A novel recovered compound phosphate fertilizer produced from sewage sludge and its incinerated ash

Current disposal methods of sewage sludge (SS) and its incinerated ash (ISSA) do not allow for the recycling of the phosphorus (P) present. The aim of this study was to fabricate a P compound fertilizer by using an optimal SS-derived biochar (SSB) with enhanced inherent Ca-P content to load P from the P extract of ISSA. For this purpose, SS was impregnated with four agents (MgCl2, CaCl2, MgO and CaO) at mass ratios of 20% or 10% and pyrolysed at 700 °C or 300 °C. Characterization of the produced SSBs indicated that those with 20% MgCl2, CaO and MgO added and pyrolysed at 700 °C exhibited high surface areas, abundant mesopores and abundant plant-valuable P. When in contact with the P extract, these three SSBs showed the highest P adsorption efficiencies among the obtained SSBs but CaO/MgO-impregnated SSBs have more metal co-precipitation. The post-sorption SSBs were P-enhanced and alkalinity decreased, which are favourable for fertilizer application. Furthermore, a pot experiment verified that these three ...