The City of Glendale anticipated that average total trihalomethane (TTHMs) concentrations at its water treatment plant would soon exceed the limit mandated by the government. They asked Malcolm Pirnie to pilot test GAC monomedia filter-absorbers, and design a filter retrofit to convert the plant’s dual media granular filters to GAC monomedia. The Pirnie team’s design for the $14 million project included a carbon dioxide addition for enhanced coagulation to reduce pH; modified backwash and filter-to-waste equalization; enhanced sludge; and retrofitted GAC transfer stations to improve access.

In a follow-up water quality optimization study, Glendale operations staff observed an improved treatment performance, reduced chemical usage as well as a reduction of running annual average TTHM concentrations in the distribution system.