Toilets, Connecting SDGs 6 and 15 : An Interview with Philippe Morier-Genoud

by Rachel Nisbet | 29 November 2019
Image Toilets, Connecting SDGs 6 and 15 : An Interview with Philippe Morier-Genoud

Toilets, Connecting SDGs 6 and 15 : An Interview with Philippe Morier-Genoud

RN: Thanks for taking the time to talk with IRHA about the importance of recycling black water and the nutrients it contains, thus linking SDGs 6 (sanitation for all) and 15 (sustainable use of ecosystems). I’m curious how you have updated a topic alluded to by the everyman hero of James Joyce's novel Ulysses, as he heads out to use the EC in his garden:

He bent down to regard a lean file of spearmint growing by the wall. Make a summerhouse here. Scarlet runners. Virginia creepers. Want to manure the whole place over, scabby soil'.

Before you began to focus on recycling blackwater (wastewater from toilets), your professional career a biologist was wide-ranging. What let you to specialise in earthworm ecology, and the role of earthworms in recycling blackwater?

PMG: My training at the University of Neuchatel included a specialisation in pedology (the study of soil formation). Understanding soil development requires generalist and specialist skills. My specialist knowledge of worm biology developed out of my desire to understand worms as 'ecosystem engineers’ that shape soil structure by decomposing organic matter.

RN: You designed the on-site, blackwater treatment facilities for the Soubeyran apartments constructed by the ecological housing cooperative 'l’equilibre’ in Geneva. Why did you decide that earthworms should be used to purify the blackwater in this installation?

PMG: In Switzerland, most domestic blackwater is piped to water treatment stations. Because it mixes with industrial effluent at these treatment plants, the solid waste it contains becomes toxic. Consequently, it has to be burnt. However, this approach leads to nutrient cycles being disrupted. Phosphates, nitrates and carbon are removed from soils, to produce crops for human consumption. When blackwater is not returned to soils, the afore-named nutrients become depleted in the top soils we use to farm crops. Chemical fertilisers are often added to maintain the productivity of fields.

Earthworms are decomposers. Their role in recycling nutrients within the soil system is of vital importance; they breakdown plant residues. They can also digest human excreta, converting it into carbon dioxide, and water that is rich in soluble nutrients that can be returned to the soil.

It is important to members of the Equilibre Housing Cooperative that their consumption of resources does not exceed the rate at which natural resources are renewed. The inhabitants of the Soubeyran apartments saw the link between the burning of human faecal waste and the depletion of bio-limiting nutrients in top soils. They did not want to be part of this trend. The blackwater treatment facility was co-designed with this community, which lives in accordance with a strong ecological vision.

RN: What design did you use for the blackwater purification system at Soubeyran?

We installed an 8-metre-wide, 1-metre-high silo to process the blackwater from the Soubeyran apartments. This silo contains a basal layer of sawdust and wood chips, a layer of compost in which the worms live, and top layer of straw. The blackwater from the apartments is sprayed over the surface of the straw through 16 jets. Underneath the straw layer, 400 kg of worms decompose the faecal material contained in the blackwater.

PMG: How long has the Soubeyran earthworm blackwater purification system been working?

The apartments became occupied in January 2017 and the system has been operating since then. It’s an experimental project, treating the blackwater from an entire apartment block. I have also designed special worm-toilets for apartments within Equilibre’s ecological housing co-operative, Les Vergers, in Meyrin (Geneva; see below for a short interview with a lady whose uses this toilet system).

Have there been any technical issues to resolve regarding the blackwater purification at Soubeyran? In the winter, we add an extra cover to the Soubeyran silo, because the worms decompose the faecal matter in the blackwater more slowly when it is cold. A bit more heat keeps them going.

People have needed time to adjust to an alternative sanitation system. The purified blackwater is reused to flush the toilets of the Soubeyran apartment block. But the recycled water is yellow, as it contains tannins from the wooden silo. People had to get used to (clean) yellow water flowing into their loos.

RN: How else is recycled blackwater used at Soubeyran?

PMG: It is used to water plants, given its high nutrient content. However, it is mainly used to water trees and shrubs, rather than the vegetable garden, and it’s never used on salad crops given the water’s bacterial content.

RN: How much does it cost to recycle blackwater using the Soubeyran earthworm system?

PMG: It costs 3000 CHF per person at Soubeyran, as compared to 15,000 CHF per person for their blackwater to be recycled in a centralised water treatment plant.

RN: Has it been easy to set up this innovative blackwater treatment system in the Swiss Canton of Geneva?

PMG: Geneva’s inhabitants are keenly aware of the importance of addressing environmental issues. The city’s Agenda 21 office is also extremely eco-positive and supportive of initiative such as ours.

RN: Could you install an earthworm-blackwater system in a private home?

PMG For fifteen years, my clients were home owners. This is where I gained my experience in designing living, blackwater treatment systems.


To find out what a private earthworm-blackwater system looks like, IRHA visited Les Vergers in Meyrin and spoke to Chloé. A mother of two little girls, Chloé is proud that her children are growing up with a 'living toilet’ in their home. There’s is a large structure made of wood, located in a toilet room that looks cosy and has no noticeable smell. Below the toilet seat, the toilet bowl diverts urine away from faecal matter. The latter is collected in a series of five pails, which are filled up one by one. Worms move between the pails, digesting their contents. The five pails are seated in hemp straw. When the waste in the oldest pails is partially digested, they are moved outside, to a narrow, closed shelving unit on the apartment’s balcony. They are stored for a few more months here, before being deposited in the housing collective’s compost system. While this may sound like a highly unusual waste management system to many readers, for Chloé’s little girls it’s their norm. When announcing they are about to use the toilet, they say 'on va nourirr les vers de terre!’ (We’re going to feed the earthworms). Now, that’s living with efficient nutrient recycling on a daily basis!

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