Sérgio R. Fontes

Biochemical Composition of Chlorella Sorokiniana Grown in a Novel Design of Hybrid Photobioreactor

The aim of this study was to assess the feasibility of a 180 L photobioreactor in which a submerged ultrafiltration system was used to maintain continuous nutrient inflow without biomass loss from the culture. After exponential growth, approximately 15% of the total volume was removed and replaced with a modified medium to induce algal physiological responses as a biochemical manipulation procedure. In this system, Chlorella sorokiniana was kept under healthy conditions, according to protein: carbohydrate ratio. C. sorokiniana was grown exponentially for 4 days up to 8.9x106 cells mL-1. The culture medium used for biochemical manipulation (72 h exposure) consisted of LC Oligo medium without nitrates or phosphates, and with 7x10-7 molL-1 total copper. The results confirmed the effectiveness of the submerged membrane and showed that algae exposure to a stressing medium resulted in intracellular carbohydrate increase, thus protein: carbohydrate (P:C) ratios, and affected lipid class composition. This novel photobioreactor configuration has the potential to improve microalgal yields and/or specific intracellular constituents, inasmuch as biochemical manipulation of the biomass is facilitated and the continuous system is operated without biomass loss.

Method of chemical impregnation applied to microporous tubes and tubular membranes for the microfiltration of emulsions and bacteria suspensions

A technique of chemical impregnation by precursor solution was developed for the formation of thin films in microporous tubes and tubular membranes. The performance of this technique was analyzed by the microfiltration process of emulsions (vegetable oil/water) and bacteria suspensions (Escherichia coli) of the whey of milk of cheese processing. The microporous tubes (nominal pore size 0.5 µm) were impregnated with a precursor zirconia solution and calcined at 600 and 900 oC to influence the improvement of the demulsification process. Ceramic membranes (nominal pore size between 0.8 µm and 1.2 µm) were impregnated with a silver precursor and calcined at 600 °C forming metallic silver to act as bactericide in the residual bacteria suspension of the dairy products. The impregnated porous medium was characterized by scanning electron microscopy. The results of the permeate analysis for values of organic carbon content refer to emulsion treatment and the value of counting of bacteria by plating analysis is related to the treatment of bacteria suspension. The results were analyzed as a function of the performance and influence of the impregnation regarding the presence of zirconia or silver for each application.

Analysis of Physical Properties and Experimental Behaviour of High Turbulent Flow in Cross-Flow Microfiltration of Açai Juice

This paper presents an experimental investigation of the cross-flow microfiltration process applied to the clarifying of acai (Euterpe oleracea Mart.) juice. Acai juice is a complex fluid, similar to a suspension of particles (fibers and cellulose) mixed in water, which contains ions of iron, zinc, maganese and pigments, as anthocyanins. In this study, a commercial membrane of α-alumina (Al2 O3 ) in the form of a tube with 1.2μm of average pore size was utilized to investigate the clarifying of juice. This pore size of the ceramic structure was utilized in an attempt to reduce the polarization phenomenon and improve the permeate flux without utilizing the usual enzymatic treatment made in the microfiltration processes. The rheological behaviour of the suspension was investigated in a cone/plate rheometer (model, DVIII-Ultra) and a cylindrical rheometer (model, DVIII+), both by Brookfield/USA, as the shear stress (τ) in function of shear rate (γ) was fitted and analyzed with the power-law and Herschel-Bulkley’s models. All the mixtures showed flow behaviour index values (n) near to one, characterizing Newtonian fluids (pseudo-plastic). The particle size distribution (PSD) of the samples of suspension and permeate were analyzed by APS100 (ultrasound spectroscopy) by Matec/USA. The analysis of the suspension showed the presence of particles of size equal 0.16micra, while the permeate did not present particles. The experiments were performed in a turbulent range higher than 2400 until 57500 and with variation to values of transmembrane pressure from 1 to 4bar; the usual and direct correlation between transmembrane flux and transmembrane pressure was not observed in the experiments and a new correlation to the dimensionless of TMP (trans-membrane pressure) and Reynolds (Re) was presented.Copyright

Mathematical Modelling of the Laminar Entrance Flow into a Circular Tube Using a Fourier Series Approximation

In this work, the permanent laminar flow in the entrance region of a cylindrical tube is analyzed using a new Fourier series-based approximation technique of similarity for velocity profiles. The similarity method used in this work is well known in the literature on fluid mechanics and can be applied in other engineering education fields. The potential of the original modified Fourier cosine series is compared with the mathematical modelling of the entrance flow. Different physical entrance flow parameters of the interest are obtained through the integral formulation of differential equations for conservation laws. The results of this mathematical approach were found to be compatible with those reported in the literature.