Controlled continuous bio-hydrogen production using different biogas release strategies

Intensification of Hydrogen Production by a Co-culture of Syntrophomonas wolfei and Rhodopseudomonas palustris Employing High Concentrations of Butyrate as a Substrate

The purpose of this study is to present an effective form of developing a sequential dark (DF) and photo (PF) fermentation using volatile fatty acids (VFAs) and nitrogen compounds as bonding components between both metabolic networks of microbial growing in each fermentation. A simultaneous (co-)culture of Syntrophomonas wolfei (with its ability to consume butyrate and produce acetate) and Rhodopseudomonas palustris (that can use the produced acetate as a carbon source) performed a syntrophic metabolism. The former bacteria consumed the acetate/butyrate mixture reducing the butyrate concentration below 2.0 g/L, permitting Rhodopseudomonas palustris to produce hydrogen. Considering that the inoculum composition (Syntrophomonas wolfei/Rhodopseudomonas palustris) and the nitrogen source (yeast extract) define the microbial biomass specific productivity and the butyrate consumption, a response surface methodology defined the best inoculum design and yeast extract (YE) yielding to the highest biomass concentration of 1.1 g/L after 380.00 h. A second culture process (without a nitrogen source) showed the biomass produced in the previous culture process yields to produce a total cumulated hydrogen concentration of 3.4 mmol. This value was not obtained previously with the pure strain Rhodopseudomonas palustris if the culture medium contained butyrate concentration above 2.0 g/L, representing a contribution to the sequential fermentation scheme based on DF and PF.

Product Inhibition of Biological Hydrogen Production in Batch Reactors

In this paper, the inhibitory effects of added hydrogen in reactor headspace on fermentative hydrogen production from acidogenesis of glucose by a bacterium, Clostridium acetobutylicum, was investigated experimentally in a batch reactor. It was observed that hydrogen itself became an acute inhibitor of hydrogen production if it accumulated excessively in the reactor headspace. A mathematical model to simulate and predict biological hydrogen production process was developed. The Monod model, which is a simple growth model, was modified to take inhibition kinetics on microbial growth into account. The modified model was then used to investigate the effect of hydrogen concentration on microbial growth and production rate of hydrogen. The inhibition was moderate as hydrogen concentration increased from 10% to 30% (v/v). However, a strong inhibition in microbial growth and hydrogen production rate was observed as the addition of H2 increased from 30% to 40% (v/v). Practically, an extended lag in microbial growth and considerably low hydrogen production rate were detected when 50% (v/v) of the reactor headspace was filled with hydrogen. The maximum specific growth rate (µmax), substrate saturation constant (ks), a critical hydrogen concentration at which microbial growth ceased (H2*) and degree of inhibition were found to be 0.976 h−1, 0.63 ± 0.01 gL, 24.74 mM, and 0.4786, respectively.

Effect of biogas sparging on the performance of bio-hydrogen reactor over a long-term operation

This study aimed to enhance hydrogen production from sugarcane syrup by biogas sparging. Two-stage continuous stirred tank reactor (CSTR) and upflow anaerobic sludge blanket (UASB) reactor were used to produce hydrogen and methane, respectively. Biogas produced from the UASB was used to sparge into the CSTR. Results indicated that sparging with biogas increased the hydrogen production rate (HPR) by 35% (from 17.1 to 23.1 L/L.d) resulted from a reduction in the hydrogen partial pressure. A fluctuation of HPR was observed during a long term monitoring because CO₂ in the sparging gas and carbon source in the feedstock were consumed by Enterobacter sp. to produce succinic acid without hydrogen production. Mixed gas released from the CSTR after the sparging can be considered as bio-hythane (H₂+CH₄). In addition, a continuous sparging biogas into CSTR release a partial pressure in the headspace of the methane reactor. In consequent, the methane production rate is increased.

Overproduction of the membrane-bound [NiFe]-hydrogenase in Thermococcus kodakarensis and its effect on hydrogen production

The hyperthermophilic archaeon Thermococcus kodakarensis can utilize sugars or pyruvate for growth. In the absence of elemental sulfur, the electrons via oxidation of these substrates are accepted by protons, generating molecular hydrogen (H₂). The hydrogenase responsible for this reaction is a membrane-bound [NiFe]-hydrogenase (Mbh). In this study, we have examined several possibilities to increase the protein levels of Mbh in T. kodakarensis by genetic engineering. Highest levels of intracellular Mbh levels were achieved when the promoter of the entire mbh operon (TK2080-TK2093) was exchanged to a strong constitutive promoter from the glutamate dehydrogenase gene (TK1431) (strain MHG1). When MHG1 was cultivated under continuous culture conditions using pyruvate-based medium, a nearly 25% higher specific hydrogen production rate (SHPR) of 35.3 mmol H₂ g-dcw⁻¹ h⁻¹ was observed at a dilution rate of 0.31 h⁻¹. We also combined mbh overexpression using an even stronger constitutive promoter from the cell surface glycoprotein gene (TK0895) with disruption of the genes encoding the cytosolic hydrogenase (Hyh) and an alanine aminotransferase (AlaAT), both of which are involved in hydrogen consumption (strain MAH1). At a dilution rate of 0.30 h⁻¹, the SHPR was 36.2 mmol H₂ g-dcw⁻¹ h⁻¹, corresponding to a 28% increase compared to that of the host T. kodakarensis strain. Increasing the dilution rate to 0.83 h⁻¹ or 1.07 h⁻¹ resulted in a SHPR of 120 mmol H₂ g-dcw⁻¹ h⁻¹, which is one of the highest production rates observed in microbial fermentation.