|
|||||||||||||||||||||||||||||||||||||
|
Wastewater DivisionRECLAIMED WATERNew! Reclaim Water Design and Construction Specifications are now available online. Click here for more information.
[Water Conserv I][Water Conserv II][Iron Bridge] Iron Bridge Regional Water Pollution Control Facility In the mid 1970s, while most of the country was trying to upgrade from primary treatment to secondary treatment, the City of Orlando was striving for advanced levels of wastewater treatment, including nutrient removal. The effluent goals were 5 mg/l BOD, 5 mg/l solids, 3 mg/l total nitrogen, and 1 mg/l total phosphorus — stringent levels set to prevent adverse impact to the Little Econlockhatchee River. After working with seven other local governments, the City applied for and received a grant for a regional wastewater treatment facility from the federal government under its 201 Facility Planning program. The grant was used to build the Orlando Easterly Iron Bridge Regional WPCF. The Iron Bridge facility is an award-winning project designed for a capacity of 24 mgd. It is one of the world’s largest treatment plants using rotating biological contactors (RBCs) for BOD removal and nitrification. It is also the first facility in the United States to use RBC technology for denitrification. One hundred seventy-one BOD/nitrification RBC units were used, configured in nineteen trains of nine RBCs. When it became evident that the submerged RBC portion of the denitrification system could not meet the stringent nutrient levels, a Consent Decree was issued, and the City quickly took action. Bench scale studies and full-scale pilot plant operations determined that the flow between the final clarifier, which included chemical phosphorus removal, and the submerged RBCs had to be reversed. An air stripping mechanism was added to control biological film thickness on the submerged RBCs. Breakpoint chlorination and dechlorination processes were also added to supplement nitrogen removal capabilities. Testing, design, and implementation were accomplished on schedule, enabling the City to meet the EPA deadline. Because the plant was operating at nearly full capacity from its beginning with no opportunity to increase its existing wasteload allocation, the City began to seek alternative means of tertiary treatment and effluent disposal. In 1984, a 30-acre hyacinth treatment system was devised as an interim solution. The hyacinth treatment system removed an additional 460 pounds of nitrogen and 100 pounds of phosphorus, thereby providing an additional 4 mgd of treatment capacity within the existing wasteload allocation limits of 600 pounds and 200 pounds of nitrogen and phosphorus, respectively. Studies to determine ways to further reduce nitrogen and phosphorus concentrations in the effluent had identified the use of a wetland treatment system. Work began on a 1,250 acre man-made wetland to provide nutrient removal to 20 mgd of advanced wastewater treatment effluent. The wetland was created in an active cattle pasture, an area which 19th century survey maps indicated had been a natural wetland. Earthen berms were constructed throughout the site to create "cells" for the water to pass through, and 2.1 million aquatic macrophytes were planted and the Orlando Easterly Wetlands Reclamation Project was formed. After passing through the wetland, water would be discharged into the environmental sensitive St. Johns River system. The wetland began receiving flow from the Iron Bridge facility in 1987. Careful, continuous monitoring has documented the project’s success. After a hydraulic detention time through the wetland of 30 days, nitrogen concentrations discharged have been consistently maintained below 1.0 mg/l and phosphorus concentrations maintained below 0.1 mg/l. The wetland’s success is also evident by the abundance of wildlife in the area. More than 150 plant species are present in the wetland, and numerous animal species have made it their home, including more than 140 bird species, as well as otters, foxes, deer, and numerous amphibians and reptiles, including alligators. The City designated a portion of the wetland to function also as a park, called the Orlando Wilderness Park. The site offers visitors the chance to enjoy the natural Florida environment. The project has received numerous awards from regulatory agencies and professional societies as a means to lessen man’s impact on the environment and for restoring and protecting natural resources. In 1988, the City completed expansion work on the Iron Bridge facility, increasing its capacity to 40 mgd through the use of a five-stage Bardenpho™ biological nutrient removal (BNR) process. This expansion not only offered increased capacity, it also decreased operating costs by over $300,000 per year and improved the treatment efficiency and nutrient removal capabilities of the plant. By biologically removing much of the nutrients, the City was able to reduce its alum consumption from approximately 180 mg/l to less than 30 mg/l, while totally eliminating the need for methanol. In this same expansion effort, the City implemented an improved sludge handling and stabilization facility to provide PSRP standards for the full 40 mgd. The system uses gas recovery techniques to maintain heat for the digestion process. Currently, the City is studying the feasibility of converting excess gas to electrical energy to supplement the plant’s power requirements. Operation of the RBC technology proved costly due to the requirement for breakpoint chlorination to remove residual ammonia. In 1989, the Clean Water Act amendments provided the mechanism for 100% repair and replacement grants for failed RBCs. Orlando was successful in obtaining a $16.5 million dollar grant under this program, and began construction of a second 12 mgd/BNR plant. Construction was completed this year, making the Iron Bridge Bardenpho™ plant among the largest in the nation. As a result of these efforts, the water quality of the Little Econlockhatchee River has greatly improved. Monitoring activities in 1990 showed a 74% reduction in total nitrogen, a 91% reduction in total phosphorus, and a 50% improvement in dissolved oxygen since 1980. Total construction costs for the Iron Bridge facility and its improvements amounted to approximately $124 million. Water Conserv II Water Reclamation Program The McLeod Road Water Pollution Control Facility was constructed in 1964 to provide sewer service to the western half of the City. The facility was rated 4 mgd and utilized primary clarifiers, trickling filters, and secondary clarifiers, followed by chlorination for treatment. The facility was expanded in 1970 to 12 mgd of capacity and the biological process was changed to an activated sludge system. Effluent was discharged to Shingle Creek, which ultimately reached Lake Tohopekaliga. At the same time that the City faced a March 1988 zero-discharge mandate for its McLeod Road plant. Orange County, whose Sand Lake Road Treatment Plant also discharged to Shingle Creek, was faced with a similar order. (The City of Orlando is located within Orange County.) To maximize federal grant funding and because of the close proximity of the two treatment plants, the City and County decided to embark upon a joint project: the Water Conserv II Water Reclamation Project. They commissioned the Southwest Orange County 201 Facilities plan to evaluate the available effluent disposal options which could provide the estimated 50 mgd of capacity required by both entities. Citrus irrigation and rapid infiltration basins (RIBs) appeared to be the most viable option for a readily implementable program. Studies showed that 10 to 15 miles west of McLeod Road and Sand Lake Road facilities, the geological features of the land were conducive to the surface application of reclaimed water. While citrus irrigation was both viable and cost effective, it could not provide an all-weather effluent disposal solution. The use of RIBs appeared to be equally viable, but required the acquisition of 4,260 acres for RIB construction, making it more costly than practical. Combining both citrus irrigation and RIBs offered the desired level of economy and flexibility. The system not only reduced demand on the Floridan aquifer by eliminating the need for well water for irrigation, it also helped replenish the aquifer and stabilize area lake levels. A list of water quality criteria was developed to protect the citrus trees from damage as a result of irrigation. A 20-year commitment from participating growers needed for federal funding compliance required the development of an agreement to formalize the terms and conditions of reclaimed water use and delivery. After hundreds of hours of intensive study and negotiation over a year’s time by the City and growers, the plan was developed. The resulting agreement represents a significant departure from conventional lease arrangements used previously for normal effluent disposal. For example, if a grower desired to stop utilizing a parcel of land as described in the agreement for the purpose of irrigation, modification or termination of the agreement prior to the end of its term could be achieved in one of the following three ways: • Quantity or quality of water specified could be modified if the water proved detrimental to citrus production. • The grower could construct facilities required to transfer his commitment from one parcel of land to another at his own cost or by compensating participants for the associated costs. • The grower’s obligation to accept his/her allocation of reclaimed water on the land specified could be terminated by the grower paying participants $3,600 per acre for the cost associated with the distribution system minus five percent that amount for each year water had been accepted up to the time of termination. The treatment process train designed for the Water Conserv II effluent disposal program met state requirements for slow rate land application (i.e., secondary treatment followed by high level disinfection with TSS level not exceeding 5 mg/l and no detectable fecal coliform or virus). Because the criteria dictated that the water be safe for human contact, one of the most critical phases of treatment related to suspended solids removal and disinfection for bacteriological and viral deactivation. Pilot testing was performed to evaluate different filtration systems and varying levels of chemical addition. Results indicated that secondary treatment, followed by flocculation with alum, filtration with dual media filters, and chlorination was effective in deactivating the virus. Numerous improvements were made to the Conserv II Water Reclamation Facility in order to meet the required water quality for citrus irrigation. The most important and difficult limit to meet is the 5 mg/l of total suspend solids (TSS) needed to prevent clogging of irrigation nozzles and to ensure complete pathogen removal. A dual medial rapid gravity filtration system was employed to coagulate and remove TSS. The filter material consists of 12 inches of graded silica sand with 12 inches of anthracite coal on top. Success of the filtration and subsequent chlorination system can be measured by the virus testing that has consistently produced less than zero plaque forming infectious units (PFUs). Following treatment, the reclaimed water is pumped by a 4,000 HP transmission pump station located at the treatment facilities through approximately 15 miles of 42- and 54-inch diameter prestressed concrete cylinder pipe to a distribution center located in west Orange County. The distribution center is equipped with four 5 mg storage tanks, pumping facilities, and operation and maintenance buildings. During normal operation, the reclaimed water is pumped from the distribution center into a 24-mile pipeline network which transports the water to participating citrus growers at a minimum residual pressure of 40 psi. When the growers do not wish to irrigate or the quantity of effluent exceeds the available irrigation capacity, the reclaimed water can be discharged into RIBs. Because disposal into the RIBs is short-term in nature, the area requirements are minimized, making efficient use of available lands. Currently, reclaimed water is being supplied to 24 growers through a series of 50 turnouts along the distribution system. Since the system began operation in December, 1986, over 35 billion gallons has been pumped to the distribution center for redistribution to the citrus groves and RIBs. In 1989, the project won the annual American Consulting Engineers Council’s Grand Conceptor Award for its attention to environmental and social concerns. As a result of ceasing discharge into Shingle Creek, 1990 water quality data reflects a 96% reduction in total phosphorus and 93% reduction in total nitrogen that was found in 1980. The City of Orlando’s total construction cost for Water Conserv II was $100 million. To accommodate the rapid growth of the City’s southeastern quadrant, a new 7.5 mgd activated sludge facility was designed. Once again, the primary challenge was effluent disposal. With a Consent Decree to eliminate discharges to Boggy Creek, the City sought innovative solutions. The result was the Water Conserv I Water Reclamation Facility. As originally conceived, Water Conserv I was to be a state-of-the-art wastewater-to-water treatment facility whose end product would not be sewage effluent, but rather potable water suitable for direct consumption. The delivery point of this high quality product would be the Floridan Aquifer. It was a revolutionary concept for its time and although the City developed plans for pilot testing the treatment process demonstrated the viability of the program and opposition forced the development of an alternate plan. With sufficient surrounding acreage at the site, induced head percolation basins were designed for effluent disposal. A naturally high water table and shallow hardpan layer meant conventional percolation basins could not be used. Instead, the system was designed to exert a positive head on the surrounding groundwater by "stacking" water from 6 to 10 feet deep in the basins. The confining action of the hardpan layer was overcome by a 17 to 20 foot deep sand and gravel exfiltration trench running through the bottom-center of each basin. Test holes were drilled to develop a site geological profile and the most promising basin locations were selected. A test cell was created before the actual basins were developed. The Water Conserv I Water Reclamation Facility utilizes a two-stage biochemical process to achieve the nitrogen level required for groundwater discharge. First, dissolved oxygen levels of 2 - 4 mg/l are maintained in the aeration basins to fully nitrify. Denitrification is accomplished by a separate stage biological treatment system using methanol as a carbon source. With nitrates consistently less than 2.0 mg/l and total nitrogen less than 2.0 mg/l (on a monthly average basins), the system has proven to be very successful. With the McCoy Annex facility off-line and no effluent being discharged into Boggy Creek, significant water quality improvements were noted. Data gathered in 1990 showed a 90% reduction in total phosphorus and a 12% reduction in total nitrogen over 1980 conditions. Construction costs incurred by Water Conserv I amounted to $85 million.
|
||||||||||||||||||||||||||||||||||||
|
|
|||||||||||||||||||||||||||||||||||||
The City of Orlando has three wastewater treatment plants that
produce reclaimed water. The northeast municipal area as well as
portions of Orange and Seminole counties are served by the Iron Bridge
Water Reclamation Facility. The west service area is served by the Water
Conserv II Water Reclamation Facility and the southeast portion of the
City is served by the Water Conserv I Water Reclamation Facility.
Reclaimed water is highly treated wastewater which can be used for a
variety of uses. Most common uses for reclaimed water in Orlando are
irrigation of green space such as golf courses, apartment complexes,
medians, schools, and parks. Each plant has different methods in their
reuse of reclaimed water.
