Fluoride removal using Alum & PACl in batch & continuous modewith subsequent microfiltration

In this study, defluoridation efficiency by aluminium sulphate (alum) and polyaluminium chloride (PACl) were compared for recommended Nalgonda dose (100%) and 80 % of this dose in both batch and continuous modes. The residual turbidity was found to be higher in case of alum as compared to PACl with 80 % dose representing lesser efficient settling of suspensions, which primarily comprise alumino-fluoro complexes that result in high residual aluminium in the treated water and this was confirmed by TEM and Zeta analysis. Moreover, the application of PACl also resulted in much lesser addition to the TDS and also required lesser lime for pH compensation due to its lower acidity. Hence this reduced dose was recommended for defluoridation. It was also observed that in case of alum, residual aluminium in treated water was 0.88 mg/L (100% dose) & 0.72 mg/L (80% dose) and in case of PACl, it was 0.52 mg/L(100% dose) & 0.41 mg/L(80% dose). After subsequent microfiltration, residual aluminium was 0.28 & 0.21 mg/L for 100 % & 80 % dose respectively and in case of alum and in case of PACl, it was 0.16 & 0.11 for 100% & 80 % dose respectively, which conform to the Al standards(<0.2 mg/L).