The role of iron-based nanoparticles (Fe-NPs) on methanogenesis in anaerobic digestion (AD) performance

Cellulosic ethanol stillage for methane production by integrating single-chamber anaerobic digestion and microbial electrolysis cell system

Anaerobic digestion provides a solution to the inefficient use of carbon resources caused by improper disposal of corn stover-based ethanol stillage (CES). In this regard, we developed a single-chamber anaerobic digestion integrated microbial electrolysis cells system (AD-MEC) to convert CES into biogas while simultaneously upgrading biogas in-situ by employing voltages ranging from 0 to 2.5 V. Our results demonstrated that applying 1.0 V increased the CH4 yield by 55 % and upgraded the CH4 content in-situ to 82 %. This voltage also promoted the well-formed biofilm on the electrodes, resulting in a 20-fold increase in current. However, inhibition was observed at high voltages (1.5-2.5 V), suppressing syntrophic organic acid-oxidizing bacteria (SOB). The dissociation between SOB and methanogens led to accumulation of propionic and butyric acid, which, in turn, inhibited methanogens. The degradation of CES was accelerated by unclassified_o_norank_c_Desulfuromonadia on the anode, likely leading to an increase in mixotrophic methanogenesis due to the synergistic interaction among Aminobacterium, Sedimentibacter, and Methanosarcina. Furthermore, the enrichment of electroactive bacteria (EB) such as Enterococcus and Desulfomicrobium likely facilitates direct interspecies electron transfer to Methanobacterium, thereby promoting the conversion of CO2 to CH4 through hydrogenotrophic methanogenesis. Rather than initially stimulating the EB in the bulk solution to accelerate the start-up process of AD, our study revealed that applying mild voltage up to 1.0 V tended to mitigate the negative impact on the original microorganisms, as it gradually enriched EB on the electrode, thereby enhancing biogas production.

Advances in the Optimization of Fe Nanoparticles: Unlocking Antifungal Properties for Biomedical Applications

In recent years, nanotechnology has achieved a remarkable status in shaping the future of biological applications, especially in combating fungal diseases. Owing to excellence in nanotechnology, iron nanoparticles (Fe NPs) have gained enormous attention in recent years. In this review, we have provided a comprehensive overview of Fe NPs covering key synthesis approaches and underlying working principles, the factors that influence their properties, essential characterization techniques, and the optimization of their antifungal potential. In addition, the diverse kinds of Fe NP delivery platforms that command highly effective release, with fewer toxic effects on patients, are of great significance in the medical field. The issues of biocompatibility, toxicity profiles, and applications of optimized Fe NPs in the field of biomedicine have also been described because these are the most significant factors determining their inclusion in clinical use. Besides this, the difficulties and regulations that exist in the transition from laboratory to experimental clinical studies (toxicity, specific standards, and safety concerns) of Fe NPs-based antifungal agents have been also summarized.

In-situ methane enrichment in anaerobic digestion of food waste slurry by nano zero-valent iron: Long-term performance and microbial community succession

In this work, nano zero-valent iron (nZVI) was added to a lab-scale continuous stirring tank reactor (CSTR) for food waste slurry treatment, and the effect of dosing rate and dosage of nZVI were attempted to be changed. The results showed that anaerobic digestion (AD) efficiency and biomethanation stability were optimum under the daily dosing and dosage of 0.48 g/gTCOD. The average daily methane (CH4) yield reached 495.38 mL/gTCOD, which was 43.65% higher than that at control stage, and the maximum CH4 content reached 95%. However, under single dosing rate conditions, high nZVI concentrations caused microbial cell rupture and loosely bound extracellular polymeric substances (LB-EPS) precipitation degradation. The daily dosing rate promoted the hydrogenotrophic methanogenesis pathway, and the activity of coenzyme F420 increased by 400.29%. The microbial analysis indicated that daily addition of nZVI could promote the growth of acid-producing bacteria (Firmicutes and Bacteroidetes) and methanogens (Methanothrix).

Mechanisms of anaerobic treatment of sulfate-containing organic wastewater mediated by Fe0 under different initial pH values

The anaerobic treatment of sulfide-containing organic wastewater (SCOW) is significantly affected by pH, causing dramatic decrease of treatment efficiency when pH deviates from its appropriate range. Fe0 has proved as an effective strategy on mitigating the impact of pH. However, systematic analysis of the influence mechanism is still lacking. To fill this gap, the impact of different initial pH values on anaerobic treatment efficiency of SCOW with Fe0 addition, the change of fermentation type and methanogens, and intra-extracellular electron transfer were explored in this study. The results showed that Fe0 addition enhanced the efficacy of anaerobic treatment of SCOW at adjusted initial pH values, especially at pH 6. Mechanism analysis showed that respiratory chain-related enzymes and electron shuttle secretion and resistance reduction were stimulated by soluble iron ions generated by Fe0 at pH 6, which accelerated intra-extracellular electron transfer of microorganisms, and ultimately alleviated the impact of acidic pH on the system. While at pH 8, Fe0 addition increased the acetogenic bacteria abundance, as well as optimized the fermentation type and improved the F420 coenzyme activity, resulting in the enhancement of treatment efficiency in the anaerobic system and remission of the effect of alkaline pH on the system. At the neutral pH, Fe0 addition had both advantages as stimulating the secretion of respiratory chain and electron transfer-related enzymes at pH 6 and optimizing the fermentation type pH 8, and thus enhanced the treatment efficacy. This study provides important insights and scientific basis for the application of new SCOW treatment technologies.

Use of magnetic powder to effectively improve the denitrification employing the activated sludge fermentation liquid as carbon source

Nitrogen removal is often limited in municipal wastewater treatment due to the lack of sufficient carbon source. Utilizing volatile fatty acids (VFAs) from waste activated sludge (WAS) fermentation broth as a carbon source is an ideal alternative to reduce the cost for wastewater treatment plants (WWTPs) and improve denitrification efficiency simultaneously. In this study, an anaerobic system was applied for simultaneous denitrification and WAS fermentation and the addition of magnetic microparticles (MMP) were confirmed to enhance both denitrification and WAS fermentation. Firstly, the addition of MMP increased the nitrate reduction rate by over 25.36% and improve the production of N2. Additionally, the equivalent chemical oxygen demand (COD) of the detected VFAs increased by 7.06%-14.53%, suggesting that MMP promoted the WAS fermentation. The electron transfer efficiency of denitrifies was accelerated by MMP via electron-transporting system (ETS) activity and cyclic voltammetry (CV) experiments, which might result in the promotional denitrification and WAS fermentation performance. Furthermore, the high-throughput sequencing displayed that, MMP enriched key microbes capable of degrading the complex organics (Chloroflexi, Synergistota and Spirochaetota) as well as the typical denitrifies (Bacteroidetes_vadinHA17 and Denitratisoma). Therefore, this study provides a novel strategy to realize simultaneous WAS utilization and denitrification for WWTPs.

Dominant factors analyses and challenges of anaerobic digestion under cold environments

With the development of fermentation technology and the improvement of efficiency, anaerobic digestion (AD) has been playing an increasingly primary role in waste treatment and resource recovery. Temperature is undoubtedly the most important factor because it shapes microbial habitats, changes the composition of the microbial community structure, and even affects the expression of related functional genes. More than half of the biosphere is in a long-term or seasonal low-temperature environment (<20 °C), which makes psychrophilic AD have broad application prospects. Therefore, this review discusses the influencing factors and enhancement strategies of psychrophilic AD, which may provide a corresponding reference for future research on low-temperature fermentation. First, the occurrence of AD has been discussed. Then, the adaptation of microorganisms to the low-temperature environment was analyzed. Moreover, the challenges of psychrophilic AD have been reviewed. Meanwhile, the strategies for improving psychrophilic AD are presented. Further, from technology to application, the current situation of psychrophilic AD in pilot-scale tests is described. Finally, the economic and environmental feasibility of psychrophilic AD has been highlighted. In summary, psychrophilic AD is technically feasible, while economic analysis shows that the output benefits cannot fully cover the input costs, and the large-scale practical application of psychrophilic AD is still in its infancy. More research should focus on how to improve fermentation efficiency and reduce the investment cost of psychrophilic AD.

Soft magnetic ferrite for enhanced anaerobic digestion of food waste: Effects on methane production and magnetic recovery

Soft magnetic ferrite (SMF) is a potentially efficient anaerobic digestion (AD) additive that can be recovered simultaneously along with the microorganisms it carries. In this study, two typical SMFs (Fe3O4 and γ-Fe2O3) were compared in batch experiments to investigate their effects on food waste AD and to examine the recovery characteristics of both the SMFs and the microorganisms they carried after AD. The results showed that Fe3O4 and γ-Fe2O3 addition increased methane production by 31% and 68% respectively, compared with the control treatment. Both SMF materials and enriched microorganisms were effectively adsorbed post-AD using a magnet. The observed enhancement in biomethanization after SMF addition was likely due to enhanced syntrophic acetate oxidation and hydrogenotrophic methanogenesis, and direct interspecific electron transfer. γ-Fe2O3 outperformed Fe3O4 due to its high recycling rate and ability to promote Methanosarcina growth. This study provides a potential economically efficient solution for developing AD enhancement technologies.

A review of application of combined biochar and iron-based materials in anaerobic digestion for enhancing biogas productivity: Mechanisms, approaches and performance

Strengthening direct interspecies electron transfer (DIET), via adding conductive materials, is regarded as an effective way for improving methane productivity of anaerobic digestion (AD). Therein, the supplementation of combined materials (composition of biochar and iron-based materials) has attracted increasing attention in recent years, because of their advantages of promoting organics reduction and accelerating biomass activity. However, as far as we known, there is no study comprehensively summarizing the application of this kind combined materials. Here, the combined methods of biochar and iron-based materials in AD system were introduced, and then the overall performance, potential mechanisms, and microbial contribution were summarized. Furthermore, a comparation of the combinated materials and single material (biochar, zero valent iron, or magnetite) in methane production was also evaluated to highlight the functions of combined materials. Based on these, the challenges and perspectives were proposed to point the development direction of combined materials utilization in AD field, which was hoped to provide a deep insight in engineering application.

Simultaneous addition of CO2-nanobubble water and iron nanoparticles to enhance methane production from anaerobic digestion of corn straw

In this research, CO₂-nanobubble water (CO₂-NBW) and iron nanoparticles (Fe⁰NPs) were added simultaneously to exploit individual advantages to enhance the methanogenesis process from both the stability of anaerobic digestion (AD) system and the activity of anaerobic microorganism aspects. Results showed that the AD performance was enhanced by supplementing with CO₂-NBW or Fe⁰NPs individually, and could be further improved by simultaneous addition of the two additives. The maximum methane yield was achieved in the CO₂-NBW + Fe⁰NPs reactor (141.99 mL/g-VS_added), which increased by 26.16% compared to the control group. Similarly, the activities of the electron transfer system (ETS) and enzyme were improved. The results of microbial community structure revealed that the addition of CO₂-NBW and Fe⁰NPs could improve the abundance of dominant bacteria (Anaerolineaceae, Bacteroidales, and Prolixibacteraceae) and archaea (Methanotrichaceae and Methanospirillaceae). Additionally, the functional metabolic prediction heatmap indicated that metabolic functional genes favorable for AD of corn straw were enhanced.

Influence of Fe2O3 Nanoparticles on the Anaerobic Digestion of Macroalgae Sargassum spp

The anaerobic digestion (AD) of biomass is a green technology with known environmental benefits for biogas generation. The biogas yield from existing substrates and the biodegradability of biomasses can be improved by conventional or novel enhancement techniques, such as the addition of iron-based nanoparticles (NPs). In this study, the effect of different concentrations of Fe2O3-based NPs on the AD of brown macroalga Sargassum spp. has been investigated by 30 days trials. The effect of NPs was evaluated at different concentrations. The control sample yielded a value of 80.25 ± 3.21 NmLCH4/gVS. When 5 mg/g substrate and 10 mg/g substrate of Fe2O3 NPs were added to the control sample, the yield increased by 24.07% and 26.97%, respectively. Instead, when 50 mg/g substrate of Fe2O3 NPs was added to the control sample, a negative effect was observed, and the biomethane yield decreased by 38.97%. Therefore, low concentrations of Fe2O3 NPs favor the AD process, whereas high concentrations have an inhibitory effect. Direct interspecies electron transfer (DIET) via Fe2O3 NPs and their insolubility play an important role in facilitating the methanogenesis process during AD.

Wastewater treatment with nanomaterials for the future: A state-of-the-art review

Aquatic and terrestrial ecosystems are both threatened by toxic wastewater. The unique properties of nanomaterials are currently being studied thoroughly for treating sewage. Nanomaterials also have the advantage of being capable of removing organic matter, fungi, and viruses from wastewater. Advanced oxidation processes are used in nanomaterials to treat wastewater. Additionally, nanomaterials have a large effective area of contact due to their tiny dimensions. The adsorption and reactivity of nanomaterials are strong. Wastewater treatment would benefit from the development of nanomaterial technology. Second, the paper provides a comprehensive analysis of the unique characteristics of nanomaterials in wastewater treatment, their proper use, and their prospects. In addition to focusing on their economic feasibility, since limited forms of nanomaterials have been manufactured, it is also necessary to consider their feasibility in terms of their technical results. According to this study, the significant adsorption area, excellent chemical reaction, and electrical conductivity of nanoparticles (NPs) contribute to the successful treatment of wastewater.

Utilization of nanoparticles for biogas production focusing on process stability and effluent quality

Abstract

One of the most important techniques for converting complex organic waste into renewable energy in the form of biogas and effluent is anaerobic digestion. Several issues have been raised related to the effectiveness of the anaerobic digestion process in recent years. Hence nanoparticles (NPs) have been used widely in anaerobic digestion process for converting organic wastes into useful biogas and effluent in an effective way. This review addresses the knowledge gaps and summarizes recent researchers’ findings concentrating on the stability and effluent quality of the cattle manure anaerobic digestion process using single and combinations nanoparticle. In summary, the utilization of NPs have beneficial effects on CH4 production, process optimization, and effluent quality. Their function, as key nutrient providers, aid in the synthesis of key enzymes and co-enzymes, and thus stimulate anaerobic microorganism activities when present at an optimum concentration (e.g., Fe NPs 100 mg/L; Ni NPs 2 mg/L; Co NPs 1 mg/L). Furthermore, utilizing Fe NPs at concentrations higher than 100 mg/L is more effective at reducing H2S production than increasing CH4, whereas Ni NPs and Co NPs at concentrations greater than 2 mg/L and 1 mg/L, respectively, reduce CH4 production. Effluent with Fe and Ni NPs showed stronger fertilizer values more than Co NPs. Fe/Ni/Co NP combinations are more efficient in enhancing CH4 production than single NPs. Therefore, it is possible to utilize NPs combinations as additives to improve the effectiveness of anaerobic digestion.

Article highlights

Impact of biosurfactant and iron nanoparticles on biodegradation of polyaromatic hydrocarbons (PAHs)

Polycyclic aromatic hydrocarbons (PAHs) are hazardous toxic contaminants and considered as primary pollutants due to their persistent nature and most of them are carcinogenic and mutagenic. The key challenge in PAHs degradation is their hydrophobic nature, which makes them one of the most complex materials and inaccessible by a broad range of microorganisms. This bioavailability can be increased by using a biosurfactant. In the present study mixed PAHs were degraded using the biosurfactant producing bacterial strains. In addition, iron nanoparticles were synthesized and the impact of iron nanoparticles on the growth of the mixed bacterial strains (Pseudomonas stutzeri NA3 and Acinetobacter baumannii MN3) was optimized. The mixed PAHs (anthracene, pyrene, and benzo(a)pyrene) degradation was enhanced by addition of biosurfactant (produced by Bacillus subtilis A1) and iron nanoparticles, resulting in 85% of degradation efficiency. The addition of the biosurfactant increased the bioavailability of the PAHs in the aqueous environment, which might help bacterial cells for the initial settlement and development. The addition of iron nanoparticles increased both bacterial biomass and PAHs adsorption over their surface. These overall interactions assisted in the utilization of PAHs by the mixed bacterial consortia. This study illustrates that this integrated approach can be elaborated for the removal of the complex PAHs pollutants from soil and aqueous environments.

Enhancement of Anaerobic Digestion with Nanomaterials: A Mini Review

In recent years, the number of articles reporting the addition of nanomaterials to enhance the process of anaerobic digestion has exponentially increased. The benefits of this addition can be observed from different aspects: an increase in biogas production, enrichment of methane in biogas, elimination of foaming problems, a more stable and robust operation, absence of inhibition problems, etc. In the literature, one of the current focuses of research on this topic is the mechanism responsible for this enhancement. In this sense, several hypotheses have been formulated, with the effect on the redox potential caused by nanoparticles probably being the most accepted, although supplementation with trace materials coming from nanomaterials and the changes in microbial populations have been also highlighted. The types of nanomaterials tested for the improvement of anaerobic digestion is today very diverse, although metallic and, especially, iron-based nanoparticles, are the most frequently used. In this paper, the abovementioned aspects are systematically reviewed. Another challenge that is treated is the lack of works reported in the continuous mode of operation, which hampers the commercial use of nanoparticles in full-scale anaerobic digesters.

Performance and Mechanism of Fe3O4 Improving Biotransformation of Waste Activated Sludge into Liquid High-Value Products

This study demonstrated that Fe₃O₄ simultaneously improves the total production and formation rate of medium-chain fatty acids (MCFAs) and long-chain alcohols (LCAs) from waste activated sludge (WAS) in anaerobic fermentation. Results revealed that when Fe₃O₄ increased from 0 to 5 g/L, the maximal MCFA and LCA production increased significantly, and the optimal fermentation time was also remarkably shortened from 24 to 9 days. Moreover, Fe₃O₄ also enhanced WAS degradation, and the corresponding degradation rate in the fermentation system increased from 43.86 to 72.38% with an increase in Fe₃O₄ from 0 to 5 g/L. Further analysis showed that Fe₃O₄ promoted the microbe activities of all the bioprocesses (including hydrolysis, acidogenesis, and chain elongation processes) involved in the MCFA and LCA production from WAS. Microbial community analysis indicated that Fe₃O₄ increased the abundances of key microbes involved in abovementioned bioprocesses correspondingly. Mechanistic investigations showed that Fe₃O₄ increased the conductivity of the fermented sludge, providing a better conductive environment for the anaerobic microbes. The redox cycle of Fe(II) and Fe(III) existed in the fermentation system with Fe₃O₄, which was likely to act as electron shuttles to conduct electron transfer (ET) from the electron donor to the acceptor, thus increasing ET efficiency. This study provides an effective method for enhancing the biotransformation of WAS into high-value products, potentially bringing economic benefits to WAS treatment.