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The work describes a method for searching for the best variant(s) of cavitation of coffee waste, taking into account the defined five criteria: sCOD/COD and DOC/TOC, which were maximised, and the others, i.e. caffeine concentration, phenols concentration and energy consumption, which were minimised. The method used in the first stage determines non-dominated variants, then a compromise variant, assuming that all criteria used are equally important. Further analysis allows determining further compromise options. The method of determining compromise solutions is based on the use of Chebyshev metric, which has been enriched with a mechanism for normalising individual criteria (which allows for their comparison) and the ability to define the importance of individual criteria. For normalisation, the so-called the ideal point, which is an internal property of the analysed variants, is determined each time for a given subset of non-dominated variants. After determining the first compromise solution, the process of generating new ideal points (their number is equal to the size of the criteria space) begins by associating the components of this solution with the components of the ideal point. Using new reference points, the method determines additional compromise solutions. The five-criteria evaluation of 20 variants obtained in the experiment showed that when adopting different values of the importance of individual criteria, some variants are never selected as a compromise. The subset of compromise variants ranged from 3 to 6. The variants that were repeatedly selected as compromise variants, with different values of the importance of individual criteria, were the variants for which the cavitation process time was: 20 or 30 minutes and the cavitation inlet pressure was 5 bar. The multi-criteria assessment showed that these are the best compromise options and can be recommended for the coffee waste cavitation process.
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