Due to occasional complaints of odors from residential and commercial neighbors, and the projected development of adjacent vacant land, an investigation was conducted at a county wastewater treatment plant (WWTP) Utilizing a physical survey of possible odor sources, an emissions measurement study, and dispersion modeling, the site was assessed for current and future odor impacts. The main compound contributing to odors was concluded to be hydrogen sulfide (H2S). Using the EPA dispersion model Industrial Source Complex Short Term (ISCST3) and ten years of meteorological data, the H2S emissions results were analyzed to estimate potential maximum H2S concentrations, as well as the annual frequency of occurrences of H2S above certain concentrations. The chief source of odor impacts was identified as fugitive emissions from the top of the grit chamber/flow splitter building, through openings for valve stems, flow gates, and the grit removal conveyor apparatus. Another ventilation fan was added, and the H2S‐laden air from the building was routed through new biofiltration units, which were being evaluated to replace an older caustic/chlorine scrubber. Since these units operated at an extremely high H2S removal efficiency, it was concluded that biofilters would replace caustic/chlorine scrubbing on a permanent basis.

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Orange County Public Utilities (OCU) operates a large, complex wastewater system consisting of three advanced wastewater treatment plants and over 500 lift stations. For over 20 years, central Florida has experienced rapid, sustained growth. As the wastewater utility expanded to accommodate this growth, the process control and SCADA systems had become a mixture of technologies and were under-utilized.OCU embarked on a series of optimization initiatives aimed at curbing cost increases. Management realized that proper use of control system technologies provided a means to control treatment plant operation and maintenance costs. Proper SCADA system deployment would provide a mechanism for minimizing SSO events and quickly responding to spills, should they occur. OCU established a set of objectives for an enhanced process control/SCADA system: 1) automate the operation of the treatment facilities to support a reduced level of operations staff; 2) simplify maintenance of the control systems; 3) provide the same look and feel at each treatment facility and for the lift station control system; 4) provide a reliable, high speed, method to interconnect the plants thereby allowing the monitoring and control of any plant or the lift stations from any other plant; 5) minimize spare parts inventory; and 6) build the system using nonproprietary hardware and software.In 1998, OCU commissioned the development of a process control and SCADA system master plan. Several technical and project delivery alternatives for meeting the objectives outlined above were evaluated. A systematic, phased implementation approach was developed. It defined a six-year plan to install the lift station SCADA system and upgrade the process control systems at each of three treatment plants. Total cost for the systems was estimated at about $16 million.During the planning phase, the two largest treatment plants were to undergo significant expansions. The South Plant is experiencing a series of expansions estimated to cost nearly $100 million using a design-build process. The Eastern Plant will undergo an expansion estimated to cost $3 million using a standard design-bid-build procedure. The lift station SCADA system was implemented using a design-build process with a firm bid. To accommodate the goal of a standardized approach to software development and to provide consistency and compatibility between facilities, OCU retained a process control system (PCS) program management firm. This firm interfaced with the design builders, the consulting engineers, and the contractors to assure a consistent approach. Contractors were responsible for system software; the program management firm was responsible for applications software.A single entity responsible to assure consistency and compatibility between all facilities is possible and beneficial despite the project delivery mechanism changing from plant to plant.