A composting toilet system must complete three separate processes:

• Compost the waste and toilet paper quickly and odorlessly

• Evaporate the liquid

• Ensure that the finished compost is safe and easy to handle

Each of these tasks need a different set of conditions in order to work optimally. Realizing this, Sun-Mar engineers set for themselves a challenge: how to create three ideal environments in one single composting unit? The answer: building a separate chamber tailored to each specific task. It is the philosophy behind every Sun-Mar toilet produced since 1979.

Now the Centrex Plus takes this proven philosophy and expands on it, with chambers modified and extended to meet the demands of this high-capacity model.

The Composting Chamber

The ideal environment for composting is warm, moist, and oxygen-rich. Sun-Mar Creates this environment in the patented Bio-drum. In the Centrex Plus, this rotating drum is extended and divided into a primary and a secondary section. It is in the primary section that the composting process begins.

• Waste and peat moss enter the primary section through a port in the top of the drum.

• Warmth is generated and held in the core of the compost by the mass of material inside the drum. By using indirect heat, the compost does not dry out prematurely.

• The drum is periodically rotated by turning a handle on the side of the unit.
• This tumbling action supplies oxygen throughout the compost for use by the aerobic bacteria. Tumbling also thoroughly mixes the compost and distributes moisture evenly.
• Compost needs to be kept moist but not saturated, as too much liquid can drive out essential oxygen. Excess liquid, if any, is drained through two screens at the rear of the primary section, directly into the evaporating chamber.
• The waste breaks down and flows gradually to the end of the primary section where it moves through a divider and into the secondary section of the drum.
• Here the composting is substantially completed. When this secondary section becomes half-full, the compost automatically begins to drop into the first finishing drawer at the end of the unit.
• If ever necessary, compost can be removed directly form the Bio-drum. When the lock is released, the drum can be rotated backwards. The compost then drops through the open drum door in the secondary section and into the second finishing drawer inside the unit. Otherwise, when the drum is being rotated to mix the compost, the drum doors close automatically.
• After rotating the Bio-drum locks in a top dead center position ready to receive new material.

The Evaporating Chamber

Compost must be kept moist but not saturated. The ideal environment for evaporating any excess liquid is a large surface area combined with heat and moving air. Sun-Mar meets these criteria in the Evaporating Chamber.

• Any liquid not absorbed by the compost in the drum drains through one of two screens, directly into the evaporating chamber.

• The liquid falls to the first of two cascading trays. When this tray is full, the liquid cascades onto the second tray immediately below, and then onto the floor of the chamber. These trays help oxygenate the liquid, and trap any peat moss particles. This three-tier design maximizes the use of space in the chamber.

• Air is drawn in through intake holes at the bottom and rear of the unit. The air flows over the evaporating surfaces (which total over 10 sq. ft.) And up through the vent stack. On electric models, air is drawn in by a fan. Non-electric models use natural draft induced by the chimney effect of the 4" vent stack. In both cases, a partial vacuum is maintained, ensuring that no odor escapes.

• Evaporation is assisted on electric models by two 250 watt thermostatically controlled heating elements. Sealed in a compartment underneath the evaporating chamber, these heaters warm the floor of the chamber without drying out the compost. A three position switch allows one, both or neither heater to be engaged.

• The cascading trays can be removed and cleaned if necessary through a large access port at the front of the unit.

The Finishing Drawers

The compost finishing drawers serve two functions: to receive the compost in an easily-accessible container and to complete the composting and sanitation processes.

• There are two compost finishing drawers in the Centrex Plus. Both are easily removed by hand and interchangeable.

• The first drawer is inside the collection housing at the side of the unit. This is where the finished compost automatically falls after leaving the second section of the Bio-drum.

• The second drawer is located inside the unit. Moving compost from the first drawer to this second station allows the composting cycle to be extended if necessary. This can help ensure that the compost is safe to handle.

• Both drawers provide a dry and safe environment for the compost, keeping the finished product isolated from fresh waste and possible contamination.