The Dalek Loo.
To be blunt - this page is about shit. If you have a problem
with this it may be time to leave.
This is it - the Dalek loo. So far it's working very well but it's only been in use for 3 months (since easter 1998). The loo was made by fibre-glassing a compost bin with an old toilet seat at the user interface end and fly proof vent holes fore and aft. A fan may be fitted in future but doesn't seem to be needed at the moment. This loo is a "batch" type - when it's full some years from now it will most likely be left in place and new toilet built to replace it. Later when the composting is complete the toilet can either be emptied or lifted off the pile and moved somewhere else. The vent holes are standard plastic plumbing fitting and can be sealed off with screw on caps.
In order for a composting loo to work properly it is essential that it remains aerobic - this kills harmfull pathigens, reduces offensive odors and is less attractive to flies. To remain aerobic the system needs oxygen throughout the pile, this means ventilation and removal of excess water but some dampness must remain for the composting to take place.
Four methods are commonly used (in combination) to achieve this.
A fan is a fairly standard feature in most composters and is worth some thought. I would expect that a factor-4 improvement would be possible in many existing designs. While the power needed to run a fan may not be an issue in a grid connected house - it sure is for a remote power system (eg. solar). For example our co-op is installing a Rota-loo, this unit comes with a 7.5 watt electric fan. The previous owner was grid connected and the fan was left to run continously. The loo was in continous use by a family and the loo was undrained.
Now we're going to use solar power.
My educated guess would be our 7.5 watt fan would require a panel of
around 60 watts and 14 days worth of energy storage. Say .624 amp@12 volt
by 24 hours a day by 14 days - around 200 amp hours @ 12 volts. The panel
would cost around $500 oz, batteries around $700 (plus replacement costs)
and maybe a regulator $??
How do we improve this?
Well lots of ways....
The fan also has another function - it stops odors from escaping when the lid is raised (and creates a refreshing breeze). It may well be worth fitting a variable speed fan which only runs at full speed when the lid is raised. It's hard to know the appropriate level of control. My guess is one voltage sensor on the battery and one humidy sensor in the chamber plus a $10 micro-controller would be good value for money - if you're handy with micros which fortunately I am. This may be another project for my project page..
As for electric heaters, that's an offensive idea to the energy conscious person. If the loo won't work without an electric heater then it's the wrong answer to the problem. Heaters aren't just to dry things out - the composting action is slowed or stopped under cold conditions. In our climate this shouldn't be a problem. Even if the composting stops in winter - so what - it'll catch up again in spring.