Project Update: Composting Toilet

It has been six months now that we've been using our self built composting toilet.  I've had a number of questions about it, so I thought it would be good to do a blog post to update everyone on our experience with it thus far.

These are links to the posts that deal with the reasons and theory behind switching to a composting toilet, the description of the build itself, and a short update about adding a normal toilet seat.  I won't re-iterate anything in these posts, so if you haven't read them it would probably be handy in order to know the background on this project.  One thing I will re-iterate though, is to urge everyone interested in this topic to go to Joe Jenkin's website, and read The Humanure Handbook.  While this topic may not be to everyone's taste, this is, in my opinion, the definitive work on the subject of all things humanure.

As for our experiences with the composting toilet, they have been very favourable.  If we had to choose again we would still convert to a composting toilet.  I'll address some specific issues, while trying to be as delicate as I can, given the topic matter, as well as my decidedly off colour sense of humour... :-)

Other than during the deposit time itself, there is very little smell given off from the toilet.  I still haven't installed the ventilation fan as of yet, but it hasn't been a problem so hasn't been a priority.  I still do plan on installing it just for completeness, and I suspect that it will help to remove the little amount of odour that we do detect from the toilet now.

There are a few things we have found that help with the smell.  The first is the choice of cover material.  As I had stated in the initial posts, we use wood chips as our cover material.  The main reason is that they are readily available in most stores that have a pet department.  As per the Humanure Handbook, sawdust would probably be a better material, but availability when travelling by boat makes this difficult to obtain.  As for the wood chips, we've found that the cedar chips work better at keeping odour down than the pine chips do, but cedar is not as easy to find, so we mostly use pine wood chips.

One source of odour that isn't often considered is from the urine.  The solution to this is to get a spray bottle, filled with a 50:50 mixture of vinegar and water, and give the urine collection part of the urine diverter a spritz a few times a day.  This pretty much eliminates any urine smell from the urine diverter.  There can be a residual urine smell from the urine collection jug, but this can be minimized by a thorough rinsing once a week or so, as well as monthly replacement with a new jug.

One area that our build lacks in is storage time for the solid waste.  Because we are covering with wood chips after each deposit the storage container fills up quickly.  We've found we get about a week before the container is full, and while I could manually compress the material and gain more time, this is another way that we reduce the odour from the toilet, by emptying it more frequently.  We have another five gallon bucket in the cockpit with a secure lid that I can store the waste in, and once compressed and double bagged there is room for about 4 bucket-fulls in the storage bucket.  Usually we are close enough to shore-side facilities that we can dispose of the bagged waste when required, so we normally don't have to use the storage bucket.

I suspect that if we had an agitator in our toilet build, as is in commercial marine composting toilets, we'd be able to get by with using less cover/bulking material, and would thus gain longer storage time between emptying.  That being said, changing it weekly is not that big a deal, and we gain the ability to be able to use a bag in the solid storage container, which we wouldn't be able to do if we had an agitator.

As for urine storage, we've found that using a one gallon jug means that we have to empty it daily with just the two of us on board.  I usually check it first thing in the morning and again in the evening before going to bed, and if it's close I'll empty it then, avoiding any unpleasant surprises in the middle of the night (don't ask... :-)).

One of the questions we received was if we had had any issues with separation of solids and liquids with the urine diverter.  There haven't been any issues with solids ending up in the wrong spot.  We have had a bit of urine end up in the solids container (anatomical differences make aim more challenging for some than others :-)) but because the amounts are so small, and the change interval of the solids container is frequent, there is no noticeable odour increase because of it.

I think that pretty much covers it.  Please feel free to ask questions in the comments section on anything that I didn't address.