Wang, Lawrence K. and Wang, Mu-Hao Sung (2021). Ecologically Sustainable Industrial Development, Better Solid and Hazardous Wastes Management, and Sustainable DAF Landfill Leachate Pretreatment: UNIDO Efforts. In: “Evolutionary Progress in Science, Technology, Engineering, Arts, and Mathematics (STEAM)”, Wang, Lawrence K. and Tsao, Hung-ping (editors). Volume 3, Number 9, September 2021; 32 pages. Lenox Institute Press, Auburndale, MA, 02466, USA. No. STEAM-VOL3-NUM9-SEPT2021; ISBN 978-0-9890870-3-2. ………ABSTRACT: This publication introduces the United Nations Industrial Development Organization (UNIDO) and its international leadership role in promoting industrial ecology (IE) and ecologically sustainable industrial development (ESID) and improving solid and hazardous wastes management in industrial and developing countries. The subjects covered in this publication are: ESID definition, criteria, activities and programs directly or indirectly related to solid waste and hazardous waste management. A sustainable process system involving the use of modern coagulation, dissolved air flotation (DAF), ozonation, nitrification, denitrification, and final clarification for treating landfill leachate is reviewed and introduced as a typical example of ESID activity.