Animal Waste-lagoon Aeration
A large industrial dairy or feedlot operation can generate as much waste as a mid-sized city. While cities spend millions of dollars each year to process and dispose of municipal waste, feedlot owners cannot afford such expenditures. Factory farms are thus limited to disposing of the manure in uncovered manure lagoons, or else spreading it on surrounding land.
The sheer magnitude of the waste often leads to its over-application onto nearby fields. The predictable result is a threat to the safety of the air as well as ground and surface water sources. The contaminants of concern are disease pathogens such as E.coli and salmonella, and a host of air pollutants such as hydrogen sulfide, ammonia, volatile organic compounds, and particulate matter. Also, there are concerns over antibiotics, metals, and toxic substances in the waste.
Feedlot owner/operators use one of the two methods to process animal waste. These methods are anaerobic digestion and aerobic metabolism. Byproducts of anaerobic digestion include high odor, formaldehyde, mercaptans, aldehydes, and other compounds that can harm crops or soil. In contrast, aerobic metabolism results in a liquid compost that can be highly beneficial to plants and soils.
The primary function of an anaerobic lagoon is to remove, destroy, and stabilize organic matter, but not to “purify” the water. The advantage of this system is in its ability to concentrate solid wastes. High levels of gas and odor are evident near these types of lagoons. These systems are characterized by a relatively solids-free liquid zone located above a layer of bottom sediment.
The end products of aerobic digestion are mainly carbon dioxide and water. Virtually any degree of processing can be obtained in the anaerobic lagoon since digestion is a function of time, oxygen availability, and carbon content.
Aerobic lagoons can be in the form of oxidation ponds or mechanically aerated ponds. Oxidation ponds are naturally occurring dissolved oxygen from the air or algae in the water and depend on it. Because the oxygen demand is high in a manure lagoon, the surface area of an oxidation pond must be large to enhance the air exchange at the water surface.