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Composting Toilets Emerge as Viable Alternatives


January 25, 2001

Composting toilets are finding their way into mainstream homes due to tightening wastewater regulations, awareness of pollution, and compatible gray-water systems.


When Rob Okun took steps to sell his home in western Massachusetts last summer, he triggered a town review process that ultimately condemned the house. His septic system was located in high groundwater and in a town water supply district – a clear pollution threat. The Board of Health wouldn’t allow him to install just a holding tank, which can be expensive to pump out (hence holding tanks have a history of “developing” holes of suspicious origin). The only acceptable solution was a zero-discharge system, one that used up the home’s effluent. And they had one in mind: an integrated composting toilet and wastewater system. In this case, an engineered garden system that manages household washwater would be enclosed in a greenhouse; built off the living room, it would offer the added benefit of passive solar heat. The home’s three toilets would be replaced with micro-flush toilets that flowed to a composting reactor. Okun ultimately got his asking price from a couple who were intrigued by the system. “The prospective owners love the idea,” says David Del Porto, whose firm, Sustainable Strategies, designed the system. “They didn’t realize that this was possible. They’re really enthusiastic.”

Composting toilets – once only the toilet choice of parks and owners of remote homes – are finding their way into mainstream homes. Tightening wastewater regulations, growing awareness of pollution sources, and compatible gray-water systems and flush toilets are making them a viable alternative to septic systems and central sewage treatment in many areas.



The “Anti-Septic” Option

Think of a composting toilet as an air-breathing septic tank. Inside the composting reactor, excrement, urine, toilet paper, and sometimes kitchen scraps are transformed into compost by mostly aerobic microorganisms, which break down the material to 10% of its original volume. In fact, these microbes process 10 to 20 times faster than the anaerobic bacteria at work in a septic tank.

“It’s nature’s way,” says Del Porto, who has sold and designed several types of composting toilets for 25 years. “You can compost in a teacup; it’s not rocket science. What is science is managing the process for a minimum of odors, cost, safety, and pathogen destruction.”

Just like commercial and backyard composting of organic wastes, composting toilets must control the primary process factors: oxygen, temperature, moisture, and a nutrient balance of 30 parts carbon to one part nitrogen, he says.



A Warmer Reception

But the prospect of maintaining these systems turns off many potential buyers, says Bill Wall of Clivus Multrum New England. Nearly all of his customers now opt for his company’s service contract. Service is available on an annual basis for about $200 and on a four-times-annually basis for about $600 (prices depend on location). It usually includes checking all parts, leveling the compost, and removing it, if necessary. “This makes the operation and maintenance easy now, so it’s a viable solution for more people,” Wall says.

Property owners are also reconsidering this alternative due to skyrocketing sewer rates and holding tank pumping costs. Others like the fact that they allow them to reduce the size of their leaching beds. Wall notes that some of his customers opted for his systems to avoid cutting trees to make way for leaching beds.

Perhaps the most important change in the public’s reception of composting toilets is that they can be coupled with micro-flush toilets. “Many people don’t like the ‘black hole’ concept,” says Wall, referring to what some users of simple compost toilet systems see when they lift the lid of a waterless toilet stool. “Now you can have a flush toilet connected to your composter. It’s more traditional. And you don’t have to have a straight chute,” he says.

Compatible micro-flush toilets include the SeaLand, which uses one pint of water flushed with a foot pedal, and Evac and SeaLand vacuum toilets, such as those used on airplanes and trains. The new Vera Waterless Toilet uses the mass of the waste itself with simple fluidic engineering to move the waste, and the Nepon toilets from Japan use foam.

The extra water from these toilets must be treated by evaporation, disposal, or utilization. AlasCan, Clivus Multrum, Phoenix, and EcoTech offer wastewater systems to treat this liquid, as well as the rest of a home’s washwater, or “gray water.” Clivus Multrum and EcoTech offer gray-water irrigation systems that treat the water through garden beds. These systems must be approved by states on a case-by-case basis. Gray-water irrigation has gained acceptance in many states, such as California and Arizona, according to Del Porto. Other companies offer evaporators. AlasCan offers a home-sized three-chambered aerobic wastewater treatment plant.

One of the major obstacles to installing a composting toilet is getting permits. Composting toilets usually require permits from town, county, or state officials, and the ease of permitting them varies widely across the country. Many health officers are simply unfamiliar with these systems. Some fear that zero-discharge systems will allow building in previously undevelopable areas. Some states require backup conventional wastewater systems. States that are more amenable than others include Massachusetts, Maine, New Mexico and Washington. Permits are rarely granted for owner-built composting toilets, unless they have rigorous monitoring or maintenance plans. Many states require certification by NSF International, essentially the “UL” of the public health industry.



Types of Composting Toilets

In terms of how they operate, most composting toilet designs are based on either “batch” or “continuous” composting. Batch composting is processing done in more than one compost chamber, which are interchanged as they fill up. The advantage, some say, is that older or finished compost is not contaminated by the new nutrients and potential disease-causing organisms in fresh waste. In some systems, the chambers can be removed from the toilet to take outside to empty.

“Continuous” composting takes place in a single-chamber composter, where fresh waste is continually deposited at the top of a composting chamber, and finished compost is removed from the other end of the unit.

Composting toilets are usually either “self-contained” or “central” systems. In a central composting system, the composting reactor is separate from the toilet bowl – usually located in the basement or in its own enclosure to the side of the building. All include fans; heaters are usually optional. Commonly the choice of year-round homes and facilities with multiple toilets, they range in price from $1,400 to $8,000 and higher for large systems.

Among the central composters, the Clivus Multrum and the CTS are inclined vault composters, essentially large inclined boxes where waste moves down the incline, which slows its passage to the bottom, helping to aerate it. Compost is removed through an access hatch at the bottom of the tank. The Phoenix is a tall vault with a stacked three-part system. Waste falls to a high area, where rotatable tines act as a mixing device to break it up and aerate it. It then falls to a grate, then to a collection box. The AlasCan is a highly mechanized composter with power-driven auger-agitators and high-velocity air flow via a fan. The Bio-Sun system is a large canister tank in which a powerful air compressor moves large volumes of air across the excrement. Increasingly, Bio-Sun is designing the composting reactor right into the foundations of buildings.

Occasional leveling of the material with a pitchfork is required in some of these systems. Users also turn the compost at the removal hatch end to prevent compaction and promote aeration. In all of these models, urine and other liquids – called “leachate” – drains to the bottom, where it is evaporated or must be drained for disposal or utilization. All but the CTS employ a leachate-recirculating system that pumps liquid from the bottom and spritzes it on the top of the composting material.

The EcoTech Carousel is a fiberglass cylindrical container consisting of an outer container that holds a rotatable inner container divided into four compost chambers. This keeps liquid separate from the compost, and compost in batches. When one chamber fills up, the next is rotated into position. The Vera Toga 2000 is a system of roll-away interchangeable 60-gallon compost reactors. Extra containers can be purchased, giving it as much capacity as one has containers. Sun-Mar’s new Centrex Plus features a two-chamber version of its patented “bio-drum,” a rotatable canister, and a finishing drawer. Sun-Mar’s Centrex, a smaller unit featuring a smaller bio-drum and just one collection tray, is typically only used in cottages.

Advantages of central systems: Larger units have long-term retention (two years or more), allowing longer composting periods and more capacity. Disadvantages: Their large sizes – a few are six to 10 feet high – require special installation considerations. The larger single-chamber units are also more susceptible to compaction of the composting mass.

“Self-contained” toilets are single-unit composters whereby the toilet seat and the compost reactor are all part of the same appliance. These can sit in the bathroom. Due to their small size, these are typically used in cottages and seasonal homes. Their capacity typically ranges from two to six adults, varying with the model. Prices range from about $850 for a Vera Cottager to $1,470 for a BioLet XL.

Sun-Mar’s series of composting toilets all feature a revolving bio-drum – a canister-like composter mounted horizontally. A hand-crank allows users to periodically rotate the bio-drum to mix and aerate the material. BioLet’s XL uses a mixing arm to slice through the composting waste and push it through a grate. Vera’s Toga series all feature interchangeable composting chambers, as does the BioLet NE. Sancor’s Envirolet has a moveable grate – called a “mulcherator” – that can be manually pulled to break up, mix, and aerate the waste.

Advantages to self-contained units: These are lower-priced and small, ensuring fewer installation issues. Disadvantages: Users must constantly remove the finished compost while adding new material. Due to their small size, they are often overloaded, and processing can be incomplete. Excess leachate is the bane of the smaller ones, and one must guard against letting the material bake and dry into a hard mass.

There’s also the do-it-yourself option. “There’s a rich history of owner-built composting toilets, from knock-offs of commercial models to various innovative uses of industrial containers,” says Del Porto, who has developed several site-built designs himself. Site-built designs range from systems using 55-gallon drums and a scissors jack to concrete-block chambers to toilet seats placed over five-gallon pails. These often cost less, but they can be difficult to get permitted. “If they provide adequate aeration and heat, they all work about as well as the amount of care their owners put into their operation and maintenance. It’s the commercial manufacturers that have to develop user-friendly technologies,” he says.

Nearly all toilets are available with fans (electrical or solar-powered) and optional heaters. Supplementary heat speeds up the composting process, although too much heat can dry out and halt composting.



Care and Feeding

Composting human waste needs added carbon to transform the nitrogen in urine, as well as to help aerate the material and absorb some excess moisture. Bill Wall recommends finely mulched wood, composted leaves, planar shavings or gerbil bedding and pine bark mulch. Although he sells an additive mix, Del Porto recommends using stale popped popcorn or dime-sized wood chips. “It has the ideal shape to create air spaces, nooks and crannies for bacteria to grow and good nutrients that are totally consumed in the composting process,” he says. Both discourage using peat moss alone. “It doesn’t really decompose,” Wall says.

Finished compost – called “humus” – has the consistency of composted leaves, and should smell earthy but not offensive. Most states require sending it to a treatment facility or burying it under at least six inches of soil, preferably within the root zones of non-edible plants that can use the nutrients.

If any leachate is emptied from composters, it must, by law, be disposed of in an approved wastewater system. It cannot be drained to the ground untreated. The nutrient value of urine is such that it can be added to gray water and safely applied to plants in a sub-surface irrigation system (approved by a local board of health, of course).

There’s no getting around it, says Del Porto: composting toilets require proper care and feeding. “Many people overload them,” he says. “Or they take material out too soon. Or lose the manual, and pretty soon they’re putting dirt in the composter. Then they’re on the phone, saying, ‘this thing doesn’t work!’ That’s classic.”

Long-time composting toilet owner Patti Nesbitt says maintaining her system is as easy as adding an occasional handful of wood mulch and emptying it once a year. A wastewater consultant to the Environmental Protection Agency, Nesbitt installed a Carousel composting toilet in her Stroudsburg, VA, house 15 years ago, to allow her to reduce the size of her septic tank system and leaching bed. Her composting reactor is located in her kitchen pantry, right underneath the toilet stool on the second floor. “It stays warmer there, and it’s more convenient to empty,” she explains. “There’s no odor. It works great.”

Mainstreaming this technology, however, may require more compromises with this country’s “flush and forget” mentality. Harvard University recently developed a simple prototype “Smart Composting Toilet” with sensors that automatically control temperature, air and moisture. “That’s the future of these systems,” Del Porto says. “More and more, they will be automated and maintained by service providers - just like a septic system or any other appliance in the house.”




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