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

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).