PRO CE S S PAG E Greetings from the FWEA Wastewater Process Committee! In October and November 2020, the Process Committee hosted a series of 10 virtual presentations under the theme, “Back to Wastewater Process Fundamentals.” Presenters covered a wide range of topics, ranging from process technology updates to supervisory control and data acquisition (SCADA) basics, design fundamentals, and lessons learned during construction. This article is a summary of the “Wastewater Treatment Facility Basis of Design Fundamentals” presentation that was hosted on Oct. 22, 2020.
Wastewater Treatment Facility Basis of Design Fundamentals Bartt Booz
What is a Basis of Design? A basis of design (BOD) for a wastewater treatment facility project documents the principles, assumptions, rationale, criteria, calculations, and decisions made that impact the final design. The BOD typically follows a master plan or a facilities plan in the project development process and defines the goals of the project and project success factors. Projects that proceed without a well-defined project and detailed BOD can lead to costly changes during the final design phase.
Project Purpose Understanding the project’s purpose is essential when developing the basis of design. Projects typically fall into one (or more) of four categories: S Rehabilitation and replacement S Permit compliance S Capacity expansion S Funding opportunities
Rehabilitation and Replacement Many plants within the United States were built during the late 1970s and early ‘80s as a result of the Clean Water Act and the prevalence of grant money. Now over 40 years old, these plants may or may not have undergone at least one major upgrade during this period and may operate equipment that is well past its expected useful life. Eventually, equipment and piping need to be replaced, concrete tanks need to be rehabilitated, and control and electrical systems become obsolete. Many projects are driven simply by rehabilitation and replacement, when the cost of maintaining the old equipment and systems becomes too high. Permit Compliance Plants may also require upgrades when new, more-stringent permit limits are issued by the regulatory agency. It’s always beneficial to try to achieve new limits using existing tankage or repurpose unused tanks whenever possible to reduce project costs. In addition, many of today’s innovative technologies use
process intensification to achieve more in a smaller volume. Capacity Expansion When growth overtakes the available capacity of a plant and process intensification is maximized (or more expensive to implement), additional treatment volume or trains should be considered to meet future growth. Ideally, some foresight was established during the original plant design for its eventual expansion. If not, you may have to implement creative ways to add capacity within the available site footprint and hydraulic profile. Funding Opportunities Plant upgrades may also be performed sooner than required simply due to the availability of grant or low-interest loan funding. Future effluent limits may also be on the horizon, and conducting upgrade projects when grant funding is available is a prudent strategy. This often occurs with plants within a total maximum daily load (TMDL) area with an established basin management action plan (BMAP) where a schedule for compliance may be forthcoming.
Discharge Standards and Permit Limits A BOD report should state the treatment plant’s current effluent limits and what should be achieved following the upgrade. Limits depend on the destination for the effluent and the location of the plant. A 100 percent reuse plant will have different effluent
28 July 2021 • Florida Water Resources Journal
