Dry toilets for all, forever?

This post was developed as a submission for The Conversation. I have to rework it because “the article covers a huge amount of ground, and that there isn’t immediately a ‘golden thread’ that can be easily identified.” I like it, so it’s going to live here in its current form 🙂

When the probability of Day Zero was first announced in January 2018, the realisation that the extreme drought in Cape Town may affect the functioning of the sewer systems became apparent to everyday people. Through my work in [resource recovery from wastewaters](http://www.futurewater.uct.ac.za/FW-WWBR) and particularly how [sanitation can contribute to the circular economy](http://www.toiletboard.org/media/17-Sanitation_in_the_Circular_Economy.pdf) I have been thinking about the benefits of dry sanitation. I am intrigued by the potential of biological means to recover value from diffuse pollution. But could they ever be introduced at large scale?

Working with [colleagues](http://www.futurewater.uct.ac.za/sewer-or-not-sewer) at the Future Water Institute, and new-found friends sharing the [same passions](https://web.facebook.com/groups/drysanitation/) it became apparent that the question of sustainable sanitation is far more complex.

Generally, all the voices agree on the nutrient value of urine. Not everyone agrees on the value of the faeces and not everyone agrees on how this urine should be recovered.

From a process engineering perspective it makes sense to try and keep the solids and the liquids separate. This is even more important when it comes to urine and faeces. The urine is the smallest volume, with the most nutrients, with the least amount of other complex stuff, like pathogens and viruses and worm eggs, but also with most of the pharmaceutical metabolites.

This makes it both a very attractive raw material for the green economy, bioeconomy or circular economy, however you wish to look at it, and urine diversion is very attractive to relieve the nutrient and ‘bad chemical’ burden on wastewater treatment works. Said another way the same size of wastewater treatment works can treat more water, and the lower amounts (we can’t say absence) of chemicals of emerging concern (CECs) makes re-use more attractive from a health perspective.

Some groups, and I used to be included here, but now I’m not sure, advocate the complete separation of the urine and faeces from the sewer system altogether. Humanure and permaculturalists fall in this category. This approach assumes that the space to safely process the material is available, very close to where it is produced, and that the people producing the waste have no recalcitrant chemicals in their system, heavy metal bioaccumulation or any worms. This is not the case for a city like Cape Town.

Even if we can innovate to have functioning dry toilet infrastructure in the context of a city while maintaining acceptable health management – and I believe this is possible – toilets don’t exist in isolation. We also need the pipes for bath/shower water, washing water, kitchen waste water and so on. Looking wider, managing the metabolism of a city is more than toilets – there is also solid wastes and moving towards dry toilets effectively makes the transport and management of the material a solid waste issue. Looking wider than that there is stormwater too.

A more useful approach for sustainable cities is by reconsidering the definition of [environmental sanitation](http://www.eawag.ch/fileadmin/Domain1/Abteilungen/sandec/schwerpunkte/sesp/CLUES/CLUES_Guidelines.pdf): this includes sanitation (and I divide that further into the faecal material, urine and greywater), stormwater and solid waste management. These need to be considered together. Of course, it is possible to reduce individual components with a myriad of tailored solutions – more recycling, greater water efficiency through low flush or greywater flush or even dry toilets, to move towards the circular economy, but these all still need to be managed.

Up to now the argument was around nutrient recovery and pathogen management, but in the context of Day Zero there is obviously the water issue. The main argument against flush toilets is that it uses water, but that water is recoverable, and in Cape Town is already recovered to an extent for industrial use. On the other hand, hydrotransportation of wastes is far more efficient than road transport, for example.

Many people question the wisdom of flushing our toilets with drinking water and suggest dual piping to the home. There are two challenges with this. Firstly, the small increase in cost to treat the water that goes straight down the toilet is worth the large decrease in risk. Secondly, much of the wastewater is already re-used at a city scale, and this fulfills the same purpose that a dual pipe system would have, at much lower cost. This raises the point that many of the systems we are suggesting for homes, have greater potential and is often already done, at larger scales, more efficiently.

## Dry toilets for Day Zero?

In the context of our current situation the best option is to keep the sewers flowing. But this needs to be absolutely guaranteed. What I would like to see is the City having a back-up plan that can be implemented if the sewer infrastructure is at risk of failing. In that event we need to divert the faecal material to reduce the pathogen burden in whatever does go through the sewers. We have existing solid waste management logistics, that should be redirected. I don’t expect the city to spend resources on this in the current moment, but I would like there to be a defined plan. Like a First Aid kit, we should have it even when we are confident we don’t need it.

## Dry toilet for me?

I have a dry toilet and I love it, I don’t see myself every going back to flush. But I work in this field, I have the space to process it, I’m comfortable that I can handle my material in a way that is safe to me, the people around me and the wider environment.

## Dry toilets for ever?

I am not sure if dry toilets will ever be a mainstream solution, but I do think we can do a lot more in terms of interrogating what sustainable, resilient environmental sanitation truly means. For now, the best solutions, while highly context specific, will probably involve hybrid systems (in terms of geographic scale and probably a lot of other things too), flush toilets with urine diversion and reticulated infrastructure for the other greywater produced, all incorporated into re-use at multiple scales.

## In closing

I am almost convinced that we need to stay with flush toilets, and reticulated infrastructure more generally, except for one thing: the discharge of – even adequately treated – effluent into receiving water bodies. We as citizens and communities have an opportunity to create a water sensitive future for ourselves and the wider communities (including the environment) we are part of. Currently I am thinking about the most appropriate scales to implement these and at this early stage neighbourhood-level interventions seem particularly promising. Engage your local council constructively, have the discussions, try things out at small scale, get involved. Let’s work on a collective will to act. Let’s do all of this gently, kindly, with an ethic of care.