BIOCHAR: ITS CHARACTERIZATION AND UTILITY FOR RECOVERING PHOSPHORUS FROM ANAEROBIC DIGESTED DAIRY EFFLUENT

Thesis (Ph.D.), Department of Crop and Soil Sciences, Washington State UniversityIn pyrolysis, an alternative to petroleum-based energy, the result of low oxygen combustion is a carbon-rich solid commonly called biochar. We evaluated biochars made from four feedstocks regionally available (wood pellets [Pseudotsuga menziesii (Mirb.) Franco], softwood bark [P. menziesii], switchgrass straw [Panicum virgatum], anaerobically digested fiber) to determine their effect on five Washington soils. Regardless of feedstock, biochars significantly raised the pH of all soil types. Biochars also increased soil C and water holding capacity (WHC) at the higher rates of amendment, depending on soil and feedstock type. Nitrogen mineralization rates decreased in three of the five soils across all feedstocks. There were significant correlations (r 0.9) between amendment rate and C increase in the amended soil regardless of feedstock or soil type. Results demonstrate that in temperate soils, biochar feedstock may not be as important a variable as soil type for increasing C content and pH, but feedstock can influence N mineralization and WHC. 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 (ADF) for sequestering phosphorus from dairy lagoons and its impact on a sandy soil. The biochar reduced P in dairy effluent by 32%. The sequestered P was predominantly in plant-available inorganic orthophosphate. The resulting fiber-coated biochar increased C mineralization, sodium bicarbonate (Olsen) and water-extractable P levels. Nitrogen mineralization rates were not significantly different from the control in three of the six treatments. Results demonstrate that biochar from anaerobically digested fiber can reduce P from dairy effluent and that the P-coated biochar may be a viable source of alternative P fertilizer. Thus, biochar produced from anaerobically digested dairy manure fiber can reduce and recover phosphorus from anaerobically digested effluent lagoons and increase plant available phosphorus in the soil, which has potential environmental benefits. This work provides a baseline understanding of biochars from Northwest feedstocks and their ability to recover P.Department of Crop and Soil Sciences, Washington State Universit