A. A. Abreu

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

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.

Strategies to suppress hydrogen‐consuming microorganisms affect macro and micro scale structure and microbiology of granular sludge

Treatment of anaerobic granules with heat and two chemical treatments, contacting with 2‐bromoethanesulfonate (BES) and with BES + Chloroform, were applied to suppress hydrogen‐consuming microorganisms. Three mesophilic expanded granular sludge bed (EGSB) reactors—RHeat, RBES, and RBES + Chlo—were inoculated with the treated sludges and fed with synthetic sugar‐based wastewater (5 gCOD L−1, HRT 20–12 h). Morphological integrity of granules and bacterial communities were assessed by quantitative image analysis and 16S rRNA gene based techniques, respectively. Hydrogen production in RHeat was under 300 mL H2 L−1 day−1, with a transient peak of 1,000 mL H2 L−1 day−1 after decreasing HRT. In RBES + Chlo hydrogen production rate did not exceed 300 mL H2 L−1 day−1 and there was granule fragmentation, release of free filaments from aggregates, and decrease of granule density. In RBES, there was an initial period with unstable hydrogen production, but a pulse of BES triggered its production rate to 700 ± 200 mL H2 L−1 day−1. This strategy did not affect granules structure significantly. Bacteria branching within Clostridiaceae and Ruminococcaceae were present in this sludge. This work demonstrates that, methods applied to suppress H2‐consuming microorganisms can cause changes in the macro‐ and microstructure of granular sludge, which can be incompatible with the operation of high‐rate reactors. Biotechnol. Bioeng. 2011; 108:1766–1775.

Advanced monitoring of high-rate anaerobic reactors through quantitative image analysis of granular sludge and multivariate statistical analysis.

Four organic loading disturbances were performed in lab‐scale EGSB reactors fed with ethanol. In load disturbance 1 (LD1) and 2 (LD2), the organic loading rate (OLR) was increased between 5 and 18.5 kg COD m−3 day−1, through the influent ethanol concentration increase, and the hydraulic retention time decrease from 7.8 to 2.5 h, respectively. Load disturbances 3 (LD3) and 4 (LD4) were applied by increasing the OLR to 50 kg COD m−3 day−1 during 3 days and 16 days, respectively. The granular sludge morphology was quantified by image analysis and was related to the reactor performance, including effluent volatile suspended solids, indicator of washout events. In general, it was observed the selective washout of filamentous forms associated to granules erosion/fragmentation and to a decrease in the specific acetoclastic activity. These phenomena induced the transitory deterioration of reactor performance in LD2, LD3, and LD4, but not in LD1. Extending the exposure time in LD4 promoted acetogenesis inhibition after 144 h. The application of Principal Components Analysis determined a latent variable that encompasses a weighted sum of performance, physiological and morphological information. This new variable was highly sensitive to reactor efficiency deterioration, enclosing variations between 27% and 268% in the first hours of disturbances. The high loadings raised by image analysis parameters, especially filaments length per aggregates area (LfA), revealed that morphological changes of granular sludge, should be considered to monitor and control load disturbances in high rate anaerobic (granular) sludge bed digesters. Biotechnol. Bioeng. 2009;102: 445–456.

Boosting dark fermentation with co-cultures of extreme thermophiles for biohythane production from garden waste.

Proof of principle of biohythane and potential energy production from garden waste (GW) is demonstrated in this study in a two-step process coupling dark fermentation and anaerobic digestion. The synergistic effect of using co-cultures of extreme thermophiles to intensify biohydrogen dark fermentation is demonstrated using xylose, cellobiose and GW. Co-culture of Caldicellulosiruptor saccharolyticus and Thermotoga maritima showed higher hydrogen production yields from xylose (2.7±0.1molmol(-1) total sugar) and cellobiose (4.8±0.3molmol(-1) total sugar) compared to individual cultures. Co-culture of extreme thermophiles C. saccharolyticus and Caldicellulosiruptor bescii increased synergistically the hydrogen production yield from GW (98.3±6.9Lkg(-1) (VS)) compared to individual cultures and co-culture of T. maritima and C. saccharolyticus. The biochemical methane potential of the fermentation end-products was 322±10Lkg(-1) (CODt). Biohythane, a biogas enriched with 15% hydrogen could be obtained from GW, yielding a potential energy generation of 22.2MJkg(-1) (VS).

Biohythane production from marine macroalgae Sargassum sp. coupling dark fermentation and anaerobic digestion

Potential biohythane production from Sargassum sp. was evaluated in a two stage process. In the first stage, hydrogen dark fermentation was performed by Caldicellulosiruptor saccharolyticus. Sargassum sp. concentrations (VS) of 2.5, 4.9 and 7.4gL(-1) and initial inoculum concentrations (CDW) of 0.04 and 0.09gL(-1) of C. saccharolyticus were used in substrate/inoculum ratios ranging from 28 to 123. The end products from hydrogen production process were subsequently used for biogas production. The highest hydrogen and methane production yields, 91.3±3.3Lkg(-1) and 541±10Lkg(-1), respectively, were achieved with 2.5gL(-1) of Sargassum sp. (VS) and 0.09gL(-1)of inoculum (CDW). The biogas produced contained 14-20% of hydrogen. Potential energy production from Sargassum sp. in two stage process was estimated in 242GJha(-1)yr(-1). A maximum energy supply of 600EJyr(-1) could be obtained from the ocean potential area for macroalgae production.

The Role of Marine Anaerobic Bacteria and Archaea in Bioenergy Production

The development of products from marine bioresources is gaining importance in the biotechnology sector. The global market for Marine Biotechnology products and processes was, in 2010, estimated at € 2.8 billion with a cumulative annual growth rate of 5–10% (Borresen et al., Marine biotechnology: a new vision and strategy for Europe. Marine Board Position Paper 15. Beernem: Marine Board-ESF, 2010).