Reviews in Environmental Science and Bio/Technology最新文献

Polyhydroxyalkanoates (PHA) are a promising bio-based alternative to traditional plastics derived from petroleum. Cyanobacteria are photosynthetic organisms that produce PHA from CO₂ and sunlight, which can potentially reduce production costs and environmental footprint in comparison to heterotrophic bacteria cultures because (1) they utilize inorganic carbon sources for growth and (2) they do not require intensive aeration for oxygenation. Moreover, supplementing precursors such as propionate, acetate, valerate, etc., can be used to obtain various copolymers with plastic customizable properties in comparison to the classical homopolymers, such as polyhydroxybutyrate, PHB. This critical review covers the latest advances in PHA production, including recent discoveries in the metabolism interplay between PHA and glycogen production, and new insights into cultivation strategies that enhance PHA accumulation, and purification processes. This review also addresses the challenges and suggests potential solutions for a viable industrial PHAs production process.

Today, the transition to renewable energy from conventional energy practices is more important than ever to establish energy security and mitigate climate change. The wastewater treatment plants (WWTP) consume a remarkable amount of energy and cause significant greenhouse gas emissions. The energy balance of WWTP can be improved by implementing energy-efficient applications such as anaerobic digestion. However, most of the existing WWTPs utilize only sewage sludge in conventional anaerobic digesters (CAD) which results in low biogas generation. Generally, co-digestion is indicated as an effective solution for the low biogas generation faced in mono-digestion. Moreover, recently, anaerobic membrane bioreactors (AnMBR) have been promoted as a prominent alternative to CADs. This paper overviews the current situation of co-digestion applications by AnMBRs for municipal WWTPs. Furthermore, the environmental and economic aspects of these applications were reviewed. Lastly, challenges and future perspectives related to the co-digestion applications by AnMBR were thoroughly discussed.

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The second cheese whey (SCW) is the liquid fraction that remains after the production of whey-cheeses. SCW appears as a white to yellow/green opalescent liquid with suspended solids and contains up to 6% lactose and variable amounts of proteins, fats, and mineral salts. Due to its organic load, SCW is characterized by levels of Biochemical Oxygen Demand and Chemical Oxygen Demand that are significantly higher than urban wastewater. Therefore, it poses an environmental challenge and represents a significant cost and a problem for cheese production facilities when it comes to disposal. On the flip side, SCW contains valuable nutrients that make it a cost-effective substrate for bio-based productions including lactose extraction, and the production of lactic acid, bioethanol, eco-friendly bioplastics, biofuels, beverages, bioactive peptides, and microbial starters. A search in Scopus database indicates that despite the numerous potential applications, interest in SCW exploitation is surprisingly limited and, accordingly, sustainable management of SCW disposal remains an unresolved issue. In this review, which marks the first exclusive focus on SCW, with the aim of contributing to increase the interest of both the scientific community and the stakeholders in the exploitation of this by-product, the processes aimed at SCW valorisation will be described, with particular attention to its use in the production of beverages, food and feed, single cell proteins and as a source of biodegradable bioplastics, organic acids and renewable energy. Moreover, to provide valuable insights into its applications and innovations, an overview on patents regarding the exploitation of SCW will be presented.

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The Sustainable Development Goal 2 of the United Nations towards 2030 aimed to end hunger, achieve food security and improved nutrition, and promote sustainable agriculture. According to the 2023 report by the Food and Agriculture Organization, the world is not on track to end hunger or promote sustainable agriculture by that time. Climate change acts as a “crisis multiplier”, resulting in lower food productivity and higher prices, contributing further to poverty, hunger, and instability. The number of undernourished people in drought-sensitive and low-income regions of the world has increased this decade. In this review, we analyze the potential of microalgae and cyanobacteria to aid conventional agriculture in providing critical services such as carbon capture, wastewater management, food/feed, biofuels, and other higher value bioproducts. Specifically, we focus on the use of filamentous N₂-fixing cyanobacteria for providing those benefits, even in semidry regions of the world with limited access to affordable nitrogen fertilizers to boost crop productivity. We comprehensively consider the eco-physiological basis of this potential, and the available alternative technologies for large-scale biomass production. We analyze venues for filamentous N₂-fixing cyanobacteria applications in standalone processes, or integrated into more complex industrial symbioses, towards increased crop productivity, and water and N-fertilizer use efficiency. Throughout the text, we highlight aspects which still require further optimization, or technological breakthroughs, for full realization of the potential of filamentous N₂-fixing cyanobacteria for contributing to Sustainable Development Goals.

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Polyethylene terephthalate (PET) is one of the most marketed aromatic polyesters in the world with an annual demand in 2022 of approximately 29 million metric tons, expected to increase by 40% by 2030. The escalating volume of PET waste and the current inadequacy of recycling methods have led to an accumulation of PET in the terrestrial ecosystem, thereby posing significant global health risks. The pressing global energy and environmental issues associated with PET underscore the urgent need for “upcycling” technologies. These technologies aim to transform reclaimed PET into higher-value products, addressing both energy concerns and environmental sustainability. Enzyme-mediated biocatalytic depolymerization has emerged as a potentially bio-sustainable method for treating and recycling plastics. Numerous plastic-degrading enzymes have been identified from microbial origins, and advancements in protein engineering have been employed to modify and enhance these enzymes. Microbial metabolic engineering allows for the development of modified microbial chassis capable of degrading PET substrates and converting their derived monomers into industrial relevant products. In this review, we describe several engineering approaches aiming at enhancing the performances of PET-degrading enzymes and we present the current metabolic engineering strategies adopted to bio-upcycle PET into high-value molecules.

Wastewater purification has been a longstanding and urgent global environmental concern. Electrospun materials have emerged as a promising solution due to large specific surface area, micro/nano-scale, hierarchical structure and flexible compositional regulation, and ease of functionalization. Making them suitable for a variety of scenarios by enabling strategies of adsorption, catalytic degradation, filtration, and distillation, with benefits of low energy consumption, high efficiency, and simplified processes. This review aims to provide an overview of the design strategies, underlying mechanisms, and application progress of electrospun nanomaterials for wastewater purification. Initially, we introduce electrospinning technology for preparing functional nanomaterials, involving the principles, advantages, and flexible product strategies. Subsequently, recent research progresses in treating wastewater contaminated by oil, dyes, heavy metal ions, and bacteria are discussed, integrating insights into their mechanisms and performance evaluation. In recent years, more than 1000 work articles have been reported annually in this field, showing a booming growth trend. Finally, a summary and outlook are provided, aiming to expedite practical water purification through synergistic collaboration between industry and research, effective materials and device optimization, and advancing new theories and technological innovations.

Activated sludge has been widely adopted as the cornerstone of conventional sewage treatment for over 50 years. This process can reduce biochemical oxygen demand (BOD) in wastewater and protect public health, with many systems able to remove nutrients as well. While activated sludge continues to satisfy many treatment targets, the demands on wastewater treatment are changing. There are concerns that toxic and difficult-to-degrade contaminants are contributing to environmental and human health issues. There is also increasing interest in potable reuse to strengthen water resiliency and the waste-to-resource paradigm; however, when biological secondary treatment is used, additional treatment is needed for reuse. Chemical oxidation may be an effective alternative to activated sludge to destroy difficult-to-degrade contaminants. Compared to biological systems, chemical oxidation may also be easier to operate and maintain, requiring less space for more effective treatment. This article presents a critical review of current activated sludge-based sewage treatment practices and explores the opportunity to replace biological secondary wastewater treatment with chemical oxidation. Some opportunities include the ability of chemical oxidation to degrade contaminants of emerging concern (CECs); rapid start up and shut down; and avoidance of issues associated with biological treatment such as toxic loadings, biomass washout, difficulties settling sludge, and sludge handling and disposal. This review focuses on chemical oxidation as an alternative to biological secondary treatment for municipal wastewater. Most works included in this review are referenced in Google Scholar and the Web of Science, with the majority being published between 2000 and 2023. Trends revealed include a substantial increase in investigations regarding biological treatment, but much less literature focused on chemical oxidation of municipal secondary wastewater. There were reports covering chemical oxidation for industrial wastewater and for tertiary treatment of municipal wastewater, but not for chemical oxidation as a secondary treatment method for municipal wastewater.”

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Antibiotics are administered to livestock animals as medications and, in some jurisdictions, as growth promotors. This review examines the impact of veterinary antibiotics on methane production from manure anaerobic digestion (AD). The animals excrete about 17–90% of the administered antibiotics in manure unchanged or as metabolites, which adversely affect microorganisms catalyzing the manure AD, thereby reducing methane yields. Different antibiotics influence methane production to different extents (0–80%). The results from studies on manure artificially spiked with antibiotics differ from those on manure from antibiotic-fed animals, likely due to the effect of other bioactive substances in the manure. Over time, the microbial culture might adapt to the antibiotics, altering its composition, and further affecting the methane yield. Such adaptation indicates that short-term studies might not fully capture the antibiotic’s long-term effects on AD. Effects of oxytetracycline and chlortetracycline on methane production are debatable, with chlortetracycline generally believed to have a slightly stronger inhibition. Correlation, nonlinear modeling/simulation, and principal component analysis (PCA) reveal that the antibiotic effects on methane yield are complex and depend on various parameters such as antibiotic type, concentration, application mode, duration, specific microbial communities, and digester conditions. The PCA showed that the temperature and concentration rather than the manure origin (pigs vs cows) dictate the magnitude of methane production inhibition. Data on the kinetics of antibiotics’ impact, isomerization, and effects of operation strategies are missing. This review summarizes the main knowledge gaps concerning AD of antibiotics-containing manure and suggestions for operational strategies and future research.

Nitrous oxide (N₂O) is a potent greenhouse gas that accumulates in the atmosphere due to anthropogenic N₂O emissions, disrupting the nitrogen balance. N₂O reductase (N₂OR) in denitrifying bacteria contributes to the nitrogen cycle by converting N₂O to molecular nitrogen as a last step. For the reduction of N₂O during denitrification, electron donors must supply two electrons. This review discusses the in vivo physiological electron donors involved in the reduction reaction of N₂OR: cytochrome c_55X and pseudoazurin, as well as the non-physiological electron donors commonly used in N₂OR studies: reduced MV/BV, dithionite, and ascorbate. The kinetic parameters of the connection between N₂OR and the electron donors are also included. This aim of this review to gain further insight into the reduction mechanism of N₂OR, presenting the electron transfer center, Cu_A, and the catalytic center, Cu_Z, of N₂OR. The state changes of Cu site have a significant impact on electron transfer and N₂O binding. Moreover, the review focuses on potential electron transfer pathways and binding sites in the electron donor → Cu_A → Cu_Z process, along with the steady-state turnover in the Cu_Z site. Additionally, the review explains the commonly used methods in mechanistic studies of N₂OR. Modulating the electron transfer pathways of N₂OR holds promise as an approach to decreasing N₂O emissions.

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The high metabolic flexibility and biodiversity of microalgae make them promising systems for the production of chemicals and high-value metabolites to be utilized in various industrial applications. Currently, microalgae are primarily cultivated in phototrophic processes or in fermenters using glucose as substrate. However, such configurations are often too costly for the majority of potential applications and require improvements. The use of acetate as substrate to enhance biomass productivity and reduce cost and environmental impacts is a promising solution. In a future bio-based economy, acetate can serve as an excellent intermediate to link many industrial facilities, as it can be synthesized using different technologies from renewable resources as CO₂ and waste. This work provides a detailed description of acetate synthesis processes alternative to the conventional methanol carbonylation, including the pros and cons of each: aerobic and anaerobic fermentations; thermochemical treatments; C1 gas fermentation; microbial electrosynthesis and artificial photosynthesis. Additionally, the utilization of acetate as substrate for microalgae growth in mixotrophic and heterotrophic conditions is reviewed, covering key metabolic and engineering aspects (strains, yields, growth rate, inhibition, productivity, process configuration). These aspects serve as guidelines for a rationale design of an algal cultivation process based on acetate as a carbon source. Finally, the review critically assesses the state of the art of coupling of acetate-rich streams with algal biomass production, highlighting the pros and cons and addressing the main knowledge gaps to be filled through future research.