Romanowska-Duda, Zdzisława, Mieczysław Grzesik, Wiktor Pszczółkowski, Agata Pszczółkowska, and Zofia Wysokińska. 2012. “Use of Sewage Sludge in the Production of Plant Biomass for Energy: Biological and Economic Conditions”. Comparative Economic Research. Central and Eastern Europe 15 (3):105-22. https://doi.org/10.2478/v10103-012-0019-5.