Enhanced fermentative hydrogen production from industrial wastewater using mixed culture bacteria incorporated with iron, nickel, and zinc-based nanoparticles

Harnessing Nanomaterials for Enhanced Biohydrogen Generation from Wastewater

Biohydrogen is considered a green fuel due to its eco-friendly nature since it only produces water and energy on combustion. However, their lower yield and production rate is one of the foremost challenges that need an instant sustainable approach. The use of nanotechnology is a potential approach for the enhanced generation of biohydrogen, owing to the significant characteristics of the nanomaterials such as greater specificity, high surface-area-to-volume ratio, better reactivity and dispersibility, enhanced catalytic activity, superb selectivity, greater electron transfer, and better anaerobic microbiota activity. This article explores the recent trends and innovations in the production of biohydrogen from wastewater through the applications of different nanomaterials. The potential of various nanomaterials employed for biohydrogen production from wastewater is evaluated and the impacts of important parameters such as the concentration and size of the nanomaterials, temperature, and pH on the production and yield of biohydrogen are explained in detail. Several pathways involved in the mechanistic approach of biohydrogen generation from wastewater are critically assessed. Lastly, numerous technological challenges are highlighted and recommendations regarding future research are also provided.

Nano-based biofuel production from low-cost lignocellulose biomass: environmental sustainability and economic approach

The use of nanomaterials in biofuel production from lignocellulosic biomass offers a promising approach to simultaneously address environmental sustainability and economic viability. This review provides an overview of the environmental and economic implications of integrating nanotechnology into biofuel production from low-cost lignocellulosic biomass. In this review, we highlight the potential benefits and challenges of nano-based biofuel production. Nanomaterials provide opportunities to improve feedstock pretreatment, enzymatic hydrolysis, fermentation, and catalysis, resulting in enhanced process efficiency, lower energy consumption, and reduced environmental impact. Conducting life cycle assessments is crucial for evaluating the overall environmental footprint of biofuel production. An economic perspective that focuses on the cost implications of utilizing nanomaterials in biofuel production is also discussed. A comprehensive understanding of both environmental and economic dimensions is essential to fully harness the potential of nanomaterials in biofuel production from lignocellulosic biomass and to move towards sustainable future energy.

Exploring the Potential of Endophytic Microorganisms and Nanoparticles for Enhanced Water Remediation

Endophytic microorganisms contribute significantly to water bioremediation by enhancing pollutant degradation and supporting aquatic plant health and resilience by releasing bioactive compounds and enzymes. These microorganisms inhabit plant tissues without causing disease or any noticeable symptoms. Endophytes effectively aid in eliminating contaminants from water systems. Nanoparticles serve as potent enhancers in bioremediation processes, augmenting the efficiency of pollutant degradation by increasing surface area and bioavailability, thereby improving the efficacy and rate of remediation. Their controlled nutrient release and ability to stabilize endophytic colonization further contribute to the enhanced and sustainable elimination of contaminated environments. The synergistic effect of endophytes and nanoparticles in water remediation has been widely explored in recent studies, revealing compelling outcomes. Water pollution poses significant threats to human health, ecosystems, and economies; hence, the sixth global goal of the Sustainable Development Agenda 2030 of the United Nations aims to ensure the availability and sustainable management of water resources, recognizing their crucial importance for current and future generations. Conventional methods for addressing water pollution exhibit several limitations, including high costs, energy-intensive processes, the production of hazardous by-products, and insufficient effectiveness in mitigating emerging pollutants such as pharmaceuticals and microplastics. Noticeably, there is an inability to effectively remove various types of pollutants, thus resulting in incomplete purification cycles. Nanoparticle-enhanced water bioremediation offers an innovative, eco-friendly alternative for degrading contaminants. A growing body of research has shown that integrating endophytic microorganisms with nanoparticles for water bioremediation is a potent and viable alternative. This review examines the potential of using endophytic microorganisms and nanoparticles to enhance water remediation, exploring their combined effects and applications in water purification. The paper also provides an overview of synthetic methods for producing endophyte-nanoparticle composites to optimize their remediation capabilities in aqueous environments. The final section of the review highlights the constraints related to integrating endophytes with nanoparticles.

Synergistic algal/bacterial interaction in membrane bioreactor for detoxification of 1,2-dichloroethane-rich petroleum wastewater

The study addressed the challenge of treating petroleum industry wastewater with high concentrations of 1,2-dichloroethane (1,2-DCA) ranging from 384 to 1654 mg/L, which poses a challenge for bacterial biodegradation and algal photodegradation. To overcome this, a collaborative approach using membrane bioreactors (MBRs) that combine algae and bacteria was employed. This synergistic method effectively mitigated the toxicity of 1,2-DCA and curbed MBR fouling. Two types of MBRs were tested: one (B-MBR) used bacterial cultures and the other (AB-MBR) incorporated a mix of algal and bacterial cultures. The AB-MBR significantly contributed to 1,2-DCA removal, with algae accounting for over 20% and bacteria for approximately 49.5% of the dechlorination process. 1,2-DCA metabolites, including 2-chloroethanol, 2-chloro-acetaldehyde, 2-chloroacetic acid, and acetic acid, were partially consumed as carbon sources by algae. Operational efficiency peaked at a 12-hour hydraulic retention time (HRT) in AB-MBR, enhancing enzyme activities crucial for 1,2-DCA degradation such as dehydrogenase (DH), alcohol dehydrogenase (ADH), and acetaldehyde dehydrogenase (ALDH). The microbial diversity in AB-MBR surpassed that in B-MBR, with a notable increase in Proteobacteria, Bacteroidota, Planctomycetota, and Verrucomicrobiota. Furthermore, AB-MBR showed a significant rise in the dominance of 1,2-DCA-degrading genus such as Pseudomonas and Acinetobacter. Additionally, algal-degrading phyla (e.g., Nematoda, Rotifera, and Streptophyta) were more prevalent in AB-MBR, substantially reducing the issue of membrane fouling.

Effects of Mixtures of Engineered Nanoparticles and Cocontaminants on Anaerobic Digestion

The widespread application of nanotechnology inevitably leads to an increased release of engineered nanoparticles (ENPs) into the environment. Due to their specific physicochemical properties, ENPs may interact with other contaminants and exert combined effects on the microbial community and metabolism of anaerobic digestion (AD), an important process for organic waste reduction, stabilization, and bioenergy recovery. However, the complicated interactions between ENPs and other contaminants as well as their combined effects on AD are often overlooked. This review therefore focuses on the co-occurrence of ENPs and cocontaminants in the AD process. The key interactions between ENPs and cocontaminants and their combined influences on AD are summarized from the available literature, including the critical mechanisms and influencing factors. Some sulfides, coagulants, and chelating agents have a dramatic "detoxification" effect on the inhibition effect of ENPs on AD. However, some antibiotics and surfactants increase the inhibition of ENPs on AD. The reasons for these differences may be related to the interactive effects between ENPs and cocontaminants, changes of key enzyme activities, adenosine triphosphate (ATP) levels, reactive oxygen species (ROS) production, and microbial communities. New scientific opportunities for a better understanding of the coexistence in real world situations are converging on the scale of nanoparticles.

Polydimethyldiallylammonium chloride inhibits dark fermentative hydrogen production from waste activated sludge

Polydimethyldiallylammonium chloride (PDDA) is an excellent flocculant for wastewater purification and sludge dewatering, but whether it poses a threat to hydrogen production from waste activated sludge is not known. In this study, the effect and underlying mechanism of PDDA on the dark fermentation of sludge was investigated. The results showed that PDDA reduced cumulative hydrogen production from 3.8±0.1 to 2.4±0.1 mL/g volatile suspended solids at 40 g/kg total suspended solids. PDDA impeded the dark fermentation process by inhibiting the activity of key enzymes, presenting a stronger inhibitory effect on the hydrogen production process than the hydrogen consumption process. Additionally, PDDA inhibited Firmicutes by enriching other microorganisms, thereby impeding hydrogen production via the acetate pathway. This study deepens the understanding of the potential effects of PDDA on sludge treatment and provides a theoretical basis for alleviating the negative effects of quaternary ammonium-based cationic flocculants.

Unraveling the mechanism of increased synthesis of hydrogen from an anaerobic fermentation by zinc ferrate nanoparticles: Mesophilic and thermophilic situations comparison

In this work, ZnFe2O4 NPs were created using the pyrolysis process, and its effects on thermophilic (TF) and mesophilic (MF) fermentation were examined. In MF, the maximum hydrogen yield (MHY) occurred in the 50 mg/L ZnFe2O4 NPs group (228.01 mL/g glucose), which was 45.24% higher than that of the control group (157.01 mL/g glucose). While in TF, MHY appeared in 100 mg/L ZnFe2O4 NPs was 149.12 mL/g glucose, which was 38.83% higher than the control group (107.41 mL/g glucose). ZnFe2O4 NPs boosted the synthesis of ferredoxin, hydrogenase, and ethanol dehydrogenase by increasing the generation of butyrate in MF and acetate in TF. Moreover, Clostridium sensu stricto 5 and 10 in MF and TF rose by 9.20% and 9.40%, respectively, due to the increased abundance of predominant hydrogen-producing bacteria by ZnFe2O4 NPs.

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.

Triggering photo fermentative biohydrogen production through NiFe2O4 photo nanocatalysts with various excitation sources

The triggering effects of nickel ferrite (NiFe₂O₄) photo nanocatalysts on photo fermentative hydrogen production (PFHP), and metabolic pathways under various excitation sources (incandescent lamp, Xenon lamp, and 532 laser) have been investigated. Compare to the control group (CG) highest cumulative hydrogen volume (CHV) and the maximum hydrogen production rate (HPR) of 568.8 mL and 9.17 mL/h, respectively were achieved at a loading centration of 150 mg/L excited with an incandescent lamp. The change in metabolites with NiFe₂O₄ incorporation suggests that bacterial activity is significantly affected by photo nanocatalysts. Triggering of NiFe₂O₄ by laser excitation showed the highest HPR of 7.83 mL /h within 24 h, which greatly reduces the lag time. The microbial community investigation showed that the addition of NiFe₂O₄ photo nanocatalysts and the change of light source effectively improved the microbial community structure and increased the abundance of hydrogen-producing bacteria (HPB) which leads to enhanced hydrogen production.

Advances in the catalyzed photo-fermentative biohydrogen production through photo nanocatalysts with the potential of selectivity, and customization

Photo nanocatalyst have shownpromise in a variety of fields, including biohydrogen production where their catalytic efficiency is related to size, surface-to-volume ratio, and increasing the number of atoms on the surface. They can harvest solar light to create electron-hole pairs which is the key mechanism to define its catalytic efficiency, thus requiring suitable excitation wavelength, band energy, and crystal imperfections. In this review, a discussion on the role of photo nanocatalysts to catalyze biohydrogen production has been carried out. Photo nanocatalysts feature a large bandgap, andhigh defect concentration, thus having the ability to be tuned for their characteristics. Customization of the photo nanocatalyst has been addressed. Mechanism of the photo nanocatalysts in catalyzing biohydrogen has been discussed. Limiting factors of photo nanocatalysts were highlighted and several recommendations have been made to enhance the effective utilization of these photo nanocatalysts to enhance photo-fermentative biohydrogen production from biomass wastes.

Application of a novel biological-nanoparticle pretreatment to Oscillatoria acuminata biomass and coculture dark fermentation for improving hydrogen production

BACKGROUND

Energy is the basis and assurance for a world's stable development; however, as traditional non-renewable energy sources deplete, the development and study of renewable clean energy have emerged. Using microalgae as a carbon source for anaerobic bacteria to generate biohydrogen is a clean energy generation system that both local and global peers see as promising.

RESULTS

Klebsiella pneumonia, Enterobacter cloacae, and their coculture were used to synthesize biohydrogen using Oscillatoria acuminata biomass via dark fermentation. The total carbohydrate content in O. acuminata was 237.39 mg/L. To enhance the content of fermentable reducing sugars, thermochemical, biological, and biological with magnesium zinc ferrite nanoparticles (Mg-Zn Fe₂O₄-NPs) pretreatments were applied. Crude hydrolytic enzymes extracted from Trichoderma harzianum of biological pretreatment were enhanced by Mg-Zn Fe₂O₄-NPs and significantly increased reducing sugars (230.48 mg/g) four times than thermochemical pretreatment (45.34 mg/g). K. pneumonia demonstrated a greater accumulated hydrogen level (1022 mLH₂/L) than E. cloacae (813 mLH₂/L), while their coculture showed superior results (1520 mLH₂/L) and shortened the production time to 48 h instead of 72 h in single culture pretreatments. Biological pretreatment + Mg-Zn Fe₂O₄ NPs using coculture significantly stimulated hydrogen yield (3254 mLH₂/L), hydrogen efficiency)216.9 mL H₂/g reducing sugar( and hydrogen production rate (67.7 mL/L/h) to the maximum among all pretreatments.

CONCLUSION

These results confirm the effectiveness of biological treatments + Mg-Zn Fe₂O₄-NPs and coculture dark fermentation in upregulating biohydrogen production.

Wastewater-derived biohydrogen: Critical analysis of related enzymatic processes at the research and large scales

Organic-rich wastewater is a feasible feedstock for biohydrogen production. Numerous review on the performance of microorganisms and the diversity of their communities during a biohydrogen process were published. However, there is still no in-depth overview of enzymes for biohydrogen production from wastewater and their scale-up applications. This review aims at providing an insightful exploration of critical discussion in terms of: (i) the roles and applications of enzymes in wastewater-based biohydrogen fermentation; (ii) systematical introduction to the enzymatic processes of photo fermentation and dark fermentation; (iii) parameters that affect enzymatic performances and measures for enzyme activity/ability enhancement; (iv) biohydrogen production bioreactors; as well as (v) enzymatic biohydrogen production systems and their larger scales application. Furthermore, to assess the best applications of enzymes in biohydrogen production from wastewater, existing problems and feasible future studies on the development of low-cost enzyme production methods and immobilized enzymes, the construction of multiple enzyme cooperation systems, the study of biohydrogen production mechanisms, more effective bioreactor exploration, larger scales enzymatic biohydrogen production, and the enhancement of enzyme activity or ability are also addressed.

Thermophilic biohydrogen production strategy using agro industrial wastes: Current update, challenges, and sustainable solutions

Continuously increasing wastes management issues and the high demand of fuels to fulfill the current societal requirements is not satisfactory. In addition, severe environmental pollution caused by generated wastes and the massive consumption of fossil fuels are the main causes of global warming. In this scenario, production of hydrogen from organic wastes is a potential and one of the most feasible alternatives to resolve these issues. However, sensitivity of H₂ production at higher temperature and lack of potential substrates are the main issues which are strongly associated with such kinds of biofuels. Therefore, the present review is targeted towards the evaluation and enhancement of thermophilic biohydrogen production using organic, cellulosic wastes as promising bioresources. This review discusses about the current status, development in the area of thermophilic biohydrogen production wherein organic wastes as key substrate are being employed. The combinations of suitable organic and cellulose rich substrates, thermo-tolerant microbes, high enzymes stability may support to enhance the biohydrogen production, significantly. Further, various factors which may significantly contribute to enhance biohydrogen production have been discussed thoroughly in reference to the thermophilic biohydrogen production technology. Additionally, existing obstacles such as unfavorable thermophilic biohydrogen pathways, inefficiency of thermophilic microbiomes, genetic modifications, enzymes stability have been discussed in context to the possible limitations of thermophilic biohydrogen production strategy. Structural and functional microbiome analysis, fermentation pathway modifications via genetic engineering and the application of nanotechnology to enhance the thermophilic biohydrogen production have been discussed as the future prospective.

Nanomaterials for biogas augmentation towards renewable and sustainable energy production: A critical review

Nanotechnology is considered one of the most significant advancements in science and technology over the last few decades. However, the contemporary use of nanomaterials in bioenergy production is very deficient. This study evaluates the application of nanomaterials for biogas production from different kinds of waste. A state-of-the-art comprehensive review is carried out to elaborate on the deployment of different categories of nano-additives (metal oxides, zero-valent metals, various compounds, carbon-based nanomaterials, nano-composites, and nano-ash) in several kinds of biodegradable waste, including cattle manure, wastewater sludge, municipal solid waste, lake sediments, and sanitary landfills. This study discusses the pros and cons of nano-additives on biogas production from the anaerobic digestion process. Several all-inclusive tables are presented to appraise the literature on different nanomaterials used for biogas production from biomass. Future perspectives to increase biogas production via nano-additives are presented, and the conclusion is drawn on the productivity of biogas based on various nanomaterials. A qualitative review of relevant literature published in the last 50 years is conducted using the bibliometric technique for the first time in literature. About 14,000 research articles are included in this analysis, indexed on the Web of Science. The analysis revealed that the last decade (2010–20) was the golden era for biogas literature, as 84.4% of total publications were published in this timeline. Moreover, it was observed that nanomaterials had revolutionized the field of anaerobic digestion, methane production, and waste activated sludge; and are currently the central pivot of the research community. The toxicity of nanomaterials adversely affects anaerobic bacteria; therefore, using bioactive nanomaterials is emerging as the best alternative. Conducting optimization studies by varying substrate and nanomaterials’ size, concentration and shape is still a field. Furthermore, collecting and disposing nanomaterials at the end of the anaerobic process is a critical environmental challenge to technology implementation that needs to be addressed before the nanomaterials assisted anaerobic process could pave its path to the large-scale industrial sector.

Enhancing biohydrogen production from lignocellulosic biomass of Paulownia waste by charge facilitation in Zn doped SnO2 nanocatalysts

The goal of this research was to study the role of excess charges in regulating biohydrogen production from Paulownia. The excess charges were generated through charge compensation in SnO₂ nanocatalysts by Zn doping. The maximum hydrogen yield of 335 mL was observed at 8%Zn doping with a concentration of 150 mg/L, 47% higher as compared to standard sample. It was observed that the hydrogen production rate increased with Zn doping and the highest value (77 mL/h) was observed for 8%Zn at 24 h. The decrease in the total amount of byproducts (2.52 g/L from 4.28 g/L) at 8% Zn indicates an increase in bacterial metabolism. The lowest value of oxidation-reduction potential (-525 mV) at 24 h for 8%Zn confirms that Zn doping provides excessive electrons to the fermentative medium which helps the bacteria to transfer electrons faster during the redox reaction, hence, enhancing the enzymatic process and eventually hydrogen production.

Novel strategies towards efficient molecular biohydrogen production by dark fermentative mechanism: present progress and future perspective

In the scenario of alarming increase in greenhouse and toxic gas emissions from the burning of conventional fuels, it is high time that the population drifts towards alternative fuel usage to obviate pollution. Hydrogen is an environment-friendly biofuel with high energy content. Several production methods exist to produce hydrogen, but the least energy intensive processes are the fermentative biohydrogen techniques. Dark fermentative biohydrogen production (DFBHP) is a value-added, less energy-consuming process to generate biohydrogen. In this process, biohydrogen can be produced from sugars as well as complex substrates that are generally considered as organic waste. Yet, the process is constrained by many factors such as low hydrogen yield, incomplete conversion of substrates, accumulation of volatile fatty acids which lead to the drop of the system pH resulting in hindered growth and hydrogen production by the bacteria. To circumvent these drawbacks, researchers have come up with several strategies that improve the yield of DFBHP process. These strategies can be classified as preliminary methodologies concerned with the process optimization and the latter that deals with pretreatment of substrate and seed sludge, bioaugmentation, co-culture of bacteria, supplementation of additives, bioreactor design considerations, metabolic engineering, nanotechnology, immobilization of bacteria, etc. This review sums up some of the improvement techniques that profoundly enhance the biohydrogen productivity in a DFBHP process.

Sustainable microalgal biomass valorization to bioenergy: Key challenges and future perspectives

The global trend is shifting toward circular economy systems. It is a sustainable environmental approach that sustains economic growth from the use of resources while minimizing environmental impacts. The multiple industrial use of microalgal biomass has received great attention due to its high content of essential nutrients and elements. Nevertheless, low biomass productivity, unbalanced carbon to nitrogen (C/N) ratio, resistant cellular constituents, and the high cost of microalgal harvesting represent the major obstacles for valorization of algal biomass. In recent years, microalgae biomass has been a candidate as a potential feedstock for different bioenergy generation processes with simultaneous treating wastewater and CO₂ capture. An overview of the appealing features and needed advancements is urgently essential for microalgae-derived bioenergy generation. The present review provides a timely outlook and evaluation of biomethane production from microalgal biomass and related challenges. Moreover, the biogas recovery potential from microalgal biomass through different pretreatments and synergistic anaerobic co-digestion (AcoD) with other biowastes are evaluated. In addition, the removal of micropollutants and heavy metals by microalgal cells via adsorption and bioaccumulation in their biomass is discussed. Herein, a comprehensive review is presented about a successive high-throughput for anaerobic digestion (AD) of the microalgal biomass in order to achieve for sustainable energy source. Lastly, the valorization of the digestate from AD of microalgae for agricultural reuse is highlighted.

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.

Advanced strategies for enhancing dark fermentative biohydrogen production from biowaste towards sustainable environment

As a clean energy carrier, hydrogen is a promising alternative to fossil fuel so as the global growing energy demand can be met. Currently, producing hydrogen from biowastes through fermentation has attracted much attention due to its multiple advantages of biowastes management and valuable energy generation. Nevertheless, conventional dark fermentation (DF) processes are still hindered by the low biohydrogen yields and challenges of biohydrogen purification, which limit their commercialization. In recent years, researchers have focused on various advanced strategies for enhancing biohydrogen yields, such as screening of super hydrogen-producing bacteria, genetic engineering, cell immobilization, nanomaterials utilization, bioreactors modification, and combination of different processes. This paper critically reviews by discussing the above stated technologies employed in DF, respectively, to improve biohydrogen generation and stating challenges and future perspectives on biowaste-based biohydrogen production.

Bioaugmentation combined with biochar to enhance thermophilic hydrogen production from sugarcane bagasse

In this study, Thermoanaerobacterium thermosaccharolyticum MJ2 and biochar were used to enhance thermophilic hydrogen production from sugarcane bagasse. MJ2 bioaugmentation notably increased the hydrogen production by 95.31%, which was further significantly improved by 158.10% by adding biochar. The addition of biochar promoted the degradation of substrate, improved the activities of hydrogenase and electron transfer system, and stimulated microbial growth and metabolism. Microbial community analysis showed that the relative abundance of Thermoanaerobacterium was significantly increased by bioaugmentation and further enriched by biochar. PICRUSt analysis showed that MJ2 combined with biochar promoted metabolic pathways related to substrate degradation and microbial metabolism. This study provides a novel enhancement method for hydrogen production of the cellulolytic microbial consortium by exogenous hydrogen-producing microorganism combined with biochar and deepens the understanding of its functional mechanism.

Graphene enhanced detoxification of wastewater rich 4-nitrophenol in multistage anaerobic reactor followed by baffled high-rate algal pond

The presence of 4-nitrophenol (4-NP) in the wastewater industry causes toxicity and inhibition of the anaerobic degrading bacteria. The anaerobes in the multistage anaerobic reactor were loaded by 30.0 mg/gVS Graphene nanoparticles (MAR-G_n) as an electron acceptor to detoxify wastewater industry. The half maximal inhibitory concentration (IC₅₀) was reduced from 455 ± 22.5 to 135 ± 12.7 μg Gallic acid equivalent/mL at 4-NP loading rate of 47.9 g/m³d. Furthermore, 4-NP was decreased by a value of 83.7 ± 4.9% in MAR-G_n compared to 65.6 ± 4.8% in control MAR. The 4-aminophenol (4-AP) recovery was accounted for 44.8% in the MAR-G_n at an average oxidation-reduction potential (ORP) of - 167.3 ± 21.2 mV. The remaining portions of 4-NP and 4-AP in the MAR-G_n effluent were efficiently removed by baffled high rate algal pond (BHRAP), resulting in overall removal efficiency of 91.6 ± 6.3 and 92.3 ± 4.6%, respectively. The Methanosaeta (52.9%) and Methanosphaerula (10.9%) were dominant species in MAR-G_n for reduction of 4-NP into 4-AP. Moreover, Chlorophyta cells (Chlorella vulgaris, Scenedesmus obliquus, Scenedesmus quadricauda and Ulothrix subtilissima were abundant in the BHRAP for complete degradation of 4-NP and 4-AP.

Function of Fe(III)-minerals in the enhancement of anammox performance exploiting integrated network and metagenomics analyses

Iron is a recognized physiological requirement for microorganisms but, for anaerobic ammonium oxidation (anammox) bacteria, its role extends well beyond that of a nutritional necessity. In this study, the function of two typical Fe(III)-minerals (ferrihydrite and magnetite) in anammox processes was evaluated in the absence/presence of Fe(II) by integrated network and metagenomics analyses. Results showed that Fe-(III) minerals addition increased the activity of cellular processes and pathways associated with granule formation, enabling the peak values of particle size to increase by 144% and 115%, respectively. Notably, ferrihydrite (5 mM) enhanced nitrogen removal by 4.8% and 4.1%, respectively, in the short-term and long-term absence of Fe(II). Ferrihydrite also promoted the retention of anammox bacteria affiliated with phylum Planctomycetes in the reactor, contributing to an 11% higher abundance with ferrihydrite amendment when compared with the control (without iron additions) in the short-term absence of Fe(II). Network-based analyses revealed that ferrihydrite facilitated the microbial community to form densely clustered and complex topologies to improve resistance to environmental disturbance (i.e., Fe(II) deficiency), and effectively increased the underlying cooperation and facilitation in the community. Metagenomic analysis revealed that there was limited promotion of anammox central metabolism by the extra addition of Fe(III)-minerals in the presence of Fe(II), highlighting the poor utilization of Fe(III)-minerals by anammox bacteria under Fe(II) sufficiency. This study deepens our understanding of the function of Fe(III)-minerals in anammox systems at the community and functional level, and provides a fundamental basis for developing Fe-based anammox enhancement technologies.

Inhibition of wastewater pollutants on the anammox process: A review

The anaerobic ammonium oxidation (anammox) process has been recognized as an efficient nitrogen removal technology. However, anammox bacteria are susceptible to surrounding environments and different pollutants, which limits the extensive application of the anammox process worldwide. Numerous researchers investigate the effects of various pollutants on the anammox process or bacteria, and related findings have also been reviewed with the focused on their inhibitory effects on process performance and microbial community. This review systemically summarized the recent advances in the inhibition, mechanism and recovery process of traditional and emerging pollutants on the anammox process over a decade, such as organics, metals, antibiotics, nanoparticles, etc. Generally, low-concentration pollutants exhibited a promotion on the anammox activity, while high-concentration pollutants showed inhibitory effects. The inhibitory threshold concentration of different pollutants varied. The combined effects of multipollutant also attracts more attentions, including synergistic, antagonistic and independent effects. Additionally, remaining problems and research needs are further proposed. This review provides a foundation for future research on the inhibition in anammox process, and promotes the proper operation of anammox processes treating different types of wastewaters.

Distribution patterns of functional microbial community in anaerobic digesters under different operational circumstances: A review

Anaerobic digestion (AD) processes are promising to effectively recover resources from organic wastes or wastewater. As a microbial-driven process, the functional anaerobic species played critical roles in AD. However, the lack of effective understanding of the correlations of varying microbial communities with different operational factors hinders the microbial regulation to improve the AD performance. In this paper, the main anaerobic functional microorganisms involved in different stages of AD processes were first demonstrated. Then, the response of anaerobic microbial community to different operating parameters, exogenous interfering substances and digestion substrates, as well as the digestion efficiency, were discussed. Finally, the research gaps and future directions on the understanding of functional microorganisms in AD were proposed. This review provides insightful knowledge of distribution patterns of functional microbial community in anaerobic digesters, and gives critical guidance to regulate and enrich specific functional microorganisms to accumulate certain AD products.

Comparison of mesophilic and thermophilic dark fermentation with nickel ferrite nanoparticles supplementation for biohydrogen production

In this work, nickel ferrite nanoparticles (NiFe₂O₄ NPs) was prepared to improve hydrogen (H₂) production by dark fermentation. Moderate amounts (50-200 mg/L) promoted H₂ generation, while excess NiFe₂O₄ NPs (over 400 mg/L) lowered H₂ productivity. The highest H₂ yields of 222 and 130 mL/g glucose were obtained in the 100 mg/L (37 °C) and 200 mg/L NiFe₂O₄ NPs (55 °C) groups, respectively, and the values were 38.6% and 28.3% higher than those in the control groups (37 °C and 55 °C). Soluble metabolites showed that NiFe₂O₄ NPs enhanced the butyrate pathway, corresponding to the increased abundance of Clostridium butyricum in mesophilic fermentation. The endocytosis of NiFe₂O₄ NPs indicated that the released iron and nickel favored ferredoxin and hydrogenase synthesis and activity and that NiFe₂O₄ NPs could act as carriers in intracellular electron transfer. The NPs also optimized microbial community structure and increased the levels of extracellular polymeric substances, leading to increased H₂ production.

Effect of zinc ion on photo-fermentative hydrogen production performance, kinetics and electronic distribution in biohydrogen production by HAU-M1

The aim of this work was to study the characteristics, kinetics and electronic distribution of photo-fermentation hydrogen production (PFHP) with Zn²⁺ addition then gave the main results that the addition of Zn²⁺ can effectively improve hydrogen production with an increasing of 1-5 mg/L Zn²⁺ concentration. The maximum hydrogen yield of 592 ± 13 mL and shortest lag time of 4.67 h were obtained at 2 mg/L Zn²⁺. 26.42% of the substrate energy was diverted to H₂. Modified Gompertz and Hane-Levenspiel models were applied to evaluate the effect of Zn²⁺ on PFHP by mixed bacteria HAU-M1, the constants n and m obtained by fitting models were 14.97 and 58.79, respectively, indicating the fermentation system was noncompetitive inhibition, the predicted critical Zn²⁺ concentration was 40.83 mg/L.

Mechanisms of enhanced hydrogen production from sewage sludge by ferrous ion: Insights into functional genes and metabolic pathways

Hydrogen production from sewage sludge was studied in the presence of Fe²⁺. The results showed that the highest cumulative hydrogen production of 26 mL/100 mL was achieved with 600 mg/L Fe²⁺ supplementation, which was 2 times of the control test. In depth analysis of organics in liquid phase revealed that Fe²⁺ addition promoted sludge disintegration and protein degradation during fermentation process. Functions prediction by PICRUSt analysis indicated the effect of Fe²⁺ on microbial metabolism and functional genes expression. The results showed that the expression of hydrogen-producing functions, like ferredoxin hydrogenase and formate dehydrogenase was activated by Fe²⁺ supplementation, while the hydrogen-consuming metabolism, like methane metabolism and homoacetogenic metabolism was inhibited. Furthermore, Fe²⁺ addition could stimulate organics utilization. This study explored the effect of Fe²⁺ on functional genes abundance, revealing the mechanisms of enhanced hydrogen production by Fe²⁺ from the perspective of microbial metabolism.

Unraveling the capability of graphene nanosheets and γ-Fe2O3 nanoparticles to stimulate anammox granular sludge

In this study, we investigated the potentials of nanomaterials to enhance anaerobic ammonium oxidation (anammox) process, in terms of nitrogen removal, microbial enrichment, and activity of key enzymes. Graphene nanosheets (GNs) and γ-Fe₂O₃ nanoparticles (NPs) were selected due to their catalytic functions as conductive material and electron shuttles, respectively. The obtained results revealed that the optimum dosage of GNs (10 mg/L) boosted the nitrogen removal rate (NRR) by 46 ± 3.1% compared to the control, with maximum NH₄⁺-N and NO₂^--N removal of 86.5 ± 2.7% and 97.1 ± 0.5%, respectively. Moreover, hydrazine dehydrogenase (HDH) enzyme activity was augmented by 1.1-fold when using 10 mg/L GNs. The presence of GNs promoted the anammox granulation via enhancement of hydrophobic interaction of extracellular polymeric substances (EPS). Regarding the use of γ-Fe₂O₃ NPs, 100 mg/L dose increased NRR by 55 ± 3.8%; however, no contribution to HDH enzyme activity and a decrease in EPS compositions were observed. Given that the abiotic use of γ-Fe₂O₃ NPs further resulted in high adsorption efficiency (~92%), we conclude that the observed promotion due to γ-Fe₂O₃ NPs was mainly abiotic. Moreover, the 16S rRNA analysis revealed that the relative abundance of genus C. Jettenia (anammox related bacteria) increased from 11.9% to 12.3% when using 10 mg/L GNs, while declined to 8.3% at 100 mg/L γ-Fe₂O₃ NPs. Eventually, nanomaterials could stimulate the efficiency of anammox process, and this promotion and associated mechanism depend on their dose and composition.

Microbial Nanotechnology for Bioremediation of Industrial Wastewater

Pollutant removal from industrial effluents is a big challenge for industries. These pollutants pose a great risk to the environment. Nanotechnology can reduce the expenditure made by industries to mitigate these pollutants through the production of eco-friendly nanomaterials. Nanomaterials are gaining attention due to their enhanced physical, chemical, and mechanical properties. Using microorganisms in the production of nanoparticles provides an even greater boost to green biotechnology as an emerging field of nanotechnology for sustainable production and cost reduction. In this mini review, efforts are made to discuss the various aspects of industrial effluent bioremediation through microbial nanotechnology integration. The use of enzymes with nanotechnology has produced higher activity and reusability of enzymes. This mini review also provides an insight into the advantages of the use of nanotechnology as compared to conventional practices in these areas.

Mg(1-x)CuxFe2O4 superparamagnetic nanoparticles as nano-radiosensitizer agents in radiotherapy of MCF-7 human breast cancer cells

Magnesium-doped copper spinel ferrite superparamagnetic nanoparticles (Mg_(1-x)Cu_xFe₂O₄ SPMNPs, 0.2 ≤ x ≤ 0.8) were successfully synthesized by a hydrothermal method. The cytotoxicity effects and cell viability of MCF-7 on human breast cancer cells pre and post exposure to the Mg_1-xCu_xFe₂O₄ SPMNPs at different concentrations of 0.1, 1, 10 and 100 μg ml^-1 under radiotherapy were studied by MTT (3-[4,5-dimethylthiazol-2-yl]-2, 5-diphenyltetrazolium bromide) assay. Here, x-ray diffraction, scanning electron microscopy, atomic force microscopy, UV-visible spectrophotometry, Fourier transform infrared spectroscopy and vibrating-sample magnetometry were evaluated for the crystal structure, morphology, optical and magnetic property of the Mg_(1-x)Cu_xFe₂O₄ SPMNPs. The results showed that the Mg_(1-x)Cu_xFe₂O₄ SPMNPs all at x values had no significant cytotoxicity at concentrations of 0.1,1 and 10 μg ml^-1, but were enhanced by increasing of Cu content. Furthermore, cell destruction of MCF-7 human breast cancer cells post exposure to Mg_(1-x)Cu_xFe₂O₄ SPMNPs under x-ray irradiation was enhanced by increasing the Cu content and concentration. Superparamagnetic properties of the Mg_(1-x)Cu_xFe₂O₄ SPMNPs cause their localization and elimination, by only an external magnetic field. In conclusion, the Mg_(1-x)Cu_xFe₂O₄ SPMNPs with optimum values of x = 0.2 (10 μg ml^-1) and x = 0.6 (1 μg ml^-1) can be considered as a nano-radiosensitizer because of the synergistic treatment effect without cytotoxicity on the MCF-7 cells.

Application of magnetic multi-wall carbon nanotube composite into fermentative treatment process of ultrasonicated waste activated sludge

This study investigated the effect of supplementing nano-sized magnetite (Fe3O4 NPs), multi-wall carbon nanotubes (MWCNTs) and Fe3O4-MWCNTs composite on bioconversion of waste activated sludge to hydrogen, in batch systems. Substrate degradation efficiency (SDE) increased from 28 ± 3.8 (control) to 49 ± 5.9, 46 ± 4.8 and 52 ± 6.3% at optimal doses of 200 (Fe3O4 NPs), 300 (MWCNTs) and 200 mg/L (Fe3O4-MWCNTs), respectively. Based on dissolved iron and sludge conductivity measurements, superior SDE in Fe3O4 and MWCNTs batches have been assigned to enhanced dissimilatory iron reduction (DIR) and high sludge conductivity, respectively. Combined impacts for sludge conductivity and DIR were revealed in Fe3O4-MWCNTs system. In 200 mg/L (Fe3O4-MWCNTs) batch, catalytic activities of hydrogenase, protease and α-amylase peaked to 596, 146 and 131% (relative to control), respectively; as well as, highest volumetric H2 production of 607 ± 59 mL/L was acquired. Performance deteriorations at high concentrations of nanoparticles were caused by cellular oxidative stress induced by generated reactive oxygen species.

Effects of biochar on ethanol-type and butyrate-type fermentative hydrogen productions

Low hydrogen yield was the bottleneck of dark fermentative hydrogen production. To solve this problem, the effects of rice straw-derived biochar on hydrogen production was investigated in different fermentation types. Ethanol-type and butyrate-type fermentations, two dominant types of dark fermentation, were carried out in batch fermentations with different concentrations of biochar. The results revealed that 3 g/L was the best concentration for both types of fermentations. Hydrogen production increased by 118.4% and 79.6% in ethanol-type and butyrate-type fermentations, respectively. The maximal hydrogen yields of ethanol-type and butyrate-type fermentations were 1.34 and 2.36 mol/mol-glucose, respectively. The addition of biochar buffered the broth pH, lowered the redox potential, and released mineral nutrients. The porosity of biochar boosted cell immobilization and thus improved the H2 productivity. This study demonstrated the enhancement effect of biochar on ethanol- and butyrate-type fermentative hydrogen productions, and enhanced the understanding of the functional mechanisms of biochar.

Robustness of anaerobes exposed to cyanuric acid contaminated wastewater and achieving efficient removal via optimized co-digestion scheme

The impact of various industrial pollutants on anaerobes and the biodegradation potentials need much emphasis. This study aims to investigate the response of anaerobic microbial systems to cyanuric acid (CA) exposure; CA is toxic and possible carcinogen. First, the long-term exposure of mixed culture bacteria (i.e., municipal sludge) to low-strength wastewater containing 20 mg/L CA was conducted in an up-flow anaerobic staged reactor. Stable performance and sludge granulation were observed, and the microbial community structure showed the progression of genus Acinetobacter known as CA degrader. Second, batch-mode experiment was performed to examine the CA biodegradability at higher doses (up to 250 mg/L of CA) in the absence and presence of glucose as a co-substrate; response surface-based optimization was used to design this experiment and to estimate the optimum CA-glucose combination. CA removal of 77-98% was achieved when CA was co-digested with glucose (250-1,000 mg/L), after 7 days-incubation at temperature of 37 °C, compared to 34% when CA was solely digested. Further, the obtained methane yield dropped when CA exceeded over 125 mg/L, though the deterioration was mitigated by addition of higher concentration of glucose. Overall, we conclude that CA is efficiently degraded under anaerobic conditions when being co-digested with readily assimilable substrate.

Synergistic effects of co-trace elements on anaerobic co-digestion of food waste and sewage sludge at high organic load

Trace elements play an indispensable role in stabilizing the performance of anaerobic co-digestion (Co-AD) of food waste (FW) and sewage sludge (SS) at greater organic load (OL). The results of high organic-loaded reactors showed that the stability of the system failed due to the buildup of volatile fatty acid (VFA) and ammonia. At the OL of 6.5 g/L, the stability of the system failed due to the buildup of propionic acid. The optimum dosage of Fe (5000 mg/L), Ni (200 mg/L), Zn (320 mg/L), and Mo (2.2 mg/L) was experimentally determined and added to reduce the inhibition condition. Consequently, the propionic acid concentration, which was above 1500 mg/L reduced to under 500 mg/L during Co-AD. Hence, higher biogas production, and biodegradability of 236 ± 23 mL/g VS, and 41.75%, respectively, were obtained. Increasing OL (9.5 g/L), the stability of the system was hindered due to only the buildup of ammonia (up to 188 ± 6 NH₃-N mg/L). Therefore, the trace elements of Cu (250 mg/L) and Co (3 mg/L) were experimentally determined and added into the Co-AD to diminish ammonia accumulation and process instability. The experimental results showed that at OL of 14 g/L, biogas production, low ammonia concentration and biodegradability of 332 ± 21 mL/g VS, and 70 NH3-N mg/L, and 57.89%, respectively, were achieved. However, the performance and stability of the system failed at the higher OL due to the more increased ammonia and VFA concentration, and the greater dosages of trace elements did not enhance the process stability.

Industrial wastewater to biohydrogen: Possibilities towards successful biorefinery route

The aim of this review is to summarize the modern developments and enhancement strategies reported for improving the biorefinery route of industrial wastewater to biohydrogen. Recent developments towards biohydrogen production chiefly involves culture enrichment, pretreatment of biocatalysts, co culture fermentation, metabolic and genetic engineering, ecobiotechnological approaches and the coupling process of biohydrogen. In addition, an overview of dark fermentation, pathways involved, microbes involved in biohydrogen production, industrial wastewater as substrate have been focused. The utilization of organic residuals of dark fermentation for subsequent value added products are highlighted. More apparently, the two stage coupling process and its possibilities towards biorefinery has been reviewed comprehensively. Moreover, comparative energy and economic aspects of biohydrogen production from industrial wastewater and its prospects towards pilot scale applications are also spotlighted. Though all the enhancement strategies have both benefits and disadvantages, coupling process is considered as the most successful biorefinery route for biohydrogen production.

Paperboard mill wastewater treatment via combined dark and LED-mediated fermentation in the absence of external chemical addition

Paperboard mill wastewater (PMWW) was treated using two subsequent dark and photo up-flow intermitted stirring tank reactors (UISTRs) under different hydraulic retention times (HRTs) without external chemical use. HRT of 12 h revealed the maximum overall H₂ productivity of 1394.1(±70.6) mL/L/d with contents of 48.9(±2.5) and 47.4(±1.4)% for dark- and photo-processes, respectively. Overall substrate removal efficiency (SDE) of 58.9(±4.5)% was registered at HRT o 12 h. High H₂ productivity was ascribed to fermentation type occurred at dark reactor, since acetate and butyrate accounted for 70.9% of volatile fatty acids. Besides, pH and carbon to nitrogen ratio of dark reactor's effluent at HRT = 12 h were 5.5(±0.1) and 30.0(±2.5), respectively which are the optimum levels for photo fermentation process. Moreover, energetic and economic analyses emphasized on the superiority of 12 h-HRT, where net gain energy, daily saving and payback period accounted for 1319.5 kWh/d, 148.7 $/d and 9.8 years, respectively.

Regulating acidogenesis and methanogenesis for the separated bio-generation of hydrogen and methane from saline-to-hypersaline industrial wastewater

Given the limitations of acidogens and methanogens activities under saline environments, this work aims to optimize the main operational parameters affecting hydrogen and methane production from saline-to-hypersaline wastewater containing mono-ethylene glycol (MEG). MEG is the main contaminant in several saline industrial effluents. Anaerobic baffled reactor (ABR), as a multi-stage system, was used at different temperatures (i.e., 19-31 °C [ambient] and 35 °C), organic loading rates (OLRs) of 0.6-2.2 gCOD/L/d, and salinity of 5-35 gNaCl/L. Mesophilic conditions of 35 °C substantially promoted MEG biodegradability (92-98%) and hydrogen/methane productivity, even at elevated salinity. Hydrogen yield (HY) and methane yield (MY) peaked to 258 and 140 mL/gCOD_add, respectively, at OLR 0.64 gCOD/L/d and salinity up to 20-25 gNaCl/L. An immobilized sludge ABR (ISABR), packed with polyurethane media, was further compared with classical ABR, resulting in 1.8-fold higher MY, at 35 gNaCl/L. Microbial analysis showed that introducing attached growth system (ISABR) substantially promoted methanogens abundance, which was dominated by genus Methanosarcina. Among bacterial genera, Acetobacterium was dominant, particularly in 1^st compartment, representing MEG-degrading/salt-tolerant genus. At high salinity up to 35 gNaCl/L, the multi-phase and attached growth configuration can efficiently reduce the induced salt stress, particularly on methanogens, towards balanced and separated acidogenesis/methanogenesis. Overall, producing hydrogen and methane from anaerobic treatment of MEG-based saline wastewater is feasible at optimized parameters and configuration.

Nutrients balance for hydrogen potential upgrading from fruit and vegetable peels via fermentation process

The sole, dual and multi-fermentations of fruit and vegetable peels (FVPs) were investigated in order to balance nutrition hierarchy for maximizing hydrogen potential via Batch experiments. The highest volumetric hydrogen production of 2.55 ± 0.07 L/L and hydrogen content of 64.7 ± 3.7% were registered for multi-fermentation of M-PTBO (25% pea +25% tomato + 25% banana +25% orange). These values outperformed sole and dual fermentation. The multi-fermentation of FVPs provided sufficient nutrients and trace elements for anaerobes, where C/N and C/P ratios were at levels of 24.7 ± 0.2 and 113.2 ± 9.4, respectively. In specific, harmonizing of macro and micro-nutrients remarkably maximized activities of amylase, protease and lipase to 4.23 ± 0.42, 0.035 ± 0.002 and 0.31 ± 0.02 U/mL, respectively, as well as, substantially incremented counts of Clostridium and Enterobacter sp. up to 5.81 ± 0.23 × 10⁵ and 2.17 ± 0.09 × 10⁶ cfu/mL, respectively. Furthermore, multi-fermentation of M-PTBO achieved the maximum net energy gain and profit of 1.82 kJ/g_feedstock and 4.11 $/kg_feedstock, respectively. Nutrients balance significantly develops bacterial activity in terms of hydrogen productivity, anaerobes reproduction, enzyme activities and soluble metabolites. As a result, overall fermentation bioprocess performance was improved.