Reduction In Cr Concentration Research Articles

Iron nanoparticles to recover a co-contaminated soil with Cr and PCBs

Little attention has been given to the development of remediation strategies for soils polluted with mixture of pollution (metal(loid)s and organic compounds). The present study evaluates the effectiveness of different types of commercial iron nanoparticles (nanoscale zero valent iron (nZVI), bimetallic nZVI-Pd, and nano-magnetite (nFe3O4)), for the remediation of an industrial soil co-contaminated with Cr and PCBs. Soil samples were mixed with nZVI, nZVI-Pd, or nFe3O4 at doses selected according to their reactivity with PCBs, homogenized, saturated with water and incubated at controlled conditions for 15, 45 and 70 days. For each sampling time, PCBs and chromium were analyzed in aqueous and soil fractions. Cr(VI) and Cr leachability (TCLP test) were determined in the soil samples. The treatment with the three types of iron nanoparticles showed significant reduction in Cr concentration in aqueous extracts at the three sampling times (> 98%), compared to the control samples. The leachability of Cr in treated soil samples also decreased and was stable throughout the experiment. Results suggested that nZVI and nZVI-Pd immobilized Cr through adsorption of Cr(VI) on the shell and reduction to Cr(III). The mechanism of interaction of nFe3O4 and Cr(VI) included adsorption and reduction although its reducing character was lower than those of ZVI nanoparticles. PCBs significantly decreased in soil samples (up to 68%), after 15 days of treatment with the three types of nanoparticles. However, nFe3O4 evidenced reversible adsorption of PCBs after 45 days. In general, nZVI-Pd reduced PCB concentration in soil faster than nZVI. Control soils showed a similar reduction in PCBs concentration as those obtained with nZVI and nZVI-Pd after a longer time (45 days). This is likely due to natural bioremediation, although it was not effective for Cr remediation. Results suggest that the addition of nZVI or nZVI-Pd and pseudo-anaerobic conditions could be used for the recovery of soil co-contaminated with Cr and PCBs.

Lemna sp. as a Chromium Heavy Metal Phytoremediator on Tannery Wastewater and its Potential Use as Fish Feed

Aims: This research aims to determine the ability of Lemna sp. as a phytoremediation agent in absorbing chromium (Cr) in tannery wastewater.
 Study Design: A total of 20 fiber tubs with size 80 x 80 x 40 cm3 and volume of 256 L were prepared and filled with 30 L each of the tannery wastewater and 1.75% bio-slurry added with a volume of wastewater as a source of nutrition for Lemna sp.. The number of Lemna sp. which is used for culture was 180 g for each fiber tube.
 Place and Duration of Study: Culturing Lemna sp. in tannery wastewater were carried out in Ciparanje Land Fisheries Area of ​​the Faculty of Fisheries and Marine Sciences Universitas Padjadjaran and for chromium analysis were carried out in Center for Natural Resources and Environment Research of Universitas Padjadjaran, between February and March 2019.
 Methodology: This research was carried out by culturing Lemna sp. in tannery wastewater for five days with 20 replications and comparing Cr concentrations in tannery wastewater and Lemna sp. at the end and beginning of the research. Chromium analysis results on the tannery wastewater and Lemna sp. the beginning and end of the research on each sample was tested by paired t-test.
 Results: by culturing Lemna sp. in the tannery wastewater as phytoremediation agent for five days the results obtained Cr concentration at the beginning of research each for tannery wastewater and Lemna sp. ranged from 0.180 to 0.194 mg/L with an average of 0.187±0.0034 mg/L and 0 mg/kg. While at the end of the research the concentration of Cr in tannery wastewater and Lemna sp. respectively ranged from 0.057-0.075 mg/L with an average of 0.068±0.0044 mg/L and 2.292-2.333 mg/kg with an average of 2.314±0.0101 mg/kg. There was a decrease in Cr concentration by an average of 64.01±1.96% in tannery wastewater and an increase in Lemna sp.. Paired t-test results showed that Lemna sp. which was cultured in tannery wastewater had a significant influence on Cr concentrations in both tannery wastewater and Lemna sp so that there were significant differences in Cr concentrations at the beginning (day 0) and at the end of the research (day 5).
 Conclusion: Average ability of Lemna sp. in absorbing and accumulating chromium in the tannery wastewater in the tissue was 2.314±0.0101 mg/kg and the average reduction in Cr concentration in liquid waste was 64.01±1.96%. Utilization of Lemna sp. containing chromium is possible to be used as a food supplement for fish to increase growth due to reduced Cr toxicity by Lemna sp.

Involvement and interaction of microbial communities in the transformation and stabilization of chromium during the composting of tannery effluent treated biomass of Vallisneria spiralis L.

Tannery effluent treated with aquatic macrophyte Vallisneria spiralis L. for 14 d showed significant improvement in physico-chemical properties and reduction in Cr concentration. Accumulation of Cr was found maximum in roots (358 μg g −1dw) as compared to shoot (62 μg g −1dw) of the plant. A laboratory scale composter was designed with the objectives to investigate the physico-chemical changes and role of microbes in stabilization and transformation of Cr in the composting material. Results revealed that the composting process was quick within 7–21 d as indicated by peak time for various physico-chemical parameters and drop in C/N ratio up to acceptable limit. The profile of microbial communities indicated that population of anaerobic, aerobic and nitrifying bacteria increased quickly at the initial phase, and reached a peak level of 4.2 × 10 6, 9.78 × 10 8 and 9.32 × 10 9 CFU g −1, respectively at 21 d; while population of actinomycetes and fungi was found maximum i.e. 3.29 × 10 7 and 9.7 × 10 6 CFU g −1, respectively, after 35 d of composting. Overall bacterial population dominated over the actinomycetes and fungi during the composting process. Cr (VI) was transformed to Cr (III) due to the microbial activity during the process. Sequential extraction of Cr fractionation showed its stabilization via changing into organic matter-bound and residual fractions during the composting.

A siderite/limestone reactor to remove arsenic and cadmium from wastewaters

A two-column reactor was designed to remove dissolved As and Cd from contaminated water. The reactor functions by equilibrating the targeted water with CO 2 and directing it via saturated flow through a column of crushed siderite. This results in siderite dissolution and an increase in dissolved Fe(II). The feedwater is then directed into the top of a second, aerated column of crushed limestone, where it passes by unsaturated flow. The Fe 2+ ion oxidizes quickly to Fe 3+ and precipitates as Fe(III) oxyhydroxide, which is an effective sorbent of AsO 4 3−. The aeration that occurs in the second column also removes dissolved CO 2 from the feedwater. This causes precipitation of Ca and Cd carbonates. Together, the two processes reduce As and Cd concentrations from 1 and 3 mg/l, respectively, to below detection (respectively <0.005 and <0.01 mg/l). A time-limited reduction in Cr concentration also occurred. Much of the As was removed in the first column of the reactor, because Fe(III) oxyhydroxides also formed there. This was due to oxidation of Fe(II) by Cr(VI) and other oxidants present in the input wastewater. Although As is removed in the reactor columns by a sorption mechanism, the sorbent responsible, Fe(III) oxyhydroxide, is continuously produced during the operation of the reactor. Thus, unlike attenuation in a system with a fixed amount of sorbent, breakthrough of the As contaminant should never occur.