Alessandra Adessi

Energy conversion of biomass crops and agroindustrial residues by combined biohydrogen/biomethane system and anaerobic digestion.

Aim of this study was to evaluate the suitability of ensiled giant reed, ensiled maize, ensiled olive pomace, wheat bran for combined systems (CS: dark fermentation+anaerobic digestion (AD)) producing hydrogen-rich biogas (biohythane), tested in batch under basic operational conditions (mesophilic temperatures, no pH control). Substrates were also analyzed under a single stage AD batch test, in order to investigate the effects of DF on estimated energy recovery (ER) in combined systems. In CS, maize and wheat bran exhibited the highest hydrogen potential (13.8 and 18.9NLkgVS(-1)) and wheat bran the highest methane potential (243.5NLkgVS(-1)). In one-stage AD, giant reed, maize and wheat bran showed the highest methane production (239.5, 267.3 and 260.0NLkgVS(-1)). Butyrate/acetate ratio properly described the dark fermentation, correlating with hydrogen production (r=0.92). Wheat bran proved to be a promising residue for CS in terms of hydrogen/methane potential and ER.

Hydrogen Production: Photofermentation

In this chapter, the production of hydrogen with purple nonsulfur (PNS) bacteria is presented, describing the main physiological features of PNS bacteria, the enzymes involved in H2 production and the technological aspects related to the process of photofermentation. In particular, the conversion yields of the substrates, both synthetic and derived from waste products, utilized for H2 production are presented, together with some considerations on the efficiency of the conversion of the light energy into hydrogen energy. The problems related with the scaling up of the process and with the use of solar light are finally discussed, presenting some of the open problems still to be solved in order to make this process economically feasible.

Combined Systems for Maximum Substrate Conversion

In this section, a number of chapters have discussed various microbial processes for producing hydrogen from different substrates, either water, or some carbon compounds. Fermentative hydrogen production would appear to have some advantages, at least for nearer term application. For example, high volumetric rates of hydrogen production from a number of waste streams can already be demonstrated over long periods of time on the pilot scale using mixed cultures and nonsterile conditions. This is possible since known, relatively reactor technology can be used, and since bioprocess parameters and controls are relatively well understood.

Agroindustrial residues and energy crops for the production of hydrogen and poly-β-hydroxybutyrate via photofermentation.

The present study was aimed at assessing the biotransformation of dark fermented agroindustrial residues and energy crops for the production of hydrogen and poly-β-hydroxybutyrate (PHB), in lab-scale photofermentation. The investigation on novel substrates for photofermentation is needed in order to enlarge the range of sustainable feedstocks. Dark fermentation effluents of ensiled maize, ensiled giant reed, ensiled olive pomace, and wheat bran were inoculated with Rhodopseudomonas palustris CGA676, a mutant strain suitable for hydrogen production in ammonium-rich media. The highest hydrogen producing performances were observed in wheat bran and maize effluents (648.6 and 320.3mLL(-1), respectively), both characterized by high initial volatile fatty acids (VFAs) concentrations. Giant reed and olive pomace effluents led to poor hydrogen production due to low initial VFAs concentrations, as the original substrates are rich in fiber. The highest PHB content was accumulated in olive pomace effluent (11.53%TS), ascribable to magnesium deficiency.

Photosynthesis and Hydrogen Production in Purple Non Sulfur Bacteria: Fundamental and Applied Aspects

Light-dependent hydrogen production by purple non sulfur bacteria (PNSB) has been studied for several decades. However the exact route that energy takes from the moment a photon is absorbed to the formation of a molecule of hydrogen is quite complex. The aim of this chapter is to review the researches carried out on the metabolic processes related to hydrogen production in PNSB, in particular stressing the issues related with the efficiency in the conversion of the energy deriving from the light in the energy-rich H2 molecule produced. The metabolic processes that bring form the light capturing to hydrogen production are described, with the relative bottlenecks and hurdles.

Polysaccharides from by-products of the Wonderful and Laffan pomegranate varieties: New insight into extraction and characterization

The main crude polysaccharides (CPS), extracted from two widely cultivated pomegranate varieties, Laffan and Wonderful, were studied and characterized. We obtained the highest CPS extraction yield (approximatively 10% w/w on dried matter) by 1h of decoction (ratio 1/40w/v). The predominant polymers (75-80%) of the CPS samples showed a hydrodynamic volume close to 2000kDa by size exclusion chromatography and the exocarp and mesocarp profiles were very similar. The proton spectra (1H NMR), according to sugar composition and gelling ability, confirmed the main polysaccharide fractions were pectin with different acylation and methylation degree. The CPS from Laffan and Wonderful mesocarp showed prebiotic properties in vitro with Lactobacillus and Bifidobacterium strains. The composition of the decoction (12% ellagitannins and 10% of CPS) obtained by a green extraction process of pomegranate by-products, makes it a suitable component of functional food formulations.

Draft genome sequence and overview of the purple non sulfur bacterium Rhodopseudomonas palustris 42OL

Rhodopseudomonas palustris strain 42OL was isolated in 1973 from a sugar refinery waste treatment pond. The strain has been prevalently used for hydrogen production processes using a wide variety of waste-derived substrates, and cultured both indoors and outdoors, either freely suspended or immobilized. R. palustris 42OL was suitable for many other applications and capable of growing in very different culturing conditions, revealing a wide metabolic versatility. The analysis of the genome sequence allowed to identify the metabolic pathways for hydrogen and poly-β-hydroxy-butyrate production, and confirmed the ability of using a wide range of organic acids as substrates.

H2 production in Rhodopseudomonas palustris as a way to cope with high light intensities

The ability of coping with the damaging effects of high light intensity represents an essential issue when purple non-sulfur bacteria (PNSB) are grown under direct sunlight for photobiological hydrogen production. This study was aimed at investigating whether H2 photo-evolution could represent, for Rhodopseudomonas palustris 42OL, a safety valve to dissipate an excess of reducing power generated under high light intensities. The physiological status of this strain was assessed under anaerobic (AnG) and aerobic (AG) growing conditions and under H2-producing (HP) conditions at low and high light intensities. The results obtained clearly showed that Fv/Fm ratio was significantly affected by the light intensity under which R. palustris 42OL cells were grown, under either AnG or AG conditions, while, under HP, it constantly remained at its highest value. The increase in light intensity significantly increased the H2 production rate, which showed a positive correlation with the maximum electron transfer rate (rETRmax). These findings are important for optimization of hydrogen production by PNSB under solar light.

Photosynthetic Purple Non Sulfur Bacteria in Hydrogen Producing Systems: New Approaches in the Use of Well Known and Innovative Substrates

During the last few years, progress has been made in developing cleaner and more efficient bioenergy producing systems. Innovative processes and novel substrates were assessed at lab scale, in order to investigate and promote a sustainable development of photobiological hydrogen production. Recent and innovative processes and the use of novel substrates are discussed in this chapter. The main focus is on photofermentation systems conducted on biomass derived substrates, as these are considered to be the applicative goal of hydrogen production. Indeed, it is also present a short excursus on some synthetic media, investigated as interesting opportunities for enlarging applicability of the hydrogen technology. The number of new findings here reported demonstrates that it is worth continuing the efforts for increasing the knowledge on the photofermentation process for H2 production, in particular owing to the need of reducing the use of fossil fuels for mitigating the emissions of GHG in the atmosphere.

Purple Bacteria: Electron Acceptors and Donors

Purple bacteria form a heterogeneous group of microorganisms capable of growing under anoxic conditions by anoxygenic photosynthesis. They can be divided into purple nonsulfur bacteria, which are able to grow both phototrophically and in darkness, and purple sulfur bacteria, all of them capable to grow in the light but only few of them in the dark. They are characterized by a remarkable complexity in the metabolism, most of them being able to grow switching from chemotrophy to phototrophy, from organotrophy to litotrophy, and from heterotrophy to autotrophy. In this article, the main electron acceptors and donors involved in the photosynthetic and in the respiratory electron transport chains are described, pointing out the crucial role of the quinone pool for the energetic processes in the cell.