Effects of size and autoclavation of fruit and vegetable wastes on biohydrogen production by dark dry anaerobic fermentation under mesophilic condition

Fermentative hydrogen production from fruit and vegetable wastes (FVWs) through Dry Fermentation Technology (DFT) was studied through three independent experiments in order to find out the effect of particle size and autoclaving pretreatment on bio-hydrogen production from FVWs and as follows: (1) autoclaved FVWs with sizes < 5 cm (experiment I); (2) raw FVWs with sizes < 5 cm (experiment II) and (3) autoclaved FVWs with sizes > 5 cm (experiment III). The assay with autoclaved waste yielded a higher percentage of hydrogen in the headspace of the dry fermenter reaching a maximum value of 44% in experiment I. However, the maximum hydrogen production was obtained in experiment III with 14573 NmL at a yield of 23.53 NmL H₂/gVS. Profiling of the microbial communities by denaturing gradient gel electrophoresis (DGGE) indicated that the most prominent species were the genera Clostridium, Bifidobacterium, and Lactobacillus.     

Improvement in energy recovery from Chlorella sp. biomass by integrated dark-photo biohydrogen production and dark fermentation-anaerobic digestion processes

Chlorella sp. biomass was used as the sole substrate for the production of hydrogen and methane through integrated dark fermentation (DF) and photo-fermentation (PF), and DF and anaerobic digestion (AD) processes. Prior to use in fermentations, the biomass was pretreated by acid-hydrothermal method, which yielded a maximum reducing sugar yield of 162.9 ± 4.2 mg g-biomass⁻¹. The use of the microalgal hydrolysate to produce hydrogen by DF gave a hydrogen yield (HY) of 47.2 ± 1.1 mL g-volatile-solids⁻¹ (VS). The subsequent use of the hydrogenic effluent in PF gave a HY of 125.0 ± 1.5 mL g-VS⁻¹, while AD of the hydrogenic effluent gave a methane yield of 152.8 ± 1.3 mL g-VS⁻¹. The total energy yield attained by the use of DF alone, the integrated DF-PF, and DF-AD processes were 0.51, 1.86 and 5.98 kJ g-VS⁻¹, respectively. These results indicate that the integrated DF-AD process was effective in recovering energy from Chlorella sp. biomass. However, an energy balance analysis indicated that the process was not energetically feasible due to the high energy demand for the acid-hydrothermal pretreatment.     

Study on the dissolved oxygen control strategy in large‐scale vitamin B12 fermentation by Pseudomonas denitrificans

BACKGROUND: There are two different routes for vitamin B₁₂ biosynthesis, which results in discrepancies and uncertainties of the dissolved oxygen (DO) concentration for vitamin B₁₂ fermentation. In this paper, the DO control strategy was explored for industrial vitamin B₁₂ fermentation by Pesudomonas denitrificans in 120000‐L fermenter. RESULTS: A DO‐stat strategy was first successfully scaled up from a 9000 L fermenter to a 120 000 L fermenter. Then a multi‐stage DO control strategy was further established in the 120 000 L fermenter, in which the DO level was shifted from 8–10% (20–48 h) to 2–5% (49–106 h) and below 2% (107–168 h) by gradually reducing the rate of aeration and agitation. As a result, 198.80 mg L^?1 of vitamin B₁₂ was obtained, which was significantly higher than those obtained under the fermentations with one‐stage DO control. CONCLUSIONS: The comparatively low DO level was favorable for vitamin B₁₂ biosynthesis, but it would have an extremely negative effect on cell growth. Compared with the low DO level maintained at all times of the fermentation process, a multi‐stage DO control strategy could not only increase the biomass but also improve vitamin B₁₂ biosynthesis. Copyright © 2012 Society of Chemical Industry     

Value‐added bioconversion of biomass by solid‐state fermentation

The value‐added bioconversion of biomass is necessary due to the depletion of fossil fuels and deterioration of the global environment situation. Based on the analysis of characteristics of solid materials and the applicability of solid agro‐industrial residues used as feedstock for solid‐state fermentation (SSF), the authors established a value‐added bioconversion system for biomass using the key technology SSF. This article gives an overview of biomass bioconversion by SSF and the corresponding advances achieved in recent years. Copyright © 2012 Society of Chemical Industry     

Conversion efficiency of glucose/xylose mixtures for ethanol production using Saccharomyces cerevisiae ITV01 and Pichia stipitis NRRL Y‐7124

BACKGROUND: Efficient conversion of glucose/xylose mixtures from lignocellulose is necessary for commercially viable ethanol production. Oxygen and carbon sources are of paramount importance for ethanol yield. The aim of this work was to evaluate different glucose/xylose mixtures for ethanol production using S. cerevisiae ITV‐01 (wild type yeast) and P. stipitis NRRL Y‐7124 and the effect of supplying oxygen in separate and co‐culture processes. RESULTS: The complete conversion of a glucose/xylose mixture (75/30 g L^?1) was obtained using P. stipitis NRRL Y‐7124 under aerobic conditions (0.6 vvm), the highest yield production being Y_p/s = 0.46 g g^?1, volumetric ethanol productivity Q_pmax = 0.24 g L^?1 h^?1 and maximum ethanol concentration P_max = 34.5 g L^?1. In the co‐culture process and under aerobic conditions, incomplete conversion of glucose/xylose mixture was observed (20.4% residual xylose), with a maximum ethanol production of 30.3 g L^?1, ethanol yield of 0.4 g g^?1 and Q_pmax = 1.26 g L^?1 h^?1. CONCLUSIONS: The oxygen present in the glucose/xylose mixture promotes complete sugar consumption by P. stipitis NRRL Y‐7124 resulting in ethanol production. However, in co‐culture with S. cerevisiae ITV‐01 under aerobic conditions, incomplete fermentation occurs that could be caused by oxygen limitation and ethanol inhibition by P. stipitis NRRL Y‐7124; nevertheless the volumetric ethanol productivity increases fivefold compared with separate culture. Copyright © 2011 Society of Chemical Industry     

Adsorption of butanol from aqueous solution onto a new type of macroporous adsorption resin: Studies of adsorption isotherms and kinetics simulation

BACKGROUND: Owing to the rapid depletion of petroleum fuel, the production of bio‐butanol has attracted much attention. However, low butanol productivity severely limits its potential industrial application. It is important to establish an approach for recovering low‐concentration butanol from fermentation broth. Experiments were conducted using batch adsorption mode under different conditions of initial butanol concentration and temperature. Batch adsorption data were fitted to Langmuir and Freundlich isotherms and the macropore diffusion, pseudo‐first‐ and second‐order models for kinetic study. RESULTS: The maximum adsorption capacity of butanol onto KA‐I resin increase with increasing temperature, ranged from 139.836 to 304.397 mg g^?1. The equilibrium adsorption data were well fitted by the Langmuir isotherm. The adsorption kinetics was more accurately represented by the macropore diffusion model, which also clearly predicted the intraparticle distribution of the concentration. The effective pore diffusivity (D_p) was dependent upon temperature, but independent of initial butanol concentration, and was 0.251 × 10^?10, 0.73 × 10^?10, 1.32 × 10^?10 and 4.31 × 10^?10 m² s^?1 at 283.13, 293.13, 303.13 and 310.13 K, respectively. CONCLUSION: This work demonstrates that KA‐I resin is an efficient adsorbent for the removal of butanol from aqueous solutions and available for practical applications for future in situ product recovery of butanol from ABE fermentation broth. Copyright © 2012 Society of Chemical Industry     

Biohydrogen production: Current perspectives and the way forward

Global research is moving forward in developing biological production of hydrogen (biohydrogen) as a renewable energy source to alleviate stresses due to carbon dioxide emissions and depleting fossil fuels resource. Biohydrogen has the potential to replace current hydrogen production technologies relying heavily on fossil fuels through electricity generation. While biohydrogen research is still immature, extensive work on laboratory- and pilot-scale systems with promising prospects has been reported. This work presents a review of advances in biohydrogen production focusing on production pathways, microbiology, as well as bioreactor configuration and operation. Challenges and prospects of biohydrogen production are also outlined.     

Biotechnological potential of industrial wastes for economical citric acid bioproduction by Aspergillus niger through submerged fermentation

Submerged citric acid (CA) bioproduction was carried out by Aspergillus niger NRRL‐567 using various industrial wastes, such as brewery spent liquid (BSL), lactoserum and starch industry water sludge. CA bioproduction was carried out by varying the temperature (25–35 °C), pH (3–5), addition of inducers, incubation time and supplementation with different proportions of apple pomace ultrafiltration sludge (APS). The results indicated that under the best conditions with 3% (v/v) methanol, the optimal concentration of 11.34 g L^?1 CA was recorded using BSL at pH 3.5 and temperature 30 °C after 120‐h incubation period. Supplementation of methanol resulted in an increase of 56% CA production. Meanwhile, under similar conditions, higher concentration of 18.34 g L^?1 CA was reported with the supplementation of BSL with 40% (v/v) APS having suspended solids concentration of 30 g L^?1. The present study demonstrated the potential of BSL supplemented with APS as an alternative cheap substrate for CA fermentation.