Evaluating Reuse of Alum Sludge as Coagulant for Tertiary Wastewater Treatment

Abstract

Ultrafiltration (UF) membrane processes have become an established technology in the treatment and reuse of secondary effluents from sewage treatment plants. However, without pretreatment, secondary-treated wastewater effluent shows high fouling potential and hence reduces the performance of UF membrane filtration significantly. This study investigates the potential reuse of alum sludge collected from a water treatment plant as primary coagulant in terms of membrane fouling reduction. The alum sludge was characterized by scanning electron microscopy with energy-dispersive spectroscopy and X-ray diffraction. A comparison was made between a conventional metal-ion coagulant—aluminum sulfate [Al2(SO4)3]—and alum sludge using a jar test and their performances were measured in terms of residual turbidity, UV254 (absorbance at 254 nm), and chemical oxygen demand (COD) removal. UF experiments were performed with CARBOSEP M3 (4 kDa) monotubular ceramic. It was shown that the application of coagulation by alum sludge restricted the fouling of membranes with a lowering of the permeate flux by only 34%. The results showed that alum sludge was effective in removal of organic matter; percent removal of COD and UV254 reached 9% and 6%, respectively, when combining alum sludge with UF.