Over the last half-century, modern-day designers and engineers have moved away from the traditional sewer and manhole infrastructure of the past 200 years toward smaller, onsite, clustered, decentralized wastewater treatment systems.
By Mark Saunders
The question about what to do with our waste has been an issue ever since the end of the last Ice Age, when early humans shifted from hunter-gatherer to agriculture-based societies. As people abandoned their nomadic traditions in exchange for a more predictable future, they were more or less forced to deal with the issue of what do with what we leave behind.
The diseases and the insects (not to mention the stench) associated with raw sewage in temperate latitudes drove ancient Mediterranean civil engineers to design—and early sanitation workers (undoubtedly slaves) to build—massive stone drainage systems that took human waste—once thrown out into the street—to the nearest river, lake, or ocean inlet.
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Photo: Natural Systems International |
| A septic system disguised by reeds |
The pull of the Industrial Revolution in Europe and North America (coupled with the promise of new life without tilling the soil from sunup to sundown in the summer months and going without in the winter) drew millions of workers across states, countries, and even continents. This dramatic migration of humanity to urban centers across the Northern Hemisphere necessitated a system of removing sewage by the most expedient and effective means possible.
According to the late Peter Casey of the National Small Flows Clearinghouse, the greatest health benefits of the 20th century were brought about by the purification of drinking water and the treatment of wastewater. These two changes increased life expectancies and had a tremendous effect on human health and survival.
Over the last half-century, however, economics, demographics, technology, and a clearer understanding of costs and benefits of various wastewater management techniques are pointing modern-day designers and engineers away from the traditional sewer-and-manhole infrastructure of the past 200 years (based on the ancient traditions mentioned above) toward smaller, onsite, clustered, decentralized systems that leave much smaller footprints. The question remains, though: What will it take for us to heed the call of wastewater pundits like Richard Pinkham, Valerie Nelson, Ed Clerico, David Orr, and Andy Lipkis to change the paradigm of how we as communities, cities, states, regions, and a nation deal with the age-old problem of what to do with our waste?
The evolution of new treatment systems allows for filtration and disinfection that can break down nitrogen and ammonia, reduce fecal coliforms to 20 counts per 100 milliliter, and drop biological oxygen demand and total suspended solids to well below 10 milligrams per liter has allowed for a expansive growth in the onsite, clustered wastewater treatment industry—wastewater that was previously sent to a large central processing plant. Instead of building extensive sewer systems (which work on the same basic principle as the ancient Greek and Roman gravity systems) and massive traditional wastewater treatment facilities (which can cost hundreds of millions of dollars to build and maintain and are underutilized because they are typically designed for “build-out” populations that are often decades away), innovative couplings of natural systems with new technological advances can now clean, polish, and sanitize wastewater and offer a virtually limitless supply of reprocessed water for use in irrigation systems, flush toilets, and cooling towers—even laundries.
The First Wave
The 1977 amendments to the 1972 Clean Water Act required communities to examine or consider alternatives to conventional systems and provided a financial set-aside for such treatment systems to be built. In 1997, the EPA wrote Response to Congress on the Use of Decentralized Wastewater Treatment Systems, which brought to life the Clean Water Act’s pledge to provide funding for publicly owned treatment works and the goal of restoring our lakes and streams. Response to Congress also opened the door for decentralized systems to become a permanent part of the wastewater infrastructure.
In the executive summary of its 1997 document, the EPA outlines the pluses and minuses of onsite, clustered, decentralized wastewater treatment options. In addition, the writers of this report state: “Properly managed decentralized wastewater systems can provide the treatment necessary to protect public health and meet water-quality standards, just as well as centralized systems … [T]hese systems can help promote better watershed management by avoiding the potentially large transfers of water from one watershed to another that can occur with centralized systems.”
Some of the many benefits of decentralized wastewater management cited in the report were the protection of public health and the environment, its appropriateness for low-density communities and varying site conditions, and the fact that these systems were well suited for ecologically sensitive areas, as well as costing significantly less while providing communities with the opportunity to recharge local aquifers.
At the National Onsite Water Recycling Association’s (NOWRA’s) March 2007 Water For All Life convention in Baltimore, a roster for who’s who in the onsite wastewater management industry signed “The Baltimore Charter,” which expanded the EPA’s 1997 list of benefits to onsite, decentralized wastewater management to include lowering the costs for water supply; lowering the costs of maintaining existing infrastructure; lowering costs of new infrastructures; lowering energy costs; increasing resilience to accidents, natural disasters, and terrorism; restoring the ecology of areas damaged by pollution and replenishing aquifers; restoring the efficiencies of nutrients in local landscapes and agriculture; ensuring such community benefits as improved air quality, preserved open spaces, creation of new jobs, and private (alternative) financing; and encouraging international competitiveness in high-tech research, manufacturing, and engineering.
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Photo: Mark Saunders |
| This water cooling tower combines treatment and architecture. |
With all these advantages and benefits to onsite, decentralized wastewater-management systems, it is difficult to understand why these types of innovations haven’t been put into place nationwide. Valerie Nelson, director of the Coalition for Alternative Wastewater Treatment, sees the current lack of availability of decentralized systems as a dearth of infrastructures and innovation. “This whole decentralized, closed-loop approach is not all that compatible with utility systems we have in this country,” she says. So we’re going to have to look to developers and individual home and commercial building owners to lead the way. Who will design it? Who will finance it? Who will install it? And who will maintain it?”
The 1997 EPA report also lists five key barriers of implementation (lack of knowledge and public misperception, legislative and regulatory constraints, lack of management programs, liability and engineering fees, and financial barriers) and how to overcome each of them. In 2007, Carl Etnier, Richard Pinkham, Ronald D. Scott Johnstone, Mary Clark, and Amy Macrellis reframed these questions in their paper, Overcoming Barriers To Evalution and Use of Decentralized Wastewater Technologies and Management. Through literature reviews and interviews, the authors whittled these barriers down to four significant categories: lack of systematic thinking applied to wastewater issues, unfavorability of the regulatory system for decentralized systems, engineer’s lack of knowledge of decentralized systems, and lack of financial reward for engineers using centralized systems.
Etnier and the rest went on to say that decentralized systems allow actual growth and demand to be more closely matched, which would delay unnecessary major capital expenditures by communities and municipalities. Decentralized options also provide communities with growth options instead of “inducing” growth down long sewer corridors.
So for every barrier of entry, there is a shining example of how it can be overcome by technical innovation, financial incentives, and entrepreneurial spirit. Regardless of whom it is you listen to, the value of onsite, clustered wastewater systems is becoming abundantly clear, and the potential for growth in the decentralized wastewater treatment and management markets is wide open in virtually any direction. What follows is a closer look at five interesting applications of leading-edge wastewater treatment.
Capital Incentives
The acceptance curve for decentralized wastewater systems and practices is much the same as the early adoption of solar energy and the use of hybrid automobiles. In the case of alternative energy and alternative transportation, early users get involved for a variety of reasons—mostly environmental and financial. The environmental concerns are typically heartfelt and generally fall into the “doing the right thing” category. Most early adopters are not deluded enough to believe that they are single-handedly saving the world; more likely they are part of a trend pointing in the right direction. The financial incentives in terms of rebates, tax benefits, or bill reductions from the developer, manufacturer, or supplier are usually what close the deal.
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Photo: Mark Saunders |
| The Solaire green roof provides a reduction of the building’s wastewater. |
Nelson categorizes early adopters in one of three ways: individual home wastewater systems with installation and management by small, private companies (Natural Systems Inc.); cluster wastewater/reuse systems with corporate/utility management (The Solaire); and urban stormwater retention with public and civic management (which are beyond the scope of this article).
Even though solar-generated power supplies electricity for less than 1% of all homes in the United States with power, the number of solar-powered homes has grown steadily for the last 20 years. According to SolarBuzz, solar electric energy demand has continued to rise 20% to 25% per year. Globally, the photovoltaic solar industry now generates $10 billion in annual revenues.
Likewise, new communities with decentralized wastewater systems are starting to pop up all over the country. According to the EPA’s Guidelines for Management of Onsite/Decentralized Wastewater Systems, “Onsite/decentralized wastewater systems serve 25% of the US population and 40% of new developments.” For many developers, what started as a way to get around the cost of connecting to the nearest sewer system has blossomed into the kind of attractive value-added feature that homeowners brag about to co-workers at a Sunday barbecue.
In the case of hybrid cars, the fuel savings from a hybrid vehicle that gets 50 miles to the gallon compared to a 30-mile-per-gallon gasoline-powered car probably won’t make up for the additional price of a hybrid over the life of the vehicle—unless fuel becomes extremely expensive or the car lasts 20 years. However, factoring in federal, state, and local tax incentives more than makes up for the price differential.
In 2004, the City of New York created an operating incentive for buildings that were using graywater and stormwater collection systems that amounted to a 25% reduction in the water and sewer bills. Obviously, every building in New York City that reduces water consumption and sewage output help save the city from building new water projects (dams, aqueducts, and water treatment facilities) as well as new sewage treatment plants and installing millions of feet of sewer main and other pipe. So every adoption of new technology that reduces consumption of potable water, decreases wastewater output, and capitalizes on stormwater runoff saves municipalities millions in new infrastructure costs and the maintenance of existing systems.
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Photo: Greg Newington |
| Wastewater treatment can be fairly inconspicuous. |
In The Solaire’s case, with approximately 50% of its water budget coming from recycled water (which costs a great deal more to produce than water that comes straight from the city), the economics even with the 25% reduction in water and sewer charges do not cover the cost of implementing this kind of technology unless you are saving very large volumes of water.
“Your economics only play favorably if you have a large enough scale, because there’s an economy-of-scale issue here,” says Ed Clerico, water resource engineer for The Solaire at Battery Park in New York City. “If you’re very small, and by that I mean 10,000 gallons a day, the economics are at their worst. If you get up into the couple-hundred-thousand-gallons-a-day range—say, you have five or 10 buildings interconnected—then the economics work right from day one.”
According to Clerico, if the city were to work together with developers on the conversion of blocks or entire neighborhoods to water-reuse systems (both sewer and stormwater), developers would find it much easier to hit that economic sweet spot.
In an attempt to find a more favorable solution for developers who are interested in decentralized solutions, Clerico and company entered into an extended conversation with the City of New York about how to entice developers. According to Clerico, one aspect of the problem is that developers, who often do not see the rewards of lowered operating costs, are paying for these innovative systems out of their own pockets. “Why would a developer want to capitalize something that he didn’t get any benefit from? Right now, people aren’t looking to rent in buildings that have water-reuse systems. There isn’t any marketing benefit in that. … Right now in New York, if you own the building yourself, you’re looking at about a nine-year payback period on the water-reuse system. And in a lot of investors’ minds, that’s not very attractive. They’d like to see two to three [years]. So if the city does create the capital incentive, you’ll have a much more vibrant model because it makes sense economically and would have the kind of payback period that development investors look for.
“If the proposed capital incentive program goes ahead, I think we’ll see the beginning of an interesting model,” says Clerico. “The way they’re doing it is what I would call a ‘reverse auction,’ whereby the city purchases reduced water and wastewater flow for the lowest-bid price, so they are open to any innovation that’s out there. If they go ahead with it, the model they are putting forward is to have entities bid to the city how much they would charge the city on a dollar-per-gallon-per-day basis to reduce water and wastewater discharge via discharge. And then they’ll buy this water/wastewater reduction from the bidders that offer the greatest advantage, thereby offsetting the future capital improvements. … It provides a really interesting model for public-private partnership. The overall approach is a win-win because the developers save money, while the city allows economic growth without the need for expanded water and wastewater services.”
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The Confluence of Art and Eco-Architecture
The Las Vegas Desert Living Center is unlike any other attraction visitors are likely to go to in the city that advertises “what plays in Vegas stays in Vegas.” The center was built on top of the original springs that brought Native Americans and the first Spanish settlers to the area.
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Photo: Mark Saunders |
| The wetland provides a habitat for desert life. |
In the early ’50s, thanks to the overpumping of groundwater, the springs stopped flowing aboveground, so water had to be brought in from the Colorado River and elsewhere. Now “the springs” act as a tourist attraction/water distribution center.
Buried at the Desert Living Center are two 40-million-gallon water reservoirs, two 10-million-gallon traditional tanks (aboveground), and one 20-million-gallon underground reservoir that are underneath the visitor parking lot. Attached to that reservoir is a $45 million-pump station that distributes water around the Las Vegas Valley. But the center’s real gems are the 30-acre flood basin and the onsite wastewater treatment, which is actually part of the gardens, displaying all manner of native vegetation from six Mojave Desert ecosystems.
The flood control basin is a working facsimile of the wetland that occupied this area before the springs were pumped dry, thanks to the innovative use of nuisance street water and occasional stormwater—both of which are cleaned and run through this wetland, recreating natural habitat for all manner of desert life.
“Our natural springs no longer flow, so we’re reusing the nuisance-water runoff (street runoff) and re-creating the look of the springs,” says Jeff Roberts, project architect from Lucchesi & Galati, the firm that designed the Desert Learning Center.
All the buildings at the Desert Learning Center are Leadership in Energy and Environmental Design (LEED) certified with a Platinum rating. One of the LEED certification innovation credits is the exemplary use of wastewater. “We collect all of the wastewater for the entire site, all facilities onsite, in a central sewer system for the entire site. It runs to the Desert Living Center, where we pull it out with a lift station, and then it starts through the wastewater aquatic cleaning system.
“We have a primary sewer line that runs through the entire system, and it ties into the city sewer. That’s really a backup more than anything.” That central system includes a 15,000-gallon primary treatment/settling tank, which is basically a very large septic system complete with microbes. The tank is designed to retain the solids for up to 10 to 12 years.
The effluent flows out of the 15,000-gallon treatment tank and into a 9,000-gallon equalization tank, which is more or less the setup tank for two wetland cells, which are below ground level to prevent any exposed water. Those cells are planted with aquatic plants that are native to our desert and river wash systems (bulrush and cattails). They have gravel over them, and the water flow is in a contained cell about 3 to 5 inches below finish grade. It is those two cells that begin the cleaning process. As it gets to the end of its process (in about a six and a half days), the water goes through a recirculation sand filter and then a tablet chlorinator.
During the summer months, when the tourist traffic is highest, the water is pumped back into the building into pressure tanks, where it is used to flush toilets. In the winter months, when there is an excess of flow and a low visitor volume, the effluent management plan calls for running the recycled water into the back-of-the-house gardens for supplemental irrigation.
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Photo: Mark Saunders |
| Water storage tanks |
“The only thing that was hard for us to deal with was at opening we had so many large events: a VIP opening, a grand opening, then a Jewel concert,” says Roberts. “The system spiked with all the toilets being flushed. So we had a bit of adjusting at the beginning with these massive peak flows. For example: We had the VIP opening on Wednesday; then we didn’t do anything for five days. It really kind of shocked the system, and the water level got really high in the pond and eventually came above [ground] level. So we had to learn how to adjust the peak flow demands.”
Distance Trumps Barriers
“How close you are to the sewer line dictates the economy of whether you put in a decentralized system or tie to a centralized system,” says Charles Turhollow, division manager of the City of Los Angeles’s Bureau of Sanitation, Department of Public Works.
For some developments, the decision to go with nontraditional wastewater technology was a no-brainer because the distance to the nearest sewer line makes the price of connecting to conventional water treatment simply beyond anything the developer could absorb and pass on to the homeowners. In addition to cost savings realized by not tying into existing wastewater infrastructures, several developments around the country tout the eco-friendly nature of a wastewater system that allows homeowners to water their backyards or flush their toilets with recycled water.
An elegant example of this kind of development is Rancho de Bosque, a boutique community near Eldorado, NM (about 14 miles northeast of Santa Fe on I-25 with a median home price of $230,000). The clustered wastewater system is currently connected to 11 houses; however, the system is designed to accommodate 23.
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Photo: Mark Saunders |
| The subterranean wetland gives little hint to the water treatment below ground. |
The development is nestled into a gentle sloping hillside overlooking the desert foliage of cactus, succulents, desert junipers, and pinion pines. Rancho de Bosque is a high-desert community that receives an average of 14 inches of rain and 32 inches of snow annually. Water is a precious commodity in this red-soil community.
Rancho de Bosque is the first subdivision in New Mexico permitted to reuse treated effluent as irrigation water. In 1995, Natural Systems International Inc.(NSI) designed Rancho de Bosque’s system, and JVS Excavating built it. This decentralized wastewater treatment system uses individual tanks for solid waste storage at each residence. Three constructed subsurface wetlands are used to polish the effluent (currently two cells are up and running; the third will go online when the community grows to 14 to 16 homes).
Like most resources, water is subject to the laws of supply and demand: The greater the need, the more precious the commodity becomes. Most arid communities in the western United States are concerned about meeting the competing water needs of its members. At Rancho de Bosque, that model gets turned on its head.
“With more people coming online, there’s more water in the system,” says Witter Tidmore, spokesman for the Rancho de Bosque Homeowners Association. “From what I understand, it makes the whole system healthier—it needs to get used.”
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Photo: Mark Saunders |
| An odor control system in use |
“The more the better,” says Loren Allen, senior engineering technician at NSI. “We’re hoping they get more online soon so we can get the third wetland cell up and running so we can have more reuse water.”
According to NSI, a community of microorganisms known as periphyton and a natural chemical process are responsible for approximately 90% of the removal of water contaminants and the breakdown of waste materials. The wetland plants (bulrushes, cattails, and others) remove approximately 7% to 10% of pollutants and act as a carbon source of microbes when they decay.
From the wetland cells, the water moves to a nearby holding pond. The holding pond water is then pumped to the top of the grade above the highest house in the community. From there, the recycled water flows down to junction boxes at each home. The wastewater system was designed to provide each home with enough recycled water to irrigate 4,000 square feet of native landscape.
“The water is solely used for irrigation,” says Tidmore. “It’s all gravity-fed, and everyone has a box, and everyone is responsible for their own maintenance and instillation of their own drip-irrigation system. We have an estimated limit of approximately 2,000 gallons per household per month. Some people use less, and some people use way more.
“In Eldorado and Santa Fe, we have some pretty tight water restrictions,” says Tidmore. “Two years ago, you were only allowed to water once a week. We started out that year with almost a full holding tank. So we were planting new plants and doing new landscaping, planting trees, and everyone else was lucky to keep what they had alive. We were able to draw up landscaping and utilize the water during a time when most other people were experiencing a drought with severe water restrictions. As long as we stay within the parameters of what water we had available to use—and plant plants that didn’t use much water—we have a buffer that other people don’t have.”
The cost of water is also a consideration. “It’s kind of expensive for us,” says Tidmore. “We pay for NSI and permitting costs. We estimated that our bills were $675 per household per year, which we pay up front. We’re hoping that with three or four more households online that those costs will go down a bit.”
In addition to the $56 per month residents pay for the permitting and maintenance of the system, they also pay a nominal electric bill and water bill. “The pump is electric,” says Tidmore. “It’s ridiculously cheap [to run], so we just keep paying it. The water bill for the hookup is about $10 per year. The electric bill is super low—maybe $10 per month for the months it’s being used, which are from April through September or October—depending on the water, when it starts freezing and whether or not we run out of water. Last year, we had these great monsoon rains around July. I practically shut the system off because there was so much rain.”
Serenbe
Another example of an exurban community built to achieve an environmental aesthetic and far enough away from a sewer main to consider traditional, centralized wastewater treatment is Serenbe, an ecologically designed community in the rolling Chattahoochee hill country of Fulton County, GA (about 35 minutes south west of Hartsfield-Jackson Atlanta International Airport). Serenbe is another example of a small community (approximately 900 homes at buildout) transforming what Turhollow calls the flush-and-forget mentality into a conservation coup that fits perfectly into a backdrop of southern hardwood and pine forest, pasture, and wetlands.
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Photo: Alliance Environmental |
| A view of the Solaire green roof in New York City |
Despite its proximity to a major metropolitan area, Serenbe is green and rural (EarthCraft Certified houses, Silver LEED-certified architecture, roads built to accommodate topography and natural vegetation, an elaborate small-diameter wastewater treatment system, and houses between $300,000 and $500,000). As Serenbe’s founder, Steve Nygren, describes it, “We laid out the community and built houses the way people built them 100 years ago—before we had bulldozers and could do anything we wanted to with the land. We’re not creating anything new; we’re just remembering how they used to do it. When the engineers ran into snags, I’d just go to some of the old Georgia towns and see how they did it a century ago. That’s where the answers are waiting for us.
“Your wastewater is treated naturally, and what’s more is that it’s great fun because people have this connotation about wastewater treatment being smelly and ugly,” adds Nygren. “And ours is a park that you can walk through, and people love it. And they don’t even realize what it is at first. They can go completely through it and then say, ‘What was that back there?’ ‘Oh, that’s our wastewater treatment.’ ‘What?’ they say.”
Enamored with John Todd’s “Living Machine” concept, Nygren created what Kevin White of the University of South Alabama calls a “centralized management of decentralized infrastructure” to fit the wastewater needs of this environmentally sensitive development project. Serenbe’s system consists of primary treatment tanks located at each home and constructed subsurface-flow wetlands coupled with recirculating sand filters and UV disinfection. The development is double-piped for providing reclaimed water to toilets and for the subsurface irrigation of landscaping and pastureland.
“That’s the goal,” says Erin English, project engineer at NSI. “Treat the water and be able to reuse it. Do that in such a way that is aesthetically pleasing and adds to the village concept and adds to the landscape at Serenbe in the rolling farmland hills and wetlands—so it fits really into that aesthetic.” As with The Solaire, Serenbe’s homeowners never even notice that their wastewater is being used to water the nearby fields and parks or to flush their toilets.
What’s Ahead
Since we have populated the planet in such a way that makes seasonal nomadic movement to greener pastures a thing of the past—and the invention of an automobile that runs on human waste part of a future envisioned by neither Jules Verne nor Philip K. Dick—it’s clear that whatever roles decentralized wastewater systems coupled with reuse plumbing and stormwater retention systems will play in global water economics are in their infancies. Perhaps the future lies in the direction of “eco-blocks” proposed at University of California–Berkeley or biogas digesters patented by University of California–Davis—or perhaps in the mining of our waste for energy, nutrients, and, who knows, maybe medicines.
On a more pragmatic level, Turhollow put the evolution of sanitation in Los Angeles into a much larger context when he said, “We’ve spent the time putting safe drinking-water systems in. We now have dependable sewer systems in. So it’s just a matter of time and patience before more of our water is recycled.”
Mark Saunders is a professor at Front Range Community College. OW - January/February 2008
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