Cleaner utilization of electroplating sludge by bioleaching with a moderately thermophilic consortium: A pilot study

A review on e-waste contamination, toxicity, and sustainable clean-up approaches for its management

Ecosystems and human health are being negatively impacted by the growing problem of electrical waste, especially in developing countries. E-waste poses a significant risk to ecological systems because it can release a variety of hazardous substances into the environment, containing polybrominated diphenyl ethers and heavy metals, brominated flame retardants, polychlorinated dibenzofurans and polycyclic aromatic hydrocarbons, and dioxins. This review article provides a critical assessment of the toxicological consequences of e-waste on ecosystems and human health and data analyses from scientific journals and grey literature on metals, BFRs, PBDEs, PCDFs, and PAHs in several environmental compartments of commercial significance in informal electronic trash recycling. The currently available techniques and tools employed for treating e-waste are sustainable techniques such as bioremediation, chemical leaching, biological leaching, and pyrometallurgy have been also discussed along with the necessity of implementing strong legislation to address the issue of unregulated exports of electronic trash in recycling practices. Despite the ongoing hurdles, implementing environmentally sustainable recycling methods have the potential to address the detrimental impacts of e-waste and foster positive economic development.

Adsorption and aggregation of Cu2+ on carboxymethylated sugarcane bagasse: Adsorption behavior and mechanism

Abundant biomass resources provide us with sufficient material basis, while a large amount of bio-waste is also produced and the high-value utilization of bio-waste is still highly desirable. Herein, we reported a facile one-pot fabrication approach towards efficient utilization of sugarcane bagasse via carboxymethylation to adsorb and recycle Cu2+ ions. The modified sugarcane bagasse possessed outstanding adsorption efficiency, with a maximum capacity of 263.7 mg g-1, owing to the functional groups such as carboxyl and hydroxyl groups, as well as aromatic structure. It was noted that the carboxymethylated sugarcane bagasse (MSB40) swelled rapidly when suffering Cu2+ ions solution, and more adsorption sites were available since the physical diffusion barrier was removed, thereby enhancing the absorption capacity. Interestingly, Cu2+ ions could induce the aggregation of MSB40 due to the Cu2+ ions compress colloid double layer, neutralizes surface charges, which benefited the following separation process. Ultimately, copper oxide was recovered and the purity reached 97.9%. Additionally, in the presence of both Ca2+ and Mg2+ ions, MSB40 exhibited excellent selectivity for the adsorption of Cu2+ ions. This strategy offers a facile and novel clue for the high-value utilization of bio-waste and the recovery of copper for biomaterial and environmental applications.

Approaches for electroplating sludge treatment and disposal technology: Reduction, pretreatment and reuse

Electroplating sludge (ES) has become an obstacle to the sustainable development of the electroplating industry. Electroplating sludge has a large storage capacity, with a high concentration of soluble pollutants (heavy metals), which has great potential to harm the local ecosystems and human health. Although much research has been done in this area, there seems to be no mature and stable solution. Therefore, the latest technologies for the reduction, pretreatment and reuse of electroplating sludge are emphatically introduced based on the analysis of the characteristics of electroplating sludge and its impact on the ecological environment. The factors hindering the treatment and disposal of electroplating sludge are pointed out, and reasonable and feasible suggestions to solve this problem are proposed. The solidification and removal mechanism of heavy metals in electroplating sludge is emphatically analyzed. The physicochemical and separation processes of heavy metals, as well as thermal treatment technique are discussed. Finally, it is proposed to establish a database of the physicochemical properties and elemental content of electroplating sludge to achieve its systematic treatment and digestion. We hope that this paper can help solve the problem of electroplating sludge and promote the sustainable development of the electroplating industry.

A review on fabricating functional materials by electroplating sludge: process characteristics and outlook

As the end product of the electroplating industry, electroplating sludge (ES) has a huge annual output and an abundant heavy metal (HM). The effective disposal of ES is attracting increasing attention. Currently, the widely used ES disposal methods (e.g. landfill and incineration) make it difficult to effectively control of HMs and synchronously utilise metal resources, leading to a waste of metal resources, HMs migration, and potential harm to the environment and human health. Therefore, techniques to limit HMs release into the environment and promote the efficient utilisation of metal resources contained within ES are of great interest. Based on these requirements, material reuse is a great potential means of ES management. This review presents an overview of the process flows, principles and feasibilities of the methods employed for the material reuse of ES. Several approaches have been investigated to date, including (1) additions in building materials, (2) application in pigment production, and (3) production of special functional materials. However, these three methods vary in their treatment scales, property requirements, ability to control HMs, and degree of utilisation of metal resources in ES. Currently, the safety of products and costs are not paid enough attention, and the large-scale disposal of HMs is not concordant with the effective management of HMs. Accordingly, this study proposes a holistic sustainable materialised reuse pattern of ES, which combines the scale and efficiency of sludge disposal and pays attention to the safety of products and the cost of transformation process for commercial application.

Advances in bioleaching of waste lithium batteries under metal ion stress

In modern societies, the accumulation of vast amounts of waste Li-ion batteries (WLIBs) is a grave concern. Bioleaching has great potential for the economic recovery of valuable metals from various electronic wastes. It has been successfully applied in mining on commercial scales. Bioleaching of WLIBs can not only recover valuable metals but also prevent environmental pollution. Many acidophilic microorganisms (APM) have been used in bioleaching of natural ores and urban mines. However, the activities of the growth and metabolism of APM are seriously inhibited by the high concentrations of heavy metal ions released by the bio-solubilization process, which slows down bioleaching over time. Only when the response mechanism of APM to harsh conditions is well understood, effective strategies to address this critical operational hurdle can be obtained. In this review, a multi-scale approach is used to summarize studies on the characteristics of bioleaching processes under metal ion stress. The response mechanisms of bacteria, including the mRNA expression levels of intracellular genes related to heavy metal ion resistance, are also reviewed. Alleviation of metal ion stress via addition of chemicals, such as spermine and glutathione is discussed. Monitoring using electrochemical characteristics of APM biofilms under metal ion stress is explored. In conclusion, effective engineering strategies can be proposed based on a deep understanding of the response mechanisms of APM to metal ion stress, which have been used to improve bioleaching efficiency effectively in lab tests. It is very important to engineer new bioleaching strains with high resistance to metal ions using gene editing and synthetic biotechnology in the near future.

Co-inoculation with beneficial microorganisms enhances tannery sludge bioleaching with Acidithiobacillus thiooxidans

Bioleaching of tannery sludge is an efficient and environmentally friendly way for chromium (Cr) removal, which supports the sustainable development of the leather industry. Acidithiobacillus thiooxidans has been reported effective in Cr bioleaching of tannery sludge. However, little is known about whether the presence of other benefiting species could further improve the Cr leaching efficiency of A. thiooxidans. Here, we studied the enhancing roles of four species namely Acidiphilium cryptum, Sulfobacillus acidophilus, Alicyclobacillus cycloheptanicus, and Rhodotorula mucilaginosa in chromium bioleaching of tannery sludge with A. thiooxidans by batch bioleaching experiments. We found that each of the four species facilitated the quick dominance of A. thiooxidans in the bioleaching process and significantly improved the bioleaching performance including bioleaching rate and efficiency. The bioleaching efficiency of Cr in the tannery sludge could reach 100% on the sixth day by co-inoculating A. thiooxidans and four auxiliary species. The achievements shed a light on the role of the community-level interactions on bioleaching and may also serve as guidance for managing bioleaching consortiums for better outcomes.

Indirect bioleaching recovery of valuable metals from electroplating sludge and optimization of various parameters using response surface methodology (RSM)

Electroplating sludge contains amounts of valuable/toxic metals as a typical hazardous solid waste, but existing technology is hard to simultaneously gain the high recovery of valuable metals and its convert into general solid waste. In this study, indirect bioleaching process was optimized by using RSM for high recovery of four valuable metals (Ni, Cu, Zn and Cr) from electroplating sludge and its shift into general waste. The results showed that the maximum leaching rate respectively was 100% for Ni, 96.5% for Cu, 100% for Zn and 76.1% for Cr at the optimal conditions. In particular, bioleaching saw a much better performance than H₂SO₄ leaching in removal of highly toxic Cr (76.1% vs. 30.2%). The extraction efficiency of Cr by H₂SO₄ leaching sharply rose to 72.6% in the presence of 9.0 g/L Fe³⁺, suggesting that Fe³⁺ played an important role in the bioleaching of Cr. Based on bioleaching dynamics analysis, it was speculated that Fe³⁺ passes through the solid shell and enter inside the sludge to attack Cr assisting by extracellular polymeric substances (EPS), leading to high extraction and low residue of Cr. Meanwhile, due to high-efficient release and removal of valuable/toxic metals by bioleaching, the bioleached residues successfully degraded into general based on TCLP test and can be reused as construction material safely.

Chemical looping gasification using Nickel-containing electroplating sludge and dyeing sludge as oxygen carrier

Nickel-containing electroplating sludge (NiES) and dyeing sludge (DS) were used to prepare oxygen carriers (OCs) for chemical looping gasification (CLG) of DS. X-ray diffraction (XRD), surface area and porosity analysis were employed to investigate the crystal structure and pore structure of NiES and DS ash OCs. It was found that OCs prepared at 850 ℃ for 8 h (850NiES8, 850DS8) exhibited good characteristics in terms of pore structure. X-ray fluorescence (XRF), hydrogen temperature programmed reduction (H2-TPR) and thermo-gravimetric (TG) were employed to explore the elemental composition, reactivity, redox behavior and their effect on DS pyrolysis of the two selected OCs. The influence of mass ratio of 850NiES8, 850DS8 to DS (850NiES8/DS, 850DS8/DS) and reaction temperature on DS CLG were investigated. It showed that the addition of two OCs significantly promoted the gas yield of DS while accelerating the gasification process. It showed a better performance of 850NiES8 than that of 850DS8 when it was below 900 ℃. On the other side, 850DS8 showed more advantage between 900 and 950 ℃. And high carbon conversion (ηC) of 80.94%,77.59% and acceptable valid gas yield (Vg) of 0.192,0.190 Nm3/kg could be obtained at 850 ℃ when 850NiES8/DS, 850DS8/DS were 1, respectively. In this process, the reduction and energy recovery of dyeing sludge were implemented, and two promising OCs (850NiES8, 850DS8) were developed. In addition, a new harmless method of NiES recycle treatment was also provided.

Bio-Based Processes for Material and Energy Production from Waste Streams under Acidic Conditions

The revolutionary transformation from petrol-based production to bio-based production is becoming urgent in line with the rapid industrialization, depleting resources, and deterioration of the ecosystem. Bio-based production from waste-streams is offering a sustainable and environmentally friendly solution. It offers several advantages, such as a longer operation period, less competition for microorganisms, higher efficiency, and finally, lower process costs. In the current study, several bio-based products (organic acids, biomethane, biohydrogen, and metal leachates) produced under acidic conditions are reviewed regarding their microbial pathways, processes, and operational conditions. Furthermore, the limitations both in the production process and in the scale-up are evaluated with future recommendations.

Growth in ever-increasing acidity condition enhanced the adaptation and bioleaching ability of Leptospirillum ferriphilum

Low pH eliminated the jarosite accumulation and improved the interfacial reaction rate during the bioleaching process. However, high acidity tends to make environments less hospitable, even for organisms that live in extreme places, so a great challenge existed for bioleaching at low pH conditions. This study demonstrated that the adaption and bioleaching ability of Leptospirillum ferriphilum could be improved after the long-term adaptive evolution of the community under acidity conditions. It was found that the acidity-adapted strain showed robust ferrous iron oxidation activity in wider pH, high concentration of ferrous iron, and lower temperature. Although the enhancement for heavy metal tolerance was limited, the resistance for MgSO₄, Na₂SO₄, and organic matter was stimulative. More importantly, both pyrite and printed circuit board bioleaching revealed the higher bioleaching ability of the acid-resistant strain. These adaptation and bioleaching details provided an available approach for the improvement of bioleaching techniques.

One-step extraction of high-purity CuCl2·2H2O from copper-containing electroplating sludge based on the directional phase conversion

The recovery of heavy metals is a vital way to turn electroplating sludge into resources and reduce its environmental hazards. However, the complex compositions of the polymetallic electroplating sludge severely limit the selective recovery of metal resources such as copper. In this study, we took a kind of copper-containing electroplating sludge (C-ES) as an example present and investigated the process of copper extraction. The copper and other metals were directional converted through an accurate phase transformation process carried out by chlorination combined with thermal regulation. Eventually, the copper was selectively recovered in the form of CuCl₂·2H₂O, while the rest of the metals were converted into stable metal salts or oxides. The HCl solution was the best regulator for selective copper recovery. Under the optimal conditions, the recovery of copper approached 97% and the purity of the CuCl₂·2H₂O product was about 95%. The kinetic reaction equation of the CuCl₂ volatilization process can be described by Power Low, G(α) = α^1/15. The economic estimate based on experimentation indicates the profit of recycling CuCl₂·2H₂O is about $23.2/kg. This work provides a novel, simple, and efficient approach to the selective recovery of heavy metal from polymetallic solid wastes.

Bioleaching of Copper-Containing Electroplating Sludge

The recovery of precious metals from solid waste through bioleaching has become a research hotspot in recent years. Thus, in this study, different strategies, such as chemical sulfuric acid leaching and mixed consortium bioleaching, were adopted to extract copper from Copper-Containing Electroplating Sludge. The results showed that, compared to chemical leaching, bioleaching showed a much better performance. Indeed, copper bioleaching efficiency reached 94.3% on day 7 (21.1% higher than that of chemical leaching). The results also indicated that the process of bioleaching involved more mechanisms and reactions than that of chemical leaching. The SEM and EDX tests showed that the surface morphology of the sludge changed significantly after bioleaching, and that an insignificant amount of copper remained in the leached residues. Furthermore, the leached residues passed the characteristic leaching toxic test and thus can be considered as non-hazardous raw materials for the construction industry. Hence, adopting a mixed consortium leaching process to extract copper from Copper-Containing Electroplating Sludge will not only significantly reduce environmental pollution, but will also use metal resources more efficiently.

Bioleaching for detoxification of waste flotation tailings: Relationship between EPS substances and bioleaching behavior

The production of large volumes of waste flotation tailings results in environmental pollution and presents a major ecological and environmental risk. This study investigates bioleaching of waste flotation tailings using Acidithiobacillus ferrooxidans. The experiments were performed with 5.00% solid concentration, pH 2.0 with 100 mL medium for 25 d in the lab. The pH, OPR, metal concentration, dissolved organic matter (DOM) in leachate and extracellular polymeric substances (EPS) were recorded. Bioleaching tailing materials were finally characterized. Results showed that microorganisms, acclimating with mine tailings, effectively accelerated the bioleaching process, achieving maximum Zn and Fe extraction efficiencies of 95.45% and 83.98%, respectively, after 25 days. Compared with raw mine tailings, bioleaching could reduce 96.36% and 95.84% leachable Zn and Pb, and Pb presented a low risk (4.13%), while Zn, Cu, and Cr posed no risk (0.34%, 0.64%, and 0%). Toxicity and environmental risk analysis revealed bioleaching process significantly reduced the environmental risk associated with mine tailings. EPS analysis indicated that the loosely-bound EPS (LB-EPS) and tightly-bound EPS (TB-EPS) fractions contained different organic substances, which played different roles in the bioleaching process. Pearson correlation analysis revealed that EPS was highly correlated with bioleaching behavior (p < 0.05), and EPS was the main factor affecting the bioleaching process, promoting bioleaching in the LB-EPS and TB-EPS fractions.

Advances in microbial remediation for heavy metal treatment: a mini review

Abstract

In recent years, microbiological treatment to remediate contamination by heavy metals has aroused public attention as such pollution has seriously threatens ecosystems and human health and impedes sustainable development. However, the aspect of actual industrial wastewater and solid waste remediation by microorganisms is not explored sufficiently. And what we focus on is technical field of microbial remediation. Therefore, in this review, we discuss and summarize heavy metal treatment via microbiological approaches in different media, including wastewater, solid waste from industrial factories and polluted sites. We also clarify the technical applicability from the perspective of biosorption, bioleaching, biominerization, etc. In particular, the exploration of the combination of microbiological approaches with chemical methods or phytoextraction are scrutinized in this review relative to real waste heavy metal remediation. Furthermore, we highlight the importance of hyperaccumulator endophytes.

Graphical abstract

Effective multi-metal removal from plant incineration ash via the combination of bioleaching and brine leaching

Plant incineration ash is the final product from the remediation of multi-metal contaminated soils by the phytoextraction process. The content of heavy metals in plant ash was found to be higher than the regulatory criteria and it was thus classified as hazardous waste. So far, no eco-friendly and cost-effective technology has been developed for the management of this residue. Herein, a cleaner strategy of bioleaching combined with brine leaching of multi-metals from plant ash was developed. The bioleaching results indicated that 88.7% (Zn), 93.2% (Cd), 99.9% (Mn) and 13.8% (Pb) were achieved under optimum conditions of Fe(ii) concentration 6.0 g L-1, pH 1.8 and pulp density 15% (w/v). Subsequently, the introduction of brine leaching using 200 g L-1 NaCl significantly increased Pb recovery to 70.6% under conditions of 15% (w/v) pulp density, thereby ultimately achieving deep recovery of all metals. An investigation of the mechanism revealed that H+ attack and microorganisms were the dominant mechanism for bioleaching of Zn, Cd and Mn, and the bioleaching kinetics of Zn in ash were controlled by interface mass transfer and diffusion across the product layer. Risk assessment tests indicated that the leached residues could pass the TCLP test standard and be safely reused as nonhazardous materials. These findings demonstrated that the two-stage leaching strategy was feasible and promising for multi-metal removal from plant ash.