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The Emerald Coast Utilities Authority (ECUA) has taken on a project of historic proportions—replacing a 73-year-old wastewater treatment plant (WWTP) with a new facility 25 miles north of the existing plant.
Originally designed and constructed in 1937 between Main and Government streets in downtown Pensacola, Fla., the Main Street WWTP, which underwent several expansions in the 1970s and mid-1990s, has been the workhorse of the community’s wastewater treatment. The plant handles two-thirds of the total flow processed by ECUA’s three plants that serve about 60,000 sewer customer connections.
Old age and constrained surroundings combined with the devastation of Hurricane Ivan in 2004, however, had taken their toll on the plant.
Startup & Benefits
Six years after Hurricane Ivan, the ECUA’s new Central Water Reclamation Facility (CWRF) started up at the end of August 2010. Flows from the old plant have been diverted to the new facility, and startup is expected to be completed by January 2011. The new facility will meet various compliance, community and environmental needs.
ECUA Manager of Water Reclamation Engineering Stephen Holcomb, P.E., said: “There are several exciting environmental benefits associated with the new CWRF and its location away from downtown Pensacola. One benefit is the elimination of the discharge from the Main Street Plant, which currently goes into Pensacola Bay. The new plant will have no surface water discharge. By replacing the old plant with a new plant 25 miles to the north, there will no longer be a WWTP located in a storm-surge, flood-prone area. By eliminating this hazard, ECUA is addressing the threat of future health hazards from discharge of untreated sewage.”
Another environmental benefit is the opportunity for reuse of the advanced wastewater-treated discharge from the plant via industrial reuse. This will reduce the impact the facility’s processes have on the environment, while enhancing the efficiency and reducing operational costs. Additionally, as the community grows and wastewater intake increases, the CWRF will be able to provide more beneficial reuse water.
Processes & Technologies
The site and layout of the new facility were selected and designed to allow gravity flow of the wastewater through the main treatment processes without the need to repump—only requiring pumping for one internal recycle stream and of the final effluent, according to Holcomb.
The facility’s biological nutrient removal system is a five-stage process that has been in service for more than 15 years. As a result, removal of nitrogen and phosphorus can be achieved with little to no chemical addition.
Rotating disc filters provide the final treatment before disinfection. The filters are very compact and take up about 10% of the footprint of a conventional mixed media gravity filter.
Sodium hypochlorite is produced on site and stored in liquid form for use in the disinfection process.
Biosolids are dewatered using six pairs of screw presses that are slow turning to minimize wear and downtime, and are enclosed to minimize or eliminate odor. The dewatered biosolids are dried in a paddle drier that is also slow turning; the heating medium used is steam generated on site.
Challenges & Funding
Execution of the replacement project did not come without its challenges.
“One of the major challenges was funding for the project,” Holcomb said. “The funding sources include FEMA [Federal Emergency Management Agency], Florida state grants and a consortium of private banks.”
Additionally, to minimize the time frame for construction, the project was broken up into multiple contracts to allow the work to be performed simultaneously and to give more contractors the opportunity to bid on the work.
To realize cost savings in the form of avoidance of state sales tax and to minimize the profit markup of the contractors, the major pieces of equipment were either selected and purchased prior to construction contract bidding or were owner direct purchased after the construction contract was awarded. This resulted in about $4 million in savings, according to Holcomb.
Portions of the transmission lines were installed in potentially archeologically sensitive areas. Prior to construction, archeological consultants were employed to survey the potential areas and the results of the investigation were included in the bid documents. During construction, the archeological consultant was on call in the event that the contractors excavated any suspected artifacts.
Opportunities & Impact
“The impact of this project cannot be overstated, economically or environmentally,” Holcomb said. “The positioning of a plant in the central area of the county provides opportunity for wastewater treatment in the central/northern area. This opens up prospects to new residential developments, industrial growth and economic development. In the downtown area, the elimination of the Main Street Plant provides an area ripe for economic and cultural development.”