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J. Kosel, et al.
Fig. 6. The In fl uence of developed cavitation (serrated rotor; circles) or supercavitation (two-teeth rotor; squares) generated inside the RGHC device on the de- struction of high ( fi lled symbols) or low (empty symbols) spiked titers of the bacteria Bacillus subtilis .
to 1.0 Log 10 CFUmL − 1 for the CRW samples. Finally, although present at lower concentrations, moulds were reduced by 0.6 Log 10 CFUmL − 1 and by 0.3 Log 10 CFUmL − 1 for the RW and CRW samples, respectively.
costs only relate to electric energy consumption of each individual run and do not include any potential cooling costs, and capital or main- tenance costs are also excluded (plant production, amortization and operation). The E EO value for the removal of the bacteria Escherichia coli (with a starting concentration of 1 x10 4 CFUmL − 1 ) from wastewater using the Venturi device was 268.6 kWh/m 3 /order [43]. For a similar starting bacterial titer (~1 × 10 5 CFU mL − 1 ) of B. subtilis, the RGHC spent 347.5 kWh/m 3 /order and 67.2 kWh/m 3 /order for the developed cavi- tation and for the supercavitation, respectively. When the RW sample was treated using supercavitation, the RGHC spent 56.2, 36.4, 39.0, 117.4 and 253.5 kWh/m 3 /order for the aerobic bacteria, anaerobic sulphate reducing bacteria, yeasts, bacterial spores and for moulds, respectively.
3.5. Economic evaluation
Operational e ff ectiveness of the RGHC equipped with the serrated (for developed unsteady cavitation) or the two-teeth rotor (for super- cavitation) was compared with the e ff ectiveness of the Venturi device, which was assembled by Arrojo et al. [43] and which could generate a developed form of cavitation. For both devices, electric energy per order ( E EO ; kWh/m 3 /order) was calculated [44], which is the amount of electric energy required to bring a decrease in viable colony counts (CFU/mL) by one order of magnitude. Its equation is presented below:
× P t V Log ( ) × f X X 10 f 0
E
EO
=
4. Discussion
(3) where P is the power input of the system [kW], V is the volume of treated water [m 3 ] in time t [h], and X 0 and X f are the starting and ending viable colony counts of bacteria per one millilitre (CFU/mL). Higher E EO values correspond to lower removal e ffi ciencies. Table 2 shows the average E EO values and approximate costs ( € /m 3 ) for each experimental run. Nevertheless, we have to keep in mind that these
In this work, we studied 2 di ff erent types of hydrodynamic cavita- tion, developed unsteady cavitation (using a serrated rotor and stator) and supercavitaiton (using a two-teeth rotor), that were generated in- side the RGHC device. The high-speed camera revealed that behind every gap between the tips of the teeth of the opposing serrated rotor and stator a developed unsteady form of cavitation was accompanied by
Fig. 7. The e ff ect of the RGHC supercavitation treatment (two-teeth rotor) on the chemical parameters of samples isolated from real process waters.
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