Recovering phosphorus as vivianite using an alternating aerobic/anaerobic biofilm and fluidized bed crystallization coupled system

Abstract

An alternating aerobic/anaerobic biofilm (AABF) and fluidized bed crystallization (FBC) coupled system was constructed to examine the feasibility of using phosphorus (P) metabolic mechanism to enrich P and the availability of large size and high-purity vivianite crystals in this study. The results demonstrated that the stable operation of AABF system could be maintained by operating the biofilm system through P metabolic mechanism of polyphosphate accumulating organisms (PAOs), and the P concentration of 204.5 ± 3.2 mg/L could be obtained. The metabolic mode of PAOs shifted from GAM to PAM as the Pbiofilm increased, which led to PAOs being able to absorb/release more P, wherein extracellular polymer substance (EPS) and cell both played an indispensable role in the metabolism of P uptake/release. In the P recovery stage, the maximum P recovery efficiency reached 94.6 ± 3.1 %, and the main crystals formed were vivianite crystals. Moreover, the percentage of FeP and CaP was 80–93 % and 3–9 % in precipitate, and the percentage of phosphate used to synthesize vivianite was 83.2 %. Furthermore, the size of vivianite crystal increased with the generated vivianite as seed crystal. What's more, the LCA revealed that carbon dioxide equivalent (CO2 eq.) emissions, sulfur dioxide equivalent (SO2 eq.) emissions and phosphate equivalent (PO4− eq.) emissions were 13.3–15.1 kg CO2 eq./kg vivianite, 0.10–0.11 kg SO2 eq./kg vivianite, 0.031–0.037 kg PO4− eq./kg vivianite, respectively. The pH = 7 and Fe: P = 1.5:1 was the optimum condition to ensure high P recovery efficiency and reduced potential environmental emissions. This process system laid the groundwork for recovering P from wastewater.