No experiment was conducted, yet, to investigate the scale effects on the dynamics of developed cavitating flow with periodical cloud shedding. The present study was motivated by the unclear results obtained from the experiments in a Venturi-type section that was scaled down 10 times for the purpose of measurements by ultra-fast X-ray imaging (Coutier-Delgosha et al. 2009). Cavitation in the original size scale section (Stutz and Reboud in Exp Fluids 23:191-198, 1997, Exp Fluids 29:545-552 2000) always displays unsteady cloud separation. However, when the geometry was scaled down, the cavitation became quasi steady although some oscillations still existed. To investigate this phenomenon more in detail, experiments were conducted in six geometrically similar Venturi test sections where either width or height or both were scaled. Various types of instabilities are obtained, from simple oscillations of the sheet cavity length to large vapor cloud shedding when the size of the test section is increased. It confirms that small scale has a significant influence on cavitation. Especially the height of the test section plays a major role in the dynamics of the re-entrant jet that drives the periodical shedding observed at large scale. Results suggest that the sheet cavity becomes stabile when the section is scaled down to a certain point because re-entrant jet cannot fully develop.
COBISS.SI-ID: 12534555
Study evaluated suspended activated sludge (SAS) and attached-growth biomass processes using lab-scale flow-through bioreactors with the addition of a mixture containing 1 µg/L of each of the compound of interest. Furthermore, the attached-growth biomass process was evaluated for two types of carriers, Kaldnes K1 and for the first time Mutag BioChipTM carriers. The SAS process showed poor and inconsistent removal of clofibric acid CLA (9 % ± 28 %), carbamazepine CBZ (21 % ± 25 %) and diclofenac DF (48 % ± 19 %), while ibuprofen IB, naproxen NP and ketoprofen KP yielded 86 %, 74 % and 78 % removal, respectively, with a measured deviation of (10 %. The results agree with published data confirming the recalcitrant nature of CLA, CBZ and DF to classical SAS treatment. In comparison to SAS, attached-growth biomass process, for both types of carriers, resulted in higher removal efficiencies for IB (94 % ± 8 % for Kaldness K1 and 94 % ± 4 % for Mutag BioChipTM carriers), while KP and CBZ were removed to a lesser degree. In the case of CLA and NP no difference in removal efficiencies between SAS and attached-growth biomass process were observed. Better results were obtained for DF using Mutag BioChipTM carriers (85 % ± 10 %) compared to reactors containing the Kaldnes K1 carriers (74 % ± 22 %) and SAS (48 % ± 19 %). To enhance the removal of pharmaceuticals hydrodynamic cavitation with hydrogen peroxide was evaluated. Optimal parameters resulted in removal efficiencies between 3 - 70 % and showed the potential to be augmented with different cavitation configuration. Coupling the attached-growth biomass biological treatment, hydrodynamic cavitation/hydrogen peroxide process and UV treatment resulted in removal efficiencies of ) 90 %. Importantly, this study proves that it is possible to remove pharmaceutical residues both consistently and to a higher degree using combination biofilm process and AOP, which has significant implications for future WWT strategies.
COBISS.SI-ID: 26582055
Nowadays, due to lack of freshwater resources a sufficient wastewater management is an environmental concern. This global issue is resulting in the rapid growth of technologies for wastewater treatment. In this study a novel rotation generator of hydrodynamic cavitation is presented, which is used as a tool for pharmaceuticals removal in water. On presented machine analysis of hydrodynamics is made, where the extent and aggressiveness of cavitation is evaluated. The study has shown, that for a sufficient treatment, hydrodynamic cavitation with combination of hydrogen peroxide is needed. The removal of four pharmaceuticals (ibuprofen, ketoprofen, carbamazepine and diclofenac) was considered, where the over 80% effect was achieved. Various operating parameters such as the rotors geometry of the cavitation generator, pressure in the treatment chamber, temperature of the liquid, amount of hydrogen peroxide and time of exposure to the cavitation was investigated. The experimental results show that hydrodynamic cavitation has a good potential for efficient removal of pharmaceuticals what suggests to continue with research in this field and to consider an appropriate design for a commercial use.
COBISS.SI-ID: 13049115
Paper evaluates hydrodynamic cavitation as a method for wastewater treatment. In collaboration with Faculty of Mechanical Engineering and Faculty for Civil and Geodetic Engineering, University of Ljubljana we evaluated the efficiency of hydrodynamic cavitation for removing micropollutants, e.g. pharmaceutical residues, from wastewaters. In this study, the removal of clofibric acid, ibuprofen, naproxen, ketoprofen, carbamazepine and diclofenac residues from wastewater, using a novel shear-induced cavitation generator has been systematically studied. The effects of temperature, cavitation time and H2O2 dose on removal efficiency were investigated. Optimisation (50 °C; 15 min; 340 mg L−1 of added H2O2) resulted in removal efficiencies of 47–86% in spiked deionised water samples. Treatment of actual wastewater effluents revealed that although matrix composition reduces removal efficiency, this effect can be compensated for by increasing H2O2 dose (3.4 g L−1) and prolonging cavitation time (30 min). Hydrodynamic cavitation has also been investigated as either a pre- or a post-treatment step to biological treatment. The results revealed a higher overall removal efficiency of recalcitrant diclofenac and carbamazepine, when hydrodynamic cavitation was used prior to as compared to post biological treatment i.e., 54% and 67% as compared to 39% and 56%, respectively. This is an important finding since diclofenac is considered as a priority substance to be included in the EU Water Framework Directive.
COBISS.SI-ID: 27217959
Treatment performance and fish production were evaluated in a small-scale cyprinid fish farm with a closed-loop system consisting of a 0.2 m³ experimental fish tank (Tank A) with initial carp load of 1 kg/m³ and of a treatment train (TT) with a vertical constructed wetland (CW) and an ultrasonic unit (US). Tank A with average water circulation of 60 L/h was compared with a control tank (Tank B) of the same dimensions and fish load but with no TT. The experiment was divided into three sequential trials using different combinations of CW media and US. A preliminary trial was performed for evaluation of US efficiency in algae control. The results showed that the system with CW filled with sand performed better for chemical oxygen demand, ammonium nitrogen, total phosphorous and ortophosphate, while the system with CW filled with expanded clay performed better for biochemical oxygen demand, nitrate-nitrogen and nitrite-nitrogen. There were no differences in total suspended solids between both systems. Specific growth rates and the fish body weight increase in Tank A were higher than in Tank B. In the third trial, the values of the above listed parameters in Tank A were higher than in the first two trials due to an accumulation of nutrients in Tank A. US reduced algae biomass in free water by 63%.
COBISS.SI-ID: 4625003