Smart Design Drives More Resilient, Sustainable, and Affordable Water Resource Recovery Plant
Wastewater treatment plants are critical parts of any community, but that doesn’t mean residents are eager to have these plants visible in the community—or to pay for them. This was the reasoning that guided the smart design decisions behind the city of Indianola’s updated water resource recovery facility (WRRF).
The under-construction facility not only exceeds all separation distances to any neighbors but the smart design is reducing the cost of the facility by $12 million over a traditional approach. More importantly for the municipality, the innovative features keeping this cost low make for an altogether more resilient and sustainable WRRF.
As the City of Indianola discovered, smart design doesn’t have to be costly. Other municipalities may find the strategies applied here can help them design and build a resilient, sustainable, and more operationally effective WRRF at an easily attainable cost.
Out of sight locale
Keeping its new WRRF out of sight and out of mind for the local community was at the forefront of the city of Indianola’s decision to purchase a 360-acre site for the future facility 20 years ago. Near the center of the site is a large hill that slopes to the north and east, where floodplains create a natural buffer. The new WRRF sits on approximately 30 acres down the slope of the hill, a location that lets gravity do some of the heavy lifting of facilitating the hydraulic flow of wastewater to the treatment units.
Of course, this hillside location offers another advantage as well. Construction into the slope, behind the barrier of the existing tree lines and landscape berms, helps hide the WRRF from public view. Beyond this protective landscaping, the city continues its longstanding lease of portions of the site to local farmers, allowing a rural feel to envelope the critical utility.
The new WRRF also rethinks the way it manages peak flows, known as one-percent flows due to the statistically rare instances in which they occur. The city’s outdated facility followed a traditional format, using large equalization basins to handle peak flows. As these events occurred, clear water would enter a leaky sanitary sewer system as inflow. The equalization basins would fill with diluted wastewater to be treated later through the wastewater treatment plant. Unfortunately, this lagoon system proved it was not resilient enough to sustain the higher wet weather events that had become more frequent as a result of climate change. The city wanted to avoid expanding the equalization basins in order to reduce odors and maintain a positive public perception.
The new WRRF design features a real-time peak flow treatment system that better manages these peak flows. The design team set a goal of treating these extreme wet weather flows in real-time. By more proactively managing these events, the WRRF can avoid hampering operations for a month after extreme weather events, as the outdated facility had previously done.
The new system is designed to divert this infrequent high-dilute flow to a small equalization tank. From there, the flow moves through a more cost-effective tertiary cloth media filtration process, followed by UV disinfection, effluent sampling, and discharge to the outfall sewer. Because these one-percent peak flows do not go through the normal secondary treatment system, the developer could more appropriately size the biological secondary treatment system and avoid a large equalization altogether, driving down the overall cost of the project.
Saving money isn’t the only priority that utilities and municipalities find themselves juggling, even if it is front of mind for most rate payers. More WRRF owners are seeking solutions that allow for more sustainable use of their resources. Strategies that support greater reuse of water and treated biosolids fit this bill.
Because the disinfected effluent that flows out of the Indianola WRRF is actually of a better quality than the Middle River into which it discharges, the new WRRF will make more efficient use of this fresh water source. The facility will divert as much as 25% of the effluent flow to use for flush down, washing or process service water in the facility, as well as for irrigation at the nearby Indianola Country Club golf course.
The sludge generated by the aerobic digesters following treatment and stabilization, known as biosolids, also has tremendous value. Biosolids can be applied to farmland as fertilizer, in accordance with EPA guidelines. The new Indianola WRRF features tremendous flexibility in the type of biosolids product it generates and stores. Biosolids can be generated from the aerobic digesters and stored at 2% solids or can be thickened in the solids processing building as 5% solids for longer storage.
Application of these biosolids has also become more sustainable. In the past, the WRRF would load up to 400 semi-trucks with biosolids to transport across gravel roads to a nearby farm site where this fertilizer could be applied each spring and fall. The new facility eliminates that transportation need by connecting a pipeline to the biosolids storage tank and using an umbilical system to pump the biosolids directly to the land application equipment. This approach eliminates the fuel consumption, dust, traffic and nuisance of the previous process.
Strike the right balance
Water resource recovery facilities are critical parts of any municipality, but they can face challenges in securing the public support needed to raise funds. WRRF projects must make every effort to reduce costs while maximizing value, and many municipalities find that a modernized design can often improve operational efficiency and drive rates down.
Smart design is critical in achieving this balance, and this is an area where HR Green can help. To learn more about innovative solutions to modernize your water resource recovery facility, contact us today.
Jim Rasmussen, PE is HR Green’s Water President, overseeing a broad range of clients, projects, and engineering professionals. In addition to project management, planning, design and construction, Jim also has experience leading project-related public involvement efforts for his clients. Jim can be reached at firstname.lastname@example.org.