Hydrodynamic Cavitation in Water and Wastewater Treatment: A Critical Review of Applications, Reactor Design, and Process Function

Hydrodynamic cavitation has attracted increasing attention in water and wastewater treatment because it can generate localized shear, pressure fluctuations, interfacial renewal, and reactive species in relatively simple continuous-flow devices. This review critically examines its main application domains, including microbial disinfection, cyanobacterial bloom control, organic micropollutant degradation, real wastewater treatment, sludge pretreatment for energy recovery, and hybrid process configurations. Rather than treating hydrodynamic cavitation as a single treatment mode, the discussion compares applications in relation to reactor design, matrix characteristics, treatment target, operating conditions, and assigned process function. The analysis shows that performance depends strongly on the interaction among device geometry, treated matrix, process configuration, and evaluation metrics. The same nominal process may therefore act as direct treatment, pretreatment, mass-transfer intensifier, oxidant-activation module, or support to downstream biological and polishing steps. The most consolidated evidence concerns microbial disinfection, sludge pretreatment, and several classes of organic contaminants, whereas PFAS treatment, field-scale validation, and system-level assessment remain less mature. Overall, hydrodynamic cavitation is best interpreted as a process-intensification platform rather than as a universally applicable stand-alone solution. Further progress will require more transparent assessment criteria, more comparable metrics, stronger validation in real matrices, more controllable reactors, and more rigorous energy, techno-economic, and scale-up evaluation.