Читать книгу Encyclopedia of Renewable Energy - James Speight G., James G. Speight - Страница 96

Animal wastes, or manure, as a source of biomass has the advantage that it is not competitive with other uses for this material. In the broader senses, animal waste can also include, in addition to animal manure, related animal waste (such as bedding and feed), dead animals, and waste from slaughter and meat processing. All such wastes generally fall in to a sub-class of biomass. Animal waste must of necessity come from confined operations such as dairy farms, cattle feedlots, and slaughter houses as well as meat processing plants.

Animal waste from farms and livestock/poultry and dairy production operations can severely threaten water quality if not managed properly and has the potential to contribute excess nutrients, pathogens, organic matter, solids, and odorous compounds to the environment. This pollution can cause eutrophication of surface waters, degradation of ground water quality, and threats to human health.

Historically, manure generated by livestock has been returned to the soil to improve its tilth and fertility. Recently, the use of animal waste to produce an renewable fuel (biogas) has become of interest. Anaerobic digestion is a renewable solution to livestock waste management that offers economic and environmental benefits.

Anaerobic digestion is a process to decompose organic material in the absence of oxygen. Biogas is produced as a waste product of digestion. In the first stage, the volatile solids in manure are converted into fatty acids by anaerobic bacteria (acid formers). In the second stage, these acids are further converted into biogas by more specialized bacteria (methane formers). With proper planning and design, this anaerobic-digestion process can be managed to convert the waste-stream from a farm into an asset and is, currently, the most appropriate option for farms and small-scale operation. The conversion of animal waste to gas by this process could result in animal husbandry operations being self-sufficient in energy.

Biogas produced in an anaerobic digester typically contains methane (60 to 70% v/v), carbon dioxide (30 to 40% v/v), various toxic gases (including hydrogen sulfide, ammonia, and sulfur-derived mercaptans), and 1 to 2% v/v water vapor.

See also: Agricultural Waste, Alternate Fuels, Anaerobic Digestion, Biogas.