Technical Abstract: We evaluated the use of biochar produced from anaerobic digester dairy fiber (ADF) to sequester phosphorus from dairy lagoons. The ADF was collected from a plugged flow digester, air dried to < 8% water content, and pelletized. Biochar was produced by slow pyrolysis in a barrel retort. The potential of biochar to reduce P in the anaerobic digester effluent (ADE) was assessed in small-scale filter systems through which the effluent was circulated. Biochar sequestered an average of 381 mg L-1 P from the ADE, and 4 g L-1 of ADF was captured as a coating on the biochar. There was an increase of total (1.9 g kg-1), Olsen (763 mg kg-1), and water extractable P (914 mg kg-1) bound to the biochar after 15 d of filtration. This accounted for a recovery of 32% of the P in the ADE. The recovered P on the biochar was analyzed using 31P NMR for P speciation, which confirmed the recovery of inorganic orthophosphate after liquid extraction of the biochar and the presence of inextractable Ca-P in the solid state. The inorganic phosphate was sequestered on the biochar through physical and weak chemical bonding. Results indicate that biochar could be a beneficial component to P reduction in the dairy system.