Granular crystallization using CFBC ash for phosphorus removal via hydroxyapatite

Abstract

Abstract To prevent eutrophication and remove phosphorus, circulating fluidized bed combustion (CFBC) ash was utilized to elute Ca2＋ and OH − for hydroxyapatite (HAP) crystallization. CFBC ash was compared with the gypsum byproduct of a domestic waste incineration plant and pure CaO reagent. CFBC ash proved to be a suitable raw material to supply Ca2＋ and OH − for HAP crystallization. CFBC ash was reprocessed as a granular crystallization agent (GCA) to improve its applicability to non-point pollution source control. In addition, a manufacturing procedure for a GCA utilizing 4.8% blast furnace slag as a binder was developed based on durability and the ion elution rate in water. Column tests with sedimentation showed that 93% and 98% of T-P and PO4-P were removed after 12 h of settling, respectively. In on-site filtration trench tests, filtration following crystallization with a 4 h retention time achieved a 63.5% and 52.8% removal efficiency with respect to T-P and PO4-P, respectively. After operation for 13 d, an increase in porosity with pore distribution on the surface of the GCA was observed. Through their long-term on-site operation, crystallization–filtration trenches using GCA provide an effective alternative process for the management of agricultural non-point source pollution.