...strategy, fewer than half of the states have developed numeric limits. “States are doing fair, not good,” at developing timetables and numeric limits to reduce nitrogen, acknowledges EPA’s Wheeler. “I really think some of the states are waiting for EPA to get more involved and develop some criteria,” he says.
An EPA inspector general’s report released in August recommended EPA take a stronger stance and identify “priority” states where efforts could be concentrated and where numeric limits could be established. Agency water officials disagree with some of the recommendations but agree the agency should create more accountability for meeting milestones for adopting nutrient water-quality standards where required. EPA has 90 days to formally respond to the report.
Agency officials say they are keeping a watchful eye on what happens with the Chesapeake Bay and efforts to develop a total maximum daily load (TMDL) for the Chesapeake Bay watershed. Later this fall, an interagency task force, led by EPA and established by an executive order from President Barack Obama, plans to issue a strategy for reducing pollution in the bay (ENR 9/21 digital issue). It will include the first steps toward developing a TMDL that holds states accountable for their efforts to reduce nutrients. “If it works well in the bay, you may see [a similar effort] in the Puget Sound, or other critical water bodies might take a similar type of approach,” Wheeler says.
Marie Burbano, principal in CDM’s Los Angeles office, says typical effluent limits are 8 mg/liter for nitrogen and 1 mg/liter for phosphorus, but other parts of the country—particularly the Northeast, mid-Atlantic and some Midwest states—are pushing limits much lower, to 3 mg/liter for nitrogen and 0.05 mg/liter for phosphorus. “The regulations that are getting more stringent in terms of nutrients are definitely going to be driving a lot of the technology and a lot of the projects coming up in the future,” she says.
But, she adds, extremely low levels can have diminishing returns. “The problem with getting to these very low limits is you are using a lot of chemicals,” she notes. “There’s a question as to the environmental impact of generating all those chemicals versus the improvements you get from going from 0.2 mg/liter to 0.05 mg/liter.”
A number of proprietary, newer technologies are being implemented, although many are of a smaller scale, on projects to reduce nitrogen and phosphorus levels to very low numbers. Many firms are using one of three types of the newest iterations of ballasted flocculation technology, which have been popular in northern Europe but have not been widely used in the U.S. until recently.
Used after effluent has passed through secondary treatment, the technology adds flocculation-aiding chemicals such as aluminum sulfate in ballasted flocculation basins to create conditions in which particles become heavier or larger, bind together, and then settle. The particles then leave the treatment stream in the tertiary sludge, and the ballast is recovered using a filter, hydraulic system or, in the case of magnetically enhanced coagulation (CoMag), a magnetic drum. Three of the flocculation systems now being used are CoMag, which uses magnetite as the ballast; Actiflo, which uses sand or grit; and Densadeg, which uses sludge itself.
Sudhir Murthy, research and laboratory manager for the District of Columbia Water and Sewer Authority (WASA), says although flocculation has been used in wastewater treatment for more than 50 years, what’s new are the technologies that “make the particles either bigger or heavier than the older processes.” Then, by creating conditions to remove the particles more efficiently, “you’re able to process a lot more water in a smaller container,” bringing down the cost to treat the water compared to conventional methods.
CDM used CoMag to successfully reduce phosphorus levels in effluent to 0.05 mg/liter on an average monthly basis in the first full-scale application of the technology, a project for the town of Concord, Mass. In 2004, the Massachusetts Dept. of Environmental Protection established a TMDL that includes phosphorus limits ...