A new 1.4-mgd treatment facility was designed to replace the existing extended aeration system at the Isle of Palms Water and Sewer Commissions (IOPWSC) Forest Trails Wastewater Treatment Plant site. A review of various treatment alternatives ensued, including contact stabilization, oxidation ditch, traditional fine bubble activated sludge, sequencing biologic reactors (SBR), and membrane bioreactors (MBR). Due to space constraints and superior treatment, the MBR process was chosen using an Options Evaluation Process, which considered monetary and non-monetary factors to select the best treatment option. Then a weighted average of various factors was used to select the specific MBR system.
Once the MBR option was chosen, a membrane selection process was completed reviewing the option of flat-plate membranes versus hollow-tube type membranes. After a review of the design and operational issues of each process, flat-plate technology was selected based on ease of operations and less frequent cleaning requirements.
In addition to membrane filtration, the facility included new influent screens, aeration, aerobic sludge thickening, odor control, disinfection modifications, a control room, and support facilities. Effluent from the facility is utilized for irrigation of golf courses, and can also be discharged to surface waters. Extensive architectural treatments were added to the plant so it “fits” into the adjacent residential neighborhood and landscaping was placed to soften the visual impact. Effects from the plant’s operation to nearby residents are lowered by limiting noise and odor from the site.
The preliminary design was completed for a 1.4-MGD with initial final design documents and construction completed for 0.7 MGD with existing flows of approximately half that. IOP has a point discharge of 0.3 MGD, so any flow over this amount may be transferred via an existing force main to the golf course irrigation system. The second phase expansion is expected to begin in 2019.
Thomas & Hutton also provided the design and detailing of the concrete process structures and concrete/masonry building to support the replacement of the wastewater treatment plant. The process structures included an elevated concrete platform for the primary screen equipment and a divided concrete treatment basin with secondary screen support. The blower and operations building is a 2-story, flood-proofed structure and is a combination of concrete and masonry. There is a monorail system supported by the building roof and system for removal of the membranes. All main structures are pile-supported.