A serial enrichment culture has been grown in an alkaline Fe(III)-citrate-containing medium from an initial inoculum from a soil layer beneath a chromium ore processing residue (COPR) disposal site where Cr(III) is accumulating from Cr(VI) containing leachate. This culture is dominated by two bacterial genera in the order Clostridiales, Tissierella, and an unnamed Clostridium XI subgroup. This paper investigates the growth characteristics of the culture when Cr(VI) is added to the growth medium and when aquifer sand is substituted for Fe(III)-citrate. The aim is to determine how the availability and chemical form of Fe(III) affects the growth of the bacterial consortium, to determine the impact of Cr(VI) on growth, and thus attempt to understand the factors that are controlling Cr(III) accumulation beneath the COPR site. The culture can grow fermentatively at pH 9.2, but growth is stronger when it is associated with Fe(III) reduction. It can withstand Cr(VI) in the medium, but growth only occurs once Cr(VI) is removed from solution. Cr(VI) reduced the abundance of Tissierella sp. in the culture, whereas the Clostridium XI sp. was Cr(VI) tolerant. In contrast, growth with solid phase Fe(III)-oxyhydroxides (present as coatings on aquifer sand) favoured the Tissierella C sp., possibly because it produces riboflavin as an extracellular electron shuttling compound allowing more efficient electron transfer to solid Fe(III) phases. Thus, it is suggested that bacterially mediated Cr(III) reduction in the soil beneath the COPR site is dependent on Fe(III) reduction to sustain the bacterial community.

Solanum nigrum L., a potential cadmium (Cd) hyper-accumulator, has not currently been investigated to identify if it has a strong simultaneous accumulative ability to Cd, copper (Cu), zinc (Zn), or lead (Pb) in contaminated soils. In this study, a pot culture experiment was conducted to investigate the phytoremediation effects of S. nigrum L. on these heavy metals. The potential hyper-accumulative characteristics of S. nigrum L. were also discussed. The results showed that S. nigrum L. remediation effects were not inhibited by multi-heavy metals in contaminated soil. On the contrary, the height and wet and dry weights of S. nigrum L. increased compared to the control treatments and to treatments using only one heavy metal contaminant. Results from the Cd treatment experiments showed 1.66- and 1.45-fold increases in stem and root levels; there were also 1.24-, 2.17-, and 1.61-fold extraction increases in the leaves, stems, and roots, respectively. The differences found in shoot and root bioaccumulation coefficient (BC) factors for multi-heavy metal (MHM) treatment were higher than for a single Cd treatment. These results indicate that S. nigrum L. could stimulate biomass production and that it has a strong ability to tolerate and accumulate Cd in contaminated soils with Pb, Zn, and Cu. This study shows that the remediation scope for S. nigrum L. is greater than currently believed and that it will also remove Pb, Zn, and Cu while extracting Cd from contaminated soils.

Different lignocellulosic substrates consisting of modified barley husk, peanut shells and sawdust were entrapped in calcium alginate beads and used as adsorbents to remove dye compounds from vinasses. For comparative purposes, a biocomposite formulated with humus was also included in this work. Kinetic studies were carried out by applying pseudo-first-order, pseudo-second-order, Chien–Clayton and intraparticle diffusion models, observing a good agreement between theoretical and experimental results when the data were adjusted to pseudo-second-order kinetic model. The results of this study show that lignocellulosic-based biocomposites could be used as an effective and low-cost adsorbent for the removal of dyes from aqueous solutions. Among the heterogeneous biopolymers evaluated, the biocomposite based on barley husk gave the best capacity for dye removal. Moreover, in all cases, it was found that there exists a direct relationship between the capacity of the biocomposites to remove dyes and the percentage of carbon contained in the lignocellulosic residues.

The current work reports on the degradation of glycerol aqueous solution via photocatalytic-Fenton technique. The CuFe₂O₄ photocatalyst was synthesized via sol-gel method and its physicochemical properties were characterized. The as-synthesized photocatalyst possessed Brunauer-Emmett-Teller (BET)-specific surface area of 104 m²/g. The large BET-specific surface area was also corroborated by the field-emission scanning electron microscopy (FESEM) images which showed porous morphology. In addition, the XRD pattern showed that the visible light-active component, CuFe₂O₄, was successfully formed with band gap energy of 1.58 eV determined from the UV-Vis diffuse reflectance spectroscopy. Significantly, it was determined from the blank run study that the visible light was an integral part of the photoreaction. Without the visible light irradiation, glycerol degradation was low (<4.0 %). In contrast, when visible light was present, the glycerol degradation improved markedly to attain 17.7 % after 4 h of visible light irradiation, even in the absence of CuFe₂O₄ photocatalyst. This can be attributed to splitting of H₂O₂ into hydroxyl (●OH) radical. In the presence of CuFe₂O₄ photocatalyst, the photocatalytic Fenton degradation of glycerol has further enhanced to record nearly 40.0 % degradation at a catalyst loading of 5.0 g/l. This has demonstrated that the CuFe₂O₄ was capable of generating additional hydroxyl radicals to attack the glycerol molecule. Moreover, this degradation kinetics can be captured by Langmuir-Hinshelwood model from which it was found that the adsorption constant related to H₂O₂ was significantly weaker compared to the adsorption constant of glycerol.

Calcium nitrate and a lanthanum-modified bentonite (Phoslock®) were investigated for their ability to control the release of phosphorus from contaminated sediment. Their effectiveness and mode of action were assessed using microcosm experiments by monitoring the variation of physiochemical parameters and phosphorus and nitrogen species over time following the treatment for 66 days. Phoslock® was more effective reducing phosphorus in overlaying water and controlling its release from sediment. Calcium nitrate improved redox condition at the sediment-water interface and temporally reduce phosphorus in overlaying water but phosphorus level returned back in a long run. Phosphorus fractionation suggested that Phoslock® converted mobile phosphorus to more stable species while calcium nitrate increased the fractions of mobile phosphorus species. Phoslock® generally showed no effect on nitrogen species. Whereas calcium nitrate temporally increased nitrate, nitrite, and ammonium concentrations but their concentrations quickly reduced likely due to the denitrification process. Results suggested that Phoslock® can be more effective in controlling the release of phosphorus from sediment than calcium nitrate. However, calcium nitrate can improve the redox condition at the sediment-water interface, which may provide other benefits such as stimulating biodegradation.

The dust removal performance of two types of modified electrode electrostatic precipitator systems was evaluated and compared with that of a conventional aluminum plate electrode using laboratory-scale experiments. In the novel electrode systems, the electrode surface was coated with activated carbon using a mixed slurry containing carbon black, polyvinyl acetate, and methanol. The modification of the electrode surface improved dust precipitation by increasing the specific capacitance of the electrode. The modification also lowered the electrode’s resistance and increased its specific surface area. The optimum electrode spacing and electric voltage supply were determined using batch-type tests. In addition, dielectric insulators were applied as a partition between the oppositely charged electrodes equipped with the modified electrode plates. Multi-layered office paper cut to the same size as the electrodes was used as an insulating material. The addition of the insulator resulted in excellent improvement in the dust removal performance by minimizing the back-corona discharge phenomenon as well as doubling the dust collecting surface. Continuous dust removal tests with the three electrode systems revealed that whereas the conventional aluminum electrode exhibited 54 % dust removal, the activated carbon (AC)-coated system showed 85 % and AC-coated + insulator system showed 90 % and higher dust removal efficiency.

Natural zeolitic tuff was modified with FeCl₃solution for the removal of fluoride, and the effect of chloride, nitrate, and sulfate ions was examined on fluoride sorption from solutions and drinking water. The unmodified zeolitic tuff (Z) and the iron-modified zeolitic tuff (Fe(III)-Z) were characterized by scanning electron microscopy and X-ray diffraction analysis. The elemental composition, the specific surface area, and the point of zero charge of the zeolitic material were also determined. The fluoride adsorption was carried out in a batch system considering the effect of contact time, the initial concentration of fluoride ions, and the effect of other anions naturally present in the drinking water. The kinetic and isotherm results were adjusted to the pseudo-second-order and Freundlich models, respectively, which indicated that the sorption mechanism was chemisorption on a heterogeneous material. The fluoride sorption capacity was higher in solutions (2.7 mg/g) than in drinking water (0.41 mg/g), and this could be attributed to the presence of other anions. Overall, the presence of chloride ions significantly diminished the fluoride adsorption capacity, while the presence of nitrate and sulfate ions did not show any significant effect; the anion removal efficiency by Fe(III)-Z followed the order F⁻ > > Cl⁻ > NO₃⁻ > SO₄²⁻.

Grape stalks, a low-cost agro-industrial by-product, were used for the first time as a biosorbent for the removal of uranium from aquatic systems. Basic operating conditions (effect of pH, biosorbent dose, uranium initial concentration, and kinetics) were investigated, and the sorption mechanism was explored. The proposed biosorbent’s efficiency to sequester uranium from different profile aquatic systems was assessed, as well as the potential uranium recovery. Biosoprtion performance increased progressively from pH 1.5 to 4.5, and uranium uptake was a rapid process, where film diffusion was the determining step. Maximum uptake ranged from 90 to 115 mg U(VI) g⁻¹at 15–33 °C, respectively. None of the commonly used adsorption models (Langmuir, Freundlich, Dubinin-Radushkevich) was able to describe the experimental isotherms, whereas the linear model seems to provide the best fit. Kinetic and thermodynamic data implied that both physical and chemical sorption are involved in the process. Species calculation experiments showed that only positively charged and uncharged uranium species can be retained on the biomass. Quantitative uranium recovery was achieved by mild desorbing agents at concentrations as low as 0.1 M. Therefore, grape stalks seem to be a promising biosorbent due to their high sequestration capacity even under high salinity and acidity conditions, low cost, and easy regeneration.

To test the hypothesis that lead (Pb) content of rice grain may be related to its transport and subcellular distribution in rice plant, the present study was conducted with six rice cultivars of different types under different soil Pb levels. The results showed that grain Pb concentrations were correlated positively and significantly (P < 0.05 or 0.01) with distribution ratios (DRs) of Pb from shoots to ears/grains, but insignificantly (P > 0.05) with the DR from roots to shoots. The DR from shoots to ears/grains was correlated positively and significantly (P < 0.05 or 0.01) with subcellular distribution ratios (SDRs) of Pb in soluble fraction of shoots, but negatively and significantly (P < 0.05 or 0.01) with the SDR in cell wall fraction of shoots. In conclusion, Pb transportation from the shoot to the grain is the key factor in determining Pb content of rice grain. The Pb distributed in soluble fraction of shoot tissue is the key source of Pb for transferring into the grain. The Pb precipitated in cell wall fraction is the key sink of Pb in shoot tissue that restricts the transport of Pb from the shoot to the grain.

Peatlands are often regarded as metal repositories, but under drought conditions may switch from sinks to sources of metals and contaminate downstream ecosystems. To evaluate whether the release of metals into soil solution in peatlands is predictable using simple, widely available soil parameters, six peatlands, with varying levels of metal contamination, including a previously limed peatland, were sampled around the Sudbury, Ontario, region, and were subjected to simulated drought. The simulated drought lowered soil water pH and dissolved organic carbon (DOC) concentrations, which is consistent with field observations. Metal partitioning (K d) values for Co, Mn, Ni, and Zn, with just one exception at one peatland, could be significantly predicted by just the pH of the soil water, although the strength of the relationship varied considerably among sites. The metal speciation model WHAM VII predicted that the free metal ion concentration of all metals tested, including Cu and Al, increased significantly with decreasing pH. At the same time, DOC-bound metal concentrations were predicted to decrease as DOC levels were lower, which for metals with strong organic matter affinities (Cu and Al) offset the increase in free metal ion concentration in soil solution following summer drought. Climate change forecasts for more frequent and sustained droughts may promote metal release from peatlands and increased mobilization to surface waters, and importantly, for some metals, the potential toxicity of the metals released from peatlands may increase to a greater extent than expected from increases in total metal concentrations because of decreased DOC following drought.