Wastewater System and Composting Toilet

In this chapter, we describe the wastewater system and toilet for the Florida Solar Cracker House. Household wastewater is classified by Health Department officials into blackwater and graywater. Blackwater is waste carried off by toilets, urinals and kitchen drains. Graywater is all other household wastewater, including bath, lavatory, laundry, and sinks, other than those in the kitchen. In some locales, kitchen sink water may be considered graywater. Normally, all wastewater drains into a public sewer system, or, in rural areas, into a septic tank, and from the septic tank into a drainfield. A septic tank is, basically, a holding tank that prevents solid waste from being discharged into the ground until it is anaerobically broken down into liquids and gases. A drainfield is a series of perforated pipes laid in a specially prepared bed of gravel and dirt that acts to filter the wastewater as it seeps into the ground.

A standard flush toilet is a tremendous waste of pure drinking water. In a typical household, 35 to 45% of all household potable water is flushed down the toilet. Also, it doesn't take much thought to realize that mixing large volumes of rather clean shower and laundry water with water from the toilet and sending it all to a tank in the ground, where the pathogen-laden overflow runs into the ground under your yard, doesn't make a lot of sense, either. We thought we could do better. This picture shows the best use we could think of for a flush toilet!

The term "composting toilet" is generally applied to two different types of toilets; true composters, and dehydrators or dry toilets. True composters have a large enough volume so that the heat generated by the aerobic decomposition of waste is sufficient to evaporate the collected liquids. They are designed so that the generated heat also provides natural ventilation, keeping the toilet fixture under slight negative pressure, which eliminates odor in the bathroom. In some models, a small fan augments ventilation. Dry toilets, on the other hand, are only slightly larger than a conventional toilet, but require a heating element to evaporate liquids, as well as a fan to draw out water vapor and odors.

The State of Florida permits the use of toilets that are American National Standards Institute (ANSI)/National Sanitation Foundation (NSF) approved. As of December, 1994, there were four manufacturers of composting toilets with models so approved: true composters, Clivus Multrum and CTS (Composting Toilet Systems), and dry toilets, Biolet and Sunmar.

The Biolet and Sunmar models certified by ANSI/NSF require electric heat to operate properly, and even at an average continuous power consumption of only 150 Watts (as listed by Sunmar for the XL model), would consume most of the power we generate during the winter. Also, from what we have learned over the internet from dry toilet users, we are wary of trying to use these toilets "unplugged". The disadvantage of true composters is that they are expensive (around $3,500) and large (a tank is mounted below the bathroom floor, connected to the toilet fixture by a chute). Because our house is elevated, the size is really no problem, so we installed a Clivus Multrum "Multrum I" toilet.

The first picture is the composting chamber located in our electric room under the house. This composting chamber is directly below the toilet fixture in our bathroom

Once the decision is made to use a composting toilet, it seems rather silly to discharge the remaining graywater and kitchen sink water into a septic tank. While solid toilet wastes need time to settle and break down, graywater is best discharged into the soil immediately. Pathogens are increased when graywater is allowed to sit. Also, water from the kitchen sink hardly seems on a par with toilet waste in terms of harmful pathogens. Of course, what we think is an appropriate solution to disposal of wastewater may not necessarily sit well with the Health Department officials, and a permit for a sewage disposal system is required before a building permit can be issued. With these ideas and plans in mind, we made an appointment to see the Environmental Health Director at the Putnam County Health Department, prepared for a battle. Much to our surprise and delight, he reacted to our ideas with enthusiasm and encouragement. However, a permit to leave the septic tank out of the system requires approval from the State (the County cannot make this decision). We were given the names and addresses of officials to contact in Tallahassee, and we discussed ideas for a proposal for our experimental system. The next day, we sent off a 9 page proposal describing the plan and requesting permission to eliminate the septic tank.

The proposal was probably longer than it needed to be. First, it described the philosophy of the house and its size and setting with a plat map, a floor plan, a woodland tracing and a soils map included. The woodland tracing is a map that had been prepared by the County Forester showing the types of habitat on the property. Next, was a section describing in detail how toilet wastes, kitchen blackwater and graywater were to be disposed of. At that time, we had proposed using a Sunmar XL toilet, but any ANSI/NSF approved toilet would be OK. We proposed to use two kitchen sinks, one for rinsing and one for washing dishes. There would be no garbage disposal, and any grease or oil would be wiped off with a tissue and put in the compost pile. The drain from the dish-washing sink would be routed directly into a large outdoor compost bin, and the drain from the other sink would be normal graywater. Of course, all tissues put into the compost will be non-bleached and bio-degradable and all cleaners used in the house will also be bio-degradable.

The graywater, estimated to be about 60 gallons per day, see Water Supply, would be run into a drainfield through a 50 gallon surge tank. The surge tank is simply an above-ground barrel to accomodate surges of water, such as a laundry tub emptying. The drainfield would be 60 square feet in area and built according to code requirements for the region. It took several months and a few phone calls, but the proposal finally was accepted as an experimental system. We had to sign a statement saying we would hold the State harmless, should the system fail, and we would allow inspections of the system.

How does our experimental system differ from a standard system? The sewage flow from a standard house the size of ours (about 1350 square feet of building area) is taken to be 450 gallons per day. This gives a minimum septic tank capacity of 900 gallons (which is the minimum size blackwater septic tank for any size house in Florida). The standard drainfield size for our type of soil would be 360 square feet. Thus, our experimental system is not incrementally smaller, but drastically smaller than the standard system. The drainfield was reduced by a factor of 6 and an enormous septic tank was eliminated altogether. The State of Florida and Putnam County are to be congratulated for their open-mindedness and willingness to allow experimentation.

A word about graywater disposal. There are several excellent books available about ways to reuse graywater for irrigation. These schemes are very beneficial in dry climates such as the Southwestern US, because scarce water resources can be fully utilized. In Florida, rainwater is abundant and the water table is normally only a few feet below the surface. Safely disposing of contaminated water is the most urgent problem. It makes little sense to reuse graywater when we will have to drain out 2/3 of the water we collect in our cistern because of abundant rainfall. In fact, the water table is so high is our area, that our drainfield is required to be mounded about 18" above the surface in order to avoid contaminating the groundwater.

Use of the Composting Toilet

We purchased our Clivus Multrum M1 composting toilet in September of 1998 from Clivus Multrum, Inc., 15 Union Street, Lawrence, MA 01840. Everything was included, even a rake. The total price was $2,375, plus $450 shipping and handling. Considering that we did not have to put in a septic tank, our drainfield was so small, and we had no plumbing to deal with, we probably just about broke even. I should start by saying we are totally happy with the toilet and how it has performed, although it had a somewhat rocky start.

During the first year, we experienced numerous outbreaks of flies, and even small crawling insects that I observed on the toilet seat! In an attempt to create a system of beneficial insects and worms inside, we added earthworms and dirt and hay from our garden. We resorted to bug spray and fly traps inside the compost chamber. Mostly, the sprays were plant-based and biodegradable, but once out of desperation we sprayed with Spectracide Bug Stop fogger. Eventually, after about a year of fighting bugs, they subsided. We began removing solid material from the composter after about 1 year, and noticed numerous beneficial insects - earwigs - in the compost, but no earthworms. After about 2 years of using the toilet, we rarely had to spray, and only used mild, plant-based sprays, such as Bioganic brand flying insect killer. Still no earthworms in the compost, but thousands of earwigs. Finally after about 3 years, we started noticing earthworms as well as earwigs. We had not added any earthworms to the compost chamber for 2 years! Now, after more than 5 years, there are thousands of earthworms and very few earwigs and no insects in the bathroom, save for the occasional fruitfly. It appears to be a healthy, balanced system.

Routine maintenance of the toilet is required about every 1 to 2 weeks. This involves opening the upper chamber and raking the accumulated pile flat. A rake is kept inside the chamber for this purpose. After raking the pile flat, about one 5 pound coffee can full of wood shavings or sawdust is added on the top. The chamber is set up to allow misting of water on the top of the compost, which we do about once a week for a few minutes. The fixture in the bathroom is very easy to keep clean. The top parts are white fiberglass which easily wipe clean, and the inside consists of a black plastic tube, 14 inches in diameter, which does not usually get dirty, and if it does, can easily be cleaned with a standard toilet brush and some water.

The Clivus Multrum does not attempt to evaporate liquids, but allows the urine and any water added to filter through the compost and collect in a separate chamber at the bottom. The capacity of the liquid chamber is 40 gallons. This liquid fertilizer is siphoned out of the holding chamber directly onto plants outside. We just use a garden hose and siphon manually, but a submersible pump that automatically turns on when the liquid reaches a certain level is also available. We remove liquid only about every 3 months, so we opted for the manual route. The liquid is completely odor free and is clear tea colored. We put a little in a jar once to show to visitors, and the same sample is still there on the table, looking just like it did 2 years ago! The flowers love it!

We remove solid material also about every 3 months. This involves digging material through the finish (lower) door using a small hand shovel into a bucket. We remove about 15 gallons at a time.

This picture shows the open lower door. We tape a paper to the bottom for easier cleanup. The compost does not small bad and just looks and smells like moist, rich dirt, full of earthworms. The following two pictures show the removed compost. Can you see the earthworms?

We use the toilet compost eventually in our vegetable garden. In this way, we are closing the nutrient cycle as much as possible. It feels very right to do this. Instead of treating a valuable resource as "waste" and possibly polluting with it, we are recycling it locally, and utilizing the nutrient value, which minimizes the need to bring in fertilizers. Before we use the compost in our garden, we layer it into an outdoor compost bin, where is stays for about a year. We monitor the temperature of the outdoor pile and ensure that it reaches a temperature sufficient to kill any pathogens. A good chart on temperatures and times for safe composting of humanure is given in "The Humanure Handbook" by J. C. Jenkins. This is a delightfully informative and funny book that is a must read if you want to begin using humanure in your garden. Beware that anyone with "fecophobia" might not be ready for Mr. Turdley! The next two pictures show Randy tending to the compost piles. At any given time, we have one pile ready for use, one maturing, and one we are actively adding to.