•Big inconsistencies in studies of utilization of cavitation exist.•Studies are many times not repeatable.•Cavitation conditions cannot be described by the σ value.•Results show obvious issues of ...using σ value.•Effort should be put into description of methods.
Within the last years there has been a substantial increase in reports of utilization of hydrodynamic cavitation in various applications. It has came to our attention that many times the results are poorly repeatable with the main reason being that the researchers put significant emphasis on the value of the cavitation number when describing the conditions at which their device operates.
In the present paper we firstly point to the fact that the cavitation number cannot be used as a single parameter that gives the cavitation condition and that large inconsistencies in the reports exist. Then we show experiments where the influences of the geometry, the flow velocity, the medium temperature and quality on the size, dynamics and aggressiveness of cavitation were assessed. Finally we show that there are significant inconsistencies in the definition of the cavitation number itself.
In conclusions we propose a number of parameters, which should accompany any report on the utilization of hydrodynamic cavitation, to make it repeatable and to enable faster progress of science and technology development.
•The paper discusses the methods of employing cavitation in wastewater treatment.•Removal of pharmaceuticals, cyanobacteria, algae, Legionella and Rotavirus is shown.•Hydrodynamic cavitation shows ...potential due to good scaling and energy efficiency.
The use of acoustic cavitation for water and wastewater treatment (cleaning) is a well known procedure. Yet, the use of hydrodynamic cavitation as a sole technique or in combination with other techniques such as ultrasound has only recently been suggested and employed.
In the first part of this paper a general overview of techniques that employ hydrodynamic cavitation for cleaning of water and wastewater is presented.
In the second part of the paper the focus is on our own most recent work using hydrodynamic cavitation for removal of pharmaceuticals (clofibric acid, ibuprofen, ketoprofen, naproxen, diclofenac, carbamazepine), toxic cyanobacteria (Microcystis aeruginosa), green microalgae (Chlorella vulgaris), bacteria (Legionella pneumophila) and viruses (Rotavirus) from water and wastewater.
As will be shown, hydrodynamic cavitation, like acoustic, can manifest itself in many different forms each having its own distinctive properties and mechanisms. This was until now neglected, which eventually led to poor performance of the technique. We will show that a different type of hydrodynamic cavitation (different removal mechanism) is required for successful removal of different pollutants.
The path to use hydrodynamic cavitation as a routine water cleaning method is still long, but recent results have already shown great potential for optimisation, which could lead to a low energy tool for water and wastewater cleaning.
The presence of Legionella pneumophila bacteria in engineered water systems can pose a significant health risk. Current prevention and outbreak treatments are cost and environmentally ineffective. ...Moreover they do not prevent rapid bacteria recolonization. Although cavitation was already suggested as a possible water treatment technique a systematic study has not yet been performed. In the present experimental campaign we set out to evaluate the efficiency of removal of L. pneumophila by three types of cavitation—the most commonly used acoustic cavitation, the aggressive developed hydrodynamic cavitation, and the supercavitation. We show that it is probably not the pressure peaks or the high local temperatures that cause the eradication of the bacteria, but the rapid pressure decrease which was initiated in supercavitating flow regime. Results of the study show promising ground for further optimization of a methodology for L. pneumophila removal by cavitation.
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