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By Bob Feinbaum
Onsite systems serve more than a quarter of the nation’s residences. But most Americans are still hooked up to sewer systems, and most wastewater is sent to large treatment plants for ultimate disposal. Municipalities have invested hundreds of billions of dollars in infrastructure and spend hundreds of millions more each year to keep their systems running. In light of the imbalance in the scale of services, onsite professionals sometimes see themselves as junior partners in dealing with the nation’s wastewater.
But, not so fast. New developments are sweeping the wastewater world. Cities are being forced to deal with stormwater, and that has led officials to question the wisdom of expanding treatment plants to deal with peak runoff. Many areas of the nation facing water shortages are starting to recycle wastewater for various applications. Recycling projects involve treating wastewater beyond secondary levels and then distributing it back to users through a network of specially marked pipes. But this process often costs more than the “worth” of the recycled water, and some urban areas are looking for new ways to treat and reuse wastewater closer to its point of origin.
Both trends auger well for introduction of decentralization as practiced in the onsite world into metropolitan areas dominated by big pipes and centralized wastewater treatment.
Graywater
Individual graywater systems are by definition a decentralized approach to wastewater treatment. In the late 1980s, a prolonged drought led California communities to severely ration water. Residents resorted to informal use of water from sinks, showers and clothes washers to keep gardens alive. In 1993, regulations were developed to allow the legal use of this so-called graywater. Health officials insisted that water not be allowed to surface and that sufficient area be set aside to absorb all the projected graywater. In effect, urban residents were encouraged to put in mini-leachfields.
Few graywater systems have actually been installed in existing California homes during the past decade. Overly strict regulations make the cost prohibitive for all but the most environmentally conscious homeowners. However, graywater is making headway in new construction where it is possible to install dual piping at relatively modest cost. Some southern California communities even reduce sewer connection fees for builders who install graywater systems.
It all makes good sense. As Dick Bennett, director of conservation for the East Bay Municipal Utility District wrote shortly after the California regulations went into effect, graywater systems provide an assured source of water for landscape irrigation—a source that is especially valuable during dry years. They reduce the use of fertilizer and create healthier landscapes. Of particular importance to wastewater utilities, graywater reuse lessens the load on treatment plants, thereby reducing the need to expand capacity.
Stormwater
New federal regulations are forcing communities to deal with pollution carried by stormwater. Rainfall washes off the detritus that typically accumulates on urban streets (oil, paper, dirt, and other, nastier substances) and makes its way to water bodies. Runoff can sometimes overwhelm treatment plants, forcing them to discharge partially treated sewage. Communities throughout the nation face serious challenges in handling stormwater within their regular wastewater operations.
The big-pipe solution would expand treatment plants to handle combined flows and build storm sewers to carry runoff to those plants.
But some communities are looking to a decentralized approach, which they expect will lead to more effective treatment at a lower cost. The Irvine Water District in Orange County plans to create as many as 37 wetlands—ranging in size from 2 to 20 acres—to filter stormwater before it reaches San Diego Creek. The $30 million project will reduce runoff and pollution flowing from the creek into the Pacific Ocean. District officials estimate that the cost to build the chain of wetlands will be significantly less than it would be to redesign the sewer system to accommodate increasing runoff from the fast-growing Irvine area.
Breaking Up Is Hard to Do
In most urban areas, wastewater typically flows through collector sewers and then into large sewer mains on its way to the treatment plant, while stormwater drains take runoff to its ultimate destination. Some communities are short-circuiting the process and starting to treat a portion of the flows locally, thereby reducing the load on main treatment plants and allowing water to be used nearer to its source. Two pioneers of this approach are the city of Santa Monica in the Los Angeles metropolitan area, and Olympia, the capital of the state of Washington.
Santa Monica’s Urban Runoff Recycling Facility (SMURRF) can take up to 500,000 gallons per day from storm drains that capture runoff from 5,000 acres of land within the city and the nearby Santa Monica mountains. The $12 million facility treats incoming runoff to levels consistent with California’s Title 22 requirements and then ships it out for landscape irrigation and for dual plumbing systems that serve the city’s public safety facility and the Water Garden. In addition to providing a steady source of water for city parks and freeway medians, the SMURRF is expected to help reduce pollution entering Santa Monica Bay.
Olympia’s Hawks Prairie Water Reclamation Plant intercepts wastewater from regional sewer lines and treats it with advanced technology so that it can be reused in the local community mainly for recharging groundwater and irrigation. Its sponsors say that the satellite plant will save hundreds of millions of gallons of potable water annually. In fact two more are on the drawing board using the same membrane bioreactor technology that allows the reclaimed water to meet Washington state’s highest reclaimed water standards.
These examples show that highly urban areas may be able to decentralize at least part of their wastewater and stormwater systems and thereby avoid some of the expense of long distribution pipe runs and associated pumping costs from a centralized treatment plant.
Integrated Planning
The newest buzzword in water circles is integrated planning. Agencies that deal with water supply, wastewater treatment and flood control come together to develop a strategy, and from that identify projects for making more efficient use of water resources. Ideally the whole process starts with a water balance, identifying the sources of water and the uses to which it will be put in the agencies’ service areas. Most integrated planning, though, seems focused on the regional level. Extending the process to local communities within the metro region promises to lead to projects that better serve local needs—and, over time, supplement the big-pipe system with a more decentralized approach.
Clearly big pipes are not going away anytime soon, but if the logic of decentralization starts to percolate into metro regions, benefits may be substantial and the costs far lower than mending, extending, and upgrading existing infrastructure. Individual graywater systems, natural ways to treat stormwater runoff, relatively small-scale interceptor plants, and fine-grain integrated planning can all contribute to better use of precious water resources.
BOB FEINBAUM is director of Hydro Nova, a nonprofit dedicated to improved technology for wastewater treatment and sensible regulation of onsite systems.
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- July/August 2006 |
