31 Oct 2017

The art and science of composting toilets

From Jesse Mulligan, 1–4pm, 1:38 pm on 31 October 2017

Everyone should have the skills and materials to create a composting toilet in an emergency, says a woman who has lived completely 'off the grid' for seven years. 

Lisa Johnston and her partner Greg Inwood are part of a group called ' Relieve - compost toilets for community resilience' and have successfully used and managed a compost toilet for several years. 

Afternoons' Jesse Mulligan poo pooed the idea of composting toilets last week, which prompted Ms Johnston to hit back.

She said the idea of composting toilets for many New Zealanders probably conjured up ideas of smelly long drops. 

"[Long drop smell] sticks in the nostrils, it's pretty bad stuff and that's probably most New Zealanders' concept of what you would think of if you say 'composting toilet'." 

However, even the long drop could be improved with the slight tweak of just adding in cover material like sawdust, she said.

What made human waste smelly was having too much urine in the mix, she said, and that could be counteracted by separating the urine out or adding more cover material, "which can take away the smell completely and it ends up smelling a little bit like a forest". 

She said everyone should probably have the skills and materials to create a composting toilet in an emergency

"We all poo and pee and we should all basically have that basic knowledge of what to do."

"All you might need for that would be a couple of buckets with lids, a little collection - maybe a sackful - of sawdust, nice untreated sawdust and a plan for what you're going to do with it afterwards. 

"It's quite good if you can keep the volume of it down ... so in that sort of scenario just recommend separating the pee, keeping the pee out because the pee is pretty much safe to just put on your garden if you dilute it a wee bit. 

"So that would just reduce the volume quite a lot, so you'd just do your business in a bucket then just transfer it when the bucket's full into a bigger container."

She said wheelie bins had been used during the Christchurch earthquake. 

"It just takes a whole year to compost in that wheelie bin, or a regional authority could come and pick it up and compost it essentially."

There were other obvious benefits on top of emergency planning.

"Gathering the resource at the end. I mean, for me that's the big thing is the end product - it's so amazing, this rich humus that we can use - rather than a waste product. 

"With a water toilet you basically take clean drinking water and you add your manure to it, taking two wonderful resources and creating a toxic problem that someone else has to fix up for you." 

She said the amount of water that could be saved was significant. 

"It's, you know, 10 litres a flush. Thirty percent of average household water use goes into it, so you're saving a lot of water if you have compost toilets."

For the more advanced composter, there were other options than just the wheelie bin however.

"One of the ways, which is the way that we do at home, is thermophyllic. 

"Because we're adding a whole lot of humanure and sawdust mixture at once it leads to an explosion in the microbes and then you get a really hot compost ... pretty much all the pathogens that we might be worried about will be nuked within a day at those temperatures. 

"If you've got your compost basics sorted then it's pretty much the same you just got to do a couple of extra things to make sure you're not contaminating anything." 

She said a slightly bigger biofilter - straw and weeds at the bottom of the pile - was needed, and the waste should be kept away from the edge, but that was really the only difference compared to a regular compost pile. 

Relieve also help organise composting toilets for concerts and other events.

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