An introduction to composting toilets

Camp Glenorchy Eco Retreat

Using composting toilets to slash water use

Flushing toilets accounts for 18% of water use in New Zealand households. In a visitor accommodation facility like Camp Glenorchy, the amount of water used for this purpose each year could easily be more than 300,000 litres – enough to fill a short course swimming pool.

Camp Glenorchy has aimed to reduce that 300,000 litres to zero, by using flushless composting toilets in all new buildings on the site. This approach will help Camp Glenorchy achieve its goal of using 50% less water than similar facilities, as well as enabling the site to provide for its own water needs as much as possible. As well as eliminating the need for flushing, composting toilets generate virtually no wastewater, reducing the need for wastewater treatment and minimising  effects on groundwater sources.

The use of composting toilets is an on-going educational journey for Camp Glenorchy. Their aim is to establish a pool of knowledge that can be used by other projects to understand the process of building and operating with composting toilets.

Composting toilets arriving to Camp Glenorchy

How do they work?

Decomposing

The composting toilets used at Camp Glenorchy require no water for flushing. When someone uses the toilet, waste drops down a pipe into a tank where natural processes break it down, transforming it into a soil-like material called humus that can be used as fertiliser for gardens. In fact, the toilets at Camp Glenorchy work much like garden compost piles, using food, air, bacteria, moisture and heat to transform waste into a usable end product.

Maintenance

Maintenance is a key requirement for composting toilets to work safely and efficiently. Depending on how frequently they’re used, owners need to perform weekly, monthly and yearly tasks. At Camp Glenorchy, frequent tasks include adding bulking agents (such as white wood shavings) to make waste more porous, and rotating a crank handle located on the tank to help with the downward movement of the pile. The moisture level of the waste and the cleanliness of the components also need to be checked every few weeks. 

When they are well maintained, composting toilets do not give off any unpleasant smells. Like a standard toilet, if they smell at all it generally means something is not working as it should and needs to be fixed.

Application

On average, finished compost is removed once a year from the bottom of the tanks. Tests are performed on the resulting humus to find out its composition and whether it is compliant with health standards. This information is used to determine if the components in the mix are actually beneficial to the soil, if it needs any additional processing to meet environmental criteria and ultimately how the compost is used in the garden.

Rotating the crank handle of the composting toilets at Camp Glenorchy helps with the downward movement of the pile.

Composting toilets at Camp Glenorchy

<p>There are 21 toilets installed on site, with six in the Amenities Building, one in the Maintenance Building and two in each cabin. Each of these buildings has a cellar or basement where the tanks are kept at a stable temperature year round. During the design stage it was estimated the 21 toilets would generate approximately 2.4 cubic metres of compost each year<sup>1</sup>.</p>

When guests open the toilet lid, air from the room is pulled down the toilet into the tank and then expelled through a vent on the roof. This means each time a composting toilet is used, the bathroom will actually smell better than before!

When using a toilet at Camp Glenorchy, guests don’t need to do anything different than they would do at home. Maintenance staff add wood shavings directly to each toilet’s tank, as frequently as once a week during peak season.

How could composting toilets benefit larger communities?

<p>Modern cities rely on a vast network of water infrastructure to deliver potable water to buildings and collect wastewater for treatment. Costs of operation, maintenance and upgrades to keep up with increasing demand are high. How high? Ratepayers across the Queenstown Lakes District, for example, will need to pay an estimated $27,000 a day every day for 10 years for new infrastructure works required to meet the demands of the growing population<sup>2</sup>.</p>

Every composting toilet used reduces demand on water infrastructure by eliminating potentially tens of thousands of litres of water needed for flushing each year.

<p>Every composting toilet used reduces demand on water infrastructure by eliminating potentially tens of thousands of litres of water needed for flushing each year<sup>3</sup>. Not only is the need to supply this water eliminated; the resultant wastewater doesn’t need to be taken away and treated. As well as reducing demands on infrastructure, users of composting toilets reduce the amount paid for both water supply and wastewater removal.</p>

In New Zealand, composting toilets currently can’t be used in urban areas where a mains sewer connection is available. However, authorities can provide a waiver and some Councils have been very receptive to the idea.

A composting toilet is lowered to a cabin's basement at Camp Glenorchy

Composting toilets can be especially beneficial to communities without a public sewer infrastructure by reducing the amount of waste sent to septic tanks and the volume of leachate in dispersal fields, helping protect underground aquifers. In Glenorchy this issue has been identified as a potential risk due to the shallow groundwater level. Increasing levels of discharge from a growing resident and visitor population may eventually impact the bore that is used for town-wide potable water supply. Sustainable technology such as composting toilets could reduce the required investment in sewage treatment facilities as well as the size and frequency of upgrades by reducing the amount of water that needs to be treated.

Footnotes
  1. In optimal conditions, the toilets used at Camp Glenorchy will produce 30 litres of compost for every 1,000 uses. Based on the number of uses per visitor, it is estimated that Camp Glenorchy will generate around 2,400 litres or 2.4 cubic meters of compost per year.
  2. Queenstown Lakes District Council, Conserving Water.
  3. Average of 12.9 flushes per day per household and an average flush volume of 6.2L (based on BRANZ study, Water End Use and Efficiency Project) = (12.9*6.2)*365.

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