A sustainable solution for alleviating hexavalent chromium from water streams using Lactococcus lactis AM99 as a novel Cr(VI)-reducing bacterium.

Chromium, extensively used in various industries, poses significant challenges due to its environmental impact. The threat of Cr(VI) causes critical concerns in aquatic ecosystems as a consequence of the fluidity of water. The conventional approach for the treatment of effluents containing Cr(VI) is reducing Cr(VI) to low-noxious Cr(III). This research is related to a Gram positive bacterium newly isolated from tannery effluent under aerobic conditions. To characterize functional groups on the isolate, Fourier transform infrared spectroscopy was utilized. The effect of different factors on Cr(VI) bioreduction was investigated, including temperature, initial Cr(VI) concentration, acetate concentration, and Tween 80 surfactant. Under optimal conditions (37 °C and 0.90 g/L sodium acetate), the bioreduction rate of the isolate, identified as Lactococcus lactis AM99, achieved 88.0 % at 300 mg/L Cr(VI) during 72 h (p < 0.05). It was observed that Cr(VI) bioreduction was enhanced by the acetate in both the quantity and intensity, while Tween 80 had no impact on the reaction. The strain AM99 exhibited remarkable characteristics, notably a marginal decrease in growth at elevated concentrations of hexavalent chromium and an exceptional potential to reduce Cr(VI) even at very low biomass levels, surpassing any prior findings in the associated research. Furthermore, The isolate could tolerate 1400 mg/L Cr(VI) in a solid medium. These distinctive features make the isolate a promising and well-suited candidate for remediating Cr(VI)-polluted environments. Additionally, the impact of biogenic extracellular polymer produced by the strain AM99 on reduction was examined at different temperatures.

An efficient approach for enhancement of gold and silver bioleaching from spent telecommunication printed circuit boards using cyanogenic bacteria: Prevention of biofilm formation.

Environmentally friendly bioleaching of gold and silver from electronic waste using cyanogenic bacteria has emerged as a promising approach. In the process of cyanide bioleaching, cyanide ions produced by cyanogenic bacteria form complexes (such as AuCN and AgCN) with metals in the waste structure and lead to their dissolution. The recovery rate of these valuable elements during bioleaching is influenced by extracellular polymeric substances (EPS). For the first time, this study presents an investigation into the role of EPS from Pseudomonas atacamensis in the bioleaching of gold and silver from spent telecommunication printed circuit boards (STPCBs). The experimental results demonstrate that, after 6 days of bioleaching, gold and silver recoveries reached 22% and 36.2%, respectively. Complementary analyses employing FE-SEM and attachment tests shed light on the interactions between EPS, bacterial attachment to particle surfaces, and biofilm development stages during gold and silver bioleaching. Notably, the most significant bacterial attachment occurred on the fourth day of bioleaching. Zeta potential tests conducted on bacteria and EPS provided insights into the potential absorption of soluble cations such as Au+ and Ag+ by EPS. Furthermore, 250 mg/L polyvinylpyrrolidone (PVP) effectively removed EPS from the particle surfaces, improving gold and silver recovery rates, reaching 26% and 43.2%, respectively. These findings highlight the importance of understanding the role of EPS in bioleaching processes and offer insights into enhancing gold and silver recovery from electronic waste.

A comprehensive review of bioleaching optimization by statistical approaches: recycling mechanisms, factors affecting, challenges, and sustainability.

A serious environmental problem is associated with the accumulation of solid waste on the Earth. Researchers are encouraged to find an efficient and sustainable method to recover highly profitable heavy metals and precious and base metals. Bioleaching is a green method of recovering valuable metals from solid waste. Optimizing the variables and conditions of the bioleaching process is crucial to achieving maximum metal recovery most cost-effectively. The conventional optimization method (one factor at a time) is well-studied. However, it has some drawbacks, such as the necessity of more experiments, the need to spend more time, and the inability to illuminate the synergistic effect of the variables. Optimization studies are increasingly utilizing response surface methodology (RSM) because it provides details about the interaction effects of variables with fewer experiments. This review discusses the application of RSM for bioleaching experiments from other solid wastes. It discusses the Central Composite and Box-Behnken designs as the most commonly used designs for optimizing bioleaching methods. The most influential factors for increasing the heavy metal recovery rate in applying RSM using the bioleaching process are recognized, and some suggestions are made for future research.

Ecofriendly recovery of copper from spent telecommunication printed circuit boards using an indigenous cyanogenic bacterium.

In recent years, electronic waste (e-waste) production has increased due to the population's growth and high consumption. As a result of the high concentration of heavy elements in these wastes, their disposal has posed many environmental problems. On the other hand, due to the non-renewability of mineral resources and the presence of valuable elements such as Cu and Au in electronic waste, these wastes are considered secondary minerals for recovering valuable elements. Among electronic waste, recovery of metals from spent telecommunication printed circuit boards (STPCBs) is significant, which has not been addressed despite their high production worldwide. This study isolated an indigenous cyanogenic bacterium from alfalfa field soil. The 16S rRNA gene sequencing results showed that the best strain has 99.8% phylogenetic affinity with Pseudomonas atacamenisis M7DI(T) with the accession number SSBS01000008 with 1459 nucleotides. The effect of the culture medium, initial pH, glycine concentration, and methionine on the cyanide production of the best strain was investigated. The results showed that the best strain could produce 12.3 ppm cyanide in NB medium with an initial pH of 7 and a concentration of glycine and methionine of 7.5 g/L and 7.5 g/L, respectively. The one-step bioleaching method was performed, which led to the recovery of 98.2% of Cu from STPCBs powder after 5 days. Finally, XRD, FTIR, and FE-SEM analyses were performed to investigate the structure of the STPCBs powder before and after the bioleaching process, confirming the high Cu recovery.

Bioleaching of valuable metals from spent LIBs followed by selective recovery of manganese using the precipitation method: Metabolite maximization and process optimization.

Despite the increased demand for resource recovery from spent lithium-ion batteries (LIBs), low Mn leaching efficiencies have hindered the development of this technology. A novel process was devised to enhance the dissolution of metals by producing citric acid using a molasses medium by Penicillium citrinum. This investigation used response surface methodology to investigate the influence of molasses concentration and media components on citric acid production, which demonstrated that molasses (18.5% w/w), KH2PO4 (3.8 g/L), MgSO4.7H2O (0.11 g/L), and methanol (1.2% (v/v)) were the optimum values leading to the production of 31.50 g/L citric acid. Afterward, optimum inhibitor concentrations (iodoacetic acid: 0.05 mM) were added to accumulate citric acid, resulting in maximum bio-production (40.12 g/L) of citric acid. The pulp density and leaching time effect on metals dissolution was investigated in enriched-citric acid spent medium. The suitable conditions were a pulp density of 70 g/L and a leaching duration of 6 days, which led to the highest dissolution of Mn (79%) and Li (90%). Based on the results of the TCLP tests, the bioleaching residue is non-hazardous, suitable for safe disposal, and does not pose an environmental threat. Moreover, nearly 98% of Mn was extracted from the bioleaching solution with oxalic acid at 1.2 M. XRD, and FE-SEM analyses were utilized for further bioleaching and precipitation mechanism analysis.

Environmentally sustainable and cost-effective recycling of Mn-rich Li-ion cells waste: Effect of carbon sources on the leaching efficiency of metals using fungal metabolites.

Metals recovery from spent lithium coin cells (SCCs) is enjoying great attention due to environmental problems and metal-rich contents such as Mn and Li. Fungi can generate many organic acids, and metals can be dissolved, but sucrose is not an economical medium. The main objective of this study is to find a suitable carbon substrate in place of sucrose for fungal bioleaching. We have developed an environmentally friendly, cost-effective, and green method for recycling and detoxifying Mn and Li from SCCs using the spent culture medium fromPenicillium citrinumcultivation. Sugar cane molasses and sucrose were selected as carbon sources. Based on the extracted fungal metabolites, the effects of pulp density, temperature, and leaching time were assessed on metal dissolution. The most suitable conditions were 30 g/L of pulp density, a temperature of 40 °C, and 4 days of leaching time in spent molasses medium, which led to a high extraction of 87% Mn and 100% Li. Based on EDX-mapping analyses, it was found that the initial concentration of ∑ (Mn + C) in the SCCs powder was almost 100% while reaching nearly 6.4% after bioleaching. After bioleaching, an analysis of residual powder confirmed that metal dissolution from SCCs was effective owing to fungal metabolites. The economic study showed that the bioleaching method is more valuable for the dissolution of metals than the chemical method; In addition to improving bioleaching efficiency, molasses carbon sources can be used for industrial purposes.

Comprehensive characterization and environmental implications of spent telecommunication printed circuit boards: Towards a cleaner and sustainable environment.

The management and prevention of environmental risks associated with spent telecommunications printed circuit boards (STPCBs) is a concerning issue worldwide. Recycling might be proposed as a proper method to overcome this issue. Despite knowing that, choosing a sustainable method is challenging because of STPCBs complexity. This problem was overcome by analyzing STPCBs using different analytical methods and metal speciation. Understanding these data is essential in selection strategies to maximize selective recycling of metals and to minimize environmental impact. This research focused on characterizing STPCBs based on their structural, morphological, physiochemical, surface, and thermal properties. The accurate measurement of metal contents, indicating 187,900 mg kg-1 Cu, 22,540 mg kg-1 Pb, 1320 mg kg-1 Ag, and 205 mg kg-1 Au elements, plus other base metals, revealed a remarkable potential value in STPCBs. The results of structural analyses indicated that the powder has a crystalline structure and consists of Cu, Sn and Pb phases as well as different functional groups. In addition, after evaluating the zeta potential of the sample, the isoelectric pH of the sample was observed to be 5.6, which indicates that the powder particles have a negative surface in an environment with a pH higher than this value. Further, the metal speciation via sequential extraction procedure was performed, which showed that a unique harsh recycling strategy is required due to the stable structure of STPCBs. According to the results of this analysis, the global contamination factor (GCF) value was 83.48, which indicates STPCBs have a high degree of contamination. Leaching tests and environmental criteria were also conducted on this waste. The findings suggest that STPCBs needs pretreatments before landfilling to lower the concentration of toxic metals. Also, waste extraction test was the most aggressive procedure to assess mobility. Achieving this information is considered an essential step to choosing the most efficient recycling methods that minimize environmental impact while maximizing selective recycling of metals.

Insights into the polysaccharides and proteins production from Penicillium citrinum during bioleaching of spent coin cells.

The essential role of polysaccharides and proteins of extracellular polymeric substances (EPS) has been well known in the bioleaching process. However, there is no information on the role of these compositions in the bioleaching of spent coin cells (SCCs). This study investigated protein and polysaccharide production as biological macromolecules during the bioleaching of SCCs at various pulp densities using adapted Penicillium citrinum. The adaptation improved the tolerance index of fungi for the bioleaching up to a pulp density of 30 g/L. The EPS analysis indicated that loosely bound EPS (LB-EPS) contained a high concentration of polysaccharides. Instead, the most protein content was concentrated at tightly bound EPS (TB-EPS). Both protein and polysaccharide keep growing up to 20 g/L of pulp density during the entire period of bioleaching, and the maximum binding rate of Mn and Li to EPS was 43% and 15%, respectively. Pearson correlation indicated the positive correlation of the protein and the polysaccharides content on bioleaching efficiencies. From the FTIR spectroscopy, the principal functional groups on Mn and Li binding were OH and carboxyl. The FE-SEM analysis revealed the deformation of EPS at 30 g/L of pulp density, which suggested the toxic effect of this pulp density.

Environmentally friendly recovery of valuable metals from spent coin cells through two-step bioleaching using Acidithiobacillus thiooxidans.

The technology for recycling the spent coin cells is pressing needed due to a large amount of generated spent coin cells. However, there is little information about the recycling technology of spent coin cells. In this work, a two-step bioleaching method for recovery of metals from spent coin cells by Acidithiobacillus thiooxidans is performed for the first time. In this regard, the growth characteristics of A. thiooxidans was investigated in pure culture and during the two-step bioleaching approach. The highest recovery of Li, Co and Mn was achieved at a pulp density of 30 g L-1, in values of 99%, 60%, and 20%, respectively. The structural analyzes confirmed the progress of bioleaching process. In addition, the kinetics models showed that the chemical reaction was the rate-controlling step of the two-step bioleaching of spent coin cells. The comparative results between bioleaching and chemical leaching showed that Acidithiobacillus thiooxidans can enhance the leaching of metals. Toxicity characteristic leaching procedure of the spent coin cells powder demonstrated that the bioleached residue met the environmental limitations for safe disposal. In fact, bioleaching is an effective and promising route to reduce the environmental hazard of spent coin cells.