Effects of light intensity on biomass, carbohydrate and fatty acid compositions of three different mixed consortia from natural ecological water bodies.

This study investigated the effect of light intensity on three various microalga consortia collected from natural ecological water bodies (named A, B and C) towards their fatty acid profiling and fractions, carbohydrate and protein production at different light intensities of 100, 200 and 300 µmol m-2 s-1. The results indicating that increasing light intensity positively correlated with the lipid production than carbohydrate and protein. Irrespective to the solids (Total and Volatile Solid) content, lipids and carbohydrate has varied significantly. Consortia C showed higher productivity toward lipids, whereas consortia A and B accumulated more carbohydrate and protein, respectively. The microscopic images revealed the breakdown of cells during the increase in light intensity, in spite, the similar algal species were observed in all consortia experimented. Principal component analysis (PCA) revealed that low light intensity aid relatively in high protein, Total Nitrogen and Total Phosphorus, meanwhile high intensity attributed carbohydrates and unsaturated fatty acids (USFA) contents.

A comprehensive review on two-stage integrative schemes for the valorization of dark fermentative effluents.

This review provides the alternative routes towards the valorization of dark H2 fermentation effluents that are mainly rich in volatile fatty acids such as acetate and butyrate. Various enhancement and alternative routes such as photo fermentation, anaerobic digestion, utilization of microbial electrochemical systems, and algal system towards the generation of bioenergy and electricity and also for efficient organic matter utilization are highlighted. What is more, various integration schemes and two-stage fermentation for the possible scale up are reviewed. Moreover, recent progress for enhanced performance towards waste stabilization and overall utilization of useful and higher COD present in the organic source into value-added products are extensively discussed.

Effect of nano-metal doped calcium peroxide on biomass pretreatment and green hydrogen production from rice straw.

In this study, calcium peroxide was modified and doped with metal-based nanoparticles (NP) to enhance the efficiency of pretreatment and biohydrogen generation from RS. The findings revealed that the addition of MnO2-CaO2 NPs (at a dosage of 0.02 g/g TS of RS) had a synergistic effect on the breakdown of biomass and the production of biohydrogen. This enhancement resulted in a maximum hydrogen yield (HY) of 58 mL/g TS, accompanied by increased concentrations of acetic acid (2117 mg/L) and butyric acid (1325 mg/L). In contrast, RS that underwent pretreatment without the use of chemicals or NP exhibited a lower HY of 28 mL/g TS, along with the lowest concentrations of acetic acid (1062 mg/L) and butyric acid (697 mg/L). The outcome showed that supplementation of NP stimulated the pretreatment of RS and improved the formation of acetic and butyric acid through the regulation of metabolic pathways during acidogenic fermentation.

Unrevealing the role of metal oxide nanoparticles on biohydrogen production by Lactobacillus delbrueckii.

The positive interaction between Clostridium sp. and lactic acid-producing bacteria (Lactobacillus sp) is commonly seen in various high-rate hydrogen production systems. However, the exact role of the hydrogen production ability of Lactobacillus sp in a dark fermentation production system is rarely studied. Lactobacillus delbrueckii was herein used for the first time, to the best of the author's knowledge, to demonstrate biohydrogen production under anaerobic conditions. At first, the pH condition was optimized, followed by the addition of nanoparticles for enhanced biohydrogen production. Under optimized conditions of pH 6.5, substrate concentration 10 g/L, and 100 mg/L of NiO/Fe2O3, the maximum hydrogen yield (HY) of 1.94 mol/mol hexose was obtained, which is 18 % more than the control. The enhanced H2 production upon the addition of nanoparticles is supported via the external electron transfer (EET) mechanism, which regulates the metabolic pathway regulation with increased production of acetate and butyrate and reduced formation of lactate.

Microbiome involved in anaerobic hydrogen producing granules: A mini review.

This mini review overviewed the latest updates on the anaerobic hydrogen fermentation using the granulation technology and the microbiome involved in the process. Additionally, the implication of various reactor design and their microbial changes were compared and provided the new insights on the role of microbiomes for rapid granules formation and long term stable operation in a continuous mode operation. The information provided in this communication would help to understand the key role of microbiomes and their importance in anaerobic hydrogen producing granular systems.

Biohydrogen fermentation of galactose at various substrate concentrations in an immobilized system and its microbial correspondence.

The effects of substrate concentration on fermentative hydrogen production from galactose at a fixed hydraulic retention time of 12 h were investigated in an immobilized continuously stirred tank reactor. Peak hydrogen production rate and hydrogen yield of 9.57 L/L-d and 1.10 mol/mol galactoseadded, respectively, were obtained at a feed substrate concentration of 30 g/L and an organic loading rate of 60 L/L-d. Quantitative polymerase chain reaction analysis showed that the variations in the performance resulted primarily from metabolic alterations within the metabolism of the established microbial community rather than modifications in the population. The results obtained showed that optimal substrate concentration is essential for the efficient, continuous production of hydrogen from galactose.

Cultivation of microalgal biomass using swine manure for biohydrogen production: Impact of dilution ratio and pretreatment.

This study assessed the impact of swine manure (SM) dilution ratio on the microalgal biomass cultivation and further tested for biohydrogen production efficiency from the mixed microalgal biomass. At first, various solid/liquid (S/L) ratio of the SM ranged from 2.5 to 10 g/L was prepared as a nutrient medium for the algal biomass cultivation without addition of the external nutrient sources over a period of 18 d. The peak biomass concentration of 2.57 ±â€¯0.03 g/L was obtained under the initial S/L loading rates of 5 g/L. Further, the cultivated biomass was subjected to two-step (ultrasonication + enzymatic) pretreatment and evaluated for biohydrogen production potential. Results showed that the variable amount of hydrogen production was observed with different S/L ratio of the SM. The peak hydrogen yield of 116 ±â€¯6 mL/g TSadded was observed at the 5 g/L grown SM mixed algal biomass.

Effect of 5-hydroxymethylfurfural (5-HMF) on high-rate continuous biohydrogen production from galactose.

This study investigated the effect of 5-hydroxymethylfurfural (5-HMF) on high-rate continuous fermentative H2 production in a lab-scale fixed bed reactor (FBR) inoculated with mixed culture granules and fed with 15g/L galactose at a hydraulic retention time of 6h and at 37°C. During the 83days of operation, 5-HMF up to 2.4g/L was spiked into the feedstock. The maximum hydrogen production performance of 26.6L/L-d and 2.9mol H2/mol galactoseadded were achieved at 5-HMF concentration of 0.6g/L. 5-HMF concentration exceeding 0.9g/L not only inhibited hydrogen production but also affected the biofilm structure and microbial community population. However, when 5-HMF was eliminated from the feedstock, the performance and microbial community population were rapidly recovered.

Recent advances on biogranules formation in dark hydrogen fermentation system: Mechanism of formation and microbial characteristics.

Hydrogen producing granules (HPGs) are most promising biological methods used to treat organic rich wastes and generate clean hydrogen energy. This review provides information regarding types of immobilization, supporting materials and microbiome involved on HPG formation and its performances. In this review, importance has been given to three kinds of immobilization techniques such as adsorption, encapsulation, and entrapment. The HPG, characteristics and types of organic and inorganic supporting materials followed for enhancing hydrogen yield were also discussed. This review also considers the applications of HPG for sustainable and high rate hydrogen production. A detailed discussion on insight of key mechanism for HPGs formation and its performances for stable operation of high rate hydrogen production system are also provided.

High-calorific bio-hydrogen production under self-generated high-pressure condition.

For the use of biologically produced H2, removal of CO2 is an indispensable process. Unlike conventional CO2 removal methods, this study proposed a self-generated high-pressure dark fermentation (HPDF) process as a novel strategy for directly producing high-calorific bio-H2. The pressure was automatically increased by self-generated gas, while the maximum pressure inside fermenter was restricted to 1, 3, 5, 7, and 10 bar in a batch operation. As the pressure increased from 1 to 10 bar, the H2 content increased from 55% to 80%, whereas the H2 yield decreased from 1.5 to 0.9 mol H2/mol hexoseadded. The highest H2 content of 80% was obtained at both of 7 and 10 bars. Increased lactate production with increased abundance of lactic acid bacteria was observed at high-pressure. Despite the lower H2 yields at high-pressure conditions, HPDF was found to be economically beneficial for obtaining high-calorific bio-H2 owing to the low CO2 removal cost.

A review of research trends in the enhancement of biomass-to-hydrogen conversion.

Different types of biomass are being examined for their optimum hydrogen production potentials and actual hydrogen yields in different experimental set-ups and through different chemical synthetic routes. In this review, the observations emanating from research findings on the assessment of hydrogen synthesis kinetics during fermentation and gasification of different types of biomass substrates have been concisely surveyed from selected publications. This review revisits the recent progress reported in biomass-based hydrogen synthesis in the associated disciplines of microbial cell immobilization, bioreactor design and analysis, ultrasound-assisted, microwave-assisted and ionic liquid-assisted biomass pretreatments, development of new microbial strains, integrated production schemes, applications of nanocatalysis, subcritical and supercritical water processing, use of algae-based substrates and lastly inhibitor detoxification. The main observations from this review are that cell immobilization assists in optimizing the biomass fermentation performance by enhancing bead size, providing for adequate cell loading and improving mass transfer; there are novel and more potent bacterial and fungal strains which improve the fermentation process and impact on hydrogen yields positively; application of microwave irradiation and sonication and the use of ionic liquids in biomass pretreatment bring about enhanced delignification, and that supercritical water biomass processing and dosing with metal-based nanoparticles also assist in enhancing the kinetics of hydrogen synthesis. The research areas discussed in this work and their respective impacts on hydrogen synthesis from biomass are arguably standalone. Thence, further work is still required to explore the possibilities and techno-economic implications of combining these areas for developing robust and integrated biomass-to-hydrogen synthetic schemes.

Surpassing the current limitations of high purity H2 production in microbial electrolysis cell (MECs): Strategies for inhibiting growth of methanogens.

Microbial electrolysis cells (MECs) are perceived as a potential and promising innovative biotechnological tool that can convert carbon-rich waste biomass or wastewater into hydrogen (H2) or other value-added chemicals. Undesired methane (CH4) producing H2 sinks, including methanogens, is a serious challenge faced by MECs to achieve high-rate H2 production. Methanogens can consume H2 to produce CH4 in MECs, which has led to a drop of H2 production efficiency, H2 production rate (HPR) and also a low percentage of H2 in the produced biogas. Organized inference related to the interactions of microbes and potential processes has assisted in understanding approaches and concepts for inhibiting the growth of methanogens and profitable scale up design. Thus, here in we review the current developments and also the improvements constituted for the reduction of microbial H2 losses to methanogens. Firstly, the greatest challenge in achieving practical applications of MECs; undesirable microorganisms (methanogens) growth and various studied techniques for eliminating and reducing methanogens activities in MECs were discussed. Additionally, this extensive review also considers prospects for stimulating future research that could help to achieve more information and would provide the focus and path towards MECs as well as their possibilities for simultaneously generating H2 and waste remediation.

Recovering hydrogen production performance of upflow anaerobic sludge blanket reactor (UASBR) fed with galactose via repeated heat treatment strategy.

This study evaluated the effect of repeated heat treatment towards the enhancement of hydrogen fermentation from galactose in an upflow anaerobic sludge blanket reactor with the hydraulic retention time of 6h and the operation temperature of 37°C. The hydrogen production rate (HPR) and hydrogen yield (HY) gradually increased up to 9.1L/L/d and 1.1mol/mol galactose, respectively, until the 33rd day of operation. When heat treatment at 80°C for 30min was applied, hydrogen production performance was enhanced by 37% with the enrichment of hydrogen producing bacteria population. The HPR and HY were achieved at 12.5L/L/d and 1.5mol/mol hexose, respectively, during further 30 cycles of reactor operation. The repeated heat treatment would be a viable strategy to warrant reliable continuous hydrogen production using mixed culture.

Mesophilic continuous fermentative hydrogen production from acid pretreated de-oiled jatropha waste hydrolysate using immobilized microorganisms.

Mesophilic hydrogen production from acid pretreated hydrolysate (biomass concentration of 100g/L and 2% hydrochloric acid) of de-oiled jatropha waste was carried out in continuous system using immobilized microorganisms at various hydraulic retention times (HRTs) ranging from 48 to 12h. The experimental results of the reusability of immobilized microorganisms showed their stability up to 10 cycles with an average cumulative hydrogen production of 770mL/L. The peak hydrogen production rate and hydrogen yield were 0.9L/L*d and 86mL/greducing sugars added, respectively at 16h HRT, with butyrate as the predominant volatile fatty acid. The microbial community analysis revealed that majority of the PCR-DGGE bands were assigned to genus Clostridium and were perhaps the key drivers of the higher hydrogen production.

Improvement of hydrogen fermentation of galactose by combined inoculation strategy.

This study evaluated the feasibility of anaerobic hydrogen fermentation of galactose, a red algal biomass sugar, using individual and combined mixed culture inocula. Heat-treated (90°C, 30 min) samples of granular sludge (GS) and suspended digester sludge (SDS) were used as inoculum sources. The type of mixed culture inoculum played an important role in hydrogen production from galactose. Between two inocula, granular sludge showed higher hydrogen production rate (HPR) and hydrogen yield (HY) of 2.2 L H2/L-d and 1.09 mol H2/mol galactoseadded, respectively. Combined inoculation (GS + SDS) led to an elevated HPR and HY of 3.1 L H2/L-d and 1.28 mol H2/mol galactoseadded, respectively. Acetic and butyric acids are the major organic acids during fermentation. Quantitative polymerase chain reaction (qPCR) revealed that the mixed culture generated using the combined inoculation contained a higher cluster I Clostridium abundance than the culture produced using the single inoculum.

Microbial responses to various process disturbances in a continuous hydrogen reactor fed with galactose.

In this study, microbial responses of a continuous hydrogen reactor fed with galactose have been investigated. Process disturbances reduced H2 production performance as well as large fluctuations in microbial diversity. The peak values of the hydrogen yield (HY) was not influenced greatly during the steady state period, and accounted as 2.01 ± 0.05 and 2.14 ± 0.03 mol/mol galactoseadded, while hydraulic retention time (HRT) was at 12 and 8 h, respectively. Microbial community analysis via 454 pyrosequencing revealed that functional redundancy following changes in the microbial community distribution led to the stability of the fermentation performance. The butyrate to acetate (B/A) ratio well correlated with changes in the microbial community. The energy generation rate and energy yield resulted in the peak values of 134 kJ/L-d and 612 kJ/moladded.

Biofabrication and characterization of silver nanoparticles using aqueous extract of seaweed Enteromorpha compressa and its biomedical properties.

Green synthesis of nanoparticles using seaweeds are fascinating high research attention nowadays and also gaining center of attention in biomedical applications. In this work, we have synthesized biocompatible and functionalized silver nanoparticles using an aqueous extract of seaweed Enteromorpha compressa as a reducing as well as stabilizing agent and their efficient antimicrobial and anticancer activity are reported here. The UV-vis spectra of AgNPs showed the characteristics SPR absorption band at 421 nm. The chemical interaction and crystalline nature of the AgNPs were evaluated by FT-IR and XRD studies. The XRD result of AgNPs shows typical Ag reflection peaks at 38.1°, 44.2°, 64.4° and 77.1° corresponding to (111), (200), (220) and (311) Bragg's planes. The surface morphology and composition of the samples were observed by HRTEM, EDS and SAED pattern analyses. Spherical shaped Ag nano structures were observed in the size ranges between 4 and 24 nm with clear lattice fringes in the HRTEM image. This report reveals that seaweed mediated synthesis of AgNPs and sustained delivery of Ag ions to the bacterial and fungal surface have been reducing their growth rate which was evaluated by well diffusion assay. The synthesized AgNPs showed favorable cytotoxicity against Ehlrich Ascites Carcinoma (EAC) cells with IC50 value was recorded at 95.35 µg mL-1. This study showed cost effective silver nanoparticles synthesis with excellent biocompatibility and thus could potentially be utilized in biomedical and pharmaceutical applications.

A review on bio-electrochemical systems (BESs) for the syngas and value added biochemicals production.

Bio-electrochemical systems (BESs) are the microbial systems which are employed to produce electricity directly from organic wastes along with some valuable chemicals production such as medium chain fatty acids; acetate, butyrate and alcohols. In this review, recent updates about value-added chemicals production concomitantly with the production of gaseous fuels like hydrogen and methane which are considered as cleaner for the environment have been addressed. Additionally, the bottlenecks associated with the conversion rates, lower yields and other aspects have been mentioned. In spite of its infant stage development, this would be the future trend of energy, biochemicals and electricity production in greener and cleaner pathway with the win-win situation of organic waste remediation. Henceforth, this review intends to summarise and foster the progress made in the BESs and discusses its challenges and outlook on future research advances.

Mixed-culture H2 fermentation performance and the relation between microbial community composition and hydraulic retention times for a fixed bed reactor fed with galactose/glucose mixtures.

This study examined the mesophilic continuous biohydrogen fermentation from galactose and glucose mixture with an initial substrate concentration of 15 g/L (galactose 12 g/L and glucose 3 g/L) as a resembling carbon source of pretreated red algal hydrolyzate. A fixed bed reactor was fed with the sugar mixture at various hydraulic retention times (HRTs) ranging 12 to 1.5 h. The maximum hydrogen production rate of 52.6 L/L-d was found at 2 h HRT, while the maximum hydrogen yield of 2.3±0.1 mol/mol hexoseadded, was achieved at 3 h HRT. Microbial communities and species distribution were analyzed via quantitative polymerase chain reaction (qPCR) and the dominant bacterial population was found as Clostridia followed by Lactobacillus sp. Packing material retained higher 16S rRNA gene copy numbers of total bacteria and Clostridium butyricum fraction compared to fermentation liquor. The finding of the study has demonstrated that H2 production from galactose and glucose mixture could be a viable approach for hydrogen production.

Microbiome involved in microbial electrochemical systems (MESs): A review.

Microbial electrochemical systems (MESs) are an attracting technology for the disposal of wastewater treatment and simultaneous energy production. In MESs, at the anode microorganisms through the catalytic activity generates electrons that can be converted into electricity or other valuable chemical compounds. Microorganisms those having ability to donate and accept electrons to and from anode and cathode electrodes, respectively are recognized as 'exoelectrogens'. In the MESs, it renders an important function for its performance. In the present mini-review, we have discussed the role of microbiome including pure culture, enriched culture and mixed culture in different BESs application. The effects of operational and biological factors on microbiome development have been discussed. Further discussion about the molecular techniques for the evaluation of microbial community analysis is addressed. In addition different electrochemical techniques for extracellular electron transfer (EET) mechanism of electroactive biofilms have been discussed. This review highlights the importance of microbiome in the development of MESs, effective operational factors for exo-electrogens activities as well their key challenges and future technological aspects are also briefly discussed.