| Material Information
||Design and Operational Results for a Large Scale Wetland Treatment System
||Post, Buckley, Schuh & Jernigan, Inc.
||North America -- United States of America -- Florida
||Design and Operational Results for a Large Scale Wetland Treatment System, by C.E. Swindell, Jr. and Wendy A. Masteller
||Box 8, Folder 3 ( Vail Conference, 1993 - 1993 ), Item 12
||Digitized by the Legal Technology Institute in the Levin College of Law at the University of Florida.
DESIGN AND OPERATIONAL RESULTS FOR
A LARGE SCALE WETLAND TREATMENT SYSTEM
C.E. Swindell, Jr. and Wendy A. Masteller
Post, Buckley, Schuh & Jernigan, Inc.
1560 Orange Avenue
Winter Park, FL 32789
The Iron Bridge wetland treatment system was designed to reduce nutrient concentrations
in 20 MGD of wastewater effluent to levels similar to adjacent natural wetlands. The
system relies on macrophytic plant communities to facilitate water treatment and to provide
wildlife habitat. The results for the first four years of operation show the wetland is capable
of reducing average annual nitrogen and phosphorus concentrations to 0.87 mg/L and 0.087
mg/L, respectively. The results indicate that management techniques are crucial for
maximizing long term nutrient uptake and storage, and that without site specific
management plans, the uptake and storage rates cannot be maintained through time.
Nitrogen, phosphorus, nutrients, wetland treatment, water quality
The City of Orlando has operated the 1,220 acre Iron Bridge Wetland Treatment System
(IBWTS) located in east Orange County, Florida, since 1988. The IBWTS forms part of the
treatment process associated with the Iron Bridge Regional Water Pollution Control Facility
(WPCF). One of the primary design considerations for the WPCF was to significantly
reduce point source nutrient loadings to the St. Johns River (SJR) system. The IBWTS
serves to augment the treatment capability of the WPCF by reducing the nutrient
concentrations to background concentrations in a portion of the WPCF waste stream.
Background concentrations for nitrogen and phosphorus were defined by a 2.5 year water
quality study in a nearby natural wetland.
The IBWTS was designed to treat 20 MGD of effluent from the WPCF, however, state
regulatory agencies required the initial flow to the wetland be limited to 8.0 MGD. The
permit provided for additional 4.0 MGD incremental increases in flow to a maximum of 20.0
MGD, once the operational data demonstrated the IBWTS could meet state and federal
permit conditions for each increment for a two year period. To date, the City has received
approval from the state to increase the influent flow to the IBWTS to 16.0 MGD.
Water discharged from the WPCF to the IBWTS flows through an array of 17 cells prior
to discharge from the IBWTS site. Each of these cells rely on macrophytic communities to
facilitate the nutrient removal and storage processes. Other major design considerations
that make the IBWTS an unique or model system include the following:
1. The wetland forms part of the overall wastewater treatment process for the WPCF,
and therefore, the regulatory monitoring point is at the system's outfall as opposed
to the influent structure. Regulations and permit conditions are applied to the
IBWTS discharge point in the same manner as those for a typical wastewater
treatment facility (i.e. the system is on-line throughout the year, and no seasonal
variations within the data set are allowed).
2. The project restored wetland habitat that was lost in the early part of this century to
agricultural activities. Ecologically, the IBWTS was divided into four distinct
community concepts: deep marsh (primarily Typha spp. and Scirpus spp. populations
growing in an average water depth of 3.0 ft.); mixed marsh (-150 grass/herbaceous
species with isolated colonies of shrubs found in depths from 0.5-3.0 ft.); hardwood
swamp (-164,000 sapling trees within a similar grass/herbaceous groundcover matrix
and average depth profile as the mixed marsh); and a lake (formed from the borrow
pit excavated for fill to construct the on-site berms).
3. Water discharged from the IBWTS was designed to flow across approximately 592
acres of state owned wetlands (Seminole Ranch) contiguous with the eastern property
boundary. Seminole Ranch was classified as a hydrologically altered Spartina baker
wetland system, that was heavily invaded by transitional and upland shrub/tree
species. Prior burn management practices generally maintained the Spartina bakeri
community, but failed to eliminate the invasive shrub/tree species from Seminole
Ranch. Water from the IBWTS was used to re-establish the hydroperiod on
Seminole Ranch, that when combined with burn management practices, will limit the
distribution of invasive shrub/tree species on Seminole Ranch through time.
4. Internally, the IBWTS was designed for water management. Any cell within the
IBWTS can be taken off-line without affecting the operation of the remaining cells.
A 3.0 ft. freeboard capacity was designed into the IBWTS to store rainfall, and to
prevent excessive fluctuations in the discharge rates from individual cells or the
IBWTS during the rainy season. The range of hydroperiod adjustments in each cell
allow for the maintenance of targeted vegetative communities and to control
mechanisms that influence the release of phosphorus from the sediments or litter