Recovering phosphorus and lithium separately from wastewater and brine using a novel coupled biofilm-precipitation system

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Phosphorus (P) and lithium (Li) are scarce resources. To address the situation of resource scarcity, a novel coupled biofilm-precipitation system was proposed to recover P and Li separately from wastewater and brine. The results indicated the denitrifying polyphosphate accumulating organisms (DPAOs) suitable for this operating process promoted their denitrifying phosphorus removal (DPR) capabilities at the aerobic phase, increasing the total P content in the biofilm (TPbiofilm) to 60.7 ± 2.7 mg/g SS. Moreover, the DPAOs performed a metabolic shift from glycogen accumulation metabolism (GAM) to polyphosphate accumulation metabolism (PAM) when TPbiofilm increased, which caused more P being released by DPAOs, and the P concentration of the enriched stream to rise to 185.8 ± 3.4 mg/L. Furthermore, the quadratic regression model was suitable for the struvite crystallization (R2 = 0.87–0.88) in the P recovery stage, and the pure struvite was obtained with a P recovery efficiency was 96.3–97.2 %. The pure lithium carbonate crystals were created with a Li recovery efficiency was 93.3–97.2 % in the Li recovery stage. Additionally, the enriched P stream was applied to natural brine, and pure struvite and lithium carbonate crystals were produced with the P and Li recovery efficiency was 94.7 % and 93.5 %, respectively. In general, using enriched P stream as P source to separate magnesium from brine and thus recover Li was a feasible option. This study provided support for the recovery of P and Li.