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Title: Changes in nutrient content and availability during the slow pyrolysis of animal wastes

item Uchimiya, Sophie

Submitted to: Book Chapter
Publication Type: Book / Chapter
Publication Acceptance Date: 8/1/2013
Publication Date: 5/15/2014
Citation: Uchimiya, M. 2014. Changes in nutrient content and availability during the slow pyrolysis of animal wastes. In He, Z. and Zhang, H., editors. Applied Manure and Nutrient Chemistry for Sustainable Agriculture and Environment. Berlin: Springer. p. 53-68.

Interpretive Summary: Basic information is necessary to understand how high-temperature processing of manures will change the chemical forms of nutrients, especially phosphorus. Different forms of phosphorus will have (1) different availability to food crops and (2) water-solubility and the risk of environmental pollution. This book chapter will summarize the state of the art in the characterization of phosphorus forms in manure and its high-temperature conversion value-added product: biochar. Literature survey indicated an intricate association of biochar and phosphorus in a complex but predictable manner that can be beneficial for controlled release of phosphorus originating from manure biochars.

Technical Abstract: Although a large number of reports are available on the total and soluble PKN (and other nutrient elements) content of manure biochars, information is lacking to understand the changes in chemical speciation of different elements during pyrolysis. Manure is intrinsically heterogeneous, and is composed of feces, urine, bedding materials, waste feed (and their degradation products formed during storage) and in some cases soils. Molecular level understandings in thermochemical transformation pathways are necessary to predict the utility of manure biochars as a sterile, renewable, organic fertilizer for different soil types. This critical review will utilize spectroscopic (XRD, XANES, HRTEM) characterization of manure biochars from slow pyrolysis and gasification as well as manure ash to understand the phosphorus speciation. Inorganic (ash) component is enriched with P and K, and can comprise over 50 wt% (on a dry weight basis) of manure biochar. “Ash” is a complex mixture of amorphous, semi-crystalline, and crystalline inorganic phases as well as organic (char) components. These ash components may be originally present in the manure feedstock or thermochemically produced (e.g., apatite). Organic carbon fraction of biochar likely stabilizes ash by various organo-mineral interactions, e.g., by serving as a template for the formation of nano-crystals during pyrolysis. Depending on the thermochemical conversion procedure, stable minerals like hydroxyapatite and whitlockite may form. Much like phosphate rock, acidulation and other pretreatments such as blending with more soluble fertilizer and compost may be necessary to fully utilize less soluble P of manure biochars under alkaline conditions.