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How a Sun-Mar Works

A composting toilet must perform three completely separate processes:

Compost the waste and toilet paper quickly and odorlessly

Ensure that the finished compost is safe and easy to handle

Evaporate the liquid


Many years ago Sun-Mar engineers realized that to work properly, these three tasks required independent chambers, each with its own separate environment. This revolutionary new three chamber approach first developed in 1979 proved so successful that today it is incorporated into all Sun-Mar units.

Our commitment to superior design makes Sun-Mar the wise choice for anyone who wants a durable and high quality product. Read on to learn the technology behind our composting toilets and the advantages of these exclusive Sun-Mar features.


  The Composting Chamber

Sun-Mar engineers found that the ideal conditions for fast, odorless composting were best provided in a rotating drum, (we call it the Bio-drum), where the compost can be kept completely oxygenated, mixed, moist and warm.

Waste and peat moss enter through a port in the top of the Bio-drum. The drum handle on the front of the unit is turned periodically to rotate the Bio-drum. This tumbling action thoroughly oxygenates and mixes every part of the compost, keeping it uniformly moist.

As the drum rotates, a door closes automatically to keep the waste inside the drum. After turning, a lock automatically maintains the Bio-drum in a top dead center position ready to receive new material.

To prevent the compost from getting saturated, a screen at the rear of the drum filters any excess liquid directly into the evaporating chamber. By protecting the compost from direct heat, the Bio-drum also keeps the compost uniformly moist.

Lastly, the Bio-drum can hold the necessary mass of material to retain the natural heat developed in the core of the compost. On some units, insulation on the outside of the drum prevents heat loss from the Bio-drum. When the drum gets full, some compost is extracted into the finishing drawer. This is done simply by pulling the drum locker, and rotating the drum backwards. Now, the drum door remains open, and compost falls into the second chamber - the compost finishing drawer.

Advantages of Composting in a Bio-Drum

Tumbling implants oxygen throughout the compost for use by aerobic bacteria

Tumbling ensures that the bulking material is well mixed into the compost.

The screen at the rear ensures the compost does not get saturated and drive out the oxygen

Tumbling distributes the moisture evenly throughout the compost

The compost is shielded from direct heat and so does not dry out.

The mass in the drum enables the compost to hold warmth in the core of the compost.

The Compost Finishing Drawer

The compost finishing drawer, the second independent chamber, is below the composting drum, and just above the evaporating chamber. Compost in this drawer is totally isolated from material in the Bio-drum, is surrounded by drying air, and is no longer subject to contamination from fresh waste. It is here that the composting and sanitation processes are completed, and the compost becomes safe to handle. The pull-out finishing drawer is removed by hand and the sanitized compost may be emptied whenever it is necessary to extract more compost from the drum. To be doubly safe, compost should not be used on edible vegetables.

Advantages of a Separate Compost Finishing Drawer

Composting can be completed in the drawer without contamination by fresh waste.

Compost in the drawer is gradually dried ready for removal

Finished compost can be simply and safely removed

   The Evaporating Chamber

The third chamber, the base of the toilet, is the evaporating surface from where any excess liquids which cannot be absorbed by the compost are evaporated or drained. Air is drawn in through intake holes at the base of the toilet, over the evaporating surface, and up the vent stack. On electric models, air is drawn in by a fan, while non electric models use natural draft induced by the chimney effect of a 4" vent stack. In both cases a partial vacuum is maintained which ensures that no odors can escape. Evaporation is assisted onelectric models by a thermostaticallycontrolledheating element in a sealed compartment underneath the evaporating chamber. This heater keeps the floor of the chamber warm.

Advantages of a Separate Evaporating Chamber

The large surface area maximizes evaporation.

A large volume of air moves directly over the evaporating surface to speed moisture removal.

A base heater directly warms the evaporate for optimum results. (Electric units only!)

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