Abstract
ABSTRACT The aim of the current study is to compare the chemical oxygen demand (COD) removal efficiency of a Venturi device to that of an orifice plate. The inlet pressure in the devices was optimized and the degradation kinetics was analyzed. In addition, the synergistic effect resulting from the combination between cavitation and H2O2 was investigated. An experimental apparatus was built to achieve these goals. A sucrose solution and an effluent from a sucrose-based soft drink industry were treated. Results showed that the Venturi device recorded 90% COD removal efficiency after three treatment minutes. On the other hand, the orifice plate recorded 90% COD removal efficiency after 9 min. The degradation kinetics-reaction order was 3.5, except for the highest Venturi inlet pressure (7.3 bar), which led to coalescence of cavities and to reduced degradation rate. The synergistic coefficient (Sc) was 185.20 and showed that the hybrid process (HC + H2O2) was much more efficient than the cavitation process applied alone. The high COD concentration in the effluent generated by the soft drink industry (2,512.8 mg L-1) was significantly decreased by 72%. The combined use of cavitation and Venturi has significant potential to remove high organic matter concentrations in short treatment periods.
Highlights
Hydrodynamic cavitation is generated by liquids passing through physical constrictions such as orifice plates (HILARES et al, 2017), Venturi devices (CHOI et al, 2018) or partially closed valves (LI; SONG; YU, 2014)
The present study investigated the hydrodynamic cavitation efficiency in removing chemical oxygen demand (COD) from sucrose solution and from an effluent generated by a soft drink industry
Experiments were conducted in an experimental closed-circuit apparatus, in which the cavitation phenomenon was generated by two devices: Venturi or orifice plate
Summary
Hydrodynamic cavitation is generated by liquids passing through physical constrictions such as orifice plates (HILARES et al, 2017), Venturi devices (CHOI et al, 2018) or partially closed valves (LI; SONG; YU, 2014). Hydrodynamic cavitation can be understood as the phenomenon encompassing the formation, growth and implosion (collapse) of vapor microbubbles (cavities) in a liquid medium (CAPOCELLI et al, 2014; RAJORIYA et al, 2018). This phenomenon happens within a short-time interval and releases substantial amounts of energy, which generate hot spots (1,000 to 10,000 K) and high-pressure regions - from 10 to 500 MPa (GOGATE; KABADI, 2009). In light of these characteristics, hydrodynamic cavitation has been used in different environmental engineering applications such as water supply and (KOSEL et al, 2017) wastewater (DULAR et al, 2016) treatments, as well as in algae removal from eutrophic lakes (BATISTA; ANHÊ; GONÇALVES, 2017)
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