A new tertiary treatment facility is being added to the Sacramento Regional Wastewater Treatment Plant, even as it continues to operate at its 181 mgd capacity. The new system will reduce ammonia, nitrate, total coliform, and turbidity. Courtesy of the Sacramento Regional County Sanitation District
A California utility is embarking on a 10-year tertiary treatment project to meet stringent new discharge requirements.
November 26, 2013—The river delta and estuary at which the Sacramento and San Joaquin rivers meet gives rise to some of the richest agricultural land in the United States. The more than 840 sq mi of farmland there yields crops valued annually at approximately $500 million.
The rich agricultural soil was once a tidal marsh and is protected by more than 1,000 mi of levees. This has created a fragile, freshwater ecosystem that is home to more than 500 species of plants and animals. Much of the land is below sea level and susceptible to salt water incursions.
In 2009, American Rivers, a nonprofit organization headquartered in Washington, D.C., listed the Sacramento-San Joaquin river system at the top of its annual list of “America’s Most Endangered Rivers.”
“The delta is a major source of California’s water supply for people and agriculture,” says Vick A. Kyotani, P.E., a program manager for the Sacramento Regional County Sanitation District (SRCSD). “There is agreement that the delta is in some kind of environmental stress. But the causes of that stress are not really known and there isn’t agreement on the factors causing those problems.”
Nevertheless, in 2010, the Central Valley Regional Water Quality Control Board (CVRWQCB) issued a National Pollutant Discharge Elimination System (NPDES) permit to the SRCSD that greatly reduced the amount of ammonia and total coliform that is acceptable in treated effluent released into the river, and also established limits on nitrates.
The permit reduces ammonia levels from a maximum of 45 mg/L per day to either 2.0 mg/L or 3.3 mg/L per day, depending on the season. Nitrate discharge, not previously controlled by the permit, is limited to 10 mg/L as the average of four weekly samples in a month. Total coliform is limited to 2.2 as the most probable number (MPN) per 100 mL, taken as the median of seven daily tests. The previous limit was 23 MPN per 100 mL. The permit also includes turbidity limits.
The SRCSD has begun awarding contracts on a new tertiary treatment facility at the Sacramento Regional Wastewater Treatment Plant to meet the standards. The plant has an existing permitted capacity of 181 mgd for the average dry-weather flow. The project has been christened the EchoWater Project, a nod to the project’s goal of returning water to the river in a clear, clean state. The team has employed a method called lowest life-cycle cost analysis to determine the best treatment train.
“We built a 0.25 mgd [average flow] pilot plant facility,” says Kyotani. “Prior to implementing that pilot, we went through a technology screening effort to determine technologies that would reliably allow us to meet our permit requirements.
“We constructed a pilot plant that starts with an air-activated sludge process—which is the biological nutrient removal process. And then we tested three different types of filtration—membrane, granular media, and granular media with preozonation,” Kyotani says.
The pilot plant added three disinfection technologies to each of those three filtration methods—chlorine, ultraviolet light, and ozone disinfection. “We tested nine different trains of treatment,” Kyotani says.
“What we learned on the filtration side was that all of those filtration technologies were effective,” Kyotani says “We did find, though, that preozonation did not provide any added benefit to meet our permit and it had a much higher cost. That left membrane and granular media filtration. Both of those technologies worked, but the membrane filtration is a significantly higher cost.”
From the pilot testing, the SRCSD found that ozone did not reliably meet the new disinfection requirements and was ruled out for the project. Although both ultraviolet light and chlorine reliably met the project’s requirements, chlorine was determined to be the most cost effective option.
The SRCSD is still appealing certain parts of the permit, leaving the project cost at between $1.5 billion and $2.1 billion. To accommodate the ambitious project on a timeline of approximately 10 years, the SRCSD has parceled the task into several smaller projects, most of which will be built concurrently. This will mean as many as 600 construction workers will be on the site of a working wastewater treatment plant, building a new system that will need to eventually be tied seamlessly into the existing process.
“There is a huge challenge in the commissioning aspect of all of these projects and the cut-over to the new facilities while we are still operating our existing facilities,” Kyotani says. The new systems will be designed with construction sequencing in mind, which will aid engineers in meeting this challenge.
“The majority of our projects will be using BIM [building information modeling],” Kyotani says. “We want to take that information—the data that gets put into BIM for all the assets, the equipment—and be able to electronically import it into our computerized maintenance and management system.”
On the design side, the team is counting on 3-D designs to identify potential clashes, enabling the many projects to be integrated seamlessly together. Kyotani says the project team is also employing reliability-centered design principles to build efficient operation into the system.
“It’s essentially reliability-centered maintenance concepts, but applying those concepts during the design phase instead of after, on an existing facility,” Kyotani explains. “What we hope to do is optimize what we are going to design and build. It will address redundant equipment needs and spare parts needs. If you take it further, it starts defining your maintenance practices.
“You optimize at the beginning, during design, so that you only build what you need, and that naturally optimizes your maintenance practices as well,” he explains. “You start making decisions that affect not only your capital cost, but long-term maintenance costs. You perform this analysis on what is required to maintain the function of that system.” Kyotani says that the questions that the designers answer as part of this process include, “What happens if it fails, and if it fails, how do you fix it?” The answers result in such plans as installing installation a spare pump, for example, or stocking a spare pump or parts. “You start asking these kinds of questions and then the results start really optimizing your system,” he says.