Challenges of Hydrodynamic Cavitation of Organic Wastes

The aim of this study was to evaluate the effectiveness of hydrodynamic cavitation (HC) as a pre-treatment method for selected organic wastes. In these HC experiments, municipal wastewater (MW) and mature landfill leachate (MLL) as well as mixtures of lignocellulosic waste (LB) suspended in these waste streams were investigated. For all HC tests, the same operational parameters were assumed: an inlet pressure of 7 bar, and 30 recirculations through the cavitation zone. A steel orifice plate with a conical concentric hole of 3/10 mm was used as the HC inductor. In almost all the materials analysed, solubilisation and decomposition of complex organic matter were observed, which were confirmed by an improved biodegradability index (BI) and soluble chemical oxygen demand (SCOD) content in the cavitated mixtures. The exception was the series with sole MW; in this case, the BI was reduced. In turn, regarding the multicomponent mixtures, more beneficial results were found for LB and MW, which were confirmed by improved BI, alkalinity and SCOD content. The results obtained indicate that HC might be applied as a pre-treatment method for selected organic wastes for further biomethane production. However, a key factor in its successful application is the selection of suitable operational conditions chosen individually for each waste type.