Markov-Perfect Optimal Fiscal Policy: The Case of Unbalanced Budgets

We study optimal income taxation and public debt policy in a neoclassical economy populated by infinitely-lived households and a benevolent government. The government makes sequential decisions on the provision of a valued public good, on income taxation and the issue of public debt. We characterize and compute Markov-perfect optimal fiscal policy in this economy with two payoff-relevant state variables: physical capital and public debt. We find two stable, steady-state equilibria: one with no income taxation and positive government asset holdings, and another with positive taxation and public debt issuances. We prove that the two steady states are associated with different policy rules, which implies a multiplicity of (expectation-driven) Markov-perfect equilibria.Optimal taxation; optimal public debt; Markov-perfect equilibrium; Time-consistent policy

Markov-perfect optimal fiscal policy : the case of unbalanced budgets

We study optimal time-consistent fiscal policy in a neoclassical economy with endogenous government spending, physical capital and public debt. We show that a dynamic complementarity between the households’ consumption-savings decision and the government’s policy decision gives rise to a multiplicity of expectations-driven Markov-perfect equilibria. The long-run levels of taxes, government spending and debt are not uniquely pinned down by economic fundamentals, but are determined by expectations over current and future policies. Accordingly, economies with identical fundamentals may significantly differ in their levels of public indebtednessThis author is grateful for financial support from the Spanish Ministerio de Ciencia e Innovación under grant 2011/00049/00

Assessment of the adequacy of different Mediterranean waste biomass types for fermentative hydrogen production and the particular advantage of carob (Ceratonia siliqua L.) pulp

ABSTRACT: The conversion of agro-industrial byproducts, residues and microalgae, which are representative or adapted to the Mediterranean climate, to hydrogen (H2) by C. butyricum was compared. Five biomass types were selected: brewery’s spent grain (BSG), corn cobs (CC), carob pulp (CP), Spirogyra sp. (SP) and wheat straw (WS). The biomasses were delignified and/or saccharified, except for CP which was simply submitted to aqueous extraction, to obtain fermentable solutions with 56.2e168.4 g total sugars L 1. In small-scale comparative assays, the H2 production from SP, WS, CC, BSG and CP reached 37.3, 82.6, 126.5, 175.7 and 215.8 mL (g biomass) 1, respectively. The best fermentable substrate (CP) was tested in a pH-controlled batch fermentation. The H2 production rate was 204 mL (L h) 1 and a cumulative value of 3.9 L H2 L 1 was achieved, corresponding to a H2 production yield of 70.0 mL (g biomass) 1 or 1.6 mol (mol of glucose equivalents) 1. The experimental data were used to foresight a potential energy generation of 2.4 GWh per year in Portugal, from the use of CP as substrate for H2 production.info:eu-repo/semantics/publishedVersio

Production and storage of biohydrogen during sequential batch fermentation of Spirogyra hydrolyzate by Clostridium butyricum

The biological hydrogen production from Spirogyra sp. biomass was studied in a SBR (sequential batch reactor) equipped with a biogas collecting and storage system. Two acid hydrolysis pre-treatments (1N and 2N H2SO4) were applied to the Spirogyra biomass and the subsequent fermentation by Clostridium butyricum DSM 10702 was compared. The 1N and 2N hydrolyzates contained 37.2 and 40.8 g/L of total sugars, respectively, and small amounts of furfural and HMF (hydroxymethylfurfural). These compounds did not inhibit the hydrogen production from crude Spirogyra hydrolyzates. The fermentation was scaled up to a batch operated bioreactor coupled with a collecting system that enabled the subsequent characterization and storage of the biogas produced. The cumulative hydrogen production was similar for both 1N and 2N hydrolyzate, but the hydrogen production rates were 438 and 288 mL/L.h, respectively, suggesting that the 1N hydrolyzate was more suitable for sequential batch fermentation. The SBR with 1N hydrolyzate was operated continuously for 13.5 h in three consecutive batches and the overall hydrogen production rate and yield reached 324 mL/L.h and 2.59 mol/mol, respectively. This corresponds to a potential daily production of 10.4 L H2/L Spirogyra hydrolyzate, demonstrating the excellent capability of C. butyricum to produce hydrogen from microalgal biomass

Fermentation of biomass-derived syngas to ethanol and acetate by clostridium ljungdahlii

In the biochemical pathway of lignocellulosics conversion into fuels, a significant portion of biomass cannot be hydrolysed to fermentable sugars and remains as waste substrate that, due to its recalcitrance, is not converted to ethanol by microorganisms. In terms of product yield, this residual biomass represents renewable feedstock that is being wasted, which contradicts the target of 100% feedstock utilisation. The gasification of this biomass constitutes an alternative to circumvent this problem, as the produced synthesis gas (syngas) can be used as substrate for microorganisms that are able to convert CO, CO2 and H2 into important bulk chemicals and biofuels, such as ethanol, acetate and butanol [1,2]. Thus, syngas fermentation to ethanol and acetate can be regarded as a possible process to increase the overall product yield from lignocellulosic feedstock. Some advantages of fuels and chemicals production through syngas fermentation over metal catalyst conversion are the possibility of utilisation of the whole biomass regardless its quality, the independence of a fixed H2:CO ratio for the bioconversion process, a higher specificity of the microbial biocatalyst over chemical catalysts, and the bioreactor operation at ambient conditions [3]. However, syngas fermentation also presents several limitations, such as low yields and poor solubility of the gaseous substrate in the liquid phase. The objective of the present study was to evaluate C. ljungdahlii as microbial catalyst capable of fermenting syngas produced by gasification of spent solids obtained after lignocellulosic biomass saccharification and fermentation into ethanol. The heterotrophic and autotrophic growth of C. ljungdahlii were compared. Parameters such as bacterial growth, acetate and ethanol production, substrate consumption, and bioconversion yields were evaluated. In order to overcome the problem of gas diffusion in the liquid phase, fermentations were conducted at different total pressure

Third generation biohydrogen pProduction by Clostridium butyricum and adapted mixed cultures from Scenedesmus obliquus microalga biomass

Scenedesmus obliquus biomass was used as a feedstock for comparing the biological production of hydrogen by two different types of anaerobic cultures: a heat-treated mixed culture from a wastewater treatment plant and Clostridium butyricum DSM 10702. The influence of the incubation temperature and the carbon source composition were evaluated in order to select the best production profile according to the characteristics of the microalgal biomass. C. butyricum showed a clear preference for monomeric sugars and starch, the latter being the major storage compound in microalgae. The highest H2 production reached by this strain from starch was 468 mL/g, whereas the mixed culture incubated at 37 C (LE37) produced 241 mL/g. When the mixed culture was incubated at 58 C (LE58), a significant increase in the H2 production occurred when xylose and xylan were used as carbon and energy source. The highest H2 yield reached by the LE37 culture or in co-culture with C. butyricum was 1.52 and 2.01 mol/mol of glucose equivalents, respectively. However, the ratio H2/CO2 (v/v) of the biogas produced in both cases was always lower than the one produced by the pure strain. In kinetic assays, C. butyricum attained 153.9 mL H2/L h from S. obliquus biomass within the first 24 h of incubation, with a H2 yield of 2.74 mol/mol of glucose equivalents. H2 production was accompanied mainly by acetate and butyrate as coproducts. In summary, C. butyricum demonstrated a clear supremacy for third generation bioH2 production from S. obliquus biomass

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

ABSTRACT: In this work, hydrogen (H-2) 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 H-2 production from Spirogyra hydrolysate was 3.9 L H-2 L-1 , equivalent to 1463 mL H-2 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 S15, respectively, thereby contributing to the cost efficiency and sustainability of the whole bioconversion process.info:eu-repo/semantics/publishedVersio

Energy requirements for the continuous biohydrogen production from Spirogyra biomass in a sequential batch reactor

The current energy market requires urgent revision for the introduction of renewable, less-polluting and inexpensive energy sources. Biohydrogen (bioH2) is considered to be one of the most appropriate options for this model shift, being easily produced through the anaerobic fermentation of carbohydrate-containing biomass. Ideally, the feedstock should be low-cost, widely available and convertible into a product of interest. Microalgae are considered to possess the referred properties, being also highly valued for their capability to assimilate CO2 [1]. The microalga Spirogyra sp. is able to accumulate high concentrations of intracellular starch, a preferential carbon source for some bioH2 producing bacteria such as Clostridium butyricum [2]. In the present work, Spirogyra biomass was submitted to acid hydrolysis to degrade polymeric components and increase the biomass fermentability. Initial tests of bioH2 production in 120 mL reactors with C. butyricum yielded a maximum volumetric productivity of 141 mL H2/L.h and a H2 production yield of 3.78 mol H2/mol consumed sugars. Subsequently, a sequential batch reactor (SBR) was used for the continuous H2 production from Spirogyra hydrolysate. After 3 consecutive batches, the fermentation achieved a maximum volumetric productivity of 324 mL H2/L.h, higher than most results obtained in similar production systems [3] and a potential H2 production yield of 10.4 L H2/L hydrolysate per day. The H2 yield achieved in the SBR was 2.59 mol H2/mol, a value that is comparable to those attained with several thermophilic microorganisms [3], [4]. In the present work, a detailed energy consumption of the microalgae value-chain is presented and compared with previous results from the literature. The specific energy requirements were determined and the functional unit considered was gH2 and MJH2. It was possible to identify the process stages responsible for the highest energy consumption during bioH2 production from Spirogyra biomass for further optimisation

Lignin syngas bioconversion by Butyribacterium methylotrophicum: advancing towards an integrated biorefinery

ABSTRACT: Hybrid bio-thermochemical based technologies have the potential to ensure greater feedstock flexibility for the production of bioenergy and bioproducts. This study focused on the bioconversion of syngas produced from low grade technical lignin to C-2-/C-4-carboxylic acids by Butyribacterium methylotrophicum. The effects of pH, medium supplementation and the use of crude syngas were analyzed. At pH 6.0, B. methylotrophicum consumed CO, CO2 and H-2 simultaneously up to 87 mol% of carbon fixation, and the supplementation of the medium with acetate increased the production of butyrate by 6.3 times. In long-term bioreactor experiments, B. methylotrophicum produced 38.3 and 51.1 mM acetic acid and 0.7 and 2.0 mM butyric acid from synthetic and lignin syngas, respectively. Carbon fixation reached 83 and 88 mol%, respectively. The lignin syngas conversion rate decreased from 13.3 to 0.9 NmL/h throughout the assay. The appearance of a grayish pellet and cell aggregates after approximately 220 h was indicative of tar deposition. Nevertheless, the stressed cells remained metabolically active and maintained acetate and butyrate production from lignin syngas. The challenge that impurities represent in the bioconversion of crude syngas has a direct impact on syngas cleaning requirements and operation costs, supporting the pursuit for more robust and versatile acetogens.info:eu-repo/semantics/publishedVersio

Microalgae biomass as fermentation substrate for hydrogen and butyric acid production by clostridium tyrobutyricum

Fossil fuels are a limited type of feedstock, increasingly expensive, and carrying strong polluting properties. The search for alternative sources which can replace fossil fuels without the severe disadvantages that its use conveys is therefore of paramount importance. Microalgae biomass represents an example of such non-food renewable biomass that can be regarded as a valid alternative to fossil fuels. As biomass, microalgae are highly desirable since they are photosynthetic organisms with a very fast growth rate in comparison to higher plants, and their production does not require arable land or potable water. Furthermore, some microalgae are able to store large amounts of oil or sugars, prime materials for the production of biofuels and bulk-chemicals [1]. Scenedesmus obliquus is a microalgae with the referred properties, easily produced at large scale and capable of storing a high amount of sugars under nitrogen shortage. The objective of the present work was to investigate the production of hydrogen and butyrate from S. obliquus hidrolysate by four hydrogen- and butyrate-producing bacterial strains previously isolated by us and identified as Clostridium tyrobutyricum 1T, 2T, 3T and 9P. S. obliquus biomass was produced locally in air-lifts. After harvest, all biomass was submitted to acid pre-treatment [2] resulting in a microalgae hydrolysate with a final concentration of 10.3 g/l of glucose, xylose, arabinose, mannose and galactose. The hydrolysate was used as carbon and energy source for hydrogen and butyrate production by the four C. tyrobutyricum isolates. Hydrogen yields ranged from 0.63, 1.29, 1.36 and 1.24 of mol H2/ mol sugars by strains 1T, 2T, 3T and 9P, respectively. Hydrogen production was accompanied by the production of carbon dioxide and organic acids, mainly butyrate. Butyrate yields were 0.29, 0.49 and 0.48 mol butyric acid/ mol sugars, respectively by C. tyrobutyricum strains 1T, 2T and 3T, and 9P. The best C. tyrobutyricum isolate for combined hydrogen and butyrate production from S. obliquus hydrolysate will be used in further studies of energetic valorisation of spent algal biomass available from both biodiesel and bioethanol processes