Although landfill is suspected to be releasing microplastics to the environment, there is few empirical researches carried out. To clarify suspicions of landfills as potential sources of ...microplastics, twelve leachate samples from four active and two closed municipal solid waste landfills were investigated. Microplastics were found in all the landfill leachate samples. In total, seventeen different types of plastics were identified in the leachate samples with calculated concentration ranging from 0.42 to 24.58 items/L. Polyethylene and polypropylene were the predominant polymer types. 99.36% microplastics were derived from the fragmentation of plastic waste buried in landfills. The size of 77.48% microplastics was between 100 and 1000 μm. The study shows that the generation, accumulation and release of microplastic in landfills is a long-term process. The results of our study provide preliminary evidence and validate that landfill isn't the final sink of plastics, but a potential source of microplastics.
•Municipal solid waste landfills are potential sources of microplastics.•Seventeen types of plastics were found in the landfill leachate.•The concentration of microplastics ranged from 0.42 to 24.58 items/L.•Polyethylene and polypropylene were the predominant polymer types.•99.36%microplastics derived from the fragmentation of plastic waste.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
The addition of 0.5–1 mm biostable biochar (10 g/L) to mesophilic anaerobic digesters inoculated with crushed granules (1 g-VS/L) and fed with 4, 6 and 8 g/L glucose shortened the methanogenic lag ...phase by 11.4%, 30.3% and 21.6% and raised the maximum methane production rate by 86.6%, 21.4% and 5.2%, respectively, compared with the controls without biochar. 75 μm biochar further shortened the lag phase by 38.0% and increased the methane production rate by 70.6% at 6 g/L glucose loading. Biochar also simultaneously enhanced the production and degradation of intermediate acids. The fingerprint and sequencing analysis used to examine the spatial distribution and temporal evolution of communities revealed that proportion of Archaea was higher in the biochar-added treatments and in the tightly-bound fractions. Methanosarcina located in the tightly-bound fractions on the biochar surface, and was most abundant in the larger 2–5 mm biochar particles. Methanosaeta was enriched in the loosely-bound fractions by all-size biochar particles and within the tightly-bound fractions by small biochar particles. Because biochar is cost-effective and can remain in digestate for direct use as soil amendment without separation, eco-compatible biochar may serve as a good substrate for highly-loaded digestion by inducing selective colonization of functional microbes.
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•Stratified distribution of microbial community around biochar particle was explored.•Treatment with both biochar and high organics had more tightly bound Methanosarcina.•Bacteria was distinguished into suspended and biochar attached.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
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•Bottom ash from municipal solid waste incinerators was a source of microplastics.•Abundance of microplastics ranged from 1.9–565 n/kg-bottom ash.•Polypropylene was the predominant ...polymer types.•Per metric ton waste will produce 360 to 102,000 MPs in bottom ash.
It is widely accepted that incineration can permanently eliminate plastic waste. However, unburned material still exists in the bottom ash that is a solid residue from incinerators. In this study, microplastics exacted from bottom ash in 12 mass burn incinerators, one bottom ash disposal center and four fluidized bed incinerators were identified by micro-Fourier transform infrared spectroscopy. The results showed that bottom ash was a neglected microplastics source with an abundance of 1.9–565 n/kg, which indicated that per metric ton waste produce 360 to 102,000 microplastic particles after incineration. Nine types of plastics were identified, of which polypropylene and polystyrene were the predominant types. Microplastics sized between 50 μm and 1 mm accounted for 74 %. Granules, fragments, film, and fibers accounted for 43 %, 34 %, 18 %, and 5 % of the microplastics, respectively. The abundance of microplastics differed significantly with whether the local waste was source-separated, the local gross domestic product per capita, and the types of furnace. The global microplastics emission from incineration bottom ash was then estimated. Our observations provide empirical evidence proving that incineration is not the terminator of plastic waste, and bottom ash is a potential source of microplastics released into the environment.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
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•Doubled microbial enrichment was found in mesophilic digesters with powdered biochar.•CH4 production increased by 32.5% in granular biochar amended mesophilic digesters.•CH4 ...production increased by 13.3% in powdered biochar amended thermophilic digesters.•Biochar relieved propionic acid accumulation in thermophilic digesters.
Oil is a desirable substrate for anaerobic digestion (AD) for its high energy recovery potential. However, low solubility of oil and long-chain fatty acids (LCFAs) inhibition hinder microbial growth and further reduce the biogas production in most cases. Biochar is a cheap but reliable additive in AD. Its functions to enrich microbial enrichment and enhance biogas production were confirmed previously. In present study, effects of biochars with different particle sizes on oil AD were investigated under thermophilic and mesophilic conditions. Results from the quantification and space distribution of microbes indicate that powdered biochar (<5 μm) aggregated more microbes than granular biochar (0.5–1 mm). Especially in the mesophilic digesters, powdered biochar doubled the number of microbes in the whole digester, which was a satisfactory result of acclimation. In addition, powdered biochar was able to adjust the microbial communities and further increased CH4 production by 13.3% in thermophilic digesters. Granular biochar enhanced the maximum CH4 potential by 32.5% under mesophilic condition, which was most promising from the perspective of energy recovery. Biochar of both particle sizes relieved propionic acid accumulation in thermophilic digesters. Hence, biochar addition might be an ideal approach to elevate energy recovery efficiency by overcoming the barriers of anaerobic microbes to utilize LCFAs.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Carbon chain elongation (CCE), a reaction within the carboxylate platform that elongates short-chain to medium-chain carboxylates by mixed culture, has attracted worldwide interest. The present study ...provides insights into the microbial diversity and predictive microbial metabolic pathways of a mixed-culture CCE microbiome on the basis of a comparative analysis of the metagenome and metatranscriptome. We found that the microbial structure of an acclimated chain elongation microbiome was a highly similar to that of the original inoculating biogas reactor culture; however, the metabolic activities were completely different, demonstrating the high stability of the microbial structure and flexibility of its functions. Additionally, the fatty acid biosynthesis (FAB) pathway, rather than the well-known reverse β-oxidation (RBO) pathway for CCE, was more active and pivotal, though the FAB pathway had more steps and consumed more ATP, a phenomenon that has rarely been observed in previous CCE studies. A total of 91 draft genomes were reconstructed from the metagenomic reads, of which three were near completion (completeness, >97%) and were assigned to unknown strains of
,
, and
The last two strains are likely new-found active participators of CCE in the mixed culture. Finally, a conceptual framework of CCE, including both pathways and the potential participators, was proposed.
Carbon chain elongation means the conversion of short-chain volatile fatty acids to medium-chain carboxylates, such as
-caproate and
-caprylate with electron donors under anaerobic condition. This bio-reaction can both expand the resource of valuable biochemicals and broaden the utilization of low-grade organic residues in a sustainable biorefinery context.
is conventionally considered model microbe for carbon chain elongation which uses the reverse β-oxidation pathway. However, little is known about the detailed microbial structure and function of other abundant microorganism in a mixed culture (or open culture) of chain elongation. We conducted the comparative metagenomic and metatranscriptomic analysis of a chain elongation microbiome to throw light on the underlying functional microbes and alternative pathways.
•Fenton has promising prospects for the degradation of refractory organic contaminants in wastewater.•·OH attacks humic substances and trace contaminants with different mechanisms.•The economics of ...conventional Fenton and three Fenton-like are compared.•Ways to improve on conventional Fenton are summarized .
Fenton process has become a research hotspot due to the nonselective and efficient degradation of dissolved organic matter (DOM) by ·OH. However, there are still many challenges and bottlenecks for conventional Fenton (CF). This study provides the first comprehensive insight into the mechanisms of DOM degradation by the Fenton process, including the various subcategories of humic substances, emerging trace contaminants, including persistent organic pollutants, endocrine disrupting chemicals, and pharmaceuticals and personal care products, and the interference of humus and low molecular weight organic acids on the removal of trace contaminants. In addition, a statistical comparison of the economics of CF and three types of Fenton-like technologies (Photo-Fenton, Electro-Fenton, and Ultrasonic-Fenton) is conducted based on existing studies, which can be used as a reference for engineering applications. Moreover, a brief overview of the categories and characteristics of heterogeneous Fenton, which have been extensively studied in recent years, and a comparison of their catalysts are presented. In the end, the paper advances a possible future research direction.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
This investigation evaluated the effectiveness of biochar of different particle sizes in alleviating ammonium (NH4+) inhibition (up to 7 g-N/L) during anaerobic digestion of 6 g/L glucose. Compared ...to the control treatment without biochar addition, treatments that included biochar particles 2–5 mm, 0.5–1 mm and 75–150 μm in size reduced the methanization lag phase by 23.9%, 23.8% and 5.9%, respectively, and increased the maximum methane production rate by 47.1%, 23.5% and 44.1%, respectively. These results confirmed that biochar accelerated the initiation of methanization during anaerobic digestion under double inhibition risk from both ammonium and acids. Furthermore, fine biochar significantly promoted the production of volatile fatty acids (VFAs). Comparative analysis on the archaeal and bacterial diversity at the early and later stages of digestion, and in the suspended, biochar loosely bound, and biochar tightly bound fractions suggested that, in suspended fractions, hydrogenotrophic Methanobacterium was actively resistant to ammonium. However, acetoclastic Methanosaeta can survive at VFAs concentrations up to 60–80 mmol-C/L by improved affinity to conductive biochar, resulting in the accelerated initiation of acetate degradation. Improved methanogenesis was followed by the colonization of the biochar tightly bound fractions by Methanosarcina. The selection of appropriate biochar particles sizes was important in facilitating the initial colonization of microbial cells.
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•Biochar promoted methanogenesis facing double stresses of high ammonium and acid.•Methanosaeta was enriched around biochar particles in the early stage of digestion.•Methanosarcina dominated in the later stage of digestion in tightly bound fraction.•Fine biochar facilitated the production of organic acids.•Biochar particle size was vital for cell accessibility and subsequent performance.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
Undesirable ammonium concentrations can lead to unstable anaerobic digestion processes, and Methanosarcina spp. are the representative methanogens under inhibition. However, no known work seems to ...exist for directly exploring the detailed metabolic regulation of pure cultured representative Methanosarcina spp. to ammonium inhibition. We used transcriptomics and proteomics to profile the metabolic regulation of Methanosarcina barkeri to 1, 4, and 7 g N/L of total ammoniacal nitrogen (TAN), where free ammonia concentrations were between 1.5 and 36.1 mg N/L. At the initial stages of ammonium inhibition, the genes participating in the acquisition and assimilation of reduced nitrogen sources showed significant upregulation where the minimal fold change of gene transcription was about 2. Apart from nitrogen metabolism, the transcription of some genes in methanogenesis also significantly increased at the initial stages. For example, the genes encoding alternative heterodisulfide reductase subunits (HdrAB), energy-converting hydrogenase subunit (EchC), and methanophenazine-dependent hydrogenase subunits (VhtAC) were significantly upregulated by at least 2.05 times. For the element translocation at the initial stages, the genes participating in the uptake of ferrous iron, potassium ion, and molybdate were significantly upregulated with a minimal fold change of 2.10. As the cultivation proceeded, the gene encoding the cell division protein subunit (FtsH) was significantly upregulated by 13.0 times at 7 g N/L of TAN; meanwhile, an increment in OD600 was observed at the terminal sampling point of 7 g N/L of TAN. The present study explored the metabolic regulation of M. barkeri in stress response, protein synthesis, signal transduction, nitrogen metabolism, methanogenesis, and element translocation. The results would contribute to the understanding of the metabolic effects of ammonium inhibition on methanogens and have significant practical implication in inhibited anaerobic digestion.
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IJS, KILJ, NUK, PNG, UL, UM
Temperature plays a primary role in anaerobic digestion, since it shapes microbial ecosystems, and consequently regulates the stability performance of anaerobic digestion process. Although changes in ...microbial community and composition at different temperatures have also previously been discussed in some experimental studies. However, until now, this aspect of the regulation of the temperature gradient on microbial communities have not yet well been reviewed. Additionally, these previous studies did not observe the classical three-peak model regarding methane production rates owing to limitations to the temperature range and the broad gradient interval. Furthermore, some microorganisms that lived at “extreme” temperatures have been reported in some previous studies, it provides a possibility for industrial applications of anaerobic digestion in cold regions or for sanitation purposes on the basis of deciphering the mechanism of their adaption. This survey aims to shove the boundaries a little further summarizing an overview of the microbial responses to the fermentation temperature gradient in each step (including hydrolysis, acidification, and methanogenesis) of the anaerobic digestion process and investigated the mechanism of adaption to extreme temperature regimes. Overall, this review covers discussion on microorganisms’ responses to broad temperature gradient, together with mechanism to adapted extreme temperature by regulating the conformation transition of their DNA, protein, and specialized enzymes.
•Temperature regulates anaerobic digestion mainly by biological response.•Biological responses to the temperature gradient during anaerobic digestion are summarized.•Microbial growth and enzymes activities in each step are discussed.•Relative abundance of homoacetogens increases with increasing temperature.•Various strategies for extreme temperature adaptation are summarized.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
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•Recycled biochar-biofilm consortia demonstrated feasible long-term application in AD.•Biochar < 5 μm more efficiently initiated methanogenesis than biochar > 1 mm.•Biochar < 5 μm ...enriched 20 times more microorganisms than larger biochar.•Methanosarcina dominated in biochar > 1 mm, while SAOB dominated in biochar < 5 μm.
Several single dose studies found that biochar was an effective additive promoting methanogenesis in anaerobic digestion. However, little attention was paid to the continuity of the biofilm formed on biochar and the subsequent evolution of microorganisms. In this study, the continuous performance and changes were quantified when biochar-biofilm consortia were applied as the recyclable inoculant to four cycles of acetate methanogenesis with increasing acetate loading. Biochar-biofilm consortia as the inoculant were found to consistently realize stable methane production, despite the removal of planktonic microorganisms in the reactor, and no extra inoculum and biochar were added. Consortia with biochar particles smaller than 5 μm promoted initiation of methanogenesis more rapidly than those with biochar particles larger than 1 mm, especially when the activity of microorganism was low. Moreover, the microorganisms were enriched throughout the continuous cycles. Biochar < 5 μm was found to accumulate 6.6–7.1 E + 11 16S copies per gram in the 3rd and 4th cycles, which was about 27–51 times that of biochar > 1 mm and also comparable to a fresh sludge inoculum. In addition, specific functional methanogens proliferated during continuous application. Methanosarcina was dominant in biochar > 1 mm, while the syntrophic acetate oxidizing bacteria Thermovirga and Mesotoga accounted for the majority of microorganisms in biochar < 5 μm. Therefore, with the competitive total cell count dominated by functional microorganisms, biochar-biofilm consortia demonstrated feasible recycling and reuse for bioaugmentation purposes or in the economical long-term application of anaerobic digestion for waste or wastewater treatment.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
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