On the Reduction of Power Consumption in Vortexing Unbaffled Bioslurry Reactors

Bioremediation of polluted soils via bioslurry reactors is an interesting option among those available nowadays, especially when recalcitrant pollutants are present. Vortexing unbaffled stirred tanks may be a valuable choice to this purpose as they were recently found to be more efficient than baffled vessels for solid suspension processes where mixing time is not a controlling factor. When operated at sufficiently high agitation speeds, the central vortex bottom reaches the impeller and air bubbles start to be distributed throughout the system, thus avoiding any sparger and related clogging issues. In the present work, a vortexing unbaffled stirred tank with solid loadings ranging from 2.5% w/w (weight of the solid/weight of the liquid) up to the very high 160% w/w was studied. Different turbine types including Rushton turbine, up- and down-pumping pitched blade turbines, and A310 were investigated. The minimum impeller speeds for complete particles' suspension (N-js) and system aeration (N-cr) along with the relevant power (P-js, P-cr) and specific power (per mass unit) consumptions (epsilon(js), epsilon(cr)) were assessed, in order to identify the geometrical configuration and operating condition providing the lowest power consumption. Results showed that the Rushton turbine and a solid concentration B of about 30% may be the most economically convenient arrangement to achieve system aeration and complete particles' suspension at the same time inside the reactor

Pollutants removal from municipal sewage by means of microalgae

Microalgae are microorganisms able to photosynthesize, namely transforming inorganic substrates and sun light into organic compounds and chemical energy. The industry of microalgae has expanded in the last decades and several applications are now developed, making their biomass interesting under an economic perspective. Nannochlopsis gaditana is one of the most interesting species already employed in industry because of its high content in lipids that could be employed as source for biodiesel synthesis but also in other fields such as cosmetic and pharmaceutic. One of the most promising application is the exploitation of microalgal grow for bioremediating wastewaters polluted with inorganic nutrients such as nitrates and phosphates that microalgae are able to employ as nutrients. Bio-treatment of wastewaters by using microalgae has the advantage to reclassify the water and preserve it from wasting while producing a valuable biomass. In this work, a microalgal strain, Nannochloropsis gaditana, was employed for testing its performance in the bioremediation of municipal sewages. The wastewater was taken from a municipal plant, after the primary treatment, and the algae processing was aimed at replacing the secondary treatment. Algal growth in its growth medium and in the sewage was compared and algal biomass was characterized. Biochemical Oxygen Demand (BOD), Chemical Oxygen Demand (COD), total nitrogen and total phosphorous levels of the sewage before and after algae treatment were also determined in order to evaluate the efficiency of this microalgal strain on wastewater bioremediation. Our results showed that N. gaditana grows better in wastewater than in the control growth medium and it is able to efficiently remove nutrients from the sewage. However, COD and BOD values did not decrease after algal treatment. These results suggest that the use of selected bacteria and/or yeast strains (together with microalgae) could improve the efficiency of wastewater treatments decreasing BOD and COD values

CFD simulation of radially stirred baffled and unbaffled tanks

Stirred tanks typically employed in process industries are provided with baffles. Although the presence of baffles is known to guarantee good mixing rates, unbaffled vessels may be compulsory in some applications as crystallization, bioremediation, biotechnology and ore industry. A better understanding of unbaffled stirred vessels flow dynamics may allow (i) a proper design to be performed and (i) conditions/processes where baffle presence can be avoided to be recognized. In the present study, the k-\u3c9 SST was used to simulate an unbaffled tank from early to fully turbulent regime (Re 48600-33,000). The unbaffled tank simulated has a diameter T=0.19m and is stirred by a standard six-bladed Rushton turbine with diameter D=T/2 and clearance C=T/3. A corresponding baffled tank was also simulated in order to compare the the two systems. A time dependent Sliding Grid approach was employed for the baffled tank to account for the impeller-to-baffle relative rotation. Conversely, for the case of the unbaffled vessel, a reference frame rotating with the impeller was adopted. Experimental literature data concerning the power and pumping numbers were employed for the simulation validation. RANS results were in good agreement with the experimental data for the baffled case at the largest Re, whereas predictions for the unbaffled vessel exhibited a less satisfactory agreement with experimental data. The latter finding may be due to the poor capability of the two-equations model to manage the anisotropic turbulence typical of high swirling flows

Biological and chemical characterization of new isolated halophilic microorganisms from saltern ponds of Trapani, Sicily

Halophilic microorganisms inhabiting hypersaline environments such as salt lakes, Dead Sea, or salt evaporation ponds, have acquired specific cell adaptation to grow within stressful conditions. In this study, we isolated heterotrophic and autotrophic microorganisms from several saltern ponds located at the Natural Reserve “Saline di Trapani e Paceco”, Sicily, Italy. The aim of the study was to investigate the biotechnological potential of new microbial strains from saltern ponds, by capturing their biological and chemical diversity. After the isolation and identification of the sampled strains, their growth capacity was determined under low and high salinity conditions. The metabolomic profiles of heterotrophs and pigments production of photosynthetic organisms were analyzed. In parallel, antiproliferative tests on human cell lines were conducted with total extracts coming from the microorganism cultures, together with repair activity assessment of non-cytotoxic extracts. Some of the isolated strains were found to synthetize known bioactive molecules and to exert bioactivity on human cells. In particular, the high salinity increases cell repair activity, probably due to an higher production of antioxidants pigments (e.g. lutein and fucoxanthin) from photosynthetic microorganisms; same culture condition augment also concentration of molecules with interesting bioactivities, such as ectoine, betaine, trigonelline, amino acids and oxiglutathione from heterotrophic microorganisms. In conclusion, this work represents the first study on the isolation of halophilic microorganisms populating the ‘Trapani-Paceco’ saltern and shows how an interdisciplinary investigation based on marine microbiology, cell biology, and modern metabolomics can disclose their biotechnological potential

Thermolytic reverse electrodialysis heat engine: model development, integration and performance analysis

Salinity gradient heat engines represent an innovative and promising way to convert low-grade heat into electricity by employing salinity gradient technology in a closed-loop configuration. Among the aqueous solutions which can be used as working fluid, ammonium bicarbonate-water solutions appear very promising due to their capability to decompose at low temperature. In this work, an experimentally validated model for a reverse electrodialysis heat engine fed with ammonium bicarbonate-water solutions was developed. The model consists of two validated sub-models purposely integrated, one for the reverse electrodialysis unit and the other for the stripping/absorption regeneration unit. The impact of using current commercial membranes and future enhanced membranes on the efficiency of the system was evaluated, along with the effect of operating and design parameters through sensitivity analyses. Results indicated that exergy efficiency up to 8.5% may be obtained by considering enhanced future membranes and multi-column regeneration units

Apparatus for synthesizing and separating synthesis products e.g. gaseous and liquid phases on bed, maintains heavier liquid phase at lower portion of first meatus due to gravity and lighter liquid phase at upper portion of meatus

NOVELTY - The apparatus has header that is set to make the heavier and lighter liquid phases flow along outer side surface of a third tube (8) as far as first closure element (13). The third tube is provided with second side openings for directly connecting the first and second meatus. The heavier liquid phase is maintained at lower portion of the first meatus due to gravity and lighter liquid phase is maintained at upper portion of the first meatus until the liquid phases fall into a fourth tube (9). The heavier liquid phase is collectible through a collection hole (12). USE - Apparatus e.g. reactor/separator for synthesizing and separating synthesis products e.g. gaseous phase and heavier and lighter liquid phases on catalytic bed, used in production of biodiesel. ADVANTAGE - Since heavier liquid phase is maintained at lower portion of the first meatus due to gravity and lighter liquid phase is maintained at upper portion of the first meatus, sedimentation separation of the liquid phases is improved. The structure of the apparatus is simplified and the apparatus is constructed easily. The efficacy and use of catalyst are maximized. DETAILED DESCRIPTION - The apparatus has synthesis module (M1) that is set with a first tube (1) which is provided with an opening at one end and closed at second end by a mesh (7). The first tube is adapted to contain a catalytic bed (6). A separation module (M2) is set to separate heavier and lighter liquid phases and gaseous phase originating from the synthesis module. A second tube (1') is arranged adjacent to second end of the first tube. A first closure element is provided with a through hole for sole passage of the second liquid and of the gaseous phase. A third tube is affixed to first end of second tube. A first meatus is set between second tube and the third tube. The fourth tube is set inside the third tube so as to define a second meatus between the third tube and the fourth tube. A separation zone is set between the heavier and lighter liquid phases. A collection hole is set in the second tube to collect the heavier liquid phase. The third tube is set with first side openings at first end, and is set with a header for collecting the liquid phases originating from the synthesis module. The first meatus is directly inserted into the third tube and subsequently into the fourth tube. A control system is set between the liquid phases, to check and maintain interface level below the upper end of the first side openings. The control system has interface level indicator that is connected to the second tube by second side holes envisaged in side surface of the second tube. One of the second side holes is arranged in proximity of the first closure element and other is positioned above the upper end of the first side openings. The protrusions are arranged along cylindrical side surface of the third tube, and are separated by spaces for passage of the liquid phases from the header to the first meatus. A redistribution module (M3) is set to redistribute the lighter liquid phase and gaseous phase originating from the fourth tube. A fifth tube (1") is arranged adjacent to second end of the second tube. The closure element is set with a central perforated area. A sixth tube (14) is set to descent and release of the gaseous phase. The central perforated area is provided with several holes for homogeneous distribution of lighter liquid phase downstream of the redistribution module. The sixth tube is affixed to a second closure element (15). The mesh is provided with a passage area. The synthesis module, separation module and redistribution module are vertically-stacked. An INDEPENDENT CLAIM is included for a method for synthesizing and separating synthesis products e.g. gaseous phase and heavier and lighter liquid phases on catalytic bed, involves synthesizing on a catalytic bed and producing the synthesis products. The liquid phases and gaseous phase are separated in the separation module