“Biogas” is a naturally occuring mixture of 60 to 70% methane and 30 to 40% CO2 with some H2S (Hydrogen Sulfide), that burns similar to so-called “natural gas”, which is actually a fossil fuel. Once generated and stored, biogas is primarily used around the world for cooking and heating at the home scale, but it also has many other important applications both domestically and industrially. Its use as a fuel to power electric generators at all scales is well established and it also has a long history of use in gas lamps and absorption refrigeration systems. When purified and compressed we see it used as an effective fuel for cars, trucks and buses (Stockholm-Sweden is a leader in this application). Thus biogas is a flexible substitute for non-renewable energy sources at many levels. Additionally, its production creates a high quality fertilizer and provides feedstock for the creation of petrochemical substitutes so biogas serves to replace fossil resources on many levels.
A “biogas digester” is a simple system which produces biogas, via the natural anaerobic decomposition of
organic material. The biogas digester, once its “starter culture” of methanogenic (CH4 producing) bacteria has been established (usually several weeks after initial loading with animal manures or lake mud) can be fed daily with kitchen and garden waste. The ecosystem of bacteria in the biogas digester extract energy from the organic material and generate methane gas. The digested organic material exits the system as a high-quality fertilizer in liquid form. This liquid anaerobic “compost” still contains all the minerals and other soil nutrients of the kitchen and garden waste, including the nitrogen that can be lost through aerobic composting.
Download PDF Biogas Digester PDF