BIOGAS Basics

BIOGAS SYSTEMS transform organic wastes into
methane and fertilizer.

Biogas is produced when microorganisms break down organic wastes in the absence of oxygen during a naturally occurring process called anaerobic digestion. A specialized community of anaerobic microorganisms leads this process through four stages: hydrolysis, acidogenesis, acetogenesis, and methanogenesis. Each digester houses a unique community of micro-organisms that perform these functions with varying degrees of efficiency depending upon the unique environmental conditions created by the feedstocks, digester design (retention time, temperature, size, etc.), system management, and other site-specific factors. The performance efficiency of anaerobic digestion varies widely within and among systems, but the average methane content of biogas is generally around 60%. In Uganda, this methane is typically used directly for cooking or lighting. It is also possible to combust biogas in a specialized generator to produce electricity or to compress biogas to produce transportation fuel. However, these end-uses are not currently cost-effective for small systems. In addition to the methane, anaerobic digestion also produces a mixture of solids and liquids called digestate or bioslurry. Biolurry includes a rich diversity of microbes, undigested fibrous solids, nutrients (including nitrogen and phosphorus), and water. Bioslurry offers farmers an affordable, sustainable alternative to imported and expensive chemical fertilizers.