Composting toilet in a caravan

Hi Keith,

My understanding is that the heater element is not essential to the operation of the toilet - it helps in drying out the compost and reduces or eliminates the need for manual emptying of the liquid compartment, but you can choose not to use it at all, or to just use it when power is plentiful.

The fan is basically a 12v computer fan, which only draws a couple of watts, but it needs to run regularly as it is the key to the function of the toilet. It dries the compost, speeds the aerobic decomposition and eliminates odour from the bathroom. I believe you can run it directly from a small solar cell with no battery, but a full-time power supply is preferred.

The exhaust passes through a charcoal filter, and that (combined with a 'healthy' aerobic action) apparently makes it essentially odourless. Theoretically, it should be even less smelly than a regular bathroom, as any bathroom smells are sucked down through the toilet instead of wafting out into the van.

I'm just starting on a small off road caravan with shower and toilet and I'm very interested in this. But I'd like to see one installed with a happy track record before taking a punt on it. The idea of not having to empty the smelly thing every few days is fantastic.

Col,

I dont think it would be a good look at roadside rest areas.

Cheers,
Heather

Looks ! your camping for crying out loud, want a flushing toilet and a bidet stay at a 5 star Hilton instead of a million star bush site. LOL.

Hi Keith,

There is something wrong with that info - those dimensions are not for the mobile. The Mobile is only about 480mm wide and about 580mm deep. I forget how tall it is as I can't find the PDF manual at the moment, but they are fairly tall (a folding footrest is included). To be honest, the 'problems' you have been told about all sound a lot like misinformation being spruiked by somebody more interested in selling you something else.

I asked the Melbourne distributor a few questions regarding the heating element etc and they gave me all kinds of info which conflicts with the manufacturer's specs (eg heater wattage, ability to separate heater function and fan function etc). I suspect that the Mobile is not a big seller here in Aus and as a result, dealers don't have a good grasp of the details.

What I can tell you (after reading the PDF and a number of reviews etc) is that these things have already been around for over 10 years and those who own them seem to swear by them. The basic principle is that you poo into a drum of compost. Use as much toilet paper as you like, and occasionally add some sawdust and compost improver (moss) but use no additional water and certainly no chemicals. Every couple of days you rotate the drum a few turns (via a lever that swings out from under the seat).

When the drum is getting full you perform an operation to drop some of the compost into a 'finishing' drawer. When the finishing drawer needs emptying it is odourless compost that can be put straight on the garden. In full-time use by a single person this would only need to be done every few weeks, even months.

A 12v fan (<5w) keeps air flowing through the compost, and out through a vent, via a zeolite and activated charcoal filter to eliminate odour (as mentioned before, a healthy aerobic digestion produces a lot less odour than most of us imagine).

There is a third tray which collects the liquid. This will evaporate off (and out through the vent) if the conditions are warm enough, and is assisted by the heater. From memory the mains heater is about 160w, but you can opt for a 12v (120w?) heater. In North America the heater is expected to operate about half of the time. In Australia presumably a lot less will get the job done.

If you don't use the heater at all, you'll have about 1L of liquid per person per day to accommodate (Northern hemisphere estimates again). The option is there for you to plumb directly to a black water holding tank which you then empty as appropriate. Obviously, in hotter/drier climates more liquid will evaporate by itself, and if you put less liquid in to start with (ie, water the trees instead) then there's even less of an issue.

Regarding the ruggedness, much is made of the additional strength and seals engineered into it to survive marine and mobile applications. Whether it is up to extended touring on corrugated roads I couldn't say, but I don't plan to do that.

I'm not associated in any way with the maker or any dealer, but I think this design really deserves a fair crack of the whip and not to be 'poo-pooed' simply because it is a departure from the normal chemical solutions.

After even more reading and research I'm almost certain that it's perfect for my needs. I'm surprised that noboidy on this forum has had experience with them but there are a number of articles and reviews on the net if anyone else is interested.

Hi Keith,

I guess you could swap the heater element out for a coil of something but you'd have a couple of issues to deal with - firstly these things aren't swimming in spare space so you'd have a task making something else fit the compact design.

Secondly, the warmth and humidity it creates is highly beneficial to the action of the microbes. You can get away without it, but the warmer you can keep the compost the faster it works, and the ideal solution is continuously. Not sure how long and how often you'd be running the HWS but its possible you could go to a lot of work to set something up that doesn't run for long enough throughout the year to make that much of an impact.

I'm leaning towards getting the version with the 12v element. I figure that whenever I've got mains I'll have plenty of 12v available, as well as when I'm actually driving. I could also feed any excess solar production straight into the element, getting some value out of it without costing me any battery capacity.

Having said all that, I don't see any reason why you couldn't install some additional heating underneath it. My plan is to have a combined shower and toilet room, and I'll probably fabricate a floor / shower pan out of stainless or ali checkplate. By extending the metal sheet to provide a floor for the toilet (suitably supported of course) and removing any timber flooring material it should be possible to warm the whole unit from underneath, make no modifications to the toilet and retain the convenience of the electric element. In fact I may well incorporate this into my design, as I don't yet have a 'winter' heating solution and I'll be living in the van permanently in a year or two.

I'm keen to stay in touch over this, I'll send you an email but it's probably good to keep related discussion to this thread in case it helps or attracts input from others.