N. Andritsos

Optimizing magnetic nanoparticles for drinking water technology: The case of Cr(VI).

The potential of magnetite nanoparticles to be applied in drinking water treatment for the removal of hexavalent chromium is discussed. In this study, a method for their preparation which combines the use of low-cost iron sources (FeSO4 and Fe2(SO4)3) and a continuous flow mode, was developed. The produced magnetite nanoparticles with a size of around 20 nm, appeared relatively stable to passivation providing a removal capacity of 1.8 μg Cr(VI)/mg for a residual concentration of 50 μg/L when tested in natural water at pH7. Such efficiency is explained by the reducing ability of magnetite which turns Cr(VI) to an insoluble Cr(OH)3 form. The successful operation of a small-scale system consisting of a contact reactor and a magnetic separator demonstrates a way for the practical introduction and recovery of magnetite nanoparticles in water treatment technology.

Characteristics of scales from the Milos geothermal plant

Samples of scales have been studied using X-ray diffraction, elemental analysis and scanning electron microscopy. Analyses have also been made of brine and steam samples. The scale consists of heavy metal sulfides and silicon compounds which account for 90-100% of the deposited mass. The composition of the scale depends on the location with respect to the fluid flashing point. Samples in the vicinity of this point largely consist of metal sulfides (PbS, ZnS and CuFeS/sub 2/), while the percentage of silica and possible of other silicon compounds tends to increase farther downstream. In all the samples, a significant part of the iron is not in the form of sulfide and is possibly bound into the silica matrix by some kind of ion-bridging. It is also observed that a silicon - rich layer adheres to the metal surface, even in places where sulfides are the main constituents of the scale.

Nominally two-dimensional waves in inclined film flow in channels of finite width

Traveling waves in inclined film flow in channels of finite width are never truly two-dimensional (2D) because of a long-range effect of sidewalls. The present study documents the characteristics of the first waves that are observed beyond the primary instability (termed nominally 2D) by taking measurements in a 3000 mm long inclined facility with adjustable width up to 450 mm using a fluorescence imaging technique. It is observed that nominally 2D waves are very persistent structures with their crests attaining a parabolic shape, which is symmetric with respect to the channel centerplane irrespective of the 3D content of the inlet forcing. The apex curvature of the parabola varies inversely with channel width and Reynolds number. The wave height is maximum at the centerplane and decreases to zero at the sidewalls, irrespective of the wetting properties of the system. The linear phase velocity of nominally 2D waves is always lower than predicted by the theory for small amplitude, 2D waves, and significant...

Cu-Zn powders as potential Cr(VI) adsorbents for drinking water

This work examines the possibility of applying CuZn alloys as a reducing medium for the efficient removal of hexavalent chromium from drinking water. In an effort to develop a route for producing powders of CuZn alloys under mild conditions and investigate the optimum composition for such application, a series of alloys in the form of powders were prepared, by a sequence of Cu and Zn ball-milling and low temperature annealing. Batch Cr(VI) removal tests, performed to evaluate and compare the efficiency of the products under typical natural water parameters (pH 7 and natural-like water), indicated that the best performing material have a composition around 50 wt% Cu. The dominant reduction mechanisms are both the corrosion of the alloy surface and the electron transfer to the solution. The behavior of granulated CuZn media was tested in rapid-scale column tests using the commercial KDF which verified the high potential of CuZn alloys in Cr(VI) removal. Nevertheless, Cu and Zn leaching problems should be also considered.

Modelling Tomato Dehydration in a Tunnel Dryer Using Geothermal Energy

Low-temperature geothermal waters can be used efficiently in drying various vegetables and fruits, replacing sun-drying or drying using conventional fuels. A “geothermal” tomato dehydration plant has been operating since 2001 in Neo Erasmio, northern Greece, producing high-quality, “sun-dried” tomatoes. The unit uses low-cost geothermal water to heat atmospheric air to 56–58°C, which is introduced in a specially designed tunnel-type dryer. The scope of this work is to model the aforementioned tomato-drying process that uses low-enthalpy geothermal energy. The modelling procedure consists of two stages: the first stage focuses on the modelling of a single tomato piece, whereas the second stage is concerned with the modelling of air drying of tomatoes in a tunnel with trays moving in batches. The influence of air velocity, air temperature, and tomato tray loading on the drying process was investigated. The effect of flow configuration, i.e., co-current or counter-current operation, on the drying characteristics was also explored. The model can be used for the design and optimization of the continuous drying process existing in Neo Erasmio and can be easily extended and modified to deal with other agricultural products and tunnel designs.