Acoustic cavitation is a promising tool to support and accelerate recycling processes. For instance, precious metal recovery from electronic or other waste by leaching or delamination has successfully been improved by application of intense ultrasonic [1, 2]. In many cases, the solvents are non- aqueous, and higher viscosities lead to reduced heat and mass transfer. This is partly compensated or overcome by acoustic cavitation effects like microstreaming and surface erosion. However, many properties of cavitation at high viscosity, like in oils, acids or ionic liquids, differ as compared to water. This work extends previous investigations on acoustic cavitation bubble structures [3] and on sound propagation and erosion of fixed bed reactor geometries [4] in ethylene glycol mixtures. Among other findings, the preliminary results suggest that certain localized bubble structures rely on confinement by reducing viscosity by cavitation heat deposition, and that surface erosion at higher viscosities is less than at the low viscosity of water.