Development of a novel polysilicate ferric coagulant and its application to coagulation-membrane filtration hybrid system in wastewater treatment

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Coagulation is one of the effective pretreatment stages in membrane filtration of wastewater to produce clean water. Using a suitable coagulant can mitigate membrane fouling. Membrane fouling is a process where solute or particles deposit onto a membrane surface or into membrane pores in a way that degrades the membrane performance. Research in this area is currently being focused on development of improved coagulation reagents such as polysilicate ferric (PSiFe), which has a high molecular weight and large number of positive surface charges with high efficiency at low doses. In this thesis, PSiFe has prepared based on the following approaches: (a) acidification of water glass solution using HCl followed by FeCl₃ addition and (b) acidification of water glass solution by passing it through an acidic ion exchange resin followed by fresh FeCl₃ addition under different Fe/Si molar ratios. These coagulants were characterised by X-ray diffraction and scanning electron microscopy. According to coagulation jar test results, when Fe/Si=1 the best performance was achieved in terms of the turbidity, the total organic carbon (TOC) and UV₂₅₄ removals. In this study, a thorough experimental program has been carried out to compare the performance of three different coagulants including the existing PSiFe, FeCl₃ and the modified PSiFe. The results clearly indicated that in a membrane filtration system using the modified PSiFe not only reduces the required transmembrane pressure (TMP) due to lower fouling, but also improves the TOC removal efficiency. The outcome of this research provides an efficient coagulant, which can create a sustainable coagulation-membrane filtration system with a lower consumption of chemicals compared to traditional coagulants, and lower fouling that consequently leads to minimum operating and maintenance costs. The findings of this research have also revealed that the performance of the target coagulant, PSiFe-γ, is superior to conventional reagents. Hence, this coagulant and the developed procedure in this study can be used in industry to enhance the coagulation process for achieving a more effective wastewater treatment procedure.
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