Due largely to the generation of combustible biogas which can be used much like natural gas, AD systems have received much attention over the past 50 years – and especially where very large quantities of organic residues are accumulated. However, in many areas around the world, the biogas is more like a very convenient by-product when compared to the other benefits from controlled exploitation of the AD process.
Perhaps most important is the sanitary treatment of organic residues fed into the digester. When allowed to go toward completion, AD results in total destruction of many/most disease vectors which may have been present in the feed materials; nearly total destruction of most of those remaining; and very significant destruction of the most recalcitrant (including ascaris and other eggs). Pathogen destruction reported through various levels of anaerobic digestion is delineated in this review and shows that AD offers significant sanitation benefits.
After AD, the remaining effluents and solids contain all nutrients originally present in the digester feed. These materials provide readily available nutrients for plant growth and soil-building humus which, when added to soils, increases nutrient and water-holding capacity. This, of course, greatly reduces the need for chemical and other fertilizers.
When biogas is used to replace biomass or coal as a cooking fuel, indoor air pollution and related health problems are greatly reduced. Indeed, AD offers perhaps the least polluting way to sustainably utilize biomass energy.
Methane is more than twenty times stronger than carbon dioxide in trapping heat in the atmosphere. Thus attending to collection and burning the biogas emitted by masses of organic residues may provide significant assistance in ameliorating growing climate chaos.