Reviews in Environmental Science and Bio/Technology最新文献

Platinum group metals (PGMs) are essential in developing the modern high-tech industry. Spent petroleum and spent automobile catalysts are vital sources of PGMs, which have relatively higher concentrations of PGMs (0.1–1%) than those found in primary sources. Therefore, recycling these secondary PGMs sources is an integral element of the PGM supply policy of many countries. In recent years, ‘bioleaching’ has emerged as a sustainable technique to extract PGMs from the spent catalysts. Bioleaching processes are based on the capability of different microorganisms to mobilize PGMs through the production of different lixiviants (cyanide, organic acids, etc.). In this review article, we aimed to explore the potential of different microorganisms (cyanogenic bacteria and fungi) in leaching PGMs (Pt, Pd, Rh, and Re) from spent petroleum refinery catalysts and spent automobile catalysts. We also shed light on the role and mechanisms of these microorganisms in extracting PGMs from these spent catalysts. A detailed discussion is also being made on the effect of various process parameters concerning cyanogenic bioleaching. We also identified different technical and environmental challenges associated with bioleaching processes that need to be addressed before their scale-up at the commercial level. Our analysis suggests that cyanogenic bioleaching (biocyanidation) has exciting potential; however, specific challenges (slower kinetics and yield, toxicity) need to be addressed to scale the process from existing lab-scale to commercial application.

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Due to pollution discharge and climate change, hypoxia is becoming more prevalent in water bodies such as lakes, rivers, and oceans. It leads to black blooms in lakes, black and odors in rivers, and dead zones in the oceans. Iron sulfide, especially amorphous mackinawite, is the main blackening substance. In this paper, the physical characteristics and detection methods of mackinawite were used to determine how to detect it in hypoxic water bodies. The population and metabolism of key microorganisms during mackinawite generation were analyzed to provide a reference for studying related microorganisms during the blackening process. Finally, the influence of macromolecular organic matter and microorganisms on the stable suspension of mackinawite was determined, and the existing patterns of mackinawite during the blackening process of hypoxic waters were illustrated. The generation of amorphous mackinawite and its stable suspension in a supernatant are two indispensable factors during the blackening process. The clarification of substance characteristics and key action processes are conducive to the accurate and targeted control of the blackening process and promote the restoration of the sustainable self-purification ability of water bodies.

Plastic pollution is a global concern due to the long half-life and high resistance of many synthetic plastics to natural biodegradation. Therefore, great effort is required to avoid littering. However, the challenge of managing the ever-increasing quantities of plastic waste is daunting. The biodegradation of synthetic plastics, such as polyethylene (PE), polyethylene terephthalate (PET), polypropylene (PP), polyvinyl chloride (PVC), polystyrene (PS), and polyurethane (PUR) by microorganisms is either slow or under investigation as to whether it occurs at all in different environmental niches (e.g., soil, aquatic systems). There is an urgent need to complement the existing knowledge on the biodegradation and biotransformation of synthetic plastics to enable effective bioremediation strategies to mitigate the effects of environmental plastic contamination. Therefore, the aim of this review is to highlight current fundamental and applied research regarding the most promising biodegradation processes for synthetic plastics, the synthesis and applications of the most effective plastic-degrading enzymes, successful biotechnological strategies to improve degradation, such as enzyme engineering and novel reactor designs, and plastic waste bioconversion into value-added products. In addition, this review is intended to depict indications for techno-economic analyses toward the valorization of plastic biodegradation processes and the environmental impacts of synthetic plastic biodegradation. Combining strategies, such as enzymatic plastic degradation followed by microbial biotransformation with the broad array of available pretreatment methods and abiotic factors, can contribute, under confined conditions, to the end-of-life utilization of plastics, consequently leading to more efficient biorecycling processes, and hence, to a circular plastic economy.

Thiosulfate is a lixiviant with potential applications for extraction of precious metals with lower environmental impact. As an alternative leaching reagent to cyanide, thiosulfate has promising gold extraction efficiency with much lower risk to operators and the environment. Thiosulfate is often produced at high temperatures via processes utilizing sulfide or sulfur and an oxidant. However, certain microorganisms can produce thiosulfate as the final product of their metabolism. This represents potential for lower emissions and costs in the manufacture of gold leaching reagents. Biotechnological applications of these processes have not been reported in the past and need to be investigated in depth. This review serves as a study of microorganisms to collect and analyze the reported species for potential utilization of biogenic thiosulfate in industrial applications, with a specific focus on precious metals extraction. Bacteria were identified and compared with respect to thiosulfate producing ability, feasibility for the mining industry, and cost of substrates. The future applications of biogenic thiosulfate and further direction of research on the topic have been identified.

Boron is an important element for plants, humans, and animals in limited amounts. However, excess amounts can cause adverse effects in both humans and plants, necessitating its removal from certain systems. Boron compounds are used in many industrial applications, including in developing sectors like alternative energy technology; as a result, the need for this element is increasing and industries are looking towards boron recovery for the sustained use of this element in their products. While the literature on boron removal strategies is abundant, there is a relative lack of studies on boron recovery, with no review papers having yet addressed this topic. In this review, both boron removal and recovery techniques involving conventional approaches and membrane processes are examined to juxtapose the states of the science in these two related—and increasingly important—processes.

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The stabilization of soil organic matter is crucial for global carbon cycling processes as soil stores large amounts of organic carbon. The occlusion of SOM within minerals sequesters these organic molecules, rendering them inaccessible to interference from biotic and abiotic factors. However, the microscopic mechanisms of occlusion are lacking. In the past few years, many researchers have focused on the elucidation of the occlusion process, and the results are summarized in this review. The occlusion of representative SOM such as natural extracted or commercial humic substances, sugars, amino acids within minerals including calcite, clay, metal oxides, were observed by various in situ and ex situ methods, such as atomic force microscopy, nano-scale secondary ion mass spectrometry and synchrotron-based infrared micro spectroscopy. These results have shown that minerals can occlude SOM either via organo-mineral aggregation or within growing hillocks, which are classical growth features on crystal surfaces, and the microscopic mechanisms have been illustrated in this review. The occlusion process is influenced by various factors, including the characteristics of minerals and the composition of SOM and soil solution conditions, which are mediated by the interactions of organo-mineral interfaces. Finally, some new perspectives for future research of occlusion are provided in order to give new possibilities for observing and comparing the detailed occlusion process in soils from different areas. In summary, SOM can be retained, protected and stabilized by soil minerals via occlusion either by aggregation or within growth hillocks, influenced by various factors. The results have implications for global carbon cycling in soil ecological systems.

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Soil organic matter could be occluded within soil minerals via aggregation and hillocks.

Microbial conversion of CO₂ and CO into chemicals is a promising route that can contribute to the cost-effective reduction of anthropogenic green house and waste gas emissions and create a more circular economy. However, the biotechnological valorization of CO₂ and CO into chemicals is still restricted by the limited number of model microorganisms implemented, and the small profit margin of the products synthesized. This perspective paper intends to explore the genetic potential for the microbial conversion of CO₂ and CO into ectoines, in a tentative to broaden bioconversion platforms and the portfolio of products from C₁ gas fermentations. Ectoine and hydroxyectoine can be produced by microorganisms growing at high salinity. They are high-value commodities for the pharmaceutical and medical sectors (1000–1200 €/kg). Currently microbial ectoine production is based on sugar fermentations, but expansion to other more sustainable and cheaper substrates is desirable. In this work, a literature review to identify halophilic microbes able to use CO₂ and CO as a carbon source was performed. Subsequently, genomes of this poll of microbes were mined for genes that encode for ectoine and hydroxyectoine synthesis (ectABCD, ask, asd and ask_ect). As a result, we identified a total of 31 species with the genetic potential to synthesize ectoine and 14 to synthesize hydroxyectoine. These microbes represent the basis for the creation of novel microbial-platforms that can promote the development of cost-effective and sustainable valorization chains of CO₂ and CO in different industrial scenarios.

Although coastal ecosystems such as mangroves have substantial productive and protective rules, this ecosystem is threatened due to inorganic and organic contaminants including polycyclic aromatic hydrocarbons (PAHs). PAHs are lipophilic, persistent, carcinogenic, mutagenic and considered as a global concern. We reviewed the occurrence, distribution and sources of PAHs in the mangrove ecosystem, providing a comprehensive discussion on this information and giving recommendations for future research. Through systematic literature search, this review considered existing studies on PAHs in the different compartments (water, sediment, aquatic fauna and plants) of mangrove system collected from field investigations. Little information is available for the levels and sources of PAHs in the water compartment of the mangrove systems. PAHs in the mangrove sediments are reported for 18 countries, and most of the levels of PAHs in mangrove sediments are considered as being low (0—100 ng g⁻¹ dry weight, DW) to moderate (100–1000 ng g⁻¹ DW). Different diagnostic ratios have been applied in order to determine the potential source of PAHs in the mangrove sediments, that are mainly attributed to mixed sources (pyrogenic and petrogenic). Studies have documented the biomonitoring of PAHs in mangrove systems, the majority of which use bivalves. Additionally, there are published studies for PAHs levels in 12 species of mangrove plants; showing a general tendency of residual PAHs accumulation in the leaves, if compared to root samples (leaves > roots). As a result of atmospheric PAH accumulation in leaf surfaces, leaves have higher concentrations of PAHs; implying that mangrove leaves can be used to monitor air quality relative to PAH pollution in coastal environments. This review has implications for future research in this field as well as coastal environmental management.

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Biogas from anaerobic digestion (AD), as an important alternative to fossil fuels, has contributed to energy recovery and environmental sustainability. Incomplete or inefficient mixing within anaerobic reactors can result in poor biogas production or energy wastage. Thus, identifying mixing performance is meaningful for the digester design, operation and maximum biogas production. Over the years, various experimental and computational fluid dynamics (CFD) techniques have been developed to characterize the mixing performance of digesters. This review described the critical impact of mixing on biogas production in AD. Then, experimental techniques available on local and global scales were reviewed and compared in terms of their advantages, disadvantages, characterization capabilities and scope of application. Moreover, the implementation, reliability, indicators and application of CFD techniques in AD were thoroughly discussed. Based on the above discussion, mixing significantly affects AD methane production, and intermittent mixing is preferred for maximum biogas production. Local experimental techniques have been considered to be the simplest and cheapest for arbitrarily sized digesters; global experimental techniques relying on computer systems have received increasing attention for their applications in AD flow fields. More research efforts are needed to discover new experimental techniques that overcome the limitations of digestate opacity and industrial reactor geometries, in addition, compartmental models based on CFD to couple hydrodynamics with biokinetics are interesting and allow for greater implementation of CFD applications.

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Maritime pine (Pinus pinaster Ait.) is native to the western Mediterranean basin and has an economic importance in southwestern Europe. This importance is based on the use of its wood in the construction, furniture, and paper industries. Bark and other parts of the plant, such as resin, needles, and cones, are by-products with potential industrial application. These parts of the tree stand out because of the presence of secondary metabolites, the main ones being phenolic compounds and terpenes. Bark contains both, while other parts of the plant are mainly composed of terpenes. All these compounds have biological potential, mainly antioxidant and antimicrobial properties. The bark has the widest range of industrial applications, and it can be used to obtain dietary supplements and functional foods, adsorbents, and bio-based resins and foams. Resin has a prominent industrial role too, especially in chemical industry. In this manuscript, an overview of these applications is described, opening an innovation opportunity for enterprises to use the by-products and residue of maritime pine. Still, albeit the described application, maritime pine has further applications that are right now being studied under the premises of circular economy.