Composting is the aerobic decomposition of organic material by microorganisms. Composting requires organic materials with a 30:1 carbon to nitrogen ratio, 50-60% moisture, and >5% oxygen. Active composting is the process whereby thermophilic bacteria decompose organic materials under aerobic conditions in a fairly rapid process. Passive composting, also called cold composting, does not involve thermophilic bacteria, is a slower process, and often involves a fair amount of anaerobic decomposition.
Active composting of manure with other organic matter is a safe and valuable way to manage animal waste. Active composting reduces the volume of manure, kills most weed seeds and fly larvae, kills or reduces many pathogens, reduces odors, and provides a slow release fertilizer which can improve your soil fertility.
Passive composting reduces the volume and decomposes the material, but does not kill weed seeds, fly larvae, and pathogens. In addition, decomposition under anaerobic conditions often produces foul odors.