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International audience; In this study, micrometer thick Ag‐TiO2 coatings were deposited in a single and facile step by spraying the precursor in an atmospheric pressure plasma jet with different concentrations of Ag nanoparticles. The homogenous distribution of Ag decreased the TiO 2 crystal size and increased the surface area. The coatings were characterized to be porous with an anatase phase with improved charge separation and visible light absorption. The photocatalytic activity of the materials was investigated for degrading rhodamine B using a white lamp as a screening method to optimize Ag‐TiO 2 coatings. Then the photodegradation of trace pharmaceutical compounds (TrPCs) was investigated by using a solar light simulator at the optimal condition of a TiO 2 coating with 0.4wt% Ag

International audience; This work is focused on synthesizing and employing one-dimensional (1D) titanium dioxide (TiO2) for hydrogen (H2) production. Based on using electron donors (EDs) (ethanol, methanol, fomic acid and 1,2,3 propanetriol), the increased H2 production, when compared to P25 TiO2 nanoparticles, was due to the large specific surface area (SSA) and enhanced electron mobility of 1D TiO2. The impact of the 1D TiO2 synthesis reaction conditions (temperature, NaOH concentration and the TiO2 precursor concentration) on the photocatalytic H2 production rate was evaluated using a 3-factor 3-level Box Behnken design (BBD). The BBD model demonstrated that the temperature and the NaOH concentration significantly affected the 1D TiO2 phase structure, crystal size, SSA, bandgap and the photocatalytic H2 production rate. The phase structure and crystal size of 1D TiO2 were key factors affecting the H2 production rate. 1D TiO2 containing an anatase phase with a mean crystal size of 20.1 ± 0.2 nm was synthesized at 126 °C, 15 M NaOH and 49 g L−1 TiO2. The maximum H2 production rate of 475 ± 12 μmol·h−1 (quantum efficiency (ε) = 20.2 ± 0.5%) for the 1D TiO2 sample was significantly enhanced when compared to commercial TiO2 P25. The H2 production rate for the optimized 1D TiO2 was significantly enhanced by decorating the structure with Pt and Au. Hydrothermal synthesized of 1D TiO2 provided an efficient and low cost method for producing H2 from ethanol, methanol, fomic acid and 1,2,3 propanetriol.

Developing a global hydrogen (H2) economy is driven by the rapid evolution of solid-state fuel cells for the automotive sector. Approximately 95% of the currently produced H2 is derived from fossil fuels, natural gas, liquid hydrocarbons, coal, and electrolysis. Depleting fossil fuels supplies, energy security, increasing carbon dioxide (CO2) emissions, and climate change are major factors causing the development of carbon-neutral renewable energy supplies, such as ethanol, diesel, and H2. Technologies to produce H2 from carbon-neutral feedstocks and water are currently under investigation using biological and heterogeneous catalyst platforms. Biological H2 production processes utilizing carbon-based agriculture feedstocks and water are examined in this chapter. Feedstocks as well as pretreatment technologies for photofermentation and dark fermentation processes are discussed. Process biochemistry, microbiology, and reactor technology are reviewed for the biophotolysis and fermentation processes together with process economics, recent advances and challenges, current trends, process limitations, and finally, future outlook.

Byproducts from a photocatalytic pretreated model lignin chemical, sodium LS (lignosulfonate), was used to produce electricity in SCMFCs (single chamber microbial fuel cells). Pretreating LS was performed using TiO 2 -UV photocatalysis. Optimization and modeling of the photocatalytic degradation process was performed using the Box-Behnken design method to achieve a maximum BOD 5 to COD ratio. LC-MS (Liquid chromatography–mass spectrometry) analysis was conducted to identify compounds produced from the photocatalysis of LS. The biofilm microbial diversity and performance of SCMFCs fed PrLS (pretreated LS) was compared to SCMFCs fed glucose at the same COD loadings and operating conditions. The PrLS fed SCMFCs, operated at 37 ± 1 °C, generated maximum current and power densities of 6556 ± 360 mA m −3 and 1881 ± 103 mW m −3 , respectively. The corresponding maximum current and power densities normalized to the cathode area were 868 ± 48 mA m −2 and 248 ± 14 mW m −2 , respectively. The SCMFCs removed 77.6 ± 2.3% of the COD of the PrLS and achieved a coulombic efficiency of 17.7 ± 1.2%. This study demonstrated the effectiveness of photocatalysis coupled with a bioelectrochemical system in treating lignin compounds and simultaneously generate electricity.

Photoactive titanium dioxide (TiO2) solids are known to mineralize a variety of organic pollutants into carbon dioxide. TiO2 solids with dimensions in nanometre have shown enhanced catalytic performance due to a large surface to volume ratio. Nano-sized TiO2 have been studied for their catalytic performance either as suspended particle or immobilized coating. From an engineering and economic perspective, immobilized TiO2 nanocatalysts are preferred in variety of applications. However, past studies have shown that using immobilized nano-sized TiO2 is associated with practical constrains of limited stability and lower catalytic performance. Hence, the objective of the present study is to fabricate an immobilized form of TiO2 catalyst with photocatalytic efficiency comparable with nanoparticles slurry, but without the associated practical constrains. An immobilized TiO2 catalyst was prepared from depositing TiO2 nanofibers onto a chemically treated metal support by sol-gel-electrospinning. The fabricated forms were thermally treated to obtain catalytic immobilized TiO2 nanofibers. The effects of varying the parameters of the electrospinning fabrication process on the diameter of the TiO2 nanofibers were also studied. The formation of smaller diameter TiO2 nanofibers was favoured under a large potential gradient and low infusion rate. The fabricated TiO2 nanofibers, with predominantly an anatase crystal structure and a mean diameter of 54.0 ±11.5 nm, were 30-50% lower than the literature values. Improved stability of the immobilized catalyst was observed using a surface-treated metal support. The catalytic performance of the immobilized TiO2 nanofibers for the photocatalysis of aqueous phenol (a toxic water pollutant) was significant and comparable to that of commercially available 5nm TiO2 nanoparticles. Thus, the study reported a novel fabricated form of immobilized TiO2 photocatalyst with comparable performance but lesser practical constraints compared to nanoparticles.

146An immobilized titanium dioxide (TiO2) photocatalyst composed of stacked nanofibers on surface etched aluminum foil was evaluated in the present study for photocatalytic (PC) performance. TiO2 nanofibers were produced by electrospinning and subsequent controlled calcination. Decrease in specific surface area of the TiO2 photocatalyst was observed with increase in calcination temperature from 400°C to 500°C due to sintering of pores and surface aggregation. Increase in rutile crystalline phase and decrease in bandgap energy (Eg) was noted in TiO2 nanofibers calcined at temperature higher than 400°C. A maximum specific surface area (259 ± 23 m2-g-1) and highest Eg (3.24 eV) was recorded for TiO2 nanofibers calcined at 400°C (NF). The PC degradation rate of the nanofiber catalyst was twice that observed for TiO2 nanoparticles (of comparable specific surface area) in slurry. The PC degradation rate of the immobilized TiO2 nanofiber photocatalyst was not noted to change significantly after repeated use.

International audience; One-dimensional TiO2 nanostructure synthesized using a hydrothermal method showed significant differences in the bandgap energies and crystal phase properties under different synthesis conditions. The objectives of this study were to evaluate the effect of the hydrothermal reaction conditions on the bandgap energy and to optimize the reaction conditions using a 3-factor 3-level Box Behnken design. The factors investigated include temperature, NaOH concentration and TiO2 concentration (BBD). A quadratic response surface model predicted optimum conditions for the maximum and minimum bandgap energy. The BBD analysis and other statistical tools provided evidence showing the temperature and NaOH concentration significantly affected the 1D TiO2 bandgap energy. Pure anatase was associated with a higher bandgap energy, whereas the biphasic anatase-rutile and anatase-TiO2-B phases were linked with decreasing the bandgap energy. In addition, the crystal size and specific surface area (SSA) impact on the bandgap energy was due to the size quantization effect.

International audience; Enhanced TiO2 nanorods (TNRs) with partially reduced graphene oxide (RGO) (designated as GT) were prepared for degrading aqueous hazardous pollutants. The degree of RGO oxidation had an important role in affecting the photoelectronic and photocatalytic activities of GT composites. The study examined the impact of the degree of RGO oxidation on the photocatalytic activities. The photocatalytic activity of the materials was investigated for degrading rhodamine b (RhB), methyl orange (MO), methylene blue (MB), and phenol by using ultraviolet (UV) light. The highest photocatalytic activity was observed when the atomic oxygen-to-carbon (O/C) ratio of RGO was 0.130 ± 0.003. This study suggested the photocatalytic performance was maximized by preserving a selected amount of the RGO oxygen-containing groups. The work reported in this study on optimizing the RGO-based TiO2 photocatalyst could serve as a promising approach for preparing and optimizing other types of carbon-based photocatalysts such as graphene-based CdS.

Enhanced TiO

International audience; Quasi-one-dimensional (Q1D) titanium dioxide (TiO2) nanomaterials have attracted attention inphotocatalytic applications because of their high oxidative potential coupled with increasing activesites. In this study, Q1D TiO2 samples with different phase structure, crystal size, and specific surfacearea were produced using a hydrothermal method by varying the reaction conditions (temperature,alkaline concentration, and the TiO2 precursor concentration). A three-factor three-level Box–Behnkendesign (BBD) with three replicates (15 conditions) at the center point was employed to evaluateand optimize the hydrothermal synthesis factors in terms of photocatalysis of rhodamine B (RhB),phenol, methyl orange, and methylene blue. The BBD demonstrated that the temperature and theNaOH concentration significantly affected the Q1D TiO2 crystal size, phase structure, bandgap, andphotocatalytic activity. A reduce temperature at 120°C and a low NaOH concentration at 5 M werefavorable in producing a biphasic anatase–rutile structure with optimum photocatalytic activity.Under a higher temperature of 190°C and with ≥ 10 M NaOH concentration, the presence of TiO2-Bphase resulted in the lowest photocatalytic activity.

Environmental damage, depleting fossil fuels and energy security are major factors driving intensive research efforts to develop carbon neutral or carbon negative technologies which can be used to produce electricity and chemicals. Technologies under development to achieve this goal include those based on bioelectrochemical, biological, thermal and chemical processes. Evolving technologies employing biological as well as electrochemical principles are grouped in the bioelectrochemical systems (BESs) category. The main focus of this chapter is on biocathodes used in BESs.

Hydrogen (H-2) production using mixed anaerobic cultures often suffers severe yield reduction due to the syntrophic association between H-2 consumers (methanogens and homoacetogens) and H-2 producers (acidogens). The objective of this study was to uncouple the syntrophic association between H-2 producers and consumers by optimizing conditions for minimum H-2 consumption using a Box-Behnken design approach. The factors investigated in this study include temperature, pH and linoleic acid (LA) concentration. A quadratic response surface model was developed to predict the H-2 consumed by mixed anaerobic cultures and the optimum conditions for minimum H-2 consumption were 38 degrees C, pH 5.5 and 2 g L-1 LA. Methanogenesis was inhibited in cultures fed 2 g L-1 LA and maintained at pH 6.0 and 53 degrees C. In comparison, both methanogenesis and homoacetogenesis were inhibited in cultures fed 1-2 g L-1 LA and maintained at a pH of 4.5 (Fig. 2B and 2E and Table 2 Expt. # 1, 2 and 11). Microbial diversity analysis revealed that LA fed cultures was dominated by spore forming Clostridium sp. in addition to Syntrophus aciditrophus. In comparison, control cultures were dominated by Eubacterium sp., Methanocalculus halotolerans and Methanococcoides alaskense. This study described an approach for regulating H-2 consumption in mixed cultures by optimizing process and environmental factors. Understanding the effects of these individual factors and their interaction is important in the full-scale operation of H-2 production facilities. Copyright (C) 2014, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.

In this study, hydrogen (H 2 ) production from the fermentation of steam exploded corn stalk (CS) liquor was statistically optimized using a fractional factorial design approach. The factors under consideration included temperature, pH and hydraulic retention time (HRT). Under optimal conditions at 53 °C, a pH at 4.5 and a 9.5 h HRT, the observed maximum H 2 yield of 98 ± 2 mL g −1 TVS together with negligible CH 4 were similar to the model predicted responses. A flux analysis revealed negligible homoacetogenic activity in cultures at 53 °C and low pH (≤5.5). Both homoacetogenic (R17) and methanogenic (R28 and R29) fluxes accounted for more than 68–90% of H 2 consumption in cultures at low temperatures. The low H 2 yields observed in cultures maintained at 21 °C and 37 °C was associated with high lactate and solvent levels. High H 2 yields in cultures at 53 °C were associated with a higher abundance of Clostrdium sp. and CH 4 production at low temperatures was due to the presence of hydrogenotrophic methanogens ( Methanothermobacter marburgensis and Methanobrevibacter ruminatum ) and aceticlastic methanogens ( Methanosaeta sp. and Methanosarcina sp.). The results obtained from this study (within the factor ranges investigated) indicated that steam exploded CS liquor could be a potential substrate for H 2 production using mixed microbial cultures.

Due to the toxicity effects and endocrine disrupting properties of phenolic compounds, their removal from water and wastewater has gained widespread global attention. In this study, the photocatalytic degradation of phenolic compounds in the presence of titanium dioxide (TiO2) nano-particles and UV light was investigated. A full factorial design consisting of three factors at three levels was used to examine the effect of particle size, temperature and reactant type on the apparent degradation rate constant. The individual effect of TiO2 particle size (5, 10 and 32 nm), temperature (23, 30 and 37 °C) and reactant type (phenol, o-cresol and m-cresol) on the apparent degradation rate constant was determined. A regression model was developed to relate the apparent degradation constant to the various factors. The largest photocatalytic activity was observed at an optimum TiO2 particle size of 10 nm for all reactants. The apparent degradation rate constant trend was as follows: o-cresol > m-cresol > phenol. The ANOVA data indicated no significant interaction between the experimental factors. The lowest activation energy was observed for o-cresol degradation using 5-nm TiO2 particles. A maximum degradation rate constant of 0.0138 min−1 was recorded for o-cresol at 37 °C and a TiO2 particle size of 13 nm at a D-optimality value of approximately 0.98. The response model adequately related the apparent degradation rate constant to the factors within the range of factors under consideration.

The impact of different chemical microbial stressors (2-bromoethanesulfonate (BES), furfural, fish oil, lauric acid (LUA) and linoleic acid (LA)) on the inhibition of mesophilic hydrogen (H-2) consumption was examined in this study. Hydrogen consumption half-life values were used to compare the extent of inhibition by the different microbial stressing agents. A statistical analysis of the percent H-2 consumed using Tukey's analysis revealed the following trend: Control > fish oil = linoleic acid (LA (C18:2)) = furfural > BES > lauric acid (LUA (C12:0). The terminal restriction fragment length polymorphism (T-RLFP) results indicated that aceticlastic methanogens (Methanosaeta sp., Methanosarcina sp.) and hydrogenotrophic methanogens (Methanococcus sp.) were inhibited by the different chemical stressing agents. Cultures fed LUA and LA had a high abundance of Clostridium sp., Clostridium propionicum and Propionibacterium acnes. In comparison, BES and furfural fed cultures contained large fractions of Clostridium sp., Eubacteria sp. and Bacteroides sp. while in the fish oil fed cultures, the dominant organism detected was Eubacteria sp. This study indicated that H-2 consumption was affected by the chemical stressing agent concentration. Copyright (C) 2013, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.

Construction materials as well as the electrode configuration are major factors affecting electricity generation in microbial fuel cells (MFCs). Three graphite plateelectrodes(HK06,G347andPOCO3)withdifferentcharacteristics(specificresistance,grainsizeandspecificgravity)wereusedtoevaluateelectricity generation and biofilm formation in MFCs. The electrodes were assessed by operating duplicate MFCs under the same conditions. Electrochemical impedance spectroscopy, cyclic voltammetry and linear sweep voltammetry were used to evaluate the performance of the electrodes. The data indicated the grade of electrode played a critical role in the MFCs performance. Higher power density was observed for the graphite electrode designated as POCO3. The trend for increasing electricity generation was as follows: POCO3 > G347 > HK06. Distinct microbial populations were detected in the biofilm community when comparing the different electrodes. Selecting electrodes for optimum electricity generation is important in the development of laboratory scale and full-scale MFCs.

In this study, a flux balance analysis (FBA) was adopted to estimate the activity of acetogenic H2-consuming reaction. Experimental data at different substrate concentrations of 10, 20, and 30 g COD/L showing the lowest, medium, and highest H2 yields, respectively, were used in the FBA to calculate the fluxes. It was interesting to note that the hydrogenase activity based on R12 (2Fd+ + 2H+ → 2Fd2+ + H2, ferredoxin (Fd)) flux was most active at 10 g COD/L. The flux of R17 (4H2 + 2CO2 → CH3COOH), a mechanism for reutilizing produced H2, increased in steps of 0.030, 0.119, and 0.467 as the substrate concentration decreased. Contradictory to our general understanding, acetate production found to have a negligible or even negative effect on the final H2 yield in dark fermentation.

The effects of furans (furfural and 5-hydroxymethylfurfural (HMF)) on hydrogen (H2) production using mixed anaerobic cultures were evaluated by conducting batch experiments. Two mixed anaerobic cultures (culture A and B) fed furans plus glucose and treated with and without linoleic acid (LA) at pH 5.5 were maintained at 37 °C. In the LA inhibited cultures A and B fed 0.75 g L−1 furfural and 0.25 g L−1 HMF, the maximum H2 yields observed were 1.89 ± 0.27 mol mol−1 glucose and 1.75 ± 0.22 mol mol−1 glucose, respectively. In cultures with maximum H2 yields, Clostridium sp. and Flavobacterium sp. were dominant. Acetate, butyrate and ethanol were the major soluble metabolites detected in cultures A and B whereas propionate was also dominant in culture B. A canonical correspondence analysis based on the byproducts and the relative abundance of the terminal-restriction fragments revealed less variation between cultures treated with LA and low correlation value between the factors and the species composition.

Optimizing sulfate removal by a mixed anaerobic mesophilic culture fed glucose, linoleic acid (LA) and sulfate under several pH conditions was performed using a three factor three level Box-Behnken design (BBD). Based on the BBD approach, a statistical model was developed to predict the residual sulfate concentration. The LA concentration, initial pH and the COD/SO4(2-) ratio were the three experimental factors under consideration. Increasing the COD/SO4(2-) ratio increased the quantity of sulfate removed. The COD/SO4(2-) ratio showed the largest effect on reducing the sulfate level. Significant interactions between the three experimental factors were confirmed by the surface plots, interaction plot and ANOVA. An analysis of residuals verified accuracy of the model. Acetate and H2 production was dominant in cultures with the pH set at 6.0 and 6.75 and fed LA. After 168 h, butyrate and H2S were associated with the largest quantity of sulfate removed. At a D-optimality value of 1.0, a minimum response (residual sulfate concentration) of 36.2 mg L(-1) was recorded at 1500 mg L(-1) LA with a COD/SO4(2-) ratio of 2.18 and a pH set at 6.0. Based on the conditions under consideration, the model provided a useful approach for predicting the residual sulfate concentration in inhibited mixed anaerobic cultures.

In this study, controlling an anaerobic microbial community to increase the hydrogen (H-2) yield during the degradation of lignocelluosic sugars was accomplished by adding linoleic acid (LA) at low pH and reducing the hydraulic retention time (HRT) of an anaerobic sequencing batch reactor (ASBR). At pH 5.5 and a 1.7 d HRT, the maximum H2 yield for LA treated cultures fed glucose or xylose reached 2.89 +/- 0.18 mol mol(-1) and 1.94 +/- 0.17 mol mol(-1), respectively. The major soluble metabolites at pH 5.5 with a 1.7 day HRT differed between the control and LA treated cultures. A metabolic shift toward H-2 production resulted in increased hydrogenase activity in both the xylose (13%) and glucose (34%) fed LA treated cultures relative to the controls. In addition, the Clostridia population and the H-2 yield were elevated in cultures treated with LA. A flux balance analysis for the LA treated cultures showed a reduction in homoacetogenic activity which was associated with reducing the Bacteriodes levels from 12% to 5% in the glucose fed cultures and 16% to 10% in the xylose fed cultures. Strategies for controlling the homoacetogens and optimal hydrogen production from glucose and xylose are proposed. Copyright (C) 2012, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.

The effects of lauric (LUA), myristic (MA), palmitic (PA), and a mixture of myristic:palmitic (MA:PA) acids on hydrogen (H-2) production from glucose degradation using anaerobic mixed cultures were assessed at 37 degrees C with an initial pH set at 5.0 and 7.131 mM of each acid. The maximum H-2 yield (2.53 +/- 0.18 mol mol(-1) glucose) was observed in cultures treated with PA. A principal component analysis (PCA) of the by-products and the microbial population data sets detected similarities between the controls and PA treated cultures; however, differences were observed between the controls and PA treated cultures in comparison to the MA and LUA treated cultures. The flux balance analysis (FBA) showed that PA decreased the quantity of H-2 consumed via homoacetogenesis compared to the other LCFAs. The control culture was dominated by Thermoanaerovibrio acidaminovorans (60%), Geobacillus sp. and Eubacterium sp. (28%), while Clostridium sp. was less than 1%. Treatment with PA, MA, MA:PA, or LUA increased the H-2 producers (Clostridium sp. and Bacillus sp.) population by approximately 48, 67, 86, and 86%, respectively. Copyright (C) 2012, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.

Enhancing hydrogen (H 2 ) production by inhibiting or controlling the growth of H 2 consuming microorganisms can be accomplished by thermal and chemical methods as well as engineering control strategies. In this study, H 2 production from a mixed anaerobic community was evaluated after applying heat shock, acid treatment, alkaline treatment or adding linoleic acid (LA). The H 2 yield trend based on the Tukey's test was as follows: LA ≅ acid ≅ heat shock ≅ alkali > control. In comparison to the control cultures (without any treatment), methanogenic activity was not detected in cultures, which were heat-shocked and chemically treated with acid or LA. However, methanogenic activity was observed in cultures treated with alkali. Lactic acid was observed in controls (720 mg L −1 ) and cultures treated with alkali (600 mg L −1 ). Even though acetic acid production was dominant in cultures treated with alkali, the H 2 yield was not the greatest in this culture. Based on the PCA, the microbial populations in the LA and heat treated cultures were more similar when compared to the other treatment methods. Note in the case of LA, the maximum H 2 yield was likely a result of a greater inhibitory effect imposed on the different H 2 consuming populations.

In this study, the long term effect of different microbial stressing agents on hydrogen (H-2) production was examined using repeated batch cultivations. When compared to thermophilic cultures, higher H-2 yields were observed in mesophilic cultures receiving repeated glucose addition. Methane production was only observed in control mesophilic cultures receiving repeated 5 glucose additions. Lower hydrogenase evolution specific activity was observed in thermophilic cultures (except alkali-treated cultures) compared to mesophilic cultures. For both mesophilic and thermophilic cultures, the hydrogenase uptake specific activity of the untreated control cultures exhibited higher levels of activity than the pre-treated cultures. A flux balance analysis (FBA) showed negligible homoacetogenic flux in mesophilic cultures pretreated with linoleic acid (IA) and loading shock (LS) after successive batch cultivations. The homoacetogenic flux accounted for approximately 98% loss in the H-2 yield in untreated mesophilic control cultures. Both homoacetogens (Eubacterium sp.) and aceticlastic methanogens (Methanosaeta sp. and Methanosarcina sp.) were abundant in the control cultures. In comparison, Clostridium sp. were dominant in mesophilic stress treated cultures whereas under thermophilic conditions, the dominant microorganisms were Flavobacterium sp., Bacillus sp., Thermoanaerobacter sp., Bacteroides sp., Lactobacillus sp. and Thioalkalivibrio sp. (C) 2015 Elsevier Ltd. All rights reserved.

Predicted increases in greenhouse gas emissions, depleting fossil fuel supplies, global conflicts, and energy security are major factors driving the search for renewable energy supplies. Based on future energy demand projections, biofuels production is expected to increase. However, this increase represents a small fraction of this growing demand because the land area required to grow sufficient biofuels crops is unavailable. Hence, fulfilling the growing energy demand after attaining peak fossil fuel production will include using a combination of energy sources such as renewables, wind, geothermal, nuclear, hydroelectric, solar, and coal. Current and potential feedstocks include grains, grasses, root crops, oil seeds, algae, and lignocellulosics. Grains, sugar crops, and lignocellulosics are the main feedstocks used in full-scale first- and second-generation ethanol processes. While first-generation biodiesel is produced mainly from corn, soybeans, canola oil, rapeseed, palm oil, Jatropha, and coconut oil, second-generation fuels are produced from lignocellulosics. Third-generation technology employs several processes to produce a variety of biofuels from algae while fourth-generation technologies, a developing concept, is intended to employ genetically modified terrestrial or aquatic plants. In another concept, fourth-generation technologies can be configured with CO2 sequestration and storage. First-generation biobutanol is produced from corn or molasses and from sugar beet as well as sugarcane, while second-generation production processes utilize lignocellulosics such as corn stover, rice straw, corn fiber, switchgrass, alfalfa, reed canary grass, sugarcane bagasse, Miscanthus, waste paper, dry distillers grain with solubles (DDGS), and soy molasses. A variety of technologies, based on the enzyme systems, are currently under investigation for producing biohydrogen. Biohydrogen production routes are divided into biophotolysis (direct/indirect), dark fermentation, and photofermentation. Increasing global demand is expected to drive increasing bioethanol and biobutanol production using food and nonfood feedstocks. At the same time, researchers are developing technologies to produce biohydrogen and biodiesel. Biohydrogen and biodiesel production technologies are in their developmental stages; however, with innovation, these technologies are expected to mature into economical processes.

The role of different chemical and physical factors in enhancing biohydrogen production from xylose using a mixed anaerobic culture was examined under mesophilic conditions. A fractional factorial design (FFD) 3 (k–p) was used to optimize pH, the oleic acid (OA) concentration and the biomass concentration. The FFD analysis indicated that the hydrogen (H 2 ) yield was affected by 3 single factors as well as by 2 factor interactions. Under optimum conditions (1600 mg L −1 of oleic acid (OA) and 1900 mg L −1 VSS and pH 6.7), the H 2 yield reached 2.64 ± 0.12 mol mol −1 of xylose (80% of the theoretical yield). Based on the ANOVA and Pareto chart analysis, the linear and quadratic OA and pH terms were significant and the linear and quadratic VSS terms were insignificant. Normally distribution of the residuals was confirmed from the Anderson-Darling (AD) plot. The studentized residuals versus the predicted values plot clearly demonstrated that the data points were randomly scattered.

Using low value lignocellulosic feedstocks to produce hydrogen (H2) could be a more economically viable option in comparison to grains derived from agriculture crops. The glucose and xylose composition of lignocellulosic feedstocks is relatively high and can vary from 55–65% to 35–45%, respectively. Mixed anaerobic cultures which are suitable for fermentative H2 production are capable of utilizing a variety of substrates. However, the H2 yields from mixed anaerobic cultures are low because of the syntrophic association between H2 producers and H2 consumers. In this study, oleic acid (OA) was used to control the growth of H2 consumers and hence, increase the H2 yield. The H2 yield was affected by changing the glucose to xylose ratio. In control cultures, the H2 yield (1.6 ± 0.32 mol H2 mol−1 glucose) was low because the electron flux was diverted towards the formation of propionate and methane in addition to acetate and butyrate. In presence of 2000 mg L−1 OA, 60–70% of the electron fluxes were diverted towards acetate and butyrate production and this resulted in a maximum H2 yield of 2.84 ± 0.24 mol H2 mol−1 glucose. This study revealed that the addition of OA to the mixed anaerobic cultures is an effective method for diverting the electron fluxes to H2 instead of CH4. Based on a principal component analysis 1 (PCA 1), the control cultures were related; however, in case of the OA treated cultures, they were related in terms of PCA 1 and PCA 2.

The internal fluxes of mixed anaerobic cultures fed 2000 mg l−1 linoleic acid (LA) plus glucose at 6 initial pH conditions and maintained at 37 °C were estimated using a flux balanced analysis (FBA). In cultures fed LA at pH 7, less than 8% of the flux was diverted to CH4. At an initial pH ≥ 5.5, the quantity of glucose removed was greater than 95%; however, at pH 4.5 and 5.0 the quantity consumed were 38% and 75%, respectively. The FBA output showed that the acetogenic H2-consumers were responsible for more than 20% of the H2 consumed. Adding LA and decreasing the pH was ineffective in reducing the activity of acetogenic H2-consumers. As the initial pH decreased, the acetogenic H2-consuming flux decreased in the presence of 2000 mg l−1 LA. A maximum H2 yield of 1.55 mol mol−1 glucose consumed (peak hydrogenase flux (R12)) was attained when the acetogenic H2-consuming flux reached 0.42 mol at a pH of 5.5.

A response surface model (RSM) for predicting the diameter of electrospun titanium dioxide (TiO 2 ) nanofibers was developed using the Box–Benkhen experimental design (BBD) technique. The three electrospinning factors in preliminary studies using the BBD design included the potential difference (kV), the infusion rate (ml h −1 ) and the separation distance between electrodes (cm). Verification of the model was accomplished through the analysis of residuals. The model was subsequently used to locate the optimal experimental values (electrospinning variables) which yielded the minimum TiO 2 nanofiber diameter. A minimum diameter of 43.3 nm was predicted by the model when the potential difference was set at 40 kV, the electrodes were separated by 32.5 cm apart and the infusion rate was set at 0.6 ml h −1 . The average experimental observed fiber diameter (47.8 ± 8.7 nm) was 9.5% greater than the predicted value (43.3 nm) under identical electrospinning settings. The nanofibers diameter was affected by the percent titanium (Ti) (by weight) in the electrospinning solution. Hence, in the final analysis, the model was refined to include a term representing the proportion of Ti in the electrospinning solution. A smaller nanofibers diameter of 39.0 ± 6.6 nm with a specific surface area (SSA) of 259 ± 23 m 2 g −1 was produced using a solution containing 1.3% Ti. The SSA value was comparable with that for commercially available 5 nm TiO 2 nanoparticles. The diameter of the immobilized TiO 2 nanofibers was significantly less than the values reported in the literature. The model could serve as a tool for researchers.

Optimizing the hydrogen (H2) yield at several initial pH conditions in a mixed batch anaerobic mesophilic culture fed with glucose and linoleic acid (LA) was performed using a three factor three level Box–Benkhen design (BBD). Based on the BBD approach, a statistical model was developed to predict the H2 yield. The variables considered for the experimental design were the LA concentration, the initial pH and the number of times glucose was added to the culture. The D-optimality method predicted a maximum H2 yield of 3.49 mol H2 mol glucose−1 for cultures fed 1.9 g l−1 LA, maintained at an initial pH of 5.15 and received 1.79 glucose additions. The response outcome (H2 yield of 3.38 ± 0.22 mol mol glucose−1) at the nearest setting of the experimental factors (2.0 g l−1 LA, an initial pH of 5.0 and two glucose additions) was 3.3% less than the predicted maximum value. The model provides a useful approach for predicting H2 production when H2 consumers are inhibited in mixed batch anaerobic cultures.

Hydrogen ( H2 ) production was maximized and methane ( CH4 ) formation was minimized in a mixed anaerobic culture which was maintained at 21°C and fed glucose plus unsaturated long chain fatty acids (LCFAs). The initial pH in the batch reactors was 7.8±0.2 . The two LCFAs under consideration included linoleic acid (LA) (two C═C bonds) and oleic acid (OA) (one C═C bond). Hydrogen production was observed when glucose was injected on Day 0 and again after Day 4. The H2 yield in cultures fed LA was less than those receiving OA. The H2 yield reached a maximum of approximately 1.1 mol H2 mol−1 glucose when the LA level was 2,000 mg L−1 . In the case of OA, a maximum yield of 1.3 mol H2 mol−1 glucose was attained with 2,000 mg L−1 . The inhibition caused by the addition of LA or OA diverted a fraction of electrons toward proton reduction. Under maximum H2 production conditions in the LA fed cultures the acetate production pathway was repressed, while in cultures fed OA the acetate pathway was dominant. T...

A four factor three level Box-Benkhen design (BBD) was developed to describe the photocatalytic degradation of phenol in an aqueous media. The four process variables under consideration in BBD model included titanium dioxide (TiO2) catalyst size, TiO2 concentration, dissolved oxygen (DO) concentration and phenol concentration. The model predicted a maximum degradation rate (0.083 min−1) with conditions set at 9.091 nm TiO2 particle size, 1.0 g/l TiO2, 31.0 mg/l DO and 40 mg/l phenol. A response outcome computed using experimental data for the 10 nm nanoparticle size catalyst was 13% less than the maximum value. The data suggest that small catalytic particle size augmented the quantum yield in the photocatalytic degradation process with the maximum located at an approximate catalyst size of 10 nm. The photocatalytic degradation rate constant followed an Arrhenius dependency with activation energy of 13.55 kJ/mol K for the 10 nm TiO2 particles.

Hydrogen production from glucose using a mixed anaerobic culture was assessed under batch conditions by adjusting the initial pH and adding linoleic acid (LA). At an initial pH of 5.0, hydrogen ( 1.9 mol H2 mol−1 glucose) was detected after the first glucose injection in the controls (no LA added). At the latter initial pH and in cultures fed 2,000 mg l−1 LA, the yield reached a maximum of 2.4 mol H2 mol−1 glucose when glucose was injected again. Hydrogen was detected after the second glucose injection in cultures with the initial pH adjusted to 5.0 and 6.0. In cultures receiving LA and adjusted to pH 7.6, the hydrogen yield reached 1.4 mol H2 mol−1 glucose when glucose was injected again. Acetate, propionate, and butyrate were detected under all conditions; however, the quantities were variable and dependent on the conditions examined. In comparison to the amount of volatile fatty acids produced, relatively low quantities of alcohols (ethanol, i-propanol, n-butanol, and i-butanol) were detected during th...

In this work, linoleic acid (LA), a long chain fatty acid bearing 18 carbons and two double bonds, inhibited hydrogen consumption in a mixed anaerobic culture acclimated to glucose. At pH=7.6 , a metabolic shift from methane to hydrogen formation was observed in cultures maintained at 37°C and fed 5,000 mg L−1 glucose in the presence of 500–2,000 mg L−1 LA. The hydrogen yield increased with increasing LA levels while the quantity of methane decreased. The major volatile fatty acids produced were acetate and butyrate with greater levels observed in cultures fed with LA. Acetate, butyrate, and hydrogen accumulation suggests inhibition of aceticlastic methanogens, hydrogenotrophic methanogens, and butyrate degrading microorganisms, respectively, in the presence of LA. A maximum hydrogen yield of 1.71±0.22 mole mole−1 glucose was observed only when glucose was reinjected into cultures receiving 2,000 mg L−1 LA plus 5,000 mg L−1 glucose.

The objective of this study was to establish the impact of different steam exploded organic fractions in municipal solid waste (MSW) on electricity production using microbial fuel cells (MFCs). In particular, the influence of individual steam exploded liquefied waste components (food waste (FW), paper-cardboard waste (PCW) and garden waste (GW)) and their blends on chemical oxygen demand (COD) removal, columbic efficiency (CE) and microbial diversity was examined using a mixture design. Maximum power densities from 0.56 to 0.83 W m(-2) were observed for MFCs fed with different feedstocks. The maximum COD removed and minimum CE were observed for a GW feed. However, a reverse trend (minimum COD removed and maximum CE) was observed for the FW feed. A maximum COD removal (78%) accompanied with a maximum CE (24%) was observed for a combined feed of FW, PCW plus GW in a 1:1:1 ratio. Lactate, the major byproduct detected, was unutilized by the anodic biofilm community. The organic fraction of municipal solid waste (OFMSW) could serve as a potential feedstock for electricity generation in MFCs; however, elevated protein levels will lead to reduced COD removal. The microbial communities in cultures fed FW and PCW was highly diversified; however, the communities in cultures fed FW or a feed mixture containing high FW levels were similar and dominated by Bacteroidetes and β-proteobacteria.

The electrochemical degradation of 1,2-dichloroethane (DCA) was examined in a synthetic groundwater medium. An undivided electrolytic reactor constructed with 304 L-type stainless-steel plate electrodes was employed in all experiments. The removal of total organic carbon (TOC) content during the electrolysis of DCA was experimentally examined. Stainless-steel plate electrodes were effective in degrading DCA under experimental conditions including varying initial concentrations, chloride concentrations, electrolyte conductivities and applied current densities. A half-life method demonstrated TOC removal followed zero-order kinetics under the experimental conditions examined. Chlorides concentration and applied current affected the TOC removal rates. An increase in current density increased the rate of TOC removal but caused a reduction in mineralization current efficiency. Increase in electrolyte conductivity had no effect on TOC removal rates but it decreased the energy consumption by reducing the cell voltage. Reaction temperature was shown to affect the TOC removal and was modeled by the Arrhenius equation.

Butyrate degradation in the presence of C18 long chain fatty acids (LCFAs) was examined under anaerobic conditions at 21 °C. Butyrate degradation rates were a function of linoleic acid (LA) and oleic acid (OA) concentration but independent of the amount of stearic acid (SA) added. Within 2–4 h, butyrate reached undetectable levels in the control cultures. However, in cultures fed with LA, butyrate was removed within between 12 and 25 h and within 2–12 h for cultures inoculated with OA or SA. Propionate was detected in cultures fed with 50 mg dm−3 LA and in cultures inoculated with OA and SA. LA exerted a greater inhibitory effect on butyrate-degrading organisms than OA and SA with longer removal times observed in cultures fed with LA. The propionate and acetate removal times and quantity produced were not related to the type and concentration of LCFA. Copyright © 2004 Society of Chemical Industry

Use of anaerobic digestion for the treatment and recovery of biogas from concentrated animal waste effluents is a technically viable approach, but widespread acceptance has been limited due to poor economics. This challenge is magnified several-fold when considering anaerobic digestion of low-strength or dilute animal slurries because of the larger digester volumes and the corresponding high energy input requirements. These constraints could be mitigated by using an anaerobic sequencing batch reactor (ASBR). This technology has shown tremendous potential to improve the economics for the treatment of dilute animal waste effluents. This article reports preliminary optimization (biogas production and organic strength reduction) of an ASBR treating dilute swine slurries from pit-recharge manure management systems commonly found in confined swine housing. Based on the results, optimum biogas yields from anaerobic digestion of low-strength swine waste (0.3% to 0.4% TS) were approximately 0.14 mL/mg COD and 0.16 mL/mg COD at 5.25 and 6 days HRT at digestion temperatures of 20°C and 35°C, respectively. Higher operational temperature improved the specific biogas yield, but the qualities of biogas produced at the two temperatures, although high (65% to 70% CH4 and 17% to 20% CO2), were not significantly different. Maximum COD reductions of approximately 90% and 84% would be achieved at 7.2 and 9.1 days HRT at digestion temperatures of 20°C and 35°C, respectively. Higher COD reduction (implying more bio-stabilization of slurry) in the lower-temperature digester was attributed to less biomass washout, which is likely due to more efficient solids settling. The volatile fatty acids at both reactor temperatures were reduced from a mean of 639 ±75 mg/L in the influent to mean values of 74 ±12 and 85 ±17 mg/L in the effluents at 20°C and 35°C, respectively, which significantly mitigated the potential of odor generation from the effluents. Additionally, it was observed that the nutrient (both N and P) levels in the effluents remained about the same as in the influent.

Lactose degradation in the presence of C18 long chain fatty acids was examined under anaerobic conditions at 37 °C. The lactose degradation rate was a function of linoleic acid (LA) and oleic acid (OA) concentrations but independent of the amount of stearic acid (SA) added. In cultures fed with LA, lactose was removed within approximately 12 h and within 6 h for cultures inoculated with OA or SA. Glucose, a product of lactose degradation, was only observed in cultures fed with 500–700 mg dm−3 LA and 1000 mg dm−3 OA. No galactose was detected under any of the conditions examined. The cause of glucose accumulation is likely due to inhibition of acidogens by LA and OA. Lactate was detected under all conditions examined. LA was more inhibitory on lactate-consuming organisms than OA and SA and larger amounts of lactate were observed in cultures fed with LA. In addition to lactate, butyrate, propionate and acetate were also observed. Accumulation of volatile fatty acids was a function of the type and concentration of long chain fatty acids. In cultures fed with SA, lower levels of butyrate and acetate were observed when compared with those inoculated with LA and OA and no propionate was detected. Copyright © 2004 Society of Chemical Industry

Long Chain Fatty Acid (LCFA) mixtures containing linoleic, oleic and stearic acids plus carbohydrates are found in a variety of effluents arising from fried food manufacture and milk processing. Accumulation of Volatile Fatty acids (VFAs) due to the presence of LCFAs may impair the operation of an anaerobic system treating effluents containing a mixture of triglycerides and carbohydrates. In this study, the effects of linoleic (C18:2), oleic (C18:1), and stearic (C18:0) acids on glucose fermentation were investigated at 21 °C using a culture acclimated to glucose. In cultures receiving ≥300 mg dm−3 LCFAs, residual amounts of glucose remained after approximately 8 h and none was detected after 24 h. Acetate degradation was inhibited in the presence of 300 or more mg dm−3 linoleic acid (LA), oleic acid (OA), or stearic acid (SA) with more acetate accumulation observed in cultures receiving LA. In comparison to the controls, similar amounts of propionate accumulation were observed in cultures receiving ≤100 mg dm−3 of each LCFA. However, in cultures receiving ≥300 mg dm−3 LCFAs, more propionate accumulated with complete removal observed within 20 days for only those cultures receiving oleic or stearic acids. Butyrate accumulation was observed only in cultures receiving ≥300 mg dm−3 LA and none was detected after 10 days of incubation. Copyright © 2004 Society of Chemical Industry

The effects of three long chain fatty acids (LCFAs) on glucose fermentation at 37 degrees C were examined during this study. Linoleic acid (LA) was more inhibitory than oleic acid (OA) and stearic acid (SA). During glucose fermentation, the carbon flow was diverted towards the production of more reduced volatile fatty acids (VFAs) in cultures fed with unsaturated LCFAs. In cultures inoculated with LA and OA, butyrate was produced with elevated levels observed in cultures inoculated with LA. Propionate degradation was unaffected by the presence of SA; however, elevated levels and longer removal times were observed in cultures receiving LA and OA. Acetate accumulation indicated the acetoclastic methanogenic population was affected only by OA and LA.

Several solvents were evaluated for extracting free long-chain FA (LCFA) from a fermentation medium. Chloroform, chloroform/methanol (1∶1), hexane, and hexane/methyl tert-butyl ether (MTBE) (1∶1) were evaluated as alternative extraction solvents. Parameters considered for optimizing LCFA recoveries included pH and ionic strength. Maximal LCFA recoveries were obtained by adding 2 mL of the hexane/MTBE (1∶1) solvent mixture, 80 μL of 50% H2SO4, and 0.05 g NaCl to 1 mL of the aqueous sample and mixing for 15 min at 200 rpm. This method quantified saturated LCFA [capric acid (C10∶0) to stearic acid (C18∶0)] and unsaturated LCFA with 18 carbons [linoleic acid (C18∶2) and oleic acid (C18∶1)] with a 98 to 100% recovery. Caproic (C6∶0) and caprylic (C8∶0) acids were characterized by 27 and 76% recoveries, respectively.

The effects of long chain fatty acids (LCFAs) on glucose degradation were examined at 21 degrees C. A competitive inhibition model was used to determine the kinetics of glucose degradation. Half velocity constants (Ks) were a function of LCFA concentration only at 100, 300 and 500 mg l(-1). The inhibitor constants (KI) for individual and mixed LCFAs were statistically the same. Glucose degradation rates for cultures receiving saturated (stearic acid (SA)) and monounsaturated (oleic acid (OA)) LCFAs were statistically the same but statistically different when compared to cultures fed with a polyunsaturated LCFA (linoleic acid (LA)). Individual and mixed LCFAs inhibited glucose degradation at threshold levels of 300 and 500 mg l(-1), respectively.

In this study, the operation of an upflow anaerobic sludge blanket reactor (UASBR) producing hydrogen (H-2) from a steam-exploded switchgrass (SWG) liquor was statistically optimized. The factors consider included pH, hydraulic retention time (HRT) and linoleic acid (LA) concentration. Under optimal operational conditions (pH 5.0, 10 h HRT and 1.75 g L-1 LA), which were close to the predicted conditions using the D-optimality index, the maximum H-2 and methane yield observed were 99.86 +/- 5.6 mL g(-1) TVS and 0.5 +/- 0.1 mL g(-1) TVS, respectively. Under maximum H-2-producing conditions, high levels of acetate plus butyrate were observed with low levels of ethanol and lactate. A principal component analysis revealed that clustering of the samples was based on the operating conditions and fermentation metabolites. The microbial profiles revealed that by lowering the HRT from 16 to 8 h or decreasing the pH from 7.0 to 5.0 in the controls caused a 50% reduction in the relative abundance of the terminal restriction fragments belonging to the methanogenic population (Methanobacteria, Methanomicrobia, Methanococci). With LA treatment, H-2 producers (Ruminococcaceae and Clostridiaceae) were dominant and methanogens were inhibited and/or washed-out from the UASBR. Copyright (C) 2013, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.

The anaerobic degradability and inhibitory effects of linoleic acid, an 18 carbon acid with two double bonds (C18:2) commonly found in vegetable oils, were examined at 21°C. Linoleic acid was anaerobically degraded to unsaturated and saturated products. Unsaturated oleic (C18:1) and palmitoleic (C16:1) acids were transiently formed while saturated palmitic (C16:0) and myristic (C14:0) acids were stoichiometrically produced and may have inhibited their own subsequent degradation. Ultimately, all detected byproducts, including lauric (C12:0) and hexanoic (C6:0) acids, were degraded with the exception of acetic acid which accumulated. Linoleic acid at concentrations of 30 mg l −1 or more completely inhibited aceticlastic methanogenesis. Although hydrogenotrophic methanogenesis was slightly inhibited by 30 mg l −1 of linoleic acid or more, hydrogen consumption remained robust. Anaerobic systems to treat wastewaters with linoleic acid-containing vegetable oils may require two separate stages to minimize the inhibition of aceticlastic methanogens by linoleic acid.