High levels of nitrogen and phosphorous are creating enough phytoplankton to destabilize the entire food chain in the Chesapeake Bay.
By Fernando Pages Ruiz
Read the label on a bag of fertilizer, and you’ll see two main ingredients: nitrogen and phosphorus. You’ll find these natural nutrients, essential to life, present in healthy ecosystems on land or water. Phosphorous helps plants convert sunlight into energy, and nitrogen is essential to the production of plant and animal tissue. So when you consider that private sewage disposal systems have contributed significant nitrogen and phosphorous to our nation’s waterways, you may ask, “So what?”
Well, too much of a good thing can create an unhealthy balance known as nutrient pollution, and that’s exactly what’s happened off the coast of Maryland in the Chesapeake Bay. Back when the environment existed in pristine condition, forest and wetland surrounded the shoreline. Woodlands, grasses and brush absorbed the vital nutrients, and very little nitrogen washed from the land into the saltwater. As urbanization increased, green fields were replaced by rooftops, pavement and sewage treatment plants, all of which now contribute to sharply increased levels of waterborne nutrients entering the bay.
The added phosphorus and especially nitrogen cause rapid growth in microscopic vegetation known as phytoplankton. Although too small to see with the naked eye, in large numbers they appear as a green coloration in the water. As the floating organisms, including blooming algae, becoming dense, they block light from deep water vegetation, killing underwater grasses and plants. The downward spiral continues with bacterial growth spawned by decomposing foliage depleting oxygen; fish and other air-breathing species die. It’s all bad news for North America’s largest and most biologically diverse estuary.
With 3,000 species of plants, fish and animals, the bay and its tributaries have sustained a region of 16 million people for three centuries. In 2004, Maryland’s Gov. Robert L. Ehrlich Jr. signed into law the Bay Restoration Fund. The law puts teeth into Maryland’s effort to eliminate its share of the nitrogen and phosphorous loading of the Chesapeake Bay by offering financial incentives. For landowners, this means planting cover crops such as rye, wheat and barley that hoard nutrients at the root level. For municipalities, it means installing high-technology purification systems at sewage plants. And for homeowners, it means upgrading private disposal systems from conventional, nitrogen-producing septic systems to advanced aerobic treatments that not only reduce nitrogen discharge by at least 50 percent or better, but can (the Bay Restoration fund is not being used to reduce drainfield size requirements) also reduce the area required for a drainage field and even save a failing system.
Why souping up theseptic tank matters
With more than 420,000 on-site sewage disposal systems (OSDSs) in Maryland, many located along the shoreline, the effort to upgrade existing and new systems to the best available technology for nitrogen removal has become a state priority. While agriculture and municipal sewage plants have already made considerable improvements since 2004, the move among homeowners has only just begun. The Bay Restoration Fund, which was signed in to law May 26, 2004, requires all users of onsite sewer disposal systems (OSDS), commonly referred to as septic systems, to pay a $30 annual fee. With priority given to failing septic systems in Critical Areas, funds can be provided for upgrades of existing systems to best available technology (BAT) for nitrogen removal or for the marginal cost of using BAT instead of conventional technology.
Although compliance remains voluntary, homeowners may want to upgrade septic systems for reasons beyond bay ecology. The new advanced aerobic sewage treatment methods improve the performance and longevity of all applications. “Aerobically treated effluent looks so clean that it looks and smells like (although it may not taste like) bottled water,” says Nancy Mayer, president of Mayer Brothers Inc., a precast manufacturer in Elkridge, Md. “If you have a drainage field that’s failing, an aerobic treatment tank can rehabilitate that field,” she says.
Mayer’s precast company produces high-quality septic tanks and now offers several Advanced Treatment Units (ATVs) that comply with Maryland’s definition of Best Available Technology (BAT). From the outside the tanks look like conventional septic tanks, manufactured with 4-inch thick 4,500 psi concrete. But the tanks are shaped and configured to receive third-party aeration systems. These vary in detail by maker but work on the same principles.
Injecting air encourages effluent-cleaning decomposition
In a conventional system, sewage flows by gravity into a watertight septic tank. In this primary treatment phase, solids settle to the bottom of the tank, and organic matter is partially consumed by anaerobic bacteria. Some tanks have one chamber, and most have two, where the anaerobic process continues until the effluent is discharged into a drain field, pit or lagoon and from there filters into the soil. Aerobic bacteria finish the job, however, copious amounts of nitrogen percolate into the soil and eventually leach into the bay. “Conventional septic systems do a great job of treating and disposing of sewage,” says John Boris, project manager for the Maryland Department of the Environment. “They just weren’t designed to remove nitrogen.”
While there are a variety of designs for aerobic systems (six of which had been reviewed so far by the EPA) and several applications are pending, all advanced treatment methods have three common features: a pretreatment chamber to settle solids and decompose the sewage anaerobically (just like a conventional system); an aeration chamber where oxygen is pumped into the wastewater; and a clarification chamber where the clear, odorless effluent rises before being released into the soil.
The heart of the system comes in the second phase, where air pumped into and circulated in the tank sustains aerobic (oxygen-consuming) bacteria. “It’s a little like a fish tank bubbler,” says Boris. By maintaining high oxygen content in the fluid, large organic molecules are more thoroughly broken into smaller molecules and eventually carbon dioxide and water. In Maryland’s Anne Arundel County, researchers at the National Association of Homebuilders Research Center found that one innovative nitrogen-reducing system installed at a residential field site averaged an 80 percent reduction in total nitrogen. This represents a significant success in the Chesapeake Bay area, where strict county and state legislation designates land within 1,000 feet of fragile tidal waters for special protection.
Oxygen must be present before the effluent decants in a third chamber, where anaerobic bacteria finish the process by turning the liquid nitrogen into a harmless gas, says Boris. The now nitrogen-free (and crystal-clear) effluent is discharged into the ground. This highly treated oxygenated effluent seeps into the soil and does not produce the anaerobic mucous that typically clogs failing leach fields.
Despite all the benefits, some people balk at the idea of installing an advanced treatment system because of the added cost and maintenance requirements. “It’s not a flush-and-forget-it-until-it-fails proposition,” says Boris, who advocates the systems, adding that the Maryland Department of the Environment hopes to encourage new installations by helping to defray the cost. The pumps require electrical wiring, and the more sophisticated technology must be maintained about every six months to assure optimal operation. However, advanced sewage treatment systems installed within durable, precast concrete tanks serve to clean up Maryland’s most precious natural resource and, if properly maintained, will assure virtually failure-free operation. Planned, periodic maintenance, explains Boris, will help prevent an unplanned system failure.
Mayer’s company has installed about 40 aerobic disposal systems so far and expects the number to grow to 200 units each year as state funding begins to accelerate. “Some counties have not used these systems in the past, or used them very sparingly, so the funding is a big boost,” says Mayer.
One county will piggyback on the initiative and start to require aerobic treatment on all new construction in critical areas. Kurt Cassell, manager for Fogles Septic in Sykesville, Md., has installed about 100 aerobic systems over the past few years, but he expects this number to increase dramatically. “The aerobic systems do such a good job, there’s really very little waste in the effluent,” he says. “You don’t need so much land for percolation.” Other than the treatment mechanism, the systems are not much different to install. According to Cassell, “The precast tanks are the most durable and user-friendly tanks available. The aerobic system just slides in on mounts in the tank and the piping is no different. It’s easy, and it’s definitely the wave of the future.”