|We highly recommend viewing the illustrated PDF version of this guide. The HTML version below is provided as a courtesy to those without a fast internet connection.|
Our acclaimed planning guide helps maintenance professionals determine capacity, choose a site, optimize building design, and devise an efficient maintenance schedule.
Choosing a Composting Toilet: Eight Key Questions
Composting is a familiar process to many people. Organic materials, such as leaves, lawn clippings and food waste, are placed in a pile or enclosure. Over time, in the presence of oxygen, heat and moisture, biochemical processes convert the waste to stabilized compost, which resembles rich, dark, potting soil. Pathogens are nearly eliminated and the volume of the organic material is reduced by 90 percent or more.
The same biochemical processes are employed by composting toilets to treat human waste. A composting toilet is a system that provides an environment within a container for aerobic (in the presence of oxygen) decomposition and stabilization of waste. It is a miniature, on-site sewage treatment plant. It is not a dehydration system that uses heat to dry waste; not a “waste reduction” system that circulates large volumes of air over the waste to evaporate liquid; not a “recycling system” that merely stores the waste for periodic removal and composting at a remote facility.Not all composting toilets are created equal. They vary in size, materials, features, effectiveness, maintenance, energy requirements and safety. In choosing a composting system, we recommend considering the following questions:
At Advanced Composting Systems, we manufacture the Phoenix Composting Toilet, a large and very rugged composting system that provides for the safe and effective stabilization of human waste on site. The insulated tank, efficient ventilation system and automatic controls assure the lowest possible heat and electrical requirements. Most often, these requirements can be met with solar energy. The Phoenix’s built-in rotating tines and vertical design assure higher quality compost and easier, safer maintenance.
|The Planning Procedure
The process for planning and designing a Phoenix composting toilet facility for a specific application requires several important steps. The following application guide will help in this process. If you need further information for a unique situation, please contact us. ACS designs, supplies, and installs complete turnkey facilities satisfying a wide range of criteria. We also perform site visits to help select a building location.
An outline for the planning process follows. Some steps will be easy, others will require research, design decisions and tradeoffs. All are important to guarantee a successful project. Our application guide follows this outline. Refer to it to assist with each step.
Capacity PlanningSizing the facility. How many tanks and how many toilets will a facility need? The answers depend on total annual use, and peak daily use. “Uses” should not be confused with the number of people in an area: “uses per person” varies depending on the nature of visitor activities in an area.
The number of total annual uses determines how many tanks are needed. The peak daily use determines how many toilets must be installed (a tank can accommodate two toilets).
When calculating rates of use, planners should account for the accelerated rates of use that can occur following the opening of a new facility (if you build it, they will come and go).
The Phoenix’s capacity is rated in average uses per day and varies according to the tank’s temperature, the type of use, and the frequency and quality of maintenance.
Predicting facility use. The total annual use for a facility can be inferred (with varying degrees of accuracy) from a surprising variety of data. Here are a few common situations:
Determining the Phoenix’s capacity. Capacity is the amount of use (expressed as “uses per day”) the Phoenix can sustain while producing stabilized, non-offensive, liquid and solid end products with low coliform counts; solids with a moist but not saturated texture; liquids with a high proportion of nitrate nitrogen. Removing compost from a Phoenix that has been (a) properly maintained, and (b) used within its capacity rating, will not be an unpleasant operation.
Our ratings are conservative, and are derived from operational experience. We have equipped representative facilities with data loggers to record key parameters. We visit many Phoenix installations to retrieve use data (the Phoenix is the only system that includes door use counters and has done so since its inception), and to assist with removing the compost. Our extensive hands-on experience with the capacity-environment-maintenance relationship has allowed us to quantify the rate of composting as a function of maintenance and ambient temperature. We continue to refine our numbers by monitoring existing facilities, and through an ongoing research and development program.
Temperature. The rate of decomposition within a Phoenix, and all other composting systems, primarily depends on the internal temperature of the compost pile. The higher the pile’s temperature, the more rapid the decomposition, and thus the higher the capacity of the tank. Moreover, a relatively small increase in compost temperature results in a relatively large increase in the rate of decomposition.
Proper temperature management is critical to successful composting. Two temperatures affect the composting process:
Compost self-heating. The biochemical reactions of the composting process produce carbon dioxide and water, and release energy, heating the compost pile. The rate of the biological and chemical processes involved in composting approximately doubles for every 18 degrees F (10 degrees C) of increase in compost temperature. Self-heating occurs when the pile has sufficient mass and oxygen, and when the ambient temperature is high enough that the reactions can be sustained. The Phoenix’s low ventilation rate and insulated tank hold the heat generated by the compost pile.
Composting activity is very slow at ambient temperatures below 55 degrees F (10 degrees C), but accelerates rapidly as the ambient temperature rises. Our target minimum ambient temperature is 65 degrees F (19 degrees C).
Ventilative and evaporative cooling. The Phoenix is kept odorless by drawing air through the toilet and tank, and expelling it through a vent in the roof.
Air flowing through the Phoenix accelerates evaporation of the liquid, cooling the pile. In addition, heat from the pile is lost when the temperature of the ambient air drawn into the tank is lower than the temperature of the pile. The Phoenix minimizes these losses by ventilating at the lowest rate necessary to control odors and supply oxygen for aerobic decomposition. It is better to use an external evaporator when liquids must be evaporated on-site.
Cold composting conditions. At ambient temperatures below 55 degrees F (13 degrees C), heat loss through the tank wall prevents significant self-heating. Consequently, supplemental heat is mandatory to promote composting. The Phoenix, which is insulated, has been designed to be heated easily. Air enters the tank at a single port that can be connected to a heat source, such as a solar collector.
The Phoenix can be used at a reduced rate at ambient temperatures colder than 55 degrees F (13 C). Liquids will still evaporate and drain. Some use is possible even while the tank is frozen, for the compost pile will melt slowly and be treated when temperatures rise. Nevertheless, it should be kept in mind that at very low temperatures, significant composting does not occur and the tank essentially functions as a holding vessel.
Unlike conventional plumbing, which can rupture when frozen, the Phoenix tank is not damaged by freezing.
MaintenanceMaintenance is the other major parameter affecting capacity. Frequent, thorough maintenance — spraying liquid, adding bulking material, and mixing the compost pile — increases the rate of decomposition.
Moisture management. The proper moisture level and porosity of the compost pile (from the addition of bulking agents, such as wood shavings) must be established. The Phoenix includes a liquid spray system to help maintain moisture levels. The addition of bulking material is a simple task when performed frequently. The Phoenix includes built-in rotating tines to mix the bulking material with waste; additional raking often is unnecessary.
Pile aeration management. Because raw fecal matter is too wet and nonporus to compost, it must be mixed with a bulking agent — we recommend white wood shavings — to provide the structural support and the airspaces necessary for aerobic decomposition. The bulking agent must be thoroughly mixed into the pile. The more frequently the bulking agent is added to the pile, the less frequently mixing the pile will be required.
User behavior. At day use facilities, the urine-to-feces ratio is higher than at overnight facilities. This translates into an increase in capacity of 30 percent.
Total sustainable use. The amount of use that the Phoenix can sustain in any month correlates reasonably well with the average ambient temperature for that month. Use at 150 percent of capacity can be sustained for long periods as long as monthly averages are within ratings. Even higher rates of use can be accommodated for short periods, such as a Fourth of July Weekend. The capacity of properly maintained Phoenix systems for different ambient temperatures is shown in Table 1. A sample capacity calculation is presented in Table 2.
Facility design & site selection requirements and tipsSelecting a site. Choosing a site for a Phoenix facility will have dramatic effects on system capacity, building design, user accessibility, energy use, maintenance effort, and construction cost. Therefore, thoughtfully consider the needs of the composting toilet (and maintenance personnel) when selecting a site.
Disposal of liquids. Suitable conditions must exist for disposing of the liquid end product from the Phoenix. If local conditions, such as high ground water, preclude a leach field, then provide a holding tank, a raised bed evapotranspiration system, or a Phoenix liquid evaporation system. A holding tank requires strict attention to prevent overflows.
Preventing unauthorized dumping and vandalism. If the Phoenix is located near a parking area, the design must prevent the emptying of recreational vehicle holding tanks into the toilet. Locate the building far enough away from the parking area that drain hoses cannot reach it, or elevate the building slightly so that the toilet is above an RV’s holding tank. Provide a waste dump near the building that offers a convenient alternative, and post signs advising users against dumping chemical toilets and holding tanks into the Phoenix.
Similarly, locate trash cans and cigarette disposal containers immediately outside the building to reduce misuse of the Phoenix. If trash collection needs to be minimized, a trash container inside the toilet room will intercept those intent upon misuse, while not attracting others to dispose of their trash.
Designing the building. Nearly any building design satisfying the following conditions is compatible with the Phoenix:
Placing the tank. The dimensions of the Phoenix’s components are shown above. Installation clearances are shown in Figure 5.Provide convenient access to the Phoenix so that the composted end product can be removed easily from the basement area. It is very convenient with a daylight basement to locate a 3-foot-wide or larger door directly in front of each Phoenix so that the composted material can be shoveled directly into a wheelbarrow or other container (we provide a bin). For full basements, a good stairway is essential. Ladders and wall-mounted rungs not only are inconvenient, they are dangerous. Lapeyre manufactures a very compact 56-degree alternating tread stair that is quite convenient for basement access.
Placing the toilets & urinals. One or two toilets can connect to a Phoenix tank. The twelve-inch diameter toilet chutes can enter the Phoenix tank top anywhere within the dashed lines in Figure 5, although centering the chutes is preferable. For a two-toilet installation, the toilets must be located back-to-back against a common partition wall. Dimensions of the Phoenix toilets and installation clearances are shown in the following figure.
A trapless porcelain or stainless steel urinal can be connected to the Phoenix with conventional 1-1/2-inch DWV pipe. The pipe must slope continuously toward the Phoenix and enter the tank at least 6 inches away from side walls. The DWV pipe connects to the urinal drain and extends vertically through the floor or horizontally through the wall.
Options for managing Phoenix Leachate. Your selection of a site and building design should accommodate a sensible system for disposing of the liquid end product from the Phoenix, as not all liquid will be evaporated. Three strategies are viable (but some are better than others):
The ventilation system. The Phoenix is equipped with a rugged, efficient, ventilation system. The fan housing mounts directly over a precut hole on either side of the tank top, or at any other accessible location in the tank top. This allows the fan to be cleaned easily without removing it from the housing, or to be replaced easily.
Four-inch flexible hose connects the fan housing to 4-inch DWV pipe. The hose and pipe are easily contained within a 2×6 framed wall. The pipe and hose should slope continuously towards the fan housing so that liquid from rain or condensation will run back to the fan drain.
The 4-inch DWV pipe should exit through the roof near the ridge to avoid potential snow loads and downdrafts. Several shroud arrangements can conceal one or several juxtaposed Phoenix and evaporator vent pipes as long as the exhaust air exits several feet above the roof in an upward direction. Do not enclose any vents in a louvered cupola.
If the Phoenix is used in subfreezing temperatures, insulating the exterior vent pipe and the interior sections passing through cold areas helps prevent condensation and freezing. The room in which the Phoenix is located should be provided with a 25-square-inch (150-square-cm) opening for ventilation makeup air.
The electrical system. All electrical devices and accessories supplied with the Phoenix operate on direct current: exhaust fans, pumps, light fixtures, and the system monitor and controller. Twelve-volt systems are the default, but 24-volt systems are available (we install both, and can help you determine which is best for your situation). If power from a utility’s electrical grid is not available, electrical requirements can be met from an independent generating system, such as our photovoltaic system. We provide an a.c. power supply for use where 120-volt a.c. is available.
Photovoltaics. If a photovoltaic system is required, provisions must be made for mounting the photovoltaic array in an unshaded area, routing the array output conductors into the building, and locating the batteries and controller in the maintenance area. If utility supplied 120-volt a.c. electricity is available, locate an electrical outlet close to the Phoenix for the power supply and controller.
Strategies for managing the tank temperature. As explained above, the Phoenix must be in a warm environment to compost effectively. The composting process itself generates energy that increases the temperature of the compost pile, but first the compost pile must be warm enough for sufficient activity to take place. As the temperature of the Phoenix is increased, the rate of composting and heat generation increases.
In a below-ground basement, the predominant influence on the temperature of the tank room is the temperature of the ground, which can be much cooler than the outside air temperature during the season of use. Moreover, in some climates the outside air temperature varies greatly throughout a 24-hour period. If the ambient temperature in the Phoenix room drops below 65 degrees F(19 degrees C), the tank cools and the rate of decomposition declines sharply, reducing capacity. At ambient temperatures of 55 degrees F (13 degrees C) and lower, composting slows to a virtual standstill.
Preventing a cold tank room. Basically, there are two strategies:
Maintenance requirementsThe Phoenix operates much like a garden compost pile, requiring adequate food, air, moisture, and heat to support the organisms that transform wastes into a stable end product. The key to successfully operating a composting toilet is maintenance and the easier it is to perform, the more reliably it will be done. The Phoenix’s design invites proper maintenance with its convenient access doors, rotating tines, separation of liquid from solid waste, and liquid spray system.
Maintenance requirements and frequency depend upon the amount of use the system receives. The bulking agent must be mixed into the waste pile thoroughly, and trash removed, at least every few hundred uses. A heavily used system requires frequent attention and considerable bulking agent (about 1 gallon/100 uses). Locate a storage bin for bulking agent, and a container for liberated trash, conveniently near the Phoenix.Waste pile moisture must be checked and either more bulking agent or liquid added as needed. Systems in hot, dry climates, or systems that are used very lightly, require more attention to moisture control. Keeping the waste pile moist also prevents fires from vandalism or misuse. All Phoenixes include a programmable automatic spray system that uses liquid end product and/or fresh water to moisten the compost pile periodically.
Under many circumstances users can add bulking material through the toilet after each use, a “wood shavings flush.” This reduces mixing requirements so that periodically rotating the tines is sufficient to maintain a homogeneous mixture.
We strongly recommend keeping a log of conditions and actions (e.g. door counter readings, amount of bulking agent added, compost pile height) for a historical record and continuity among maintenance persons. We provide a suggested format and a get-started set of log pages along with our operating manual.
The finished end product must be handled carefully since it can contain some parasites and pathogens. However, it also contains valuable nutrients. Burying it near some plants will allow these nutrients to be reused. If it is pasteurized first, the small quantity of Phoenix solid end product can be used for revegetation (the pasteurizer’s heat source can be a solar collector).
Our complete manual, Phoenix Operation and Maintenance Instructions, is available on our Literature Rack.
Solid end product (compost). The amount of end product, and the frequency of its removal from the Phoenix, depends upon the amount of use, the rate of decomposition, and the quality of maintenance the system receives. The volume of finished end product is reduced by evaporation, draining (which also carries away dissolved and suspended solids), and decomposition. Coarse wood shavings, recommended for a bulking agent, do not decompose completely. However, they do compact and smaller particles fill some of the air voids.
Finished material should be removed from the Phoenix at least every two years. Approximately 12 bins of material (90 U.S. gallons, 350 liters, or 12 cubic feet) should be removed from beneath the tines. The amount of solid end product which must be removed from the Phoenix so use is sustainable will be about 30 liters (8 gallons) for every 1,000 uses, less if the tank is used at a lower rate or receives mostly urine. If this is too much, some material can be reintroduced at the top of the tank to maintain the compost level or some loosened material can be left in the clean out area below the tines.
Under the EPA’s sludge rule, 40 CFR part 503, Phoenix compost is a class B material suitable for land disposal in an area with restricted public access, e.g., burying on site. Finished compost must be handled carefully since it can contain some parasites and pathogens. However, it also contains valuable nutrients which can be reused by plants. If the compost is pasteurized, (a solar pasteurizer is easy to construct and very effective in sunny areas) it can satisfy EPA Class A requirements and may be applied on site with no restrictions.
Liquid end product. After filtering through the compost pile, the liquid receives secondary treatment in the well-aerated, stable, peat moss medium beneath the bottom baffle. The stability and tremendous surface area of peat provides an excellent filtering medium for treating liquid.
The amount of liquid discharged from the Phoenix depends upon the amount of use it receives, and the temperature and relative humidity of the ventilation air. Approximately 20 liters (5 gallons ) of liquid is added to the Phoenix for every 100 uses.
Incoming ventilation air circulating above the secondary liquid treatment medium can evaporate some of this liquid. The remaining liquid draining from the tank should be directed to a leaching field, holding tank, or a secondary evaporator. The liquid end product contains considerable bacteria and dissolved salts, but generally has a low coliform indicator concentration (<200 org/100 ml), low BOD, (<50mg/liter) and low TSS (<100 mg/1itre) compared to septic tank effluent, so a short (10-foot) leach line is all that is necessary.
Zero discharge on-site. If the Phoenix is located in an area where zero discharge is desired or mandatory, the liquid can be stored in a holding tank for periodic removal, or it can be eliminated with a secondary evaporation system. Either a small evapotranspiration bed or a compact active evaporator system can be employed. We can assist with design of the former and can supply the latter. Our liquid evaporation system includes a storage tank for peak loading, and a vent system and controls to optimize evaporation while using energy efficiently. Please get in touch with us for additional information.