Composting Toilets

DEFINITION
CONSIDERATIONS
COMMERCIAL STATUS
IMPLEMENTATION ISSUES
GUIDELINES

  1. Types of Composting Toilets
  2. Characteristics
  3. Suitability for Austin conditions

CSI Numbers:

027 400
152 180


DEFINITION:

A waterless composting toilet uses no water and produces a valuable fertilizer. There are some composting toilets that use a very small amount of water or foam. The water using kinds will typically be part of a total wastewater system.


CONSIDERATIONS:

Composting toilets are lawful in Austin provided the units are approved by the National Sanitation Foundation (NSF) or engineered by a registered Professional Engineer.

Austin presently composts sewage waste derived from its central wastewater system. The composted product is marketed as a landscape fertilizer called Dillo Dirt. For this reason, it may be difficult to justify the extra expense and maintenance needs of a composting toilet in order to gain compost when a city sewer line is available. Additionally, the low volume of water required to be used by toilets in Austin (1.6 GPF) makes the water savings from using a waterless toilet quite low.

If a home does not have central wastewater services, a composting toilet may be practical. Coupled with a sub-surface greywater irrigation system, the composting toilet can avoid the installation of a blackwater septic system. Although kitchen sink wastewater is defined as blackwater along with toilet wastewater, the Austin-Travis County Health Department may permit the discharge of kitchen wastewater with greywater in a sub-surface irrigating system if the site conditions are suitable.

There are commercial products available that range in cost from $1000 for simpler units to $10,000+ for fully integrative wastewater/composting systems. In areas where these systems can supplant large investments in septic systems, they are cost competitive.

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Composting Toilets Satisfactory Satisfactory in most conditions Satisfactory in limited conditions Unsatisfactory or Difficult Unsatisfactory or Difficult Satisfactory in limited conditions
Legend
Satisfactory Satisfactory
Satisfactory in most conditions Satisfactory in most conditions
Satisfactory in limited conditions Satisfactory in Limited Conditions
Unsatisfactory or Difficult Unsatisfactory or Difficult


COMMERCIAL STATUS

TECHNOLOGY:

The technology for composting toilets is greatly improved from models offered over 10 years ago. Odor problems are eliminated in the better models and performance is satisfactory. Newer models that offer complete self contained wastewater integration with greywater systems are now available.

SUPPLIERS:

Local availability limited.

COST:

Composting toilets are cost competitive with many septic systems. From a user’s standpoint they are not cost competitive with centralized wastewater systems, particularly those that compost the sludge such as Austin’s.


IMPLEMENTATION ISSUES

FINANCING:

Fear of limited resale opportunities and values may affect lenders.

PUBLIC ACCEPTANCE:

There is limited appeal for composting toilets. The maintenance requirement, although minor for many systems, prevents wider interest.

REGULATORY:

Ordinances #880310-H and #880310-I address composting toilets and are a part of Chapters 6-10 of the Austin City Code. The Austin-Travis County Health Department must issue a permit to install a composting toilet. The permit cost is $200 for an NSF-approved unit, or $300 for an engineered unit. The composting toilet is considered an alternative system and must be inspected annually by the Health Department. The inspection fee is $30. When the composting toilet is outside of the City, there is not an annual inspection requirement. The licensing procedure outlined in the Greywater Irrigation Section is required for composting toilets (percolation tests do not apply if a sewer is present).


GUIDELINES

1.0 Types of composting toilets

1.1 Self-contained/free standing
Contain and store the composting waste in one unit that can sit on the bathroom floor.

1.2 Split units
A separate storage chamber for wastes must sit lower than the commode section.The separate storage chamber needs to be accessible to remove the compost. This is a design consideration that must be addressed in a home that may typically use a slab floor on a flat site.

Some split units may flush the commode with a small amount of water or foam.

2.0 Characteristics

All units have a vent to prevent odors and some may be fan assisted.Several manufacturers offer heaters to accelerate the decomposition process in cold temperatures. There are different sized models available to meet the needs of various sized households.

3.0 Suitability for Austin conditions

Average household use of a composting toilet can be readily accomplished with commercial units. Professional engineering services are generally unnecessary unless unusual installation or size requirements must be met.

To use solar energy to help in the decomposition process (by heating the wastes), an engineered system would be needed.