Selective collection and conversion method for the reuse of used oils and greases for energy purposes, which method comprises the following steps: (a) producing and separating ester-based waste from other substances or compounds, (b) collecting the waste (c) gathering/storing the waste in at least a collection and/or regeneration facility, (d) regenerating or treating the waste, (e) reusing the collected or regenerated or treated waste, wherein step (c) further comprises a chemical-physical characterization step for the waste, during which said waste is chemically and physically identified such that it can fall within at least a specific relevant class chosen among one of the following: waste containing natural and/or synthetic ester- based oil/grease or mixtures of natural and/or synthetic ester-based oils/greases suitable for the regeneration process, waste containing natural and/or synthetic ester- based oil/grease or mixture of natural and/or synthetic ester-based oils/greases which waste cannot be regenerated but, after a specific treatment, in the reuse step, it is made suitable for the production of electrical energy waste containing natural and/or synthetic ester- based oil/grease or mixture of natural and/or synthetic ester-based oils/greases which waste cannot be regenerated but, after a specific treatment, in the reuse step, it is made suitable for the production of second generation biodiesel, waste containing natural and/or synthetic ester-based oil/grease or mixture of natural and/or synthetic ester-based oils/greases which waste cannot be regenerated or treated, but in the reuse step, it is made suitable for the thermal destruction or combustion with the recovery of produced heat, said waste being an oil or a grease or a mixture containing at least a natural and/or synthetic ester-based oil and/or grease, which oil or grease or which mixture is the by-product or waste of an industrial processes. (a) producing and separating ester-based waste from other substances or compounds, (b) collecting the waste (c) gathering/storing the waste in at least a collection and/or regeneration facility, (d) regenerating or treating the waste, (e) reusing the collected or regenerated or treated waste, waste containing natural and/or synthetic ester- based oil/grease or mixtures of natural and/or synthetic ester-based oils/greases suitable for the regeneration process, waste containing natural and/or synthetic ester- based oil/grease or mixture of natural and/or synthetic ester-based oils/greases which waste cannot be regenerated but, after a specific treatment, in the reuse step, it is made suitable for the production of electrical energy waste containing natural and/or synthetic ester- based oil/grease or mixture of natural and/or synthetic ester-based oils/greases which waste cannot be regenerated but, after a specific treatment, in the reuse step, it is made suitable for the production of second generation biodiesel, waste containing natural and/or synthetic ester-based oil/grease or mixture of natural and/or synthetic ester-based oils/greases which waste cannot be regenerated or treated, but in the reuse step, it is made suitable for the thermal destruction or combustion with the recovery of produced heat,