Properties of ashes formed after the combustion of sewage sludge Elżbieta Bezak-Mazur, Małgorzata Widłak, Jarosław Gawdzik, Renata Stoińska, Justyna Zapała-Sławeta and Joanna Ciopińska E3S Web Conf., 44 (2018) 00012 Published online: 03 July 2018 DOI: 10.1051/e3sconf/20184400012