Greeley and Hansen, A TYLin Company, partnered with the City of St. Petersburg to optimize treatment at the Cosme Water Treatment Plant.
The City is providing permanent bypass piping and modifications to existing chemical facilities at the Cosme WTP, to allow bypass of Regional Water provided by Tampa Bay Water, to save energy and chemical costs, while maintaining the City’s water treatment goals. The City completed two bypass demonstration tests, during which potable water from the Regional System bypassed the Cosme WTP aeration, softening, filtration and high service pumping processes and was routed directly to the City’s finished water transmission mains after chemical treatment for disinfection, pH and fluoridation. Prior to the bypass demonstration testing, the City’s AWWA RTW process model was utilized to determine
the range of conditions under which the bypass could be undertaken, and the operational parameters and chemical addition that would be required. During the bypass demonstration testing, the water quality data in the City’s distribution system were monitored to verify that the City’s water quality standards were being met, and corrosion control was being maintained. The bypass demonstration indicated that when the water supplied by the Regional System is comprised of a mix of Regional sources that meet a minimum alkalinity threshold and do not exceed a threshold of calcium hardness, all or a portion of the Regional Water can bypass the City’s softening, filtration and high service pumping facilities.
During the bypass demonstration test, significant operational savings were realized because the chemical dosage requirements were reduced and the bypassed water did not have to be re-pumped to the City. This bypass also allowed the City to perform maintenance activities that are usually difficult, because facilities could be taken out of service and dewatered, including inspection of facilities that had not been viewed since the plant was constructed in the 1950s. The bypass demonstration test also established that the quantity of water that can be bypassed is subject to the mix of Regional waters, specifically the amount of source water that has lower hardness (such as surface water or desalination sources) versus higher hardness (ground water).
Capital, operations and maintenance cost savings
Preliminary design verified the average daily flow, maximum daily flow and peak hourly flow
Facilities included a new caustic storage and feed facility, precast concrete chemical piping trench for the water plant site, new softened carrier water facility, new ammonia metering pumps, permanent chlorine solution booster pumps, new fluoride pumps, permanent bypass piping with associated flow metering, control valves and SCADA, replacement of 1960s vintage valves on the surge control facilities.