Explore the vast range of titles available.

Simultaneous bioproduction of hydrogen and ethanol from cheaper waste feedstock has the potential for the development of a more cost-effective biofuel generation process. Crude glycerol (CG), a by-product of the biodiesel industry, is a renewable resource, abundant, sold at low prices and available worldwide. However, the main CG limitations in fermentation processes are mainly related to the presence of impurities and the lack of nitrogen sources, both acting on microbial activity. In this study, a fermentation process with CG was improved using a highly specific microbial consortium called GlyCeroL (GCL). The process was developed in fed-batch fermentation mode using not diluted substrate and carried out under non-sterile conditions and at increasing amounts of the substrate (from 20 to 80 gL−1 of glycerol). The results showed higher H2 (from 6 to 8 LL−1) and EtOH (from 13 to 20 gL−1) production by increasing glycerol concentration from 20 to 40 gL−1. On the other hand, a decrease in glycerol degradation efficiency (from 75 to 56%) was observed. Then, the nitrogen sparging strategy was applied. Using CG of 40 gL−1, process improvement was achieved, leading to the increased production of hydrogen (10 LL−1) but not that of ethanol (20 gL−1). A further increase to 60 gL−1 of glycerol produced a slight increment of EtOH (21 gL−1) and H2 (11 gL−1) but a sharp decrease in glycerol degradation efficiency (41%). Acetate, as the main impurity of CG, was an additional carbon source for GCL microorganisms contributing to EtOH production and increasing that of lactic acid to restore the redox balance. The Denaturing Gradient Gel Electrophoresis (DGGE) fingerprint at the end of all fed-batch fermentations supported the robustness of GCL functional units and their adaptability to fermentation conditions.

This study evaluated different strategies to increase gas–liquid mass transfer in a randomly packed gas stirred tank reactor (GSTR) continuously fed with second cheese whey (SCW), at thermophilic condition (55 °C), for the purpose of carrying out in situ biogas upgrading. Two different H2 addition rates (1.18 and 1.47 LH2 LR−1 d−1) and three different biogas recirculation rates (118, 176 and 235 L LR−1 d−1) were applied. The higher recirculation rate showed the best upgrading performance; H2 utilization efficiency averaged 88%, and the CH4 concentration in biogas increased from 49.3% during conventional anaerobic digestion to 75%, with a methane evolution rate of 0.37 LCH4 LR−1 d−1. The microbial community samples were collected at the end of each experimental phase, as well as one of the thermophilic sludge used as inoculum; metanogenomic analysis was performed using Illumina-based 16S sequencing. The whole microbial community composition was kept quite stable throughout the conventional anaerobic digestion (AD) and during the H2 addition experimental phases (UP1, UP2, UP3, UP4). On the contrary, the methanogens community was deeply modified by the addition of H2 to the GSTR. Methanogens of the Methanoculleus genus progressively increased in UP1 (47%) and UP2 (51%) until they became dominant in UP3 (94%) and UP4 (77%). At the same time, members of Methanotermobacter genus decreased to 19%, 23%, 3% and 10% in UP1, UP2, UP3 and UP4, respectively. In addition, members of the Methanosarcina genus decreased during the hydrogen addition phases.

This study aimed at evaluating the economic performances of and carbon footprint associated with innovative systems for the energetic valorization of second cheese whey (SCW), a by-product of whey cheese manufacture, through anaerobic digestion processes. Three systems were modeled: a conventional single-stage anaerobic digester (FAD), located at about 50 km from the dairy factory; an on-site conventional single-stage anaerobic digester (CAD), located at the dairy industry; and an on-site two-stage anaerobic digester (TAD). The TAD technology enables the simultaneous production of hydrogen and methane on site. The biogases produced were combusted in combined heat and power plants (CHP), but only the onsite systems provided process heat to the dairy factory. In the specific conditions assumed, TAD configuration exhibited a higher energy output, which led to a GHG emission reduction of about 60% compared to FAD, mostly thanks to the additional hydrogen (H2) production and the improved engine performances. A detailed cost analysis confirmed the results of the environmental analysis, pointing to the TAD solution as the most economically viable, with a payback period of 9 years, while the CAD had a payback time of 12 years. The results here presented aim at providing the dairy industry with a robust economic analysis on the opportunity of building an innovative system for SCW valorization, as well as providing policymakers with environmental reliable data to support the promotion of this technology.

Bioaugmentation strategies were tested to improve energetic valorization of shrimp processing waste (SPW) by anaerobic digestion (AD). A fermenting bacteria pool (F210) obtained from coastal lake sediments and two strains of anaerobic fungi (AF), Orpynomyces sp. and Neocallimastix sp., commonly found as components of microbial community of AD plants, were used with the aim of improving the fermentative and hydrolytic phases of AD, respectively. The experiment was carried out by testing single bioaugmentation at an SPW concentration of 6.5 gVS L−1 and combined bioaugmentation at three SPW concentrations (6.5, 9.7 and 13.0 gVS L−1, respectively), in batch mode and mesophilic conditions. Cumulative CH4 productions were higher in the combined bioaugmentation tests and increased in line with SPW concentration. The F210 played a key role in enhancing CH4 production while no effect was attributable to the addition of AFs. The CH4 content (%) in the biogas increased with substrate concentrations, with average values of 67, 70, and 73%, respectively. Microbial community abundance increased in line with the SPW concentration and the acetoclastic Methanosarcina predominated within the methanogen Archaea guild in the combined bioaugmentation test (in all cases > 65%).

In this study, we investigated thermophilic (55 °C) anaerobic digestion (AD) performance and microbial community structure, before and after hydrogen addition, in a novel hybrid gas-stirred tank reactor (GSTR) implemented with a partial immobilization of the microbial community and fed with second cheese whey (SCW). The results showed that H2 addition led to a 25% increase in the methane production rate and to a decrease of 13% in the CH4 concentration as compared with the control. The recovery of methane content (56%) was reached by decreasing the H2 flow rate. The microbial community investigations were performed on effluent (EF) and on interstitial matrix (IM) inside the immobilized area. Before H2 addition, the Anaerobaculaceae (42%) and Lachnospiraceae (27%) families dominated among bacteria in the effluent, and the Thermodesulfobiaceae (32%) and Lachnospiraceae (30%) families dominated in the interstitial matrix. After H2 addition, microbial abundance showed an increase in the bacteria and archaea communities in the interstitial matrix. The Thermodesulfobiaceae family (29%)remained dominant in the interstitial matrix, suggesting its crucial role in the immobilized community and the SHA-31 family was enriched in both the effluent (36%) and the interstitial matrix (15%). The predominance of archaea Methanothermobacter thermoautrophicus indicated that CH4 was produced almost exclusively by the hydrogenotrophic pathway.

Some livestock farms rely on anaerobic digestion (AD) technology for manure disposal, thus obtaining energy (biogas) and fertilizer (digestate). Mixtures of antibiotics used for animal health often occur in organic waste and their possible synergistic/antagonistic effects on microorganisms involved in AD are still poorly studied. This work focuses on the effects of adding ciprofloxacin, alone (5 mg L−1) and in combination with sulfamethoxazole (2.5–5–10 mg L−1), on AD efficiency and microbial community structure. The experiment consisted of 90-day cattle manure batch tests and antibiotic removal percentages were assessed. Adding antibiotics always promoted CH4 and H2 production compared to untreated controls; however, CH4 production was lowered with the highest ciprofloxacin (CIP) concentrations. The overall results show antibiotic degradation caused by acidogenic Bacteria, and CH4 was mainly produced through the hydrogenotrophic-pathway by methanogenic Archaea. Shifts in microbial community abundance (DAPI counts) and composition (Illumina-MiSeq and FISH analyses) were observed.

In situ Bio-Methanation (BM) is a recently developed biogas upgrading technique which finds application also in the Power to Gas (P2G) field. In this study a novel configuration of BM digester, the randomly packed Gas Stirred Tank Reactor (GSTR), was modelled. A 49 L reactor, in thermophilic conditions (55 °C) and at atmospheric pressure, was filled up with random packing on which the microbial populations could adhere. The feedstock used was Second Cheese Whey (SCW), liquid waste of cheese factories, rich in lactose (38 g/L), and its flowrate was chosen to obtain a Hydraulic Retention Time (HRT) of 30 days. The process was analyzed for different hydrogen inlet flowrates of 10 mL/min and 50 mL/min. The produced biogas was also recirculated in the reactor in order to transfer, into the liquid phase, as much hydrogen as possible. The model parameters were estimated by means of stationary state information of the reactor working without hydrogen injection, while a dynamical fitting was necessary to evaluate the value of the hydrogen mass transfer coefficient during BM. The model well described the reactor behavior and, by means of a dimensionless analysis in which the numbers of Stanton (St) and β were defined, it was found out that the mass transfer coefficient is the limiting step of the process.

Lake Averno sediment was used to isolate the facultative anaerobic bacteria having the potential for H 2 production. Twenty-five out of 35 isolates recovered from the sediment sample produced hydrogen under anaerobic conditions from glucose with yields ranging from 0.1 to 0.49 mol H 2 /mol glucose. Identification based on 16S rRNA gene sequence analysis revealed that most of them belong to the Firmicutes group, with a prevalence of the Paenibacillus polymyxa species. Seven distinct genomic fingerprints among the 11 P. polymyxa isolates were obtained using the random amplified polymorphic DNA (RAPD) technique. Glucose fermentation by P. polymyxa isolates was investigated. Glucose was totally consumed after 3 days of fermentation. The fermentation products were hydrogen (0.18–0.47 mol H 2 /mol glucose), ethanol (0.1–0.5 mol ethanol/mol glucose), and 2,3-butanediol (0.1 mol 2,3-butanediol/mol glucose). Lower amounts of acetic, butyric, formic, lactic, and propionic acids were detected. All metabolic data concerning P. polymyxa isolates were analyzed by cluster analysis to reveal similarities and/or differences with clustering based on RAPD profiles. Despite the high metabolic similarity among almost all P. paenibacillus isolates, results of cluster analyses of metabolic and genetic data do not match completely.

Background Sustainable biohydrogen production can be achieved by dark fermentation of organic wastes, and studies were carried out using a range of substrates and inocula. The bacterial populations involved were mainly identified as facultative anaerobes ( Enterobacteriaceae ) and strictly anaerobes ( Clostridiales ), and their dynamics in relation to H 2 and metabolite production depends on the physical and environmental conditions of the bioreactor. This study has evaluated the use of length heterogeneity (LH)-PCR fingerprinting to detect changes in the microbial community during continuous hydrogen production under dark fermentation. Methods A mesophilic continuous dark fermentation was established using coastal lake sediment as an inoculum in a synthetic medium with glucose as a substrate. The LH-PCR profiling associated to the sequencing of 16S rRNA genes was used for the characterization of the bacterial community and identification of species during a continuous production of H 2 . Results The resulting dominant units of the communities present at both 24 h (batch) and 210 h (continuous culture) were affiliated to species of the genus Clostridium . Fluctuations based on their relative abundance over time were observed. At 24 h, a higher ratio was detected for the group Clostridium butyricum - Clostridium tertium followed by Clostridium bifermentans and Clostridium perfringens , while at 210 h, the group Clostridium aurantibutyricum - Clostridium acetobutylicum was the most abundant. Conclusions The LH-PCR profiling has proven to be a sensitive and rapid method for the evaluation of the dynamics of a functional consortium formed by species of the genus Clostridium and has a potential for studies aimed at the optimization of biohydrogen production.

Sustainable biohydrogen production can be achieved by dark fermentation of organic wastes, and studies were carried out using a range of substrates and inocula. The bacterial populations involved were mainly identified as facultative anaerobes (Enterobacteriaceae) and strictly anaerobes (Clostridiales), and their dynamics in relation to H2 and metabolite production depends on the physical and environmental conditions of the bioreactor. This study has evaluated the use of length heterogeneity (LH)-PCR fingerprinting to detect changes in the microbial community during continuous hydrogen production under dark fermentation. A mesophilic continuous dark fermentation was established using coastal lake sediment as an inoculum in a synthetic medium with glucose as a substrate. The LH-PCR profiling associated to the sequencing of 16S rRNA genes was used for the characterization of the bacterial community and identification of species during a continuous production of H2. The resulting dominant units of the communities present at both 24 h (batch) and 210 h (continuous culture) were affiliated to species of the genus Clostridium. Fluctuations based on their relative abundance over time were observed. At 24 h, a higher ratio was detected for the group Clostridium butyricum - Clostridium tertium followed by Clostridium bifermentans and Clostridium perfringens, while at 210 h, the group Clostridium aurantibutyricum - Clostridium acetobutylicum was the most abundant. The LH-PCR profiling has proven to be a sensitive and rapid method for the evaluation of the dynamics of a functional consortium formed by species of the genus Clostridium and has a potential for studies aimed at the optimization of biohydrogen production.[PUBLICATION ABSTRACT]