Biohydrogen production from arabinose and glucose using extreme thermophilic anaerobic mixed cultures

Abstract

BackgroundSecond generation hydrogen fermentation technologies using organic agricultural and forestry wastes are emerging. The efficient microbial fermentation of hexoses and pentoses resulting from the pretreatment of lingocellulosic materials is essential for the success of these processes.ResultsConversion of arabinose and glucose to hydrogen, by extreme thermophilic, anaerobic, mixed cultures was studied in continuous (70°C, pH 5.5) and batch (70°C, pH 5.5 and pH 7) assays. Two expanded granular sludge bed (EGSB) reactors, Rarab and Rgluc, were continuously fed with arabinose and glucose, respectively. No significant differences in reactor performance were observed for arabinose and glucose organic loading rates (OLR) ranging from 4.3 to 7.1 kgCOD m-3 d-1. However, for an OLR of 14.2 kgCOD m-3 d-1, hydrogen production rate and hydrogen yield were higher in Rarab than in Rgluc (average hydrogen production rate of 3.2 and 2.0 LH2 L-1 d-1 and hydrogen yield of 1.10 and 0.75 molH2 mol-1substrate for Rarab and Rgluc, respectively). Lower hydrogen production in Rgluc was associated with higher lactate production. Denaturing gradient gel electrophoresis (DGGE) results revealed no significant difference on the bacterial community composition between operational periods and between the reactors. Increased hydrogen production was observed in batch experiments when hydrogen partial pressure was kept low, both with arabinose and glucose as substrate. Sugars were completely consumed and hydrogen production stimulated (62% higher) when pH 7 was used instead of pH 5.5.ConclusionsContinuous hydrogen production rate from arabinose was significantly higher than from glucose, when higher organic loading rate was used. The effect of hydrogen partial pressure on hydrogen production from glucose in batch mode was related to the extent of sugar utilization and not to the efficiency of substrate conversion to hydrogen. Furthermore, at pH 7.0, sugars uptake, hydrogen production and yield were higher than at pH 5.5, with both arabinose and glucose as substrates.

Hydrogen fermentation of different galactose–glucose compositions during various hydraulic retention times (HRTs)

“…It could be clearly noticed that the amount of ethanol production was relatively higher and more amount of ethanol has been observed while the HRT was longer. This could be mainly due to the longer HRT that turns the metabolic pathway from acetogenesis to solventogenesis and also the accumulation of undissolved VFA, which could bring the pH to very lower extent which is suitable for the solvent formation; this is energy limitation step in the H 2 metabolism [21,41,42]. The total organic acid production was ranged from 6844 to 10,400 mg COD/L, whereas soluble metabolic products (SMP) levels were also in the range of 8036e13,035 mg COD/L.…”

Thermophilic fermentations of lignocellulosic substrates and economics of biofuels: prospects in Pakistan

“…The maximum theoretical yield of H 2 is 4 mol per mol of glucose both from hexoses and pentoses and is obtainable with acetate as the fermentation product (Eqs. 8 and 9) [63,64]:…”

“…If butyric acid or more reduced end products compared to acetate, such as butyrate, propionate and alcohols (ethanol, butanol) are the final end products, the theoretical value decreases to 2 mol of H 2 per mol or more of glucose utilized [5,64,65]:…”

- Microbial Community Functional Structures in Wastewater Treatment Plants as Characterized by GeoChip

“…Fermentative H 2 production using complex microbial communities therefore has the advantage of a high hydrogen production rate utilizing complex organic wastes as fermentation substrates with limited amounts of additional external energy input [24]. Bacteria and other microbes capable of hydrogen production exist widely in natural environments rich in organic nutrients such as soil, wastewater sludge, and compost [25][26][27]. Microbial populations sampled from these habitats can thus be used as cheap and highly efficient inocula for fermentative hydrogen production.…”