Bioleaching Of Heavy Metals Research Articles

Bioleaching of heavy metals from contaminated soil using Acidithiobacillus thiooxidans: effect of sulfur/soil ratio

Bioleaching of heavy metals from contaminated soil was carried out using indigenous sulfur oxidizing bacterium Acidithiobacillus thiooxidans. Experiments were carried out by varying sulfur/soil ratio from 0.03 to 0.33 to evaluate the optimum ratio for efficient bioleaching of heavy metals from soil. The influence of sulfur/soil ratio on the bioleaching efficiency was assessed based on decrease in pH, increase in oxidation–reduction potential, sulfate production and solubilization of heavy metals from the soil. Decrease in pH, increase in oxidation–reduction potential and sulfate production was found to be better with the increase in sulfur/soil ratio. While the final pH of the system with different sulfur/soil ratio was in the range of 4.1–0.7, oxidation reduction potential varied from 230 to 629 mV; sulfate production was in the range of 2,786–8,872 mg/l. Solubilization of chromium, zinc, copper, lead and cadmium from the contaminated soil was in the range of 11–99%. Findings of the study will help to optimize the ratio of sulfur/soil to achieve effective bioleaching of heavy metals from contaminated soils.

Changes in nutrient profile of soil subjected to bioleaching for removal of heavy metals using Acidithiobacillus thiooxidans

Studies were carried out to assess changes in nitrogen, phosphorus and potassium contents in soil during bioleaching of heavy metals from soil contaminated by tannery effluents. Indigenous sulfur oxidizing bacteria Acidithiobacillus thiooxidans isolated from the contaminated soil were used for bioremediation. Solubilization efficiency of chromium, cadmium, copper and zinc from soil was 88, 93, 92 and 97%, respectively. However, loss of nitrogen, phosphorus and potassium from the soil was 30, 70 and 68%, respectively. These findings indicate that despite its high potential for removal of heavy metals from contaminated soils, bioleaching results in undesirable dissolution/loss of essential plant nutrients. This aspect warrants urgent attention and detailed studies to evaluate the appropriateness of the technique for field application.

Degradation of inhibitory substances by heterotrophic microorganisms during bioleaching of heavy metals from anaerobically digested sewage sludge

The presence of organic acids was found to be inhibitory to the bioleaching of sewage sludge and the objective of the present study was to elucidate the roles of heterotrophic microorganisms in removing organic acids during the bioleaching of heavy metals from anaerobically digested sewage sludge. Microbiological analysis showed that acetic and propionic acids posed a severe inhibitory effect on iron-oxidizing bacteria as reflected by a sharp decrease in their viable counts in the first 4 d and it only started to increase 2 d after the depletion of both acids. Biodegradation of these inhibitory organic acids was revealed by sharp increases in total fungi and acidophiles between day 3 and day 5 which coincided with degradation of organic acids. This was further confirmed by the increases in total counts of both acetate and propionate degraders in the same period. Two yeast strains Y4 and Y5 with strong ability to degrade acetate and/or propionate were isolated and identified as Pichia sp. and Blastoschizomycetes capitatus, respectively. B. capitatus Y5 was an more important player in removing the inhibitory organic acids during the bioleaching process since it could utilize both acetate and propionate as sole carbon source while Pichia sp. Y4 was an strict acetate degrader. Results from the present study not only provided the evidence for biodegradation of organic acids by heterotrophs, but also disclosed a biological mechanism for the initiation of bioleaching of organic acid-laden sewage sludge.

Influence of initial pH on bioleaching of heavy metals from contaminated soil employing indigenous Acidithiobacillus thiooxidans

Bioleaching of heavy metals from contaminated soil was carried out employing indigenous sulfur oxidizing bacterium Acidithiobacillus thiooxidans. Experiments were carried out to assess the influence of initial pH of the system on bioleaching of chromium, zinc, copper, lead and cadmium from metal contaminated soil. pH at the end of four weeks of bioleaching at different initial pH of 3–7 was between 0.9 and 1.3, ORP between 567 and 617 mV and sulfate production was in the range of 6090–8418 mg l −1. Chromium, zinc, copper, lead and cadmium solubilization ranged from “59% to 98%” at different initial pH. A. thiooxidans was not affected by the increasing pH of the bioleaching system towards neutral and it was able to utilize elemental sulfur. The results of the present study are encouraging to develop the bioleaching process for decontamination of heavy metal contaminated soil.

Effect of oxygen limitation on solid-bed bioleaching of heavy metals from contaminated sediments

The effects of oxygen limitation on solid-bed bioleaching of heavy metals (Me) were studied in a laboratory percolator system using contaminated sediment supplemented with 2% elemental sulfur (S o). Oxygen limitation was realized by controlling the gas flow and oxygen concentration in the aeration gas. The oxygen supply varied between 150 and 0.5 mol O 2 mol S o - 1 over 28 d of leaching. Moderate oxygen limitation led to temporarily suppression of acidification, rate of sulfate generation and Me solubilization. Lowering the oxygen supply to 0.5 mol O 2 mol S o - 1 resulted in retarding acidification over a period of three weeks and in poor Me solubilization. Oxidation of S o occurred even under strong oxygen limitation at a low rate. High surplus of oxygen was necessary for almost complete oxidation of the added S o. The maximum Me solubilization was reached at an oxygen supply of 7.5 mol O 2 mol S o - 1 . Thus, the oxygen input during solid-bed bioleaching can be reduced considerably by controlling the gas flow without loss of metal removal efficiency. Oxygen consumption rates, ranging from 0.4 × 10 −8 to 0.8 × 10 - 8 kg O 2 kg dm - 1 s - 1 , are primarily attributed to high reactivity of the sulfur flower and high tolerance of indigenous autotrophic bacteria to low oxygen concentrations. The S o related oxygen consumption was calculated assuming a molar yield coefficient Y O 2 / S of 1.21. The oxygen conversion degree, defined as part of oxygen feed consumed by S o oxidation, increased from 0.7% to 68% when the oxygen supply was reduced from 150 to 0.5 mol O 2 mol S o - 1 .

Effect of Sludge Dissolved Organic Matter on Oxidation of Ferrous Iron and Sulfur by Acidithiobacillus Ferrooxidans and Acidithiobacillus Thiooxidans

Although two species of chemolithoautotrophic bacteria, Acidithiobacillus ferrooxidans and Acidithiobacillus thiooxidans, are widely considered to be the main microorganisms that control the process of bioleaching of heavy metals from sewage sludge, little is known about the effect of dissolved organic matter (DOM) present in sewage sludge on bacterial oxidation of energy substrate. Batch cultures studies showed that sludge DOM significantly inhibited ferrous iron and sulfur oxidation by Acidithiobacillus ferrooxidans LX5 and Acidithiobacillus thiooxidans TS6, respectively. The toxicity of sludge DOM appeared when the concentration was higher than 150 mg DOC L−1. Among the organic compounds tested, the monocarboxylic organic acids including formic acid, acetic acid, propionic acid, and butyric acid exhibited a marked toxicity to Acidithiobacillus species. Of these organic acids, formic acid was the most toxic one as indicating that iron and sulfur oxidation almost were entirely inhibited at a concentration of 1.67 mM. In addition, it was found that A. ferrooxidans LX5 was more sensitive to glucose, starch, and citric acid than A. thiooxidans TS6, while the former seemed to be more acetic, propionic, and butyric acid resistant than the latter. In the selected 150 mg DOC L−1 of DOM derived from Sludge-H, the concentrations of formic acid and acetic acid were 8.94 mM and 2.09 mM, respectively, being a contributing factor causing 95% inhibition of iron oxidation and 70% inhibition of sulfur oxidation. To exploit specific heterotrophic microorganisms to eliminate these toxic organic compounds should be further studied.

Effect of different types of elemental sulfur on bioleaching of heavy metals from contaminated sediments

The application of two different types of elemental sulfur (S 0) was studied to evaluate the efficiency on bioleaching of heavy metals from contaminated sediments. Bioleaching tests were performed in suspension and in the solid-bed with a heavy metal contaminated sediment using commercial sulfur powder (technical sulfur) or a microbially produced sulfur waste (biological sulfur) as substrate for the indigenous sulfur-oxidizing bacteria and thus as acid source. Generally, using biological sulfur during suspension leaching yielded in considerably better results than technical sulfur. The equilibrium in acidification, sulfur oxidation and metal solubilization was reached already after 10–14 d of leaching depending upon the amount of sulfur added. The metal removal after 28 d of leaching was higher when biological sulfur was used. The biological sulfur added was oxidized with high rate, and no residual S 0 was detectable in the sediment samples after leaching. The observed effects are attributable to the hydrophilic properties of the biologically produced sulfur particles resulting in an increased bioavailability for the Acidithiobacilli. In column experiments only poor effects on the kinetics of the leaching parameters were observed replacing technical sulfur by biological sulfur, and the overall metal removal was almost the same for both types of S 0. Therefore, under the conditions of solid-bed leaching the rate of sulfur oxidation and metal solubilization is more strongly affected by transport phenomena than by microbial conversion processes attributed to different physicochemical properties of the sulfur sources. The results indicate that the application of biological sulfur provides a suitable means for improving the efficiency of suspension leaching treatments by shortening the leaching time. Solid-bed leaching treatments may benefit from the reuse of biological sulfur by reducing the costs for material and operating.

Bioleaching of spent fluid catalytic cracking catalyst using Aspergillus niger

The use of the fungus Aspergillus niger for the bioleaching of heavy metals from spent catalyst was investigated, with fluid catalytic cracking (FCC) catalyst as a model. Bioleaching was examined in batch cultures with the spent catalysts at various pulp densities (1–12%). Chemical leaching was also performed using mineral acids (sulphuric and nitric acids) and organic acids (citric, oxalic and gluconic acids), as well as a mixture of organic acids at the same concentrations as that biogenically produced. It was shown that bioleaching realised higher metal extraction than chemical leaching, with A. niger mobilizing Ni (9%), Fe (23%), Al (30%), V (36%) and Sb (64%) at 1% pulp density. Extraction efficiency generally decreased with increased pulp density. Compared with abiotic controls, bioleaching gave rise to higher metal extractions than leaching using fresh medium and cell-free spent medium. pH decreased during bioleaching, but remained relatively constant in both leaching using fresh medium and cell-free spent medium, thus indicating that the fungus played a role in effecting metal extraction from the spent catalyst.

Optimisation on bioleaching of incinerator fly ash by Aspergillus niger – use of central composite design

Previous work has shown that heavy metals may be bioleached from municipal solid waste (MSW) incinerator fly ash. The bioleaching of heavy metals from the ash depends on physical, chemical and biological factors. Our research objective is to establish the factors that exert a greater impact on the bioleaching process, and to determine the optimal bioleaching conditions in order to achieve the maximum metal leaching efficiency for selected metals. Four factors were investigated: sucrose concentration, inoculum spore concentration, fly ash pulp density, and the time of addition of fly ash to the fungus Aspergillus niger. Using the central composite design (CCD), 31 batch bioleaching tests were run under high and low values of these four factors. Empirical models obtained through second-order (Taylor series approximation) regression provided the optimal bioleaching conditions. Results showed that sucrose concentration and pulp density were more important factors than spore concentration and the time of addition of the fly ash. The concentration of Al, Fe, Zn, citric acid, and gluconic acid attained in the leached liquor was 12.3, 12.3, 77.6 ppm, 51 and 281 mM, respectively.

CHARACTERIZATION OF AN INDIGENOUS IRON-OXIDIZING BACTERIUM AND ITS EFFECTIVENESS IN BIOLEACHING HEAVY METALS FROM ANAEROBICALLY DIGESTED SEWAGE SLUDGE

The objective of the present study was to isolate the indigenous iron-oxidizing bacterium and compare its effectiveness in bioleaching of heavy metals from fresh anaerobically digested sludge and aged sludge which had undergone a storage period in a sludge holding tank. An acidophilic iron-oxidizing bacterium Acidithiobacillus ferrooxidans strain ANYL-1 was successfully isolated from the sludge collected from a wastewater treatment plant at Yuen Long district in Hong Kong. It was a Gram negative, non-motile rod shaped bacterium which used ferrous iron, elemental sulfur or thiosulfate as energy source, but did not utilize tetrathionate or glucose as energy source. The optimal temperature and pH for its growth and iron oxidation were 30-35°C and pH 2.0-2.5, respectively. When it was used in the bioleaching of anaerobically digested sewage sludge, an inhibition on metal solubilization was observed in fresh sludge except for Zn whose dissolution was solely a chemical process. Compared to the 3 and 4 days required for solubilization of Cu and Cr respectively from the sludge sample collected after the sludge holding tank (Sludge SHT), 6 days were required to bioleach Cu and Cr from fresh sludge (Sludge AD). The fresh sewage sludge posed an unfavorable condition for bioleaching of heavy metals from anaerobically digested sludge as reflected by the prolonged bioleaching time. Therefore, further studies were needed to understand the inhibitory effects in the fresh anaerobically digested sludge and develop measures to remove it in order to improve the heavy metal bioleaching efficiency.

Bioleaching of heavy metals from contaminated sediment by indigenous sulfur-oxidizing bacteria in an air-lift bioreactor: effects of sulfur concentration

The effects of sulfur concentration on the bioleaching of heavy metals from the sediment by indigenous sulfur-oxidizing bacteria were investigated in an air-lift reactor. Increasing the sulfur concentration from 0.5 to 5 g/l enhanced the rates of pH reduction, sulfate production and metal solubilization. A Michaelis–Menten type equation was used to explain the relationships between sulfur concentration, sulfate production and metal solubilization in the bioleaching process. After 8 days of bioleaching, 97–99% of Cu, 96–98% of Zn, 62–68% of Mn, 73–87% of Ni and 31–50% of Pb were solubilized from the sediment, respectively. The efficiency of metal solubilization was found to be related to the speciation of metal in the sediment. From economical consideration, the recommended sulfur dosage for the bioleaching of metals from the sediment is 3 g/l.

Identification of inhibitory substances affecting bioleaching of heavy metals from anaerobically digested sewage sludge.

Significant inhibitory effects of the filtrate medium of anaerobically digested sewage sludge on iron oxidation by Acidithiobacillus ferrooxidans ANYL-1 were observed in our preliminary experiments, indicating the presence of inhibitory substances in anaerobically digested sewage sludge. The objectives of the present study were to identify the possible inhibitory substances and to evaluate their impacts on metal solubilization during bioleaching of sewage sludge. The results showed that the concentrations of total reducing sugars, all tested metal ions, and anions were too low to suppress iron oxidation, and only organic acids, especially acetic and propionic acids, were found at concentrations higher than their inhibitory levels. The presence of 10.8 mM acetic acid and 9.88 mM propionic acid in sewage sludge (sludge N) led to long lag periods of 6 and 7 days for solubilization of Cu and Cr, respectively, as compared to a lag period of only 1 day in the control and another sludge (sludge S) with a low level of organic acids. Meanwhile the leaching time for maximum solubilization of Zn also extended to 6 days in the presence of organic acids as compared to 3 days in the control. Acetic and propionic acids posed an unfavorable bioleaching condition for anaerobically digested sewage sludge; therefore, further studies are required to explore the means to remove the inhibitory effects to improve the heavy metal bioleaching efficiency.

Bioleaching of heavy metals from anaerobically digested sewage sludge using FeS 2 as an energy source

The effect of using FeS 2 as an energy source, on the bioleaching of heavy metals (Zn, Cr, Cu, Pb and Ni) and nutrients (nitrogen and phosphorus) from anaerobically digested sludge using isolated indigenous iron-oxidizing bacteria was investigated in this paper. Addition of FeS 2 in the range of 0.5–4.0 g l −1 accelerated the acidification of sludge and raised the oxidation–reduction potential of sludge medium with an inoculation of 15% (v/v) of active bacteria, thus resulting in an overall increase in metal dissolution efficiency. After 16 days of bioleaching at 28 °C and an initial pH of 3.0, up to 99% of Zn, 65% of Cr, 74% of Cu, 58% of Pb and 84% of Ni can be removed from the sludge. In contrast, only 94% of Zn, 12% of Cr, 21% of Cu, 32% of Pb and 38% of Ni were leached out in the control without inoculation of iron-oxidizing bacteria and the addition of FeS 2. Less than 15% of nitrogen and 6% of phosphorous were lost after 16 days of bioleaching when using FeS 2 as the energy source. Comparing to 39% and 45% loss respectively for these two nutrients when using FeSO 4 · 7H 2O as the energy source, FeS 2 appears to be a more suitable energy source for preserving nutrients in sludge while removing heavy metals from sludge.

Effects of ferric ion on bioleaching of heavy metals from contaminated sediment

Bioleaching is one of the promising procedures for removal of heavy metals from contaminated sediments. The advantages of this biotechnology are that it is easy, efficient, less costly and friendly to the environment. However, the principal disadvantage of this process is its slow kinetics in metal solubilization, which may limit practical application of the bioleaching process. In order to enhance the rate and efficiency of metal solubilization, the ferric ion was used as a catalytic agent in the bioleaching process. It was found that the sediment pH apparently decreased in the bioleaching after addition of ferric ion. The metal solubilization increased quickly after the addition of ferric ion. The rate of metal solubilization was enhanced by the addition of ferric ion, especially for Cr and Pb. An increase in the amount of ferric ion added increased the final efficiency of metal solubilization. The highest final efficiency of metal solubilization was obtained in the bioleaching with 1 g/L of ferric ion. Besides, the growth of sulfur-oxidizing bacteria was not affected by addition of ferric ion in the bioleaching. It was concluded that the kinetics of metal solubilization were enhanced by addition of ferric ion in the bioleaching process.

Comparison of bioleaching of heavy metals from sewage sludge using iron- and sulfur-oxidizing bacteria

The aim of the present study was to compare the bioleaching efficiency of Cu, Zn and Cr from anaerobically digested sewage sludge using iron- and sulfur-oxidizing bacteria. Bioleaching was performed on sewage sludge collected from the Yuen Long wastewater treatment plant. A 15% (v/v) inoculation of either iron- or sulfur-oxidizing bacteria with 4 g FeSO 4 l −1 and 0.75% elemental sulfur, respectively, was added to sewage sludge with or without autoclaving in the bioleaching experiment. The mixtures were shaken continuously in an incubator at 30 °C for 16 days and samples were tested at 2-day intervals for pH, ORP and metal determination. The results showed that the iron-oxidizing system required only 2 days as compared to 4 days for the sulfur-oxidizing system to reduce the sludge pH from 7 to 2. Both systems achieved a maximum Cr removal of 52–58% after 12 days of bioleaching, but for iron-oxidizing bacteria with iron-sulfate as an energy source it was 20% higher at the beginning of leaching process. Although it took only 2 days to solubilize Cu by iron-oxidizing bacteria as compared to 8 days for sulfur oxidizing bacteria, the iron-oxidizing system removed only 80% of the total Cu, which was 20% lower than that of the sulfur-oxidizing system. Both iron- and sulfur-oxidizing bacteria achieved 95% Zn removals after 4 days of bioleaching. The results demonstrated that the iron-oxidizing system had a faster removal rate than the sulfur-oxidizing bacteria. Nevertheless, further work should be done to improve the bioleaching efficiency of iron-oxidizing bacteria, especially for Cu and Cr.

PH requirement for the bioleaching of heavy metals from anaerobically digested wastewater sludge

Bioleaching has been demonstrated to be a feasible technology for removing heavy metals from sewage sludge, but the leaching medium needs to be pre-acidified to less than 4. The objective of the research presented in this paper was to investigate the pH requirement for isolated indigenous Thiobacillus ferrooxidans for bioleaching heavy metals from wastewater sludge in Hong Kong. Isolated sludge-indigenous iron-oxidizing bacteria were used for the bioleaching experiments to investigate the dissolution behaviour of heavy metals (Zn, Cu, Ni and Cr) from sludge set at an initial pH ranging from 3–7 with the purpose to reduce the acid consumption. The results showed that the inoculation of 15% of isolated indigenous iron-oxidizing bacteria and addition of 4.0 g L-1 Fe2+ (in the form of FeSO4⋅7H2O) resulted in a sharp decrease in sludge pH from an initial pH 3–7 to 2.1–2.4 and an increase in ORP (oxidation-reduction potential) from –200–38 mV to > 500 mV within the first 6 days. After 16 days of bioleaching, 50.2–78.4% of Cr, 63.7–74.1% of Cu, 74.9–88.2% of Zn and 15.5–38.6% of Ni can be leached out from the sludge at an initial pH range of 3–7. In contrast, only 1.5% of Cr, 1.7% of Cu, 15.3% of Zn and 15.5% of Ni was solubilized in the control run at pH 7.0. At the end of bioleaching, the dissolution of nutrients N and P from the organic matrix at pH 6 was significantly less than that at pH 3–5. Hence, the bioleaching efficiency could still be maintained at an initial pH of > 4 using the isolated indigenous T. ferrooxidans which would reduce the cost of operation.

Bioleaching of heavy metals from sediment: significance of pH

Bioleaching process, which causes acidification and solubilization of heavy metals, is one of the promising methods for removing heavy metals from contaminated sediments. The solubilization of heavy metals from contaminated sediments is governed by the sediment pH. In the present study, the significance of pH in bioleaching of heavy metals from contaminated sediment was evaluated at different solid contents of sediments in a bench-scale reactor. Results showed that a temporal change of pH in the bioleaching process was effected by the buffering capacity of the sediment particulates. The variations of pH in this bioleaching process were calculated by a modified logistic model. It was observed that solubilization of heavy metals from sediments is highly pH-dependent. In addition, a non-linear equation for metal solubilization relating pH value in the bioleaching process was established. This allows an easier and faster estimate of metal solubilization by measuring pH in the bioleaching process.

Influence of solid content on bioleaching of heavy metals from contaminated sediment byThiobacillus spp

The bioleaching process is one of the promising methods for removing heavy metals from contaminated sediments. In this study the effects of sediment solid content on the performance of the bioleaching process using a mixed culture of two sulfur-oxidizing bacteria were investigated. The results showed that the rate of pH reduction decreased with increasing sediment solid content because of the buffering capacity of sediment solids. It was found that there was a linear relationship between buffering capacity and sediment solid content. For different solid contents (10–100 gdm−3), 82–95% (w/w) of Cu; 58–70% (w/w) of Zn; 55–73% (w/w) of Mn; 33–72% (w/w) of Pb; 35–65% (w/w) of Ni and 9–20% (w/w) of Cr were leached from sediments in this bioleaching process. The rate of metal leaching was found to decrease with an increase in sediment solid content. The solubilization of heavy metal from sediments was well described by a solid content-related kinetic equation. © 2000 Society of Chemical Industry

Adaptation of indigenous iron‐oxidizing bacteria for bioleaching of heavy metals in contaminated soils

Abstract Indigenous iron‐oxidizing bacteria in soil were acclimated in three different contaminated soils to remove toxic heavy metals. The adaptation was carried out at a pH of 4.0 and a room temperature of 24 ± 2°C in a gyratory shaking incubator. The iron‐oxidizing microflora was adapted in three to four successive transfers. Ferrous iron was supplemented by addition of FeSO4.7H2O. The oxidation of ferrous iron was associated with an increase in ORP up to 500 to 600 mV. The final pH in the soil solution after bacterial adaptation was lower than 2.5 for all the soils tested. Amendment of the soil with ammonium sulphate and dipotassium hydrogen phosphate increased the rate of iron oxidation by iron‐oxidizing microflora. The acclimation of the indigenous microflora reduced the metal leaching period from 18–30 days to 2–8 days. The metal leaching capacity of the indigenous iron‐oxidizing bacteria seems to be influenced by the speciation of the metals in the different soils. This process of bioleaching appe...

Kinetics of heavy metal bioleaching from sewage sludge—I. Effects of process parameters

Abstract The bioleaching of heavy metals from sewage sludges can be accomplished by indigenous sulfur-oxidizing bacteria present in the sludge. The performance of the bioleaching process is influenced by various parameters such as sludge solids concentration, pH, acid concentration etc. Effects of such parameters on system performance were experimentally evaluated. It was found that the sludge suspended solids concentration plays a major role in regulating the acid production indirectly, by influencing the nature of the pH drop in the system; the sludge solids concentration does not directly affect the metal solubilization process. An initial sludge pH of 4.0 produced the maximum sulfate production rate, but the initial sludge pH had little effect on the final metal solubilization levels achieved. Growth rates of the two bacterial species present in the system were found to have a linear relationship with the natural logarithm of the system pH. To take this dependence into account, a new system parameter called the buffering capacity index of the sludge was defined. BCI was found to bear a linear relationship with sludge solids concentration, for a given type of sludge (non-digested, aerobically digested or anaerobically digested).