Better Wastewater Treatment
OUR COUNTRY'S SEWER infrastructure is failing. Many centralized sewer systems were built right after World War II and are nearing the end of their useful lives, and untreated sewage regularly spills into our lakes and rivers from overburdened treatment plants.
A home or other structure that is hooked up to an aging centralized sewer has no control over the impact of its wastewater once it leaves the property. Every foot that untreated wastewater travels increases the chance it will breach a leaky pipe and contaminate soil and water. It is also letting go of valuable resources—water and nutrients—that could be benefiting the local ecosystem.
Then there’s the energy-water connection. Four percent of the nation’s energy expenditure goes to water and wastewater treatment. Treating water and wastewater can eat up 35 percent of a city’s budget.
The EPA estimates that replacing our ailing infrastructure will cost around $298 billion over the next 20 years. But onsite or decentralized wastewater treatment offers an inherently sustainable alternative. Wastewater doesn’t have to travel long distances, reducing pumping energy and the chance for contamination via leaky pipes. Some systems require very little (or no) energy to operate. Treated effluent (the liquid portion of wastewater) recharges groundwater, or can even be used for irrigation or toilet flushing, which reduces the demand for potable water. Programs such as LEED and the Living Building Challenge reward or mandate onsite water harvesting and wastewater treatment, and pilot projects demonstrating the effectiveness of small-scale wastewater treatment are popping up all over the country, even in dense urban places like New York City. As communities contemplate how to replace aging systems, and as people become more concerned about water security, interest in onsite systems is likely to spike.
Decentralized treatment systems include individual septic systems, “clustered” systems, composting toilets, constructed wetlands and various types of advanced treatment. Though some are more effective and efficient than others, they all use biological processes to break down or consume potentially harmful substances and/or convert them into benign (or even beneficial) ones.
When it comes to the quality of effluent, or sewage outflow, the two terms you’ll hear most are Biological Oxygen Demand (BOD) and Total Suspended Solids (TSS). BOD measures the amount of oxygen required by organisms to process contaminants in the water—the higher the BOD, the higher the concentration of contaminants. TSS measures the solid material suspended in wastewater—the higher the number, the “dirtier.” Other concerns are specific pathogens like fecal coliform bacteria and compounds containing nitrogen. While nitrogen is a plant nutrient, too much can overwhelm aquatic ecosystems.
Conventional Septic Systems: Dead in the Water?
Traditional septic systems are an imperfect way to treat blackwater waste, and should be upgraded with equipment that treats waste to a higher degree. Meanwhile, here are four practices that compromise conventional septic system effectiveness:
Chemical Conundrum. Using bleach to clean the toilet or regularly applying Draino to keep sinks unclogged can kill the “bugs” that do the work of cleaning effluent.
Garbage Disposal Blues. Regularly sending solid food waste to the septic system overburdens it with nutrients and can cause the tank to fill faster.
Medical Waste. Pharmaceuticals don’t get taken up by soil organisms, and instead end up in groundwater or waterways, where they can impact fish and other aquatic creatures—or people, if the water body serves as a source of drinking water.
Additives Detract. Septic tank additives break down the solids into liquids, which then leave the tank and clog the drain field.
Septic systems require very little energy (and if the system is gravity-fed, virtually none), and no chemicals; once the water moves through the drain field, it is “clean”—free of harmful pathogens—and replenishes the groundwater below it.
But septic systems have issues. They require “Goldilocks” soil conditions—not too much clay, not too much sand—and more mindfulness and maintenance than centralized system. Septic systems don’t do a good job of removing nitrogen, which can be a problem if the effluent eventually drains into a bay or estuary. Septic tanks have to be pumped regularly—the frequency depends on the size of the tank, condition of the drain field and number of users—and they can leak, which causes problems both ways: water from outside the tank can infiltrate in, overburdening the system; untreated waste in the tank can exfiltrate out, contaminating the soil with fecal coliform bacteria and overwhelming the drain field.
In any case, drain fields have lifespans.
“I call it ‘progressive failure,’” says Grant Denn, senior manager for Engineered Projects at Orenco Systems, Inc.
Organisms form a “biomat” on the near side of the drain field, closest to the septic tank; this mat can eventually cover the entire trench. When this happens, decomposition shifts from an aerobic to an anaerobic (i.e., stinky) process, and effluent cannot filter down and instead ponds on top of the drain field. In worst-case scenarios, sewage can back up into the house.
Septic systems can be a part of a sustainable wastewater treatment solution. Septic tank effluent pumping (STEP) systems use tanks to capture most of the solids, then send the effluent to a centralized or distributed system. STEP systems ease the burden on treatment plants, so they can be smaller, which equates to less costly infrastructure. Alternatively, combining a septic tank or system with some type of advanced treatment ensures wastewater is treated adequately before it is released into the soil.
Advanced Treatment Pros
- Treats wastewater to high degree, including nitrogen.
- No chemicals.
- Compact—allows reduction in drain field size, or potentially eliminates altogether.
- Can extend drain field life.
- Treated effluent can be used to irrigate landscaping or flush toilets.
Advanced treatment systems function as mini-wastewater treatment plants, “cleaning” wastewater (including nitrogen) to a high degree—the equivalent of tertiary treatment, in industry parlance. They can be installed as an emergency measure to restore an ailing septic system, or to extend the life of a properly functioning one. In some cases they can reduce the size of the drain field required, or even eliminate it. If codes allow, the treated effluent can instead be used to irrigate landscaping or flush toilets.
Many advanced treatment units, or ATUs, utilize a pump to continually add oxygen-rich air into the septic tank; “suspended growth”—organisms that are freely suspended in the effluent—reduce the nutrient loads before the effluent reaches the drain field. Aero-Stream offers its Remediation System, consisting of the aeration tank, diffusers, filter and Bio-Brush, a natural fiber medium on which organisms can grow, that can be retrofit into a failing septic system—or used to extend the life of a properly functioning one. The unit containing the pump is compact and can be installed away from the septic tank itself, so long as the tubing can reach it.
The downside to ATUs is that they operate continuously, and require a significant amount of energy to power the pump. “Packed-bed” systems offer an alternative. Organisms aren’t suspended in the tank itself, but instead grow on a medium in a separate compartment, whether sand or gravel or synthetic textile. The effluent then trickles through the medium and is often recirculated so it makes several “passes.”
The classic sand filter, which Orenco helped pioneer, is one type of packed-bed system. More recently, Orenco developed a packed-bed system called the AdvanTex, which utilizes a textile medium with an “incredible” amount of surface area—10 to 20 times as great as a sand bed filter. The company claims the AdvanTex can reduce BOD and TSS by 90 percent, and nitrogen up to 70 percent. The system still uses a pump to recirculate effluent through the medium, but it only operates an average of 20 to 30 minutes per day and uses a fraction of the energy compared to aerobic suspended growth systems.
Still another variation on the advanced treatment theme is Presby Environmental’s Enviro-Septic system. It utilizes 10’ lengths of 12”-diameter pipe that is ringed inside with geotextile fabric and coarse fibers. Organisms grow on the fibers and consume nutrients in the effluent as it passes through the pipe; sludge accumulates on the bottom. The pipes are installed after the septic tank, but before the drain field. The company claims their system can remove up to 90 percent of wastewater contaminants.
Pressure System Pros
- Less intrusive on land.
- Allows for flexibility when siting structures.
- Requires less energy than gravity sewer system.
- Less expensive to install and maintain than gravity system.
Sometimes septic systems aren’t allowed or practical; for instance, if the soil is too clayey or sandy, or if water table is high. On the other hand, rocky or hilly terrain makes conventional gravity sewer systems difficult and expensive, especially if multiple lift stations are required to move wastewater uphill. New York-based company Environment One (E/One) has developed a pressure system that works in all of these conditions. Grinder pumps installed at individual residences grind wastewater into a slurry, then feed it into small-diameter pipe. These lateral pipes range from 1-1/4” to 4”, depending on the community being served. Instead of requiring deep trenches to ensure adequate fall, they can follow the contour of the land, minimizing environmental disturbance.
Because buildings don’t have to be uphill of sewer lines, “the system gives builders free reign on siting,” says George Vorsheim, communications director for E/One. “Viewsheds can open up.”
Waterfront communities are prime candidates for upgrading to pressure systems. For example, septic systems in the community of Port Orchard, Washington—an area with clay soils, steep lots and high rainfall—were failing; in some cases, drain fields were nonexistent, and effluent was draining directly into Puget Sound. The community formed a utility district, and after evaluating several options decided on a pressure system with grinder pumps, both for its low initial cost ($1.9 million, compared to $8.4 million for a gravity system and lift stations) and lower operating and maintenance costs ($10,710 annually, compared to $25,000).
Vorsheim believes that, ideally, the municipality should take control of the whole system, including the maintenance of grinder pumps on private property. If there’s a problem with one, the core pops out, which maintenance personnel can replace with a temporary unit.
Pressure systems offer another compelling advantage over gravity systems. Centralized sewer infrastructure has often been used to enable growth. The pressure system is flexible enough to use as a tool for managing growth, says Vorsheim. Specifying a pipe size to serve only the current number of homes allays fears that a centralized system will open the floodgates to development.
Though E/One has systems all over the U.S., and in several other countries, Vorsheim admits to dealing with “transformational resistance.”
“It’s disruptive; it’s different,” he says. As more case studies come online verifying their affordability and effectiveness, they will doubtless become a more popular choice.
Constructed Wetlands Profs
- Affordable, low-tech solution
- Flexible and scalable.
- Low or no energy required.
- High level of (tertiary) treatment; effluent can be used for irrigation.
- Low maintenance, long lasting.
- Attractive, provide wildlife habitat
Constructed Wetlands: The Natural Choice
Natural wetlands function as nature’s sponge, absorbing and filtering nutrients and pathogens, improving water quality of lakes and bays. Constructed wetlands can harness that “biotechnology” and use it to clean wastewater. In fact, many municipal wastewater treatment plants incorporate constructed wetlands to treat overflow, and cities often use them to process stormwater. (These often become prime bird habitat, which explains why birders frequent wastewater treatment plants.)
Whole Water Systems, based in Seattle, Washington, specializes in holistic and sustainable onsite wastewater treatment, including the use of “Constructed Wetland Bioreactors,” or CWBs. These clean wastewater to EPA Tertiary Standards—levels suitable for subsurface irrigation. Wastewater first flows through a settling tank or basin, where solids are separated from liquids, just as in a traditional septic system. The CWB consists of a shallow gravel bed topped with a layer of finer material, which lines up with the surrounding terrain. A berm and impermeable barrier ensure the water in the CWB doesn’t run off into the surrounding landscape. The water level sits several centimeters below the top of the gravel, ensuring the wetland doesn’t become a breeding pond for mosquitoes and preventing accidental contact with pathogens. Microbes that live on the gravel process nutrients in the water, as do the roots of water-loving plants that landscape the CWB. Patented inlets and outlets control the water flows. The variety of micro-habitats and interactions between roots and microbes ensure the water is completely treated.
Constructed wetlands are a truly sustainable solution, says Brown. “They aren’t expensive, they’re low maintenance and they look good.” They also don’t require energy, chemicals or mechanical parts, and unlike septic drain fields, their service life is virtually unlimited.
Composting Toilet Pros
- Requires little energy (except to operate fans).
- Requires little to no water.
- No chemicals.
- End product can be used as fertilizer.
Composting Toilets: Not Just for Hippies Anymore?
I still remember my “aha moment,” which occurred while reading Sim Van der Ryn’s The Toilet Papers: “Mix one part excreta with one hundred parts clean water,” he writes. “Send the mixture through pipes to a central station where billions are spent in futile efforts to separate the two. Then dump the effluent, now poisoned with chemicals but still rich in nutrients, into the nearest body of water.”
That’s when I understood the folly of “treating” our waste as somebody else’s problem, instead of the valuable resource that it is. Composting toilets opt out of this system and offer a sustainable option for harvesting this resource, but few people—in this country, anyway—want to go there. Don Mills, sales director for composting toilet manufacturer Clivus Multrum, insists it’s a matter of (mis)perception.
“If you’ve had a bad experience with a composting toilet, it’s because you’ve either used one without a properly functioning fan or you used a pit toilet,” he says. Even so, the problem of perception has marginalized composting toilets, and they’re largely the provenance of dyed-in-the-wool environmentalists who refuse to compromise, or people who live in remote or rural areas and have no other alternative.
It’s true that composting toilets require more mindfulness than simply flushing, and proper functioning depends on several factors: the right moisture content, adequate aeration and the proper ratio of “ingredients.” One potential problem is the urine, which can create an environment that’s too moist. Clivus Multrum composting systems solve this problem with a unique sloped design (clivus multrum means “inclined chamber”), which separates urine from feces. The urine breaks down into stable components and can be removed; meanwhile, a host of organisms, including bacteria, fungi and worms, break down the feces into usable compost over the course of a year or more. A continuously operating fan pulls air down from the toilet itself, eliminating odors.
Though there are many variations on the theme, composting toilets fall into two broad categories: all-in-one systems and those with a separate toilet and composting chamber. Greywater Action warns against installing an all-in-one system in a home that functions as a main residence; most aren’t designed for regular residential use and are more suitable for seasonal cottages.
High-profile projects like the Bullitt Center in Seattle, which uses Phoenix composting toilets throughout the building’s six stories, might help elevate their reputation.
Even if a home is hooked up to a centralized sewer system, capturing graywater—water from sinks, showers and washing machines—can save thousands of gallons of water per year, ease the burden on the wastewater treatment plant, nourish landscaping and replenish groundwater.
Many people like the idea of graywater reuse, but are intimidated by the logistics. What happens if the home doesn’t produce enough graywater to meet plants’ needs? What if it produces too much? How will I even know?
Paul James, cofounder of Morrow Water Savers, has developed a drip system specifically for graywater that removes much of the guesswork. The IrriGRAY system works in tandem with a sophisticated Smart Controller, which can be programmed remotely via the Internet or tablet. It uses a small pumping station (which includes a unique self-cleaning filter) to send graywater to up to 16 zones, and can be programmed to prioritize zones and/or automatically supplement with potable water or rainwater if there’s not enough graywater.
The genius of the IrriGRAY system is that the water stays in the root zone, creating a “water blanket” that’s four to six inches deep. This results in more efficient use of graywater and healthier, happier plants.
James says the IrriGRAY system is more efficient than typical “branched-drain” graywater systems, which utilize mulch basins. These systems are labor-intensive and depend on grade to function correctly; nutrients can also accumulate in the mulch basins.
After developing graywater systems in Australia—a country much further down the path when it comes to graywater reuse—James partnered with Paul Morrow to create Morrow Water Savers. Since establishing headquarters in Texas, the company has been targeting new developments for its IrriGRAY systems, says James.
“The cost for a new system averages $5,000. By comparison, a cheap irrigation system costs between $2,000 and $2,500.” But the system starts paying for itself immediately. The annual savings can be $200—more in a state like Texas, which is imposing a tiered price structure to encourage conservation.