COAGULATION OF UPLAND COLORED WATER WITH POLYFERRIC SULFATE COMPARED TO CONVENTIONAL COAGULANTS

Polyferric Sulphate (PFS) is a polymeric Fe(III) coagulant which consi sts of a range of preformed Fe(III) hydrolysis species with both high cationic potential and medium to high molecular weights. This study ha s investigated the potential advantage of using PFS in the treatment o f upland coloured waters, compared with conventional metal coagulants. Laboratory experiments were carried out to compare the coagulation pe rformance of the PFS, ferric sulphate (FS) and aluminium sulphate (AS) , and to investigate the nature of the solid phase formed by the hydro lysis of the PFS and FS. The results indicate that the treatment effic iency of PFS for the removal of colour, UV-absorbance and DOC was sign ificantly higher than that of the FS and AS, and was virtually unaffec ted at a low water temperature of 4 degrees C, but slightly affected a t 1.5 degrees C. The nature of the natural coloured waters can be part ially characterised by the value of SUVA and the E(4)/E(6) ratio, and these can be used to predict the extent of coagulation. It is suggeste d that preformed PFS species with high cationic potential are able to persist during the flocculation process and this may be the reason for the superior treatment performance of PFS.