Integrating Smart Sewers with Smart Wet-Weather Treatment to Increase Capacity and Water Quality Resiliency

PURPOSE This presentation will increase awareness of emerging dual-use auxiliary treatment strategies and benefits (both economic and non-economic) during dry and wet weather along with considerations compared to other wet-weather management strategies. BENEFITS OF PRESENTATION Attendees will learn about pile cloth filters, an innovative enhanced high-rate treatment (EHRT) technology. This technology has proven to be more cost-effective and simpler to construct, operate and maintain than previous generation EHRT technologies, particularly for satellite facilities located in collection systems. STATUS OF COMPLETION Case studies feature completed projects that Johnson County Wastewater (JCW) and Little Rock Water Reclamation Authority (LRWRA) began operating in 2021. BACKGROUND Black & Veatch helped JCW and LRWRA complete major improvements in 2021 to mitigate wet-weather flows and improve treatment capacity and resiliency. Both utilities added dual-purpose auxiliary treatment systems featuring largest-scale units of latest generation pile cloth filters that cost-effectively treat at high flow peaking factors and polish normal dry-weather effluent, providing year-round water quality benefits instead of just during peak wet-weather events. No chemicals or biology required. JCW upgraded its Tomahawk Creek Wastewater Treatment Facility (WWTF) to meet new nutrient limits and expand design capacity to 19 mgd average and 172 mgd peak. New pile cloth disk filters polish effluent up to 57 mgd and provide auxiliary treatment of wet weather flows up to 115 mgd, making it the world's largest capacity dual-purpose pile cloth disk filter installation to date. The improvements are a major milestone in JCW's Integrated Plan to identify, assess, and prioritize infrastructure initiatives and investments. The Kansas Department of Health and Environment authorized the improvements through major modifications to its National Pollutant Discharge Elimination System (NPDES) permit with no objections from the United States Environmental Protection Agency (USEPA). LRWRA added a similar 58-mgd system to its Adams Field Water Reclamation Facility for auxiliary treatment in parallel with 36 mgd of nitrifying activated sludge treatment to bring peak flow capacity up to 94 mgd. When not used for auxiliary parallel treatment, the new filters can polish secondary effluent to increase the performance and reliability of the effluent UV disinfection system. The Arkansas Department of Energy and Environment's Division of Environmental Quality authorized the improvements through NPDES permit renewal with major modifications and no objections from USEPA. A key regulatory consideration was the 2013 decision by the Eighth Circuit of the U.S. Court of Appeals in Iowa League of Cities v. EPA that upheld the practice of parallel treatment and blending. OBJECTIVES To maximize stakeholder benefits, both utilities sought auxiliary facilities that increase wet-weather treatment capacity most cost-effectively and can also polish effluent during normal flow conditions to decrease effluent total phosphorus (JCW objective) or improve operation and maintenance of UV disinfection and support reuse opportunities (LRWRA objective). METHODS AND RESULTS The JCW team conducted applied research and assessments of technologies prior to design and delivery under a construction-manager-at-risk framework. Activities and milestones include: - 2005/7/8 - Jar testing of chemically enhanced settling and ballasted flocculation at the Douglas L. Smith WWTF. Full-scale trials of chemically enhanced settling at the 75th and Nall Peak Excess Flow Treatment Facility. Side-by-side pilot testing of three different high-rate filter technology alternatives at the Nelson Complex (Fitzpatrick et al, 2010). - 2016 -- Conceptual design studies to refine recommended alternatives, project costs and schedule; conceptual level site plan to support public outreach and site permitting; negotiate and finalize discharge permit for new facilities. Results summarized in a Preliminary Design Report. Auxiliary treatment strategy estimated to save over $200M compared to storage and equalization alternatives. - 2018 -- Detailed facility design complete. Pile cloth disk filters selected after evaluation of 60% designs with both pile cloth and compressible media alternatives. Value engineering alternatives save the project over $40M. - 2021 -- Startup and testing of dual-purpose filters demonstrates achievement of specified performance criteria and effluent limitations (see Figure 1). The LRWRA team conducted similar applied research and assessments to support design-bid-build project delivery, which included: - 2001 -- Onsite pilot studies demonstrated performance of chemically enhanced high-rate settling (CEHRS) technologies. - 2016 -- Onsite side-by-side piloting of pile cloth and compressible media technologies demonstrated similar removals as CEHRS alternatives but did not require chemicals, were found to be simpler to operate and control, and improved downstream UV disinfection performance. Conceptual facility designs for five different technology alternatives were evaluated based on economic and non-economic factors. The team conducted further investigations of the top two candidates (ballasted flocculation and pile cloth filtration) including site visits to reference facilities and recommended pile cloth filter technology. The new filter system eliminated 34 million gallons of collection system storage and equalization expansion, immediately saving $10M in construction costs, and was found to be more feasible because it: (1) provides better resiliency by optimizing both storage and treatment capacities, (2) does not limit peak flow management to a finite volume, (3) requires a much smaller site, (4) does not require additional odor control, and (5) has lower life-cycle costs (Fitzpatrick et al, 2018). - 2018 - Detailed designs issued for construction including nitrification and clarification upgrades to existing activated sludge treatment process, new dual-purpose filters, expanded UV disinfection and effluent pump station. - 2021 -- Substantial completion and startup of the improvements (see Figure 2). CONCLUSIONS AND RELEVANCE Results from JCW and LRWRA agree favorably with those found from other auxiliary EHRT applications. Wet weather capacity with EHRT technologies is in many cases more affordable than other storage or treatment alternatives, and their small footprint makes EHRT facilities more feasible for constrained sites in urban and suburban settings, whether located at existing treatment sites or remotely at key points in the collection system. The simple physical process of filter technologies offers operational advantages over chemical and biological alternatives, particularly for remote facilities or intermittent operations. For all practical purposes, EHRT effluent quality is equivalent to that from conventional secondary treatment technologies when treating peak wet-weather flows. EHRT alternatives should not be pigeon-holed into the same regulatory category as traditional 'blending' technologies that achieve primary treatment equivalency. Existing NPDES regulations appear to have the flexibility to further legitimize EHRT technologies as 'auxiliary treatment' facilities within the codified definition of 'secondary treatment' (40 CFR 122 and 133). The U.S. Eighth Circuit Court refers to EHRT as 'non-biological secondary treatment' in Iowa League of Cities v. EPA This regulatory flexibility is critical as integrated wastewater and stormwater utility plans gain momentum and are implemented. Some utilities challenged with water scarcity are considering these same EHRT technologies for stormwater reuse. Over 100 POTWs worldwide operate auxiliary EHRT facilities with the earliest adopters having over 25 years of experience.