Zeolite addition to improve biohydrogen production from dark fermentation of C5/C6-sugars and Sargassum sp. biomass

Thermophilic biohydrogen production by dark fermentation from a mixture (1:1) of C5 (arabinose) and C6 (glucose) sugars, present in lignocellulosic hydrolysates, and from Sargassum sp. biomass, is studied in this work in batch assays and also in a continuous reactor experiment. Pursuing the interest of studying interactions between inorganic materials (adsorbents, conductive and others) and anaerobic bacteria, the biological processes were amended with variable amounts of a zeolite type-13X in the range of zeolite/inoculum (in VS) ratios (Z/I) of 0.065–0.26 g g⁻¹. In the batch assays, the presence of the zeolite was beneficial to increase the hydrogen titer by 15–21% with C5 and C6-sugars as compared to the control, and an increase of 27% was observed in the batch fermentation of Sargassum sp. Hydrogen yields also increased by 10–26% with sugars in the presence of the zeolite. The rate of hydrogen production increased linearly with the Z/I ratios in the experiments with C5 and C6-sugars. In the batch assay with Sargassum sp., there was an optimum value of Z/I of 0.13 g g⁻¹ where the H₂ production rate observed was the highest, although all values were in a narrow range between 3.21 and 4.19 mmol L⁻¹ day⁻¹. The positive effect of the zeolite was also observed in a continuous high-rate reactor fed with C5 and C6-sugars. The increase of the organic loading rate (OLR) from 8.8 to 17.6 kg m⁻³ day⁻¹ of COD led to lower hydrogen production rates but, upon zeolite addition (0.26 g g⁻¹ VS inoculum), the hydrogen production increased significantly from 143 to 413 mL L⁻¹ day⁻¹. Interestingly, the presence of zeolite in the continuous operation had a remarkable impact in the microbial community and in the profile of fermentation products. The effect of zeolite could be related to several properties, including the porous structure and the associated surface area available for bacterial adhesion, potential release of trace elements, ion-exchanger capacity or ability to adsorb different compounds (i.e. protons). The observations opens novel perspectives and will stimulate further research not only in biohydrogen production, but broadly in the field of interactions between bacteria and inorganic materials.

Enhancement of methane production from 1-hexadecene by additional electron donors

1-Hexadecene-contaminated wastewater is produced in oil refineries and can be treated in methanogenic bioreactors, although generally at low conversion rates. In this study, a microbial culture able to degrade 1-hexadecene was enriched, and different stimulation strategies were tested for enhancing 1-hexadecene conversion to methane. Seven and three times faster methane production was obtained in cultures stimulated with yeast extract or lactate, respectively, while cultures amended with crotonate lost the ability to degrade 1-hexadecene. Methane production from 1-hexadecene was not enhanced by the addition of extra hydrogenotrophic methanogens. Bacteria closely related to Syntrophus and Smithella were detected in 1-hexadecene-degrading cultures, but not in the ones amended with crotonate, which suggests the involvement of these bacteria in 1-hexadecene degradation. Genes coding for alkylsuccinate synthase alpha-subunit were detected in cultures degrading 1-hexadecene, indicating that hydrocarbon activation may occur by fumarate addition. These findings are novel and show that methane production from 1-hexadecene is improved by the addition of yeast extract or lactate. These extra electron donors may be considered as a potential bioremediation strategy of oil-contaminated sites with bioenergy generation through methane production.

Perspectives on carbon materials as powerful catalysts in continuous anaerobic bioreactors

The catalytic effect of commercial microporous activated carbon (AC) and macroporous carbon nanotubes (CNT) is investigated in reductive bioreactions in continuous high rate anaerobic reactors, using the azo dye Acid Orange 10 (AO10) as model compound as electron acceptor and a mixture of VFA as electron donor. Size and concentration of carbon materials (CM) and hydraulic retention time (HRT) are assessed. CM increased the biological reduction rate of AO10, resulting in significantly higher colour removal, as compared to the control reactors. The highest efficiency, 98%, was achieved with a CNT diameter (d) lower than 0.25 mm, at a CNT concentration of 0.12 g per g of volatile solids (VS), a HRT of 10 h and resulted in a chemical oxygen demand (COD) removal of 85%. Reducing the HRT to 5 h, colour and COD removal in CM-mediated bioreactors were above 90% and 80%, respectively. In the control reactor, thought similar COD removal was achieved, AO10 decolourisation was just approximately 20%, demonstrating the ability of CM to significantly accelerate the reduction reactions in continuous bioreactors. AO10 reduction to the correspondent aromatic amines was proved by high performance liquid chromatography (HPLC). Colour decrease in the reactor treating a real effluent with CNT was the double comparatively to the reactor operated without CNT. The presence of AC in the reactor did not affect the microbial diversity, as compared to the control reactor, evidencing that the efficient reduction of AO10 was mainly due to AC rather than attributed to changes in the composition of the microbial communities.

High-intensity Interval Training in the Boundaries of the Severe Domain: Effects on Sprint and Endurance Performance

In order to compare the effects of two 4-week interval training programs performed at the lower (Critical Power, CP) or at the higher (The highest intensity at which V˙O₂max is attained, I_HIGH) intensities of the severe exercise domain on sprint and endurance cycling performance, 21 recreationally trained cyclists performed the Wingate Anaerobic Test (WAnT) and a 250-kJ time trial. Accumulated oxygen deficit (AOD), surface electromyography (RMS), and blood lactate kinetics were measured during the WAnT. Subjects were assigned to 105% CP or I_HIGH groups. During the WAnT, significantly greater improvements in peak (Mean ±95%CI) (5.7±2.3% vs. 0.2±2.2%), mean power output (MPO) (3.7±2.0% vs. 0.5±1.8%), and RMS (17.8±7.4% vs. -15.7±7.9%) were observed in the I_HIGH group (P<0.05). Higher and lower AOD, respectively, at the start and during the second half of the WAnT were observed after I_HIGH training. The changes in RMS and MPO induced by the training were significantly correlated (r=0.584). The 2 interventions induced improvements in the 250-kJ time trial. In conclusion, although the improvements in endurance performance were similar, training at I_HIGH led to higher gains in WAnT performance than training at 105%CP.

Delayed-type hypersensitivity and humoral immunity modulation by dietary lipids in a murine model of pulmonary tumorigenesis induced by urethan

Mice fed on semisynthetic formulas containing 15% of corn oil (CO), cod fish liver oil (FO), oleic acid (O) or a mixture of 46% of palmitic and 50% of stearic acids (PS) were treated with urethan during 18 weeks for lung tumor induction. Delayed-type hypersensitivity (DTH) assay, hemagglutination assay and the amount of lung nodes (alveolar adenocarcinomas) were recorded. Results showed significantly greater DTH in CO and FO with respect to O and PS feeding mice; the two last ones induced an essential fatty acid (EFA) deficiency (EFAD). In the O lot there was a non-significant diminution of the humoral response. EFAD animals exhibited a tendency to increase number of lung nodes in relation to CO and FO lots. Splenomegalia was recorded in FO lot. Confront between spleen weight and DTH showed a 72% correlation, suggesting an increase in cellular immunity as increasing unsaturation. It may be concluded that in this suitable model of tumorigenesis the manipulation of dietary lipids may be a strategy to modify the immune system response.