Augmented biohydrogen production from rice mill wastewater through nano-metal oxides assisted dark fermentation

Kinetic models in environmental biotechnological processes: Origin, derivation and applications

Environmental biotechnological processes encompass the utilization of microorganisms for various applications, such as wastewater treatment, bioproduct formation, and waste management. Kinetic modeling plays a crucial role in optimizing and designing these processes. This paper provides a comprehensive understanding of the kinetic models used in environmental biotechnological processes, focusing on the kinetics of microbial growth, bioproduct formation, substrate consumption, and pollutant degradation. Firstly, by investigating their origins, derivations, and development, we clarified the theoretical basis and practical implications of key models, such as the Gompertz, Logistic, first-order, Cone, Monod, Andrews, Shepherd, Stover-Kincannon, Grau, and Arrhenius models. Secondly, we highlighted the extension of the models from microbial growth kinetics to bioproduction kinetics, showcasing their versatility and applicability across different domains. In addition, critical parameters within the models were discussed, providing insights into their importance for characterizing and predicting biotechnological processes. Overall, this paper will deepen the understanding of biotechnological kinetic processes and lay the foundation for their practical applications.

Mechanism of carbonized humic acid and magnesium aluminum-layered double hydroxide promoting biohydrogen generation

Dark fermentation (DF) is prone to low hydrogen (H2) yield. In this work, magnesium aluminum-layered double hydroxide and carbonized humic acid (MgAl-LDH/CHA) was synthesized by co-precipitation to reveal the mechanism in rising bioH2 generation. The results indicated that MgAl-LDH released Mg and Al ions slowly in DF system, improving the activity of H2-producing microbes (HPM) for more H2. The H2 yield increased from 169.3 mL/g glucose to 244.9 mL/g glucose, which was 44.7 % higher than that for the control yield. MgAl-LDH/CHA increased Proteobacteria content from 30.9 % to 43.7 %, making it form a complex microbial community and participate in DF metabolism with Firmicutes and other microbes together. Besides, MgAl-LDH/CHA could serve as an electron shuttle that likely effectively promotes electron transfer in DF, significantly reduced the energy requirements of HPM, thus raising metabolic activity. It provides direction for the multi-element composite applied in DF system.

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.

Improving Biohydrogen Production by Dark Fermentation of Milk Processing Wastewater by Physicochemical and Enzymatic Pretreatments

Biohydrogen is considered an alternative energy reserve. Dark fermentation is one of the important green hydrogen production techniques that utilizes organic waste as raw material. It is a promising bioconversion, easy, not expensive, and cost-effective process. Milk processing wastewater (MPWW) is an organic effluent generated in large volumes on a daily basis and disposed directly into the environment. In this research, the study of biochemical hydrogen potential (BHP) test of MPWW was evaluated and used as substrate (S). A waste sludge was used as an inoculum (I) and source of bacteria. Both substrate and inoculum were analyzed and the study was based mainly on the ratio of volatile solids (VS) of inoculum and substrate subsequently, which was noted as I/S. Different substrate pretreatments were performed: ultrasonic, thermal, chemical, and enzymatic hydrolysis. The I/S ratio impact was investigated and evaluated the hydrogen production improvement. Modified Gompertz and modified Logistic kinetic models were employed for the kinetic modeling of cumulative hydrogen production values. Results show that I/S ratio of 1/4 gVS/gVS resulted from the best hydrogen production of 59.96 mL during 30 days of MPWW fermentation without pretreatment. It was also shown that all the adopted pretreatments enhanced hydrogen production, whereas ultrasonic pretreatment for 5 min increased the production by only 14.84%. Heat pretreatment was more efficient, where the hydrogen production increased from 60 to 162 mL (170% of improvement) using heat shock at 90 °C for 30 min. The impact of chemical pretreatment was different from a reagent to another. Pretreatment using calcium hydroxide resulted in the biggest hydrogen production of 165.3 mL (175.5%) compared to the other chemical pretreatments. However, the best hydrogen production was given by the biological pretreatment using enzymatic hydrolysis (Lactase) resulting in 254 mL of hydrogen production, which is equivalent to 323.62% of production improvement. Modified Gompertz and Logistic kinetic models fitted well with experimental data. Thus, the enzymatic hydrolysis of MPWW proved to be a promising technique for biohydrogen production enhancement.

A bibliometric analysis of the role of nanotechnology in dark fermentative biohydrogen production

Recently, nanoparticles have drawn a lot of interest as catalysts to enhance the effectiveness and output of biohydrogen generation processes. This review article provides a comprehensive bibliometric analysis of the significance of nanotechnology in dark fermentative biohydrogen production. The study examines the scientific literature from the database of The Web of Science© while the bibliometric investigation utilized VOSviewer© and Bibliometrix software tools to conduct the analysis. The findings revealed that a total of 232 articles focused on studying dark fermentation for hydrogen production throughout the entire duration. The extracted data was used to analyze publication trends, authorship patterns, and geographic distribution along with types and effects of nanoparticles on the microbial community responsible for dark fermentative biohydrogen production. The findings of this bibliometric analysis provide valuable insights into the advancements and achievements in the utilization of nanoparticles in the dark fermentation process used to produce biohydrogen.

Enhanced fermentative hydrogen production from potato waste by enzymatic pretreatment

Biological pretreatment and enzymatic hydrolysis have a potential role in the economic production of sugars and fuels from starch biomass. In this study, the Inoculum/Substrate (I/S) ratio effect and enzymatic pretreatments of potato peels for biohydrogen production in batch reactors were investigated. Two enzymes, α-Amylase and Cellulase, were tested separately and coexistent. Results showed that enzymatic hydrolysis using α-Amylase in mesophilic conditions enhanced carbohydrate concentration from 24.10 g/L to 53.47 g/L, whereas, the use of Cellulase and equi-volumetric mixture of both tested enzymes resulted in 47.16 and 48.16 g/L, respectively. The maximum biohydrogen cumulative production of 263 mL (equivalent to 430.37 mL H2/gVSadded) was obtained using the optimum I/S ratio of 1/6 gVS/gVS at pH 5.5 and incubation temperature of 55°C after 20 days of dark fermentation of potato waste without enzymatic treatment. Under the same operating conditions of the I/S ratio, pH, temperature and the best enzymatic treatment (3 h of substrate enzymatic hydrolysis by α-Amylase), the maximum yield of biohydrogen was 1088 mL (1780.39 mL H2/gVSadded). The enzymatic hydrolysis method adopted in this study can make overall biohydrogen production an effective process. The modified Gompertz model was found to be an adequate fit for biohydrogen production.

Rice mill wastewater management in the era of circular economy

Several nations around the world use rice as their primary food staple because of its tremendous nutritional value. India's expanding population has sparked a proliferation of rice mills as a result of the country's growing rice demand. However, small and medium-scale industries lack adequate facilities for processing effluents and other waste generated. Paddy is typically processed by parboiling, which involves soaking it in water, boiling it with steam, and then drying and milling. Around 1-1.5 L of water is necessary to partially cook 1 kg of unhusked rice, with approximately half of this water being discharged as effluent. Disposal of rice mill effluent (RME) in water bodies or on the land causes severe damage to soil and water. An inclusive examination of diverse approaches for the treatment and stabilization of partially cooked rice milling effluents is provided. Moreover, the document provides a concise overview of contemporary and environmentally friendly technologies for treating RME. Adsorption, electrocoagulation, chemical coagulation, and bioremediation using microbes, plants, and microalgae are all included in these methods. This manuscript discusses the concept of a circular economy, which is focused on enhancing environmental sustainability through the recycling and repurposing of generated waste into raw materials for the creation of new products. In addition, this review aims to focus on the impact of RME on soils and water species and the status of sustainable management at the point of circular economy with RME bioenergy production (bioelectricity, biomethane, and bio-hydrogen).

Nanotechnology based technological development in biofuel production: Current status and future prospects

Depleting fossil fuels and net carbon emissions associated with their burning have driven the need to find alternative energy sources. Biofuels are near-perfect candidates for alternative energy sources as they are renewable and account for no net CO2 emissions. However, biofuel production must overcome various challenges to compete with conventional fuels. Conventional methods for bioconversion of biomass to biofuel include chemical, thermochemical, and biological processes. Substrate selection and processing, low yield, and total cost of production are some of the main issues associated with biofuel generation. Recently, the uses of nanotechnology and nanoparticles have been explored to improve the biofuel production processes because of their high adsorption, high reactivity, and catalytic properties. The role of these nanoscale particles and nanocatalysts in biomass conversion and their effect on biofuel production processes and yield are discussed in the present article. The applicability of nanotechnology in production processes of biobutanol, bioethanol, biodiesel, biohydrogen, and biogas under biorefinery approach are presented. Different types of nanoparticles, and their function in the bioprocess, such as electron transfer, pretreatment, hydrolysis, microalgae cultivation, lipid extraction, dark and photo fermentation, immobilization, and suppression of inhibitory compounds, are also highlighted. Finally, the current and potential applications of nanotechnology in biorefineries are also discussed.

Taguchi Parametric Optimization and Cost Analysis of Hexavalent Chromium Sequestration From Aqueous Solution by NaOH-Modified Garcinia kola Hull Particles

The presence of chromium in industrial wastewater is unavoidable due to its large usage as part of chemical constituents used in many industries. Its removal from wastewater is imperative because it's toxic in nature. This study investigated the application of NaOH-modified Garcinia kola hull particles (cMGK-HP) for Cr(VI) sequestration from aqueous solution. The optimization of process parameters was executed using Taguchi of Design Expert software for optimum point prediction, analysis of variance, parameters interaction and mathematical model development. A proposed model was used for the adsorption cost analysis. The predicted and experimental percentage of Cr(VI) sequestration were recorded at optimum point to be 99.02% and 98.76% with pH, adsorbent dose, contact time, initial concentration, and temperature of 2, 8 g/L, 20 minutes, 10 mg/L, and 20°C respectively. A correlation coefficient of .9937 between experimental and predicted values of percentage Cr(VI) sequestration affirmed high efficacy of the developed model. ANOVA showed the order of parameter contribution to be pH > adsorbent dose > initial concentration > contact time > temperature. A maximum adsorption capacity of 217.39 mg g-1 was obtained for cMGK-HP. Cost analysis revealed using cMGK-HP to be cost effective for Cr(VI) sequestration with a total operational cost of 0.824 $/mole Cr(VI) ions when compared with commercial activated carbon. Adsorbent characterization revealed the presence of active functional groups enhancing the sequestration process. It could be deduced that cMGK-HP is effective to remove Cr(VI) from solution.

Revealing the roles of carbonized humic acid in biohydrogen production

For low yield in dark fermentation (DF), in this study, the carbonized humic acid (CHA) was produced and added to DF for enhancing biohydrogen (bioH2) yield at mesophilic condition. The highest bioH2 yield was 151.08 mL/g glucose with the addition of CHA at 80 mg/L, which was 35.27% and 16.53% higher than those of 0 mg/L CHA and 80 mg/L mineral humic acid (MHA) groups, respectively. Electrons preferentially conducted via the butyrate pathway due to CHA amendments, which corresponded to the prediction of relevant functional genes. Furthermore, CHA possessed distinctive advantages over MHA, which acted as an electron shuttle to facilitate electron transfer, released metal ions as an essential signal mediator and favored the reduction of ferredoxin, obtaining more H2. The use of CHA in the field of H2-DF depicted the high-value utilization and industrial chain extension of MHA.

Magnetic nitrogen-doped activated carbon improved biohydrogen production

Low biological hydrogen (bioH2) production due to non-optimal metabolic pathways occurs frequently. In this work, magnetic nitrogen-doped activated carbon (MNAC) was prepared and added into the inoculated sludge with glucose as substrate to enhance hydrogen (H2) yield by mesophilic dark fermentation (DF). The highest H2 yield appeared in 400 mg/L AC (252.8 mL/g glucose) and 600 mg/L MNAC group (304.8 mL/g glucose), which were 26.02% and 51.94% higher than that of 0 mg/L MNAC group (200.6 mL/g glucose). The addition of MNAC allowed for efficient enrichment of Firmicutes and Clostridium-sensu-stricto-1, accelerating the metabolic pathway shifted towards butyrate type. The Fe ions released by MNAC facilitated electron transfer and favored the reduction of ferredoxin (Fd), thereby obtaining more bioH2. Finally, the generation of [Fe-Fe] hydrogenase and cellular components of H2-producing microbes (HPM) during homeostasis was discussed to understand on the use of MNAC in DF system.

Fruit peel crude enzymes for enhancement of biohydrogen production from synthetic swine wastewater by improving biohydrogen-formation processes of dark fermentation

Biohydrogen is a promising clean fuel but with a low yield. This study aims to enhance biohydrogen production from synthetic swine wastewater by employing crude enzymes obtained from different fruit peels (orange, mandarin, and banana) to improve the biohydrogen-formation processes of dark fermentation. Results indicated that dosing with crude enzymes affected volatile fatty acids (VFAs) and biogas composition insignificantly, while increased biohydrogen yield from 1.62 ± 0.00 (blank) to 1.90 ± 0.08 (orange peel), 2.01 ± 0.00 (mandarin peel), and 1.96 ± 0.01 (banana peel) mol H₂/mol glucose, respectively. Banana peel crude enzyme was the most effective additive, with 1 g/L protein improving 97.41 ± 3.72 % of biohydrogen yield. The crude enzymes wielded less influence on acetic acid and butyric acid pathways but enhanced other biohydrogen production pathways. These observations demonstrated that fruit peel-based crude enzymes as additives are advantageous to improving biohydrogen yield towards higher biohydrogen production.

Simultaneous production of renewable biohydrogen, biobutanol and biopolymer from phytogenic CoNPs-assisted Clostridial fermentation for sustainable energy and environment

Considering the environmental impacts, rapid fossil fuel depletion and production costs, sustainable production of clean biofuels from alternative sources is required to meet the increasing demand for energy while avoiding environmental pollution. In this study, phytogenic cobalt nanoparticles (CoNPs)-assisted dark fermentation process was developed for the simultaneous production of biohydrogen, biobutanol and biopolymer from glucose using Clostridium acetobutylicum NCIM 2337. The maximum biohydrogen yield of 2.89 mol H₂/mol glucose was achieved at 1.5 mg of CoNPs, which is 1.6 folds higher than that of the control experiment. The high level of soluble metabolites, specifically acetate and butyrate, confirmed the production of biohydrogen through acetate/butyrate pathways. The modified Gompertz model fitted well with experimental results of CoNPs-assisted biohydrogen production. The CoNPs could act as an electron carrier in intracellular metabolism to enhance the activity of ferredoxin and hydrogenase enzymes, thus improving biohydrogen production. Furthermore, biobutanol and biopolymer yields of 975 ± 2.5 mg/L and 1182 ± 1.4 mg/L were achieved, with 2.0 mg and 2.5 mg of CoNP, respectively, which were 1.27 and 1.19 folds higher than the control values. Hence, the inclusion of CoNPs in the fermentation medium seems to be a promising technique for the enhanced simultaneous production of biohydrogen, biobutanol and biopolymer. The environmental perspectives of the obtained renewable biohydrogen, biobutanol and biopolymer are also discussed.

Carbon-based photocatalysts for hydrogen production: A review

Future energy crises and environmental deterioration may only be avoided by converting solar energy into sustainable, safe, cost-effective, and environmentally friendly technologies such as water splitting. Many researchers and governments throughout the globe have stressed the imperative need for affordable, environmental benign, resistive to corrosion, and earth-abundant nanostructured photocatalysts. This has led scientists to look for a green and cost-effective way to generate energy. As a result, the significance of photo catalyst engineering and reactor design difficulties connected to the performance of the photocatalytic reactions, as well as the examination and analysis of photocatalyst behaviors for adaptable and cost effective H2 production, is emphasized and summarized. The carbon-based materials have an appealing band structure, strong chemical stability, is plentiful on Earth, and is relatively easy to produce, making them suitable for hydrogen production. As example, graphene oxide (GO) with the oxygenated functional groups and graphene and its counterparts, including Graphene quantum dots (GQDs), GO, reduce graphene oxide (rGO), have been demonstrated to be ideal nanocomposite materials due to their superior properties and distribution in matrix and CNTs with excellent electronic transmission efficiency, low cost, stability, and environmental friendly are a great alternative of electron mediators for photocatalytic devices to boost light absorptivity for efficient hydrogen generation but some of them have limited photocatalytic activity due to their low sunlight usage efficiency, therefore the numerous methods, such as doping ions, constructing heterostructure, and functionalizing carbon-based materials, have recently been proven to promote the photocatalytic activity of them. The pore structure of carbon material functions as an acceptor of photogenerated electrons, improved the photocatalyst's specific surface area. Generally low-dimensional carbon materials demonstrated immense promise as highly efficient, low-cost, and environmentally friendly catalysts for hydrogen generation as an energy source. This article reviews the recent research progress on carbon-based materials for hydrogen evolution for the first time. It commences with a quick overview of the present state of affairs and fundamental concepts of hydrogen production in carbon-based nanomaterials for use in this field. We anticipate that this study will inspire readers to expand the use of carbon-based materials in H₂ generation in a more environmentally friendly way.

A novel conversion of marine macroalgal biomass to biofuel (biohydrogen) via calcium hypochlorite induced dispersion

Environmental pollution due to the consumption of non-renewable energy lead the search for alternative eco-friendly renewable fuel. The study details the biohydrogen production efficiency by potential macroalgal (Ulva reticulata) biomass improved by a disperser combined with calcium hypochlorite pretreatment technology. Calcium hypochlorite was added to decrease the surface energy of the medium induced by sole disperser pretreatment. Optimum condition for algal disperser treatment was 10,000 rpm with 30 min as dispersion time. The specific energy spent for the disintegration of the macroalgal biomass was 1231.58 kJ/kg TS. COD solubilization rate of 11.79% was attained with mechanical pretreatment whereas increased to 20.23% with combined pretreatment. Combination of disperser with calcium hypochlorite significantly reduced the specific energy input spent to 500 kJ/kg TS. The amount of organic materials such as carbohydrates, proteins and lipids released were 680 mg/L, 283 mg/L and 136 mg/L respectively. Thus, the combinative pretreatment with disperser rotor speed (10,000 rpm) for pretreatment time (12 min) and calcium hypochlorite dosage (0.1 g/g) derived as optimum condition for effective solubilization of macroalgal biomass. Biohydrogen production potential was maximum in the macroalgae pretreated with both disperser and calcium hypochlorite recorded highest yield (54.6 mL H₂/g COD) compared to the macroalgae pretreated with disperser alone (31.7 mL H₂/g COD) and untreated macroalgae (11.5 mL H₂/g COD).

Effects of soil ingestion on nutrient digestibility and rumen bacterial diversity of Tibetan sheep

Tibetan sheep (Ovis aries) are the most numerous livestock in Tibet Plateau pasture ecosystem and have strong ecological adaptability. In the natural grazing system, soil as a natural nutrient carrier and involuntarily or intentionally ingested by Tibetan sheep contribute as an important feed approach. However, quantifying the dosages of soil ingestion for the Tibetan sheep still needs to be clarified. This study aims to characterize nutrient digestibility and rumen bacterial communities by Tibetan sheep in response to different levels of soil ingestion. Thirty sheep were selected and divided into five treatments with soil ingestion (0%, 5%, 10%, 15%, and 20%). The conclusion demonstrated that soil ingestion improved the dry matter digestibility (59.3-62.97%), ether extract (59.79-67.87%) and crude protein (59.81-66.47%) digestibility, particularly 10% soil ingestion has highest nutrient digestibility. The rumen fermentation environment adjusted after soil ingestion by improvement of pH, ammonia nitrogen and volatile fatty acids. Appropriate soil ingestion reduced the bacterial diversity ranged from 946 to 1000 OUTs as compared control (1012), and the rumen bacterial community dominant by typical fiber digestion associated Firmicutes (47.48-53.56%), Bacteroidetes (34.93-40.02%) and Fibrobacteres (4.36-9.27%). Especially, the highest digestible feed capacity and stronger environment adaptability present in 10% soil ingestion Tibetan sheep. Overall, soil ingestion stimulates rumen metabolism by creating a favorable environment for microbial fermentation, improved bacterial community abundance associated with cellulose and saccharide degradation, contribute nutrient digestibility and growth performance of Tibetan sheep.

Nickel-Cobalt Oxide Nanoparticle-Induced Biohydrogen Production

The positive effects of metal oxide nanoparticles (NPs) on dark fermentation (DF) for biohydrogen synthesis have been increased, and the mechanism still needs to be further revealed. In this study, nickel-cobalt oxide (NiCo₂O₄) NPs were prepared to increase H₂ yield via DF. The highest (259.67 mL/g glucose) and the lowest (188.14 mL/g glucose) yields were achieved at 400 and 800 mg/L NiCo₂O₄ NPs added, respectively, with their corresponding 33.97% increase and 2.93% decrease compared with the control yield (193.82 mL/g glucose). Meanwhile, the microbial community further confirmed that NiCo₂O₄ NPs increased the abundance of the dominant H₂-producing Clostridium sensu stricto 1 by 23.05%. The gene prediction also showed that NiCo₂O₄ NPs increased the abundance of genes encoding the rate-limiting enzyme pyruvate kinase in glycolysis, thus increasing the substrate conversion. Moreover, the gene abundance of key enzymes directly related to H₂ evolution was also increased at different levels.

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.

Biodegradation of crude oil in seawater by using a consortium of symbiotic bacteria

This work presents the enhancement of oil biodegradation in seawater using a mixture of oil and microorganisms. Retardation of crude oil biodegradation in seawater is hypothetically due to the inhibiting of metabolites produced by the oil bacterium which inhibit its enzymes. For this purpose, the bacteria consortium consisting of an active oil-oxidizing bacterium (AR3-Pseudomonas pseudoalcaligenes) and two oil-resistant and active heterotrophic bacteria (OG1 and OG2-Erythrobacter citreus) were formed. The heterotrophic bacteria, OG1 and OG2 were able to remove metabolites produced during oil degradation. It was found that AR3 was retarded by metabolites, while OG1 and OG2 were able to grow in the metabolites. OG1 and OG2 were applied together to enhance growth and removal of the metabolites. About 59.9% of crude oil degradation was degraded by AR3 pure culture, while 68.6% was degraded by the bacteria consortium. About 31.4% of the crude oil was found to remain in seawater due to the presence of asphaltenes and resin hydrocarbons. The bacteria consortium was able to degrade 84.1% of total hydrocarbons while 67.0% was degraded by AR3. A total of 99.8% of the aliphatic content and 38.4% of the total aromatic hydrocarbons were degraded by the bacteria consortium, while a lower 79.4% of total aliphatic and 31.0% of total aromatic were degraded by AR3 under the same experimental conditions. The results which were obtained from this study support the hypothesis that the retardation of oil degradation by AR3 is due to the inhibition of metabolites on the growth.

Improved biohydrogen evolution through calcium ferrite nanoparticles assisted dark fermentation

Dark fermentation (DF) is a green hydrogen (H₂) production process, but it is far below the theoretical H₂ yield. In this study, calcium ferrite nanoparticles (CaFe₂O₄ NPs) were produced to augment H₂ yield via DF. The highest H₂ yield of 250.1 ± 6.5 mL/g glucose was achieved at 100 mg/L CaFe₂O₄ NPs. Furtherincreasein CaFe₂O₄ NPs above 100 mg/L, such as 600 mg/L, would slightly lower H₂ yield to 208.6 ± 2.6 mL/g glucose. The CaFe₂O₄ NPs in DF system released calcium and iron ions, promoting granular sludge formation andDF microbial activity. Soluble metabolites revealed that butyric acid was raised by CaFe₂O₄ NPs, which indicated the improved metabolic pathway for more H₂. Microbial structure composition further illustrated that CaFe₂O₄ NPs could increase the abundance of dominant microbial populations, with the supremacy of Firmicutes up to 71.22 % in the bioH₂ evolution group augmented with 100 mg/L CaFe₂O₄ NPs.

Algae in wastewater treatment, mechanism, and application of biomass for production of value-added product

The pollutants can enter water bodies at various point and non-point sources, and wastewater discharge remains a major pathway. Wastewater treatment effectively reduces contaminants, it is expensive and requires an eco-friendly and sustainable alternative approach to reduce treatment costs. Algae have recently emerged as a potentially cost-effective method to remediate toxic pollutants through the mechanism of biosorption, bioaccumulation, and intracellular degradation. Hence, before discharging the wastewater into the natural environment better solutions for environmental resource recovery and sustainable developments can be applied. More importantly, algae are a potential feedstock material for various industrial applications such as biofuel production. Currently, researchers are developing algae as a source for pharmaceuticals, biofuels, food additives, and bio-fertilizers. This review mainly focused on the potential of algae and their specific mechanisms involved in wastewater treatment and energy recovery systems leading to important industrial precursors. The review is highly beneficial for scientists, wastewater treatment plant operators, freshwater managers, and industrial communities to support the sustainable development of natural resources.

Bio-hydrogen production by dark anaerobic fermentation of organic wastewater

Using organic wastewater to produce hydrogen by fermentation can generate clean energy while treating wastewater. At present, there are many inhibitory factors in the hydrogen production process, resulting in unsatisfactory hydrogen yield and hydrogen concentration during the fermentation process, and there are still great obstacles to the industrial promotion and commercial application of organic wastewater fermentation hydrogen production. This paper summarizes the hydrogen production of organic wastewater dark anaerobic fermentation technology. The current anaerobic fermentation hydrogen production systems and technologies are summarized and compared, and the factors and potential conditions that affect the performance of hydrogen production are discussed. The further requirements and research priorities for the market application of fermentation biohydrogen production technology in wastewater utilization are prospected.

Microbiomes of biohydrogen production from dark fermentation of industrial wastes: current trends, advanced tools and future outlook

Biohydrogen production through dark fermentation is very attractive as a solution to help mitigate the effects of climate change, via cleaner bioenergy production. Dark fermentation is a process where organic substrates are converted into bioenergy, driven by a complex community of microorganisms of different functional guilds. Understanding of the microbiomes underpinning the fermentation of organic matter and conversion to hydrogen, and the interactions among various distinct trophic groups during the process, is critical in order to assist in the process optimisations. Research in biohydrogen production via dark fermentation is currently advancing rapidly, and various microbiology and molecular biology tools have been used to investigate the microbiomes. We reviewed here the different systems used and the production capacity, together with the diversity of the microbiomes used in the dark fermentation of industrial wastes, with a special emphasis on palm oil mill effluent (POME). The current challenges associated with biohydrogen production were also included. Then, we summarised and discussed the different molecular biology tools employed to investigate the intricacy of the microbial ecology associated with biohydrogen production. Finally, we included a section on the future outlook of how microbiome-based technologies and knowledge can be used effectively in biohydrogen production systems, in order to maximise the production output.

Revealing the mechanisms of alkali-based magnetic nanosheets enhanced hydrogen production from dark fermentation: Comparison between mesophilic and thermophilic conditions

In the present study, a dark fermentation system inoculated with mixed culture bacteria (MCB) was developed using prepared alkali-based magnetic nanosheets (AMNSs) to facilitate biohydrogen (BioH₂) production. The highest BioH₂ yields of 232.8 ± 8.5 and 150.3 ± 4.8 mL/g glucose were observed at 100 (mesophilic condition) and 400 (thermophilic condition) mg/L AMNSs groups, which were 65.4% and 43.3%, respectively, above the 0 mg/L AMNSs group. The fermentation pathway revealed that AMNSs enhanced the butyrate-type metabolic pathway and the corresponding nicotinamide adenine dinucleotides (NADHand NAD⁺) ratio, and hydrogenase activity was enhanced in mesophilic fermentation. The interaction of AMNSs and MCB suggested that AMNSs could assist in electron transfer and that the released metal elements might be responsible for elevated hydrogenase activity. AMNSs also promoted the evolution of the dominant microbial community and altered the content of extracellular polymers, leading to increased production of BioH₂.

Algae as potential feedstock for various bioenergy production

Depletion of non-renewable feedstock and severe wastewater pollution due to human activities have created negative impact to living organisms. The potential solution is to implement wastewater treatment and bioelectricity production through algae-based microbial fuel cell. The algae biomass produced from microbial fuel cell could be further processed to generate biofuels through their unique compositions. The consumption of nutrients in wastewater through algae cultivation and biomass produced to be utilized for energy supply have showed the potential of algae to solve the issues faced nowadays. This review introduces the background of algae and mitigation of wastewater using algae as well as the bioenergy status in Malaysia. The mechanisms of nutrient assimilation such as nitrogen, phosphorus, carbon, and heavy metals are included, followed by the application of algae in microbial fuel cell's chambers. Lastly, the status of algae for bioenergy production are covered.

Treatment of Hospital wastewater with submerged aerobic fixed film reactor coupled with tube-settler

In this study, Hospital wastewater was treated using a submerged aerobic fixed film (SAFF) reactor coupled with tubesettler in series. SAFF consisted of a column with an up-flow biofilter. The biological oxygen demand (BOD)₅, chemical oxygen demand (COD), nitrate and phosphate were the chosen pollutants for evaluation. The pollutants removal efficiency was determined at varying organic loading rates and hydraulic retention time. The organic loading rate was varied between 0.25 and 1.25 kg COD m^-3 d^-1. The removal efficiency of SAFF and tubesettler combined was 75 % COD, 67 % BOD and 67 % phosphate, respectively. However, nitrate saw an increase in concentration by 25 %. SAFF contribution in the removal of COD, BOD₅ and Phosphate was 48 %, 46 % and 29 %, respectively. While for accumulation of nitrate, it was responsible for 56%, respectively. Tubesettler performed better than SAFF with 52 %, 54 % and 69 % reduction of COD, BOD₅ and phosphate, respectively. But in terms of nitrate, tubesettler was responsible for 44 % accumulation. The nutrient reduction decreased with an increase in the organic loading rate. Nitrification was observed in the SAFF and tubesettler, which indicated a well-aerated system. An anaerobic unit is required for completing the denitrification process and removing nitrogen from the effluent. The better performance of tubesettler over SAFF calls for necessitates extended retention time over design criteria. Further studies are beneficial to investigate the impact of pharmaceutical compounds on the efficiency of SAFF.

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.

Renewable hydrogen production from biomass and wastes (ReBioH2-2020)

Growing consumption of fossil reserves to meet the rising demand of energy has led to climate deterioration and simultaneous waste generation, urging modern society to find sustainable energy resource that can meet the growing energy demands and reduce greenhouse gas emissions and carbon footprints. In this aspect, hydrogen (H₂) is one of the most promising sustainable clean fuels that has gained significant interest in recent years. This article highlights the major research progress on biohydrogen production from renewable bioresources such as organic wastes, lignocellulosic biomass, algal biomass, and industrial wastewaters. It summarizes the research highlights of manuscripts published in the special issue (VSI: ReBioH2-2020), which contains twenty-two articles, including seven critical reviews and fifteen research articles, focusing on biotechnological and thermochemical routes for biohydrogen production from renewable feedstocks. The major findings of the research works in this special issue can be used as a road-map for sustainable renewable hydrogen production from bioresources.

Food Waste Biorefinery: Pathway towards Circular Bioeconomy

Food waste biorefineries for the production of biofuels, platform chemicals and other bio-based materials can significantly reduce a huge environmental burden and provide sustainable resources for the production of chemicals and materials. This will significantly contribute to the transition of the linear based economy to a more circular economy. A variety of chemicals, biofuels and materials can be produced from food waste by the integrated biorefinery approach. This enhances the bioeconomy and helps toward the design of more green, ecofriendly, and sustainable methods of material productions that contribute to sustainable development goals. The waste biorefinery is a tool to achieve a value-added product that can provide a better utilization of materials and resources while minimizing and/or eliminating environmental impacts. Recently, food waste biorefineries have gained momentum for the production of biofuels, chemicals, and bio-based materials due to the shifting of regulations and policies towards sustainable development. This review attempts to explore the state of the art of food waste biorefinery and the products associated with it.

Main Hydrogen Production Processes: An Overview

Due to its characteristics, hydrogen is considered the energy carrier of the future. Its use as a fuel generates reduced pollution, as if burned it almost exclusively produces water vapor. Hydrogen can be produced from numerous sources, both of fossil and renewable origin, and with as many production processes, which can use renewable or non-renewable energy sources. To achieve carbon neutrality, the sources must necessarily be renewable, and the production processes themselves must use renewable energy sources. In this review article the main characteristics of the most used hydrogen production methods are summarized, mainly focusing on renewable feedstocks, furthermore a series of relevant articles published in the last year, are reviewed. The production methods are grouped according to the type of energy they use; and at the end of each section the strengths and limitations of the processes are highlighted. The conclusions compare the main characteristics of the production processes studied and contextualize their possible use.

Bio-Hydrogen Production from Wastewater: A Comparative Study of Low Energy Intensive Production Processes

Billions of litres of wastewater are produced daily from domestic and industrial areas, and whilst wastewater is often perceived as a problem, it has the potential to be viewed as a rich source for resources and energy. Wastewater contains between four and five times more energy than is required to treat it, and is a potential source of bio-hydrogen—a clean energy vector, a feedstock chemical and a fuel, widely recognised to have a role in the decarbonisation of the future energy system. This paper investigates sustainable, low-energy intensive routes for hydrogen production from wastewater, critically analysing five technologies, namely photo-fermentation, dark fermentation, photocatalysis, microbial photo electrochemical processes and microbial electrolysis cells (MECs). The paper compares key parameters influencing H2 production yield, such as pH, temperature and reactor design, summarises the state of the art in each area, and highlights the scale-up technical challenges. In addition to H2 production, these processes can be used for partial wastewater remediation, providing at least 45% reduction in chemical oxygen demand (COD), and are suitable for integration into existing wastewater treatment plants. Key advancements in lab-based research are included, highlighting the potential for each technology to contribute to the development of clean energy. Whilst there have been efforts to scale dark fermentation, electro and photo chemical technologies are still at the early stages of development (Technology Readiness Levels below 4); therefore, pilot plants and demonstrators sited at wastewater treatment facilities are needed to assess commercial viability. As such, a multidisciplinary approach is needed to overcome the current barriers to implementation, integrating expertise in engineering, chemistry and microbiology with the commercial experience of both water and energy sectors. The review concludes by highlighting MECs as a promising technology, due to excellent system modularity, good hydrogen yield (3.6–7.9 L/L/d from synthetic wastewater) and the potential to remove up to 80% COD from influent streams.

The role of deep eutectic solvents and carrageenan in synthesizing biocompatible anisotropic metal nanoparticles

Plasmonic metal nanoparticles are widely used for many applications due to their unique optical and chemical properties. Over the past decade, anisotropic metal nanoparticles have been explored for imaging, sensing, and diagnostic applications. The variations and flexibility of tuning the size and shape of the metal nanoparticles at the nanoscale made them promising candidates for biomedical applications such as therapeutics, diagnostics, and drug delivery. However, safety and risk assessment of the nanomaterials for clinical purposes are yet to be made owing to their cytotoxicity. The toxicity concern is primarily due to the conventional synthesis route that involves surfactants as a structure-directing agent and as a capping agent for nanoparticles. Wet chemical methods employ toxic auxiliary chemicals. However, the approach yields monodispersed nanoparticles, an essential criterion for their intended application and a limitation of the green synthesis of nanoparticles using plant extracts. Several biocompatible counterparts such as polymers, lipids, and chitosan-based nanoparticles have been successfully used in the synthesis of safe nanomaterials, but there were issues regarding reproducibility and yield. Enzymatic degradation was one of the factors responsible for limiting the efficacy. Hence, it is necessary to develop a safer and nontoxic route towards synthesizing biocompatible nanomaterials while retaining morphology, high yield, and monodispersity. In this regard, deep eutectic solvents (DESs) and carrageenan as capping agent for nanoparticles can ensure the safety. Carrageenan has the potential to act as antibacterial and antiviral agent, and adds enhanced stability to the nanoparticles. This leads to a multidimensional approach for utilizing safe nanomaterials for advanced biomedical and clinical applications.