Assessing the performance of conventional and nano iron as a water coagulant: A comparative study

The main objective of this study is to investigate the efficiency of coagulation-flocculation process for surface water treatment, using the conventional coagulants (ferric chloride (FeCl3) and polyferric sulphate (PFS)), magnetic nanoparticles (MNPs), Fe-based metal-organic framework MIL-53(Fe), magnetic metal organic framework (MMOF), and evaluate the effect of combination of these coagulants on the coagulation process. MNPs were synthesized using the co-precipitation method and MIL-53(Fe) was synthesized using solvothermal process. The synthesized coagulants were characterized using point of zero charge (pHpzc), X-ray diffraction (XRD), Fourier Transform Infrared (FTIR) and Brunauer–Emmett–Teller (BET) techniques. The point zero of charge pH (pHPZC) values for the prepared MNPs, MIL-53(Fe) and MMOF were for found to be 7.8, 5.0 and 3.0, respectively, while the respective surface area for MIL-53(Fe) and MMOF were 23.8 and 11.8 m2/g. In addition, pore sized MMOF was found to be 59.455 Å which is larger than that for MIL-53(Fe) (34.705 Å). The results obtained from this study revealed that turbidity removal exceeded 98 % when using 30 mg/L of FeCl3 at pH 7. The same removal efficiency required less dose of PFS (10 mg/L) at a pH 8.5. The combination of MNPs with FeCl3 enhanced the removal efficiency to more than 99 % at the optimized condition of FeCl3. However, using MIL-53(Fe) slightly enhanced the FeCl3 coagulation at low dosage (10 mg/L) at pH 7, whereas, MMOF recorded better enhancement for the FeCl3 coagulation at the same conditions, reaching up to 98 %. Moreover, the combination of PFS and MNPs provided the best coagulation performance with turbidity removal of more than 99 % at low dose and at pH 7.