The Metropolitan Water Reclamation District of Greater Chicago is adding a nutrient recovery system that will reduce nutrient releases and produce a marketable fertilizer at its massive Stickney Water Reclamation Plant in Cicero, Illinois. Courtesy of the Metropolitan Water Reclamation District of Greater Chicago
One of the largest water recovery plants in the world, located near Chicago, is planning to add a process that will remove phosphorus and nitrogen from its side streams in a form that will be marketable as fertilizer.
November 5, 2013—Ostara Nutrient Recovery Technologies, Inc., of Vancouver, British Columbia, has teamed with Black & Veatch, of Overland Park, Kansas, to design and construct a nutrient recovery system at the massive Stickney Water Reclamation Plant (WRP), in Cicero, Illinois. Owned and operated by the Metropolitan Water Reclamation District of Greater Chicago (MWRD), the WRP has a design flow rate of 1,200 mgd and treats an average flow of roughly 750 mgd, making it among the largest such facilities in the world. Upon the system’s completion, which is expected in 2015, the Stickney plant will be by far the largest to have adopted Ostara’s process for removing phosphorus and nitrogen from the nutrient-heavy side streams that result from various solids-handling processes. With the MWRD looking to adopt a nutrient recovery approach at another of its large WRPs in the near future, the changes will go far in helping the district meet its goal of recovering resources rather than simply disposing of waste products.
The MWRD chose to adopt the nutrient recovery process even though the Stickney facility has been operating under a permit that imposes no discharge limits on nutrients. Aware of the national emphasis on reducing discharges of nutrients to waterways, the MWRD sought to answer the question, “What can we do as responsible utility owners that can take the lead to address issues in a way that is responsive to our ratepayers and the environment and provides a model for other utilities?” asks David St. Pierre, P.E., the MWRD’s executive director. To this end, the district has been working with the State of Illinois to voluntarily impose a limit of 1 mg/L for phosphorus on the basis of a monthly average discharge limit as part of a new permit for the Stickney facility that is likely to take effect by year’s end.
The MWRD has also worked to implement the biological removal of phosphorus within the four batteries for the aeration tanks that constitute the secondary treatment process at the Stickney WRP, which St. Pierre describes as a “fairly typical activated sludge plant.” The district is accomplishing biological phosphorus uptake by turning down aerators in the feed channel and in the first stage of the activated sludge process, thereby creating anaerobic zones. In early October St. Pierre estimated that three of the batteries would be complete by the end of the month. Once operational, the revamped batteries are expected to result in “significant phosphorus uptake in our secondary process” with little financial investment on the part of the MWRD, St. Pierre says. However, “one of the downsides” of capturing phosphorus in this manner, he notes, is that the nutrients tend to pass through the ensuing solids-handling processes, necessitating the return of a nutrient-laden side stream to the head of the WRP. In this way phosphorus tends to be recirculated rather than removed during the treatment process.
It is this problem that the Ostara nutrient recovery system is intended to address. As it passes through fluidized-bed reactors, the side stream receives magnesium to convert the nutrients into magnesium ammonium phosphate, which is also known as struvite. As it makes its way downward through the fluidized-bed reactors, the struvite forms small crystal-like pellets that are eventually harvested at a predetermined size at the bottom of the reactors. In this way approximately 80 to 90 percent of the phosphorus and 10 to 20 percent of the ammonia present in the feed are removed, says Steve Wirtel, P.E., a senior vice president of technology sales for Ostara. Known as Crystal Green, the finished product is sold by Ostara as fertilizer to agricultural, turf, and ornamental greenery growers. These customers value the product for the slow release of the fertilizer, which increases efficiency and makes possible lower application rates and reduced nutrient loss than is the case with conventional fertilizers, Wirtel says.
Under the terms of a contract awarded last June, Black & Veatch is responsible for design, procurement, and construction services, while Ostara will provide the nutrient recovery system, including equipment. To be implemented in two stages, the contract includes a $1.3-million fee for Black & Veatch to conduct process and design engineering. Once the design is complete next year, the three parties will negotiate a construction fee. All told, the cost to design and construct the project could range from $17 million to $29 million, says Dave Koch, P.E., the project director for Black & Veatch’s water business.
A more precise cost estimate will be available upon completion of the process engineering, Koch says. “The Stickney WRP is a complex operation, and it’s critical to identify the best means of implementing the Ostara process through evaluation of the resulting impacts on liquid processing, solids processing, and operation and maintenance costs,” he says. Chief among the considerations is which of the plant’s various side streams to treat, including feed to the digesters, feed from the digesters, and feed from thickening processes. “All those side streams are going to be evaluated to decide which way is the best, most efficient, and [most] cost-effective way to implement the technology,” Koch says.
Once construction is complete, Ostara will assist the MWRD with operations and maintenance. The company will also purchase all nutrients recovered from the Stickney WRP. The MWRD anticipates that the new system will generate between 10,000 and 15,000 tons of Crystal Green a year, and Ostara is committed to purchasing this quantity at a price of $400 per ton, St. Pierre says. At this rate the district expects to achieve a payback on its capital costs within five to seven and a half years, he notes, and any increase in operations and maintenance costs is expected to be minor.
The MRD also views the project as a key step in advancing its goals regarding sustainability. “We believe it’s important to turn what we do into a product instead of just a way to deal with waste,” St. Pierre says.
The MWRD would also like to install a nutrient recovery system at its Calumet WRP, which treats average flows of 354 mgd. However, the district will first have to overcome a deficiency of carbon within the plant’s secondary treatment process, a deficiency that is making it difficult to adopt a biological approach for capturing phosphorus during secondary treatment. Once the MWRD has addressed this problem, it will implement a nutrient recovery system at the plant, although the exact type of system has not yet been determined, St. Pierre says.