The City of Massillon, Ohio retained CTI Engineers, Inc. to provide planning, design, and construction administration services for the expansion of its existing 12.5-MGD wastewater treatment plant. The upgraded plant (15.8 MGD) has been designed to serve the City of Massillon and portions of western Stark County for the next 20 years.

Several innovative processes were employed during planning and design. A new 5.6- MG flow equalization basin with two separate compartments (one to equalize diurnal flows and one to contain storm-related flows) has been provided. Tipping buckets have been installed in each basin to facilitate cleaning after major rainfall events.

For the aeration basins, the existing energy-intensive horizontal rotors were replaced with a fine bubble diffused aeration system and vertical mixers. This allows the aeration and mixing system to be controlled independently.

The VFD-driven blowers for the diffused aeration system are controlled by dissolved oxygen sensors, optimizing concentrations at minimum energy costs. New VFD-driven mixers keep the tank contents well-mixed and suspended. At the time of installation, the vertical mixers were the largest operating installation of this kind in the U.S.

A new 30,000-cfm odor control system consisting of a scrubber for ammonia removal and a water-regenerated carbon system for hydrogen sulfide removal was installed. The carbon system is the largest of its kind in North America and the first to be coupled with an ammonia scrubber.

Construction of the $30 million upgrade was completed in 2005.