Biohydrogen production by co-fermentation of antibiotic fermentation residue and fallen leaves: Insights into the microbial community and functional genes

Multiple effects of carbon, sulfur and iron on microbial mercury methylation in black-odorous sediments

Black-odorous sediments provide ideal conditions for microbial mercury methylation. However, the multiple effects of carbon, sulfur, and iron on the microbial methylmercury of mercury in black-odorous sediments remains unclear. In this study, we conducted mercury methylation experiments using sediments collected from organically contaminated water bodies, as well as black-odorous sediments simulated in the laboratory. The results showed that black-odorous sediments exhibit a high capacity for mercury methylation. By simulating the blackening and odorization process in sediments, it was confirmed that dissolved oxygen, organic matter and sulfide were the primary factors triggering the black-odorous phenomenon in sediments. Regarding the influence of key factors in sediments on methylmercury formation, the batch tests demonstrated that high concentrations of organics additions (above 200 mg/L) may reduce bacterial activity and weaken mercury methylation in sediments. Under five different iron-sulfur ratios, the concentrations of methylmercury in the black-odorous sediments showed an increasing trend, the ratio of 5.0 Fe/S exhibited the highest MeHg accumulation. The iron-sulfur ratio in the sediment had a significant effect on the mercury methylation process, which was mainly due to the competition between Fe2+ and Hg2+ for sulfide sites and the adsorption/coprecipitation of Hg2+ by FeS. These findings offer a potential avenue for further understanding and controlling mercury methylation, contributing to the mitigation of the potential threat of mercury pollution to the environment and human health.

Insights into the role of electrochemical stimulation on sulfur-driven biodegradation of antibiotics in wastewater treatment

The presence of antibiotics in wastewater poses significant threat to our ecosystems and health. Traditional biological wastewater treatment technologies have several limitations in treating antibiotic-contaminated wastewaters, such as low removal efficiency and poor process resilience. Here, a novel electrochemical-coupled sulfur-mediated biological system was developed for treating wastewater co-contaminated with several antibiotics (e.g., ciprofloxacin (CIP), sulfamethoxazole (SMX), chloramphenicol (CAP)). Superior removal of CIP, SMX, and CAP with efficiencies ranging from 40.6 ± 2.6 % to 98.4 ± 1.6 % was achieved at high concentrations of 1000 μg/L in the electrochemical-coupled sulfur-mediated biological system, whereas the efficiencies ranged from 30.4 ± 2.3 % to 98.2 ± 1.4 % in the control system (without electrochemical stimulation). The biodegradation rates of CIP, SMX, and CAP increased by 1.5∼1.9-folds under electrochemical stimulation compared to the control. The insights into the role of electrochemical stimulation for multiple antibiotics biodegradation enhancement was elucidated through a combination of metagenomic and electrochemical analyses. Results showed that sustained electrochemical stimulation significantly enriched the sulfate-reducing and electroactive bacteria (e.g., Desulfobulbus, Longilinea, and Lentimicrobiumin on biocathode and Geobactor on bioanode), and boosted the secretion of electron transport mediators (e.g., cytochrome c and extracellular polymeric substances), which facilitated the microbial extracellular electron transfer processes and subsequent antibiotics removal in the sulfur-mediated biological system. Furthermore, under electrochemical stimulation, functional genes associated with sulfur and carbon metabolism and electron transfer were more abundant, and the microbial metabolic processes were enhanced, contributing to antibiotics biodegradation. Our study for the first time demonstrated that the synergistic effects of electrochemical-coupled sulfur-mediated biological system was capable of overcoming the limitations of conventional biological treatment processes. This study shed light on the mechanism of enhanced antibiotics biodegradation via electrochemical stimulation, which could be employed in sulfur-mediated bioprocess for treating antibiotic-contaminated wastewaters.

A cyclic shift-temperature operation method to train microbial communities of mesophilic anaerobic digestion

Temperature is the critical factor affecting the efficiency and cost of anaerobic digestion (AD). The current work develops a shift-temperature AD (STAD) between 35 °C and 55 °C, intending to optimise microbial community and promote substrate conversion. The experimental results showed that severe inhibition of biogas production occurred when the temperature was firstly increased stepwise from 35 °C to 50 °C, whereas no inhibition was observed at the second warming cycle. When the organic load rate was increased to 6.37 g VS/L/d, the biogas yield of the STAD reached about 400 mL/g VS, nearly double that of the constant-temperature AD (CTAD). STAD promoted the proliferation of Methanosarcina (up to 57.32 %), while severely suppressed hydrogenophilic methanogens. However, when the temperature was shifted to 35 °C, most suppressed species recovered quickly and the excess propionic acid was quickly consumed. Metagenomic analysis showed that STAD also promoted gene enrichment related to pathways metabolism, membrane functions, and methyl-based methanogenesis.

Recovery and characterization of cellulose microfibers from fallen leaves and evaluation of their potential as reinforcement agents for production of new biodegradable packaging materials

In the present work, cellulose microfibers (CMFs) isolated from fallen autumn leaves of cherry plum (Prunus cerasifera pissardii nigra), white mulberry (Morus alba) and plane (Platanus orientalis) trees were characterized and used as reinforcement agents in sodium alginate-based biodegradable films. Fourier transform infrared spectroscopy (FT-IR) characterization showed that the CMFs were successfully isolated from the leaves with high purity. The extracted CMFs had a particle size ranging from 321.20 nm to 632.26 nm and negative zeta potential values (-27.33 to -21.40). The extraction yield of CMFs ranged from 19.53% to 26.00%. Incorporation of the leaf-derived CMFs into sodium alginate based films (1%, w:w) increased their tensile strength (from 153.73 to 187.78 MPa) and elongation at break values (from 105.97% to 89.90%) and significantly decreased oxygen (from 121.46 to 75.56 meq kg-1) and water vapor permeabilities (from 2.36 to 1.60 g mm h-1 m-2 kPa-1)(p < 0.05). Furthermore, the supplementation of CMFs into the biopolymer matrix had no significant effect on the color (L*: 85.35-85.67; a*: -0.75-0.71; b*: 4.23-4.94) and moisture content (44.64-48.42%) of the film samples, although the thickness increased (40.33-94.66 μm). Scanning electron microscopy (SEM) images showed that CMFs were homogeneously dispersed in the film matrix. Overall, this study confirms that fallen cherry plum, white mulberry, and plane leaves are valuable sources of CMFs which could be used in the manufacturing of biodegradable nanocomposite films as reinforcement agents.

Improved biohydrogen production by co-fermentation of corn straw and excess sludge: Insights into biochemical process, microbial community and metabolic genes

The global climate change mainly caused by fossil fuels combustion promotes that zero-carbon hydrogen production through eco-friendly methods has attracted attention in recent years. This investigation explored the biohydrogen production by co-fermentation of corn straw (CS) and excess sludge (ES), as well as comprehensively analyzed the internal mechanism. The results showed that the optimal ratio of CS to ES was 9:1 (TS) with the biohydrogen yield of 101.8 mL/g VS, which was higher than that from the mono-fermentation of CS by 1.0-fold. The pattern of volatile fatty acids (VFAs) indicated that the acetate was the most preponderant by-product in all fermentation systems during the biohydrogen production process, and its yield was improved by adding appropriate dosage of ES. In addition, the content of soluble COD (SCOD) was reduced as increasing ES, while concentration of NH4+-N showed an opposite tendency. Microbial community analysis revealed that the microbial composition in different samples showed a significant divergence. Trichococcus was the most dominant bacterial genus in the optimal ratio of 9:1 (CS/ES) fermentation system and its abundance was as high as 41.8%. The functional genes prediction found that the dominant metabolic genes and hydrogen-producing related genes had not been significantly increased in co-fermentation system (CS/ES = 9:1) compared to that in the mono-fermentation of CS, implying that enhancement of biohydrogen production by adding ES mainly relied on balancing nutrients and adjusting microbial community in this study. Further redundancy analysis (RDA) confirmed that biohydrogen yield was closely correlated with the enrichment of Trichococcus.

Enhancement of vitamin B6 production driven by omics analysis combined with fermentation optimization

BACKGROUND

Microbial engineering aims to enhance the ability of bacteria to produce valuable products, including vitamin B6 for various applications. Numerous microorganisms naturally produce vitamin B6, yet the metabolic pathways involved are rigorously controlled. This regulation by the accumulation of vitamin B6 poses a challenge in constructing an efficient cell factory.

RESULTS

In this study, we conducted transcriptome and metabolome analyses to investigate the effects of the accumulation of pyridoxine, which is the major commercial form of vitamin B6, on cellular processes in Escherichia coli. Our omics analysis revealed associations between pyridoxine and amino acids, as well as the tricarboxylic acid (TCA) cycle. Based on these findings, we identified potential targets for fermentation optimization, including succinate, amino acids, and the carbon-to-nitrogen (C/N) ratio. Through targeted modifications, we achieved pyridoxine titers of approximately 514 mg/L in shake flasks and 1.95 g/L in fed-batch fermentation.

CONCLUSION

Our results provide insights into pyridoxine biosynthesis within the cellular metabolic network for the first time. Our comprehensive analysis revealed that the fermentation process resulted in a remarkable final yield of 1.95 g/L pyridoxine, the highest reported yield to date. This work lays a foundation for the green industrial production of vitamin B6 in the future.

Occurrence and fate of CECs (OMPs, ARGs and pathogens) during decentralised treatment of black water and grey water

Decentralised wastewater treatment is becoming a suitable strategy to reduce cost and environmental impact. In this research, the performance of two technologies treating black water (BW) and grey water (GW) fractions of urban sewage is carried out in a decentralised treatment of the wastewater produced in three office buildings. An Anaerobic Membrane Bioreactor (AnMBR) treating BW and a Hybrid preanoxic Membrane Bioreactor (H-MBR) containing small plastic carrier elements, treating GW were operated at pilot scale. Their potential on reducing the release of contaminants of emerging concern (CECs) such as Organic Micropollutants (OMPs), Antibiotic Resistance Genes (ARGs) and pathogens was studied. After 226 d of operation, a stable operation was achieved in both systems: the AnMBR removed 92.4 ± 2.5 % of influent COD, and H-MBR removed 89.7 ± 3.5 %. Regarding OMPs, the profile of compounds differed between BW and GW, being BW the matrix with more compounds detected at higher concentrations (up to μg L-1). For example, in the case of ibuprofen the concentrations in BW were 23.63 ± 3.97 μg L-1, 3 orders of magnitude higher than those detected in GW. The most abundant ARGs were sulfonamide resistant genes (sul1) and integron class 1 (intl1) in both BW and GW. Pathogenic bacteria counts were reduced between 1 and 3 log units in the AnMBR. Bacterial loads in GW were much lower than in BW, being no bacterial re-growth observed for the GW effluents after treatment in the H-MBR. None of the selected enteric viruses was detected in GW treatment line.

Diversity, composition, metabolic characteristics, and assembly process of the microbial community in sewer system at the early stage

Sewer systems play vital roles in wastewater treatment facilities, and the microbial communities contribute significantly to the transformation of domestic wastewater. Therefore, this study conducted a 180-day experiment on a sewer system and utilized the high-throughput sequencing technology to characterize the microbial communities. Additionally, community assembly analysis was performed to understand the early-stage dynamics within the sewer system. The results demonstrated that the overall diversity of microbial communities exhibited fluctuations as the system progressed. The dominant phyla observed were Chloroflexi, Bacteroidetes, Firmicutes, and Proteobacteria, accounting for over 85.4% of the total relative abundances. At the genus level, bacteria associated with fermentation displayed a high relative abundance, particularly during days 75 to 180. A random-forest machine-learning model identified a group of microbes that confirmed the substantial contribution of fermentation. During the process of fermentation, microorganisms predominantly utilized propionate formation as the main pathway for acidogenesis, followed by acetate and butyrate formation. In terms of nitrogen and sulfur cycles, dissimilatory nitrate reduction and assimilatory sulfate reduction played significant roles. Furthermore, stochastic ecological processes had a dominant effect during the experiment. Dispersal limitation primarily governed the assembly process almost the entire experimental period, indicating the strong adaptability and metabolic plasticity of microorganisms in response to environmental variations. This experiment provides valuable insights into the metabolic mechanisms and microbial assembly associated with sewer systems.

Mixed culture biotechnology and its versatility in dark fermentative hydrogen production

Over the years, extensive research has gone into fermentative hydrogen production using pure and mixed cultures from waste biomass with promising results. However, for up-scaling of hydrogen production mixed cultures are more appropriate to overcome the operational difficulties such as a metabolic shift in response to environmental stress, and the need for a sterile environment. Mixed culture biotechnology (MCB) is a robust and stable alternative with efficient waste and wastewater treatment capacity along with co-generation of biohydrogen and platform chemicals. Mixed culture being a diverse group of bacteria with complex metabolic functions would offer a better response to the environmental variations encountered during biohydrogen production. The development of defined mixed cultures with desired functions would help to understand the microbial community dynamics and the keystone species for improved hydrogen production. This review aims to offer an overview of the application of MCB for biohydrogen production.

Phytoremediation with application of anaerobic fermentation residues regulate the assembly of ecological clusters within co-occurrence network in ionic rare earth tailings soil: A pot experiment

The cultivation of energy plants (Pennisetum hybrid) with anaerobic fermentation residues has become an important phytoremediation approach in ionic rare earth elements (REEs) tailings because of its advantages in low cost and sustainability recently. In this study, a comparative pot experiment was carried out to determine the interaction pattern and key ecological clusters in microbial community respond to phytoremediation. Results showed that the application of biogas residues or slurry could effectively mitigate soil acidification, increase soil nutrients, alter REEs bioavailability and promote plant growth. Without fertilization, plant growth was restricted and soil acidification and nutrient-deficiency would be further aggravated. This difference in phytoremediation effect was associated with the assembly of seven key ecological clusters in co-occurrence network of rhizosphere soil. And such assembly pattern of cluster, determined by the environmental preference (e.g. pH, REEs), nutrient demand and interaction among clusters, could alter the microbial communities in response to the changes in soil context rapidly and exert corresponding ecological function during phytoremediation, such as participating in soil nutrient cycling, affecting plant biomass and altering REEs bioavailability. These findings provided new insights for anaerobic fermentation residues application, and can be beneficial to support for studying microbe-plant combined remediation in the future.

Effect of zero-valent iron nanoparticles on taxonomic composition and hydrogen production from kitchen waste

This study investigated the effects of varying zero-valent iron (ZVI) (0 to 5,000 mg/L) on fermentative hydrogen (H2) production, metabolic pattern, and taxonomic profile by using kitchen waste as substrate. The study demonstrated that the supplementation of 500 mg ZVI/L resulted in the highest H2 yield (219.68 ± 11.19 mL H2/g-volatile solids (VS)added), which was 19% higher than the control. The metabolic pattern analysis showed that acetic and butyric acid production primarily drove the H2 production. The taxonomic analysis further revealed that Firmicutes (relative abundance (RA): 80-96%) and Clostridium sensu stricto 1 (RA: 68-88%) were the dominant phyla and genera, respectively, during the exponential gas production phase, supporting the observation of accumulation of acetic and butyric acids. These findings suggest that supplementation of ZVI can enhance H2 production from organic waste and significantly influence the metabolic pattern and taxonomic profile, including the metalloenzymes.

Volatile fatty acids recovery and antibiotic degradation from erythromycin fermentation residues by combined thermal pretreatment and anaerobic fermentation: Insights into microbial communities and metabolic pathways

High resistance of erythromycin has been the key factor restricting the disposal of erythromycin fermentation residues (EFR). Considering the high sensitivity of erythromycin to acidic conditions, anaerobic fermentation may be a good approach for EFR treatment, through which pH decreases along with the volatile fatty acids (VFA) accumulation. This study firstly explored the EFR treatment by combined thermal pretreatment and anaerobic fermentation. Results showed that thermal pretreatment and anaerobic fermentation exhibited a synergistic effect on erythromycin removal. Erythromycin concentration decreased to 20.0 mg/L with the maximum removal rate of 60.0%, which was 140% and 71.4% higher than erythromycin removal by sole thermal pretreatment and anaerobic fermentation. Thermal pretreatment induced the increased VFA production by 22.3% with the highest VFA concentration of 5325.4 mg/L. Microbial analysis shows that thermal pretreatment stimulated erythromycin degradation and VFA production by increasing the microbial diversity and enriching the functional enzymes involved in acetate-producing pathways.

Comprehensive assessment of toxicity and environmental risk associated with sulfamethoxazole biodegradation in sulfur-mediated biological wastewater treatment

Incomplete mineralization of sulfamethoxazole (SMX) in wastewater treatment systems poses a threat to ecological health. The toxicity and environmental risk associated with SMX biodegradation in the sulfur-mediated biological process were examined for the first time through a long-term (180 days) bioreactor study and a series of bioassays. The results indicated that the sulfur-mediated biological system was highly resistant and tolerant to SMX toxicity, as evidenced by the enrichment of sulfate-reducing bacteria (SRB), the improved microbial metabolic activity, and the excellent performance on pollutants removal under long-term SMX exposure. SMX can be effectively biodegraded by the cleavage and rearrangement of the isoxazole ring, hydrogenation and hydroxylation reactions in sulfur-mediated biological wastewater system. These biodegradation pathways effectively reduced the acute toxicity, antibacterial activity, and ecotoxicities of SMX and its biotransformation products (TPs) in the effluent of the sulfur-mediated biological system. The TPs produced via hydrogenation (TP1), hydroxylation, and isoxazole ring cleavage (TP3, TP4, TP5, TP8, and TP9) exhibited lower toxicity than SMX. Under SMX stress, although the abundance of sulfonamide resistance genes increased, the total abundance of ARGs decreased due to the extrusion of some intracellular SMX by the efflux pump genes and the inactivation of some SMX through the biodegradation process. Efflux pump and inactivation, as the main resistance mechanisms of antibiotics in the sulfur-mediated biological system, play a crucial role in microbial self-defense. The findings of this study demonstrate the great potential of the sulfur-mediated biological system in SMX removal, detoxication, and ARGs environmental risk reduction.

Antidepressant properties of voluntary exercise mediated by gut microbiota

Although regular exercise has been reported to prevent depression, it has not been clarified whether the gut microbiota is involved in the factors that prevent depression through exercise. We investigated the effects of voluntary exercise on the gut microbiota and the prevention of depression-like behaviors using mice. C57BL/6 J male mice were subjected to 10 weeks of sedentary control or wheel running, then they were subjected to social defeat stress (SDS). Exercise attenuated that sucrose drinking was decreased by SDS treatment. Exercise increased the expression of Bdnf and decreased expression of Zo-1 and Claudin5 in the brain. Fecal Turicibacter, Allobaculum, and Clostridium sensu stricto, and propionate in the cecum were decreased by the exercise. Voluntary exercise-induced antidepressant properties might be partially caused by suppression of serotonin uptake into gut microbiota and increase the permeability of the blood-brain barrier via reduced propionate production.

Mediation of Bacterial Interactions via a Novel Membrane-Based Segregator to Enhance Biological Nitrogen Removal

The regulation of microbial subpopulations in wastewater treatment plants (WWTPs) with desired functions can guarantee nutrient removal. In nature, "good fences make good neighbors," which can be applied to engineering microbial consortia. Herein, a membrane-based segregator (MBSR) was proposed, where porous membranes not only promote the diffusion of metabolic products but also isolate incompatible microbes. The MBSR was integrated with an anoxic/aerobic membrane bioreactor (i.e., an experimental MBR). The long-term operation showed that the experimental MBR exhibited higher nitrogen removal (10.45 ± 2.73 mg/L total nitrogen) than the control MBR (21.68 ± 4.23 mg/L) in the effluent. The MBSR resulted in much lower oxygen reduction potential in the anoxic tank of the experimental MBR (-82.00 mV) compared to that of the control MBR (83.25 mV). The lower oxygen reduction potential can inevitably aid in the occurrence of denitrification. The 16S rRNA sequencing showed that the MBSR significantly enriched acidogenic consortia, which yielded considerable volatile fatty acids by fermenting the added carbon sources and allowed efficient transfer of these small molecules to the denitrifying community. Moreover, the sludge communities of the experimental MBR harbored a higher abundance of denitrifying bacteria than those of the control MBR. Metagenomic analysis further corroborated these sequencing results. The spatially structured microbial communities in the experimental MBR system demonstrate the practicability of the MBSR, achieving nitrogen removal efficiency superior to that of mixed populations. Our study provides an engineering method for modulating the assembly and metabolic division of labor of subpopulations in WWTPs. IMPORTANCE This study provides an innovative and applicable method for regulating subpopulations (activated sludge and acidogenic consortia), which contributes to the precise control of the metabolic division of labor in biological wastewater treatment processes.

Hydrothermal carbon microspheres and their iron salt modification for enhancing biohydrogen production

Dark fermentation (DF) for hydrogen (H₂) evolution is often limited to industrial application due to its low H₂ yield. In this work, hydrothermal carbon microspheres (HCM) and iron modified HCM (Fe-HCM) were prepared by hydrothermal process using waste corn cob. Subsequently, HCM and Fe-HCM were used in DF for more H₂. The highest H₂ yields amended with HCM and Fe-HCM at 600 mg/L were achieved to be 119 and 154 mL/g glucose (0.87 and 1.2 mol H₂/mol glucose), respectively, being 24% and 59% higher than that of control yield. Soluble metabolites revealed HCM and Fe-HCM promoted butyric acid-based DF. Microbial composition depicted that HCM and Fe-HCM improved the abundance level of Firmicutes from 35% to 41% and 56%, while the abundance level of Clostridium_sensu_stricto_1 rose from 25% to 38% and 51%, respectively. This provides valuable guidance for hydrothermal carbon used in biofuel production.

Metagenomic insights into the inhibitory mechanisms of Cu on fermentative hydrogen production

Cu is widely present in the feedstocks of dark fermentation, which can inhibit H₂ production efficiency of the process. However, current understanding on the inhibitory mechanisms of Cu, especially the microbiological mechanism, is still lacking. This study investigated the inhibitory mechanisms of Cu²⁺ on fermentative hydrogen production by metagenomics sequencing. Results showed that the exposure to Cu²⁺ reduced the abundances of high-yielding hydrogen-producing genera (e.g. Clostridium sensu stricto), and remarkably down-regulated the genes involved in substrate membrane transport (e.g., gtsA, gtsB and gtsC), glycolysis (e.g. PK, ppgK and pgi-pmi), and hydrogen formation (e.g. pflA, fdoG, por and E1.12.7.2), leading to significant inhibition on the process performances. The H₂ yield was reduced from 1.49 mol H₂/mol-glucose to 0.59 and 0.05 mol H₂/mol-glucose upon exposure to 500 and 1000 mg/L of Cu²⁺, respectively. High concentrations of Cu²⁺ also reduced the rate of H₂ production and prolonged the H₂-producing lag phase.

Inhibitory effect of acetic acid on dark-fermentative hydrogen production

This study examined the working mechanisms of acetic acid inhibition on dark fermentative hydrogen production. It was found that undissociated acetic acid (UAA) concentration was the critical factor in acetic acid inhibition. Hydrogen production activity decreased by 50 % and 90 % when UAA concentrations was 76.3 mg/L (1.27 mmol/L) and 686.7 mg/L (11.44 mmol/L), respectively. Dominant microbes were changed from genus Clostridium_sensu_stricto_1 to genus Inhella, Aquabacterium and Caulobacter under the stress of acetic acid inhibition. Functional enzyme analysis showed that acetic acid inhibited the hydrogen production by activating the lactate formation pathway when UAA concentration was below the inhibition threshold, while by impairing most hydrogen-producing pathways when UAA concentration was over the inhibition threshold. In brief, acetic acid inhibited the hydrogen production by altering the dominant microbial community and regulating the metabolic pathways, controlling the UAA concentration would be a good strategy to alleviate the acetic acid inhibition.

Effects of metronidazole on mesophilic and thermophilic fermentation: Biodegradation mechanisms, microbial communities, and reversibility

Metronidazole (MNZ), an antibiotic that is specifically used for the treatment of anaerobic infections, may inhibit anaerobic fermentation. This work was designed to understand the fate and effects of MNZ in mesophilic fermentation (MF) and thermophilic fermentation (TF), respectively. The results showed that the removal of MNZ mainly occurred via biodegradation, rather than adsorption, and that MNZ could be completely degraded by opening the imidazole ring. MFs were more strongly inhibited by MNZ than TFs. MNZ concentration increased from 0 to 25 mg/L, hydrogen yield (HY) decreased from 167.5 to 16.8 mL/g glucose (90.0% decrease), and butyrate yield almost completely disappeared in MFs, whereas in TFs, HY decreased only from 101.1 to 89.3 mL/g glucose (11.7% decrease), and ethanol yield increased by 39.8%. Illumina MiSeq sequencing analysis showed that MNZ reduced the abundance of hydrogen-producing bacteria. Furthermore, the inhibition of MNZ on anaerobic fermentation was reversible.

Research progress of additives in photobiological hydrogen production system to enhance biohydrogen

Photosynthetic biohydrogen has the advantages of extensive raw materials, clean and renewable, etc. But, its low substrate utilization rate limit its commercial application. It is reported that the use of additives in the process of biohydrogen by photofermentation is beneficial to increase biohydrogen. However, in practical application, the mechanism of additives in hydrogen production is not understood. This paper, the promotion effect of some additives on biohydrogen by photofermentation was reviewed. Whatever, the existing problems and development trends of various additives are also discussed. It is necessary to select appropriate additives according to the hydrogen-producing characteristics. The use of composite additives may further enhance biohydrogen, but the specific situation needs further exploration. The research results of this paper can help readers to further understand the role of additives in the crouse of photofermentative biohydrogen, provide reference for the research of photofermentative biohydrogen.

Co-fermentation of sewage sludge and lignocellulosic biomass for production of medium-chain fatty acids

Medium-chain fatty acids (MCFAs) production from sewage sludge and lignocellulosic biomass (fallen leaves and grass) was explored. Co-fermentation of sludge and lignocellulosic biomass significantly accelerated the caproate production and promoted the longer-chain MCFAs formation. Co-fermentation of sludge and grass achieved the highest caproate production of 89.50 mmol C/L, which was 18.04 % and 41.73 % higher than the mono-fermentation of grass and sludge, respectively. Co-fermentation of sludge and leaves produced 63.80 mmol C/L caproate, which was 11.09 % and 1.03 % higher than the mono-fermentation of leaves and sludge, respectively. Microbial analysis showed that co-fermentation enriched CE microbes like genus Clostridium_sensu_stricto_13, Caprocipiproducens, Terrisporpbacter and Praraclostridium, and suppressed the competitive microbes like genus norank_f_Caldilineaceae and Desulfomicrobium. Functional enzymes analysis revealed that co-fermentation of sludge and leaves promoted MCFAs production through strengthening reverse β oxidation (RBO) pathway, while co-fermentation of sludge and grass stimulated MCFAs production by strengthening fatty acid biosynthesis (FAB) pathway.

Production of medium-chain fatty acids by co-fermentation of antibiotic fermentation residue with fallen Ginkgo leaves

The co-fermentation of antibiotic fermentation residues (AFRs) and fallen Ginkgo leaves at C/N ratios of 10-60 was conducted for medium-chain fatty acids (MCFA) production. It was found that a proper C/N ratio could largely promote the MCFA accumulation. Group with C/N ratio of 50 exhibited highest MCFA production of 133.14 mmol C/L, which was 42 %-121 % higher than the other groups. Through the co-fermentation, substrate condition was optimized with rich micro-nutrients in AFRs and abundant polysaccharides in Ginkgo leaves, the hydrolysis of leaves was promoted by the active microbes in AFRs, and the predominance of CE microbes was also stimulated with the dilution of AFRs. The increased C/N ratio significantly affected the SCFA producers like genus Escherichia Shigella and Proteiniphilum, and enriched CE microbes like genus Romboutsia, Eubacterium and Clostridium_sensu_stricto_12. Functional enzymes analysis showed that both reverse β oxidation and fatty acid biosynthesis pathways were strengthened with the increased C/N ratio.

Unraveling the roles of lanthanum-iron oxide nanoparticles in biohydrogen production

Low hydrogen (H₂) yield via dark fermentation often occurs, being mainly due to H₂ generation pathway shift. In this study, lanthanum-iron oxide nanoparticles (LaFeO₃ NPs) were prepared to investigate their effects on bioH₂ production. The highest H₂ yield of 289.8 mL/g glucose was found at 100 mg/L of LaFeO₃, being 47.6% higher than that from the control (196.3 mL/g glucose). The relative abundance of Firmicutes increased from 54.2% to 67.5%. The large specific surface area of LaFeO₃ provided sufficient sites for the colonization of Firmicutes and increased the bacterial access to nutrients. Additionally, the La³⁺ gradually released from LaFeO₃ NPs raised microbial transmembrane transport capacity, promoting glycolytic efficiency and Fe availability, thereby increasing hydrogenase content, and shifting the bioH₂ evolution to butyrate pathway for more H₂. This provides the novelty for biochemical utilization of La and new insights into the improved H₂ yield amended with LaFeO₃.

Enhanced antibiotic degradation and hydrogen production of deacetoxycephalosporin C fermentation residue by gamma radiation coupled with nano zero-valent iron

Antibiotic fermentation residue (AFR) has been categorized as hazardous waste in China. Anaerobic biohydrogen fermentation may be a promising technology for handling AFR, which could achieve dual goals of waste treatment and clean energy production at the same time. However, the low hydrogen yield and low removal efficiency of residual antibiotics are two major factors limiting the AFR biohydrogen fermentation process. This work firstly applied gamma radiation (50 kGy) to remove the residual antibiotic in AFR and improve the bioavailability of organic matters, then adding nano zero-valent iron (nZVI) (100-1000 mg/L) to further enhance the AFR biohydrogen fermentation performance. Results showed that residual deacetoxycephalosporin C in AFR was removed with a high efficiency of 98.6%, and hydrogen yield achieved 20.45 mL/g-VS_added with the combined approach of gamma radiation pretreatment and 500 mg/L nZVI addition, which was 139.2% higher compared to the control experimental result. The combined approach also promoted the biohydrogen production rate, decreased the lag phase of hydrogen production, and increased the organics utilization. Microbiological analysis revealed that highly efficient hydrogen-producing genera Clostridium sensu stricto were enriched in much higher abundance with the combined approach, which might be the fundamental mechanism for the enhanced AFR fermentation performance.

Comparison of copper and aluminum doped cobalt ferrate nanoparticles for improving biohydrogen production

Two various materials, copper and aluminum doped cobalt ferrite nanoparticles (NPs) were fabricated for investigating their effects of addition amounts on hydrogen (H₂) synthesis and process stability. CoCu_0.2Fe_1.8O₄NPs enhanced H₂ production more than CoAl_0.2Fe_1.8O₄ NPs under same condition. The highest H₂ yield of 212.25 ml/g glucose was found at optimal dosage of 300 mg/L CoCu_0.2Fe_1.8O₄ NPs, revealing the increases of 43.17% and 6.67% compared with the control without NPs and 300 mg/L CoAl_0.2Fe_1.8O₄ NPs groups, respectively. NPs level of more than 400 mg/L inhibited H₂ generation. Further investigations illustrated that CoCu_0.2Fe_1.8O₄ NPs were mainly distributed on extracellular polymer substance while CoAl_0.2Fe_1.8O₄ NPs were mostly enriched on cell membrane, which facilitated electron transfer behavior. Community structure composition demonstrated that CoCu_0.2Fe_1.8O₄ and CoAl_0.2Fe_1.8O₄ separately caused a 9.67% and 9.03% increase in Clostridium sensu stricto 1 compared with the control reactor without NPs exposure.