Building a Better Composting Toilet

 

The Thunder Mug

I'll be taking the shrink wrap off Magic Moments shortly and putting the arm on my brother to take the trailer, pick up the boat at the ramp, and bring it back to the house. (Are ya with me here Kevin ol' buddy??) Once the boat is back, I can clean the hull and deck, finish installing the new outboard motor mount, measure for the stainless steel bimini parts, etc. I have a lot of design work to do too: the rigid solar bimini, a new composting toilet, the new mast lowering system, etc. – all which have to come into focus on the computer before any dollars begin to fly. I haven't used SolidWorks (the CAD program) for years, so I expect to be staring at a blank screen for a while and making a lot of dumb mistakes while I get my head around it again. It's a pricy program, and one I wouldn't even have were it not for the Army's decision to fund a few years worth of R&D for improvements to conventional suspension systems currently on their vehicles. Soooo… I have broom out the CAD cobwebs between my ears before getting carried away with design and validation of those new boat systems.

composting_toilet_1I did make a bit of progress with my first CAD effort last week, beginning the design for a different type of composting toilet. There are already a variety of composting toilets on the market, but I'm always trying to make a better mousetrap. In particular, headroom on Magic Moments is limited, so the head itself needs to be close to the ground – only a foot (or 27 cm) from top to bottom. Natures Head and Air Head make some (pricey) composting heads, but they're too tall (about 20 inches, or nearly 51 cm). I'm 6'2″ (the metric me is 188 cm), and sitting on one of those commercial composting toilets would require that I have an open hatch directly overhead. Interesting visual, isn't it? For those who are curious about my weight, I'm just a little over 14ΒΌ stone – you can work out the imperial or metric equivalent yourself!

There are a couple of issues I'd like to address in a new composting toilet design:

  • I don't believe existing composting toilets are legal for boats in Canadian waters. Part of Canadian maritime law requires that the head must be permanently affixed to the boat, and must be set up so the only way to empty it is to use a shore based pump out facility. Many port-a-potties commonly installed on smaller recreational vessels are illegal under this second criteria , since the head cannot legally be emptied by removing a tank and taking it ashore to empty it. The same holds true for composting toilets; no bags or jugs can be disposed of or emptied ashore.
  • In addition, a composting toilet would ideally allow solids to sit undisturbed a month or more while completing the composting process, but units currently on the market such as Nature's Head, Air Head, and C-Head have only a single composting chamber, so when it's time to empty the unit, there will be fresh umm… payload in the mix. You can read more about other conventional composting toilets online; you'll find that many land based composting toilets are designed to hold compost in a second chamber for a full year before being emptied. The design I'm working on uses 3 common 5 gallon buckets (about 19 liters each for readers in most of the world). The proposed design segregates the composting bin into two chambers for solids – and yes, ultimately there will be a liquid compartment too! A moveable divider will isolate one solid chamber from the other, and helical agitator bars will help push the composting material away from the drop zone. Whew! enough with the euphemisms…

composting_toilet_1_section

When in service, the user turns the central rod after each use, causing the helical bars along the barrel walls to aerate and move the compost laterally within the barrels. There will be a divider secured to that central rod, which will normally be at one end of the threads on the rod or at the other end. When one side of the composting toilet becomes full, the user would reverse the direction of rotation of the rod – moving the divider to the other end of the threads on the rod. The ‘full' side of the head would then be isolated, and able to compost in peace while the other side took over ‘active' duty. Compost on both sides of the divider is aerated each time the user turns the rod.

Incidentally, the term ‘Thunder Mug' was used by my Dad to refer to the little stool and mug my brothers & sisters & I used to potty train. It just seemed appropriate for this little venture – and it amuses me.

There's more CAD work to do, but hopefully the design intent is apparent. Stay tuned for part 2 of this exciting saga!

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