Site-specific approaches move forward
“The current emphasis on developing water quality criteria for nitrogen and phosphorus presents tremendous challenges,” says Clifton Bell, Brown and Caldwell technical leader for watersheds and TMDLs. “We need to make progress in solving problems like hypoxia, algae blooms and degraded habitat. However, solving these issues can be complex and costly.”
Because no two water bodies are exactly alike and sometimes the rules fail to acknowledge this, the development of scientifically sound nutrient goals is one of the most high-profile challenges facing states and the regulated community. Efforts are being made to set reduction targets that are specific to a particular geographic region, taking into account that a body of water’s response to nutrient load often depends on a variety of characteristics.
In 2012, the Water Environment Research Foundation set out to create a toolbox that would serve as guidance for using models to set site-specific nutrient goals. In partnership with BC, Limno Tech and Tufts University, WERF is helping states and NPDES permit holders link nutrient management strategies to ecological response indicators for aquatic systems.
The resulting research report, Modeling Guidance for Developing Site-Specific Nutrient Goals, was the subject of a workshop Saturday during the conference. According to Bell, the Nutrient Modeling Toolbox contains 30 models capable of quantifying the relationship between nutrient loads and their impacts, as well as a Model Selection Decision Tool to help users select potential models for their specific site, condition, response indicators and available data and resources. The team also has developed technology-based and water quality-based approaches that might be applicable in cases where more complex methods are not feasible due to available data or cost.
Proven technology makes timelines possible
Sacramento’s effort to deal with lower nutrient requirements in its effluent permit will be featured in three sessions during WEFTEC. Faced with state mandates that it must construct and operate new treatment processes by 2021, the Sacramento Regional County Sanitation District decided to launch a $2 billion upgrade, known as the EchoWater Project. The more significant permit requirements include lower discharge limits for ammonia and nitrate and Title 22 or equivalent reclaimed water treatment standards, and requiring filtration and enhanced disinfection processes.
According to Kurt Ohlinger, EchoWater Project chief scientist, the short time-frame they had to work with was a major driver. “This really limited the alternatives we could consider to proven, mature technologies because there was no time to explore and test emerging nutrient removal technologies, such as shortcut nitrogen removal,” he says. “Viable alternatives had to be proven at large plants, be cost-effective, and be adaptable to meet anticipated future regulatory requirements.”
During the district’s comprehensive technology screening process, all options were on the table. Alternatives considered included keeping the high purity oxygen activated sludge system and achieving nitrogen removal in subsequent processes, as well as bioaugmentation of the HPOAS process. Suspended growth and fixed film process alternatives also were weighed.
“In the end, the primary drivers of mature technology at large plants, cost-effectiveness and adaptability to anticipated future treatment requirements drove the decision to select the air-activated sludge, biological nutrient removal (BNR) process,” Ohlinger says. In addition, he added, the new treatment processes will produce water that is reuse quality, which fits in nicely with the district’s water management plans.
SRCSD recognized the value of piloting and included it within its 10-year plan for BNR implementation. A pilot plant was built in 10 months and operated for 11 months in order to evaluate the efficacy of new and existing technologies for nutrient removal from engineering and operations perspectives. It used deep aeration tanks and sufficiently large secondary clarifiers and minimum filter sizes to accurately mimic full-scale performance.
This ultimately allowed SRCSD to lower cost estimates for the upgrades and reduce its homeowner rate increase over seven years from $24 to $46 instead of the previously projected rate of $68. This pilot plant is providing crucial data for the district's 10-year implementation program for upgraded treatment facilities that ultimately will serve 1.4 million customers. BC, together with HDR, is leading the program management team working with SRCSD to implement the EchoWater Project.
New technology offers promising results
As wastewater technologies continue to advance, more municipal agencies are looking to apply new processes that help reduce costs, support decision making and meet future requirements.
Pierce County, Wash., successfully piloted and is implementing an Anammox sidestream treatment process (called DEMON®, short for DEamMONification) for anaerobic sludge dewatering centrate. Anammox, the cutting-edge nutrient removal technology, has been used in Europe for 10 years and is increasingly being used in the United States to efficiently remove nitrogen in ammonia-rich process streams.
This was the first U.S. pilot study of the DEMON® technology for "shortcut" nitrogen removal. Once completed, the Chambers Creek WWTP six miles outside of Tacoma, Wash., will be one of the largest North American installations of the DEMON® technology. The piloting work was presented on the podium at WEFTEC 2012.
Public interest in protecting Puget Sound created the impetus to move ahead with nutrient control investments before they became compliance issues in Pierce County. The county took advantage of the favorable economic climate and created a pro-active 30-year plan to accommodate looming capacity needs and regulatory requirements, including nitrogen removal. The $353 million expansion project will increase plant capacity from 28 to 50 mgd, introduce new technologies to protect the environment, and repair and replace aging infrastructure.
According to Chris Cleveland, senior vice president in BC’s Olympia, Wash., office, this proved to be cost-effective as well, because it eliminated potential sunk investments and provided overall opportunities to jointly manage countywide nutrient control responses with the surface water management group.
Now in its construction phase, Chambers Creek designers devised a strategy to adjust treatment performance for nutrient removal, water reclamation and “zero discharge,” and developed a capital improvement plan based on service and asset management principles. Addition of new unit processes, and upgrades to existing processes, can be expanded to accommodate additional needs so the county can speed up or slow down level-of-service improvements to correspond with the changing regulatory environment, public demand and available funding.
“Pierce County should be commended for their foresight and courage to take on this project,” Cleveland says. “The technologies, GC/CM process, financial planning and asset management practices are all on the forefront of what is happening in other sewer utilities across the country.”
This expansion will add 50 percent more capacity, provide the first steps for water recycling, and significantly increase the level of treatment using biological nutrient removal. As an added benefit, the design transformed the 180-acre utility site into a community asset by seamlessly integrating it into the master plan for a 920-acre regional waterfront park that includes a championship golf course. Work is expected to wrap up in 2016.
“One of my top priorities is creating livable communities, and having a cost-effective, environmentally responsible sanitary sewer system is a key part of that mission,” Pierce County Executive Pat McCarthy said. “The expansion will benefit this growing community for years to come, and the results truly support what it means to have livable communities.”