How to Build a Solar Waste Compost System
Composting human waste is an important aspect of off-the-grid living that many people do not consider ahead of time. Wastes need to be safely processed before entering the ground or water supply. However, wastes also accumulate quickly, and finding places to deposit them is a challenge. You can create a good system that is part septic tank and part composter with minimal resources, and adding solar energy will dramatically enhance the efficiency of the disposal process.
Building the Basin
The first step is to choose an appropriately-sized basin to hold the waste. A 4x8x3 concrete basin or large poly container should do the trick. You will also need to install a spring-hinged release door that opens out to drain the waste. The door should be at least a few inches tall and be long enough to cover about 80% of the width of the basin. This will allow wastes to escape while minimizing the chances of getting clogged on the way out. However, you should do some research in order to develop a customized system based on your needs. Bury the basin so it is set just below the level of the ground.
Constructing the Frame
The next step is to build a box that will rest atop the basin. The edges of the frame should be constructed with 2×4 pieces of wood that will be between ½ and a foot high. Use plywood to create the outer edges. You can place a small layer of insulation between the base of the frame and the basin in order to provide a tight seal and regulate temperatures inside. The next step is to build a frame for the top of the box. You will place a plywood sheet on top of the box later. Add another layer of insulation between the plywood and the top portion of the frame.
You need to install two large PVC elbow joints on opposite ends of one side of the box. One pipe will be for dumping your waste. The other one will be for a vent pipe that will allow evaporated moisture and gases to escape. You want to attach a vertical piece of PVC pipe to the vent pipe joint that is about a foot to two feet in length. Cap off the dump pipe but don’t seal it. It can be removed and re-attached while dumping waste into the system.
Constructing the Roof
The final component is the roof. You want to use a single piece of plywood and install windows or glass over as much of the surface area as possible. Old windows work well because they are cheap, readily available and already come framed. Simply cut out sections of the plywood, add some sealant and pop in the windows. You don’t need high quality windows or glass for this project. The aim is to allow as much sunlight in as possible to speed up the composting process.
You can also add some cross-beams beneath the plywood between the windows for additional structural support. Place a thin layer of insulation between the top of the frame and the roof before laying it in place. You don’t have to secure the components together, but if you live in an area where wind or other disturbances may dismantle the system, then using some screws or nails will make the unit more stable. You may also want to consider angling the box so that water can run off when it rains or snow melts.
All you need to do now is add your waste. This system is intended to be used in conjunction with a composting toilet that has a bucket that can be transported to the tank and dumped accordingly. Do not put in paper or sanitary products, and do not use this system for waste water from showers, laundry or washing dishes. This is only intended to process waste. Adding additional liquid will cause the tank to fill up and lengthen the overall decomposition process.
The beauty of this system is that the heat from the sun can warm internal temperatures well above 100 degrees. Actual temperatures will vary depending on your location and intensity of the sunlight. However, it is the heat that causes microbes to eat away at the waste. Since most waste is comprised of more than 90% water, the water evaporates through the vent pipe and leaves a minimal amount of solid material behind. Chances are that you will never have more than an inch or two of solids on the bottom at any given point in time, even if your whole family is using the system for years.
Make sure that you place it far enough away and downwind from your home. This will minimize the smell of the decomposing waste as it vents into the atmosphere. Try this out for yourself and see how easy it is to safely dispose of human waste without the need to dig holes and bury wastes after your compost toilet fills up.
