Improving the non-sterile food waste bioconversion to hydrogen by microwave pretreatment and bioaugmentation with Clostridium butyricum.

This work targeted the energy recovery from food waste (FW), aiming at the implementation of a potentially participative process of FW conditioning before the non-sterile biological conversion to hydrogen (H2). Food waste conversion was initially performed under sterile conditions, achieving a maximum H2 productivity of 249.5 ±â€¯24.6 mL H2 (L h)-1 and a total H2 production to 4.1 ±â€¯0.2 L L-1. The non-sterile operation was implemented as a way of process simplification, but the total H2 production decreased by 59% due to the FW native microorganisms. To counteract this effect, FW was submitted to acid, microwave (MW), and combined acid and MW pretreatment. The application of 4 min MW, 550 W, efficiently controlled the FW microbial counts. The Clostridium butyricum bioaugmented conversion of MW-pretreated FW accelerated the H2 production to 406.2 ±â€¯8.1 mL (L h)-1 and peaked the total H2 production and conversion yield to 4.6 ±â€¯0.5 L L-1 and 234.6 ±â€¯55.6 mL (g sugar)-1, respectively. These results exceeded in 63, 12 and 4%, respectively, the H2 productivity, total production and sugar conversion yield obtained under sterile conditions, and are encouraging for the future implementation of increasingly responsible waste valorisation practices.

Enhancement of fermentative hydrogen production from Spirogyra sp. by increased carbohydrate accumulation and selection of the biomass pretreatment under a biorefinery model.

In this work, hydrogen (H2) was produced through the fermentation of Spirogyra sp. biomass by Clostridium butyricum DSM 10702. Macronutrient stress was applied to increase the carbohydrate content in Spirogyra, and a 36% (w/w) accumulation of carbohydrates was reached by nitrogen depletion. The use of wet microalga as fermentable substrate was compared with physically and chemically treated biomass for increased carbohydrate solubilisation. The combination of drying, bead beating and mild acid hydrolysis produced a saccharification yield of 90.3% (w/w). The H2 production from Spirogyra hydrolysate was 3.9 L H2 L-1, equivalent to 146.3 mL H2 g-1 microalga dry weight. The presence of protein (23.2 ± 0.3% w/w) and valuable pigments, such as astaxanthin (38.8% of the total pigment content), makes this microalga suitable to be used simultaneously in both food and feed applications. In a Spirogyra based biorefinery, the potential energy production and food-grade protein and pigments revenue per cubic meter of microalga culture per year was estimated on 7.4 MJ, US $412 and US $15, respectively, thereby contributing to the cost efficiency and sustainability of the whole bioconversion process.

Bio-oil upgrading strategies to improve PHA production from selected aerobic mixed cultures.

Recent research on polyhydroxyalkanoates (PHAs) has focused on developing cost-effective production processes using low-value or industrial waste/surplus as substrate. One of such substrates is the liquid fraction resulting from pyrolysis processes, bio-oil. In this study, valorisation of bio-oil through PHA production was investigated. The impact of the complex bio-oil matrix on PHA production by an enriched mixed culture was examined. The performance of the direct utilization of pure bio-oil was compared with the utilization of three defined substrates contained in this bio-oil: acetate, glucose and xylose. When compared with acetate, bio-oil revealed lower capacity for polymer production as a result of a lower polymer yield on substrate and a lower PHA cell content. Two strategies for bio-oil upgrade were performed, anaerobic fermentation and vacuum distillation, and the resulting liquid streams were tested for polymer production. The first one was enriched in volatile fatty acids and the second one mainly on phenolic and long-chain fatty acids. PHA accumulation assays using the upgraded bio-oils attained polymer yields on substrate similar or higher than the one achieved with acetate, although with a lower PHA content. The capacity to use the enriched fractions for polymer production has yet to be optimized. The anaerobic digestion of bio-oil could also open-up the possibility to use the fermented bio-oil directly in the enrichment process of the mixed culture. This would increase the selective pressure toward an optimized PHA accumulating culture selection.

Biohydrogen production from microalgal biomass: energy requirement, CO2 emissions and scale-up scenarios.

This paper presents a life cycle inventory of biohydrogen production by Clostridium butyricum through the fermentation of the whole Scenedesmus obliquus biomass. The main purpose of this work was to determine the energy consumption and CO2 emissions during the production of hydrogen. This was accomplished through the fermentation of the microalgal biomass cultivated in an outdoor raceway pond and the preparation of the inoculum and culture media. The scale-up scenarios are discussed aiming for a potential application to a fuel cell hybrid taxi fleet. The H2 yield obtained was 7.3 g H2/kg of S. obliquus dried biomass. The results show that the production of biohydrogen required 71-100 MJ/MJ(H2) and emitted about 5-6 kg CO2/MJ(H2). Other studies and production technologies were taken into account to discuss an eventual process scale-up. Increased production rates of microalgal biomass and biohydrogen are necessary for bioH2 to become competitive with conventional production pathways.