Inhibition of Bio-Hydrogen Production by Un-Dissociated Acetic and Butyric Acids

Department of Civil and Environmental Engineering, Penn State University, University Park, PA 16802, USA.
Environmental Science and Technology (Impact Factor: 5.48). 12/2005; 39(23):9351-6. DOI: 10.1021/es0510515
Source: PubMed

ABSTRACT Glucose fermentation to hydrogen results in the production of acetic and butyric acids. The inhibitory effect of these acids on hydrogen yield was examined by either adding these acids into the feed of continuous flow reactors (external acids), or by increasing glucose concentrations to increase the concentrations of acids produced by the bacteria (self-produced). Acids added to the feed at a concentration of 25 mM decreased H2 yields by 13% (acetic) and 22% (butyric), and 60 mM (pH 5.0) of either acid decreased H2 production by >93% (undissociated acid concentrations). H2 yields were constant at 2.0 +/- 0.2 mol H2/mol glucose for an influent glucose concentration of 10-30 g/L. At 40 g glucose/L, H2 yields decreased to 1.6 +/- 0.1 mol H2/mol glucose, and a switch to solventogenesis occurred. A total undissociated acid concentration of 19 mM (self-produced acids) was found to be a threshold concentration for significantly decreasing H2 yields and initiating solventogenesis. Hydrogen yields were inhibited more by self-produced acids (produced at high glucose feed concentrations) than by similar concentrations of externally added acids (lower glucose feed concentrations). These results show the reason hydrogen yields can be maximized by using lower glucose feed concentrations is that the concentrations of self-produced volatile acids (particularly butyric acid) are minimized.

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    • "The presence of acetic acid within the range of 4e10 g/L could inhibit the microbial growth in subsequent fermentation process. It suppresses the fermentation by entering the cell membrane and decreasing the intracellular pH, thus affecting the metabolism of the microorganism [1] [29] [32] [40] [41]. This study revealed that the highest amount of acetic acid (4.33 g/L) was obtained at 8% sulfuric acid concentration and this concentration of acetic acid was sufficient to restrain the fermentation efficiency. "
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    ABSTRACT: a b s t r a c t Carbohydrates from hydrolyzed biomass has been a potential feedstock for fermentative hydrogen production. In this study, oil palm empty fruit bunch (OPEFB) was treated by sulfuric acid in different concentrations at 120 C for 15 min in the autoclave. The optimal condition for pretreatment was obtained when OPEFB was hydrolyzing at 6% (w/v) sulfuric acid concentration, which gave the highest total sugar of 26.89 g/L and 78.51% of sugar production yield. However, the best conversion efficiency of OPEFB pretreatment was 39.47 at sulfuric acid concentration of 4%. A series of batch fermentation were performed to determine the effect of pH in fermentation media and the potential of this prehydrolysate was used as a substrate for fermentative hydrogen production under optimum pretreat-ment conditions. The prehydrolysate of OPEFB was efficiently converted to hydrogen via fermentation by acclimatized mixed consortia. The maximum hydrogen production was 690 mL H 2 L À1 medium, which corresponded to the yield of 1.98 molH 2 /mol xylose achieved at pH 5.5 with initial total sugar concentration of 5 g/L. Therefore, the results implied that OPEFB prehydrolysate is prospective substrate for efficient fermentative hydrogen con-ducted at low controlled pH. No methane gas was detected throughout the fermentation.
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    • "Co-culture fermentation with AH 2 QDS suggests a more practical strategy to improve biohydrogen production by providing both an economical method for regenerating the reduced extracellular electron shuttle AH 2 QDS and a means to diminish product inhibition. Low pH due to the accumulation of volatile organic acids (e.g., acetic acid and butyric acid) is known to trigger a shift from the acidogenic phase to the solventogenic phase and lower hydrogen production in Clostridium fermentation (Gottwald and Gottschalk, 1985; Gottschal and Morris, 1981; Grupe and Gottschalk, 1992; Monot et al., 1984; Riebeling et al., 1975; Terracciano and Kashket, 1986; Van Ginkel and Logan, 2005). G. metallireducens in the co-culture can utilize acetate and regenerate AH 2 QDS in situ, opening the possibility of a continuous production mode. "
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    ABSTRACT: To enhance biohydrogen production, Clostridium beijerinckii was co-cultured with Geobacter metallireducens in the presence of the reduced extracellular electron shuttle anthrahydroquinone-2, 6-disulfonate (AH(2) QDS). In the co-culture system, increases of up to 52.3% for maximum cumulative hydrogen production, 38.4% for specific hydrogen production rate, 15.4% for substrate utilization rate, 39.0% for substrate utilization extent, and 34.8% for hydrogen molar yield in co-culture fermentation were observed compared to a pure culture of C. beijerinckii without AH(2) QDS. G. metallireducens grew in the co-culture system, resulting in a decrease in acetate concentration under co-culture conditions and a presumed regeneration of AH(2) QDS from AQDS. These co-culture results demonstrate metabolic crosstalk between the fermentative bacterium C. beijerinckii and the respiratory bacterium G. metallireducens and suggest a strategy for industrial biohydrogen production. Biotechnol. Bioeng. © 2012 Wiley Periodicals, Inc.
    Biotechnology and Bioengineering 01/2013; 110(1). DOI:10.1002/bit.24627 · 4.16 Impact Factor
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    • "Results show that end product formation increases proportionally when glucose concentration is 5– 20 mM (Fig. 2). Above 20 mM concentration, a no further increase is observed which could possibly be explained by substrate inhibition [32] or inhibition by the low pH caused by accumulation of acetate and lactate. Hydrogen production is also sensitive to hydrogen concentrations and are subject to end product inhibition [33]. "
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    ABSTRACT: Combined biohydrogen and bioethanol (CHE) production from monosugars, polymeric carbohydrates and hydrolysates made from various lignocellulosic biomasses was investigated by strain AK54, a saccharolytic, thermophilic ethanol and hydrogen producing bacterium isolated from a hot spring in Iceland. Optimum growth conditions for the strain were between pH 5.0–6.0 and at 65 °C. As determined by full 16S rRNA analysis, strain AK54 belongs to the genus Thermoanaerobacterium, most closely affiliated with Thermoanaerobacterium aciditolerans (99.0%). Effect of increased initial glucose concentration on growth and end product formation was investigated and good correlations were observed between increased substrate loadings and end product formation of up to 50 mM where clear inhibition was shown. The ability to utilize various carbon substrates was tested with positive growth on xylose, glucose, fructose, mannose, galactose, sucrose and lactose. The major end products in all cases were ethanol, acetate, lactate, hydrogen and carbon dioxide. By lowering the partial pressure of hydrogen during glucose degradation, the end product formation was directed towards hydrogen, acetate and ethanol but away from lactate. Hydrogen and ethanol production from hydrolysates from biomass (7.5 g L−1 (dw)); cellulose, newspaper, grass (Phleum pratense), barley straw (Hordeum vulgare), and hemp (Cannabis sativa L), was investigated. The biomass was chemically (acid/alkali) and enzymatically pretreated. The highest ethanol production was observed from cellulose hydrolysates (24.2 mM) but less was produced from lignocellulosic biomasses. Chemical pretreatment of biomass hydrolysates increased hydrogen and ethanol yields substantially from barley straw, hemp and grass but not from cellulose or newspaper. The highest hydrogen was also produced from cellulose hydrolysates or 6.7 mol-H2 g−1 TS pretreated with alkali (12.2 mol-H2 g−1 glucose equivalents) but of the lignocellulosic biomass, highest yields were from grass pretreated with base (4.9 mol-H2 g−1 TS).
    Applied Energy 09/2012; 97:785–791. DOI:10.1016/j.apenergy.2011.11.035 · 5.61 Impact Factor
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