Abstract

Hydrodynamic cavitation (HC) is evaluated as a process intensification method for wastewater treatment, sludge pretreatment, ballast water treatment, disinfection, and oxidation of refractory organic contaminants. The article examines aqueous reaction zones, reactor configurations, hydraulic operating windows, hybrid oxidation, sludge disintegration, biological inactivation, scale up, energy accounting, materials, and control requirements. The reviewed evidence indicates that treatment performance is governed by the controlled sequence of cavity inception, growth, transport, and collapse and by interaction with the water matrix rather than by cavitation number or pressure alone. Static and rotational reactors can intensify oxidation, mass transfer, particle disintegration, microbial inactivation, precipitation, and anaerobic digestion, but response depends strongly on contaminant properties, dissolved gas, solids, radical scavenging, backpressure, temperature, residence time, and auxiliary chemistry. Case studies demonstrate nonmonotonic pressure response, limited standalone mineralization in strongly scavenging matrices, improved methane yield after optimized sludge disintegration, and enhanced micropollutant removal when HC is coupled with hydrogen peroxide, ozone, Fenton chemistry, plasma, or other advanced oxidation processes. Scale up should preserve process function and be verified through continuous pilot testing, energy normalization, byproduct and toxicity assessment, and asset condition monitoring. HC is therefore most effectively implemented as a targeted unit operation within an integrated treatment train rather than as a universal replacement for conventional treatment.