Reactive Oxygen Species Triggered Oxidative Degradation of Polystyrene in the Gut of Superworms (Zophobas atratus Larvae).

Oxidative decomposition of polystyrene (PS) by insects has been previously demonstrated, yet little is known about the oxidation mechanism and its effect on the metabolism of plastics within the insect gut. Here, we demonstrate the generation of reactive oxygen species (ROS) in the gut of superworms (Zophobas atratus larvae) under different feeding trails, which in turn induced the oxidative decomposition of ingested PS. The ROS were commonly generated in the larva gut, and PS consumption resulted in a significant increase of ROS with a maximum ·OH of 51.2 µmol/kg, which was five times higher than in the bran feeding group. Importantly, scavenging of ROS significantly decreased the oxidative depolymerization of PS, indicating a vital role of ROS in effective PS degradation in the gut of superworms. Further investigation suggested that the oxidative depolymerization of PS was caused by the combinatorial effect of ROS and extracellular oxidases of gut microbes. These results demonstrate that ROS were extensively produced within the intestinal microenvironment of insect larvae, which greatly favored the digestion of ingested bio-refractory polymers. This work provides new insights into the underlying biochemical mechanisms of plastic degradation in the gut.

Sustainable Conversion of Microplastics to Methane with Ultrahigh Selectivity by a Biotic-Abiotic Hybrid Photocatalytic System.

Efficient conversion of microplastics into fuels provides a promising strategy to alleviate environmental pollution and the energy crisis. However, the conventional processes are challenged by low product selectivity and potential secondary pollution. Herein, a biotic-abiotic photocatalytic system is designed by assembling Methanosarcina barkeri (M. b) and carbon dot-functionalized polymeric carbon nitrides (CDPCN), by which biodegradable microplastics-poly(lactic acid) after heat pretreatment can be converted into CH4 for five successive 24-day cycles with nearly 100 % CH4 selectivity by the assistance of additional CO2 . Mechanistic analyses showed that both photooxidation and photoreduction methanogenesis worked simultaneously via the fully utilizing photogenerated holes and electrons without chemical sacrificial quenchers. Further research validated the real-world applicability of M. b-CDPCN for non-biodegradable microplastic-to-CH4 conversion, offering a new avenue for engineering the plastic reuse.

Hybrid mechanism of microplastics degradation via biological and chemical process during composting.

Little is known about the synergistic effects of abiotic aging and biodegradation on microplastics (MPs) transformation in the environment. Herein, a hybrid process of MPs degradation was proposed by analyzing the effect of microorganisms and abiotic aging on aging MPs and non-aging MPs degradation during composting. The results showed that composting facilitated the oxidation and depolymerization of aging MPs, and its degradation efficiency was about three times that of non-aging MPs. Further investigation revealed that aging MPs contained higher abundance of plastic-degrading bacteria and enzyme activity than non-aging MPs. In addition, free radicals also influenced the degradation of MPs. However, path model and shielding experiments confirmed that free radicals mainly facilitated the non-aging MPs degradation (contribution was 68.8 %), while aging MPs was easily degraded by microorganisms (contribution was 72.6 %). This study provides promising strategies for scaling up plastic treatment in bioreactors through a hybrid collaboration of biological and abiotic processes.

Phage lysate can regulate the humification process of composting.

Phages play a crucial role in orchestrating top-down control within microbial communities, influencing the dynamics of the composting process. Despite this, the impact of phage-induced thermophilic bacterial lysis on humification remains ambiguous. This study investigates the effects of phage lysate, derived explicitly from Geobacillus subterraneus, on simulated composting, employing ultrahigh-resolution mass spectrometry and 16S rRNA sequencing techniques. The results show the significant role of phage lysate in expediting humus formation over 40 days. Notably, the rapid transformation of protein-like precursors released from phage-induced lysis of the host bacterium resulted in a 14.8 % increase in the proportion of lignins/CRAM-like molecules. Furthermore, the phage lysate orchestrated a succession in bacterial communities, leading to the enrichment of core microbes, exemplified by the prevalence of Geobacillus. Through network analysis, it was revealed that these enriched microbes exhibit a capacity to convert protein and lignin into essential building blocks such as amino acids and phenols. Subsequently, these components were polymerized into humus, aligning with the phenol-protein theory. These findings enhance our understanding of the intricate microbial interactions during composting and provide a scientific foundation for developing engineering-ready composting humification regulation technologies.

Comamonas guangdongensis sp. nov., isolated from subterranean forest sediment, and emended description of the genus Comamonas.

A facultatively anaerobic bacterium, strain CY01(T), isolated from subterranean forest sediment collected from Guangdong Province, China, was investigated using a polyphasic taxonomic approach. The cells were short rods, Gram-negative, non-sporulating and motile. Phylogenetic analysis based on 16S rRNA gene sequences showed that strain CY01(T) showed highest sequence similarities to Comamonas thiooxydans S23(T) (98.0 %), Comamonas testosteroni JCM 5832(T) (97.9 %), Comamonas koreensis KCTC 12005(T) (97.7 %) and Comamonas odontotermitis LMG 23579(T) (97.0 %). The major respiratory quinone was ubiquinone-8. The major cellular fatty acids were summed feature 3 (C16 : 1ω6c and/or C16 : 1ω7c), C16 : 0 and summed feature 8 (C18 : 1ω6c and/or C18 : 1ω7c). Based on the phylogenetic analysis, DNA-DNA hybridization, whole-cell fatty acid composition as well as biochemical characteristics, strain CY01(T) was clearly distinguishable from all recognized species of the genus Comamonas and should be classified as a representative of a novel species of the genus, for which the name Comamonas guangdongensis sp. nov. is proposed. The type strain is CY01(T) ( = CCTCC AB 2011133(T) = KACC 16241(T)).

Enhanced degradation of microplastics during sludge composting via microbially-driven Fenton reaction.

It has been increasingly documented that the hydroxyl radical (•OH) can promote the transformation of organic contaminants such as microplastics (MPs) in various environments. However, few studies have sought to identify an ideal strategy for accelerating in situ MPs degradation through boosting the process of •OH production in practical applications. In this work, iron-mineral-supplemented thermophilic composting (imTC) is proposed and demonstrated for enhancing in situ degradation of sludge-based MPs through strengthening •OH generation. The results show that the reduction efficiency of sludge-based MPs abundance was about 35.93% in imTC after treatment for 36 days, which was 38.99% higher than that of ordinary thermophilic composting (oTC). Further investigation on polyethylene-microplastics (PE-MPs) suggested that higher abundance of •OH (the maximum value was 408.1 µmol·kg-1) could be detected on the MPs isolated from imTC through microbially-mediated redox transformation of iron oxides, as compared to oTC. Analyses of the physicochemical properties of the composted PE-MPs indicated that increased •OH generation could largely accelerate the oxidative degradation of MPs. This work, for the first time, proposes a feasible strategy to enhance the reduction efficiency of MPs abundance during composting through the regulation of •OH production.

Degradation of microplastics by hydroxyl radicals generated during microbially driven humus redox transformation.

The production of ·OH during transformation of redox active substances has been increasingly documented, and it causes the ageing or degradation of microplastics (MPs) in natural systems. However, the contribution of the humus redox cycle to ·OH generation and MPs transformation has previously been overlooked, even though it is ubiquitous in alternating anoxic-oxic environments. In this work, the integrated pathways of ·OH generation during the redox transformation of humic acids (HAs) and the contribution of this ·OH to the transformation of MPs were investigated for the first time. It was found that ·OH could be produced continuously during successive cycles of redox transformation of HAs mediated by Bacillus thermotolerans SgZ-8 through exogeneous HAs dependent and independent pathways. O2·- and H2O2 were identified as the key intermediate species, which were produced by both microbial aerobic respiration and HA oxidation. The ·OH generated by HA redox cycles could lead to a weight loss of PS-MPs of 18.1% through oxidative degradation during a period of 8 weeks of anoxic-oxic incubation. The EDC of HAs is closely related to ·OH production, which could have a large influence on the effectiveness of oxidative degradation of PS-MPs during various HAs redox cycles in temporarily anoxic environmental systems. These findings provide new insights into ·OH formation and MPs transformation through microbially driven humus redox cycles in alternating anoxic-oxic environments.

Mechanisms of polystyrene microplastic degradation by the microbially driven Fenton reaction.

Natural hydroxyl radical (·OH) production, which partially occurs through the microbially driven Fenton reaction, can enhance the degradation of polystyrene microplastics (PS-MPs). However, ·OH causes damage to microorganisms, which might in turn restrain the microbially driven Fenton reaction. Thus, whether PS-MPs can be continuously degraded by the microbially driven Fenton reaction and how they are degraded are still unknown. A pure-culture system using Shewanella putrefaciens 200 was set up to explore the effect and mechanism of microbially driven Fenton reaction on PS-MP degradation. In a 14-day operation, ·OH produced by the microbially driven Fenton reaction could degrade PS-MPs with a weight loss of 6.1 ± 0.6% and an O/C ratio of 0.6 (v.s. 0.6 ± 0.1% and 0.1, respectively, in the ·OH quenched group). Benzene ring derivatives such as 2-isopropyl-5-methyl-1-heptanol and nonahexacontanoic acid were the main soluble products of PS-MP degradation. The ·OH-induced oxidative damage on microorganisms did not affect ·OH production significantly when there was timely replenishment of organic carbon sources to promote reproduction of microorganisms. Thus, PS-MPs can be continuously degraded by microbially driven Fenton reactions in natural alternating anaerobic-aerobic environments. This study also provides a new microbial technique for MP degradation that is different from previous technologies based on microbial plastic-degrading enzymes.

Solar-driven methanogenesis with ultrahigh selectivity by turning down H2 production at biotic-abiotic interface.

Integration of methanogens with semiconductors is an effective approach to sustainable solar-driven methanogenesis. However, the H2 production rate by semiconductors largely exceeds that of methanogen metabolism, resulting in abundant H2 as side product. Here, we report that binary metallic active sites (namely, NiCu alloys) are incorporated into the interface between CdS semiconductors and Methanosarcina barkeri. The self-assembled Methanosarcina barkeri-NiCu@CdS exhibits nearly 100% CH4 selectivity with a quantum yield of 12.41 ± 0.16% under light illumination, which not only exceeds the reported biotic-abiotic hybrid systems but also is superior to most photocatalytic systems. Further investigation reveal that the Ni-Cu-Cu hollow sites in NiCu alloys can directly supply hydrogen atoms and electrons through photocatalysis to the Methanosarcina barkeri for methanogenesis via both extracellular and intracellular hydrogen cycles, effectively turning down the H2 production. This work provides important insights into the biotic-abiotic hybrid interface, and offers an avenue for engineering the methanogenesis process.

Free radicals accelerate in situ ageing of microplastics during sludge composting.

Composting is the last "barrier" for microplastics (MPs) in the entry of organic solid wastes into the environment. The transformation of MPs is thought to be mainly driven by microorganisms during composting, whereas the contribution of abiotic processes that involve free radicals is often overlooked. Herein, we provide initial evidence for the generation of free radicals during sludge composting, including environmental persistent free radicals and reactive oxygen species, which accelerate the oxidative degradation of MPs. The ·OH yield of composting fluctuated greatly from 23.03 to 277.18 µmol/kg during composting, which was closely related to the dynamic changes in Fe(II) (R2 = 0.926). Analyses of the composted MPs physicochemical properties indicated that MPs were aged gradually with molecular weights decrease from 18% to 27% and carbonyl index value increase from 0.23 to 0.52. Further investigation suggested that the microbially-mediated redox transformation of iron oxides could occur on the MPs surface accompanied by the production of abundant free radicals, thereby leading to the damage of MPs during composting. These results reveal the critical role of free radicals in MPs ageing under oxic/anoxic alternation conditions of composting and provide new insights into the bio-chemical mechanism of contaminant removal or transformation during sludge composting.

Enhanced aging of polystyrene microplastics in sediments under alternating anoxic-oxic conditions.

Aging of microplastics (MPs) (i.e., degradation and weathering) is ubiquitous in the environment. The MP aging process is thought to be limited to light and static areas, while aging in dark and fluctuating anoxic-oxic areas is poorly understood. Here, we provide initial evidence for aging of polystyrene microplastics (PS-MPs) under different anoxic/oxic conditions in sediments, and we further explored these mechanisms using sediment column experiments and pure-culture experiments. The results showed that PS-MPs in alternating anoxic-oxic sediments displayed the highest degree of aging. In the in-situ experiment, both the weight losses and O/C ratios of PS-MPs aged under alternating anoxic-oxic conditions were ∼2 times higher than those aged under static oxic and static anoxic conditions during 2-month experiments. In a 2-month column experiment, the PS-MPs in the alternating anoxic-oxic group showed weight losses and O/C ratios that were, respectively, triple and double the corresponding values for the static oxic and static anoxic groups. Column and pure-culture experiments demonstrated that dark production of ·OH which showed a positive correlation with a Fe redox process could explain enhanced MP aging under the alternating anoxic-oxic conditions. These findings provide a basis for risk assessment and management of MPs in the natural environment, such as in intertidal zones and paddy fields, and also have implications for engineering of optimized MP degradation processes.

Alkali lignin and sodium lignosulfonate additives promote the formation of humic substances during paper mill sludge composting.

Alkali lignin (AL) and sodium lignosulfonate (SLS) are by-products of the papermaking industry and could influence composting processes due to their rich aromatic structures. In this study, the roles of AL and SLS additives in the formation of humic substances (HS) during paper mill sludge composting were investigated. Results showed that HS content and degree of polymerization of the final products in AL (44.42 mg·g-1 and 0.70, respectively) and SLS (45.87 mg·g-1 and 1.14, respectively) treatments were appreciably higher than those of the control sample (34.36 mg·g-1 and 0.67). Excitation-emission matrix-parallel factor coupled with two-dimensional FT-IR correlation spectroscopy analysis suggested that AL and SLS additives could speed the transformation of quinone-like substances by increasing the amounts of low molecular weight lignin depolymerized products, which led to higher HS concentrations. This work provided a way of promoting HS formation and the comprehensive utilization of papermaking wastes.

[Biodegradation of Polystyrene by Geobacillus stearothermophilus].

Biodegradation is the most sustainable treatment method for waste polystyrene (PS). Thermophiles possess highly efficient biotransformation capabilities that could enhance the biodegradation efficiency of organic solid wastes. However, detailed research on the degradation of PS plastics by thermophile is scarce. Here, the degradation performance of a strain of Geobacillus stearothermophilus FAFU011 (FAFUA011) isolated from compost was examined. The results showed that strain FAFUA011 could utilize PS as the sole carbon source for growth and formed a stable biofilm on the surface of PS fragments. During 56 days of degradation, FAFU0011 caused a total mass loss of PS of 4.2% and decrease in molecular weight of 17.4%-18.2%. Based on SEM observations, FAFUA011 causes erosion hollows on the surface of PS, thus increasing the type and number of oxygen-containing structures that alter its hydrophilic properties. These changes facilitate the colonization of other microorganisms and further promote biodegradation. Based on 2D-COS analysis, the chronological order of the change in functional groups during the degradation process were identified as follows:1491 cm-1(C-H) > 1450 cm-1(C-H) > 1601 cm-1(C=C) > 1027 cm-1(C-O) > 1068 cm-1(C=O) > 1366 cm-1(C-OH). Overall, these results reveal that FAFU011 could promote the thermophilic bio-oxidative degradation of PS plastic.

Impact of extracellular polymeric substances on the settlement ability of aerobic granular sludge.

Instability of aerobic granular sludge (AGS), which is mainly caused by filamentous outgrowth, is a bottleneck in applying this technology to treat wastewater. In order to reduce the effect of filamentous outgrowth on settlement ability of AGS, the role of the distribution of extracellular polymeric substances (EPS) in settlement ability was investigated in this study. Chemical oxygen demand (COD) of influent increased gradually from 1000 mg L(-1) to 2000 mg L(-1) to 4000 mg L(-1) as organic loading rate (OLR) changed from 2 to 4 to 8 kg COD m(-3) d(-1) in the synthetic influent. The relationship between settlement ability and EPS was investigated. The sharp increase in loosely bound EPS (LB-EPS) content reduced the settlement ability, whereas the highest content of tightly bound EPS (TB-EPS) was observed in the sludge with best settlement ability. The TB-EPS plays an important role in maintaining the matrix structure of AGS. Abundance of LB-EPS did not favour the settlement ability of AGS. These results would provide useful information for improvement of stability of AGS.

Enhanced in situ biodegradation of microplastics in sewage sludge using hyperthermophilic composting technology.

Land spreading of sewage sludge is a major source of environmental microplastics (MPs) contamination. However, conventional sludge treatments are inefficient at removing sludge-based MPs. Herein, hyperthermophilic composting (hTC) technology is proposed and demonstrated in full-scale (200 t) for in situ biodegradation of sludge-based MPs. After 45 days of hTC treatment, 43.7% of the MPs was removed from the sewage sludge, which is the highest value ever reported for MPs biodegradation. The underlying mechanisms of MPs removal were investigated in lab-scale polystyrene-microplastics (PS-MPs) biodegradation experiments. The hTC inoculum degraded 7.3% of the PS-MPs at 70 °C in 56 days, which was about 6.6 times higher than that of the conventional thermophilic composting (cTC) inoculum at 40 °C. Analyses of the molecular weight and physicochemical properties of the PS-MPs residuals indicated that hyperthermophilic bacteria in hTC accelerated PS-MPs biodegradation through excellent bio-oxidation performance. High-throughput sequencing suggested that Thermus, Bacillus, and Geobacillus were the dominant bacteria responsible for the highly efficient biodegradation during hTC. These results reveal the critical role of hyperthermophilic bacteria in MPs biodegradation during hTC, highlighting a promising strategy for sludge-based MPs removal from the real environment.

Enhancing sludge methanogenesis with improved redox activity of extracellular polymeric substances by hematite in red mud.

Different conductive materials have been employed to stimulate direct interspecies electron transfer (DIET) during methanogenesis, but few studies have been concerned with the interaction between conductive materials and extracellular polymeric substances (EPS) such as the effect on sludge aggregation and redox activity of EPS. This study aims to systematically investigate the role of red mud with 45.46 wt% hematite on methanogenesis during the anaerobic digestion of waste activated sludge. The results showed that the multivalent cations from hematite effectively promoted the formation of large and compact aggregates, which might contribute to the rapid direct electron exchange during the DIET process. Meanwhile, more redox-active mediators including c-type cytochromes (c-Cyts) and humic substances, particularly in tight-bound EPS (TB-EPS), and more redox-active metals such as Fe introduced by red mud could take part in the interspecies electron transfer process between syntrophic bacteria and methanogenic archaea, which also promoted methane production (35.52 ±â€¯2.64% increase compared with the control). This study provided initial scientific evidence to comprehensively assess the role of conductive materials during methanogenesis, with important implications for the biogeochemical redox processes of conductive minerals in natural and engineered environments.

The effects of three commonly used extraction methods on the redox properties of extracellular polymeric substances from activated sludge.

Recently, the redox properties of extracellular polymeric substances (EPS) have attracted the attention of scientists due to their associated environmental significance, such as organic pollutant (e.g. nitroaromatics and substituted nitrobenzenes) degradation and heavy metal (e.g. Cr(VI) and U(VI)) detoxification. Although the separation of EPS from bacterial cells is more often the first step in studies on EPS, and studies have demonstrated that extraction procedures can influence the sorption properties of EPS, few attempts have been made to investigate how separation methods affect the redox properties of the obtained EPS. In this study, three common extraction approaches, that is, centrifugation, formaldehyde+NaOH and ethylene diamine tetra-acetic acid (EDTA), were employed to extract EPS from activated sludge, and the obtained EPS were evaluated for their redox properties using electrochemical means, including cyclic voltammetry and chronoamperometry. In addition, spectroscopic techniques were utilized to explore the structural characteristics and composition of EPS. The results indicated that EPS extracted by EDTA clearly displayed reversible oxidation-reduction peaks in cyclic voltammograms and significantly higher electron-accepting capacity compared with EPS extracted using the other two approaches. Fourier transform infrared spectra and three-dimensional excitation-emission matrix spectra suggested that the EPS extracted with EDTA presented better redox properties because of the effective and efficient extraction of the humic substances, which are important components of the EPS of activated sludge. Therefore, extraction method has an impact on the composition and redox properties of EPS and should be chosen according to research purpose and EPS source.

Membrane-less cloth cathode assembly (CCA) for scalable microbial fuel cells.

One of the main challenges for scaling up microbial fuel cell (MFC) technologies is developing low-cost cathode architectures that can generate high power output. This study developed a simple method to convert non-conductive material (canvas cloth) into an electrically conductive and catalytically active cloth cathode assembly (CCA) in one step. The membrane-less CCA was simply constructed by coating the cloth with conductive paint (nickel-based or graphite-based) and non-precious metal catalyst (MnO(2)). Under the fed-batch mode, the tubular air-chamber MFCs equipped with Ni-CCA and graphite-CCA generated the maximum power densities of 86.03 and 24.67 mW m(-2) (normalized to the projected cathode surface area), or 9.87 and 2.83 W m(-3) (normalized to the reactor liquid volume), respectively. The higher power output of Ni-CCA-MFC was associated with the lower volume resistivity of Ni-CCA (1.35 x 10(-2)Omega cm) than that of graphite-CCA (225 x 10(-2)Omega cm). At an external resistance of 100 Omega, Ni-CCA-MFC and graphite-CCA-MFC removed approximately 95% COD in brewery wastewater within 13 and 18d, and achieved coulombic efficiencies of 30.2% and 19.5%, respectively. The accumulated net water loss through the cloth by electro-osmotic drag exhibited a linear correlation (R(2)=0.999) with produced coulombs. With a comparable power production, such CCAs only cost less than 5% of the previously reported membrane cathode assembly. The new cathode configuration here is a mechanically durable, economical system for MFC scalability.