Raffaella Villa

Impacts of microalgae pre-treatments for improved anaerobic digestion: Thermal treatment, thermal hydrolysis, ultrasound and enzymatic hydrolysis

Anaerobic digestion (AD) of microalgae is primarily inhibited by the chemical composition of their cell walls containing biopolymers able to resist bacterial degradation. Adoption of pre-treatments such as thermal, thermal hydrolysis, ultrasound and enzymatic hydrolysis have the potential to remove these inhibitory compounds and enhance biogas yields by degrading the cell wall, and releasing the intracellular algogenic organic matter (AOM). This work investigated the effect of four pre-treatments on three microalgae species, and their impact on the quantity of soluble biomass released in the media and thus on the digestion process yields. The analysis of the composition of the soluble COD released and of the TEM images of the cells showed two main degradation actions associated with the processes: (1) cell wall damage with the release of intracellular AOM (thermal, thermal hydrolysis and ultrasound) and (2) degradation of the cell wall constituents with the release of intracellular AOM and the solubilisation of the cell wall biopolymers (enzymatic hydrolysis). As a result of this, enzymatic hydrolysis showed the greatest biogas yield increments (>270%) followed by thermal hydrolysis (60-100%) and ultrasounds (30-60%).

Preparative Biotransformations: Oxidation of Alcohols

Oxidation of primary and secondary alcohols, to their corresponding aldehydes or carboxylic acids and ketones respectively, are among the most important reactions in organic synthesis. The oxidation occurs through the transfer of two-hydrogens, and can be achieved using metal oxides. Classical chemical oxidizing metal-based agents include: Ag-, Mn-, or Croxides (e.g. Jones, Sarett, Collins, and Cornforth reagents). Metal-free alternatives include the explosive hypervalent organoiodane (Dess–Martin reactions) or the S-based oxidants (Swern, Corey–Kim, and Pfitzner–Moffatt reactions). In addition, catalytic oxidations with metals such as Os, Ru, Rh, and Ir are also used, as are conventional Oppenauer oxidations. However, all of these reactions have some potential disadvantages in terms of their environmental impact (e.g. energy use, toxic byproducts etc.). Following the principles of green chemistry, a very useful and interesting alternative to convert alcohols into their corresponding carbonyl compounds is to use N-oxoammonium salts as oxidants. TEMPO (2,2,6,6-tetramethylpiperidin-1-yl)oxidanyl) or derivatives thereof, when used in catalytic amounts, exploit cheap sodium hypochlorite as a stoichiometric oxidant and generate in situ oxoammonium salt. TEMPO is still very expensive, but cheaper derivatives have been introduced. Molecular oxygen is an ideal oxidant, but the application of chemocatalysis to mimic the activation of molecular oxygen at ambient temperature is far from practical to date. Green oxidations have been discussed in detail by Sheldon et al. Beside environmental and technical limitations, standard chemical oxidations of alcohols are still often poorly stereoselective. Biological oxidations of alcohols occur under mild conditions of temperature, pressure and pH, and may display their activity with high chemo-, regio-, and stereoselectivity. The preparative impact of enzyme-mediated oxidations in organic chemistry has been brilliantly reviewed recently, including the important biocatalytic systems for alcohol oxidation using dehydrogenases or oxidases. The present review gives an overview of the preparative methods for the oxidation of alcohols available for organic chemists, highlighting the advantages and the limitations of classical and innovative bioprocesses. When possible, suggestions for combining recent improvements of the techniques used in biocatalysis (high throughput screening, (meta)genomics, protein engineering, metabolic engineering, and bioprocess engineering) with green and efficient synthetic approaches are made. Alcohol Oxidation: The Biocatalysts, the Problems and the Solutions

Multimedia fate of petroleum hydrocarbons in the soil: Oil matrix of constructed biopiles

A dynamic multimedia fugacity model was used to evaluate the partitioning and fate of petroleum hydrocarbon fractions and aromatic indicator compounds within the soil: oil matrix of three biopiles. Each biopile was characterised by four compartments: air, water, soil solids and non-aqueous phase liquid (NAPL). Equilibrium partitioning in biopile A and B suggested that most fractions resided in the NAPL, with the exception of the aromatic fraction with an equivalent carbon number from 5 to 7 (EC(5-7)). In Biopile C, which had the highest soil organic carbon content (13%), the soil solids were the most important compartment for both light aliphatic fractions (EC(5-6) and EC(6-8)) and aromatic fractions, excluding the EC(16-21) and EC(21-35). Our starting hypothesis was that hydrocarbons do not degrade within the NAPL. This was supported by the agreement between predicted and measured hydrocarbon concentrations in Biopile B when the degradation rate constant in NAPL was set to zero. In all scenarios, biodegradation in soil was predicted as the dominant removal process for all fractions, except for the aliphatic EC(5-6) which was predominantly lost via volatilization. The absence of an explicit NAPL phase in the model yielded a similar prediction of total petroleum hydrocarbon (TPH) behaviour; however the predicted concentrations in the air and water phases were significantly increased with consequent changes in potential mobility. Further comparisons between predictions and measured data, particularly concentrations in the soil mobile phases, are required to ascertain the true value of including an explicit NAPL in models of this kind.

Evaluation of engineered nanoparticle toxic effect on wastewater microorganisms: current status and challenges.

The use of engineered nanoparticles (ENPs) in a wide range of products is associated with an increased concern for environmental safety due to their potential toxicological and adverse effects. ENPs exert antimicrobial properties through different mechanisms such as the formation of reactive oxygen species, disruption of physiological and metabolic processes. Although there are little empirical evidences on environmental fate and transport of ENPs, biosolids in wastewater most likely would be a sink for ENPs. However, there are still many uncertainties in relation to ENPs impact on the biological processes during wastewater treatment. This review provides an overview of the available data on the plausible effects of ENPs on AS and AD processes, two key biologically relevant environments for understanding ENPs-microbial interactions. It indicates that the impact of ENPs is not fully understood and few evidences suggest that ENPs could augment microbial-mediated processes such as AS and AD. Further to this, wastewater components can enhance or attenuate ENPs effects. Meanwhile it is still difficult to determine effective doses and establish toxicological guidelines, which is in part due to variable wastewater composition and inadequacy of current analytical procedures. Challenges associated with toxicity evaluation and data interpretation highlight areas in need for further research studies.

The synthesis of (R)-(+)-lipoic acid using a monooxygenase-catalysed biotransformation as the key step

2-(2-Acetoxyethyl)cyclohexanone (4) was converted into the lactone (-)-(5) regio- and enantioselectively using 2-oxo-delta 3-4,5,5-trimethylcyclopentenyl acetyl-CoA monooxygenase, an NADPH-dependent Baeyer-Villiger monooxygenase from camphor grown Pseudomonas putida NCIMB 10007. The lactone (-)-(5) was converted into (R)-(+)-lipoic acid in six steps. In contrast cyclopentanone monooxygenase, an NADPH-dependent Baeyer-Villiger monooxygenase from cyclopentanol-grown Pseudomonas sp. NCIMB 9872 selectively oxidized the (S)-enantiomer of the ketone (4) giving better access to optically enriched, naturally occurring lipoic acid.

Chemoselective oxidation of primary alcohols to aldehydes with Gluconobacter oxydans

Abstract The production of aliphatic and aromatic aldehydes by oxidation of primary alcohols was achieved with Gluconobacter oxydans DSM 2343. The biotransformation was optimised studying the oxidation of 2-phenyl-1-ethanol to 2-phenylacetaldehyde. A high molar conversion (95% chromatographic conversion, 83% of isolated yield) was obtained using cells grown on glycerol as the main carbon source and directly used in the cultural medium after 24 h at 28°C, pH 4.5 and 5 g L −1 substrate concentration. The conversion of structurally different primary alcohols was performed under these conditions allowing the chemoselective production of aldehydes, sometimes with very good yields.

Aldehyde production by alcohol oxidation with Gluconobacter oxydans

The microbial oxidation of various primary alcohols to the corresponding aldehydes has been investigated. A focused screening performed amongst some acetic acid bacteria showed that a newly isolated strain of Gluconobacter oxydans oxodizes various short-chain aliphatic alcohols to the corresponding aldehydes with negligible acid production. 3-Methyl-1-butanol (isoamyl alcohol) proved to be the better substrate with high yields (more than 90%) without by-product formation. This biotransformation also occurs with continuous or semicontinuous addition of substrate since the volatile product is removed from the medium under vigorous aeration conditions. Product recovery is attained either by the use of cold traps or by reversible complex formation.

Enantioselective oxidation of prochiral 2-methyl-1,3-propandiol by Acetobacter pasteurianus

The microbial oxidation of prochiral 2-methyl-1,3-propandiol into (R)-3-hydroxy-2-methyl propionic acid with Acetobacter pasteurianus DSM 8937 is reported. The biotransformation was optimised furnishing (R)-3-hydroxy-2-methyl propionic acid with 97% enantiomeric excess and 100% molar conversion of 5 g/L within 2 h. A simple fed-batch procedure allowed for the obtainment of 25 g/L of the enantiomerically enriched acid. (R)-3-Hydroxy-2-methyl propionic acid is an important building block for the synthesis of Captopril, a widely used antihypertensive drug.

Production of geranyl acetate and other acetates by direct esterification catalyzed by mycelium of Rhizopus delemar in organic solvent

Dry mycelium of Rhizopus delemar MIM catalyzed the formation of geranyl acetate using 110 mM geraniol and acetic acid at 55°C in heptane to give 11.9 g/l (55% molar conversion). Geranyl acetate was produced at 72.5-75 g/l after 10 days by semi-continuous addition of the substrates. Rhizopus delemar also catalyzed the direct acetylation of different primary alcohols with molar conversions ranging from 65 to 98%.

Oxidative biotransformations by microorganisms: production of chiral synthons by cyclopentanone monooxygenase fromPseudomonas sp. NCIMB 9872

Abstract Cyclopentanone monooxygenase, an NADPH- plus FAD-dependent enzyme induced by the growth ofPseudomonas sp. NCIMB 9872 on cyclopentanol, has been utilised as a biocatalyst in Baeyer-Villiger oxidations. Washed whole-cell preparations of the microorganism oxidised 3-hexylcyclopentanone in a regio- but not enantioselective manner to give predominantly the racemic γ-hexyl valerolactone. similar preparations biotransformed 5-hexylcyclopent-2-enone exclusively by regio- plus enantioselective oxidation to the equivalent α, β-unsaturated (S)-(+)-δ-hexyl valerolactone (ee = 78%), with no reductive biotransformations catalysed by either EC 1.1.x.x- or EC 1.3.x.x-type dehydrogenases. An equivalent biotransformation of 5-hexylcyclopent-2-enone was catalysed by highly-purified NADPH- plus FAD-dependent cyclopentanone monooxygenase from the bacterium. The regio- plus enantioselective biotransformation by the pure enzyme of 2-(2′-acetoxyethyl)cyclohexanone yielded optically-enriched (S)-(+ )-7-(2′-acetoxyethyl)-2-oxepanone (ee = 72%). The same biotransformation when scaled up again provided optically-enriched (S)-(+)-e-caprolactone which was converted, using methoxide, to (S)-(−)-methyl 6,8-dihydroxyoctanoate (ee = 42%). thereby providing a two-step access from the substituted cyclohexanone to this important chiron for the subsequent synthesis of (R-(+)-lipoic acid. Some characteristics of pure NADPH- plus FAD-dependent cyclopentanone monooxygenase were determined including the molecular weight of the monomeric subunit (50000) of this homotetrameric enzyme, and the N-terminal amino acid sequence up to residue 29, which includes a putative flavin nucleotide-binding site.