Physical and hydrodynamic properties of flocs produced during biological hydrogen production

Abstract

Dense flocs readily form in continuous culture bioreactors used for hydrogen production, but the fractal and hydrodynamic properties of these flocs have not been previously analyzed. We therefore examined the size distribution, fractal dimension, and hydrodynamic properties of flocs formed in a continuous flow, well-mixed reactor treating synthetic wastewater at a fixed condition of a 4.5 h hydraulic detention time (23jC, pH 5.5). The reactor was operated for a total of 3 months at three different organic loading rates (27, 53, and 80 g-COD/L-d) with influent glucose concentrations of 5, 10, and 15 g-COD/L. At all three loading rates the removal of glucose was nearly complete (98.6 -99.4%) and biomass was produced in proportion to the organic loading rate (0.86 F 0.11, 2.40 F 0.26, and 4.59 F 1.55 g/L of MLVSS in the reactor). Overall conversion efficiencies of glucose to hydrogen, evaluated on the basis of a maximum of 4 mol-H 2 /molglucose, increased with organic loading rates in the order 17.7%, 23.1%, and 25.6%. The gas contained 56.1 F 4.9% hydrogen, with the balance as carbon dioxide. No methane gas was detected. Under these conditions, flocs were produced with mean sizes that increased with organic loading, in the order 0.12 cm (5 g-COD/L), 0.35 cm (10 g-COD/L), and 0.58 cm (15 g-COD/L). As the average floc size increased, the flocs became on average denser and less fractal, with fractal dimensions increasing from 2.11 F 0.17 to 2.48 F 0.13. Floc porosities ranged from 0.75 -0.96, and resulted in aggregate densities that allowed little intra-aggregate flow through the floc. As a result, average settling velocities were not appreciably larger than those predicted by Stokes' law for spherical, impermeable flocs. Our results demonstrate that dense, relatively impermeable flocs are produced in biohydrogen reactors that have settling properties in reasonable agreement with Stokes' law. B 2004 Wiley Periodicals, Inc.

Improvement of fermentative biohydrogen production by Clostridium butyricum CWBI1009 in sequenced-batch, horizontal fixed bed and biodisc-like anaerobic reactors with biomass retention

“…Many bacteria and mixed cultures are known to form biofilms, granules or flocs that were characterized by microscopy, physicochemical or biomolecular techniques [21][22][23][24][25]. Most of them highlighted that Clostridia were the dominant strains in the mixed microbial populations.…”

“…Indeed experiments not reported here showed floc formation of pure C. butyricum CWBI1009 cultures after a few sequences of SBR in 250 mL serum bottles without mixing. Zhang et al [24] and many authors already mentioned floc formation containing Clostridium hydrogen-producing strains. The experiments reported here confirm these observations for the pure C. butyricum CWBI1009 strain and that the sieve used at each sequence for the removal of spent culture medium was suitable to keep large flocs inside the bioreactor.…”

Sequential hydrogen and methane coproduction from sugary wastewater treatment by “CSTRHyd-UASBMet” system

“…ethanol, butyrate) [2.3].It is found in previous studies [4,5,6] that the effluents of the hydrogen bioproduction process including mainly volatile fatty acids (VFAs) and alcohols can be reutilized to recover the thermal enthalpies and further produce methane. In this study, the anaerobic fermentation process was established using CSTR to investigate the potentiality of hydrogen bioproduction for various substrate COD concentrations and HRTs from sugary wastewater.…”

Experimental and numerical analysis of the hydrodynamic behaviors of aerobic granules

“…It is found that aerobic granules are fractal-like aggregates composed by small particles. [7][8][9][10] For fractal aggregates, fractal dimension has been widely used to describe their irregular and complex structure, and it is useful in explaining some phenomena of aerobic granules.…”