1,721,114 research outputs found
Size dependency of citric acid monohydrate growth kinetics
No full textAn experimental study concerned with the growth kinetics of citric acid monohydrate crystals is presented. Due to the properties of the system, which is very soluble, with low solid-liquid density difference and high liquid viscosity, two different techniques were used: large crystals (710-850 mu m) were grown in a fluidized bed crystallizer; small crystals, belonging to three size ranges from 90 to 355 mu m, were grown in the cell of a laser light diffraction granulometer. A first order growth kinetics resulted in both cases; a comparative analysis of both the present data and those reported in the literature relevant to larger or smaller crystals, indicates that the system exhibits size-dependent growth, which increases linearly with the crystal size. (C) 1998 Elsevier Science S.A. All rights reserved
Critical flux analyses on a differently pretreated olive vegetation waste water stream: some case studies
No full text
Critical flux analyses on differently pretreated olive vegetation waste water streams: Some case studies
No full textone of the main disadvantages of batch membrane processes is the increase of the pollutant concentration in the feedstock throughout the operation. Operating the plant at constant process conditions leads in many cases to weaker performances and, moreover, to heavy fouling on the membranes. Critical flux-based methods are one of the most used approaches to overcome fouling problems. Within critical flux conditions, only reversible fouling can occur, which can be periodically soft-cleaned. This work studies the relationship between particle size distributions in the feed stream and critical flux values when different pretreatment processes are applied to an olive vegetation waste water stream. The considered pretreatment processes were: coagulation (with aluminum hydroxide and aluminum sulphate), aerobic biodigestion (by means of fungi) and photocatalytic organic matter reduction (by means of nanometric titanium dioxide anatase powders irradiated by UV light). The study was carried out at pilot plant scale (100 L batch capacity). These results were compared with performances and effects on the critical flux value for MF, UF and NF membranes. The different pretreatment on the same waste water stream shifts differently the particle size distribution mainly by organic matter degradation, and this influences heavily the critical flux value and thus the filtration outcome. Finally, the purification of the olive vegetation waste water stream can be performed with a MF, UF, NF and RO membrane system in series, being very careful in choosing the correct operating conditions to avoid the quick formation of an unsustainable fouling. (C) 2009 Elsevier B.V. All rights reserved
Fatty acid composition and technological quality of the lipids produced by the microalga Scenedesmus dimorphus 1237 as a function of culturing conditions
Full text linkScendesmus 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
Monitoring and Control of the Fines Content in the Crystal Product from a DTB Crystallizer
No full textSize distribution is one of the key features of a crystal product to be controlled to ensure good technological characteristics. Controlling the entire size distribution is often unnecessary: in order to obtain a stable crystal size distribution (CSD) and suppress the disturbances, the manipulation of the fines removal rate can be effectively used, as suggested by Rohani and Lee (1987). However, an on-line measurement device must be available.
The target of such a measuring instrument may be measuring either the magma density of fines or the entire product size distribution. As far as the magma density of fines is concerned, turbidimetry is one of the most suitable techniques for its determination, whereas light reflectance or diffraction-based instruments are usually adopted to measure the entire size distribution. The former technique, currently adopted in the Lasentec FBRM, only gives a qualitative indication of the size distribution; light diffraction, on the other hand, requires a troublesome dilution of the suspension.
The present work deals with a control scheme of a continuous cooling crystallizer based on the use of a specifically developed on-line measuring device which is cheap and easy to apply and operate. The control system was checked on a continuous pilot-scale crystallizer of potassium sulphate from aqueous solutions
Production of the freshwater microalgae Scenedesmus dimorphus and Arthrospira platensis by using cattle digestate
Full text linkMicroalgae are considered one of the most promising feedstocks for biofuels; these microorganisms are also able to enhance the nutritional content of conventional food preparations, or can be converted into other fuel products, such as hydrogen, ethanol, long-chain hydrocarbons resembling crude oil, or biogas.
Scendesmus dimorphus 1237 is an oleaginous eukaryotic microalga, able to produce and accumulate lipids up to a fraction around 43%. In condition of nitrogen starvation this percent grow sup to 50% of dry weight. Therefore this microalga is considered a promising feedstocks for biofuels. Arthrospira platensis is a cyanobacterium with a considerable potential as a source of high biologic value proteins (“superfood”), pigments (phycocyanin and beta-carotene) and poly-unsaturated fatty acids (PUFA) which have been shown to have therapeutic effects on humans.
Anaerobic digestion liquid effluents feature the presence of nutrients, such as nitrogen and phosphorous, which makes them interesting for a potential application in microalgal biomass production.
Aim of this work is investigating the use of liquid anaerobic cattle manure digestate for the photosynthetic growth of these microalgae
Growth Kinetics of Monohydrate Citric Acid
No full textThe growth kinetics of monohydrate citric acid crystals in the size ranges 90÷355 and 710÷850 μm was studied using two different techniques. Basing on the present results, integrated with literature ones, the system appears to exhibit size-dependent growth
- …
