Effect of Al coagulant type on natural organic matter removal efficiency in coagulation/ultrafiltration process

Coagulation followed by ultrafiltration has been studied in order to improve water quality for surface water treatment. Three aluminium-based coagulants: Al2(SO4)3, NaAlO2, and polyaluminium chloride (PAC) have been used. The influence of coagulant type and the water pH on investigated process performance was analyzed. Two ultrafiltration membranes (cut-off 30 kDa) made of regenerated cellulose and polyethersulphone were used in the tests. The nature of aluminium-based coagulant and solution pH strongly affected the performance of coagulation/ultrafiltration process. Under the given dose of aluminium (3.59 g Al/m3), the best results were observed when alum or prehydrolized coagulant were used. For those coagulants the best results of NOM separation in the integrated process were observed in the pH range 6-8. Application of sodium aluminate resulted in much worse elimination of organic matter and a rather high residual aluminium concentration in coagulation as well as in the coagulation/ultrafiltration process.