• Energy Research

In this work, sludge adapted to anaerobic/aerobic conditions, AN/AE, showing a high capacity of P accumulation, was submitted to aerobic dynamic substrate feeding (ADF). The fermenter was operated as a Sequencing Batch Reactor, with propionate as carbon substrate. Propionate is an important waste product from several industrial processes that can be valued, using it as a precursor for hydroxyvalerate in PHA production. Under the operational conditions used, apart from 3-hydroxyvalerate as its major component, 3-hydroxy-2-methylvalerate, 2-hydroxyisovalerate and 4-oxovalerate were also produced. A second reactor operated under the same conditions was adapted for the use of acetate as carbon substrate. The global metabolism of the organisms involved on PHA production, utilizing acetate or propionate, was studied using in vivo 13C Nuclear Magnetic Resonance (NMR).

The fermentation of reducing sugars from hardwood (eucalypt) spent sulphite liquor (HSSL) into ethanol by Pichia (Scheffersomyces) stipitis is hindered by concomitant inhibitors of microbial metabolism. The conditions for the HSSL biological treatment step by Paecilomyces variotii were evaluated and optimised. Two different strategies of reactor operation were compared using single batch (B) and sequential batch reactor (SBR). Biological treatment of HSSL in the SBR revealed the best results with respect to the removal of microbial inhibitors. Also, most of inhibitory compounds, acetic acid, gallic acid, pyrogallol, amongst others, were removed from HSSL by P. variotii before the ethanol fermentation. The bio-detoxified HSSL was subjected to a successful fermentation by P. stipitis, attaining a maximum ethanol concentration of 2.4 g L(-1) with a yield of 0.24 g ethanol g sugars(-1).

Hardwood spent sulfite liquor (HSSL) is a by-product from pulp industry with a high concentration of pentose sugars, besides some hexoses suitable for bioethanol production by Scheffersomyces stipitis. The establishment of optimal aeration process conditions that results in specific microaerophilic conditions required by S. stipitis is the main challenge for ethanol production. The present study aimed to improve the ethanol production from HSSL by S. stipitis through a two-stage aeration fermentation. Experiments with controlled dissolved oxygen tension (DOT) in the first stage and oxygen restriction in the second stage were carried out. The best results were obtained with DOT control at 50% in the first stage, where the increase of oxygen availability provided faster growth and higher biomass yield, and no oxygen supply with an agitation rate of 250 rpm, in the second stage allowed a successful induction of ethanol production. Fermentation using 60% of HSSL (v/v) as substrate for S. stipitis provided a maximum specific growth rate of 0.07 h−1, an ethanol productivity of 0.04 g L h−1 and an ethanol yield of 0.39 g g−1, respectively. This work showed a successful two-stage aeration strategy as a promising aeration alternative for bioethanol production from HSSL by S. stipitis.

In this work Escherichia coli strain CML3-1 was engineered through the insertion of Cupriavidus necator P(3HB)-synthesis genes, fused to a lactose-inducible promoter, into the chromosome, via transposition-mediated mechanism. It was shown that polyhydroxyalkanotes (PHAs) production by this strain, using cheese whey, was low due to a significant organic acids (OA) synthesis. The proton suicide method was used as a strategy to obtain an E. coli mutant strain with a reduced OA-producing capacity, aiming at driving bacterial metabolism toward PHAs synthesis. Thirteen E. coli mutant strains were obtained and tested in shake flask assays, using either rich or defined media supplemented with lactose. P8-X8 was selected as the best candidate strain for bioreactor fed-batch tests using cheese whey as the sole carbon source. Although cell growth was considerably slower for this mutant strain, a lower yield of OA on substrate (0.04 Cmol(OA)/Cmol(lac)) and a higher P(3HB) production (18.88 g(P(3HB))/L) were achieved, comparing to the original recombinant strain (0.11 Cmol(OA)/Cmol(lac) and 7.8 g(P(3HB))/L, respectively). This methodology showed to be effective on the reduction of OA yield by consequently improving the P(3HB) yield on lactose (0.28 Cmol (P(3HB))/Cmol(lac) vs 0.10 Cmol(P(3HB))/Cmol(lac) of the original strain).

Winemaking is one of the main Portuguese industries and has significantly grown in recent years, thus increasing the quantity of obtained residues. These wastes have a complex chemical composition and structure, and, for this reason, their treatment and valorisation are simultaneously a challenge and an opportunity. After an overview of the wine industry and its wastes, this article intends to review the different solid winemaking wastes, highlighting their chemical composition and structural characteristics, as well as their main potential applications. These wastes, such as grape stalks, can be directly applied as a source of bioenergy in the form of pellets or subjected to chemical/biological processing, resulting in valuable food additives, materials, or chemicals. Grape seeds provide food grade oil with potential biomedical applications. Grape skins are a promising source of biologically active substances. The sugar fraction of grape pomace can be biologically converted to a wide variety of bioproducts, like bioethanol, biogas, polyhydroxyalkanoates, and bacterial cellulose. The integration of the different processes into a biorefinery is also discussed, considering the characteristics of the Portuguese wine industry and pointing out solutions to valorise their wastes.

Second-generation bioethanol production’s main bottleneck is the need for a costly and technically difficult pretreatment due to the recalcitrance of lignocellulosic biomass (LCB). Chemical pulping can be considered as a LCB pretreatment since it removes lignin and targets hemicelluloses to some extent. Chemical pulps could be used to produce ethanol. The present study aimed to investigate the batch ethanol production from unbleached Kraft pulp of Eucalyptus globulus by separate hydrolysis and fermentation (SHF). Enzymatic hydrolysis of the pulp resulted in a glucose yield of 96.1 ± 3.6% and a xylose yield of 94.0 ± 7.1%. In an Erlenmeyer flask, fermentation of the hydrolysate using Saccharomyces cerevisiae showed better results than Scheffersomyces stipitis. At both the Erlenmeyer flask and bioreactor scale, co-cultures of S. cerevisiae and S. stipitis did not show significant improvements in the fermentation performance. The best result was provided by S. cerevisiae alone in a bioreactor, which fermented the Kraft pulp hydrolysate with an ethanol yield of 0.433 g·g−1 and a volumetric ethanol productivity of 0.733 g·L−1·h−1, and a maximum ethanol concentration of 19.24 g·L−1 was attained. Bioethanol production using the SHF of unbleached Kraft pulp of E. globulus provides a high yield and productivity.

AbstractThe characterization of polyhydroxyalkanoates (PHA) produced by mixed cultures is fundamental for foreseeing the possible final applications of the polymer. In this study PHA produced under aerobic dynamic feeding (ADF) conditions are characterized. The PHA produced shows a stable average molecular weight ($\overline M _{\rm w}$), in the range (1.0–3.0) × 106, along three years of reactor operation. Attempts to improve the amount of PHA produced did not introduce significant variations on the values of $\overline M _{\rm w}$. Along this period, the polydispersity indices (PDI) were between 1.3 and 2.2. The use of different carbon sources allowed the tailoring of polymer composition: homopolymers of poly(3‐hydroxybutyrate), P(3HB), were obtained with acetate and butyrate, whereas a mixture of acetate and propionate, and propionate and valerate, gave terpolymers of 3‐hydroxybutyrate (3HB), 3‐hydroxyvalerate (3HV), and 2‐methyl‐3‐hydroxyvalerate (2M3HV). All of these PHA had $\overline M _{\rm w}$ between 2.0 × 106 and 3.0 × 106. Thermal characterization of the produced polymers showed values of glass transition temperature, melting temperature, melting enthalpy, and crystallinity slightly lower than those obtained for PHA from pure cultures. The introduction of a purification step during the polymer extraction process allowed the elimination of possible contaminants but did not significantly improve the polymer quality.magnified image

Abstract Bacterial Cellulose (BC), produced by many bacteria specially those belonging to the Gluconacetobacter genus, is a very peculiar cellulose form that bears unique mechanical and structural properties that can be exploited in numerous applications. However, the production costs of BC are very high because of the use of quite expensive culture media. In this sense, the purpose of this work was to evaluate the possibility of use residues from the olive oil production industry as nutrient and carbon source for the production of BC by Gluconacetobacter sacchari . The dry olive mill residue (DOR) was submitted to water extraction at 40 and 100 °C (DOR40 and DOR100) and to hydrolysis with H 2 SO 4 1M (DOR100H) in order to obtain sugar rich aqueous extracts to be used for BC production. The BC production obtained without addiction of any type of nutrients was 0.81 g L −1 for DOR40 and 0.85 g L −1 for DOR100 after 96 h incubation, which corresponded respectively to 32 and 34% of the production achieved with conventional HS culture medium (around 2.5 g L −1 ). In order to enhance the production of BC, the residues were supplemented with nitrogen (N) and phosphate (P) sources to overcome possible nutritional limitations. It was verified an increase on the BC production between 21.5% (N8 P4,5) and 43.2% (N1 P8) when compared with no supplementation. These are promising results to overcome high BC production costs.