This study examines energy recovery, specifically electricity generation, from waste in incineration plants. This study decomposes the incinerator system into waste treatment process and energy generation process via a two-stage network structure. We build a Russell multi-activity network data envelopment analysis (RMNDEA) model considering the weak disposability technology, and measure productivity changes over time and assess the plants’ returns-to-scale. We validate the model with an empirical study of 23 incinerators operating between 2011 and 2020 in Taiwan. Our finding that the waste treatment process itself is the major cause of inefficiency indicates that incinerator operators should reallocate input resources. Throughout the study period, there are minor productivity changes and most plants maintain constant returns-to-scale. However, some incinerators in Southern Taiwan having inefficient scale sizes should be rescaled for productivity improvement. The results validate the need to conduct routine eco-efficiency evaluations of solid waste management (SWM) in incinerators.