Florida City Upgrades Wastewater Operations with Advanced Processes
The new 4 mgd Blue Heron Water Reclamation Facility, which had its full operational startup a year ago, incorporates the <%=company%> A2/O process, an advanced form of the activated sludge process; the ATAD aerobic digestion system, also from <%=company%>, for sludge disinfection and stabilization; and an integrated SCADA-based controls and instrumentation system from the same manufacturer.
The construction of the $12 million (approximately $3/gal of capacity) wastewater and sludge treatment facility was part of a $37 million water production and reclamation project designed by Professional Engineering Consultants of Orlando, Florida. The undertaking also included the construction of a 300-acre artificial wetland; modifications to the city's existing 2.75 mgd Sand Point Water Reclamation Facility; the Titusville/Cocoa interconnect and pumping facility; and the construction of a new master pump station and accompanying sewer lines.
Besides using a multi-stage biological nutrient removal (BNR) treatment process, and a high-rate sludge disinfection and stabilization system, the Blue Heron plant also incorporates equipment selected to minimize operation and maintenance costs, and common wall tankage to reduce construction costs.
Oxidation Ditch System Found to be Efficient and Flexible
The combination of the high-rate A2/0 process with the flexible characteristics of an oxidation ditch has resulted in a compact BNR treatment plant that is simple to operate and which consistently produces high-quality effluent.
The A2/O (anaerobic/anoxic/oxic) process consists of a staged anaerobic selector followed by multiple anoxic tanks, oxic reactors and secondary anoxic zones operating in series. This is followed by secondary clarification.
According to Matt Hixson, superintendent of the plant, the process is well suited to meet the city's tight 5-5-3-1 (CBOD-TSS-TN-TP) effluent limits. He said the effluent concentrations have been good since startup. "We initially had some difficulty due to erratic loadings that affected phosphorous removal rates. However once flows to the plant were stabilized, total effluent phosphorus immediately dropped to 0.2 - 0.3 mg/l."
Although the Titusville plant was designed to treat 4 mgd, flows have been averaging 2 mgd. More conventional designs and equipment tend to be built for long-term flow rates, with no accommodation for the low-load early years of operation. This can result in a serious waste of energy. The new oxidation ditch processes, however, are energy efficient regardless of flow rate.
"Because biosolids in the oxidation ditch system do not settle when aeration is deactivated, only the volume of oxygen necessary to treat the actual loading is needed," according to Hixson. This minimizes energy consumption, is expected to extend equipment life, and enhances plant performance. Hixson reports that the new plant treats wastewater at AWT (advanced wastewater treatment) levels for the same cost as the previous activated sludge plant, which produced lower-quality effluents.
The plant also incorporates an up-to-date SCADA system which provides automated monitoring and control of key processes. With this in place the plant staff have a facility that they say is easy to operate, has accurate process control, and that can be maintained efficiently
Second New Process Streamlines Land Application Program
Also incorporated in the makeup of the Blue Heron plant is Krüger's Autothermal Thermophilic Aerobic Digestion (ATAD) process for sludge disinfection and stabilization. This process is an EPA-approved, PFRP alternative that has been in use for more than 20 years. The system produces high reaction rates achieved at thermophilic temperatures in a completely mixed and aerated environment. This leads to high stabilization and pathogen reduction factors with low retention times. Thermophilic temperatures are attained and sustained without supplemental heat.
According to Jesse Carpenter, pretreatment coordinator and chief operator, the addition of the new system has streamlined the city's land application program significantly. "Before the installation of the ATAD system, we were producing only Class B sludge, which is becoming more and more difficult to dispose of. The requirements are so rigorous for Class B sludge that, in some instances, we could only apply sludge to very narrow strips out of entire 50-acre fields. But with Class AA sludge, which is Florida's equivalent of the USEPA's Class A sludge, there are virtually no use restrictions."
The ATAD-processed biosolids are liquid-applied alongside interstate highways and other roadways through an agreement with the State Department of Transportation. "I no longer have to spend my time developing ag-use plans for the state," says Carpenter, "or trying to get farmers to get the cows out of fields for 30 days so we can spread."
The process also has shown it can reduce sludge volume to a more manageable level. "At our old plant we used to haul as many as five or six loads of sludge every day, seven days a week:" says Carpenter. Now the hauling frequency is down to about two-and-a-half weeks per month. He noted the system is easy to operate and maintain.
Edited by Ian Lisk