Recovery of phosphate with chemically modified biochars

The use of biochar for the recovery of phosphate has potential for environmental and socio-economic benefits but it is often characterised by relatively low nutrient adsorption capacity. The aim of this study was to investigate the potential for improving biochar phosphate adsorption capacities following chemical modification with metal salts, acids and alkali. Modified biochars were produced from oak wood and paprika waste (greenhouse waste) following either chemical treatment of biomass (in-situ modification) or biochar (post modification). Other chemical treatments investigated included chemical oxidation, activation and salt treatment. Phosphate adsorption uptake capacities were determined by laboratory batch sorption tests, and results indicated that phosphate adsorption could be enhanced from relatively low levels (2.1% - 3.6%) to relatively high levels (66.4% - 70.3%) by impregnation with magnesium. These findings suggest that biochar mineral composition is a key property influencing biochar phosphate adsorption uptake capacity while surface area has less influence on sorption.