Simultaneous Compliance of TOC and Turbidity Related to Pathogen Breakthrough and THMs Control by Enhanced Coagulation

Abstract

Since discovery of harmful disinfection by products (DBPs) like trihalomethanes (THMs)
 and haloacetic acids (HAAs) in chlorinated waters the removal of organic DBPs precursors
 gained priority in drinking water treatment. Historically, coagulation process was arranged
 to remove turbidity, typically related to pathogens occurrence, but nowadays it is usually
 optimized/enhanced for total organic carbon (TOC) reduction.
 This work dealt with the removal of TOC and turbidity by means of enhanced coagulation
 process using Al2(SO4)3⋅18 H2O and FeCl3⋅6H2O as coagulants for jar test without pH
 adjustment according to USEPA procedure. 15% of TOC removal required by USEPA
 D/DBPs rule (1998) was achieved using 30-50 mg l-1 of both coagulants. On the other
 hand, for compliance with more stringent MCL for total THMs in Italy (30 μg l-1) higher
 TOC removal (>30%) which needed of higher coagulants doses (80 mg l-1), was obviously
 required. Those high coagulant doses were also to be used for the compliance with the
 turbidity standard (<1NTU).