Recovery of gold from electronic wastewater by Phomopsis sp. XP-8 and its potential application in the degradation of toxic dyes

Diversity of fungus-mediated synthesis of gold nanoparticles: properties, mechanisms, challenges, and solving methods

Fungi-mediated synthesis of Gold nanoparticles (AuNPs) has advantages in: high efficiency, low energy consumption, no need for extra capping and stabilizing agents, simple operation, and easy isolation and purification. Many fungi have been found to synthesize AuNPs inside cells or outside cells, providing different composition and properties of particles when different fungi species or reaction conditions are used. This is good to produce AuNPs with different properties, but may cause challenges to precisely control the particle shape, size, and activities. Besides, low concentrations of substrate and fungal biomass are needed to synthesize small-size particles, limiting the yield of AuNPs in a large scale. To find clues for the development methods to solve these challenges, the reported mechanisms of the fungi-mediated synthesis of AuNPs were summarized. The mechanisms of intracellular AuNPs synthesis are dependent on gold ions absorption by the fungal cell wall via proteins, polysaccharides, or electric absorption, and the reduction of gold ions via enzymes, proteins, and other cytoplasmic redox mediators in the cytoplasm or cell wall. The extracellular synthesis of AuNPs is mainly due to the metabolites outside fungal cells, including proteins, peptides, enzymes, and phenolic metabolites. These mechanisms cause the great diversity of the produced AuNPs in functional groups, element composition, shapes, sizes, and properties. Many methods have been developed to improve the synthesis efficiency by changing: chloroauric acid concentrations, reaction temperature, pH, fungal mass, and reaction time. However, future studies are still required to precisely control the: shape, size, composition, and properties of fungal AuNPs.

A novel S,N-rich MOF for efficient recovery of Au(III): Performance and mechanism

A novel S,N-rich MOF with adenine and 4,4'-thiodiphenol as organic ligands was synthesized via the one-step solvothermal method, and used for gold recovery. The pH impact, adsorption kinetics, isotherms, thermodynamics, selectivity, and reusability were investigated accordingly. The adsorption and desorption mechanism were also explored comprehensively. The electronic attraction, coordination, and in situ redox account for the Au(III) adsorption. The Au(III) adsorption is affected strongly by the pH of solutions, and best at pH of 2.57. The MOF exhibits exceptional adsorption capacity as high as 3680 mg/g at 55 °C, fast kinetics with 8 min for 9.6 mg/L Au(III), and excellent selectivity for gold ion in real e-waste leachates. The adsorption process of gold on the adsorbent is endothermic and spontaneous, and influenced visibly by temperature. The adsorption ratio still maintained 99% after seven adsorption-desorption cycles. The column adsorption experiments show that the MOF has outstanding selectivity for Au(III) with 100% of removal efficiency in a complex solution containing Au, Ni, Cu, Cd, Co, and Zn ions. A glorious adsorption with a breakthrough time of 532 mins was obtained for the breakthrough curve. This study not only provides an efficient adsorbent for gold recovery, but also guidance for designing new materials.

Sustainable and efficient technologies for removal and recovery of toxic and valuable metals from wastewater: Recent progress, challenges, and future perspectives

Due to their numerous effects on human health and the natural environment, water contamination with heavy metals and metalloids, caused by their extensive use in various technologies and industrial applications, continues to be a huge ecological issue that needs to be urgently tackled. Additionally, within the circular economy management framework, the recovery and recycling of metals-based waste as high value-added products (VAPs) is of great interest, owing to their high cost and the continuous depletion of their reserves and natural sources. This paper reviews the state-of-the-art technologies developed for the removal and recovery of metal pollutants from wastewater by providing an in-depth understanding of their remediation mechanisms, while analyzing and critically discussing the recent key advances regarding these treatment methods, their practical implementation and integration, as well as evaluating their advantages and remaining limitations. Herein, various treatment techniques are covered, including adsorption, reduction/oxidation, ion exchange, membrane separation technologies, solvents extraction, chemical precipitation/co-precipitation, coagulation-flocculation, flotation, and bioremediation. A particular emphasis is placed on full recovery of the captured metal pollutants in various reusable forms as metal-based VAPs, mainly as solid precipitates, which is a powerful tool that offers substantial enhancement of the remediation processes' sustainability and cost-effectiveness. At the end, we have identified some prospective research directions for future work on this topic, while presenting some recommendations that can promote sustainability and economic feasibility of the existing treatment technologies.

Industrial wastewater treatment: Current trends, bottlenecks, and best practices

Rapid urbanization and industrialization have inextricably linked to water consumption and wastewater generation. Mining resources from industrial wastewater has proved to be an excellent source of secondary raw materials i.e., proficient for providing economic and financial benefits, clean and sustainable resilient environment, and achieving sustainable development goals (SDGs). Treatment of industrial wastewater for reusable resources has become a tedious task for decision-makers due to several bottlenecks and barriers, such as inefficient treatment options, high-cost expenditure, poor infrastructure, lack of financial support, and technical know-how. Most of the existing methods are conventional and fails to provide an economic benefit to the industries and have certain disadvantages. Also, the untreated industrial wastewater is discharged into the open drains, lakes, and rivers that lead to environmental pollution and severe health hazards. This paper has consolidated information about the current trends, opportunities, bottlenecks, and best practices associated with wastewater treatment and scope for the advancement in the existing technologies. Along with the efficient resource recovery, the wastewater could be ideally explored in the development of value-added materials, energy, and product recovery. The concepts, such as the circular economy (CE), partitions-release-recover (PRR), and transforming wastewater into bio factory are anticipated to be more convenient options to tackle the industrial wastewater menace.

Challenges and opportunities for more efficient water use and circular wastewater management. The case of Campania Region, Italy

By 2050, global demand for water is expected to increase by some 55% due to population growth and urbanization. The utilization of large amounts of freshwater in the world, generate huge volumes of wastewater of which, globally, more than 80% is discharged without treatment, thus causing impacts on aquatic ecosystems, human health and economic productivity. More sustainable practices of wastewater management are expected as a way towards circular bioeconomy (CBE) processes, whose goal is to implement closed systems promoting the systematic use of recycling, reuse and recovery of bioproducts and by-products and the reduction of waste generation. This approach, if adopted in the water and wastewater sector, can ensure environmental, economic and social benefits. The reuse of wastewater, on the one hand, reduces the volume of wastewater and the pressure on water bodies; on the other hand, the recovery of nutrients (P or N) and/or other high value bioproducts (biogas, cellulose, biopolymers) from wastewater offers numerous advantages in terms of supplying new raw bio-based materials that can be refed back to supply chains (thus substituting fossil resources) and, at the same time, producing cleaner water to be reused. Nevertheless, while in Europe many industries have demonstrated the ability to recycle and reuse water, in many regions of Italy the sustainable management of water and wastewater is not yet consolidated. In this study we explore the available technological, economic and environmental options concerning water use and wastewater treatment and we apply them to design appropriate scenarios for improved use efficiency and circular management. A comprehensive literature review of the most promising wastewater treatment processes for resources and energy valorization was conducted. The recovery of PHAs, struvite, nitrogen and algal biomass, as potential substitutes for conventional PET, phosphate and nitrogen chemical fertilizers and electricity, respectively, in addition to reusable treated water, were hypothesized and carefully discussed. Resulting scenarios are tested against the present situation of Campania Region (situated in Southern Italy) based on population and demand statistics, in order to develop strategies and policies potentially applicable locally and elsewhere.

The capability of Bacillus pseudomycoides from soil to remove Cu(II) in water and prevent it from entering plants

AIMS

Copper ion is widespread in wastewater and threatens the condition and human health. Micro-organisms have unique advantages to remove heavy-metal ions from water, but are rarely reported in the removal of copper ion. This aims to develop micro-organisms that can remove copper ion in water, characterize their properties and analyse their potential application in practice.

METHODS AND RESULTS

Sewage sludge was used as the source to isolate wild bacteria that can remove copper ion in water. The most efficient strain was screened out from 23 obtained isolates, identified as Bacillus pseudomycoides and coded as C6. The properties of C6 in the removal of copper ion in water were investigated in the aspects of reaction conditions, reaction groups, reaction dynamic and the application in oat planting. The reaction at pH 7 within 10 min yielded the highest removal rate of copper ion, 83%. The presence of lead ion in the reaction system could promote the removal rate of copper ion. Carboxyl groups and amidogen of C6 biomass were mainly involved in the removal of copper ion. The removal of copper ion was in accord with single-layer adsorption and Langmuir adsorption isotherm model. In application, C6 biomass reduced the copper content in the oat seedlings grown in copper ion containing water by more than seven times.

CONCLUSIONS

B. pseudomycoides C6 can efficiently remove copper ion in water and inhibit it from entering plants.

SIGNIFICANCE AND IMPACT OF STUDY

This is the first time to report the capability of B. pseudomycoides to remove copper ion in water, which is also more efficient than the currently reported chemical and biological methods.

Recovery of Ag+ by cyclic lipopeptide iturin A and corresponding chain peptide: reaction mechanisms, kinetics, toxicity reduction, and applications

Iturin A, a cyclic lipopeptide produced by Bacillus subtilis, has great potential in removal of Ag⁺ from water, but the mechanisms and kinetic remain unclear. By comparison with the chain peptide (CP) that has the same amino acid sequence as iturin A, the mechanisms were found as iturin A reduced Ag⁺ to Ag⁰ and formed silver nanoparticles (AgNPs) via the groups of Ar-OH, CO, -NH-, O=C-O, and -C(CH).The cycle peptide fraction played an important role for the faster formation of AgNPs by iturin A than by CP. The overall Ag⁺ removal process by iturin A and CP could be well described by a Freundlich isotherm, with the equilibrium Ag⁺ removal capacity ranging from 58.41 to 61.03 mg/g within 293.15-333.15 K for iturin A. With the application of iturin A, the overall removal rate of Ag⁺ reached 91.8% in wastewater, the formed AgNPs could be easily recovered via charging the direct electric current, and the toxicity of Ag⁺ to paddy growth was greatly reduced.

Filamentous fungal in situ biosynthesis of heterogeneous Au/Cd0.5Zn0.5S nano-photocatalyst: A macroscopic assembly strategy for preparing composite mycelial pellets with visible light degradation ability

Visible light degradation is a green and economic technology for sewage treatment receiving widespread attention. Here, the filamentous fungus Phomopsis sp. XP-8 was developed as a bioreactor to successively biosynthesize Cd_0.5Zn_0.5S quantum dots and gold nanoparticles (AuNPs) in situ and formed heterogeneous Au/Cd_0.5Zn_0.5S nano-photocatalyst inside cells. This strategy synchronously mediates the microscopic and macroscopic assembly of zero-dimensional materials by microorganisms. The heterogeneous catalyst functionalized composite mycelium pellets (CMP) not only have excellent visible light degradation activity but some unique characteristics. The outstanding organic dye biosorption capacity of CMP increases the contact rate between organic dyes and nano-catalysts, improving catalytic activity. High mechanical strength makes CMP easy to separate and recycle, which overcomes the difficulty of nano-catalyst recovery after use and avoids creating secondary pollution to the environment. This study not only broadens the means of heterogeneous nano-catalyst synthesis but also provides a new perspective on the macroscopic assembly of nanomaterials.

Capability of Bacillus Subtilis to remove Pb2+ via producing lipopeptides

Lead contamination is widely found in soil and waters, which makes great threat to animal and human health. Environmentally friendly, efficient, and economical methods for the removal of Pb²⁺ pose significant challenges for environmental protection. Bacillus subtilis lipopeptide was firstly used to remove Pb²⁺ from water. In mechanisms, the lipopeptides formed complexes and chelated with Pb²⁺ via OH, CO, OCO, and NH. In kinetics, the Pb²⁺ removal process closely followed a pseudo-first-order model, and the equilibrium Pb²⁺ adsorption capacity ranged from 112.6 to 113.7 mg/g within a temperature range of 293.13-313.13 K. The Pb²⁺ removal process could be well described by a Langmuir isotherm. The maximum Pb²⁺ removal capability of lipopeptides was 164.4 mg/g in manually metal contaminated water and 130.4 mg/g in actual wastewater. Furthermore, the lipopeptides can not only decrease the amount of lead in oats grown, but also promote oat growth under Pb²⁺ stress. The results showed that lipopeptides can be used as a highly efficient adsorbent to remove Pb²⁺ from water, which means the great potential of lipopeptides in practical environments.

Phycoremediation of Precious Metals by Cladophora fracta From Mine Gallery Waters Causing Environmental Contamination

We have presented a study to determine the possibility for the usage of Cladophora fracta as bioaccumulator of the metals (Au) and silver (Ag) both have characteristics of pollutant and precious in mine water. The highest concentrations accumulated by C. fracta were determined as 5.8 ± 0.3 and 5323 ± 75 µg/kg for Au and Ag, respectively. The results showed that the accumulation of the metals measured followed the order of Ag > Au. The Metal Pollution Index (MPI) values calculated between 39.37 × 10^-3 and 175.7 × 10^-3 were used to determine the pollution degree of C. fracta. As a result, it was determined that C. fracta highly accumulated the precious metals from the gallery water. Therefore, C. fracta was a good bioaccumulator for the remediation of Au and Ag in mine gallery waters. In this way, it is possible to minimize or eliminate the environmental risks of the precious metals in the gallery waters.

Towards the Implementation of Circular Economy in the Wastewater Sector: Challenges and Opportunities

The advancement of science has facilitated increase in the human lifespan, reflected in economic and population growth, which unfortunately leads to increased exploitation of resources. This situation entails not only depletion of resources, but also increases environmental pollution, mainly due to atmospheric emissions, wastewater effluents, and solid wastes. In this scenario, it is compulsory to adopt a paradigm change, as far as the consumption of resources by the population is concerned, to achieve a circular economy. The recovery and reuse of resources are key points, leading to a decrease in the consumption of raw materials, waste reduction, and improvement of energy efficiency. This is the reason why the concept of the circular economy can be applied in any industrial activity, including the wastewater treatment sector. With this in view, this review manuscript focuses on demonstrating the challenges and opportunities in applying a circular economy in the water sector. For example, reclamation and reuse of wastewater to increase water resources, by paying particular attention to the risks for human health, recovery of nutrients, or highly added-value products (e.g., metals and biomolecules among others), valorisation of sewage sludge, and/or recovery of energy. Being aware of this situation, in the European, Union 18 out of 27 countries are already reusing reclaimed wastewater at some level. Moreover, many wastewater treatment plants have reached energy self-sufficiency, producing up to 150% of their energy requirements. Unfortunately, many of the opportunities presented in this work are far from becoming a reality. Still, the first step is always to become aware of the problem and work on optimizing the solution to make it possible.

Recent advances in the recovery of metals from waste through biological processes

Wastes containing critical metals are generated in various fields, such as energy and computer manufacturing. Metal-bearing wastes are considered as secondary sources of critical metals. The conventional physicochemical methods of metals recovery are energy-intensive and cause further pollution. Low-cost and eco-friendly technologies including biosorbents, bioelectrochemical systems (BESs), bioleaching, and biomineralization, have become alternatives in the recovery of critical metals. However, a relatively low recovery rate and selectivity severely hinder their large-scale applications. Researchers have expanded their focus to exploit novel strain resources and strategies to improve the biorecovery efficiency. The mechanisms and potential applicability of modified biological techniques for improving the recovery of critical metals need more attention. Hence, this review summarize and compare the strategies that have been developed for critical metals recovery, and provides useful insights for energy-efficient recovery of critical metals in future industrial applications.