What happens to the faeces and urine after flushing?
Faeces, toilet paper and flushwater are transported via the sewers to the treatment plant along with the other wastewater. The urine, in most cases, ends up in agriculture, where the nutrients are used as a fertiliser, although more or less complex treatment is required for this purpose. At Eawag, a technology was developed which is to be commercialised by the spin-off Vuna. With this system, urine is stabilised by nitrification, a biological process which converts ammonium to nitrate while also lowering the pH. This is necessary to prevent the release of ammonia during subsequent treatment. Organic micropollutants are then removed by activated carbon, and finally the liquid is evaporated to produce a 20-fold concentrated nutrient solution. The end product, called Aurin, has been approved by the Federal Office for Agriculture for use – without any restrictions – as a liquid fertiliser.
Isn’t a connection to the sewer network compulsory in Switzerland?
Yes, that’s true, although in our experience at Eawag, there’s no problem getting permission for urine-diverting toilets in Switzerland. But if they are to widely installed, they would have to be accepted as standard by the authorities and specified as a requirement, for example, for new housing developments. Before that can happen, there will need to be pilot projects – which are now possible with the save toilet. Housing associations, especially, are interested in pilot projects of this kind, and with appropriate preparations I wouldn’t expect there to be any problems gaining permission.
What about the question of financing?
Initially, new green technologies are always expensive – they gradually become cheaper. We can see that happening in the renewable energy sector, and it won’t be any different for urine-diverting toilet installations. Sewers and treatment plants were also subsidised at first. In France, from 2019, subsidies will cover 80 per cent of the additional investment costs for all installations of urine-diverting toilets in new public buildings and apartment blocks in the Seine-Normandie agglomeration – from the toilet to fertiliser production. There, the source separation technology is expected to offer a cheaper alternative to the expansion of wastewater treatment plants in Paris – which will soon be necessary as a result of increased nitrogen loads from the growing city. We also expect that, at some point, mature source separation technology will provide an economic alternative to nutrient elimination at treatment plants. But at the moment we’re still in a pilot phase where installations are not yet financially attractive.
What are the next steps?
The new urine-diverting toilet will probably come onto the market at the beginning of 2020. At Eawag, they’ll be installed in the new FLUX building, and we’re expecting a series of pilot projects in this country and abroad. This toilet is designed for Europe, and we’ve received enquiries mainly from Switzerland but also from Germany, Sweden and France. Colleagues in Australia, Canada and the US would also like to carry out pilot projects – for example, on their own campus. These we will also support, as far as possible. At Eawag, research and development in the field of urine treatment will continue, not only for the Vuna technology but also for other systems such as Blue Diversion Autarky. In addition, within the Water Hub research platform, various source separation projects are being integrated – for instance, greywater treatment or recovery of energy resources from wastewater.