in an innovative way. The results of the study prove the thesis put forward of a low application extent of the load-bearing capacity of cast iron column used.

Removal of hexavalent chromium in natural groundwater using activated carbon and cast iron combined system

A permeable reactive barrier (PRB) using activated carbon and cast iron combined system was to be built at a field site in Northern China to remove Cr(VI) in the groundwater. In this study, laboratory column experiments were conducted to evaluate the efficiency of the combined system at mass ratios of 1:1 and 3:1. The results showed that the combined system has a higher removal rate than that of the single material and leads no secondary pollution. Different mass ratio was proved to have much effect on the Cr(VI) removal capacity (mg Cr/g materials), the removal capacity was 3.806 mg/g at 1:1, while it was only around 0.776 mg/g in the single cast iron column. Larger carbon particles and higher flow rate can lead to a significant decrease in Cr(VI) removal due to lower specific surface area and lower hydraulic residence time (HRT), respectively. The breakthrough curves could be adequately reproduced by the Dose-Response model, for security, the half-life time used in the PRB thickness calculation was 0.4d chosen at the break through time. The results could be useful to groundwater remediation at chromium-polluted sites.

Modelling long-term hydraulic conductivity behaviour of zero valent iron column tests for permeable reactive barrier design

In this paper, a numerical model to simulate the hydraulic conductivity reduction observed during long-term laboratory column tests is proposed. The column tests are carried out to study dissolved heavy metals removal by using granular zero valent iron (ZVI). The proposed model is also used to analyse the main causes of hydraulic conductivity reduction observed during laboratory column tests. Expansive iron corrosion, precipitation of reaction products, and gas formation are the processes considered in the proposed model. Numerical simulation results show that to reproduce hydraulic behaviour of the experimental systems, the change of pores geometry due to expansive iron corrosion and precipitation of reaction products, which determines a possible stoppage of gas bubbles, should be considered. Furthermore, model results show that only a small percentage of the iron available is corroded during the tests (from 0.4% to 1.9%). According to the model, the average diameter of gas bubbles that better fit the experimental results varies between 0.16 and 0.19 mm. While assuming gas absence (or its possible escape), higher values of iron corrosion rate should be considered to fit the experimental results.

Removal of arsenic from aqueous solutions using waste iron columns inoculated with iron bacteria

Arsenic contamination of water resources is one of the serious risks threatening natural ecosystems and human health. This study investigates arsenic removal using a waste iron column with and without iron bacteria in continuous and batch phases. In batch experiments, the effects of pH, contact time, initial concentration of arsenic and adsorbent dose were investigated. Results indicated that the highest arsenate removal efficiency occurred at pH 7 (96.76%). On increasing the amount of waste iron from 0.25 to 1 g, the removal rate changed from about 42.37%–96.70%. The results of continuous experiments on the column containing waste iron showed that as the empty bed contact time increased from 5 to 60 min, the secondary arsenate concentration changed from 23 to 6 µg/l. In experiments involving a waste iron column with iron bacteria, an increase in residence time from 5 to 60 min decreased the secondary arsenate concentration from 14.97 to 4.86 µg/l. The results of this study showed that waste iron containing iron bacteria is a good adsorbent for removal of arsenic from contaminated water.

Enhanced nitrobenzene removal and column longevity by coupled abiotic and biotic processes in zero-valent iron column

Abstract Nitrobenzene (NB) infiltrated in groundwater has caused serious threats to the safety of drinking water due to its persistence and high toxicity. In this study, abiotic zero-valent iron (ZVI) column and biotic ZVI column were employed to investigate abiotic and biotic effects between iron and microorganisms on NB removal and column longevity. Physical removal and kinetics analysis revealed that NB was largely removed through adsorption and/or co-precipitation and the reduction of NB to aniline (AN) via abiotic reaction in the abiotic column and via both abiotic and biotic reactions in the biotic column. Due to the interactive effect of ZVI and microorganisms, more effective iron consumption and more reactive minerals such as green rust and iron sulfide were found in the biotic column. This led to approximately 50% higher total NB removal and 6 times higher AN production in the biotic column as compared to the abiotic column during the entire operation. According to the NB breakthrough curves, longer stability and longer life-span of the column system could be maintained in regard of microbial activity. It indicated that additional microorganisms might improve the performance of iron-based permeable reactive barrier (PRB) for groundwater remediation.

Process control factors for continuous microbial perchlorate reduction in the presence of zero-valent iron

Process control parameters influencing microbial perchlorate reduction via a flow-through zero-valent iron (ZVI) column reactor were investigated in order to optimize perchlorate removal from water. Mixed perchlorate reducers were obtained from a wastewater treatment plant and inoculated into the reactor without further acclimation. Examined parameters included hydraulic residence time (HRT), pH, nutrients requirement, and perchlorate reduction kinetics. The minimum HRT for the system was concluded to be 8 hr. The removal efficiency of 10 mg·L−1 influent perchlorate concentration was reduced by 20%–80% without control to the neutral pH (HRT = 8 hr). Therefore pH was determined to be an important parameter for microbial perchlorate reduction. Furthermore, a viable alternative to pH buffer was discussed. The microbial perchlorate reduction followed the first order kinetics, with a rate constant (K) of 0.761 hr−1. The results from this study will contribute to the implementation of a safe, cost effective, and efficient system for perchlorate reduction to below regulated levels.

黒鉛潤滑を応用した直置き型鋼構造建物柱脚の摩擦低減

Free standing steel structures, whose column bases are not fixed to a foundation, contribute to decrease damage to the structures under large earthquakes. However, the friction coefficient of normal steel column bases is 0.8 and too high to the strengths of normal steel structures. In this study, a steel column base lubricated by graphite well known as a lubricant and a cast iron column base containing much more graphite than steel are proposed to realize the low friction column base. Shaking table tests are conducted to investigate the friction characteristics. The tests show that the friction coefficient of the cast iron column base is 0.25 and that of the graphite lubricated steel column base is 0.20. Dynamic response analyses representing these friction characteristics show reasonable correlations with the test results.

Haloacetic acid removal by sequential zero-valent iron reduction and biologically active carbon degradation

An innovative haloacetic acid (HAA) removal process was developed. The process consisted of a zero-valent iron (Fe0) column followed by a biologically active carbon (BAC) column that were efficient in degrading tri- and di-HAAs, and mono- and di-HAAs, respectively. The merit of the process was demonstrated by its performance in removing trichloroacetic acid (TCAA). An empty bed contact time of 10min achieved nearly complete removal of 1.2μM TCAA and its subsequent products, dichloroacetic acid (DCAA) and monochloroacetic acid (MCAA). HAA removal was a result of chemical dehalogenation and biodegradation rather than physical adsorption. Preliminary kinetic analyses were conducted and the pseudo-first-order rate constants were estimated at ambient conditions for Fe0 reduction of TCAA and biodegradation of DCAA and MCAA by BAC. This innovative process is highly promising in removing HAAs from drinking water, swimming pool water, and domestic or industrial wastewater.

Modeling Gas Formation and Mineral Precipitation in a Granular Iron Column

In granular iron permeable reactive barriers (PRBs), hydrogen gas formation, entrapment and release of gas bubbles, and secondary mineral precipitation have been known to affect the permeability and reactivity. The multicomponent reactive transport model MIN3P was enhanced to couple gas formation and release, secondary mineral precipitation, and the effects of these processes on hydraulic properties and iron reactivity. The enhanced model was applied to a granular iron column, which was studied for the treatment of trichloroethene (TCE) in the presence of dissolved CaCO(3). The simulation reasonably reproduced trends in gas formation, secondary mineral precipitation, permeability changes, and reactivity changes observed over time. The simulation showed that the accumulation of secondary minerals reduced the reactivity of the granular iron over time, which in turn decreased the rate of mineral accumulation, and also resulted in a gradual decrease in gas formation over time. This study provides a quantitative assessment of the evolving nature of geochemistry and permeability, resulting from coupled processes of gas formation and mineral precipitation, which leads to a better understanding of the processes controlling the granular iron reactivity, and represents an improved method for incorporating these factors into the design of granular iron PRBs.

Enhanced biodegradation of 2‐chloronitro‐benzene using a coupled zero‐valent iron column and sequencing batch reactor system

AbstractBACKGROUND: This study focused on the effectiveness of the zero‐valent iron (ZVI) pre‐treatment for enhancing the biodegradability of 2‐chloronitrobenzene (2‐ClNB), and further to evaluate the performance and mechanism of a coupled ZVI column–sequencing batch reactor (SBR) system treating 2‐ClNB contained wastewater.RESULTS: 2‐ClNB was readily transformed into 2‐chloroaniline (2‐ClAn) with the efficiency over 99.9% by ZVI column, and its biodegradability was significantly enhanced via ZVI pretreatment. The transformed effluent was subsequently fed into the SBR followed by 2‐ClAn loading of 3.4–117.2 g m−3 d−1 and COD loading around 1000 g m−3 d−1. A 2‐ClAn removal efficiency over 99.9% and COD removal efficiency of 82.0–98.1% were obtained. Moreover, 91.9 ± 0.1% TOC removal efficiency and 107.1 ± 6.0% chloride recovery efficiency during one cycle confirmed the complete biodegradation of 2‐ClAn in the coupled system. 16S rDNA PCR‐DGGE analysis suggested that ZVI pretreatment enhanced the diversity of the microbial community and promoted enrichment of the functional microorganisms degrading 2‐ClAn in the following SBR.CONCLUSION: ZVI pretreatment significantly enhanced the biodegradability of 2‐ClNB, and the coupled ZVI–SBR system demonstrated excellent performance when treating wastewater containing 2‐ClNB. Copyright © 2011 Society of Chemical Industry

Factors Affecting the Reductive Transformation of Nitroaromatics by Zero-Valent Iron: Dissolved Anions, Adsorption, Iron Loss, and Possibility of Clogging

ABSTRACT Factors affecting the reduction of nitroaromatics by zero-valent iron in groundwater were investigated by using 2,4-dinitrotoluene, nitrobenzene, and 2,4,6-trinitrotoluene. Batch experiments showed that the ratio of adsorbed nitrobenzene to cast iron surface area was approximately 30%, similar to those of 2,4-dinitrotoluene and 2,4,6-trinitrotoluene. Dissolved chloride (0.1 mM) and sulfate ions (0.01 mM) could enhance the reduction of 2,4-dinitrotoluene by zero-valent iron via the enhancement of iron corrosion. Long-term column experiments showed the iron consumption in the column to be attributable to the reduction of 2,4-dinitrotoluene in groundwater. Therefore, the longevity of the iron column may be predicted stoichio- metrically by the amount of 2,4-dinitrotoluene in groundwater. The use of Ottawa sand in the iron column did not result in a significant clogging problem during 2,4,6-trinitrotoluene reduction under the specified conditions. However, the use of either silica sand or a high concentration of dissolved bicarbonate/carbonate in solutions was shown to effect clogging of the iron column. The results suggest that some important factors should be considered when applying an iron reduction process for the treatment of nitroaromatics in groundwater.

TCE reduction modeling in soil column: Effect of zero-valent iron, ferrous iron, and iron-reducing bacteria

A model was developed to simulate the reduction of trichloroethylene (TCE) by permeable reactive barriers (PRBs). The model based on an axial transport model with chemical reaction terms was operated for a TCE solution, incorporating dispersion, convection, and reaction along the column flow-path and time. Reaction terms included TCE reduction by zero-valent iron (ZVI) or ferrous iron produced from ferric iron by iron-reducing bacteria (IRB). ZVI was oxidized by TCE to ferric iron which has no ability to reduce TCE. IRB reduced ferric iron to ferrous iron by transferring electrons from organic carbon sources such as lactate or glucose. Ferrous iron, thus produced, constantly reduced TCE although it had a relatively low reducing power compared to ZVI. The TCE concentration at the mid-port of the ZVI column was lower than one-tenth of the influent concentration until 200 h, but reached a 99% breakthrough at 1,390 h. The TCE reduction efficiency by the ZVI column was not recovered after the breakthrough. On the other hand, the life of ferrous iron column was prolonged in the presence of IRB. The TCE reduction efficiency was maintained at over 60% with 10,000 mg-IRB/L–pore volume of IRB. These results indicate that the application of IRB would be economical for a long-term operation of iron-based PRBs.

Column studies on transport of deicing additive benzotriazole in a sandy aquifer and a zerovalent iron barrier

Benzotriazole (BTA), a chemical with wide industrial applications, is a typical additive in deicer/anti-icer used at airport. To achieve a better understanding of the transport behaviour and environmental fate of BTA, laboratory column studies have been performed on subsoil samples from Oslo Airport, Gardermoen. To explore possibilities for aquifer remediation, BTA behaviour was also studied in a column of granular zerovalent iron (Fe 0). The subsoil column study demonstrates a very limited retardation of BTA. Consecutive loadings of BTA of the subsoil column showed no change of the break-through curve (BTC) and complete desorption was observed. The sorption behaviour of BTA to metallic iron (Fe 0) was rather complex. Considerable retardation was observed in the Fe 0 column and repeated BTA loading resulted in an earlier break-through. Between 20% and 50% of the input concentration was retained permanently in the iron (Fe 0) column. The BTA sorption to metallic iron was found to be enhanced by chloride which lowered the break-through concentration (i.e the C/ C 0 plateau). The fraction of BTA remaining in the iron column was found to vary with the flow rate, indicating a time dependant multilayer sorption mechanism. The steady increase in the amount of adsorbed BTA to the iron column during loading corresponds to a rather strong bonding of 4–15 BTA layers to the iron surface. A very slow desorption of BTA was observed; even after flushing with 753 pore volumes of BTA free water, 7.5% of the BTA remained in the column. A geochemical model was developed based on PHREEQC-2 to simulate the sorption and transport of BTA in the tested materials. The BTA sorption was modelled with Freundlich sorption isotherms, as earlier determined in batch experiments. A slight adjustment of the Freundlich parameters was required to fit the observed column break-through. However, our model was not able to simulate the long-term retainment of BTA in the granular iron columns. The simulations confirm the high mobility of BTA in groundwater aquifers and suggest that zerovalent iron could be used to retain a BTA plume, although oxidation of the sorbent might reduce the long-term performance of such a remediation scheme and slow desorption has been observed.

Zero-valent iron treatment of RDX-containing and perchlorate-containing wastewaters from an ammunition-manufacturing plant at elevated temperatures

The use of zero-valent iron for treating wastewaters containing RDX and perchlorate from an army ammunition plant (AAP) in the USA at elevated temperatures and moderately elevated temperature with chemical addition was evaluated through batch and column experiments. RDX in the wastewater was completely removed in an iron column after 6.4 minutes. Increasing the temperature to 75 degrees C decreased the required retention time to 2.1 minutes for complete RDX removal. Perchlorate in the wastewater was completely removed by iron at an elevated temperature of 150 degrees C in batch reactors in 6 hours without pH control. Significant reduction of perchlorate by zero-valent iron was also achieved at a more moderate temperature (75 degrees C) through use of a 0.2 M acetate buffer. Based on the evaluation results, we propose two innovative processes for treating RDX-containing and perchlorate-containing wastewaters: a temperature and pressure-controlled batch iron reactor and subsequent oxidation by existing industrial wastewater treatment plant; and reduction by consecutive iron columns with heating and acid addition capabilities and subsequent oxidation.