• Energy Research

AbstractThe performance of biofilters inoculated with the fungus Scedosporium apiospermum was evaluated. This fungus was isolated from a biofilter which operated with toluene for more than 6 months. The experiments were performed in a 2.9 L reactor packed with vermiculite or with vermiculite‐granular activated carbon as packing material. The initial moisture content of the support and the inlet concentration of toluene were 70% and 6 g/m3, respectively. As the pressure drop increased from 5–40 mm H2O a strong initial growth was observed. Stable operation was maintained for 20 days with a moisture content of 55% and a biomass of 33 mg biomass/g dry support. These conditions were achieved with intermittent addition of culture medium, which permitted a stable elimination capacity (EC) of 100 g/m3reactorh without clogging. Pressure drop across the bed and CO2 production were related to toluene elimination. Measurement of toluene, at different levels of the biofilter, showed that the system attained higher local EC (200 g/m3rh) at the reactor outlet. These conditions were related to local humidity conditions. When the mineral medium was added periodically before the EC decreases, EC of approximately 258 g/m3rh were maintained with removal efficiencies of 98%. Under these conditions the average moisture content was 60% and 41 mg biomass/g dry support was produced. No sporulation was observed. Evaluation of bacterial content and activities showed that the toluene elimination was only due to S. apiospermum catabolism. © 2001 John Wiley & Sons, Inc. Biotechnol Bioeng 76: 61–69, 2001.

The production of biofuels from lignocellulosic biomass includes a pretreatment step to alter the biomass structure and facilitate the enzymatic degradation of the polymers to obtain assimilable compounds. In this study, agave bagasse (AB) was used as a feedstock for obtaining methane, for which AB was pretreated with steam explosion and enzymatically hydrolyzed. The pretreatment conditions corresponded to severity factors (SFs) within a range from 1.65 to 2.89, while enzymatic hydrolysis was performed with enzyme loads of Cellic CTec2 within a range from 0.12 to 3.6 mgprotein g−1AB. The best global yields (including pretreatment and enzymatic hydrolysis) of total carbohydrates (TCs), glucose (GLU), xylose (XYL), and chemical oxygen demand (COD) were 0.7 g TC g−1AB, 0.12 g GLU g−1AB, 0.03 g XYL g−1AB, and 0.20 g O2 g−1AB obtained using 2.4 mgprotein g−1AB of Cellic CTec2 with agave bagasse pretreated with an SF of 2.41. The contribution of pretreatment to the global TC yield ranged from 13 to 34% for the different systems evaluated. The biochemical potential of methane (BMP) of hydrolysates (pretreatment at SF 2.41 and 2.4 mgprotein g−1AB of Cellic CTec2) was 0.284 ± 0.02 in NL CH4 g−1 COD with a COD removal of 78.4 ± 1.3. This BMP value was 40% higher than the BMP obtained in the system without enzymatic hydrolysis, indicating the impact of this step on conversion to biomethane. The results at the BMP level indicated the potential of this residue for biofuel production.

This paper reports the treatment of gaseous hydrogen sulfide, H2S, in a biotrickling filter (BTF) under extreme acidic pH conditions (≈ 1.2). The effect of adding thiosulfate (Na2S2O3.5H2O) to promote biomass growth, feeding low concentrations of ozone to control excess biomass, and the carbon dioxide, CO2, consumption by the chemolithoautotrophic consortium were evaluated. The results showed a global removal efficiency over 98.0% with loads of H2S > 50 g m-3 h-1 (at 639 ppmv) and a linear relation between H2S elimination capacity with the CO2 consumption rate of around 0.1 gCO2/gH2S. Supplementing sulfur in the medium with 2 g L-1 thiosulfate resulted in negative effect performance. Respirometry tests proved that the consortium could not utilize this sulfur form at this pH. Additionally, continuous and intermittent O3 feeding to the BTF in gaseous concentrations of 98 ± 5.4 mg m-3 caused a slight decreased in the performance but the biomass activity in the BTF was only slightly affected allowing a quick performance recovery once O3 addition was suspended.

Bacterial biofilters usually exhibit a high microbial diversity and robustness, while fungal biofilters have been claimed to better withstand low moisture contents and pH values, and to be more efficient coping with hydrophobic volatile organic compounds (VOCs). However, there are only few systematic evaluations of both biofiltration technologies. The present study compared fungal and bacterial biofiltration for the treatment of a VOC mixture (propanal, methyl isobutyl ketone-MIBK, toluene and hexanol) under the same operating conditions. Overall, fungal biofiltration supported lower elimination capacities than its bacterial counterpart (27.7 ± 8.9 vs 40.2 ± 5.4 gCm(-3) reactor h(-1)), which exhibited a final pressure drop 60% higher than that of the bacterial biofilter due to mycelial growth. The VOC mineralization ratio was also higher in the bacterial bed (≈ 63% vs ≈ 43%). However, the substrate biodegradation preference order was similar for both biofilters (propanal>hexanol>MIBK>toluene) with propanal partially inhibiting the consumption of the rest of the VOCs. Both systems supported an excellent robustness versus 24h VOC starvation episodes. The implementation of a fungal/bacterial coupled system did not significantly improve the VOC removal performance compared to the individual biofilter performances.

The use of biomass for alternative energy production has experienced a boom because of the low cost of raw material and the high added value of the product as far as hydrogen is concerned. Steam explosion is used as pretreatment of lignocellulosic biomass to increase the accessibility of sugars. An approach based on sustainability and development of biorefineries allows proposing the integrated use of agave bagasse pretreatment fractions to produce bio-hydrogen. In this work, hydrolysates from steam-explosion pretreated agave bagasse were used as substrate in microbial electrolysis cells (MEC). Hydrolysates were evaluated at concentrations of 20 %, 40 % and 100 % (v/v). Besides, the use of hydrolysates was compared by analyzing two inoculum sources, compost leachate and granular sludge. The highest hydrogen production was 8.5 mL L-1 d-1, which was achieved using 20 % hydrolysate, 10 % compost leachate at the anodic potential of 0.8 V/Ag/AgCl in a two-chamber microbial electrolysis cell.

Abstract The objective of this work was to evaluate different operational strategies for photobioreactors to remove carbon dioxide using the cyanobacteria, Aphanothece microscopica Nageli. Two types of reactor configuration, bubble column and airlift were evaluated under three different operational conditions to treat air containing 15% carbon dioxide: simple operation, air recirculation and two sequential reactors. The results obtained showed that the reactor configuration and the operational mode were both determinant criteria for the performance of photobioreactors in the biological conversion of carbon dioxide. Operations with air recirculation showed possibilities for use in small-scale operations, but two-stage sequential photobioreactors (elimination capacity and removal efficiency of 12,217 gcarbon/m3reactor day and 52.5%, respectively) were shown to be the operational mode with greatest potential for application on an industrial scale by the increased removal efficiency.

Abstract In this study, agave bagasse (a lignocellulosic residue) was pretreated by steam explosion to increase the solubility of carbohydrates in the hydrolysates. The operational variables studied were pressure (0.28, 0.47, and 0.67 MPa, corresponding to 116, 142, and 154 °C, respectively) and pretreatment time (5, 10, 15, and 20 min). The conditions that favored the highest solubilization of glucose (66 ± 4 mg L−1), arabinose (160.31 ± 3.2 mg L−1), and the chemical oxygen demand (COD, 4395.71 ± 22.44 mg L−1) were 154 °C and 10-min. On the other hand, the maximum solubilization of total carbohydrates (TC, 2177.99 ± 197.22 mg L−1) and xylose (43 ± 2.8 mg L−1) was obtained at 154 °C and 15-min. Pretreatments catalyzed with H2SO4 at 154 °C and 10-min resulted in 3, 2.7, and 100-times TC, glucose and xylose concentrations, respectively, as compared to the uncatalyzed pretreatment. However, concentrations of potential inhibitor compounds (i.e., acetic acid, furfural, and hydroxymethylfurfural) increased as well, 26, 120 and 18-times, respectively. A biochemical methane potential (BMP) test of the hydrolysates resulting from the 154 °C-10 min conditions was used to calculate the energy balance of their conversion to methane. When considering only the energy invested in the pretreatment, the process showed an efficiency of 247%, thus being energetically feasible. The integration of methane production to the tequila processes could be implemented using the steam flow already present in the process, improving energy efficiency and reducing the environmental impact of this industry.