A typical urine-diverting toilet collects solid and liquid waste, which could be processed into fertilizer, removing nitrogen from the waste stream

Considering that we all flush at least three times a day, it’s surprising how little we know about where our waste goes. Into a white bowl and then down a pipe— never to be seen, smelled, or thought of again.

But as many Cape Codders are beginning to realize, that’s not really the case. The by-products of our waste are seeping out of underground septic systems and into the groundwater, flowing finally into coastal ponds. The nutrients are harmless by themselves, but in concentrated form, throw off the ecological balance of sensitive estuarine systems.

Though there are many nutrients and “contaminants of concern” to be worried about, nitrogen is known as the culprit for changing pristine harbors into algae-filled swamps, devoid of marine life. Or so we fear.

Last night, Falmouth selectmen approved a town-wide comprehensive wastewater management plan (CWMP), developed over the course of several months last year by a panel of community members. It calls for over $300 million to install a sewer system in the neighborhoods south of Route 28 from Little Pond to Seapit Peninsula. Millions more are expected to sewer the next phases north of Route 28.

The CWMP committee and selectmen also set aside funding for the study of alternatives to sewering, which could lower the overall cost of the plan.

Several of these options were covered in a forum held earlier this month at the Waquoit Bay National Estuarine Research Reserve (WBNERR), in which four experts in various areas of wastewater treatment delivered “The Scoop on the Poop” from the perspective of traditional sewer systems, alternative systems, shellfish aquaculture, and coastal engineering.

It’s not as complicated as it sounds. In fact, it should be taught in grade schools.

The big pipe method

Falmouth's wastewater treatment plant on Blacksmith Shop Road is one of just five such facilities on Cape Cod

Michael Giggey, the senior vice president of Wright-Pierce, an engineering and consulting firm, started off the evening with an overview of the municipal treatment options, from individual “on-site” systems to cluster and satellite systems to centralized wastewater treatment facilities.

As an advisor to the Town of Orleans on its comprehensive wastewater management plan and an islandwide wastewater plan on Martha’s Vineyard, Mr. Giggey noted that each watershed has different needs, which can be met through a combination of technologies.

The simplest option, he pointed out, is to simply eliminate the main controllable source of nitrogen pollution by removing enough septic tanks to meet the TMDL and connecting those homes to a sewer system, discharging the treated effluent outside the watershed.

However, across the Cape, that strategy has proven to not be so simple, and certainly is not cheap.

In Falmouth alone, the cost of sewering homes south of Route 28 from Little Pond to Seapit Peninsula is expected to cost $310 million for the first two phases, to be paid for by a combination of taxes and homeowner betterments. Across the Cape and Islands, these figures add up to billions.

In a report compiled last April by the Barnstable County Wastewater Cost Task Force, the study found the most important factor when choosing a wastewater treatment strategy is the amount of nitrogen that each system can remove per dollar spent. Centralized wastewater treatment facilities can reduce nitrogen down to 3 milligrams per liter, whereas effluent from on-site denitrifying systems ranges from 10 to 19 mg/L, Mr. Giggey said.

Though sewer mains and wastewater treatment facilities require a large amount of capital up front, the task force found that operation and maintenance costs for a centralized sewer system were far lower than on-site denitrifying systems, cluster, or satellite systems.

“It’s not just about cost, but cost-effectiveness,” said Mr. Giggey, who served on the task force. “It would seem the most cost-effective option is with the larger systems.”

David Dow, president of the Cape and Islands chapter of the Sierra Club, asked Mr. Giggey whether wastewater managers on Cape Cod have had any experience with removing “contaminants of concern” from effluent. These chemicals are the byproducts of pharmaceuticals, personal care products, and detergents that most wastewater systems do not treat, or even monitor.

“Unfortunately, there’s not a lot of local experience. We’re just now getting our arms around what nitrogen does. Contaminants of concern are not just one compound, it’s thousands,” Mr. Giggey said.

Innovative & Alternative systems

The British-designed "Loowatt" toilet was originally built with the waste disposal needs of developing countries in mind.

Also serving on the task force was panelist George Heufelder, director of the Barnstable County Department of Health and the Environment, who established the Massachusetts Alternative Septic System Test Center at the Massachusetts Military Reservation in 1999.

Mr. Heufelder noted that every wastewater treatment option works on basically the same principle: to “manipulate the nitrogen cycle inside a black box.” Though some methods are more efficient than others, the basic idea is to break down nitrates into nitrogen gas, a major component of the air we breathe.

In over a decade of testing, Mr. Heufelder found that innovative and alternative (I/A) systems “remove about 50 percent of the nitrogen 70 percent of the time.”

Emerging membrane technologies, such as the Nitrex, is capable of removing 90 percent of nitrogen from groundwater. The Nitrex, which Mr. Heufelder referred to as “a box of proprietary cellulose material, otherwise known as wood chips,” and other membrane systems are also becoming cheaper and easier to maintain.

A composting toilet: the only difference is the pipe

Another affordable and effective option for individual homeowners is the composting toilet, which Mr. Heufelder noted has an added benefit of separating toilet waste from graywater—the shower, sink, and dishwasher water that usually goes down the drain.

In an earlier comment from North Falmouth resident Alison Robb about the need to keep drinking water from becoming wastewater, Mr. Heufeulder agreed that the tradition of defecating into potable water “is lunacy, but we do it.”

However, he said it would probably require “mass hypnosis” to get every resident to install a composting toilet and never put kitchen scraps or chemicals down the drain. Even if Town Meeting members bought into composting toilets as a nitrogen management strategy, the Department of Environmental Protection would need a way to ensure its regulations were being met, he said.

“It’s trust and verify. Not everyone’s composting nicely in the back yard. There will be some nitrogen [in the system], and we need to know what it is,” said Mr. Heufelder.

The Eco-flush urine diverting toilet can remove 90% of the nitrogen from human waste, using 80% less water than a traditional toilet

Another innovative home nitrogen removal method on the market is the urine-diverting toilet, which was on display at WBNERR, thanks to Conrad Geyser, president of Cotuit Solar.

Though Mr. Heufelder admitted that he and other men might have a problem sitting down to use the toilet, he said one day the market for phosphorus and nitrogen would put a premium on mankind’s most abundant waste product.

Because urine contains up to 90 percent of the nitrogen and 50 percent of the phosphorus in domestic wastewater, separating and collecting it is also a simple way to prevent nutrients from reaching the groundwater.

“I envision a day when someone comes to your door to write you a check for good-quality urine,” Mr. Heufelder said, estimating that there is a total of 150 more years of phosphorus left in traditional mines.

Mr. Heufelder noted that membrane systems can be “a little power hungry,” using five to eight kilowatt hours per day in a typical home. However, the Nitrex makes use of a trickling system with lower energy use, he said.

There are other costs associated with on-site systems that should be factored into their overall costs, said Mr. Heufelder, estimating that one full-time employee would be required for every 1,500 on-site systems to ensure they meet environmental standards.

Furthermore, homeowners are required by regulations to have a maintenance contract for their on-site system, and any residual waste would have to be disposed or converted into fertilizer by a private company, he said.

“I cannot imagine DEP allowing composting or urine-diverting toilets unless the residuals leave the watershed completely,” he said.

The shellfish solution

The Sippewissett oyster, a product of local aquaculture efforts

While town officials and residents tend to focus on technical solutions for wastewater treatment, local scientists are turning to Mother Nature to help reduce the nitrogen load.

Diane Murphy, an aquaculture and fisheries specialist for the WHOI Sea Grant and Cape Cod Cooperative Extension, gave an overview of the potential for shellfish aquaculture to remove nitrogen from sensitive coastal embayments.

While shellfish are becoming more accepted as a method for meeting total maximum nitrogen loads (TMDLs), Ms. Murphy emphasized that aquaculture should not be considered the only solution for reducing nitrogen loads.

“Oysters can serve a crucial role in the uptake of nitrogen. Aquaculture should not be the sole source, but should be integrated into a nitrogen management plan,” she said.

Acting as grazers on the sea floor, oysters and other shellfish consume the phytoplankton that tend to grow in the presence of elevated nitrogen levels. The more food there is, the more the oysters grow.

Though there are conflicting reports on how much water oysters are capable of filtering each day, the accepted number is about 20 gallons per day, Ms. Murphy said. Studies have found that a market-size oyster can sequester an average of 0.52 grams of nitrogen and 0.16 grams of phosphorus over its lifetime.

When harvested, all that nitrogen is removed from the ecosystem “free of charge,” she said.

Based on a study of the 2006 oyster harvest in Wellfleet, Ms. Murphy said that 20,000 bushels of oysters can assimilate 282 kilograms of nitrogen. The oyster feces become buried in the sediment, stimulating denitrifying bacteria, a process that results in nitrogen gas being released to the atmosphere. In Wellfleet that year the total nitrogen removed was 2.3 tons.

Even though oysters are good to eat, Ms. Murphy does not advocate turning every coastal pond into an aquaculture site, noting the impact on recreational users’ access to and enjoyment of the water.

A large-scale oyster aquaculture project could clean up Falmouth's coastal ponds, create jobs and increase local food production

About 2.5 million oysters would be needed to filter all the water in Waquoit Bay, Ms. Murphy said, requiring about 10,000 square meters, or about 2.5 acres, for all of the gear.

According to an estimate by Woods Hole resident and aquaculture consultant Ron Zweig, many more oysters may be necessary to adequately filter the water, covering up to 30 acres of the 825-acre bay.

The ecosystem also has a certain “carrying capacity” for aquaculture production, and even oysters have their limits before disease, predation, and lack of food inhibit their growth, she said. Because each estuary is different, she recommended a feasibility study to determine how extensive an aquaculture operation the ecosystem is capable of supporting.

Mashpee Shellfish Constable Rick York. said that conditions in the estuary also determine the type of shellfish most suitable for aquaculture. In the low salinity of the Mashpee River, he had great success in growing half a million oysters without fear of predation or disease. Since 2005, the oysters have removed over a ton of nitrogen, he said, which increased the dissolved oxygen content to the point of being safe again for fish.

However, he said the Mashpee River is unique, and in other areas he would recommend seeding quahogs instead of oysters.

“I take issue with oysters having the most potential,” he said. “Quahogs don’t filter as much water, but they consume as much nutrient.”

Flushing the bays

Another strategy to decrease the impacts of nitrogen in sensitive embayments is to increase the amount of “flushing,” or exchange, between the ocean and the estuary.

Nitrogen concentration is higher at the head of coastal ponds, but becomes diluted in areas of greater flushing

The adage, “the solution to pollution is dilution” rings true in this case, said John Ramsey, a senior coastal engineer at Applied Coastal Research and Engineering, a Mashpee firm.

If the tidal conditions are right, nitrogen concentrations can be decreased to acceptable levels, even if the load remains high, he said. Since people tend to live near the water, the nitrogen load at the head of the bay tends to be higher than that near the tidewater.

Due to coastal geology, estuary inlets tend to become filled with sand, or even become blocked by the formation of barrier beaches, he said, showing slides of such events. Unless the inlets are dredged, flushing will decrease over time, Mr. Ramsey said.

Even if the inlets are maintained, all tides are not created equal. While Cape Cod Bay has a 13-foot tide, Vineyard Sound only has a 1.5-foot fluctuation, and Buzzards Bay tides are about 4.5 feet.

“The size of the pump matters,” Mr. Ramsey said. Some towns, he said, “are at a huge disadvantage for tidal flushing.”

Green Pond, Bournes Pond, and Eel Pond in East Falmouth

In Falmouth, Bournes Pond has been cited as one area that does get a generous amount of flushing activity. Mr. Ramsey said if the inlet could be widened from 50 to 100 feet, the coastal pond’s nitrogen concentration would be reduced from 0.6 milligrams per liter to 0.46 mg/L. That reduction would mean that half as many homes in the Bournes Pond watershed would have to be connected to a sewer, he said.

Although on paper widening the inlet seems like a win-win solution, wetland protection regulations place restrictions on projects of this kind because of the impacts on barrier beaches, which protect coastal zones from storms and flooding and provide habitat for endangered species, said Mr. Ramsey.

“Widening the Bournes Pond inlet will create a bigger footprint of impact on the barrier beach system. It’s something regulators will struggle with,” he said.