Recycling Nutrients from Poultry Litter.

Concentrated poultry areas have significant surpluses of poultry litter phosphorus (P) that are building up in soils and causing water quality concerns associated with excess algae.  Economical and environmentally beneficial options are needed for recycling the surplus poultry litter P.  Transporting raw litter out of concentrated poultry areas has significant logistical and economical limitations.  Combusting or gasifying poultry litter provides renewable energy and can facilitate nutrient recycling because all the poultry litter nutrients except for nitrogen (N) are concentrated in the ash; the N is converted to nitrogen gas (N₂) in most of these systems.  The primary options for recycling the poultry litter ash nutrients are: (1) transport the ash to areas that can beneficially use the P and potassium (K) in fertilizers or (2) use the ash locally as a mineral feed supplement to supply P and calcium (Ca) in poultry diets.  There is increasing interest in anaerobic digestion of poultry litter to produce methane as an energy source and nutrient co-products which can be recycled.  With anaerobic digestion, most of the poultry litter P and Ca are in the solid co-product and most of the N and K are in the liquid co-product.  The primary options for recycling nutrients in the solid co-product are: (1) transportation to areas that can beneficially use the P in fertilizers or (2) combust or gasify the solids and use the ash locally to supply P and Ca in poultry diets.  The liquid stream can be used locally as a fertilizer to supply N and K.  Approaches for optimizing recycling nutrient co-products from combustion/gasification or anaerobic digestion of poultry litter will be discussed.