In March 2016, regulations go into effect to control emissions from sewage sludge incinerators, such as this one owned by the Metropolitan St. Louis Sewer District. Courtesy of Black & Veatch
Engineers work on a tight deadline to update sewage sludge incinerators to comply with new regulations that go into effect in March 2016.
February 4, 2014—The Metropolitan St. Louis Sewer District (MSD) is in the early design phase of a $35-million project to install scrubbers on the biosolids incinerators at the Bissell Point and Lemay wastewater treatment plants to comply with emission standards that go into effect in March 2016.
In 2011, the U.S. Environmental Protection Agency enacted maximum achievable control technology (MACT) emission standards for sewage sludge incinerators (SSI). The measure sets limits for mercury, lead, cadmium, hydrogen chloride, particulate matter, and other pollutants in SSI emissions.
MSD recently selected Black & Veatch, headquartered in Overland Park, Kansas, to determine the current emissions conditions at the facilities, recommend the best scrubber technology to employ for this application, and design how best to install it while interfering as little as possible with the operations at two of MSD’s key wastewater treatment facilities.
The project will likely employ a single, adjustable venturi scrubber followed by train impingement scrubbers on each of the incinerators, according to Tom Ratzki, P.E., M.ASCE, a project director for Black & Veatch. Such scrubbers collect and remove particulate pollutants from gases. “They essentially spray a mist of the water through the exhaust air, and that mist captures the particulates that are in the air,” Ratzki explains. The mist lowers the temperature of the exhaust and traps particulates in water. The system will then collect that water and return it to the wastewater stream for treatment.
Although the scrubber technology is a straightforward solution to remove particulates, the project presents several key challenges. The facilities are busy wastewater treatment plants. Contractors will find tight conditions and limited access into the existing buildings that house the incinerators—six at Bissel Point and four at Lemay.
“These are very old facilities and there is a lot packed into a very small area,” Ratzki says. “[The contractors] are going to need to know what they can remove and what they can’t remove.”
To develop an accurate model of the facilities, MSD approved the team’s request to utilize three-dimensional laser scanning. The technology will enable the team to develop a highly detailed computer model that will document the piping, ductwork, and structural members of the buildings, which date to the 1960s.
“We think it’s going to be a very powerful tool,” Ratzki says of the modeling, which will help the team accomplish two key goals. One, it will “expedite the project—because we didn’t have the data and we need to get a design done in a very short time frame. And two, [it will] keep all the unknowns and issues that might come up during construction to a minimum.”
With the model complete, and the current emissions picture detailed, Black & Veatch will then make recommendations on which scrubber technology to employ so MSD will be able to select the best option.
“The operators have a lot of different conditions that they need to operate under,” Ratzki notes. Variations in temperature, sludge quality, and operating conditions at the wastewater treatment plant can all impact incinerator emissions.
“We want to give them some flexibility so they are not always right up against the limits,” Ratzki says. The team will include in the design a “factor of safety” so that the system can comfortably handle a higher level of particulates than the analysis reveals are commonly present.
The models will also help the team determine how best to fit the equipment into the structures. Ratzki says the team is hoping to impact no more than three levels of the large incinerator buildings, which are approximately equivalent to a five-story building. One option actually limits impacts to a single level.
“That would avoid us having to tear out the structural support for various levels and all the pipes that are hanging off those levels. We gave ourselves 90 days to complete this evaluation and to come up with a design report for how to move forward,” Ratzki says.
With the scrubber technology selected and its manufacture under way, the team will have to devise the best way to get the massive equipment into the structures. The buildings have only one large overhead door, limited walkways that are shared with operators at the plant, and light-duty elevators.
Ratzki says options under consideration to improve ingress include creating openings in the walls or the roof at strategic locations and employing cranes to bring in the heavy equipment and materials required for the project.
“It’s an exciting project to us because of the schedule. We like the complex projects. We like the challenge,” Ratzki says. “We think that’s where our best talents come out.”
Construction is tentatively scheduled to begin in April 2015. Ratzki says the team will install scrubbers on one incinerator at a time, each taking approximately three months. The goal is to have at least two incinerators at each plant fitted with scrubbers and to be in compliance by the March 2016 deadline.