May 2011, Vol. 23, No.5

Clipping stormwater pollution


Faced with the challenge of meeting strict new limits on nutrient loads in Chesapeake Bay, watershed managers are taking aim at stormwater runoff. States are enacting lawn fertilizer bans to make quick and cheap nutrient cuts. And a growing number of cities are adopting plans to “green” city landscapes to treat urban runoff at the source, before it hits stormwater pipes.  

U.S. Environmental Protection Agency (EPA) officials on Dec. 29 announced a cleanup plan for Chesapeake Bay that puts the seven bay states on a strict “pollution diet” (see News, April WE&T). By 2025, states must reduce their nitrogen and phosphorus loads by roughly one-quarter from current levels. If the targets aren’t met, EPA may require more reductions from wastewater treatment plants. Experts say Virginia’s lawn fertilizer ban, passed on Feb. 18, is a key strategy for meeting the nutrient targets at a low cost.

Urban stormwater is responsible for about 10% of the nitrogen and 17% of the phosphorus reaching the bay and is the third-largest nutrient source after agriculture and wastewater. It’s also the fastest-growing source, said Tom Schueler, executive director of the Chesapeake Stormwater Network, an educational organization (Baltimore). “Because wastewater treatment plants have already made aggressive cuts in nutrient loads, states are turning to the estimated 6.1 million ‘turf grass farmers’ in the watershed who spend nearly $5 billion a year grooming and feeding their lawns,” he said.

Turf now covers 1.5 million ha (3.8 million ac), or 9.5%, of the Chesapeake Bay watershed, making it the biggest crop in the watershed, Schueler said. Roughly 75% of that turf is devoted to home lawns. In the last three decades, turf acreage grew 8% per year in Virginia, faster than population or impervious cover, he said.

Because bay managers have focused largely on other nutrient sources, “fertilizer bans are the proverbial low-hanging fruit,” said Harry Campbell, a senior scientist in the Harrisburg (Pa.) office of the Chesapeake Bay Foundation (Annapolis, Md.), an environmental group. Many soils in the bay watershed have more than enough phosphorus for plant growth, and any additional applications of phosphorus just run off into streams and contribute to eutrophication, he said.

Virginia’s new law bans the sale of fertilizer containing phosphorus for use on established lawns. The law is projected to reduce phosphorus runoff by at least 104,000 kg/yr (230,000 lb/yr), or 22% of Virginia’s phosphorus reduction goal by 2017. The Scotts Miracle-Gro Co., which has cornered about 60% of the fertilizer market, already has volunteered to cut phosphorus from its lawn maintenance products in Virginia by 2012.

Phosphorus bans have a long history of making reductions in nutrient pollution at little cost, Campbell pointed out. States began in the early 1970s to restrict phosphorus in laundry detergents, and in the last decade, 17 states have enacted low- or no-phosphate requirements for automatic dishwashing detergents.

One year after Ann Arbor, Mich., banned phosphorus in fertilizers, phosphorus levels in the Huron River dropped an average of 28%. A 50% reduction in phosphorus concentrations in runoff was achieved in Minnesota after a fertilizer ban in Minneapolis took effect, said Mike Gerel, a senior scientist in the Norfolk, Va., office of the Chesapeake Bay Foundation.

“It costs about $30,000/lb [$66,000/kg] of phosphorus removed using stormwater retrofit technologies, such as treatment ponds, swales, and pervious pavement,” Gerel said. In contrast, a fertilizer ban is virtually without cost.

Statewide restrictions on turfgrass fertilizer already are approved in eight states: Minnesota, Maine, Florida, Wisconsin, Illinois, Michigan, New York, and New Jersey. Maryland and Pennsylvania are considering similar legislation, Gerel said.

“By changing attitudes and behaviors about what constitutes a green lawn, it may be possible to achieve major runoff and nutrient reductions,” Schueler said.


Philadelphia replaces concrete with grass

“Philadelphia is a shining example of how to cut pollution from stormwater runoff,” Campbell said. The city has a problem with combined sewer overflows (CSOs), but instead of focusing on “end-of-pipe” solutions alone, the city is taking a more holistic approach with its “Green Cities, Clean Waters” plan, said Chris Crockett, director of planning and research for the Philadelphia Water Department. The aim is to meet water quality standards in a way that reduces the city’s carbon footprint, mitigates heat island effects, beautifies neighborhoods, boosts parkland and green jobs, and improves the health of residents.

In 25 years, the city hopes to decrease CSO volume by 30.1 million m3/yr (7.96 billion gal/yr), or 83.6% of the current CSO volume. “[The department] is committed to reduce overflows further beyond the 25-year timeframe as affordability allows,” Crockett said.

“The total program is aimed at achieving 12,080 ‘Greened Acres’ [4890 ha] within the CSO drainage, accounting for roughly 45% of the impervious cover within the drainage,” Crockett said. A greened acre (0.4 ha) converts an acre of impervious cover so that the runoff from the site, instead of entering storm drains, is managed by “green infrastructure.” Green stormwater infrastructure can include rain gardens, grassy roadside swales, green roofs, water barrels, pervious pavements, and stormwater tree trenches. One greened acre will manage the first inch (24.5 mm) of rainfall that normally would flow into storm drains, Crockett said.

“Key to the success of Philadelphia Water Department’s strategy is that immense opportunity exists for implementation on publicly owned land, including streets and rights-of-way, which constitute almost one-half of the impervious land area of the city,” Crockett said. For new private developments greater than 1400 m2 (15,000 ft2), the city mandates that they must manage the first inch of runoff from the site.

The city also has overhauled its billing program. Historically, the city assessed stormwater charges based on the amount of water consumed by a property as measured at the water meter. “Such an approach creates an inequity, as the size of the water meter bears limited relationship to the volume of stormwater runoff from a property, and properties without meters, such as parking lots, did not pay a stormwater charge,” Crockett said. Now, using a geographic information system, the city assesses every nonresidential property and charges fees based on the gross area and impervious area of each property. “The parcel-based approach establishes a reasonable relationship between the stormwater burden imposed by a property and the stormwater charge assessed from that property,” he said. Landowners who manage the first inch of runoff on their property can earn credits that cut their bill.

In the process of greening its stormwater infrastructure, the city will reduce the need for building costly underground systems, such as pipes and storage tanks. These conventional capture and storage technologies would have cost Philadelphia more than $7 billion. The green program has a price tag of $1.6 billion across a 20-year period.

Meanwhile Lancaster, Pa., has opted for an approach much like Philadelphia’s. Each year, the city of 59,000 people generates about 3.8 million m3 (1 billion gal) of CSOs. It would cost more than $250 million to treat the city’s CSOs using “gray infrastructure,” such as new underground drains and tanks, said Charlotte Katzenmoyer, the director of public works for Lancaster. She estimates that green infrastructure can do the job for about half the cost. The city plans to leverage the ongoing renovation of its public parks. For instance, the city’s Brandon Park will manage 19,000 m3/yr (5 million gal/yr) of runoff from the surrounding neighborhood after it has been retrofitted with rain gardens and pervious pavement, she said.


— Janet Pelley, WE&T

Algae wars

Is dual nutrient control necessary to curb algal blooms?

Since the 1970s, the conventional wisdom has been that phosphorus, not nitrogen, controls blooms of freshwater algae. But new research suggests that wastewater managers may now have to worry about the levels of both nutrients in their effluent if they wish to avoid triggering toxic algal blooms. Although controversy over dual nutrient control still reigns in some scientific quarters, regulatory agencies across the globe are moving to control loading of both nitrogen and phosphorus to sensitive waterbodies.

Lake Taihu, China’s third-largest freshwater lake, is a prime example of the need for multiple nutrient control, according to Hans Paerl, an aquatic ecologist at the University of North Carolina (Chapel Hill). Each summer through the fall, the hypereutrophic lake cranks out massive algal blooms dominated by Microcystis, a non-nitrogen fixing cyanobacterium. Excessive nutrient inputs from urban, industrial, and agricultural growth in the Taihu Basin are driving these blooms.

Algae thrive on both nitrogen and phosphorus. In general, when the ratio of nitrogen to phosphorus is low, growth is limited by nitrogen, and when the ratio is high, phosphorus controls the growth rate. Paerl and his colleague, Boqiang Qin, a limnologist at the Chinese Academy of Sciences (Nanjing), wondered which nutrient was controlling growth in Lake Taihu.

The researchers added phosphorus and nitrogen to 90-L-sized incubators of lake water samples, held for 4 to 6 days in a floating frame in the lake. These so-called bottle experiments revealed that Lake Taihu shifts from phosphorus limitation in winter and spring to nitrogen limitation in cyanobacteria-dominated summer and fall months. The researchers triggered the most algal growth when they added both nitrogen and phosphorus to the incubators. “We are writing a recommendation report to the administrative agency to suggest that we need to control both nitrogen and phosphorus, rather than phosphorus only,” Qin said.

Until now, a lot of effort has gone into controlling phosphorus emissions through wastewater treatment and wetland restoration around the lake, Qin said. “But Lake Taihu is so loaded up with stored phosphorus that the algae don’t run out of phosphorus in the summer,” Paerl said. It could take decades of cuts in the external phosphorus load before internal lake levels decline to the point that they limit growth, he said. Because nitrogen in the lake is partially reduced and lost to the atmosphere as nitrogen gas through denitrification, nitrogen is in lower supply, compared to phosphorus, and could control growth in the short term.


The phosphorus paradigm

However, research going back almost 40 years suggests that cutting nitrogen inputs to freshwater lakes will have no effect on growth, according to Dave Schindler, an aquatic ecologist at the University of Alberta (Edmonton). He silenced the debate over which nutrient limits algal growth in the 1970s when he curtained off the midpoint of a remote Canadian lake and fertilized one half with phosphorus. The photos of the pea-green phosphorus-enriched side launched a worldwide move to clean up lakes by cutting phosphorus loads. Lake productivity is phosphorus-limited, because nitrogen is never far from hand. If lake water is low in nitrogen, the algal community becomes dominated by nitrogen-fixing cyanobacteria, which can fix atmospheric nitrogen to meet their needs, Schindler said.

“I think the crux of the argument is that people are confusing measures of proximate, or short-term, limitation with ultimate limitation,” Schindler said. In the short term, a culturally eutrophic lake is nitrogen-limited because it has been overfertilized with phosphorus. But on a year-after-year basis, the lake is phosphorus-limited, he said.

“In addition, results of short-term bioassays are unlikely to accurately predict the results of years of nutrient treatment,” Schindler said. Long-term whole-lake experiments where the response to nutrient manipulation is observed are the only reliable way to judge which nutrient limits growth, he added. There are many lakes where phosphorus control has worked but no examples where decreased nitrogen loading has successfully reduced eutrophication of lakes, he said.

Management mistakes could be costly. “For the Baltic Sea, controlling phosphorus costs one-eighth as much as controlling both elements,” Schindler said.

Targeting both nitrogen and phosphorus may even promote blooms of nitrogen-fixing cyanobacteria, especially in cases of high internal phosphorus loading, Schindler said.


Multiple nutrients control saltwater productivity

But during the last 20 years, a growing body of research suggests that dual nutrient control is essential for coastal watersheds, according to Daniel Conley, a biogeochemist at Lund University in Sweden. Many factors, including biogeochemistry, abundant natural sources of phosphorus, and unique biotic communities, combine to make marine waters nitrogen-limited.

Nitrogen-driven eutrophication has been documented at coastal sites across the globe, including Chesapeake Bay, the Gulf of Mexico, portions of the North Sea, and China’s Pearl River Delta, Paerl said. His research on North Carolina’s Neuse River estuary has demonstrated that phosphorus controls in the upper freshwater reaches of the watershed boost export of nitrogen to the downstream marine portion of the estuary, generating nuisance blooms of algae and hypoxic zones devoid of oxygen. “This research has motivated North Carolina to control both phosphorus and nitrogen inputs, starting in the headwaters of river basins,” Paerl said.

In Denmark, aggressive control of nitrogen and phosphorus from wastewater treatment plants and agriculture has led to decreased algal biomass in coastal waters and elimination of some of the big summertime blooms, Conley said. In Florida’s Sarasota Bay, advanced wastewater treatment and nonpoint source controls have cut nitrogen inputs to the bay by 64%, clearing the water and allowing seagrasses to carpet 24% more of the estuary bottom than in the 1950s.

Conley cautions that coastal ecosystems that have been heavily loaded with nutrients can display limitation by phosphorus or nitrogen or both nutrients. “It’s prudent to implement a dual nutrient reduction strategy to alleviate eutrophication along the land-ocean continuum,” he concluded.

Regulatory agencies worldwide seem to agree. Many European countries are implementing dual nutrient control for coastal watersheds, Conley said. The U.S. Environmental Protection Agency (EPA) “national nutrient program has always focused on all nutrients, not just phosphorus,” said Amy Parker, a private consultant in Athens, Ga., and former national nutrient coordinator at EPA. The nutrient criteria that EPA recently set for Florida’s surface waters will lead to dual nutrient control, she said. States in Chesapeake Bay are taking on dual nutrient control, and EPA is pushing for control of nitrogen, as well as phosphorus, in the Mississippi River watershed in order to trim the dead zone in the Gulf of Mexico. Numerous freshwater New Zealand lakes have nitrogen reduction targets.


Keeping an open mind

Schindler’s ecosystem experiments on the Canadian lake prove that phosphorus controls productivity in oligotrophic lakes. “But we don’t know if it’s a good analogy for everyplace else,” said Bob Sterner, a limnologist at the University of Minnesota (St. Paul).

In some cases, there is value in cutting nitrogen inputs, Sterner said. For instance, it’s not practical to cut phosphorus low enough to control hypoxia in the Gulf of Mexico, because there is so much phosphorus coming off the land and moving in to the gulf through exchange with the open ocean. “Whereas if nitrogen is controlling productivity now, nitrogen limits could have an immediate effect,” he said.

“My reading of the best science is that you need to manage both nitrogen and phosphorus for marine and nearshore marine ecosystems,” Sterner said. For oligotrophic freshwater lakes, phosphorus limits are the way to ensure a healthy ecosystem over a multiyear time scale.

“But we don’t know if there is cost-effective additional control through cutting both nitrogen and phosphorus for highly eutrophic freshwater lakes,” Sterner said. Theoretically, those systems could be co-limited by nitrogen and phosphorus. “I would not want to say that a sole focus on phosphorus is always the best strategy in all lakes,” he said. But if managers opt for dual nutrient control for freshwaters, they need to be very careful, because there is always a risk that declines in nitrogen concentrations could favor dominance by toxic nitrogen-fixers, he said.

Janet Pelley, WE&T


From roof, to reuse, to land

An organic farming institute incorporates stormwater and wetlands wastewater treatment in its new restroom facility

When the staff at the Rodale Institute (Kutztown, Pa.), an organization dedicated to promoting organic farming through research and outreach, decided to build a new restroom facility for the institute’s visitor center, they could have used a traditional septic system.

“It would have been easy,” said Jeff Moyer, farm manager at the institute. “We wouldn’t have had to go to the Pennsylvania [Department of Environmental Protection (DEP)] for help.”

But Moyer said the staff wanted to stretch itself, so it approached DEP and obtained a $695,000 grant from the U.S. Environmental Protection Agency to do something unique and novel at the restroom facility that would attract attention to the project.

Staff members explored different technologies, including greenhouses and biospheres but ultimately reined in their ideas.

“We thought that if we went too far out with biosystems and biospheres, people would look at it and say, ‘That’s really cool, but I don’t want that for myself,’” Moyer said. He said they wanted something more practical that people would consider installing in their own homes or communities.

The staff, with the aid of DEP and other consultants, finally decided to go with a 3-m3/d (800-gal/d) waste-
water treatment system that incorporates stormwater treatment, wetlands, and irrigation.

As Moyer describes it, stormwater is collected on the roof of the roughly 90-m2 (1000-ft2) restroom facility and then flows to an underground cistern. Nonpotable water is used in the facility’s toilets. Potable water is brought in through traditional means to be used in the facility’s sinks.

“There was an assumption that people would drink from the sinks, so the water had to be potable,” Moyer explained.

Wastewater leaves the facility and goes to a settling tank for solids removal. The facility also has a flow equalization tank to accommodate the daily and seasonal fluctuations that can occur at a visitor’s center. The effluent then flows to nearby wetlands, where Escherichia coli and nitrates are removed, Moyer said.

“The water that leaves the wetlands and is filtered there is of stream-discharge quality,” Moyer said.

 Next, the effluent goes to a shallow drip-irrigation system on the institute’s property that will be used to water plants native to the region, as well as a vegetable garden.

The grand opening is scheduled for June. Moyer said that so far, the system has been mostly maintenance-free.

“The biggest problem that we have seen is the fats, oils, and greases in the wetlands,” Moyer said. “They don’t easily biodegrade.”

But Moyer does not foresee that being a major issue in the system. “Our particular system will not have very much of these materials entering the wetlands, since it is mainly treating waste from visitors who are simply using the toilet facilities,” he said. “There will be very little, if any, cooking taking place.”

Moyer said the project also has a research component. The institute is tracking pH levels in the wastewater, total dissolved solids, nitrate–nitrogen, alkalinity, phosphorus, sulfate, hardness, and E. coli. Because the vegetable garden is watered by the drip-irrigation system using treated wastewater from the wetlands, the vegetables grown there also are being monitored.

“Depending on what we find — and we suspect nothing harmful — we’ll treat the vegetables just like anything else we produce here on the farm, in that we’ll sell them at the visitor center or through any one of our other channels,” Moyer said.

Moyer said he hopes the project “has the ability to change how people see wastewater. We’re convinced this system will become the Rolls-Royce of wastewater treatment. It will be very easy and economical to install and run.”

Moyer said that the system is scalable. “You can use it in a single-family home or in a small development or in a commercial building.” But he admitted that the staff does not know how the system would handle wastewater with high concentrations of heavy metals. Therefore, they are wary of recommending it to municipalities that have multiple industrial dischargers.


— LaShell Stratton-Childers , WE&T


©2011 Water Environment Federation. All rights reserved.