Chemical Extraction of Phosphorus from Dairy Manure and Utilization of Recovered Manure Solids

Repeated land application of dairy manure can increase soil phosphorus above crop requirements because of manure's low nitrogen (N) to phosphorus (P) ratio (N:P < 4:1). This soil P build-up can lead to off-site P transport and impairment of surface water quality. We evaluated a treatment process to extract P from manures, called Quick Wash, integrated with a double-stage solids separation system to recover coarse and fine manure solids. The Quick Wash process uses a combination of acid, base, and organic polymers to extract and recover P from manures, improving the N:P ratio of recovered manure solids (RMS). Results showed that coarse RMS could have use as bedding materials for dairy cows, and the fine acidified RMS with N:P > 10:1 can be used as a low-P organic soil amendment. A soil incubation test showed that acidified RMS stimulated N mineralization and nitrification having higher nitrate levels than untreated dairy slurry when incorporated into soil. Our results suggest that the inclusion of Quick Wash in a dairy manure management system can improve manure's value, lowering costs of bedding material and manure hauling, and recover P for use as fertilizer while reducing the environmental impact of land spreading manure P.