Dark Fermentation Effluent Research Articles

Immobilized purple bacteria for light‐driven H2 production from starch and potato fermentation effluents

The goal of the study was to show that immobilized purple bacteria could photoproduce H(2) using dark fermentation effluent (FE) as substrate. Simple pretreatment of an inexpensive glass-fiber matrix accelerated the immobilization process. Photobioreactors (PhBR) containing immobilized Rhodobacter sphaeroides GL produced 0.128 L H(2) h(-1) L(-1) of PhBR volume (0.570 L h(-1) L(-1) of matrix) for up to 3 months when continuously fed artificial media with volatile fatty acids (VFAs) or FE from potato and starch fermentations. Hydrogen production was insensitive to NH(4)(+) up to 1 mM and saturated at 8 mM lactate or 1.5% potato FE (diluted in water and supplemented with critical micronutrients). The efficiency of VFA transformation to H(2) was 50-70% of theoretical. At nonlimiting substrate concentrations in artificial media or FE, acetate was utilized before butyrate. High volumetric rates of continuous H(2) photoproduction and stability of the process are advantages of using immobilized cultures. Use of H(2) photoproduction as a polishing step in the treatment of FEs from dark fermentations increased the total amount of H(2) produced from 0.9 to 4.7 mol mol(-1) glucose equivalent in the original potato homogenate.

Photofermentative hydrogen production using dark fermentation effluent of sugar beet thick juice in outdoor conditions

In the present study, photofermentative hydrogen production on thermophilic dark fermentation effluent (DFE) of sugar beet thick juice was investigated in a solar fed-batch panel photobioreactor (PBR) using Rhodobacter capsulatus YO3 (hup−) during summer 2009 in Ankara, Turkey. The DFE was obtained by continuous dark fermentation of sugar beet thick juice by extreme thermophile Caldicellulosiruptor saccharolyticus and it contains acetate (125 mM) and NH4+ (7.7 mM) as the main carbon and nitrogen sources, respectively. The photofermentation process was done in a 4 L plexiglas panel PBR which was daily fed at a rate of 10% of the PBR volume. The DFE was diluted 3 times to adjust the acetate concentration to approximately 40 mM and supplemented with potassium phosphate buffer, Fe and Mo. In order to control the temperature, cooling was provided by recirculating chilled water through a tubing inside the reactor. Hydrogen productivity of 1.12 mmol/Lc/h and molar yield of 77% of theoretical maximum over consumed substrate were attained over 15 days of operation. The results indicated that Rb. capsulatus YO3 could effectively utilize the DFE of sugar beet thick juice for growth and hydrogen production, therefore facilitating the integration of the dark and photo-fermentation processes for sustainable biohydrogen production.

Photo fermentative hydrogen production using dominant components (acetate, lactate, and butyrate) in dark fermentation effluents

Engineering strategies were applied to promote the phototrophic H 2 production of an indigenous purple nonsulfur bacterium Rhodopseudomonas palustris WP3-5 using major components (i.e., acetate, butyrate, and lactate) of dark fermentation effluents as carbon sources. First, performance of cell growth and photo-H 2 production on each carbon source was examined individually. It appeared that acetate was the most effective carbon source for photo-H 2 production, giving an overall H 2 production rate and H 2 yield of 12.68 ml/h/l and 67.1%, respectively. Next, the effect of substrate concentration of each carbon source on photo-hydrogen production was investigated. Kinetic models were developed to describe the correlation between maximum specific growth rate/specific H 2 production rate and the substrate concentration. The results show that using acetate and lactate as the carbon source, the kinetics for the cell growth and photo-hydrogen production can be described by Monod-type and Michaelis–Menten models, respectively, whereas substrate inhibition occurred when using butyrate as the carbon source. The continuous cultures were also conducted at a hydraulic retention time of 96 h using synthetic dark fermentation soluble metabolites (with a 5 and 10 fold dilution) as the influent. The phototrophic H 2 production efficiency was stably maintained for over 30 days with an overall H 2 yield 10.30 and 11.97 mol H 2/mol sucrose, when using 5-fold and 10-fold diluted dark fermentation effluent, respectively, as the substrate for dark fermentation. This demonstrates the feasibility of using the sequential dark and photo fermentation for high-yield biohydrogen production.

Hydrogen production: Two stage processes for waste degradation

The dark fermentation process generates hydrogen by biological means. It presents two main advantages: fulfilling requirements for mild operational conditions and gaining benefit from the residual biomass. The process itself may be seen as a pre-treatment step in a complete stabilisation chain, with the aim of attaining the valorisation of residual biomass. However, increasing the yield of H 2 production is an imperative task. In this manuscript, a review of recent work in the field of fermentative hydrogen production is presented. As dark fermentation has a maximum yield of 33% (on sugars), a description is also presented of possible second stage processes for the degradation of dark fermentation effluents. Alternatives considered were photofermentation and bioelectrochemical systems (BES) as processes capable of converting fermentation sub-products into H 2. Anaerobic digestion as a final stabilisation stage was also considered owing to the wide application of this technology in the treatment of bio-wastes.

Photo-fermentative hydrogen gas production from dark fermentation effluent of acid hydrolyzed wheat starch with periodic feeding

Hydrogen gas production by photo-fermentation of dark fermentation effluent of acid hydrolyzed wheat starch was investigated at different hydraulic residence times (HRT = 1–10 days). Pure Rhodobacter sphaeroides (NRRL B-1727) culture was used in continuous photo-fermentation by periodic feeding and effluent removal. The highest daily hydrogen gas production (85 ml d −1) was obtained at HRT = 4 days (96 h) while the highest hydrogen yield (1200 ml H 2 g −1 TVFA) was realized at HRT = 196 h. Specific and volumetric hydrogen formation rates were also the highest at HRT = 96 h. Steady-state biomass concentrations and biomass yields increased with increasing HRT. TVFA loading rates of 0.32 g L −1 d −1 and 0.51 g L −1 d −1 resulted in the highest hydrogen yield and formation rate, respectively. Hydrogen gas yield obtained in this study compares favorably with the relevant literature reports probably due to operation by periodic feeding and effluent removal.

Biohydrogen production in an outdoor panel photobioreactor on dark fermentation effluent of molasses

Hydrogen is regarded as an ideal energy carrier if it is produced from renewable resources such as biomass. Sequential operation of dark and photofermentation allows a highly efficient production of hydrogen from biomass, as maximal conversion of the energy in the carbohydrates to hydrogen can be achieved. In this study photofermentative hydrogen production was carried out in a solar panel photobioreactor by Rhodobacter capsulatus wild type (DSM 1710) and Rhodobacter capsulatus hup − (YO3) strain on the molasses dark fermentation effluents which were obtained using an extreme thermophile Caldicellusiruptor saccharolyticus in the dark fermentation step. Continuous hydrogen production on the molasses dark fermentation effluents was achieved up to 55 days with R. capsulatus wild type and 75 days with R. capsulatus hup − in outdoor conditions during summer 2009, in Ankara Turkey. The maximum hydrogen yield obtained using R. capsulatus hup- was 78% (of the theoretical maximum) and the maximum hydrogen productivity was 0.67 mmol H 2/L c.h. The maximum hydrogen productivity and yield of the wild type strain on the molasses dark fermentation effluents were 0.50 mmol H 2/L c.h and 50%, respectively. The changes in climatic conditions, particularly daily global solar radiation, affected the hydrogen productivity and yield.

Hydrogen productivity of photosynthetic bacteria on dark fermenter effluent of potato steam peels hydrolysate

Hydrogen productivities of different photosynthetic bacteria have been searched on real thermophilic dark fermentation effluents (DFE). The results obtained with potato steam peels hydrolysate (PSP) DFE were compared to glucose DFE. Photobiological hydrogen production has been carried out in indoor, batch photobioreactors using several strains of purple non-sulfur (PNS) bacteria such as Rhodobacter capsulatus (DSM1710), Rhodobacter capsulatus hup- (YO3), Rhodobacter sphaeroides O.U.001 (DSM5864), Rb. sphaeroides O.U.001 hup- and Rhodopseudomonas palustris. The efficiency of photofermentation depends highly on the composition of the effluent and the PNS bacterial strain used. Rb. sphaeroides produced the highest amount of hydrogen on glucose DFE. Rb. capsulatus gave better results on PSP DFE. This study demonstrates that photobiological hydrogen production with high efficiency and productivity is possible on thermophilic dark fermentation effluents. Consequently, a sequential operation of dark fermentation and photofermentation is a promising route to produce hydrogen, and it provides a higher hydrogen yield compared to single step processes.

Bio-hydrogen production by photo-fermentation of dark fermentation effluent with intermittent feeding and effluent removal

Pure culture of Rhodobacter sphaeroides (NRRL- B1727) was used for continuous photo-fermentation of volatile fatty acids (VFA) present in the dark fermentation effluent of ground wheat starch. The feed contained 1950 ± 50 mg L −1 total VFA with some nutrient supplementation. Hydraulic residence time (HRT) was varied between 24 and 120 hours. The highest steady-state daily hydrogen production (55 ml d −1) and hydrogen yield (185 ml H 2 g −1 VFA) were obtained at HRT = 72 hours (3 days). Biomass concentration increased with increasing HRT. Volumetric and specific hydrogen formation rates were also maximum at HRT = 72 h. High extent of TVFA fermentation at HRT = 72 h resulted in high hydrogen gas production.

Potential use of thermophilic dark fermentation effluents in photofermentative hydrogen production by Rhodobacter capsulatus

Biological hydrogen production by a sequential operation of dark and photofermentation is a promising route to produce hydrogen. The possibility of using renewable resources, like biomass and agro-industrial wastes, provides a dual effect of sustainability in biohydrogen production and simultaneous waste removal. In this study, photofermentative hydrogen production on effluents of thermophilic dark fermentations on glucose, potato steam peels (PSP) hydrolysate and molasses was investigated in indoor, batch operated bioreactors. An extreme thermophile Caldicellulosiruptor saccharolyticus was used in the dark fermentation step, and Rhodobacter capsulatus (DSM1710) was used in the photofermentation step. Addition of buffer, Fe and Mo to dark fermentor effluents (DFEs) improved the overall efficiency of hydrogen production. The initial acetate concentration in the DFE needed to be adjusted to 30–40 mM by dilution to increase the yield of hydrogen in batch light-supported fermentations. The thermophilic DFEs are suitable for photofermentative hydrogen production, provided that they are supplemented with buffer and nutrients. The overall hydrogen yield of the two-step fermentations was higher than the yield of single step dark fermentations.

Photo-fermentative hydrogen gas production from dark fermentation effluent of ground wheat solution: Effects of light source and light intensity

Dark fermentation effluent of wheat powder solution was subjected to light fermentation for bio-hydrogen production using different light sources and intensities. Tungsten, fluorescent, infrared (IR), halogen lamps were used as light sources with a light intensity of 270 Wm −2 along with sunlight. Pure culture of Rhodobacter sphaeroides-RV was used in batch light fermentation experiments. Halogen lamp was found to be the most suitable light source yielding the highest cumulative hydrogen formation (CHF, 252 ml) and yield (781 ml H 2 g −1 TVFA). In the second set of experiments, light fermentations were performed at different light intensities (1–10 klux) using halogen lamp. The optimum light intensity was found to be 5 klux (approx. 176 Wm −2) resulting in the highest CHF (88 ml) and hydrogen yield (1037 ml H 2 g −1TVFA). Hydrogen formation was limited by the availability of light at low light intensities below 5 klux and was inhibited by the excess light above 5 klux.

Engineering strategies for the enhanced photo-H 2 production using effluents of dark fermentation processes as substrate

The major obstacle of combining dark and photo fermentation for high-yield biohydrogen production is substrate inhibition while using dark fermentation effluent as the sole substrate. To solve this problem, the dark fermentation broth was diluted with different dilution ratio to improve photo-H 2 production performance of an indigenous purple nonsulfur bacterium Rhodopseudomonas palustris WP3-5. The best photo-H 2 production performance occurred at a dilution ratio of 1:2, giving a highest overall H 2 production rate of 10.72 ml/l/h and a higher overall H 2 yield of 6.14 mol H 2/mol sucrose. The maximum H 2 content was about 88.1% during the dilution ratio of 1:2. The photo-H 2 production performance was further improved by supplying yeast extract and glutamic acid as the nutrient. The results indicate that the overall H 2 production rate and H 2 yield increased to 17.02 ml/l/h and 10.25 mol H 2/mol sucrose, respectively. Using a novel solar-energy-excited optical fiber photobioreactor (SEEOFP) with supplementing tungsten filament lamp (TL) irradiation, the overall H 2 production rate was improved to 17.86 ml/l/h. Meanwhile, the power consumption by combining SEEOFP and TL was about 37.1% lower than using TL alone. This study demonstrates that using optimal light sources and proper dilution of dark fermentation effluent, the performance of photo-H 2 production can be markedly enhanced along with a reduction of power consumption.

Enhanced bio-hydrogen production from corncob by a two-step process: Dark- and photo-fermentation

Enhanced bio-hydrogen production from pretreated corncob by integrating dark-fermentation with photo-fermentation process was investigated in this study. In the first step, the maximum bio-hydrogen yield and rate from corncob by dark-fermentation was 120.3 ± 5.2 mL H 2/g-corncob and 150 mL H 2/(L h), respectively. In the second step, a hydrogen yield of 713.6 ± 44.1 mL H 2/g-COD was obtained from digesting the effluent of dark-fermentation by photosynthetic bacteria. Meanwhile, COD removal efficiency achieved 90%. Bio-hydrogen production in the first step was mainly attributed to the bioconversion of the reducing sugars and oligosaccharides in the hydrolyzate of corncob. Bio-hydrogen production in the second step was due to the biodegradation of acetic acid, butyric acid, butyl alcohol and ethanol in the effluent of dark-fermentation.

Sequencing batch reactor enhances bacterial hydrolysis of starch promoting continuous bio-hydrogen production from starch feedstock

Bio-hydrogen production from starch was carried out using a two-stage process combining thermophillic starch hydrolysis and dark H 2 fermentation. In the first stage, starch was hydrolyzed by Caldimonas taiwanensis On1 using sequencing batch reactor (SBR). In the second stage, Clostridium butyricum CGS2 was used to produce H 2 from hydrolyzed starch via continuous dark hydrogen fermentation. Starch hydrolysis with C. taiwanensis On1 was operated in SBR under pH 7.0 and 55 °C. With a 90% discharge volume, the reducing sugar (RS) production from SBR reactor reached 13.94 g RS/L, while the reducing sugar production rate and starch hydrolysis rate was 0.92 g RS/h/L and 1.86 g starch/h/L, respectively, which are higher than using other discharge volumes. For continuous H 2 production with the starch hydrolysate, the highest H 2 production rate and yield was 0.52 L/h/L and 13.2 mmol H 2/g total sugar, respectively, under a hydraulic retention time (HRT) of 12 h. The best feeding nitrogen source (NH 4HCO 3) concentration was 2.62 g/L, attaining a good H 2 production efficiency along with a low residual ammonia concentration (0.14 g/L), which would be favorable to follow-up photo H 2 fermentation while using dark fermentation effluents as the substrate.

Efficient hydrogen gas production from cassava and food waste by a two-step process of dark fermentation and photo-fermentation

Abstract A two-step process of sequential anaerobic (dark) and photo-heterotrophic fermentation was employed to produce hydrogen from cassava and food waste. In dark fermentation, the average yield of hydrogen was approximately 199 ml H2 g−1 cassava and 220 ml H2 g−1 food waste. In subsequent photo-fermentation, the average yield of hydrogen from the effluent of dark fermentation was approximately 611 ml H2 g−1 cassava and 451 ml H2 g−1 food waste. The total hydrogen yield in the two-step process was estimated as 810 ml H2 g−1 cassava and 671 ml H2 g−1 food waste. Meanwhile, the COD decreased greatly with a removal efficiency of 84.3% in cassava batch and 80.2% in food waste batch. These results demonstrate that cassava and food waste could be ideal substrates for bio-hydrogen production. And a two-step process combining dark fermentation and photo-fermentation was highly improving both bio-hydrogen production and removal of substrates and fatty acids.

Hydrogen gas production by electrohydrolysis of volatile fatty acid (VFA) containing dark fermentation effluent

Dark fermentation effluents of wheat powder (WP) solution containing different concentrations of volatile fatty acids (VFAs) were subjected to low voltage (1–3 V) DC current to produce hydrogen gas. Graphite and copper electrodes were tested and the copper electrode was found to be more effective due to higher electrical conductivity. The effects of solution pH (2–7), applied voltage (1–3 V) and the total VFA (TVFA) concentration (1–5 g L −1) on hydrogen gas production were investigated. Hydrogen production increased with decreasing pH and became maximum at pH = 2. Increases in applied voltage and the TVFA concentration also increased the cumulative hydrogen formation. The most suitable conditions for the highest cumulative hydrogen production was pH = 2, with 3 V applied voltage and 5 g TVFA L −1. Up to 110 ml hydrogen gas was obtained with 5 g L −1 TVFA at pH = 5.8 and 2 V applied voltage within 37.5 h. The highest energy efficiency (56%) was obtained with the 2 V applied voltage and 10.85 g L −1 TVFA. Hydrogen production by electrolysis of water in control experiments was negligible for pH > 4. Hydrogen production by electrohydrolysis of VFA containing anaerobic treatment effluents was found to be an effective method with high energy efficiency.

Light fermentation of dark fermentation effluent for bio-hydrogen production by different Rhodobacter species at different initial volatile fatty acid (VFA) concentrations

Three different Rhodobacter sphaeroides (RS) strains (RS–NRRL, RS–DSMZ and RS–RV) and their combinations were used for light fermentation of dark fermentation effluent of ground wheat containing volatile fatty acids (VFA). In terms of cumulative hydrogen formation, RS–NRRL performed better than the other two strains producing 48 ml H 2 in 180 h. However, RS–RV resulted in the highest hydrogen yield of 250 ml H 2 g −1 TVFA. Specific hydrogen production rate (SHPR) with the RS–NRRL was also better in comparison to the others (13.8 ml H 2 g −1 biomass h −1). When combinations of those three strains were used, RS–RV + RS–DSMZ resulted in the highest cumulative hydrogen formation (90 ml H 2 in 330 h). However, hydrogen yield (693 ml H 2 g −1 TVFA) and SHPR (12.1 ml H 2 g −1 biomass h −1) were higher with the combination of the three different strains. On the basis of Gompertz equation coefficients mixed culture of the three different strains gave the highest cumulative hydrogen and formation rate probably due to synergistic interaction among the strains. The effects of initial TVFA and NH 4–N concentrations on hydrogen formation were investigated for the mixed culture of the three strains. The optimum TVFA and NH 4–N concentrations maximizing the hydrogen formation were determined as 2350 and 47 mg L −1, respectively.

Photofermentative hydrogen production from volatile fatty acids present in dark fermentation effluents

Abstract In the present study, the growth and hydrogen production of Rhodobacter sphaeroides O.U. 001, was investigated in media containing five different volatile fatty acids (VFA) individually (malate, acetate, propionate, butyrate and lactate) and in media containing mixtures of these acids that reflect the composition of dark fermentation effluents. The highest hydrogen production rate was obtained in malate (24 ml hydrogen /l reactor h) and the highest biomass concentration was obtained in acetate containing media (1.65 g/l). The substrate conversion efficiencies for different volatile fatty acids were found to vary between 14 and 50%. The malate and butyrate consumption rates were first order with consumption rate constants of 0.026 h −1 and 0.015 h −1 , respectively. In the case of substrate mixtures, it was observed that the bacteria consumed acetate first, followed by propionate and then butyrate. It was also found that the consumption rate of the main substrate significantly increased when the minor substrates were depleted.

Biological hydrogen production from olive mill wastewater with two-stage processes

In the present work two novel two-stage hydrogen production processes from olive mill wastewater (OMW) have been introduced. The first two-stage process involved dark-fermentation followed by a photofermentation process. Dark-fermentation by activated sludge cultures and photofermentation by Rhodobacter sphaeroides O.U.001 were both performed in 55 ml glass vessels, under anaerobic conditions. In some cases of dark-fermentation, activated sludge was initially acclimatized to the OMW to provide the adaptation of microorganisms to the extreme conditions of OMW. The highest hydrogen production potential obtained was 29 l H 2 / l OMW after photofermentation with 50% (v/v) effluent of dark fermentation with activated sludge. Photofermentation with 50% (v/v) effluent of dark fermentation with acclimated activated sludge had the highest hydrogen production rate ( 0.008 l l - 1 h - 1 ) . The second two-stage process involved a clay treatment step followed by photofermentation by R. sphaeroides O.U.001. Photofermentation with the effluent of the clay pretreatment process (4% (v/v)) gives the highest hydrogen production potential ( 35 l H 2 / l OMW ) , light conversion efficiency (0.42%) and COD conversion efficiency (52%). It was concluded that both pretreatment processes enhanced the photofermentative hydrogen production process. Moreover, hydrogen could be produced with highly concentrated OMW. Two-stage processes developed in the present investigation have a high potential for solving the environmental problems caused by OMW.

Adaptation of CIV3 to evaluate hyperfine structure

Dark fermentation is an anaerobic digestion process of biowaste, used to produce hydrogen as a fuel, which however releases high amounts of polluting volatile fatty acids in the environment. In order for the process to become more competitive, the acids stream can be utilized through conversion to high added-value docosahexaenoic acid by the microalga Crypthecodinium cohnii. Docosahexaenoic acid is one of the two main omega-3 fatty acids, necessary for human nutrition. The purpose of this work was to optimize the production of omega-3 fatty acids by the cells, utilizing the organic content of a dark fermentation effluent. For that purpose, the effect of different fermentation conditions was examined, such as incubation temperature, nitrogen source and concentration, the addition of chemical modulators, as well as the feeding composition. The volatile fatty acid content of the effluent was totally depleted in a fed-batch culture of the microalga, while the cells accumulated DHA in a percentage of 35.6% of total lipids, when fed with yeast extract or 34.2% when fed with ammonium sulfate. Taking into consideration the economic feasibility of the culture conditions proposed it was concluded that the use of yeast extract could be substituted by the much economic ammonium sulfate.