Acetogenic Research Articles

Microbial symbiotic electrobioconversion of carbon dioxide to biopolymer (poly (3-hydroxybutyrate)) via single-step microbial electrosynthesis cell

This study proposes an novel single-stage microbial electrosynthesis system (MES) that bioelectrochemically converts CO2 into poly(3-hydroxybutyrate) (PHB). This innovative approach utilizes a symbiotic co-culture of electroactive acetogenic bacteria and PHB-accumulating bacteria within a single reactor, bypassing the need for separate acetate production and extraction. Systematic optimization of key operational parameters, including applied voltage, carbon source, and cathode material, was conducted to maximize PHB production. Results demonstrate that using a voltage of 2.5 V yielded a 7.14-fold increase in PHB content compared to open circuit conditions. Furthermore, functionalizing the cathode with a conductive and hydrophilic PEDOT: PSS polymer coating significantly enhanced the system’s performance, resulting in a 1.5-fold increase in both acetate and PHB production compared to unmodified carbon felt electrodes. The long-term stability and effectiveness of the co-culture system were validated through comprehensive microbial and metagenomic analyses. Results revealed a significant enrichment of CO2-utilizing electrotrophs within the cathode biofilm, including Acetobacterium and Clostridium. Concurrently, a 4 to 14-fold increase in the relative abundance of PHB-biosynthesizing bacteria, such as Pseudomonas, Rhodobacter and Caulobacter was observed in the planktonic phase. This study offers a promising pathway towards a circular bioeconomy by enabling the valorization of CO2 into valuable bio-based products via single-stage MES, utilizing a symbiotic co-culture.

Study on changes of bioactive substances and flavour characteristics during fermentation of jujube vinegar

SummaryJujubes are an excellent source of sugar and nutrients, making them well‐suited for fermentation. Previous research on jujubes has primarily focused on their use in fermented beverages and fruit wines, but their potential for vinegar production has not been sufficiently explored. Therefore, this study produced jujube vinegar from jujube as raw material using microbial fermentation technology, and the changes in bioactive substances and volatile components during different fermentation stages were monitored. Results revealed that the primary organic acids in jujube vinegar were acetic acid, malic acid and lactic acid. The levels of phenolic compounds, such as epicatechin and ferulic acid, increased significantly by 3.5‐fold and 3.2‐fold, respectively, after acetic fermentation, resulting in an improvement in antioxidant activity. In addition, a total of seventy‐three volatile substances were detected in jujube vinegar, with acids accounting for 72.13% of the overall content. Isoamyl alcohol, ethyl phenylacetate, benzaldehyde and 3‐hydroxy‐2‐butanone were also the principal flavour compounds of jujube vinegar, which are the main source of its intense flavour. This study reveals the dynamic law of nutrients and flavour compounds during the fermentation process of jujube vinegar. The findings provide a theoretical reference and practical basis for the production of jujube vinegar.

Bioleaching of Manganese from Ferromanganese Nodules Utilizing Acetogenic Bacteria in a Symbiotic Community of Bacteria and Yeast

Bioleaching of Manganese from Ferromanganese Nodules Utilizing Acetogenic Bacteria in a Symbiotic Community of Bacteria and Yeast

Effects of acetic acid fermentation on the phytochemicals content, taste and aroma of pineapple vinegar

Acetic acid fermentation of pineapple vinegar was processed by self-priming fermenter, and this study aimed to show the relationship between flavor and metabolic substances in industrial production. E-nose and E-tongue respectively characterized the changes in aroma and taste. Meanwhile, the organic acids, free amino acids, volatile components were monitored in real time by HPLC and HS-SPME-GC-MS. The results show that the most significant flavor changes took place in the initial stage (0–4 days). The floral aromas initially provided by ethanol diminished, was replaced by the emergence of rich fatty and fruity aromas attributed to acetic acid and Ethyl-2-methylbutanoate, respectively. The bitter of pineapple vinegar was reduced, acidity and astringency were significantly increased, which may be due to changes in amino acids and organic acids. In addition, the DPPH radical and FRAP scavenging activity remain stable, while HFRC radical scavenging activity increased significantly in pineapple vinegar, reached 55.78%. Our study findings provided valuable information on the functional characteristics and quality of pineapple vinegar.

Impact of pre-fermentative maceration techniques on the chemical characteristics, phenolic composition, in vitro bioaccessibility, and biological activities of alcoholic and acetic fermented products from jaboticaba (Plinia trunciflora)

The jaboticaba is a fruit with a highly promising chemical profile for producing fermented products with biological activity. In this context, evaluating pre-fermentative maceration techniques in jaboticaba fermentations is essential to optimize the extraction of phenolic compounds and other metabolites of interest, imparting antioxidant characteristics to the product and offering potential health benefits. This study evaluated the impact of two pre-fermentative maceration techniques on the phenolic composition, bioaccessibility, and biological activities (α-amylase, α-glucosidase, and ACE inhibition) of alcoholic and acetic fermented products from jaboticaba. Three treatments were performed: one without pre-fermentative maceration and two with maceration, one cold (4 °C for 24 h) and the other thermal maceration (50 °C until 16 °Brix). The resulting musts were subjected to alcoholic and acetic fermentation. The results showed that the fermented products obtained after thermal maceration had higher concentrations of phenolic compounds, with ellagic acid (5,393.78 µg/L) standing out for thealcoholic beverage and 2.5-DHBA (1,552.33 µg/L) and 3.4-DHB (863.15 µg/L) acids for the vinegar. Regarding bioaccessibility, both pre-fermentative maceration techniques contributed to more bioaccessible compounds (with indices above 20 %) compared to the samples without maceration. A more significant inhibition of α-amylase and α-glucosidase was observed in the samples subjected to thermal maceration, along with notable ACE inhibition. Additionally, the sensitivity of E. coli, S. aureus, L. monocytogenes, and S. Enteritidis to the fermented jaboticaba products was verified, with distinct sensitivity patterns for each type of bacteria. In summary, this study offers a new perspective for valorizing fermented jaboticaba products through pre-fermentative techniques, enriching the understanding of this technique and its potential nutritional and bioactive contributions.

Dynamic changes and correlation of quality, flavor and microorganisms of Mei (Prunus mume) vinegar during fermentation and clarification

Mei (Prunus mume) is a highly nutritious fruit whose value is often underutilized due to its perishable nature and challenges in post-maturation storage. This study evaluated the changes and correlations among quality, volatile flavor compounds (VFCs), and microorganisms in Mei vinegar (MV) during acetic acid fermentation (AAF) and low temperature clarification (LTC) using various clarifiers. The results indicated that AAF enhanced the bioactive components and antioxidant capacity of MV. A total of 73 VFCs were identified, comprising 9 alcohols, 28 esters, 5 aldehydes, 18 acids, 4 phenols, 1 ketone, 5 alkanes, and 3 others. Among these, the number and relative content of esters and acids exhibited dominance both in AAF and LTC. Firmicutes and Pediococcus were predominant at the phylum and genus levels, respectively. After 1 d of AAF, the relative abundances of Firmicutes and Pediococcus increased significantly, while LTC reduced their abundance. Among the 20 stable VFCs in MV, most esters and alcohols showed positive correlations with the top 10 bacteria at the phylum and genus levels, while certain acids were negatively correlated with these bacteria. Therefore, these findings offer valuable insights for the development of MV, the selection of clarifiers, and offer a theoretical basis for improving MV quality and flavor.

Identification of aroma active compounds in Shanxi aged vinegar and tracing the source in the entire production process

The aroma-active compounds (AACs) of traditional vinegars are formed through complexed pathways. Moreover, their source is not clear yet. The composition of AACs throughout the entire process of Shanxi aged vinegar (SAV) production from the raw materials, alcohol fermentation (AF), acetic acid fermentation (AAF), fumigation and aging stages were analyzed. A total of 121 AACs were determined by GC × GC-O-TOF-MS, of which 88 were identified by GC–MS/MS. There were 27 and 41 AACs (FD ≥ 400) detected in before-aging and after-aging SAV, respectively. Furthermore, it can be concluded the AAF and fumigation were the main sources of AACs. Also, the AAF was the main source of the compounds with caramel, creamy, floral, fruity, sour, cheesy notes, while the compounds owned roasted, nutty, spicy and woody aromas mainly came from fumigation. Finally, the potential transformation pathway of AACs was mapped and discussed. Overall, GC × GC-O-TOF-MS was a useful technique to enrich the AACs of SAV.

Improving the alcohol respiratory chain and energy metabolism by enhancing PQQ synthesis in Acetobacter pasteurianus.

Pyrroquinoline quinone (PQQ) is one of the important coenzymes in living organisms. In acetic acid bacteria (AAB) it plays a crucial role in alcohol respiratory chain, as a coenzyme of alcohol dehydrogenase. In this work, the PQQ biosynthetic genes were overexpressed in Acetobacter pasteurianus CGMCC 3089 to improve the fermentation performance. The result shows that the intracellular and extracellular PQQ contents in the recombinant strain A. pasteurianus (pBBR1-p264-pqq) were 152.53% and 141.08% higher than those of the control A. pasteurianus (pBBR1-p264), respectively. The catalytic activity of alcohol dehydrogenase and aldehyde dehydrogenase increased by 52.92% and 67.04%, respectively. The results indicated that the energy charge and intracellular ATP were also improved in the recombinant strain. The acetic acid fermentation was carried out using a 5 L self-aspirating fermenter, and the acetic acid production rate of the recombinant strain was 23.20% higher compared with the control. Furthermore, the relationship between the PQQ and acetic acid tolerance of cells was analyzed. The biomass of recombinant strain was 180.2%, 44.3%, and 38.6% higher than those of control under 2%, 3%, and 4% acetic acid stress, respectively. After treated with 6% acetic acid for 40 min, the survival rate of the recombinant strain was increased by 76.20% compared with the control. Those result demonstrated that overexpression of PQQ biosynthetic genes increased the content of PQQ, therefore improving the acetic acid fermentation and the cell tolerance against acetic acid by improving the alcohol respiratory chain and energy metabolism.

Nutritional Requirements and Fermentation Condition for Acetic Acid Production From Agricultural Fruit Waste

AbstractStudies on agricultural fruit waste fermentation for acetic acid production have focused on understanding its nutrient requirements. The present systematic literature review aimed to assess the potential and additional nutrients necessary for optimised acetic acid production from fruit waste. Fermentation conditions and techniques employed for the alcoholic and acetous fermentation stages were also evaluated to establish their significant effects on acetic acid yield.

Optimization of fermentation conditions and analysis of the changes in flavor compounds for lemon vinegar

The flavor composition is an important index to evaluate the quality of fruit vinegar, including volatile and non-volatile components. The flavor quality of fruit vinegar is related to fermentation technology. This study analyzed the acetic acid fermentation conditions and the changes in the flavor composition of lemon vinegar. After optimization, the pH, alcohol content, and inoculum were 3.0, 6%, and 10%. The statistical analysis showed significant changes in flavor components during the whole fermentation. After acetic acid fermentation, the highest organic acid changed from citric acid to acetic acid. The content of amino acids showed a decreasing trend, mainly used for the growth and metabolism of microorganisms and the precursor of aroma compounds. Terpenoids were the main aroma compounds before the fermentation, while the main aroma compounds were esters after the fermentation. Linalool, the characteristic aroma compound in lemon, was well preserved. Isoamyl acetate was the main aroma compound during the fermentation. Almost all the flavor compounds had significant changes during the lemon vinegar fermentation. This study helps to understand the changes in flavor compounds during lemon vinegar brewing and lays the foundation for further improving the quality of lemon vinegar.

Salmonella Typhimurium screen identifies shifts in mixed-acid fermentation during gut colonization

How enteric pathogens adapt their metabolism to a dynamic gut environment is not yet fully understood. To investigate how Salmonella enterica Typhimurium (S.Tm) colonizes the gut, we conducted an invivo transposon mutagenesis screen in a gnotobiotic mouse model. Our data implicate mixed-acid fermentation in efficient gut-luminal growth and energy conservation throughout infection. During initial growth, the pathogen utilizes acetate fermentation and fumarate respiration. After the onset of gut inflammation, hexoses appear to become limiting, as indicated by carbohydrate analytics and the increased need for gluconeogenesis. In response, S.Tm adapts by ramping up ethanol fermentation for redox balancing and supplying the TCA cycle with α-ketoglutarate for additional energy. Our findings illustrate how S.Tm flexibly adapts mixed fermentation and its use of the TCA cycle to thrive in the changing gut environment. Similar metabolic wiring in other pathogenic Enterobacteriaceae may suggest a broadly conserved mechanism for gut colonization.

Clostridium autoethanogenum alters cofactor synthesis, redox metabolism, and lysine-acetylation in response to elevated H2:CO feedstock ratios for enhancing carbon capture efficiency

BackgroundClostridium autoethanogenum is an acetogenic bacterium that autotrophically converts carbon monoxide (CO) and carbon dioxide (CO2) gases into bioproducts and fuels via the Wood–Ljungdahl pathway (WLP). To facilitate overall carbon capture efficiency, the reaction stoichiometry requires supplementation of hydrogen at an increased ratio of H2:CO to maximize CO2 utilization; however, the molecular details and thus the ability to understand the mechanism of this supplementation are largely unknown.ResultsIn order to elucidate the microbial physiology and fermentation where at least 75% of the carbon in ethanol comes from CO2, we established controlled chemostats that facilitated a novel and high (11:1) H2:CO uptake ratio. We compared and contrasted proteomic and metabolomics profiles to replicate continuous stirred tank reactors (CSTRs) at the same growth rate from a lower (5:1) H2:CO condition where ~ 50% of the carbon in ethanol is derived from CO2. Our hypothesis was that major changes would be observed in the hydrogenases and/or redox-related proteins and the WLP to compensate for the elevated hydrogen feed gas. Our analyses did reveal protein abundance differences between the two conditions largely related to reduction–oxidation (redox) pathways and cofactor biosynthesis, but the changes were more minor than we would have expected. While the Wood–Ljungdahl pathway proteins remained consistent across the conditions, other post-translational regulatory processes, such as lysine-acetylation, were observed and appeared to be more important for fine-tuning this carbon metabolism pathway. Metabolomic analyses showed that the increase in H2:CO ratio drives the organism to higher carbon dioxide utilization resulting in lower carbon storages and accumulated fatty acid metabolite levels.ConclusionsThis research delves into the intricate dynamics of carbon fixation in C. autoethanogenum, examining the influence of highly elevated H2:CO ratios on metabolic processes and product outcomes. The study underscores the significance of optimizing gas feed composition for enhanced industrial efficiency, shedding light on potential mechanisms, such as post-translational modifications (PTMs), to fine-tune enzymatic activities and improve desired product yields.

Effects of acetic acid fermentation product and its components on defense signaling in rice.

Acetic acid fermentation product made from isomalto-oligosaccharide as the main raw material is composed of isomalto-oligosaccharide and acetic acid. In this paper, we have shown that the fermentation product enhanced the expression of disease resistance genes in rice, and that its main functional component was acetic acid. It has been reported so far that acetic acid enhances the jasmonic acid signaling pathway, while the role of isomalto-oligosaccharide in plant defense signaling remains unclear. In this study, we demonstrated the possibility that isomalto-oligosaccharide shifted part of the jasmonic acid signaling pathway, which is enhanced by acetic acid, to the salicylic acid signaling pathway, which is the other major defense pathway. Furthermore, glucose, a constituent monosaccharide of isomalto-oligosaccharide, and a disaccharide maltose had little effect on the signaling pathway, but a trisaccharide maltotriose tended to have a similar effect to isomalto-oligosaccharide on the defense signaling pathway.

A Review on the Interaction of Acetic Acid Bacteria and Microbes in Food Fermentation: A Microbial Ecology Perspective.

In fermented foods, acetic acid bacteria (AAB), kinds of bacteria with a long history of utilization, contribute to safety, nutritional, and sensory properties primarily through acetic acid fermentation. AAB are commonly found in various fermented foods such as vinegar, sour beer, fermented cocoa and coffee beans, kefir beverages, kombucha, and sourdough. They interact and cooperate with a variety of microorganisms, resulting in the formation of diverse metabolites and the production of fermented foods with distinct flavors. Understanding the interactions between AAB and other microbes is crucial for effectively controlling and utilizing AAB in fermentation processes. However, these microbial interactions are influenced by factors such as strain type, nutritional conditions, ecological niches, and fermentation duration. In this review, we examine the relationships and research methodologies of microbial interactions and interaction studies between AAB and yeasts, lactic acid bacteria (LAB), and bacilli in different food fermentation processes involving these microorganisms. The objective of this review is to identify key interaction models involving AAB and other microorganisms. The insights gained will provide scientific guidance for the effective utilization of AAB as functional microorganisms in food fermentation processes.

(Invited) Photocatalyst Sheets for Scalable Solar Fuels Production from Water and CO2

The development of sunlight-driven water splitting or CO2 reduction systems with high efficiency, scalability, and cost-competitiveness is a central issue for mass production of fuels and energy-rich chemicals.1 Z-scheme photocatalytic systems, employing the two-step photoexcitation of photocatalyst I (PC I) and photocatalyst II (PC II), have garnered significant attention. These systems can utilize narrow bandgap semiconductors capable of either water/CO2 reduction or oxidation potential, enabling the conversion of solar energy. The challenge in developing a Z-scheme system lies in ensuring efficient electron transfer between PC I and PC II.2 To address these challenges, we have developed all-solid-state devices—photocatalyst sheets—for photocatalytic water splitting.3,4 These sheets establish a direct connection between PC I and PC II particles via a conductive layer or conductive nanoparticles, effectively facilitating electron transfer between them. Consequently, these photocatalyst sheets achieve a high solar-to-H2 conversion efficiency exceeding 1%. They outperform analogous powder suspension and photoelectrochemical systems in their optimal reaction solutions due to the effective electron transfer enabled by the conductive layer or nanoparticles bridging PC I and PC II. Compared to traditional photoelectrochemical systems, the photocatalyst sheet design significantly reduces the effects of H+/OH− concentration overpotentials and the IR drop due to the proximity of PC I and PC II in the sheet. Hence, the design of these photocatalyst sheets proves highly suitable for efficient large-scale applications.Additionally, efforts to demonstrate fuel production from CO2 powered by sunlight are currently hampered by the requirements of sacrificial electron donors or external bias, and lack of efficiency, selectivity and scalability. To overcome those barriers, we integrate a selective molecular catalyst on semiconductor light absorbers to form a wireless and monolithic photocatalyst sheet.5 For instance, by incorporating a phosphonated cobalt(II) bis(terpyridine) catalyst (CotpyP) onto a modified SrTiO3:La,Rh|Au|BiVO4:Mo sheet, we have achieved a solar-to-formate conversion efficiency of 0.08%. This configuration harnesses the high selectivity of molecular catalysts for CO2 reduction and the strong water oxidation power of semiconductors, yielding a formate selectivity of 97±3% through the coupled process of CO2 reduction and water oxidation. We have also developed a bio-abiotic hybrid system by combining a photocatalyst sheet, capable of scalable photocatalytic water splitting, with nonphotosynthetic bacteria acting as biocatalysts.6 When pairing CO2-fixing acetogenic bacteria, Sporomusa ovata, with a SrTiO3:La,Rh|ITO|BiVO4:Mo sheet, a solar-to-acetate conversion efficiency of ~0.7% was achieved (as shown in the figure). This coupling exhibited an impressive selectivity for acetate production in CO2 reduction reactions, reaching ~100%.Our study offers novel and versatile strategies toward sustainable solar fuel production.References Q. Wang, C. Pornrungroj, S. Linley, E. Reisner. Nat. Energy 7 , 13–24 (2022)Y. Sasaki, H. Nemoto, K. Saito, A. Kudo. J. Phys. Chem. C 113, 17536–17542 (2009)Q. Wang, T. Hisatomi, Q. Jia, H. Tokudome, M. Zhong, C. Wang, Z. Pan, T. Takata, M. Nakabayashi, N. Shibata, Y. Li, I. D. Sharp, A. Kudo, T. Yamada, K. Domen. Nat. Mater. 15,611–615 (2016)Q. Wang, T. Hisatomi, Y. Suzuki, Z. Pan, J. Seo, M. Katayama, T. Minegishi, H. Nishiyama, T. Takata, K. Seki, A. Kudo, T. Yamada, K. Domen. J. Am. Chem. Soc. 139, 1675–1683 (2017)Q. Wang, J. Warnan, S. Rodríguez-Jiménez, J. J. Leung, S. Kalathil, V. Andrei, K. Domen, E, Reisner. Nat. Energy 5, 703–710 (2020)Q. Wang, S. Kalathil, C. Pornrungroj, D. C. Sahm, E. Reisner. Nat. Catal. 5, 633–641 (2022) Figure 1

Isolation and characterization of novel acetogenic Moorella strains for employment as potential thermophilic biocatalysts.

Thermophilic acetogenic bacteria have attracted attention as promising candidates for biotechnological applications such as syngas fermentation, microbial electrosynthesis, and methanol conversion. Here, we aimed to isolate and characterize novel thermophilic acetogens from diverse environments. Enrichment of heterotrophic and autotrophic acetogens was monitored by 16S rRNA gene-based bacterial community analysis. Seven novel Moorella strains were isolated and characterized by genomic and physiological analyses. Two Moorella humiferrea isolates showed considerable differences during autotrophic growth. The M. humiferrea LNE isolate (DSM 117358) fermented carbon monoxide (CO) to acetate, while the M. humiferrea OCP isolate (DSM 117359) transformed CO to hydrogen and carbon dioxide (H2 + CO2), employing the water-gas shift reaction. Another carboxydotrophic hydrogenogenic Moorella strain was isolated from the covering soil of an active charcoal burning pile and proposed as the type strain (ACPsT) of the novel species Moorella carbonis (DSM 116161T and CCOS 2103T). The remaining four novel strains were affiliated with Moorella thermoacetica and showed, together with the type strain DSM 2955T, the production of small amounts of ethanol from H2 + CO2 in addition to acetate. The physiological analyses of the novel Moorella strains revealed isolate-specific differences that considerably increase the knowledge base on thermophilic acetogens for future applications.

Seasonal environmental factors drive microbial community succession and flavor quality during acetic acid fermentation of Zhenjiang aromatic vinegar.

This study investigated the impact of seasonal environmental factors on microorganisms and flavor compounds during acetic acid fermentation (AAF) of Zhenjiang aromatic vinegar (ZAV). Environmental factors were monitored throughout the fermentation process, which spanned multiple seasons. Methods such as headspace solid phase microextraction gas chromatography-mass spectrometry (HS-SPME-GC-MS), high performance liquid chromatography (HPLC), and high-throughput sequencing were employed to examine how these environmental factors influenced the flavor profile and microbial community of ZAV. The findings suggested that ZAV brewed in autumn had the strongest flavor and sweetness. The key microorganisms responsible for the flavor of ZAV included Lactobacillus acetotolerans, Lactobacillus plantarum, Lactobacillus reuteri, Lactobacillus fermentum, Acetobacter pasteurianus. Moreover, correlation analysis showed that room temperature had a significant impact on the composition of the microbial community, along with other key seasonal environmental factors like total acid, pH, reducing sugar, and humidity. These results provide a theoretical foundation for regulating core microorganisms and environmental factors during fermentation, enhancing ZAV quality.

Characterization of cellulose produced by bacteria isolated from different vinegars

Traditional vinegars are naturally produced from sugar- or starch-containing raw materials, through alcoholic fermentation followed by acetic fermentation. Fermentation is a spontaneous and complex process involving interactions between various microorganisms. In this study, we produced vinegar using traditional methods from six fruits: rosehip, pear, fig, wild pear, apple, and plum. Bacteria that produce bacterial cellulose (BC) were isolated from these vinegars and identified. In addition, we investigated the properties of BC produced from these bacteria. The strains isolated from vinegars were identified as Gluconobacter oxydans strain MG2022, Acetobacter tropicalis strain MG2022, Acetobacter fabarum strain MG2022, Komagataeibacter saccharivorans strain MG2022, K. saccharivorans strain EG2022, and Acetobacter lovaniensis strain OD2022. In total, 0.83–2.04 g/L BC was produced and the bacterial strain isolated from pear vinegar yielded the most BC. BC produced by the bacterial strain isolated from wild pear vinegar had the highest thermal stability and crystallinity (87.44 %). Overall, this study shows that different fruits contain different BC-producing bacteria in their natural flora and vinegars obtained from fruits can be used in BC production. Also, different BC-producing bacteria can be isolated from different vinegars, and BC produced by these bacteria might have different properties.

Carbon sources influence on heterotrophic ammonia assimilation: Performance and mechanism

Different carbon contents of organic carbon sources can be used as the reaction substrates of heterotrophic ammonia assimilation (HAA), which effectively dominates the recovery of available nutrients in wastewater. However, the influences of organic carbon sources on nutrient metabolism, degradation kinetics, and functional microbes of HAA were largely unknown. Here, HAA bioreactors fed with acetate, glucose, sucrose, starch, methanol, and sludge alkaline fermentation liquid (SAFL) were constructed to compare the nitrogen recovery performance, kinetic analysis, sludge characteristics, and microbial community structure. Higher COD and NH4+-N removal efficiencies were found in bioreactors supplied with acetate, glucose, and SAFL. Kinetic analysis showed that the acetate-fed bioreactor had more efficient organic utilization for assimilation. Corynebacterium, Pseudohoeflea, and Methylophaga emerged as the primary assimilation bacteria for typical carbon sources of organic acids, sugars, and alcohols, whereas Halomonas, Corynebacterium, and Marinobacter dominated in SAFL. Acetate- and SAFL-supported sludge particles displayed enhanced internal and external oxygen mass transfer, along with heightened sedimentation performance and deconsolidation ability. High-quality assimilative gene expression, assimilative enzyme activity, and assimilated organic nitrogen product synthesis with direct effects were observed in a reactor supplied with acetate and SAFL. The cost-effectiveness of SAFL preparation positions it as a promising candidate for practical engineering applications. This research underscored the pivotal role of different carbon contents in the nutrient recovery process of the HAA reaction, providing essential insights for optimizing wastewater treatment strategies and enhancing environmental sustainability.

A novel strategy combining hydrogenotrophic methanogens' bioaugmentation and biochar biostimulation for simultaneous polycyclic aromatic hydrocarbon biodegradation and bioenergy recovery.

A novel strategy combining bioaugmentation using methanogenic archaea and biostimulation using biochar was proposed for the first time to obtain simultaneous improvement of mixed PAHs' anaerobic biodegradation and bioenergy production. The results showed that the addition of PHAs immediately resulted in inhibition in methane production and accumulation of VFA, indicating that PHAs are more toxic to methanogens than the acetogenic bacteria. The coupling of biochar with hydrogenotrophic methanogen alleviated the inhibitory effects of PAHs, allowing the anaerobic fermentation system to recover its methane production capability rapidly. Compared to the Fe3+ + bioaugmentation group, the biochar + bioaugmentation group exhibited a 7.5% higher restored cumulative methane production. This coupling strategy ultimately facilitated the degradation of most PAHs, achieving a removal rate of over 90%. Moreover, the coupled biochar and bioaugmentation induced significant changes in the archaeal community structure. Direct interspecies electron guilds (i.e., Streptococcus and Methanosarcina) were enriched in the presence of biochar and bioaugmentation, responsible for prominent PAH removal and methane recovery. This study demonstrated the feasibility of simultaneous PAH biodegradation and bioenergy production using electron acceptor and enriched microorganisms.