Mass transfer, light pulsing and hydrodynamic stress effects in photobioreactor development

Photobioreactor scalability involves multiple different interacting aspects including mass transfer, light pulsing and hydrodynamic stress. An efficient carbon dioxide supply and a frequent displacement of cells from poorly to highly illuminated zones is desired to maximise the achieveable specific growth rate. However, a strong mixing is energy consuming and may reduce the specific growth rate because of induced cell damage. The current work examines mass transfer effects in photobioreactor development and estimates their relationship to light pulsing and hydrodynamic stress effects with a special reference to the novel inclined, thinlayer, wavy-bottomed cascading photobioreactor

Fatty acid composition and technological quality of the lipids produced by the microalga Scenedesmus dimorphus 1237 as a function of culturing conditions

Scendesmus dimorphus is an oleaginous eukaryotic microalga, able to produce and accumulate lipids up to a weight fraction of 49%. Aim of the present work is investigating the production of lipids by S. dimorphus 1237 and characterize them at a fatty-acid level. The variables accounted for were: the nutrient supply level and the extraction system (Soxhlet and bead beating). Two lipid phases were extracted by sequential, twin-solvent system (hexane and a chloroform:methanol mixture), the quantified gravimetrically and analyzed for their individual fatty acid composition by gas chromatography. The maximal total lipid concentration was measured by Soxhlet extraction in deficient nitrogen conditions (0.88 mg/L) and was found to be 49% (dw). In particular, palmitic acid was increased from 15% to 58% under phosphorous starvation and oleic acid content was increased from 8% to 40% under nitrogen starvation. Finally palmitic, palmitoleic and linolenic acid represented together more than 70% of the extracted lipids

Development of semi-theoretical light radiation and photosynthetic growth model for the optimal exploitation of wastewaters by microalgae

In the last decade, interest toward the potential application of microalgae has grown considering their potential use in industrial sectors as human nutrition and health, animal feed and biopolymers. Their ability to use light or/and organic carbon as energy source, makes them able to grow in a wide range of conditions. Because of that, the possibility to use alternative nutrients and water sources for their cultivation has been investigated. The microalgal cultivation using wastewaters mixed with synthetic medium might be a good combination that could reduce costs of water, nutrients and wastewater treatment. Anyway, wastewaters are frequently dark colored and contain toxic compounds that could have a negative impact on microalgal light uptake and metabolism. In this study, an experimental first principles hybrid method for the estimation of microalgal growth in non-transparent media was developed as a guide in the choice of the best formulation of wastewater-based culture media for microalgae. To carry out several experimental runs in parallel with different conditions (dilution of the wastewater, different light sources, etc.) a cylindrical bubble column PhotoBioReactor (PBR) was adopted. Its simple geometry allows the analysis of inside light fluxes. A non-metabolizable and non-toxic dye, in condition of purely light-radiative growth limitation, was added to the medium mimicking the reduced transparency of wastewaters. As final step to test the model, culture mediums with wastewater addiction were used for microalgal cultivation, showing their nutritive effects on growth

Techno-economic evaluation of heterotrophic microalgal cultivation approaches

This work focuses the attention on the evaluation of different heterotrophic microalgal cultivation approaches, finding the best process solution to achieve the accumulation of high value-added metabolites, such as astaxanthin and polyunsaturated fatty acids (PUFA), trying also to use a wastewater as carbon source. Three different approaches are evaluated: 1) Classical batch cultivation in sterilized fermenter; 2) Impulse nutrient feeding without sterilizing the reactor; 3) Impulse nutrient approach coupled with wastewaters’ usage in two different parallel reactors. This latter strategy is the one adopted in the European Project MEWLIFE (MicroalgaE biomass from phototrophic-heterotrophic cultivation using olive oil Wastewaters) that aims to produce microalgal biomass in an integrated photo-heterotrophic cultivation system using preconcentrated (in a membrane filtration plant) olive oil mill wastewater (OOMWW) as carbon source for growing algae, thus contributing to waste reuse and valorisation. Thanks to the Aspen Custom Modeler software, it is possible to write codes to represent the fermentation units, which are normally not present in the databases of most common simulators. Finally, a technical-economic analysis is conducted to evaluate the most advantageous process. At present, the pulse technique represents an extremely promising strategy with margins of improvement, deserving thus further investigation

Design and Bench-Scale Hydrodynamic Testing of Thin-Layer Wavy Photobioreactors

In a thin-volume photobioreactor where a concentrated suspension of microalgae is circulated throughout the established spatial irradiance gradient, microalgal cells experience a time-variable irradiance. Deploying this feature is the most convenient way of obtaining the so-called flashing light effect, improving biomass production in high irradiance. This work investigates the light flashing features of sloping wavy photobioreactors, a recently proposed type, by introducing and validating a computational fluid dynamics (CFD) model. Two characteristic flow zones (straight top-to-bottom stream and local recirculation stream), both effective toward light flashing, have been found and characterized: a recirculation-induced frequency of 3.7 Hz and straight flow-induced frequency of 5.6 Hz were estimated. If the channel slope is increased, the recirculation area becomes less stable while the recirculation frequency is nearly constant with flow rate. The validated CFD model is a mighty tool that could be reliably used to further increase the flashing frequency by optimizing the design, dimensions, installation, and operational parameters of the sloping wavy photobioreactor

Histological Features and Biocompatibility of Bone and Soft Tissue Substitutes in the Atrophic Alveolar Ridge Reconstruction

The reconstruction of the atrophic alveolar ridges for implant placement is today a common procedure in dentistry daily practice. The surgical reconstruction provides for the optimization of the supporting bone for the implants and a restoration of the amount of keratinized gingiva for esthetic and functional reasons. In the past, tissue regeneration has been performed with autogenous bone and free gingival or connective tissue grafts. Nowadays, bone substitutes and specific collagen matrix allow for a complete restoration of the atrophic ridge without invasive harvesting procedures. A maxillary reconstruction of an atrophic ridge by means of tissue substitutes and its histological features are then presented

Analysis of microalgae growth in residual light: A diagnostics tool for low-cost alternative cultural media

Most microalgae grow in photoautotrophy and some benefit from mixotrophy and their growth essentially depends on the effective available light intensity. Non transparent media are frequently obtained as the byproduct of bioprocessing but laboratory testing on the suitability of such media may provide misleading results even in laboratory scale photobioreactors. Chapter 2 Cicci et al. (2013) introduced the procedure for calculating a semi-empirical normalised growth rate accounting for a time-varying light limitation inside symmetric photobioreactors and permitting to cancel out the effects of unknown quantities in the photosynthetic response of the microalgal biomass and help diagnose the nutritional suitability of the composite medium. This paper presents the results of applying the semi-empirical normalised growth rate to microalgal growth experiments carried out on media obtained from an anaerobic cattle digestate and from an olive oil mill wastewater (OOMW) and discusses use, inherent opportunities of the proposed diagnostic tool

Detoxification of olive oil mill wastewaters by liquid-liquid extraction with natural deep eutectic solvents

Olive oil mill wastewaters (OOMWs) are the main waste stream of olive processing into olive oil and, although the polyphenolic fraction contained therein can find numerous uses as a nutraceutical and cosmeceutical ingredient, they still have a very hard time to be considered a byproduct rather than a waste. The deployment of this large volume resources has, so far, been hindered by the fact that the polyphenolic mixture that can be extracted from it also contained phenol, which is highly toxic for humans, thus requiring a purification step which adds up to the complexity and cost of the separation. A method capable of separating the toxic compound directly from the liquid stream would therefore be highly desirable. In this work the hydrophobic character of three hydrophobic natural deep eutectic solvents (NaDES) recently developed by Florindo et al. (2017 and 2018), which are composed by pairs of substances among C8 and C12 fatty acids and menthol, has been used to investigate Liquid-Liquid Extraction for detoxifying olive mill wastewaters (OMW) from endogenous phenol. Explorative experiments were carried out on a synthetic mixture containing water, tyrosol (representing desired polyphenols) and phenol, representing a model OMW, at different pH of the treated mixture. Experimental results show that the C8:C12 NaDES exhibits the most favourable extraction features among the three solvents and that neutral pH yields an optimal selectivity

Alveolar ridge augmentation with titanium mesh. A retrospective clinical study

An adequate amount of bone all around the implant surface is essential in order to obtain long-term success of implant restoration. Several techniques have been described to augment alveolar bone volume in critical clinical situations, including guided bone regeneration, based on the use of barrier membranes to prevent ingrowth of the epithelial and gingival connective tissue cells. To achieve this goal, the use of barriers made of titanium micromesh has been advocated. A total of 13 patients were selected for alveolar ridge reconstruction treatment prior to implant placement. Each patient underwent a tridimensional bone augmentation by means of a Ti-mesh filled with intraoral autogenous bone mixed with deproteinized anorganic bovine bone in a 1:1 ratio. Implants were placed after a healing period of 6 months. Panoramic x-rays were performed after each surgical procedure and during the follow-up recalls. Software was used to measure the mesial and the distal peri-implant bone loss around each implant. The mean peri-implant bone loss was 1.743 mm on the mesial side and 1.913 mm on the distal side, from the top of the implant head to the first visible bone-implant contact, at a mean follow-up of 88 months. The use of Ti-mesh allows the regeneration of sufficient bone volume for ideal implant placement. The clinical advantages related to this technique include the possibility of correcting severe vertical atrophies associated with considerable reductions in width and the lack of major complications if soft-tissue dehiscence and mesh exposures do occur

Toward an efficient biorefining of microalgae and biomass alike. A unit operating view on how to mimick the optimisation history of the crude oil refining industry

One major hindrance to biomass deployment, and one which only benefitted from an unbalanced development, is refining into the different fractions which have a market value. Indeed, most products obtained from oil refining owe to the level of sophistication and optimisation reached by energy-integrated fractioning (mostly, distillation) networks. The separation stage of microalgal and lignocellulosic biomass could be addressed by using a converging approach employing a multipurpose solvent which may be adapted by one single and simple operation to different extractions. Such a single-solvent separation approach would lend itself to scaleup to a solvent-integrated fractionation network that might help mimicking the success story of the oil refining industry