title: Biochar and enhanced phosphate capture: Mapping mechanisms to functional properties.
abstract: A multi-technique analysis was performed on a range of biochar materials derived from secondary organic resources and aimed at sustainable recovery and re-use of wastewater phosphorus (P). Our purpose was to identify mechanisms of P capture in biochar and thereby inform its future optimisation as a sustainable P fertiliser. The biochar feedstock comprised pellets of anaerobically digested sewage sludge (PAD) or pellets of the same blended in the ratio 9:1 with ochre sourced from minewater treatment (POCAD), components which have limited alternative economic value. In the present study the feedstocks were pyrolysed at two highest treatment temperatures of 450 and 550 °C. Each of the resulting biochars were repeatedly exposed to a 20 mg l-1PO4-P solution, to produce a parallel set of P-exposed biochars. Biochar exterior and/or interior surfaces were quantitatively characterised using laser-ablation (LA)-ICP-MS, X-ray diffraction, X-ray photo-electron spectroscopy (XPS) and scanning electron microscopy coupled with energy dispersive X-ray. The results highlighted the general importance of Fe minerals in P capture. XPS analysis of POCAD550 indicated lower oxidation state Fe2p3 bonding compared to POCAD450, and LA-ICP-MS indicated stronger covariation of Fe and S, even after P exposure. This suggests that low-solubility Fe/S compounds are formed during pyrolysis, are affected by process parameters and impact on P capture. Other data suggested capture roles for aluminium, calcium and silicon. Overall, our analyses suggest that a range of mechanisms for P capture are concurrently active in biochar. We highlighted the potential to manipulate these through choice of form and composition of feedstock as well as pyrolysis processing, so that biochar may be increasingly tailored towards specific functionality.
authors.affiliation: School of GeoSciences, University of Edinburgh, Alexander Crum Brown Road, Edinburgh, EH9 3FF, UK; UK Biochar Research Centre, University of Edinburgh, Alexander Crum Brown Road, Edinburgh, EH9 3FF, UK. Electronic address: jessica.shepherd@ed.ac.uk.
authors.forename: Jessica G
authors.initials: JG
authors.lastname: Shepherd
authors.affiliation: School of Environmental and Life Sciences, University of Newcastle, Office C325, Chemistry, Callaghan, New South Wales, 2308, Australia; School of Materials Science and Engineering, University of New South Wales, Kensington, NSW, 2052, Australia; Nanjing Agricultural University, Nanjing, 210095, China; Department of Applied Physics. University of Wollongong, Wollongong, NSW, 2522, Australia.
authors.forename: Stephen
authors.initials: S
authors.lastname: Joseph
authors.affiliation: School of GeoSciences, University of Edinburgh, Alexander Crum Brown Road, Edinburgh, EH9 3FF, UK; UK Biochar Research Centre, University of Edinburgh, Alexander Crum Brown Road, Edinburgh, EH9 3FF, UK.
authors.forename: Saran P
authors.initials: SP
authors.lastname: Sohi
authors.affiliation: School of GeoSciences, University of Edinburgh, Alexander Crum Brown Road, Edinburgh, EH9 3FF, UK.
authors.forename: Kate V
authors.initials: KV
authors.lastname: Heal
mesh_terms: D000327:Adsorption; D002606:Charcoal / Q000737:chemistry*; D005308:Fertilizers; D010710:Phosphates; D010758:Phosphorus / Q000302:isolation & purification*; D059027:Recycling; D012722:Sewage / Q000737:chemistry*; D062065:Wastewater / Q000737:chemistry*; D014961:X-Ray Diffraction
chemical_list: D002606:Charcoal; D005308:Fertilizers; D010710:Phosphates; D010758:Phosphorus; D012722:Sewage; D062065:Wastewater; C540010:biochar
keywords: Anaerobically digested sewage sludge; Biochar; Ochre; Phosphorus capture mechanisms; Phosphorus recycling; Wastewater treatment