M.S. Thesis: Anaerobic Digestion of Biodegradable Organics in Municipal Solid Wastes
By Shefali Verma
Advisors: Profs. Nickolas J. Themelis and A.C. (Thanos) Bourtsalas
Department of Earth and Environmental Engineering
Fu Foundation School of Engineering & Applied Science
Columbia University
May 2002
This study examined in depth the current status of the anaerobic digestion technologies for the treatment of the organic fraction of municipal solid wastes (MSW). Anaerobic digestion (AD) consists of the degradation of organic material in the absence of oxygen. It produces mainly 55 % methane and 45 % carbon dioxide gas and a compost product suitable as a soil conditioner. A review of systems in operation worldwide was made, including types of process design and their engineering and environmental performance.
The study also provided information on the trend in installed capacity and size of plants, which indicated that in the late 90’s there was a notable rise in size of new plants. The report compares various AD systems such as mesophilic vs thermophilic operation, low-solids vs high-solids feed, multi-stage vs single stage reactors, and AD systems treating mixed wastes vs biowaste. The report also describes in detail the most important AD processes based on the total solids (TS) content of the slurry in the digester reactor. Some of these processes are further explained with case studies.