The Valrico Advanced Wastewater Treatment Plant needed to expand its capacity to handle anticipated growth in the Hillsborough County area. The county chief had hesitations about the expansion because of a limited budget and the necessity to change the plant’s current chlorine gas disinfection technology, which would result in the formation of disinfection by-products (DBPs).

Malcolm Pirnie provided engineering services for the project including design, permitting, bidding assistance, construction administration and initial operational assistance. The team coordinated efforts to select a new ultraviolet (UV) disinfection technology to replace the chlorine gas system, which eliminated DBP formation potential. They also advised the county on the proposed UV design―the first of its kind in the county―and sought input from state regulatory agencies. Based on findings from the Pirnie team’s site-specific UV transmissivity testing, they reduced the size and cost of the proposed UV system.

When expansion is completed, Hillsborough County’s Valrico facility will serve as a model for disinfection technology, providing high quality effluent while eliminating safety and DBP issues associated with gaseous chlorine use. The expansion project will support the county’s growing customer base for many years.