A hybrid toilet system separates three kinds of wastes:  urine, solids, and blackwater/greywater. It combines a urine-diverting (UD) toilet, a separator and composting system for the solids, and a blackwater/greywater drain.

An eco-toilet is any toilet that uses less water and recovers more nutrients than a conventional flush toilet. Ideally, it should do both – use no water and recover all nutrients.

Starting June 2014, we have have been using and testing a new eco-toilet design that meets these high standards. It combines a waterless, urine-diverting toilet from Sweden, and a modular-bin composting system from Vermont. The result is an eco-toilet that  is pleasant for the user, waterless, urine-diverting, energy efficient, meets high sanitation standards, is easy to use and maintain, and recovers virtually all the nutrients.

This hybrid design is being monitored by the Barnstable County Department of Health and Environment as part of Falmouth’s Eco-Toilet Demonstration Program to determine the degree to which the system reduces the amount of nutrients in wastewater.

Please read below, or download the Hybrid Eco-Toilet Report. You can also read about other commercially-available hybrid systems.


Nutrient storage & recovery

The urine storage tank can be either in the basement or outside in the ground near the house.

It should be large enough to hold at least six months of urine, so a two-person household should have a tank that is at least 150 gallons in size. The capacity actually needed is affected by the number of people in the household and the lifestyle of the household (ranging from rarely home to entertaining lots of guests). The total capacity can include more than one tank. We recommend an on-site capacity to hold a year’s volume to reduce the number of pump-outs required.

The urine can be removed from the tank by either filling five-gallon sealable buckets or jugs with tight lids via a spigot located near
the bottom of the storage tank for removal. An electronic system can be installed that warns the homeowner and/or the service company that the tank is nearly full and service is needed in a few weeks.

The compost starts as a layered mixture of feces, toilet paper, wood shavings and optionally facial tissues and paper towels in the blue bin. When used by two people, it takes about 6-12 months for the bin to fill up.

Fig. 1: Removal of a full bin from the chute
Fig. 1: Removal of a full bin from the chute

To see if bin is full, the homeowner can either open the lid and look, or install an optional electronic warning sensor. When a bin becomes full it is disconnected from the chute, (Fig.1) and a new empty bin is put in its place, (Fig. 2).

Once it’s filled, the bin is set aside for secondary composting. After topping it off with some garden soil, a layer of wood shavings and some water, a new lid is put on and connected to continuous aeration, using the same fan system that provides ventilation for the active bin, allowing it to compost more completely for a longer retention time. During that time pathogens are gradually eliminated in the process.

Fig. 2: Installation of a new empty bin to the chute
Fig. 2: Installation of a new empty bin to the chute

The volume and weight of the finished compost will be much less than the starting material, due to more complete decomposition and evaporation of moisture. The volume of compost in the bin, after a one-year retention time, is reduced by 50-80%. The volume of finished compost produced by one person in one year is about 18 gallons. Further retention time will reduce the volume more.

The finished compost material removed from the bin is slightly moist and looks like rich garden compost. The bin can be wheeled outdoors to be emptied. The empty bin is stored for later use.

Please read about home-scale nutrient recycling for more information about the next steps.

For more information, please visit the following pages:

Why Recycle Nutrients?

Large Bin Composting Systems

Large Batch Composting Systems

Self-Contained Waterless Systems

Urine-Diverting Systems

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