Characteristics of a phototrophic sludge producing hydrogen from acetate and butyrate

A mixed phototrophic sludge was enriched from the sediment of a local river for continuous hydrogen production from acetate and butyrate in a complete-mix reactor. At pH 7.0–7.5 and , the optimal hydrogen production rate at 48 h of hydraulic retention time (HRT) for 150 days of steady-state operation averaged with of biomass. The sludge yield averaged -VSS/g-COD. Results of batch experiments showed an optimal pH of 8.5 and an optimal concentration of 2 mM for hydrogen production. At 10 mM, severely inhibited the hydrogen production. Three of the five OTUs classified from 26 clones developed from the seed sludge were phototrophs, based on phylogenetic analysis. Among them, OTU LA15, which is closely related to Rhodobacter sp., was most likely responsible to the hydrogen production.     

Extreme-thermophilic biohydrogen production from lignocellulosic bioethanol distillery wastewater with community analysis of hydrogen-producing microflora

Extreme-thermophilic biohydrogen production from distillery wastewater was investigated in batch and continuous-mode operation. Hydrogen-producing mixed culture was enriched by repeated batch cultivations. Effect of temperature and pH on biohydrogen yield was investigated in batch experiments. The highest hydrogen yield of 196. mL/g-volatile solids_addded (VS_added) was obtained at 70 °C and pH 7.0 in batch culture. Continuous biohydrogen production was performed in CSTR reactor with yield of 172.0 mL/g-VS_added at HRT (hydraulic retention time) of 4 days. The main metabolic products were acetate, lactate, and ethanol. Community structure of hydrogen-producing microflora was investigated by 16S rRNA gene sequence analysis. The microorganisms involved in both batch and continuous-mode operation were similar and hydrogen production was carried out by a group of extreme-thermophilic bacterial species related to Thermotoga, Coprothermobacter, Caldanaerobacter, Thermobrachium, and Caldicellulosiruptor.     

16S rRNA gene based analysis of the microbial diversity and hydrogen production in three mixed anaerobic cultures

To explore of role of microbial diversity and its functionality in commercial bioreactors, three anaerobic microbial communities from Ontario, Canada were characterized using 16S rRNA gene-based, clone library sequencing and terminal restriction fragment length polymorphism (T-RFLP) and compared with the hydrogen (H₂) and methane yields. The T-RFLP method showed more operational taxonomic units than the clone library sequence analysis; however, the two methods showed similar dominant species and relative diversity while Spearman's Rank correlation coefficient (r) values ranged from 0.82 to 0.91. The Chao 1 and Shannon-Wiener indices revealed that the cultures samples have highly diverse microbial communities. Comparatively, cultures from a municipal wastewater treatment plant (CA) showed more diversity than those from facilities treating effluents from a baby food processor and a brewery. Even though culture CA has the highest microbial diversity, low H₂ and methane production yield was attributed to the presence of sulphate reducers, propionate producers and a low percentage of methanogens. This study confirms that the selection of the source of mixed anaerobic cultures plays an important role in H₂ and methane production.     

Bacterial community analyses by pyrosequencing in dark fermentative H2-producing reactor using organic wastes as a feedstock

Hydrogen(H₂)-producing bacterial community structures of the dark fermentation system in a batch reactor were investigated during 48 h by analyzing 16S rRNA gene sequences obtained from pyrosequencing. Organic wastes composed of food waste and sewage sludge were used as a feedstock. After heat treatment (90 °C for 20 min) of the feedstock, H₂ was naturally evolved under anaerobic mesophilic conditions, showing a H₂ yield of 2.26 mol H₂/mol hexose_added. The bacterial community structure of the initial inoculum (microbial community at the starting point (0 h)) combined with heat treated food waste and sewage sludge was mainly comprised of Proteobacteria and Bacteroidetes. After 6 h operation, the sequences that belong to other groups except Firmicutes decreased dramatically and were not observed at all in the latter samples. Clostridium spp., which were negligible in the inoculum, took over the main bacterial community by taking charge of H₂ production. Among the phylum Firmicutes, the sequences closely related with Clostridium sordellii ATCC 9714^T, Clostridium perfringens ATCC 13124^T, and Clostridium butyricum ATCC 19398^T became predominant in the time series within 48 h. Overall, the results showed how fast the Clostridium spp. overwhelmed the bacterial community in dark fermentative H₂ production conditions, where they were at a negligible amount at the start.     

Performance and composition of bacterial communities in anaerobic fluidized bed reactors for hydrogen production: Effects of organic loading rate and alkalinity

This study evaluated the effects of the organic loading rate (OLR) and pH buffer addition on hydrogen production in two anaerobic fluidized bed reactors (AFBRs) operated simultaneously. The AFBRs were fed with glucose, and expanded clay was used as support material. The reactors were operated at a temperature of 30 °C, without the addition of a buffer (AFBR1) and with the addition of a pH buffer (AFBR2, sodium bicarbonate) for OLRs ranging from 19.0 to 140.6 kg COD m⁻³ d⁻¹ (COD: chemical oxygen demand). The maximum hydrogen yields for AFBR1 and AFBR2 were 2.45 and 1.90 mol H₂ mol⁻¹ glucose (OLR of 84.3 kg COD m⁻³ d⁻¹), respectively. The highest hydrogen production rates were 0.95 and 0.76 L h⁻¹ L⁻¹ for AFBR1 and AFBR2 (OLR of 140.6 kg COD m⁻³ d⁻¹), respectively. The operating conditions in AFBR1 favored the presence of such bacteria as Clostridium, while the bacteria in AFBR2 included Clostridium, Enterobacter, Klebsiella, Veillonellaceae, Chryseobacterium, Sporolactobacillus, and Burkholderiaceae.     

Diversity of cultivable hydrogen-producing bacteria isolated from agricultural soils, waste water sludge and cow dung

This project aimed to study the diversity of cultivable hydrogen-producing bacteria, isolated from agricultural soils, waste water sludge and cow dung by analyzing 16S rRNA gene. Isolation performed anaerobically on nutrient agar using environmental samples as inoculum yielded 106 pure isolates. These isolates were tested for their capability to produce hydrogen. Then 16S rRNA gene of the 11 isolates having such ability were PCR amplified and subjected to restriction fragment length polymorphism (RFLP) analysis in order to group them into operational taxonomic units (OTUs). RFLP was evaluated for its ability to group the 1500-1600 bp PCR products into OTUs. Isolates were presumptively identified by analysis of partial 16S rRNA gene sequence data. Each OTU was found to be phylogenetically cohesive. The 11 isolates were put into 2 main groups. Group 1 composted of WS-2-2, AS_I-1 and AS_I-2 whose partial 16S rRNA genes showed similarity of 98-99% to members of the genus Paenibacillus. Group 2 composted of WS-4-2, Lao-1-2, WS-7-11, AS-1, AS-4, CD-5 and CD-6 having highest similarity of 98-99% to members of four genera in the family Enterobacteriacea. AS_I-2 which produced the highest amount of hydrogen gas of 2.70 ml had the highest 16S rRNA gene similarity of 99% to Paenibacillus polymixa.     

Hydrogen production from rotten dates by sequential three stages fermentation

This study was devoted for H₂ production from rotten fruits of date palm (Phoenix dactylifera L.) by three fermentation stages. A facultative anaerobe, Escherichia coli EGY was used in first stage to consume O₂ and maintain strict anaerobic conditions for a second stage dark fermentative H₂ production by the strictly anaerobic Clostridium acetobutylicum ATCC 824. Subsequently, a third stage photofermentation using Rhodobacter capsulatus DSM 1710 has been conducted for the H₂ production. The maximum total H₂ yield of the three stages (7.8 mol H₂ mol⁻¹ sucrose) was obtained when 5 g L⁻¹ of sucrose was supplemented to fermentor as rotten date fruits. A maximum estimated cumulative H₂ yield of the three stages (162 LH₂ kg⁻¹ fresh rotten dates) was estimated at the (5 g L⁻¹) sucrose concentration. These results suggest that rotten dates can be efficiently used for commercial H₂ production. The described protocol did not require addition of a reducing agent or flashing with argon which both are expensive.     

Evaluation of Bunsen reaction at elevated temperature and high pressure in continuous co-current reactor in iodine-sulfur thermochemical process

Bunsen reaction is one of the three reaction steps of iodine-sulfur process. In present study, Bunsen reaction is carried out in co-current reactor to identify effect of different operating conditions on concentrations of Bunsen reaction product mixture. Bunsen reaction studies have been done in tubular reactor, which is made of tantalum tube and stainless steel jacket, in 50–80 °C temperature range, 2–6 bar (g) pressure range. Feed flow rates are varied for HIx (mixture of hydroiodic acid, water and iodine) 1.2 l/h - 3 l/h, SO₂ 0.02 g/s – 0.24 g/s and O₂ 0.008 g/s ?0.016 g/s. It has been observed that, increasing SO₂ feed flow rate and pressure results in increased mole fraction of HI in HIx phase and H₂SO₄ in sulfuric acid phase. Increase in temperature increased the mole fraction of HI in HIx phase but decreased the mole fraction of H₂SO₄ in sulfuric acid phase. Increase in feed I₂/H₂O ratio and HIx feed flow rate, decreased the mole fraction of HI in HIx phase. Higher pressure improved the conversion of Bunsen reactants to products.     

Electricity generation and microbial community structure of air-cathode microbial fuel cells powered with the organic fraction of municipal solid waste and inoculated with different seeds

The organic fraction of municipal solid waste (OFMSW), normally exceeding 60% of the waste stream in developing countries, could constitute a valuable source of feed for microbial fuel cells (MFCs). This study tested the start-up of two sets of OFMSW-fed air-cathode MFCs inoculated with wastewater sludge or cattle manure. The maximum power density obtained was 123 ± 41 mW m⁻² in the manure-seeded MFCs and 116 ± 29 mW m⁻² in the wastewater-seeded MFCs. Coulombic efficiencies ranged between 24 ± 5% (manure-seeded MFCs) and 23 ± 2% (wastewater-seeded MFCs). Chemical oxygen demand removal was >86% in all the MFCs and carbohydrate removal >98%. Microbial community analysis using 16S rRNA gene pyrosequencing demonstrated the dominance of the phylum Firmicutes (67%) on the anode suggesting the possible role of members of this phylum in electricity generation. Principal coordinate analysis showed that the microbial community structure in replicate MFCs converged regardless of the inoculum source. This study demonstrates efficient electricity production coupled with organic treatment in OFMSW-fueled MFCs inoculated with manure or wastewater.     

Hydrogen supply chain and challenges in large-scale LH2 storage and transportation

Hydrogen is considered to be one of the fuels of future and liquid hydrogen (LH2) technology has great potential to become energy commodity beyond LNG. However, for commercial widespread use and feasibility of hydrogen technology, it is of utmost importance to develop cost-effective and safe technologies for storage and transportation of LH2 for use in stationary applications as well as offshore transportation. This paper reviews various aspects of global hydrogen supply chain starting from several ways of production to storage and delivery to utilization. While each these aspects contribute to the overall success and efficiency of the global supply chain, storage and delivery/transport are the key enablers for establishing global hydrogen technology, especially while current infrastructure and technology are being under development. In addition, while all storage options have their own advantages/disadvantages, the LH2 storage has unique advantages due to the familiarity with well-established LNG technology and existing hydrogen technology in space programs. However, because of extremely low temperature constraints, commercialization of LH2 technology for large-scale storage and transportation faces many challenges, which are discussed in this paper along with the current status and key gaps in the existing technology.     

Optimization of substrates for Bioelectricity production by Ochrobactrum pseudintermedium KF026284 in a single chambered microbial fuel cell

A new strain of bacterium Ochrobactrum pseudintermedium KF026284 was isolated from a single chambered microbial fuel cell operated with rumen fluid. The bacterium produced maximum power density of 114 mW/m² (0.7 V, 0.6 mA) when nutrient broth was used as the growth medium. The optimization of electricity generation by O. pseudintermedium KF026284 was carried out using various substrates like cellulose, cellobiose, starch, sucrose, and glucose. The bacterium when fed with cellobiose showed an appreciable and sustainable electricity generation with a power density of 150 mW/m² from the 5th day and a maximum power density of 247 mW/m² on the 11th day.     

Process modeling and optimization of an eco-friendly process for acid gas conversion to hydrogen

Hydrogen sulfide conversion to hydrogen is an attractive alternative for addressing energy problems, waste management, global warming, and supplying hydrogen in petrochemical and refinery plants. This research is focused on the development of an environmentally friendly process for the decomposition of hydrogen sulfide into hydrogen and elemental sulfur. The developed process includes a thermal cracker to produce hydrogen from hydrogen sulfide and a catalytic isothermal reactor to minimize emissions of sulfur contaminants. In the first step, a process flowsheet is planned for hydrogen sulfide conversion considering a real feed case. In the next step, the planned process is modeled based on the governing equations considering the heat and mass transfer resistances in the steady state condition. Then, optimum operating conditions of the designed process are determined considering the maximum hydrogen productivity and minimum contaminant emissions as objective functions. The results show that the designed process is capable to produce 51.03 kmol h^?1 hydrogen and 84.92 kmol h^?1 sulfur as main products. In addition, the rate of CS₂ and COS emission is negligible in the proposed process.     

Modeling and analysis of miniaturized methanol reformer for fuel cell powered mobile applications

In this paper a miniaturized packed bed reactor is analyzed, in which autothermal reforming of methanol occurs to produce sufficient hydrogen for generating 100 W of power. Mass balance equations are developed for each species in the reactor and an energy balance is developed for modeling non-isothermal operation. The pressure drop is modeled via the Ergun equation. Simulations are conducted in MATLAB to determine the effect of process parameters (e.g. steam to methanol ratio, inlet pressure, inlet temperature) on the production of hydrogen. It is shown that the pressure drop is negligible. Simulation results are compared with experimental results from the literature and it shown that there is excellent agreement between the simulation results and experimental results. Process conditions that lead to the generation of sufficient hydrogen for generating 100 W of power are developed.     

Separation and storage of hydrogen by steam-iron process: Effect of added metals upon hydrogen release and solid stability

During the last decade, the steam-iron process has re-emerged as a possible way to separate and/or storage pure hydrogen through the use of metallic oxides subjected to redox cycles. The most renamed candidate to achieve this goal has traditionally been iron oxide. Nevertheless, the study of its behaviour along repetitive reduction/oxidation stages has shown that the hydrogen storage density diminishes abruptly from the first cycle on.To cope with this problem, the inclusion of a second metal oxide in the solid structure has been tried. Isothermal experiments of reduction with hydrogen rich flows and oxidation with steam have been carried out with Al, Cr and Ce as second metals, in nominal amounts from 1% to 10 mol% added to the hematite structure, which has been synthesized in laboratory by coprecipitation. Series of up to seven cycles (reductions followed by oxidations in a thermogravimetric system acting as differential reactor for the gas) have shown that to that point, an almost repetitive behaviour can be obtained, recovering the magnetite (Fe₃O₄) structure after each oxidation step.Since the second metal oxide does not intervene in the reduction/oxidation process, the optimum content of second metal for each species has been determined with the aim to keep the highest hydrogen storage density along cycles.