Development of a new poly silicate ferric coagulant and its application to coagulation- membrane filtration hybrid system in wastewater treatment

Coagulation is one of the effective pretreatment stages in membrane filtration of wastewaters to produce clean water. Using a suitable coagulant, one can mitigate membrane fouling. Membrane fouling is a process where particles deposit onto a membrane surface or into membrane pores in a way that degrades the membrane's performance. Research in this area is currently being focused on development of improved coagulation reagents such as poly silicate ferric (PSiFe), which has a high molecular weight and large number of positive surface charges with high efficiency at low doses. In this paper, PSiFe was prepared by following two approaches: (a) acidification of water glass solution using HCl followed by FeCl3 addition (old-PSiFe); (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 (new-PSiFe). 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 turbidity, total organic carbon (TOC) and UV254 removals. Another aspect is the comparison of the old-PSiFe, FeCl3 and new-PSiFe which showed that in a membrane filtration system, using the new-PSiFe not only reduces the required transmembrane pressure (TMP) due to lower fouling, but also improves the TOC removal efficiency.