Application of hydrodynamic cavitation to improve the biodegradability of mature landfill leachate

• Hydrodynamic cavitation was studied as a pretreatment of mature landfill leachate.
• Orifice plate with a 3/10 mm diameter and 0.033 cavitation number was recommended.
• Biodegradability index increased from 0.046 to 0.056 in 30 recirculation passes.
• Energy efficiency was evaluated.
• Degradation of refractory compounds was confirmed.

In this study, the application of hydrodynamic cavitation to improve the biodegradability of mature landfill leachate was investigated. Three configurations of cavitation device were examined and operational parameters of the process were selected. The study indicated that the orifice plate with a 3/10 mm diameter conical concentric hole, characterized by the cavitation number of 0.033, is a reasonable choice to ensure the enhanced biodegradability of mature leachate. Using such a configuration and maintaining 30 recirculation passes through the cavitation zone at inlet pressure of 7 bar, the highest increase of biodegradability index (BI) of approximately 22% occurred, i.e., from the value of 0.046 to 0.056. The FT-IR/PAS analysis confirmed a degradation of refractory compounds that typically prevail in mature leachate.An evaluation of energy efficiency was made in terms of the actual consumed energy measured by using the Kyoritsu KEW6310 Power Quality Tester. A cavitational yield of 9.8 mg COD kJ−1 was obtained for the optimum configuration and 30 recirculation passes. Regarding energy efficiency, the application of 10 cavitation cycles appeared to be the most profitable. This was due to an almost threefold higher cavitational yield of 27.5 mg COD kJ−1. However, the preferable option should be selected by considering a satisfactory effect in the biodegradability enhancement.