Biochar Sorption of Phosphorus From Dairy Manure Lagoons.

Rising production costs and environmental concerns over phosphorus fertilizer and dairy nutrient management have prompted investigations of phosphorus recovery from anaerobic digesters.  We evaluated the use of biochar produced from anaerobic digested fiber (APF) and soft wood pellets for sequestering phosphorus from dairy lagoons.  The APF was collected from a Plugged Flow (GHD™) digester; air dried to < 8% water content, pelletized under pressure (2250 kg/cm²) and stored dry.  To produce biochar a barrel retort slow pyrolysis unit was constructed.  Phosphorus sorption capacity of biochars were measured using a KH₂PO₄ phosphorus standard and anaerobic digested effluent (ADE). Samples were incubated on an oscillating shaker for 48hrs; each filtrate was analyzed for total P and char for Olsen P.  Nearly all P from the KH₂PO₄ standard remained in the filtrate after incubation, with < 3 mg PO₄ L^-1 sorbed by either of the chars. The biochars amended with ADE sorbed the P present in the ADE subsample, with only 23 mg PO₄ L^-1 of the initial 81 mg PO₄ L^-1 found in the filtrate. Olsen P concentrations were higher in the ADE amended biochars than those amended with the P-standard. Finally, small scale filter systems (1:4 biochar to ADE) were constructed to measure P reduction in the ADE.  The analysis showed reductions of 50% P in the ADE (340 to 170 ppm) and an increase of Olsen P on the char from 8 to 45 mg/kg.  This paper will summarize the effectiveness of biochar to sequester phosphorus from dairy manure lagoons.