Phosphorous recovery from key pyrolyzates
The exploitation of phosphorus (P) ore for soil fertilization supports the high demand of modern agriculture, but limitations of P sources encourage research in sustainable P use, recovery and reuse. Here we propose the integration of pyrogenic carbon (i.e. biochar) production into waste management systems for phosphorus (P) reuse and recovery by pyrolysis (PRP). A meta-analysis indicated animal manure, human excreta, and plant-biomass collected from P polluted sites to be sources of P-enriched biomass, all of which have been examined as feedstocks for biochar. As a soil amendment, biochar could serve to both supply P and reduce P loss. The release, sorption and desorption of P by biochar will codetermine the potential of P replenishment by biochar and P loss from biochar-amended soils. Factors such as pH, metal content, colloidal-sized particles, and activities of soil biota (arbuscular mycorrhizal fungi and phosphorous solubilizing microorganisms) are expected to affect sorption- desorption of P between biochar and soil aggregates and P acquisition by plants. Phosphorus in biochar is expected to participate in P equilibrium in soil. Chemical extraction, using acid or alkaline solutions, is considered as a means for P retrieval from high P biochar, especially for biochars with high heavy metal contents. To bridge the gap between academia and practice, this paper stresses key objectives for PRP: 1) identification of key biomass for pyrolysis; 2) retrieval of P from biochar in soils or by chemical leaching; 3) biochar modification by inorganic nutrients, P solubilizing microorganisms and other organic matter; and 4) compatible pyrolysis equipment fit to the current waste management context, such as waste water plants.
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