聚乙烯废弃塑料生物解聚与高值化转化

聚乙烯废弃塑料在环境中日益积累不仅导致视觉污染,也形成潜在的生态污染问题,开发回收和高值化转化聚乙烯废弃塑料的新方法是大势所趋。近年来,废弃塑料生物处理技术因其绿色可持续等优点,成为国内外研究热点,有望成为未来废弃塑料回收管理的重要手段。本文重点综述了聚乙烯废弃塑料生物解聚技术的研究进展,并对聚乙烯废弃塑料化学高值化和生物高值化产品的差异进行分析,在此基础上,总结和展望了目前聚乙烯废弃塑料生物解聚与生物高值化中的挑战以及相应的解决方案,期望联合多学科交叉技术协同生物技术实现聚乙烯废弃塑料的升级循环。     

温和酸催化解聚木质素磺酸盐产物的分离与分析北大核心CSCD

木质素解聚产物是异常复杂的混合物体系,本文以温和酸催化条件下的木质素磺酸盐解聚产物为研究对象,建立分离和分析测试木质素磺酸盐解聚产物和解聚效率的有效方法。采用超高效凝胶渗透色谱对解聚产物实现了高效分离,结果表明木质素磺酸盐高分子获得了高效解聚,解聚获得的产物分子量组成主要分布在三个低聚物区间;采用GC-MS鉴定了主要的木质素基单酚和双酚类官能团化合物9种,约占解聚液的30 wt%,表明解聚产物中含有大量的单体化合物;采用SEM和EDS分析测试木质素解聚后残渣,其结果也进一步证实了在温和酸催化条件下,木质素磺酸盐在解聚过程中还原位脱除了磺酸盐。木质素磺酸盐由于具有特有的Cα-SO3M基团,在酸催化条件下β-O-4键易于断裂,促进了木质素磺酸盐快速解聚,获得了解聚效率达95 wt%以上的解聚产物。     

微生物解聚木质素合成聚羟基脂肪酸脂的研究进展

聚羟基脂肪酸脂(PHAs)作为一种具高生物降解性和易加工性的细胞内储能物质,有希望代替石油基塑料,在全球生物塑料市场受到越来越多的关注。木质素作为地球上最为丰富的天然可再生芳香聚合物,可作为底物通过微生物降解转化为苯酚等单环芳香化合物,然后芳香化合物进一步转化,最终合成PHAs。综述了木质素降解转化合成PHAs的微生物及其相关途径,阐述了目前存在的问题和困难。深入探讨了提高木质素降解转化合成PHAs的生产效率及产物性能的研究进展。同时提出了木质素转化合成PHAs面临的挑战以及对未来发展的展望。     

生物炼制过程中木质素高值转化研究进展

木质素高值转化对于提升生物炼制经济性,促进社会经济绿色发展具有重要意义。然而,木质素结构复杂且不均一,其高值化利用仍存在技术壁垒,使得木质素应用尚未形成规模。文中首先综述了当前生物炼制过程中木质素高值转化面临的主要挑战。然后通过比较不同预处理技术对木质素分离、性质及其利用的主要影响,详细阐述了基于生物炼制理念发展的新型组合预处理技术。其次,针对木质素本征结构特性导致其利用效率低等问题,进一步详述了溶剂分级、膜分级、梯度沉淀分级等分级利用策略对克服木质素不均一性,改善其可加工性能的重要影响。再次,针对木质素利用策略,系统比较了木质素热化学转化和生物转化,结合生物质预处理及木质素分级,阐述了以生物炼制理念进行木质素高值转化的新策略。最后,总结了木质素利用过程中存在的挑战性问题,展望了木质素高效分离、分级及转化过程发展的新策略和新趋势。     

环境微生物介导的木质素代谢及其资源化利用研究进展

木质素是一种丰富的芳烃生物大分子聚合物,其分解代谢与地球元素循环和生物资源利用密切相关。但由于木质素结构的复杂性和无规则性导致其难以降解,使得木质素降解的研究成为全球碳循环和生物质资源利用研究的难点。近年来,来自不同环境的微生物陆续被发现具有木质素降解能力,并解析出参与木质素分解代谢的多种氧化还原酶。然而对木质素详细的代谢过程仍不十分清楚,因此,探究木质素降解酶系、作用机理和代谢网络是研究微生物代谢木质素机理的关键。本文综述环境中参与木质素降解的微生物,重点解析其木质素解聚酶系组成、分泌机制和木质素的代谢途径,并在此基础上阐明近年来木质素生物转化的最新研究进展,以期为今后环境微生物代谢木质素机理及其资源化利用的研究提供参考。     

Comamonas serinivorans C35木质素降解性能

【目的】探讨菌株Comamonas serinivorans C35降解木质素的能力。【方法】测定Comamonas serinivorans C35在木质素培养基中的生长趋势、化学需氧量的去除、木质素降解率、脱色率和相关酶的分泌。分别采用扫描电子显微镜和傅里叶变换红外光谱分析仪检测木质素降解前后的外观结构和化学键的变化。【结果】Comamonas serinivorans C35能够在木质素培养基上生长,在培养7 d后,化学需氧量去除率为44.4%,木质素降解率和脱色率分别为43.57%和42.26%。Comamonas serinivorans C35能够分泌木质素过氧化物酶、锰过氧化物酶和漆酶,粗酶液酶活分别能达到648.4、177.8和70.1 U/L。Comamonas serinivorans C35可以使木质素解聚且对其苯环结构、醚键以及C=O键等具有明显的破坏作用。【结论】Comamonas serinivorans C35可以降解木质素,在木质素的生物转化中具有潜在的应用价值。     

微生物法降解木质素的研究进展

生物质是代替石化资源生产能源和化学品的关键资源,木质素作为植物细胞壁的主要成分已经在很多行业中得到了广泛的应用。然而,由于木质素结构复杂且难以降解,成为生物质资源利用的最大障碍,因此,去除或者降解木质素是利用细胞壁中其他成分的关键步骤。许多行业使用有害化学物质降解木质素,严重危害了生态环境,自然界中木质素经常被包括真菌和细菌在内的微生物降解,因此,研究微生物降解木质素的机制为解决这一问题提供了可能性。本文讨论了木质素的化学组成成分,重点讨论了自然界降解木质素的微生物种类及其降解机制,包括各种真菌和细菌的木质素降解活性,描述了由各种微生物特别是白腐真菌、褐腐真菌和细菌产生的木质素降解酶,并展望了今后木质素生物降解的研究和应用的可能方向。     

微生物降解秸秆木质素的研究进展

我国秸秆资源丰富,每年产生逾8亿t作物秸秆。通过秸秆直接还田或肥料化还田不仅可以减少化肥的施用量,缓解农业污染压力,还能实现农作物秸秆的循环利用。木质素结构复杂,且与纤维素和半纤维素相互缠绕,因此秸秆的自然腐解过程中,木质素是主要的限速因子,为了提高降解效率,木质素降解菌的发掘和降解机制也逐渐成为研究热点。本文综述了降解木质素的真菌和细菌的研究现状,对比其真菌和细菌降解特性的优缺点并分析复合降解菌群的优势。随后对木质素降解酶系的酶学性质、在不同微生物中的表达特性进行总结,对木质素降解机制及衍生芳烃代谢路径的研究进展进行综述。最后整理木质素降解微生物在秸秆肥料化技术中的应用进展,并探讨了微生物降解秸秆木质素的应用前景和未来的研究方向。     

木质素的微生物降解机制

研究微生物降解木质素的反应机理,可以从根本上解释微生物或酶对木质素的作用过程,对提高木质素降解效率,治理环境污染等具有非常重要的意义。从木质素结构的差异出发,总结了近年来研究木质素微生物降解机制所采用的主要模型化合物、研究方法,概述了微生物对木质素的三大作用机理:侧链氧化、去甲基化和芳香环断裂,以及参与这三个反应的主要微生物。     

Microbial lignin valorization through depolymerization to aromatics conversion

Lignin is the most abundant source of renewable aromatic biopolymers and its valorization presents significant value for biorefinery sustainability, which promotes the utilization of renewable resources. However, it is challenging to fully convert the structurally complex, heterogeneous, and recalcitrant lignin into high-value products. The in-depth research on the lignin degradation mechanism, microbial metabolic pathways, and rational design of new systems using synthetic biology have significantly accelerated the development of lignin valorization. This review summarizes the key enzymes involved in lignin depolymerization, the mechanisms of microbial lignin conversion, and the lignin valorization application with integrated systems and synthetic biology. Current challenges and future strategies to further study lignin biodegradation and the trends of lignin valorization are also discussed.     

Green and sustainable route for oxidative depolymerization of lignin: New platform for fine chemicals and fuels

Depolymerization of lignin biomass to its value-added chemicals and fuels is pivotal for achieving the goals for sustainable society, and therefore has acquired key interest among the researchers worldwide. A number of distinct approaches have evolved in literature for the deconstruction of lignin framework to its mixture of complex constituents in recent decades. Among the existing practices, special attention has been devoted for robust site selective chemical transformation in the complex structural frameworks of lignin. Despite the initial challenges over a period of time, oxidation and oxidative cleavage process of aromatic building blocks of lignin biomass toward the fine chemical synthesis and fuel generation has improved substantially. The development has improved in terms of cost effectiveness, milder reaction conditions, and purity of compound individuals. These aforementioned oxidative protocols mainly involve the breaking of C-C and C-O bonds of complex lignin frameworks. More precisely in the line with environmentally friendly greener approach, the catalytic oxidation/oxidative cleavage reactions have received wide spread interest for their mild and selective nature toward the lignin depolymerization. This mini-review aims to provide an overview of recent developments in the field of oxidative depolymerization of lignin under greener and environmentally benign conditions. Also, these oxidation protocols have been discussed in terms of scalability and recyclability as catalysts for different fields of applications.     

Microbial valorization of underutilized and nonconventional waste streams

The growing burden of waste disposal coupled with natural resource scarcity has renewed interest in the remediation, valorization, and/or repurposing of waste. Traditional approaches such as composting, anaerobic digestion, use in fertilizers or animal feed, or incineration for energy production extract very little value out of these waste streams. In contrast, waste valorization into fuels and other biochemicals via microbial fermentation is an area of growing interest. In this review, we discuss microbial valorization of nonconventional, aqueous waste streams such as food processing effluents, wastewater streams, and other industrial wastes. We categorize these waste streams as carbohydrate-rich food wastes, lipid-rich wastes, and other industrial wastes. Recent advances in microbial valorization of these nonconventional waste streams are highlighted, along with a discussion of the specific challenges and opportunities associated with impurities, nitrogen content, toxicity, and low productivity.     

Lignin valorization meets synthetic biology

Lignin, an abundant renewable resource in nature, is a highly heterogeneous biopolymer consisting of phenylpropanoid units. It is essential for sustainable utilization of biomass to convert lignin to value‐added products. However, there are technical obstacles for lignin valorization due to intrinsic heterogeneity. The emerging of synthetic biology technologies brings new opportunities for lignin breakdown and utilization. In this review, we discussed the applications of synthetic biology on lignin conversion, especially the production of value‐added products, such as aromatic chemicals, ring‐cleaved chemicals from lignin‐derived aromatics and bio‐active substances. Synthetic biology will offer new potential strategies for lignin valorization by optimizing lignin degradation enzymes, building novel artificial converting pathways, and improving the chassis of model microorganisms.     

Biotransformation of lignin: Mechanisms,applications and future work

As one of the most abundant polymers in biosphere, lignin has attracted extensive attention as a kind of promising feedstock for biofuel and bio-based products. However, the utilization of lignin presents various challenges in that its complex composition and structure and high resistance to degradation. Lignin conversion through biological platform harnesses the catalytic power of microorganisms to decompose complex lignin molecules and obtain value-added products through biosynthesis. Given the heterogeneity of lignin, various microbial metabolic pathways are involved in lignin bioconversion processes, which has been characterized in extensive research work. With different types of lignin substrates (e.g., model compounds, technical lignin, and lignocellulosic biomass), several bacterial and fungal species have been proved to own lignin-degrading abilities and accumulate microbial products (e.g., lipid and polyhydroxyalkanoates), while the lignin conversion efficiencies are still relatively low. Genetic and metabolic strategies have been developed to enhance lignin biodegradation by reprogramming microbial metabolism, and diverse products, such as vanillin and dicarboxylic acids were also produced from lignin. This article aims at presenting a comprehensive review on lignin bioconversion including lignin degradation mechanisms, metabolic pathways, and applications for the production of value-added bioproducts. Advanced techniques on genetic and metabolic engineering are also covered in the recent development of biological platforms for lignin utilization. To conclude this article, the existing challenges for efficient lignin bioprocessing are analyzed and possible directions for future work are proposed.     

Directed bioconversion of Kraft lignin to polyhydroxyalkanoate by Cupriavidus basilensis B-8 without any pretreatment

This work presents here a new fundamental strategy for bio-converting Kraft lignin (KL) into useful products. Cupriavidus basilensis B-8 (here after B-8) was able to use KL as the sole carbon source. Fully 41.5% of lignin, 37.7% of total carbon (TC) and 43.0% of color were removed after 7 days of incubation. At the same time, lignin was depolymerized into small fragments, which was confirmed by scanning electron microscopy (SEM) and gel permeation chromatography (GPC). Bacterial biomass accumulated to 735.6 mg/L at the initial KL concentration of 5 g L⁻¹, and the corresponding volumetric productivity of polyhydroxyalkanoate (PHA) was 128 mg/L. PHA productivity was significantly improved through fed batch fermentation and reached to 319.4 mg/L. GC–MS analysis showed that PHA polymer was composed of three basic monomers: 98.3 mol% of (S)-3-hydroxy-butanoic acid (S3HB), 1.3 mol% of ^®-3-hydroxybutyric acid (R3HB) and 0.4 mol% of 3-hydroxy-butanoic acid (3HB).     

Optimized pulse-feeding fed-batch fermentation for enhanced lignin to polyhydroxyalkanoate transformation

With an anticipated growth of Bio-Circular-Green economy, the amount of lignin generated as by-product from biorefineries is increasing. Hence, lignin valorising strategies become a very interesting option to improve economic viability of the biorefineries. This study revealed the development of bioprocesses for upgrading lignin into bioplastic. Specifically, a novel strain of Pseudomonas fulva has been applied for microbial bioconversion of organosolv lignin to fermentative polyhydroxyalkanoate (PHA) production. Fed-batch fermentation of lignin-to-PHA with pulse-feeding approach was optimized using Design of Experiment. Effects of C:N ratio and feeding profiles on PHA accumulation in P. fulva were investigated to determine optimal operation. Under optimized fed-batch, the PHA concentration of 195.2 ± 6.6 mg/L could be reached and the PHA content was more than 2 folds enhancement compared to batch process. Type of PHA produced was also characterized for chemical composition via GC–MS analysis. The established lignin to PHA conversion could provide platform for developing integrated lignin bioprocessing to promote cost-effective biorefineries.     

Microbial utilization of lignin: available biotechnologies for its degradation and valorization

Lignocellulosic biomasses, either from non-edible plants or from agricultural residues, stock biomacromolecules that can be processed to produce both energy and bioproducts. Therefore, they become major candidates to replace petroleum as the main source of energy. However, to shift the fossil-based economy to a bio-based one, it is imperative to develop robust biotechnologies to efficiently convert lignocellulosic streams in power and platform chemicals. Although most of the biomass processing facilities use celluloses and hemicelluloses to produce bioethanol and paper, there is no consolidated bioprocess to produce valuable compounds out of lignin at industrial scale available currently. Usually, lignin is burned to provide heat or it remains as a by-product in different streams, thus arising environmental concerns. In this way, the biorefinery concept is not extended to completion. Due to Nature offers an arsenal of biotechnological tools through microorganisms to accomplish lignin valorization or degradation, an increasing number of projects dealing with these tasks have been described recently. In this review, outstanding reports over the last 6 years are described, comprising the microbial utilization of lignin to produce a variety of valuable compounds as well as to diminish its ecological impact. Furthermore, perspectives on these topics are given.