Verdi uses Composting Toilet instead of Chemical Port-a-John

Far nicer than your average plastic portable john

Here’s a great example of thinking “outside the box,” in terms of green building.  Verdi builders have decided against the standard smelly, chemical portable construction toilet for their Dewees Island on-site construction needs.  Instead, they have built an enclosure (using leftover structurally insulated panels, or SIPS) for a composting toilet, which is a far “greener” option.  It doesn’t even smell bad!

After hearing that it was actually cheaper, we caught up with Amy Hill, the builder, to ask her about choosing this option and the math involved. She says,

When we bid the project, we realized that no other port-a-jons were being used on the island, and so in order for us to have it serviced, it would cost quite a bit to get trucks over. The cost for a regular port-a-jon would be $300/month since they would supply us with two – that way they wouldn’t have to come over as often (yuck!). And that didn’t include the cost for the barge transportation. It would have cost over $5000. The composting toilet was $1800 plus about $500 in material and labor to build the enclosure (we recycled some left over SIPs pieces).

This model is an electric, heated model, which allows waste to decompose faster. The waste remains in the unit until it is completely composted.  Right now, they are using the company’s starter mulch, but they are looking into ways to use local cast-offs, like leftover sawdust.

posted instructions

The instructions for use are printed inside the enclosure, and involve adding mulch and turning a manual mixer knob to stir up the mixture.  There is a vent on top of the enclosure which helps with the smell, and when the weather gets cold, there will need to be a small heated bulb to keep the ambient temperature warm enough.  I asked Amy how it all works, and she answered,

The toilet starts with the mulch.  Each time the toilet is used, a small scoop of mulch is added.  There is a manual mixer knob that is turned after each use to mix the mulch, the waste and toilet paper.   A combination of heat, moisture and the organic matter mix to create an environmentally safe humus that can be disposed of like any other compost.  It falls to the bottom of the toilet in a chamber that can be emptied when full.  I anticipate it will be emptied every couple of months.  With full time use, it might be emptied every few weeks.  Right now, it looks like I will be the one doing it.  I have been monitoring  – keeping the liquid content low is key.  There is a dial to control the fan.  If there is a lot of liquid, you turn up the fan.  Another important aspect is the temperature.  The enclosure needs to keep the toilet above 68 F in order for the waste to decompose.  That is why we constructed the enclosure with Structural Insulated Panels.  Obviously temperature is not a problem right now.  We will be installing a light that can be left on to generate heat in the winter when necessary.  The unit is vented out the top of the enclosure so there is no smell. 

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